chapter – chapter ––– ii iiii...
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CHAPTER CHAPTER CHAPTER CHAPTER –––– II II II II
Aldehydes, Micelles & N-Bromophthalimide – a Brief Review
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CHAPTER II
REVIEW OF THE PRESENT WORK
2.1 A REVIEW ON OXIDATION OF ALDEHYDE:
An aldehyde is an organic compound containing a terminal
carbonyl group. Aldehydes are considered to be the derivatives of
the hydrocarbons in which two hydrogen atoms attached to a
carbon atom at the end of the chain have been replaced by
bivalent oxygen.
H-C-H
H |
|H
-2H
+ OH - C = O
H |
Aldehydes are characterized by the presence of a functional
group,
C
H |
R O This group is called aldehyde group.
The name aldehyde was derived from ‘alcohol dehydrogenatum’,
as aldehydes are obtained by dehydrogenation or oxidation of
alcohols.
The common names of aldehydes are derived from the names of
the corresponding carboxylic acids by replacing –ic acid by –
aldehyde.
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In the case of formaldehyde both the valencies of the carbonyl
carbon are satisfied by hydrogen, where as in higher aldehydes
one of the valency is satisfied by the hydrogen and other by a
hydrocarbon radical, R- or Ar-.
Aldehydes are easily oxidized to their corresponding acids hence
they are reducing agents. C=O is the carbonyl group that largely
determines the chemistry of aldehydes. Aldehydes are formed by
partial oxidation of primary alcohol and form carboxylic acids
when they are further oxidized.
Aldehydes are quite easily oxidized and usually more reactive
toward nucleophilic addition.1
Aldehydes are easily oxidized to carboxylic acids containing the
same number of carbon atoms, as in parent aldehyde.
The reason of this easy oxidation is the presence of a hydrogen
atom on the carbonyl carbon, which can be converted into –OH
group without involving the cleavage of any other bond. Thus
even weak oxidizing agents like bromine water, Ag+, Cu2+ etc are
effective. As a result aldehydes act as strong reducing agent.
Oxidation of aldehyde depends on whether the reaction is done
under acidic or alkaline conditions. Under acidic conditions, the
aldehyde is oxidized to a carboxylic acid. Under alkaline
conditions, this could not be formed because it would react with
the alkali and a salt is formed instead.
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The following reaction is given for this:
C
H |
R O
R C
O
OH
R C
O-
oxidation un
der
acidic condi
tions
oxidation under
alkaline conditions
O
2.1.0 PHYSICAL PROPERTIES:
(a) Formaldehyde is a gas, lower aldehydes other than
formaldehyde are colorless and volatile liquids and higher
members are solids.
(b) Lower members have unpleasant odour, whereas higher
members possess fruity smell.
(c) Though the lower members are soluble in water,
presumably because of hydrogen bonding between solute
and solvent molecules, the solubility decreases with
increase of molecular weights.
(d) Their specific gravities and boiling points show increase
with increase of molecular weight.
(e) The polar carbonyl group makes aldehydes polar
compounds and hence they have higher boiling points than
non-polar compounds of comparable molecular weight.
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2.1.1 PREPARATION OF ALDEHYDES:2
Some of the methods of preparation of aldehydes involve
oxidation or reduction in which an alcohol, hydrocarbon, or acid
chloride is converted into an aldehyde of the same carbon
number. Other methods involve the formation of new carbon-
carbon bonds, and yield aldehydes of higher carbon number than
the starting materials.
2.1.2 PROPERTIES AND USES OF ALDEHYDES TAKEN:
1. ACETALDEHYDE
Acetaldehyde is a colorless, mobile liquid having a pungent
suffocating odour that is some what fruity and pleasant in dilute
concentrations.
Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and
it is produced by plants as part of their normal metabolism.
The manufacturers use about 95% of the acetaldehyde produced
internally as an intermediate for the production of other organic
chemicals.
Acetaldehyde is used as an antiseptic inhalant in nose troubles. It
is used in the preparation of paraldehyde and metaldehyde. In the
preparation of acetaldehyde ammonia ( a rubber accelerator). In
the preparation of acetic acid, acetic anhydride, ethyl acetate,
chloral, 1,3-butadiene (in rubbers), dyes and drugs.
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2. BUTYRALDEHYDE
It is also known as butanal, it is an organic compound with the
formula CH3(CH2)2CHO. It is a colorless flammable liquid with
an acrid smell. It is miscible with most organic solvents. In the
open air it is oxidized to butanoic acid.
Butyraldehyde mainly serves as the precursor to acetic acid, now
prepared by carbonylation of methanol. It is used as chemical
intermediate in production of chemicals.
3. FORMALDEHYDE
Formaldehyde is gas at room temperature, it is colorless with
irritating pungent odour. Its uses are as follows:
The 40% solution of formaldehyde (formalin) is used as
disinfectant, germicide and antiseptic. It is basically used for the
preservation of biological specimens.
It is used in silvering of mirror, employed in manufacture of
synthetic dyes. It is used in the manufacture of formamint (by
mixing formaldehyde with lactose) a throat lozenge. It is used for
making synthetic plastics like bakelite, urea-formaldehyde resin,
etc. It is used in the preparation of hexamethylene tetramine
(urotropine) which is used as an antiseptic and germicide.
4. ISOVALERALDEHYDE
In the pure state isovaleraldehyde is colorless to yellow liquid
with unpleasant fruity smell. It is slightly soluble in water. Its
IUPAC name is 3-Methylbutanal and is also known as 3-
Methylbutyraldehyde. It occurs in low concentrations in fruits,
vegetables and beverages (e.g. bourbon whisky).
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A small portion of isovaleraldehyde is added to food like the taste
of butter, cocoa, chocolate and coffee to imitate. Larger portion of
isovaleraldehyde produced is used as an intermediate product in
the synthesis of aroma substances and other pharmaceutical
substances.
5. SALICYLALDEHYDE
Salicylaldehyde (HO-C6H4-CHO) is the common name for 2-
hydroxybenzaldehyde, an oily organic liquid that has the odour of
buckwheat. It is a simple derivative of the hexagonal ring
compound benzene. Salicylaldehyde is a powerful tool in
chelation chemistry and in ring generating condensation
chemistry.
The most important use of salicylaldehyde involves chelates
molecules that act, as the name suggests, like crab claws.
Salicylaldehyde is almost always chemically modified before use.
A particular derivative is formed and is applicable in a very
specific situation.
Salicylic acid is used for preserving fruit products of all kinds,
including beverages. It is frequently sold by drug stores as fruit
acid.
6. 2-METHYLBUTYRALDEHYDE
2-Methylbutyraldehyde occurs naturally in green and roasted
coffee. It is highly inflammable, volatile, colorless to yellow
liquid. It is suitable as an intermediate for the preparation of
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alcohols, acids, esters, amines etc. So it is used for the production
of odors and flavors.
2.1.3 WORK DONE IN OXIDATION OF ALDEHYDES
The oxidations of various aldehydes with various oxidants have
been studied earlier.
