contents structure of carboxylic acids nomenclature physical properties of carboxylic acids...

CONTENTS

• Structure of carboxylic acids

• Nomenclature

• Physical properties of carboxylic acids

• Preparation of carboxylic acids

• Chemical properties of carboxylic acids

• Reduction of Carboxylic acids

• Esters

• Acyl chlorides and its reactions

• Triglycerides and fats

• Biofuels

• Polyester

CARBOXYLIC ACIDSCARBOXYLIC ACIDS

Before you start it would be helpful to…

• Recall the definition of a covalent bond

• Recall the difference types of physical bonding

• Be able to balance simple equations

• Be able to write out structures for simple organic molecules

• Understand the IUPAC nomenclature rules for simple organic compounds

• Recall the chemical properties of alkanes and alkenes

CARBOXYLIC ACIDSCARBOXYLIC ACIDS

STRUCTURE OF CARBOXYLIC ACIDSSTRUCTURE OF CARBOXYLIC ACIDS

• contain the carboxyl functional group COOH

• the bonds are in a planar arrangement




• include a carbonyl (C=O) group and

a hydroxyl (O-H) group




• include a carbonyl (C=O) group and

a hydroxyl (O-H) group

• are isomeric with esters :- RCOOR’

HOMOLOGOUS SERIESHOMOLOGOUS SERIES

HCOOH CH3COOH C2H5COOH

Carboxylic acids form a homologous series

Carboxylic acids form a homologous series

HOMOLOGOUS SERIESHOMOLOGOUS SERIES

HCOOH CH3COOH C2H5COOH

With more carbon atoms, there can be structural isomers

C3H7COOH (CH3)2CHCOOH

INFRA-RED SPECTROSCOPYINFRA-RED SPECTROSCOPY

IDENTIFYING CARBOXYLIC ACIDS USING INFRA RED SPECTROSCOPY

Differentiation Compound O-H C=O

ALCOHOL YES NO

CARBOXYLIC ACID YES YES

ESTER NO YES

ALCOHOL CARBOXYLIC ACID ESTER O-H absorption O-H + C=O absorption C=O absorption

Acids are named according to standard IUPAC rules

• select the longest chain of C atoms containing the COOH group;

• remove the e and add oic acid after the basic name

• number the chain starting from the end nearer the COOH group

• as in alkanes, prefix with alkyl substituents

• side chain positions are based on the C in COOH being 1

e.g. CH3 - CH(CH3) - CH2 - CH2 - COOH is called 4-methylpentanoic acid

NAMING CARBOXYLIC ACIDSNAMING CARBOXYLIC ACIDS








METHANOIC ACID ETHANOIC ACID PROPANOIC ACID








BUTANOIC ACID 2-METHYLPROPANOIC ACID



Many carboxylic acids are still known under their trivial names, some having been called after characteristic properties or their origin.

Formula Systematic name (trivial name) origin of name

HCOOH methanoic acid formic acid latin for ant

CH3COOH ethanoic acid acetic acid latin for vinegar

C6H5COOH benzenecarboxylic acid benzoic acid from benzene

101°C 118°C 141°C 164°C

PHYSICAL PROPERTIESPHYSICAL PROPERTIES

BOILING POINT

Increases as size increases - due to increased van der Waals forces

Greater branching = lower inter-molecular forces = lower boiling point

Boiling point is higher for “straight” chain isomers.

101°C 118°C 141°C 164°C

164°C 154°C


BOILING POINT



BOILING POINT


Carboxylic acids have high boiling points for their relative mass

The effect of hydrogen bonding on the boiling point of compounds of similar mass

Compound Formula Mr b. pt. (°C) Comments

ethanoic acid CH3COOH 60 118

propan-1-ol C3H7OH 60 97 h-bonding

propanal C2H5CHO 58 49 dipole-dipole

butane C4H10 58 - 0.5 basic V der W


BOILING POINT


Carboxylic acids have high boiling points for their relative mass

• arises from inter-molecular hydrogen bonding due to polar O—H bonds

AN EXTREME CASE... DIMERISATION

• extra inter-molecular attraction = more energy to separate molecules

HYDROGEN BONDING

Boiling temperature comparision

Alcohol london forces and Hydrogen bonding

Halagenoalkane C-F bonds stronger than C-C

Aldehyde / Keytone/ester permanent diplole – permanent dipole forces

Alkenes only london forces

Carboxylic Acid london forces and Hydrogen bonding (more london forces than alcohol as moreElectrons in carboxylic acid

BoilingTemp.

