matriculation chemistry ( carboxylic acid )
TRANSCRIPT
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CARBOXYLIC ACID AND ITS DERIVATIVES
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C OHR
O
RCOOH or RCO2H
(R ≡ alkyl, aryl or H)
Structure
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NOMENCLATURE
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HCOOH
Methanoic acid
Formic acid
CH3COOH
Ethanoic acid
Acetic acid
CH3CH2COOH
Propanoic acid
Propionic acid
CH3CH2CH2COOH
Butanoic acid
Butyric acid
CH3CH2CH2CH2COOH
Pentanoic acid
Valeric acid
IUPAC Nomenclature & Common Name
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•The longest chain must contain the carboxyl group.
•The carboxyl group is at the terminal, therefore the carbon of the carboxyl group is not numbered.
One COOH – carboxyl group is at one end Two COOH – carboxyl groups are at both ends
•Name the compound as alkane, drop ‘e’ in alkane and add ‘oic acid’ (eg: methanoic acid)
IUPAC Nomenclature
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4-bromo-3-methylpentanoic acid
5-hydroxyhexanoic acid
CH CHCH2 CH CH3COH
O CH3
5-methyl-3-hexenoic acid
CH CH2CH C OH
O
CH3
Br CH3
CH2 CH2CH2 C OH
O
CHOH
CH3
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• Two COOH groups, the compound will be named as alkanedioic acid’ (Example: ethanedioic acid, propanedioic acid and etc)
CH2 CH2CH2 C OH
O
COH
O
pentanedioic acid
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C C
H
CH2 H
CH2 COOH
HOOC
trans 3-hexenedioic acid
CH2 CH2CH C OH
O
CH2COH
O CH3
3-methylhexanedioic acid
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• When R is an aryl group, the parent name is benzoic acid
COOHCl
4-chlorobenzoic acid
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CH
CH3
CH3
HOOC
COOH
HOOC
COOH
1,3-benzenedicarboxylic acid
2-isopropyl-1,4-benzenedicarboxylic acid
• An aromatic dicarboxylic acid is named as 1,x-benzenedicarboxylic acid
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• A cyclic carboxylic acid is named as cycloalkanecarboxylic acid
• The C atom which is attached to —COOH is numbered as C1
COOH
cyclopentanecarboxylic acid
1
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COOH
CH3
Br
4-bromo-2-methylcyclohexanecarboxylic acid
1
COOH
cyclohexanecarboxylic acid
1
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COOH
COOH
COOH
COOHCl
1,2-cyclohexanedicarboxylic acid
4-chloro-1,2-cyclohexanedicarboxylic acid
A cyclic dicarboxylic acid is named as 1,x-cycloalkanedicarboxylic acid
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COOH
CH3
3-methyl-2-cyclohexenecarboxylic acid
• When a compound contains a carboxyl group and other functional group(s), the priority is given to the carboxylic acid as the parent name.
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PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS
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Boiling Point
The boiling point of carboxylic acid is higher than an alcohol, a ketone or an aldehyde (with Mr that almost the same) because:
i. it exists as stable dimers that form hydrogen bond.
ii. molecules in dimers are arranged closely packed, therefore the hydrogen bonds are relatively strong.
iii. high energy is needed to overcome the intermolecular forces ,
boiling point
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C
O
O
R
H
C
O
O
R
H
Hydrogen bond
Hydrogen bond
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C
O
O
R
H
O
H
H
C
O
O
R
H
O H
H
Solubilitya) Solubility in water
• Carboxylic acids are soluble in water due to the formation of hydrogen bond between the water molecules and carboxylic acid molecules.
Hydrogen Bonds
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• The solubility of carboxylic acid in water is almost the same as alcohol.
• Aliphatic carboxylic acids with C > 5 are insoluble in water. Size of R ↑, hydrophobic area ↑.
R C OH
Ohydrophilic
hydrophobic
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• Aromatic carboxylic acids are slightly soluble in water due to the huge aromatic ring.
• Dicarboxylic acids are relatively more soluble since more hydrogen bonds are formed.