Credit for the first kinetic study of aldehydes by Chromic Acid
goes to Lucchi.3 He examined the oxidation of series of aldehydes
in acetic acid solution, using sulphuric acid as catalyst in 1941.
Reaction was found out to be first order.
S.K Sharma and V.P Kudesia studied Kinetic study of the
oxidation of Isobutyraldehyde by Aqueous Chlorine in 1980.4 It
was investigated in 11.6% aqueous acetic acid and the reaction
was first order with respect to both substrate and chlorine. The
influence of various factors, e.g. ionic strength, inorganic salts,
D2O and temperature have been calculated and a possible
mechanism is suggested.
M.S Ramachandran, T.S Vivekanandam and V. Arunachalam
studied Kinetics of oxidation of Carbonyl Compounds by
Peroxomonosulfate. Acetaldehyde, Propionaldehyde and
Butyraldehyde in 1986.5 Reaction took place in presence of H+
ion and showed first order dependence on PMS and aldehyde.
Oxidations of the aldehydes were carried out under pseudo first-
order conditions, with [aldehydes] have been higher than, at least
five times, that of [peroxomonosulfate].
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Kalyan K Banerji studied the Kinetics and Mechanisms of
substituted Benzaldehydes by N-Bromobenzamide in 1986.6 He
founded that oxidation of eighteen meta- and para- substituted
benzalehydes by NBB, to the corresponding benzoic acid, is first
order with respect to aldehyde, NBB and hydrogen ion. The rates
of the oxidation of meta- and para- substituted benzaldehydes
were separately correlated in Taft’s and Swain’s dual substituent
parameter equations. A mechanism involving transfer of a hydride
ion from the aldehyde to the oxidant, in the rate-determining step,
has been proposed.
Gowda and Rao7 studied the kinetic and mechanism of oxidation
of formaldehyde and formic acid by Bromamine-T in perchloric
acid medium in 1987.
C.Goswami and K.K Banerji studied Mechanism of oxidation of
acetaldehyde by Chromic Acid in 1970.8
Chromic acid oxidations of aromatic aldehydes9,10 and
formaldehyde11 have been studied in detail, but these aldehydes
cannot enolize. Some preliminary studies have been carried out
on the oxidation of acetaldehyde by Rocek12 and by Chaterji and
Antony.13
Oxidation of Benzaldehydes by Peroxomonophosphoric Acid. A
kinetic and mechanistic study in acid and alkaline media was
done by G.P Panigrahi and Radhashyam Panda in 1978.14 The
oxidation mechanisms are discussed in terms of a nucleophilic
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attack of the peroxomonophosphoric acid species on the carbonyl
carbon centre.
Effect of reaction product on the rate of oxidation of
Crotonaldehyde was studied by O.E Fedevich, S.S Levush, E.V
Fedevich and Yu. V Kit in 2003.15 Study of the oxidation of
crotonaldehyde revealed an appreciable inhibitory effect of the
products on the process.
Quinolinium Dichromate in sulphuric acid oxidizes Benzaldehyes
to the corresponding acids in 50%(v/v) acetic acid-water medium.
Kinetics of oxidation of benzaldehyde by Quinolinium
Dichromate was studied by H.A.A Medien in 2003.16 The reaction
is first order each in [QDC], [substrate] and [H+]. The reaction
rates have been determined at different temperatures and the
activation parameters calculated.
Kinetic data on the rates of Quinolinium Dichromate oxidation of
a series of aliphatic aldehydes have been determined and
discussed with reference to aldehyde hydration equilibria, by G.S
Choubey, Simi Das and M.K Mahanti in 2003.17 Kinetic results
support s pathway proceeding via a rate-determining oxidative
decomposition of a chromate ester of an aldehyde hydrate.
Kinetics and mechanism of Chloramine-T oxidation of
Cinnamaldehyde in two acid media is studied by C.K Mythily,
K.S Rangappa and N.M.M Gowda in 2004.18 The reaction has
been studied in solutions containing HCl and H2SO4 at 313K.
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The kinetics of the oxidation of a number of para- and meta-
monosubstituted benzaldehydes by ethyl N-
chlorocarbamate(ECC) were studied in aqueous acetic acid
solution in the presence of perchloric acid in 2004, by S.
Varshney, S. Kothari and K.K Banerji.19 The main oxidation
product was the corresponding benzoic acid. The reaction is first
order with respect to the aldehyde, ECC and hydrogen ions.
Kinetics and mechanism of oxidation of Aromatic aldehydes by
Imidazolium Dichromate in aqueous acetic acid has been studied
by S.S Mansoor and S.S Shafi in 2009.20 The reaction was studied
in presence of perchloric acid. Here the reaction was first order
each in IDC, Substrate and H+. The reaction rates have been
determined at different temperatures and the activation parameters
are calculated. The products of the reaction are found out to be the
corresponding acids.
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2.2 REVIEW ON MICELLE :
A micelle is an aggregate of surfactant molecules dispersed in a
liquid colloid. A micelle is formed when a variety of molecules
including soaps and detergents are added to water. At low
concentration in water, detergents exists mostly as monomer.21
The molecule may be a fatty acid, a salt of a fatty acid (soap),
phospholipids, or other similar molecules.
Surface active molecules self-assemble as micelles or vesicles in
dilute aqueous solutions so as to minimize the contact between
their hydrophobic tails and water. As a result, the interior of
micelles and the spherical shells of vesicles are highly non-polar,
capable of accommodating other non-polar molecules.22
The molecules have a strong polar head and a non-polar
hydrocarbon chain tail. When this type of molecule is added to
water, the non-polar tails of the molecules clump into the center
of a ball like structure called a micelle, because they are
hydrophobic or water hating. The polar head of the molecule
presents itself for interaction with the water molecules on the
outside of the micelle.
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A typical micelle in aqueous solution forms an aggregate with
the hydrophilic head regions in contact with surrounding solvent,
segregate the hydrophobic single tail regions in the micelle centre.
This phase is caused by the insufficient packing issues of single
tailed lipids in a bilayer. The difficulty filling all the volume of
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the interior of a bilayer, while accommodating the area per head
group forced on the molecule by the hydration of the lipid head
group leads to the formation of the micelle. This type of micelle is
known as a normal phase micelle i.e. oil-in-water micelle. Inverse
micelles23-30 have the head groups at the centre with the tails
extending out i.e. water-in-oil micelle. Surfactant solubilized
water pools in the hydrocarbon solvent are referred to as reverse
or inverse micelles.31-35 Micelles are approximately spherical in
shape.
Other phases, including shapes such as ellipsoids, cylinders,
and bilayers are also possible. The formation of “rodlike”
structures occurs relatively quickly with increasing concentration,
and this is then followed by hexagonal phases.36
Surfactant short for surface active agent designates a substance
which exhibits some superficial or interfacial activity.
Surfactants are wetting agents that lower the surface tension of a
liquid, allowing easier spreading, and lower the interfacial
tension between two liquids.