No. of carbon atoms


SOLUBILITY

• carboxylic acids are soluble in organic solvents

• they are also soluble in water due to hydrogen bonding

HYDROGEN BONDING


SOLUBILITY

• carboxylic acids are soluble in organic solvents

• they are also soluble in water due to hydrogen bonding

• small ones dissolve readily in cold water

• as mass increases, the solubility decreases

• benzoic acid is fairly insoluble in cold but soluble in hot water

HYDROGEN BONDING

PREPARATION OF CARBOXYLIC ACIDSPREPARATION OF CARBOXYLIC ACIDS

Oxidation of aldehydes RCHO + [O] ——> RCOOH

Hydrolysis of esters RCOOR + H2O RCOOH + ROH

Hydrolysis of acyl chlorides RCOCl + H2O ——> RCOOH + HCl

Acid Hydrolysis of nitriles

PREPARATION OF CARBOXYLIC ACIDS HY PREPARATION OF CARBOXYLIC ACIDS HY HYDROLISING NITRILESHYDROLISING NITRILES

RCN —————————> RCOOH + NH4ClHeat with dilute HCl (aq)

RCN —————————> RCOOH + NH4Cl

Base Hydrolysis of nitriles

Heat with dilute NaOH(aq)

If you wanted the free carboxylic acid in this case, you would have to acidify the final solution with a strong acid such as dilute hydrochloric acid or dilute sulphuric acid. The ethanoate ion in the sodium ethanoate will react with hydrogen ions as mentioned above.

PREPARATION OF ESTERS - 1PREPARATION OF ESTERS - 1

Reagent(s) alcohol + carboxylic acid

Conditions reflux with a strong acid catalyst (e.g. conc. H2SO4 )

Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l)

ethanol ethanoic acid ethyl ethanoate

Notes Conc. H2SO4 is a dehydrating agent - it removes watercausing the equilibrium to move to the right and thusincreases the yield of the ester

For more details see under ‘Reactions of carboxylic acids’


Reagent(s) alcohol + acyl chloride

Conditions reflux under dry conditons

Equation e.g. CH3OH(l) + CH3COCl(l) ——> CH3COOCH3(l) + HCl(g)

methanol ethanoyl methyl chloride ethanoate

Notes Acyl chlorides are very reactivebut must be kept dry as they reactwith water.


Reagent(s) alcohol + acid anhydride

Conditions reflux under dry conditons

Equation e.g. CH3OH(l) + (CH3CO)2O(l) ——> CH3COOCH3(l) + CH3COOH(l)

methanol ethanoic methyl ethanoic anhydride ethanoate acid

Notes Acid anhydrides are not as reactive asacyl chlorides so the the reaction is slower.

The reaction is safer - it is less exothermic.

Acid anhydrides are less toxic.

CHEMICAL PROPERTIESCHEMICAL PROPERTIES

ACIDITY

weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq)

form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)

2RCOOH + Mg(s) ——> (RCOO¯)2Mg2+(aq) + H2(g)


ACIDITY




The acid can be liberated from its salt by treatment with a stronger acid.

e.g. RCOO¯ Na+(aq) + HCl(aq) ——> RCOOH + NaCl(aq)

Conversion of an acid to its water soluble salt followed by acidification of the salt to restore the acid is often used to separate acids from a mixture.


ACIDITY




The acid can be liberated from its salt by treatment with a stronger acid.

e.g. RCOO¯ Na+(aq) + HCl(aq) ——> RCOOH + NaCl(aq)

Conversion of an acid to its water soluble salt followed by acidification of the salt to restore the acid is often used to separate acids from a mixture.

QUALITATIVE ANALYSISCarboxylic acids are strong enough acids to liberate CO2 from carbonatesPhenols are also acidic but not are not strong enough to liberate CO2.

REDUCTIONREDUCTION

Dry ether

CHLORINATION OF CARBOXYLIC ACIDSCHLORINATION OF CARBOXYLIC ACIDS

Chlorination involves replacing the OH with a Cl

Product acyl chloride

Reagent thionyl chloride SOCl2

Conditions DRY conditions

Equation CH3COOH + PCl5 ——> CH3COCl + POCl3 + HCl

phosphorus(V) chloride

Alternative CH3COOH + SOCl2 ——> CH3COCl + SO2 + HClmethod

ACYL CHLORIDESACYL CHLORIDES

More reactive than carboxylic acid so using acyl chloride to make esters are faster

OTHER REACTIONS OF ACYL CHLORIDEOTHER REACTIONS OF ACYL CHLORIDE

ESTERIFICATIONESTERIFICATION

Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 )