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Example : Descending order of solubility
CH CH2 CH2CH3
COOH COOH
CH2 CH2 CH2CH3
COOH
CH3 CH2 CH2
COOH
COOH
> >
>
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b. Solubility in non polar solvent
• Carboxylic acids are soluble in non polar solvent such as benzene due to the Van der Waals forces between the benzene and alkyl group of carboxylic acids .
C
O
O
R
H
C
O
O
R
H
Van der Waals forces Van der Waals forces
Hydrogen bonds
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Acidity of Carboxylic Acid
• The acidity of carboxylic acid is influenced by:
i. Resonance effect
ii.Inductive effect
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Carboxylate ion :
Phenoxide ion :
R C O-
O
O-
Resonance Effect
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• Carboxylic acids are more acidic due to the resonance stabilisation of the carboxylate ion.
• The electrons in carboxylate ion are delocalised between two oxygen atoms, whereas in phenoxide ion, the electrons are delocalized in the benzene ring.
• The C=O group in carboxylic acid is a electron-withdrawing group which reduce the electron density of –OH, therefore the –OH bond becomes weaker.
• Thus H+ is easily donated and carboxylic acid is more acidic than phenol.
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• Carboxylic acid is relatively a weak acid, however it is stronger than phenol & alcohol
R C OH
O
>
OH
> OH2 > R OH
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OH O-
+ H3O+
⇌phenoxide ion
(resonance structure)
+ H2O
phenol
CR
O
OH
+ H2O + H3O+
carboxylate ion (resonance structure)
CR
O
O-
CR
O-
O⇌
carboxylic acid
R—O—H + H2O ⇌ R—O– + H3O+ alkoxide ionalcohol
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Inductive Effect
An electron withdrawing group (deactivating group)
that attached to a carboxylate ion will
delocalise the negative charge, thereby stabilises the carboxylate ion and
increases acidity.
An electron donating group, (activating group)
will destabilise the carboxylate ion and decreases acidity.
CEWG
O
O-
CEDG
O
O-
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i. The inductive effect electron-withdrawing group in the compound
• electron-withdrawing groups (e.g –NO2 ,-F,-Cl,-Br, -I ) reduce the electron density of –O H.
• Thus the O-H bond becomes weaker and H+ can be easily released.
• The compound is said to be more acidic Electron- withdrawing group increases the acidity.
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• Example:
CH3CHCl-COOH and CH3CH2COOH
• Cl is an electron-withdrawing groups, therefore reduce the electron density of –OH.
• Thus the O-H bond becomes weaker and H+ can be easily released.
• Acidity :
– CH3CHCl-COOH > CH3CH2COOH
• Electron-withdrawing groups increase the acidity.
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• Example:CH3CHF-COOH and CH3CHCl-COOH
• Both F and Cl are electron-attracting group.
• The electronegativity of F > Cl
• The electron density of –OH in CH3CHF-COOH is less, thus the –OH bond is weaker than in CH3CHCl-COOH. Therefore, H+ is easily donated.
• Acidity : CH3CHF-COOH > CH3CHCl-COOH
ii) The electronegativity of electron-withdrawing group in the compound
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• Example:
CH3C(Cl)2-COOH and CH3CHCl-COOH
• CH3C(Cl)2-COOH contains 2 Cl atoms that make the bond of –OH weaker than CH3CHCl-COOH (with only one Cl atom). Thus, H+ is easily donated.
• Acidity : CH3C(Cl)2-COOH > CH3CHCl-COOH
iii) Number of electron-attracting group in the compound.
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• Example:
CH3CH2CH(Cl)COOH and CH2(Cl)CH2CH2COOH
• The distance between Cl atom and carboxyl group in CH3CH2CHCl-COOH is nearer compare to in CH2ClCH2CH2-COOH.
• The –OH bond in CH3CH2CH(Cl)COOH is weaker than in CH2ClCH2CH2-COOH, so H+ is easily donated.
• Acidity :
CH3CH2CH(Cl)COOH > CH2(Cl)CH2CH2COOH
iv) The position of electron-attracting group
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• Example:CH3COOH and CH3CH2COOH
• -R is an electron –releasing group.
• The size of –R group in CH3CH2COOH is larger than in CH3COOH, so CH3CH2- is a stronger releasing group than CH3-.