Surfactants are usually organic compounds that are amphiphilic,
meaning they contain both hydrophobic groups and hydrophilic
groups. Therefore, they are soluble in both organic solvents and
water.
2.2.0 MICELLAR CATALYSIS
The special properties of surfactants are important in a wide
variety of applications in chemistry, biology, engineering,
materials science, and other areas. Surface activity property is
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usually due to the fact that the molecule of substance are
amphipathic or amphiphilic, meaning that each contains both
hydrophilic and hydrophobic group or we can say having two
affinities, as a polar group that is attracted to water or water
soluble group and a non-polar group or water insoluble
hydrocarbon chain that is repelled by it. The polar region, called
the headgroup, may be neutral, cationic, anionic, or zwitterionic.
The hydrophobic tail has one or more chains of varying length,
composed usually of a hydrocarbon. Common examples are:
Polyoxyethylene(6) octanol:
CH3(CH2)7(OCH2CH2)6OH (neutral)
Cationic :
CH3(CH2)15(CH3)3N+Br-
N+
Br-
Cetyltrimethylammonium bromide
Anionic:
CH3(CH2)11OSO3-Na+
Na+
SO O
O
O-
Sodium dodecyl sulfate
Zwitterionic:
CH3(CH2)11(CH3)2N+CH2COO
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NH
O
OH
N-dodecyl-N,N-dimethylglycine
In dilute surfactant solutions the aggregation of surfactant
molecules have relied heavily on the theory of micellar self
assembly.37,38 Surfactants dissolve completely in water at very low
concentrations, but above a certain level, the critical micelle
concentration (CMC), the molecules form globular aggregates,
called micelles.39,40 In contact with the aqueous environment the
hydrophobic tails assemble together to create a non polar interior
with the head groups located at the surface of the glob. Micelles
vary in size and shape, but are commonly rough-surfaced spheres
with aggregation numbers on the order of 50-100.The presence of
micelles can have marked effects on chemical reactions. The
thermodynamic favorability of, for example, an acid dissociation
can be shifted significantly. Of particular interest in this
experiment is the alteration in chemical kinetics. Reaction rates
can be either accelerated or decelerated, depending on the
chemical system, the type and concentration of the surfactant, and
other factors, such as pH, ionic strength, etc. The effect of
surfactants on reaction kinetics is often called micellar catalysis.
There are several contributing factors for physical basis for
micellar catalysis. First, there is the effect of the micellar
environment on the rate-controlling step in the reaction
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mechanism. When the reaction takes place in the micellar phase
instead of the bulk water the relative free energies of the reactants
and the transition state can be altered. This concept is suggestive
of catalysis by an enzyme, and many initial studies of rates in
micellar systems focused on this possibility.41
However, further studies have shown that this effect is often
rather small and cannot account for the very large rate changes in
many micellar systems. A more important consideration is the
localization of the reacting species in the relatively small volume
of the micelles compared to the bulk solution. This leads to a
large increase in the effective concentration and the observed rate
(in terms of moles per unit time per liter of the entire solution)
increases accordingly.
2.2.1 PROPERTIES OF SURFACTANT
A surfactant in general posses the following characteristic
properties:42
1. It must be soluble in at least one phase of a liquid system.
2. Its molecules are composed of groups with opposing
solubility tendencies.
3. At the interphase of a liquid system it must form oriented
monolayer and its equilibrium concentration at a phase
interphase is greater than its concentration in bulk of the
solution.
4. It forms micelles if the concentration of the solute exceeds
a limiting value in the bulk of the solution.
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5. A surfactant- solute usually displays maximum surface
activity and functional effectiveness when it is near the
threshold of insolubility.
6. The solubility of surfactants is markedly affected by
temperature and electrolyte concentrations. Thus for each
set of conditions there is usually an optimum solubility
balance for each type of surfactants.
7. A surfactant changes the properties of a solvent in which it
is dissolved to a much greater extent than would be
expected from its concentration.
8. Solutions of surfactants exhibit detergency, foaming,
wetting, emulsifying, solubilizing and dispersing properties
either individually or collectively.
2.2.2 TYPES OF MICELLES
Depending on their charge characteristics, the surface-active
molecules may be anionic, cationic, zwitterionic (ampholytic) or
non-ionic.
(a) Anionic surfactant:
Anionic Surfactants are dissociated in water in an amphiphilic
anion and a cation which is generally alkaline metal or a
quaternary ammonium. They are the most commonly used
surfactants. They include alkylbenzene sulfonates (detergents),
(fatty acids) soaps, lauryl sulphate (foaming agent), di-alkyl
sulfosuccinate (wetting agent), lignosulfonates (dispersant) etc.
anionic surfactants account for about 50% of the world
production.
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Anionic surfactant is very soluble in water at room temperature,
and is used pharmaceutically as a skin cleaner, having
bacteriostatic action against gram-positive bacteria, and also in
medicated shampoos. It is a component of emulsifying wax.
Sodium Lauryl Sulphate is a mixture of sodium alkyl sulphates,
the chief of which is sodium dodecyl sulphate, C12H25SO4-Na+ .
(b) Cationic surfactant:
Cationic Surfactants are dissociated in water into an amphiphilic
cation and an anion, most often of the halogen type. A very large
proportion of this class corresponds to nitrogen compounds such
as fatty amine salts and quaternary ammoniums, with one or
several long chain of the alkyl type, often coming from natural
fatty acids.
The quaternary ammonium and pyridinium cationic surfactants
are important pharmaceutically because of their bacterial activity
against a wide range of gram-positive and some gram-negative
organisms. They may be used on the skin, especially in the
cleaning of wounds. Their aqueous solutions are used for
contaminated utensils.
(c) Non-ionic surfactants:
Non-ionic Surfactants are about 45% of the overall industrial
production. They do not ionize in aqueous solution, because their
hydrophilic group is of a non-dissociable type, such as alcohol,
phenol, ether, ester or amide.
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(d) Zwitterionic surfactants:
When a single surfactant molecule exhibit both anionic and
cationic dissociations it is called Amphoteric or Zwitterionic. This
is the case of synthetic products like betaines or sulfobetaines and
natural substances such as aminoacids and phospholipids. Some
amphoteric surfactants are insensitive to pH.
(e) Polymeric Surfactants:
These surfactants result from the association of one or several
macromolecular structures exhibiting hydrophilic and lipophilic
characters, either as separated blocks or as grafts. They are
commonly used in formulating products as different as cosmetics,
paints, food stuffs, and petroleum production additives.
2.2.3 MICELLAR AGGREGATES (STRUCTURE)
Surfactants molecules also called amphiphiles or detergents unite
a polar or ionic head and a nonpolar tail within the same
molecule. The nonpolar part which is typically made up of one or
more alkyl chains causes these compounds to be sparingly soluble
in water, whereas the polar or ionic part interacts strongly with
water, at certain point the solubility limit will be reached and
phase separation will set in. Due to the efficient interactions
between the polar head groups and the surrounding water
molecules, a complete phase separation is usually unfavorable.