Conditions reflux

Product ester

Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l)

ethanol ethanoic acid ethyl ethanoate

Notes Conc. H2SO4 is a dehydrating agent - it removes water

causing the equilibrium to move to the right and thusincreases the yield of the ester

Naming esters Named from the original alcohol and carboxylic acid

CH3OH + CH3COOH CH3COOCH3 + H2O

from ethanoic acid CH3COOCH3 from methanol

METHYL ETHANOATE

H2SO4

Heat under reflux

ESTERSESTERS

Structure Substitute an organic group for the H in carboxylic acids

Nomenclature first part from alcohol, second part from acide.g. methyl ethanoate CH3COOCH3

ETHYL METHANOATE METHYL ETHANOATE

ESTERSESTERS



Preparation From carboxylic acids, acyl chlorides and acid anhydrides

Reactivity Unreactive compared with acids and acyl chlorides


ESTERSESTERS



Preparation From carboxylic acids, acyl chlorides and acid anhydrides

Reactivity Unreactive compared with acids and acyl chlorides

Isomerism Esters are structural isomers of carboxylic acids


PHYSICAL PROPERTIES OF ESTERPHYSICAL PROPERTIES OF ESTER

Common esters such as ethyl ethanoate are volatile liquidsAnd only slightly soluable in water

The reason for the solubility is that although esters can't hydrogen bond with themselves, they can hydrogen bond with water molecules. As chain lengths increase, the hydrocarbon parts of the ester molecules start to get in the way.

ester formulasolubility (g per 100 g of water)

ethyl methanoate HCOOCH2CH3 10.5

ethyl ethanoate CH3COOCH2CH3 8.7

ethyl propanoate CH3CH2COOCH2CH3

1.7

Soluability of esters

PHYSICAL PROPERTIES OF ESTERPHYSICAL PROPERTIES OF ESTER

Boiling points of esters

molecule type boiling point (°C)

CH3COOCH2CH3 ester 77.1

CH3CH2CH2COOH carboxylic acid 164

The small esters have boiling points which are similar to those of aldehydes and ketones with the same number of carbon atoms. Like aldehydes and ketones, they are polar molecules and so have dipole-dipole interactions as well as van der Waals dispersion forces. However, they don't form hydrogen bonds, and so their boiling points aren't anything like as high as an acid with the same number of carbon atoms.For example:

Classification CARBOXYLIC ACID ESTER

Functional Group R-COOH R-COOR

Name PROPANOIC ACID METHYL ETHANOATE

Physical properties O-H bond gives rise No hydrogen bondingto hydrogen bonding; insoluble in waterget higher boiling pointand solubility in water

Chemical properties acidic fairly unreactivereact with alcohols hydrolysed to acids

STRUCTURAL ISOMERISM – STRUCTURAL ISOMERISM – FUNCTIONAL GROUPFUNCTIONAL GROUP

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

HCOOH + C2H5OHMETHANOIC ETHANOL ACID

ETHYL METHANOATE





ETHYL METHANOATE

METHYL ETHANOATE





CH3COOH + CH3OHETHANOIC METHANOL ACID

ETHYL METHANOATE

METHYL ETHANOATE




The products of hydrolysis depend on the conditions used...

acidic CH3COOCH2CH3 + H2O CH3COOH + CH3CH2OH





acidic CH3COOCH2CH3 + H2O CH3COOH + CH3CH2OH

alkaline CH3COOCH2CH3 + NaOH ——> CH3COO¯ Na+ + CH3CH2OH

If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt





acidic CH3COOCH3 + H2O CH3COOH + CH3OH

alkaline CH3COOCH2CH3 + NaOH ——> CH3COO¯ Na+ + CH3CH2OH

If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt

The carboxylic acid can be made by treating the salt with HCl

CH3COO¯ Na+ + HCl ——> CH3COOH + NaCl

USES OF ESTERSUSES OF ESTERS

Despite being fairly chemically unreactive, esters are useful as ...