• The electron density of –OH in CH3CH2COOH increases and H+ is difficult to be donated.
Electron-releasing groups reduce the acidity of a carboxylic acid.
(v ) The inductive effect of electron- releasing (electron-donating) group in the compound
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SYNTHESIS OF CARBOXYLIC ACIDS
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C OHR
H
H
C O
R
H
C O
R
OH
oxidizing agent
oxidizing agent
1o alcohol aldehyde carboxylic acid
Common oxidizing agents are :•KMnO4 / H2SO4
potassium permanganate
•K2Cr2O7 @ Na2Cr2O7 /H2SO4
potassium /sodium dichromat (VI)
1. Oxidation of primary alcohol and aldehyde
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2. Oxidation of Alkyl Benzene
Roxidizing
agent COOH
KMnO4 , H+
Δ
+ CO2 + H2O
COOH
Cl
CH
CH3
CH3
Cl
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3. Formation and Hydrolysis of nitrile
R CH2 XNaCN
R CH2 CNH2O,H+
R CH2 COOH
NaCN H2O,H+
CH2 CNCH2 Br CH2 COOH
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4. Carbonation of Grignard Reagents
R—MgX O C O
CO2
H2O, H+
R—COOH + Mg(OH)X
CH2MgBr
H2O, H+
CH2 COOH
+ Mg(OH)Br
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CHEMICAL PROPERTIES OF CARBOXYLIC ACIDS
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• Main reactions of carboxylic acid,
a. The reaction that involves the donation of H+ from –OH group.
b. The reaction that involves the substitution of OH group
c. The reaction that involves the reduction with LiAlH4 to primary alcohol
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a. The reaction that involves the donation of H+ from –OH group
1. Neutralisation• Carboxylic acids are acidic, it can react with base such as
NaOH (aq) to give metal carboxylate salts,
CR
O
OH
+ NaOH CR
O
O-Na+
+ H2O
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+ NaOH + H2O
COOH COO– Na+
Sodium benzoate
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2. Reaction with electropositive metals such as Na, K, Ca, Mg and Fe.
R C OH
O
+ R C O
O
M + H2M
Exercise:
COH
OCl
+ K
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b. The reaction that involves the substitution of –OH group (to form its derivatives)
1. Acid chloride formation Acid chloride can be prepared from the reaction of
carboxylic acids with thionyl chloride, SOCl2 ; phosphorous pentachloride, PCl5 ; phosphorous trichloride, PCl3
R C OH
O
R C Cl
O
R C Cl
O
R C Cl
O
+ SO2 + HCl
+ POCl3 + HCl
+ H3PO3
SOCl2
PCl5
PCl3
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SOCl2
PCl5
PCl3
CH C OHCH3
CH3
O
Exercise :
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+ H—OR’C OHR
O
C OR R'
O
⇌ + H2OH+
2. EsterificationCarboxylic acids react with alcohols in the presence of mineral
acid catalyst to produce esters.
+ HOCH2CH3 ⇌H+ CH2 CCH3 OCH2
O
CH3CH2 CCH3 OH
O
+ H2O
carboxylic acid alcohol ester
propanoic acid ethanol ethyl propanoate
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3. Acid anhydride formation Acid anhydrides can be prepared from carboxylic acids by the loss of water through heating.
R C OH
O
RCOH
O
+ heat
CH3 C O C CH3
O O
R C O C R
O O
+ H2O
CH3 C OH
O
CH3 C OH
O
+ heat
+ H2O
ethanoic anhydride
acid anhydride
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4. Amides formation Reaction of carboxylic acids with an ammonia or amine give amide.
R C OH
O
NH3
RNH2
R2NH
R C NH2
O
R C NHR
O
R C NR2
O
+ H2O
+ H2O
+ H2O
1o amide
2o amide(1o amine)
(2o amine) (3o amide)
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CH C Cl
OCH3
CH3
CH3 NH2
CH3 NH
CH3
NH3
Exercise :
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c. The reaction that involves the reduction with LiAlH4 to primary alcohol
Carboxylic acid are reduced to primary alcohols by reaction with lithium aluminium hydride, LiAlH4 .