Instead, the process will be arrested in an intermediate stage with
concomitant formation of aggregates of amphiphilic material,
where in the nonpolar parts stick together and are shielded from
water, whereas the head groups are located in the outer regions of
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the aggregates. A multitude of different aggregates can be formed
in this way.43
The morphology of these assemblies is mainly determined by the
shape of the individual surfactant molecules. Ninham and
Israelachvilli have introduced the concept of the packing
parameter, allowing prediction of the type of aggregate formed by
considering the cross-sectional head group area and the length and
volume of the nonpolar part of the amphiphile molecules.44
Surfactants containing a single alkyl chain usually form micelles
when dissolved in water.
The formation of micelles sets in after a certain critical
concentration of surfactant (CMC) has been reached. Beyond this
concentration the addition of more surfactant molecules will
result in an increase in the number of micelles, while the
concentration of monomeric surfactant remains almost constant.
In a homogeneous surfactant solution (above the CMC), the
reactive site might exist in one or more of the following
environments: the micelle interior (hydrophobic region), the
hydrophilic region (stern layer), the micelle water-interface, and
the bulk solvent.45-49
Micellisation is usually driven by an increase in entropy.
Resulting from the liberation of the water molecules from the
hydrophobic hydration shells of the monomeric amphiphiles
molecules, whereas the enthalpy change is generally close to
zero.50
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Micelles are extremely dynamic aggregates. Rates of uptake of
monomers into micellar aggregates are close to diffusion
controlled.51 The residence time of the individual surfactant
molecules in the aggregate are typically in the order of 10-5 – 10-6
seconds,52 whereas the lifetime of the micelles entity is about
10-3 – 10-1 seconds. Factors that lower the CMC usually increases
the lifetimes of the micelle as well as the residence times of the
surfactant molecules in the micelle.53 Due to this dynamic
character, the size and shape of micelles are subject to appreciable
structural fluctuations. Hence, micellar aggregates are
polydisperse, as in the range of 40 – 100.54
2.2.4 SOLUBILISATION
One of the most important characteristic of micelles is their
ability to take up all kinds of substances. Binding of these
compounds to micelles is generally driven by hydrophobic and
electrostatic interactions. The dynamics of solubilisation into
micelles are similar to those observed for entrance and exit of
individual surfactant molecules. Their uptake into micelles is
close to diffusion controlled, whereas the residence time depends
on the structure of the molecule and the solubilisate, and is
usually in the order of 10-4 to 10-6 seconds.
Many studies reported about various aspects of solubilisation, for
example, the capacity of micelles for solubilisation of different
additives, the distribution equilibrium of an additive between the
micelles and solvent, the distribution of an additive between the
micelles, the specificity of solubilisation of additives in micelles,
the location of an additive in the micelles, the thermodynamics of
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solubilisation, and the dynamics and mechanism of
solubilisation.55-61
Solubilisation is usually treated in terms of the pseudo phase
model, in which the bulk aqueous phase is regarded as one phase
and the micellar pseudo phase as another.
The incorporation of nonionic solutes into micelles has recently
been subject to multi-parameter analysis.62 These studies attribute
a dominant role to the volume of the solubilisate in determining
the partition coefficient.
2.2.5 CMC DETERMINATION
In colloidal and surface chemistry, the critical micelle
concentration (CMC) is defined as the concentration
of surfactants above which micelles form and almost all
additional surfactants added to the system go to micelles.63
The surfactants can assemble in solution and CMC is an
important solution property of surfactants.64-65
Surfactants are the substances that lower the surface tension of a
liquid and interfacial tension between two liquids, and thus
allowing easier spreading. In surfactants the hydrophilic groups
points towards the aqueous phase and hydrocarbon chains points
towards the air or oil phase. Surfactants spontaneously aggregate
above a certain concentration called Critical Micellar
Concentration (CMC) to form micelle66, whose determination has
considerable practical importance, normally to understand the
self-organizing behavior of surfactants in exact ways. The
difference among the CMC values arises from the well-known
effect of added electrolyte, which lowers the CMC by causing a
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decrease in the repulsion between the polar head groups at the
micelle surface.
Much work was also done on how the additives affect the CMC
of the surfactants, and more recently, how the additives affect the
dynamic behavior of the micelles or the micellar structure; i.e. the
size and shape of the micelles.67-75
In most of these studies, surfactant system were used in which
spherical micelles existed, and it was observed in most of the
investigations that the solubilised samples often caused the
spherical micelles to grow to rods.76-80
There are several frequently used methods like tensiometry,
conductometry, fluorimetry and caloriemetry for determining
CMC.81-82 Here we have used conductometric method to
determine the CMC.
The CMC values were determined from plots of the specific
conductivity (k) versus surfactant concentration using
conductometeric determination method at constant temperature
308 K. The break point of nearly two straight line portions in the
plot is taken as an indication of micelle formation, and this
corresponds to the CMC of surfactants.
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Table 2.2.5.0 showing CMC of the aldehydes in presence
of CTAB:
Solution CMC x 10-4
mol dm-3
Water + [Acetaldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 1.0
Water + [Butyraldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 0.5
Water + [Formaldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 1.0
Water + [Isovaleraldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 0.5
Water + [Salicylaldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 0.5
Water + [2-Methylbutyraldehyde] + H+ + Hg++
+ CH3COOH + [NBP] + [CTAB] 0.5
Reaction Conditions: [NBP] = 1 x 10-4 mol dm-3, [Aldehyde] = 1
x 10-2 mol dm-3, [H+] = 1 x 10-2 mol dm-3(5 x 10-3 mol dm-3 for
Isovaleraldehyde and 2-Methylbutyraldehyde), [Hg(OAc)2] = 2 x
10-4 mol dm-3, CH3COOH = 50% (30% for formaldehyde, 40%
for Isovaleraldehyde & 45% for Salicylaldehyde), Temp. = 308K.
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Table 2.2.5.1 showing CMC of the aldehydes in presence
of SDS:
Solution CMC x 10-3
mol dm-3
Water + [Acetaldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 2.0
Water + [Butyraldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 2.0
Water + [Formaldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 1.0
Water + [Isovaleraldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] 1.0
Water + [Salicylaldehyde] + H+ + Hg++ +
CH3COOH + [NBP] + [CTAB] -
Water + [2-Methylbutyraldehyde] + H+ + Hg++
+ CH3COOH + [NBP] + [CTAB] 1.0
Reaction Conditions: [NBP] = 1 x 10-4 mol dm-3, [Aldehyde] = 1
x 10-2 mol dm-3, [H+] = 1 x 10-2 mol dm-3(5 x 10-3 mol dm-3 for
Isovaleraldehyde and 2-Methylbutyraldehyde), [Hg(OAc)2] = 2 x
10-4 mol dm-3, CH3COOH = 50% (30% for formaldehyde, 40%
for Isovaleraldehyde & 45% for Salicylaldehyde), Temp. = 308K.
2.2.6 KINETIC MODELS
A micelle-bound substrate will experience a reaction environment
different from bulk water, leading to a kinetic medium effect.
Hence, micelles are able to catalyze or inhibit organic reactions.
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Research on micellar catalysis has focused on the kinetics of the
organic reactions involved.83-89 The kinetic data are essentially
always treated using the pseudophase model, regarding the
micellar solution as consisting of two separate phases. The
simplest case of micellar catalysis applies to unimolecular
reactions where the catalytic effect depends on the efficiency of
binding of the reactant and the rate constant of the reaction in the
micellar pseudophase km and in the aqueous phases kw.
Reviews on the structure and properties of micelles have been
published by Fisher and Oakenfull90, Mukherjee91, Menger92. In
order to account for the organic reaction, the micelle is condensed
as a separate phase. Rate of acceleration or inhibition arises from
different rates in micellar and bulk phase. The distribution of the
substrate has been discussed quantitatively using different
quantitatively using quantitative models.
(a) HARTLEY MODEL
Hartley is the pioneer worker in elucidating the structure of
micelle.93 His model is a roughly spherical aggregate of 50-200
monomer, the polar groups being held at the surface in contact
with aqueous phase.94 The hydrocarbon moieties are put together
in closed juxtaposition so that the total contact area of the solute
molecule with water is reduced. The micelle has hydro-carbon
core and polar surface. The head groups and associated counter
ions of ionic micelles are found in the compact stern layer, the
remaining counterions form the diffuse Gouy-Chapman electrical
double layer. The counterions present in this region are
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completely dissociated from the charged aggregate and are able to
exchange with ions in the bulk solution. The interior of micelle is
essentially anhydrous and liquid like. However, this model fails to
explain the facts that micellar radii exceed the length of a fully
extended chain plus the head group and the micelles have an
intermediate behavior between water and hydrocarbon.
(b) MENGER AND PORTNOY MODEL
In order to describe the kinetic effects of micelles Menger and
Portnoy95 in 1979 have constructed a model in which the
hydrocarbon chains are bent to fill the cavities.96 Some of the
carbon chains protrude outside and thus are in direct contact with
water. It has rough surface with water filled pockets and a central
hydrocarbon core. Similar to stern layer of Hartley micelle it
possesses a stern region that constitutes most part of a micelle.
This model was quantitative pseudophase model which was
represented by scheme-I.
kw kmProduct
KSDnSDn + S
Scheme-I
According to this model, the substrate ‘S’ forms complex (DnS)
with the micelle Dn, and km and kw are the rate constant for the
product formation in micellar and aqueous phase respectively.
The observed rate constant for the product formation is given by
equation:
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1
(kw-kobs)
= 1
(kw-km)+
(kw-km) ks
1
[Dn] --(1)
This equation predicts that a plot of (kw-kobs)-1 versus [Dn]-1
(where [Dn]-1 = CSURF - CMC) should be linear. The Menger and
Portnoy model allows us to determine kinetically the binding
constant ks and the rate constant km in the micellar phase.
But this model is not able to explain the distribution of two
substrates in a bimolecular reaction.
(c) BEREZIN MODEL
Berezin and co-workers developed the first general treatment
based on the pseudo phase model and successfully simulated
spontaneous and bimolecular reactions between neutral and
organic reactants. The inhibition of rates at higher concentration
of surfactant may be explained with the help of Berezin’s
model97, which involves solubilisation of both the reactants in the
micellar phase. According to the Berezin’s approach, a solution
above the CMC may be considered as a two-phase system,
consisting of an aqueous phase and a micellar pseudo-phase. The
reactants (S=substrate and O=oxidant) may be distributed as
shown in scheme-II
(Substrate)w + (Oxidant)W
(Substrate)M + (Oxidant)MkM
KS K0
kw(Product)w
(Product)M
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65
A quantitative rate expression for a bimolecular reaction
occurring only in aqueous (kw path) and micellar (km path) phase
for the pseudo- first order rate constant is given by Equation
kW + k'M KS K0 (CSurf-CMC)
[ 1+ KS (CSurf - CMC) ][ 1+ K0 (CSurf - CMC)]=kobs
------(2)
Where, Ks and Ko are the association constant of substrate and
oxidant with surfactant, respectively; Csurf is the analytical
concentration of surfactant; K’m = (Km/V), V being molar volume
of the micelle; and Kw and Km are the pseudo-first order rate
constant in the absence and prescence of micelles, respectively.
Since the oxidant will be charged species and the substrate is
large molecules, the hydrophobic and electrostatic interactions
will be expected that Kw>>K’ mKsKo (Csurf – CMC), so that the
Eq.(3) takes the form represented by the Eq.(2)
kW
1+ (KS + K0) (CSurf - CMC) ] + KS K0 (CSurf - CMC)2
=kobs --(3)
Again, since (Csurf – CMC) is very small, the terms containing
(Csurf – CMC)2 may be neglected, and the Eq. (3) may be
rearranged to Eq.(4).
1 1 KS + K0 + (CSurf - CMC)kW
=kobs kW ---------(4)
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(d) DILL AND FLORY MODEL
Dill and Flory98 have proposed their model in 1981. This model
postulates the negligible penetration of water into the
hydrocarbon core, which is similar to Hartley model, but in
contrast to the Hartley model they suggest crystalline nature of
the hydrocarbon core. In this model the core is divided into a
number of lattices.
(e) ROMSTED MODEL
Romsted has developed a theoretical model for predicting the
rate-surfactant profile for reactions involving ions.99
This model has the following limitations –
1. Reactions occur independently in the micellar and aqueous
pseudophase and the rate constant can be estimated for
these reactions.
2. Micelle surface is saturated with counterions.
In this respect Romsted’s treatment differs from all previous
models. The counterions exchange on the micellar surface is
described by equation –
Nm + Xw ↔ Nw + Xm ---------(4)
‘N’ and ‘X’ are the reactive and unreactive counterions.
If mN’ s and mX’s are the concentration of the reactive (N) and
unreactive (X) counterions in the stern layer, measured in terms of
the ratio of counterions to ionic heads in the micelle, then
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mN’s = [Nm]/[Dn] ---------(5)
mX’ s = [Xm]/[Dn] ---------(6)
where, [Xm] and [Nm] are the molar concentrations of micellar
bound X and N respectively.
If the ratio of counterions bound to the micelle is defined by ‘ẞ’,
then ẞ = mNs + mXs --------(7)
So substitution of the values for [Nm] and [Xm], the value of
equilibrium constant is given by the equation -
k =[Nw] mXs
[Xw]mN s ---------(8)
Nw and Xw are the molar concentration of the counterions in
water.
This approach explains qualitatively a number of micellar effects
upon reaction rates and equilibria.