C OR R'
O
LiAlH4
etherCH2 OHR
1o alcohol
+ R’OH
C O CH2CH CH3CH3
O
CH3
LiAlH4
etherCH2OHCHCH3
CH3
+ HO—CH2CH3
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Methanoic acid, HCOOH as a reducing agent
• Methanoic acid molecule, has both C OHH
O
C OH
Oand
• It shows the properties of both carboxylic acid and aldehyde.
• It also shows reducing properties in reactions with acidified KMnO4 or K2Cr2O7 and Tollens’ reagent.
C
O
H
carboxyliccarbonyl
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C OHH
OKMnO4 / H+
CO2 + H2O + MnO2
Ag(NH3)2+
Ag + CO2 + H2O
(Brown)
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DERIVATIVES OF CARBOXYLIC ACIDS
R C Cl
O
acid chloride
O CC RR
O O
acid anhydride
R C NH2
O
amideC OR R'
O
ester
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Reactions of carboxylic acid derivatives
i. Hydrolysis of acid chlorides
R C Cl
O
H2O R C OH
O
+ HClacid chloride carboxylic acid
ii. Hydrolysis of acid anhydrides
O CC RR
O O
H2O
carboxylic acid
2 C OHR
O
acid anhydride
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Reactions of carboxylic acid derivatives
iii. Hydrolysis of esters
H2OH+
carboxylic acid
+ ROH
H2ONaOH + ROH
alcohol
alcoholNa+C O
-R
OC ORR
O
ester
R C OH
O
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Reactions of carboxylic acid derivatives
iii. Hydrolysis of amide (acidic hydrolysis)
R C NH2
OH2OH+
R C OH
O+ NH4
+
amide Carboxylic acid
Ammonium ion
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Reactions of carboxylic acid derivatives
iii. Hydrolysis of amide (alkaline hydrolysis)
R C NH2
OH2OOH- + NH3
amideammonia
R C O-
O
Carboxylate ion
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Reactions of carboxylic acid derivatives
iii. Hydrolysis of amide (alkaline hydrolysis)
- if dilute acid is added to the carboxylate salt, the carboxylic acid are formed.
+
Carboxylic acid
R C O-
O
Carboxylate ion
H+ R C OH
O
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benzoyl chloride
H2OC Cl
O
Example :
C O CCH3 CH3
O O
ethanoic anhydride
H2O
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methyl ethanoate
H2OH+
Example :
C O CH3CH3
O
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• The reactivity of a carboxylic acid derivative depends on the basicity of the substituent (leaving group) that
attached to the acyl group
• The less basic the substituent, the more reactive the carboxylic acid derivative.
Relative Reactivity Of Carboxylic Acid Derivatives
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Cl– < RCOO– < RO– < HO– < NH2–
Relative basicities of the leaving group (substituent)
acidchloride
acidanhydride
ester carboxylicacid
amide
reactivity increases
R C Cl
O
C O CR
O
R
O
C ORR
O
R C NH2
O
R C OH
O
, , , ,
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ACYL CHLORIDE
• Acyl chloride is the most reactive because of its
electropositive carbonyl group is attach to the
electronegative Cl atom (which is a releasing group).
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ANHYDRIDE ACID
• Anhydride acid is more reactive than ester and amide because the carboxyl group of anhydride is attached to the carbonyl carbon.
• This makes the carbonyl carbon becomes more electropositive and can be easily attack by nucleophile.
R C O
O
C R'
O
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ESTER
• Ester is less reactive towards nucleophile because the delocalization of electron makes the positive charge of carbon can be shifted to oxygen.
• That makes the carbonyl carbon less electropositive.
C O
CH3
OR
C+
O-
CH3
OR
C O-
CH3
O+
R
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AMIDE
• Amide is the least reactive because, NH2 group is an electron-donating group that makes the carbonyl less electropositive.
• The resonance structure of amide shows that the carbonyl carbon is not electropositive.
N
R
O H
HN
+R
O-
H
H
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The Uses of Carboxylic Acid
Carboxylic acid / derivatives Uses
Polyamide (Nylon) carpet, apparel
Ester Artificial flavors
Acetic acid Vinegar
Ethanoic anhydride Drug aspirin
Salicylic acid analgesic