(f) BUNTON MODEL
Bunton et al have proposed a general relation between rate constant
and the surfactant concentration in micellar catalysed bimolecular
reaction taking into account the distribution of both the reagents
between aqueous and micellar phase.100 the first order rate constant
k, with respect to the substrate and the nucleophile is written by
equation:
k =kw [Nw] + kw ks [Nm]
1 + ks [Dn] ----------(9)
[Nm] is the molarity of the micellar bound nucleophile (N) in terms
of total solution volume. Considering the binding of the
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nucleophile with the micelles, the binding constant, kM can be
represented by the equation:
KM = [Nm] / [Nw] [Dn]
(g) FROMHERZ MODEL
Fromherz101 envisaged a surfactant block model for micelle. He has
constructed a model which accounts both the structural features of
McBain bilayer and energetic features of Hartley model. He has
modified the bilayer model such that the energetic features of the
droplet model are attained. This model successfully explains the
phenomenon occurring in presence of micelle. His model is an
antithesis of Menger model.
(h) PISZKIEWICZ MODEL
Piszkiewicz102 proposed an entirely different model for micellar
catalyzed reactions analogous to Hill model as in the case of
enzyme kinetics. The micellar catalysis or inhibition could be
applied theoretically by making certain simplifications and
assuming that only one substrate is incorporated into the micelle
and that the aggregation number N of the micelle is independent of
the substrate. On the basis of these assumptions Piskiewicz
proposed a model for micellar catalyzed reaction analogous to the
Hill model of enzyme kinetics. This model is applicable especially
at low surfactant concentrations. This model assumes that an ‘n’
number of surfactant molecules (D) and substrate (S) aggregate to
yield the catalysis DnS which then reacts to yield the product (P).
This is represented by the following scheme-III
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kw km
Products
KD DnSnD + S
Products
Where kD is the dissociation constant of micelle back to its free
components and km is the rate constant within the micelle. In the
scheme-III the observed rate constant kobs is expressed as a function
of surfactant concentration D, by the equation:
km[D]n + kwKD
KD + [D]n
kobs =
--------(10)
Following rate expression was obtained on rearrangement and
taking
log of above equation we get:
Log (kobs - kw / km - kobs) = n log [D] – log kD -------(11)
The values of positive cooperativity (n) are found for the substrate.
If the value of n is less than 6 it shows good agreement with earlier
observations of Piskiewicz and this is viewed as an index of
positive cooperativity, i.e., induced interaction of the micelle with
the substrate molecule. The value of log kD was calculated from the
intercept of the plot.
This equation has been successfully applied to experimental data
with rate maxima in micellar catalysed reactions and assumes the
cooperativity in micelle-solute binding.
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(i) RAGHVAN AND SRINIVASAN MODEL
For bimolecular micellar catalyzed reactions, Raghvan and
Srinivasan103 developed a model. The distribution of the reactants
in aqueous and micellar phase has been considered in the model.
This model predicts constancy in kobs values at high surfactant
concentrations. The product formation is assumed to result from
the decomposition of a ternary complex involving substrate,
nucleophile and micelle. The analysis of the data on the basis of the
model showed that almost all the nucleophile was present in the
bulk phase. A similar idea has also been given by Romsted.104 The
model is represented in scheme-IV
nD + S DnS
DnS + N DnSN
DnSN products
S + N products
K2
km
kw
K1
Where, D, S and N refer to detergent monomer, substrate and the
nucleophile, respectively. While DnS and DnSN refer to binary and
ternary complexes, respectively. According to the above model, the
observed rate constant in the presence of a surfactant is given by
the following equation:
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kobs =kw + km K1 K2 [D]
n
1 + K1 [D]n {1 + K2 [S]T} ----(12)
kobs - kw
kobs [D]n
=kobs
- K1{1 + K2 [S]T}(k1k2)1 km
-----(13)
This equation predicts a linear relationship between (kobs -
kw/kobs)1/[D]n and km/kobs . we apply this model by using the value
of n obtained from Piskiewicz’s Cooperativity model. The plot (kobs
- kw/kobs)1/[D]n and km/kobs is linear.
The values of k1 and k2, binding constants can also be evaluated
with the help of intercepts and slopes of these linear plots.
2.2.7 WORK DONE USING MICELLES
Susana Criado105 and co-workers have studied kinetic studies of the
photosensitized oxidation of tryptophan-alkyl esters in triton X-100
micellar solutions. In this, an important decrease in the photo-
oxidation quantum efficiency of the esterified compounds was
observed due to the presence of the micellar medium. . The
characterization of the solute-micelle interaction indicates that trp-
methyl ester, trp-butyl ester and trp-octyl ester bind Triton X-100
micelles to a different extent, depending on the hydrocarbon length
of their ester chains.
Asha Radhakrishnan106 and co-workers studied, micellar catalysed
autoxidation of iso-butanol, amyl alcohol and iso-amyl alcohol by
N-Bromobenzamide – A kinetic study. This study has been found
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in two stage i.e. slow first stage followed by relatively faster
second stage. In both the stages the reaction follows first order
behaviour with respect to each substrate and the oxidant, NBB. The
reactions have been found out to be catalysed by Sodium Dodecyl
Sulphate.
M.S. Krishnamachari107 and co-workers studied, kinetics of
oxidation of vanadium(IV) by iron(III)-1,10-phenanthroline
complex: Micellar effect of sodium dodecyl sulphate. In this study
the reaction is markedly accelerated by sodium dodecyl sulphate.
The rate-[surfactant] profile exhibits a maximum. The kinetic
analysis of the micellar effect has been carried out.
Kabir-ud-Din108 and co-workers studied, influence of sodium
dodecyl sulfate/tritonX-100 micelles on the oxidation of D-fructose
by chromic acid in presence of HClO4. In this study the reaction is
acid catalysed and is associated with an induction period which is
dependent on [H+], [surfactant] and temperature. The order of
oxidation during induction under [D-fructose] > [chromic acid]
conditions is fractional in each reagent in both media. The rate
constant was found to increase with [Mn(II)]. The micelles produce
a catalytic effect in the range of SDS and TX-100 concentrations
used, and the effect is explained by means of the pseudophase
mass-action model.
Masood Ahmad Malik and Zaheer Khan109 studied submicellar
catalytic effect of cetyltrimethylammoniumbromide in the
oxidation of ethyleneddiaminetetraacetic acid by MnO4. In this
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73
study they found that the premicellar environment of CTAB
strongly catalyses the reaction rate which may be due to the
favourable electrostatic binding of both reactants with positive
head groups of the aggregates. The influence of different
parameters was also calculated.
Mansur Ahmed and K. Subramani110 studied, kinetics of oxidation
of cobalt(III) complexes of ɑ-hydroxy acids by hydrogen peroxide
in the presence of surfactants. In this reaction the rate of oxidation
shows first order each in [cobalt(III)] and [H2O2]. Hydrogen
peroxide induced electron transfer in [(NH3)5CoIII-L]2+ complexes
of a-hydroxy acids readily yields 100% of cobalt(II) with nearly
100% of C-C bond cleavage products suggesting that it behaves
mainly as one equivalent oxidant in micellar medium. With
increasing micellar concentration an increase in the rate is
observed.
G.P Panigrahi and S.K Mishra111 studied, micellar-catalysis: effect
of sodium lauryl sulphate in the oxidation of lactic acid by chromic
acid. In this the oxidation rate however is observed to increase with
the detergent concentration and reaches maximum at the critical
micelle concentration of the detergent and then decreases as the
surfactant concentration increases further. The kinetic data have
been rationalized by Berezin’s model and the binding constants for
both the reactants with micelle have been computed.
Asim K. Das112 studied micellar effect on the kinetics and
mechanism of chromium (VI) oxidation of organic substrates. The
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74
micellar media can influence the mechanistic path of reduction of
Cr(VI) to Cr(III). Such studies in micro-heterogeneous systems are
important from the standpoint of understanding the mechanism of
redox activity and toxicity of Cr(VI). The possible use of suitable
surfactants in the two-phase oxidation of organic substances by
chromic acid is discussed.
Jagannath Panda and G.P Panigrahi113 studied, kinetic investigation
of the oxidation of sulphanilic acid by peroxomonophosphoric acid
in anionic surfactant sodium lauryl sulphate. In this the rate reaches
a maximum and then decreases. The oxidation rate-[micelle]
profile is rationalized by Berezin model and binding constants with
the micelle have been computed using the model.
M.Yousuf Hussain and Firoz Ahmad114 studied effect of micelles
on kinetics and mechanism of the oxidation of seriene by acid
permanganate. In this the reaction is retarded by the hydrogen ion
in the absence of SDS but catalysed in the presence of SDS.
Dennis Piszkiewicz115 studied positive cooperativity in micelle-
catalysed reactions. In this he studied that the rate constants of
micelle-catlysed reactions, when plotted versus detergent
concentration gives sigmoid shaped curves. This behaviour is
analogous to positive cooperativity in enzymatic reactions, a
sigmoid shaped dependence of velocity on substrate concentration.
Ekta Pandey and Santosh K. Upadhyay116 studied effect of micellar
aggregates on the kinetics of oxidation of ɑ-aminoacids by
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75
chloramines-T in perchloric acid medium. In this the presence of
any surfactant well below its critical micelle concentration strongly
enhanced the rate of reaction suggesting a premicellar aggregation.
The kinetic data have been analyzed in terms of earlier reported
models for micellar catalysis. The binding constants between two
models proposed by Piszkiewicz and Raghvan and Srinivasan are
in good agreement.
A.Lonescu117 and co-workers studied micellar effect on tyrosine
one-electron oxidation by azide radicals. In this it is shown that,
whatever the interfacial charge is, micelles exert an efficient
protection against tyrosine oxidation when compared to aqueous
solutions. Such an effect is related to different location of the
reactants in the different media.
Zoya Zaheer and Rafiuddin118 studied sub- and post-micellar
catalytic and inhibitory effects of cetyltrimethylammonium
bromide in the permanganate oxidation of phenylalanine. In this
the rate shows first and fractional order dependence on [MnO4-]
and [phe] in presence of CTAB. At lower values of [CTAB] the
catalytic ability of CTAB aggregates are strong. In contrast at
higher values of [CTAB], the inhibitory effect was observed in
absence of H2SO4.
Abu Mohammad, Azmal Morshed, Zaheer Khan and Kabir-ud
Din119 studied micellar effects on the oxidation of D-glucose by
chromic acid in perchloric acid medium. In this it was observed
that the reaction has a non-autocatalytic followed by an
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autocatalytic pathway. The rate of initial stage increases with
increase in [glucose], [HClO4] and temperature. Due to
precipitation, the effect of cationic micelles of
cetyltrimethylammonium bromide (CTAB) could not be studied
whereas the oxidation is catalyzed by anionic micelles of SDS and
nonionic micelles of Triton-X-100. The results are discussed in
terms of pseudo-phase kinetic model.
Y.R Katre et120-125 al has done work in the field of micellar
oxidation of various substrates in presence of various surfactants.
Kabir-ud-Din126 and co-workers have done work on micelle
catalysed oxidation of D-Mannose by Cerium (IV) in Sulfuric Acid
medium at 40˚C both in presence and absence of ionic micelles.
Satya P. Moulik, Gargu Basu Ray and Indranil Chakraborty127 have
studied pyrene absorption can be a convenient method for probing
critical micellar concentration and indexing micellar polarity.
Amir Abbas Rafati, Husein Gharibi and Mehdi Rezaie-Sameti128
studied the investigation of aggregation number degree of alcohol
attachment and premicellar aggregation of sodium dodecyl sulfate
in alcohol-water mixtures.
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2.3 REVIEW ON N-BROMOPHTHALIMIDE:
Halogens are highly reactive, and can be harmful to biological
organisms in sufficient quantities. This high reactivity is due to
the atoms being highly electronegative due to their high effective
nuclear charge. Chlorine and bromine are used as disinfectants.
They kill bacteria and other potentially harmful microorganisms
through a process known as sterilization. All the halogens form
binary compounds with hydrogen known as the hydrogen
halides (HF, HCl, HBr, HI, and HAT), all of which are
strong acids with the exception of HF. When in aqueous solution,
the hydrogen halides are known as hydrohalic acids.
The organic functional group called an imide contains two acyl
groups that are attached to NH or NR. Most imides are derived
from dicarboxylic acids. Example succunimide derived
from succinic acid and phthalimide derived from phthalic acid.
The nitrogen in imides is not very basi, which allows it to form
stable compounds with halogens. Treatment of imides with
halogens and base gives the N-halo derivatives. Examples NBP,
NBS etc.. The N-halo derivatives are useful compounds and their
field is very vast.129-135 They may be used as halogenating agents
as well as oxidizing agents136 or for dehydrogenation reactions.
2.3.0 N-BROMOPHTHALIMIDE
Properties:
N-Bromophthalimide has the molecular formula C8H4BrNO2 with
the following structure:
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78
O
O
N Br
N-bromophthalimide
Its molecular weight is 226.04. It is slight yellow fine crystal. It is
soluble in acetic acid, ethyl acetate, acetone, acetic anhydride and
in water, benzene, tetrachloromethane and chloroform. Its melting
point is greater than 200˚C, and it decomposes at room
temperature. Solution of N-Bromophthalimide is kept in black
coated vessel to prevent it from photochemical deterioration.137
N-Bromophthalimide has been found to be an efficient and
selective reagent for the mild oxidative cleavage of oximes to
yield the corresponding carbonyl compounds in good to excellent
yields.
R1 R2
NOHNBP
acetone, H2O R1 R2
O
Where R1, R2 = Alkyl or Aryl group.
An interesting example of the chemoselectivity of these reactions
includes deoximation in the presence of primary benzylic
alcohols.
Similar reactions were also carried out under microwave
irradiation in very short times. NBP has been used for the
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79
oxidation of various organic compounds in the presence of
mercuric acetate as well as in acetic acid medium.
N-halo compounds react with olefins and add bromine to the
double bonds or act as source of hypohalous and acid in aqueous
solution. Wohl was the first to observe this. N-bromoacetamide
was thus used as an agent for allylic bromination. Ziegler and his
co-workers extended in 1942 used N-bromosuccinimide for allylic
bromination. The work was generalized and was named ‘Wohl-
Ziegler’ reaction.138
N-Bromophthalimide is an important member of the class of
reagents namely N-halo compounds which have been used widely
as oxidizing and halogenating agent in organic compounds.139-143
It has been reported by several workers that NBP is stable
oxidising and brominating agent because of large polarity of N-Br
bond. NBP is capable of producing Br- ions reasonably shows that
NBP, like other similar N-halo imides, may exist in various forms
in acidic medium,144 i.e. free NBP, (NBPH)+, Br+, HOBr,
(H2OBr)+
, as per the following equilibria:
NBP + H+ NHP + Br
+
NBP + H+ (NBPH)+
NBP + H2O HOBr + NHP
HOBr + H+
(H2OBr)+
N-Bromophthalimide has been used in organic synthetic
methodology especially in the oxidation and bromination
reactions. In most cases these reagents are converted to
phthalimide in the end of reactions, as a nontoxic chemical.
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80
This field of chemistry has become an interesting field for
researchers and number of work has been done with the chemistry
of N-halo compounds. For example Bromamine-T145,
Chloramine-T146, N-bromoacetamide147, N-bromosuccinimide148,
N-chloroacetamide149, N-iodosuccinimide150, N-
bromophthalimide151, N-bromobenzamide152 and Bromamine-B153
have been successfully tested as halogenating agents oxidizing
agent and dehydrating agents. The chemistry of N-halo reagents
was the subject of several review articles.155-160
2.3.1 WORK DONE USING BROMO COMPOUNDS
Amena Anjum and P.Srinivas161 in 2005 studied, kinetics and
mechanistics aspects of oxidation of acetophenones by N-
Bromophthalimide in presence of mercuric acetate. The reactions
of NBP with Acetophenone have been studied in presence of
excess of Mercuric Acetate in aqueous acetic acid medium. NBP
acts as moderate oxidant with a redox potential of 1.09 V. the
reaction kinetics were first order in [NBP] and fractional order in
[acetophenone]. Variation of phthalimide, mercuric acetate and
ionic strength had an insignificant effect on reaction rate.
Kinetics and mechanism of oxidation of some hydroxyl acids by
N-bromoacetamide is studied by Madhu Saxena162 and co-
workers in 1991. They found out that the reaction follows
identical kinetics, being zero order in substrate and first order in
each NBA, Ir(III) and mercuric acetate. A negative effect of
hydrogen ions, acetamide and Cl- is observed, while ionic strength
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81
has no effect on reaction velocity. A suitable mechanism
consistent with the above observations is proposed.
In 1990 Kakuli Chowdhury and K.K Banerjii163 studied the
kinetics and mechanism of the oxidation of organic sulfides by N-
Bromobenzamide. They found out that corresponding sulfoxides
were the products of the reaction and the reaction followed first
order with respect to the sulfide, NBB and hydrogen ions. There
is no effect of added benzamide. Protonated NBB has been
postulated as the oxidizing species.
Ajay K. singh164 and co-workers studied, mechanistic study of
novel oxidation of paracetamol by chloramines-T using micro-
amount of chloro-complex of Ir(III) as a homogeneous catalyst in
acidic medium. They found out that the reaction followed first
order kinetics with respect to chloramines-T, paracetamol and
chloride ion in their lower concentration range, and tended to zero
order at their higher concentrations. The first order rate constant
increased with decrease in the dielectric constant of the medium.
Ardeshir Khazaei and Abbas Amini Manesh165 studied, facile
regeneration of carbonyl compounds from oximes under
microwave irradiations using N-Bromophthalimide. They found
out new and selective method for the cleavage of oximes by a
simple reaction of a ketoxime or an aldoxime with N-
Bromophthalimide in acetone under microwave irradiations.
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N.M.I. Alhaji and S.Sofiya Lawrence Mary166 in 2011 studied,
kinetics and mechanism of oxidation of glutamic acid by N-
Bromophthalimide in aqueous acidic medium. This study was
done in presence of perchloric acid medium at 30˚C by
potentiometric method. The reaction is first order in each NBP
and glutamic acid and is negative fractional order in hydrogen
ion.
Jagdish V. Bharad167 and co-workers in 2010 studied,
phosphotungstic acid catalysed oxidation of benzhydrols by N-
Bromophthalimide. A kinetic study. In absence of mineral acids,
the oxidation kinetics of benzhydrols by NBP in presence of
phosphotungstic acid shows first order dependence on NBP and
fractional order on benzhydrols and phosphotungstic acid.
E. Kolavari168 and co-workers studied application of N-halo
reagents in organic synthesis in 2007. This review article
summarizes published data on the application of N-halo reagents
in various organic functional group transformation such as:
oxidation reaction, deprotection and protection of different
functional groups, halogenation of saturated and unsaturated
compounds, acylation of alcohols, phenols, amines or thiols,
epoxidation of alkenes, aziridination and etc.
Neerja Sachdev169 and co-workers studied, oxidation of d-glucose
by N-Bromophthalimide in the presence of chlorocomplex of
iridium(III): a kinetic and mechanistic study.(report) The reaction
followed first order kinetics with respect to NBP.
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M.Kavitha170 and coworkers studied Kinetics and mechanistic
investigation of N-bromonicotinamide oxidation of aromatic
aldehydes. It was investigated in aqueous acetic acid and
perchloric acid medium over the temperature range of 313-328 K.
The reaction exhibits first order dependence on oxidant and the
zero order dependence on substrate. The fractional order
dependence of rate on H+ suggests complex formation between
oxidant and H+.
Govindrajnaj171 and coworkers studied oxidation of 2-
hydroxynaphthaldehyde by alkaline N-bromosuccinimide. A
kinetic and mechanistic study. The reaction is of first order in
NBS and of fractional order in both substrate and alkali.
Increasing ionic strength and decreasing dielectric constant of the
medium increases the rate of the reaction.
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2.4 PRESENT INVESTIGATION
In the present investigation following aspects have been studied:
1. Determination of basic kinetic parameter such as order of
reaction with respect to [substrates], [N-Bromophthalimide],
[perchloric acid] for the oxidation reaction of Aldehydes by N-
Bromophthalimide.
2. To study the effect of cationic surfactant (CTAB) and
anionic surfactant (SDS) on the oxidation of aldehydes by N-
Bromophthalimide. Effect of surfactants explained on the basis of
Berezin’s model.
3. Effect of acetic acid, mercuric acetate, phthalimide and
salts (KBr & KCl) has been studied on the kinetics of oxidation of
aldehydes.
4. Effect of temperature has been studied on the kinetics of
oxidation of all aldehydes by N-Bromophthalimide and different
thermodynamic parameters have been calculated.
5. Experimental results are presented for absence and
presence of (cationic and anionic) surfactants and on the basis of
different kinetic parameters probable reaction path has been
proposed.
The study includes both the experimental results and the
prediction of the outcome of experiments.
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85
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