• flavourings apple 2-methylbutanoatepear 3-methylbutylethanoatebanana 1-methylbutylethanoatepineapple butylbutanoaterum 2-methylpropylpropanoate

• solvents nail varnish remover - ethyl ethanoate

• plasticisers

TRIGLYCERIDES AND FATSTRIGLYCERIDES AND FATS

TriglyceridesTriglycerides

• are the most common component of edible fats and oils

• are triesters of the alcohol glycerol, (propane-1,2,3-triol) and fatty acids

glycerola triglyceride

TRIGLYCERIDES AND FATSTRIGLYCERIDES AND FATS

TriglyceridesTriglycerides

• are the most common component of edible fats and oils

• are triesters of the alcohol glycerol, (propane-1,2,3-triol) and fatty acids

SaponificationSaponification

• alkaline hydrolysis of triglycerol esters produces soaps

• a simple soap is the salt of a fatty acid

• as most oils contain a mixture of triglycerols, soaps are not compounds

• the quality of a soap depends on the oils from which it is made

FATTY ACIDSFATTY ACIDS

Carboxylic acids that are obtained from natural oils and fats; they can be…

SaturatedSaturated CH3(CH2)16COOH octadecanoic acid (stearic acid)




9UnsaturatedUnsaturated CH3(CH2)7CH=CH(CH2)7COOH octadec-9-enoic acid

(oleic acid)

cis (Z) isomer

trans (E) isomer




9UnsaturatedUnsaturated CH3(CH2)7CH=CH(CH2)7COOH octadec-9-enoic acid

(oleic acid)

cis (Z) isomer

trans (E) isomer

12 9

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

octadec-9,12-dienoic acid (linoleic acid)

FATTY ACIDS AND HEALTHFATTY ACIDS AND HEALTH

SaturatedSaturated • solids at room temperature• found in meat and dairy products• are bad for health• increase cholesterol levels - can lead to heart problems



MonoMonounsaturatedunsaturated • contain just one C=C

• thought to be neutral to our health• found in olives, olive oil, groundnut oil, nuts, avocados



MonoMonounsaturatedunsaturated • contain just one C=C

• thought to be neutral to our health• found in olives, olive oil, groundnut oil, nuts, avocados

PolyPolyunsaturatedunsaturated • are considered to be ‘good fats’

• contain more than one C=C bond• tend to be liquids at room temperature, eg olive oil. • can be split into two main types...

Omega 3 - fatty acidsOmega 3 - fatty acids

Omega 6 - fatty acidsOmega 6 - fatty acids

OMEGA 3 and 6 FATTY ACIDSOMEGA 3 and 6 FATTY ACIDS

Omega 3 - fatty acidsOmega 3 - fatty acids lower the total amount of fat in the bloodand can lower blood pressure and decreasethe risk of cardiovascular disease

33 (omega) end CH3CH2CH=CHCH2CH2CH2CH2CH=CH(CH2)7COOH

The omega numbering system starts from the opposite end to the carboxylic acid group

OMEGA 3 and 6 FATTY ACIDSOMEGA 3 and 6 FATTY ACIDS

Omega 3 - fatty acidsOmega 3 - fatty acids lower the total amount of fat in the bloodand can lower blood pressure and decreasethe risk of cardiovascular disease

33 (omega) end CH3CH2CH=CHCH2CH2CH2CH2CH=CH(CH2)7COOH

Omega 6 - fatty acidsOmega 6 - fatty acids reduce the risk of cardiovascular disease but can contribute to allergies and inflammation

66

(omega) end CH3CH2CH2CH2CH2CH=CHCH2CH=CH(CH2)7COOH

CHOLESTEROLCHOLESTEROL

• a fatty substance which is found in the blood

• it is mainly made in the body

• plays an essential role in how every cell in the body works

• eating too much saturated fat increases cholesterol levels

• too much cholesterol in the blood can increase the risk of heart problems

CHOLESTEROLCHOLESTEROL

• a fatty substance which is found in the blood

• it is mainly made in the body

• plays an essential role in how every cell in the body works

• eating too much saturated fat increases cholesterol levels

• too much cholesterol in the blood can increase the risk of heart problems

Ways to reduce cholesterol levelsWays to reduce cholesterol levels

• cut down on saturated fats and trans fats (trans fats are more stable and difficult to break down in the body)

• replace them with monounsaturated fats and polyunsaturated fats

• eat oily fish

• have a high fibre diet; porridge, beans, fruit and vegetables

• exercise regularly

BIOFUELSBIOFUELS

What are they?What are they?Liquid fuels made from plant material and recycled elements of the food chain

BiodieselBiodieselAn alternative fuel which can be made from waste vegetable oil or from oil produced from seeds. It can be used in any diesel engine, either neat or mixed with petroleum diesel.

It is a green fuel, does not contribute to the carbon dioxide (CO2) burden and produces drastically reduced engine emissions. It is non-toxic and biodegradable.

vegetable oil glycerol biodiesel

BIOFUELSBIOFUELS

AdvantagesAdvantages

Reuses/reduces waste (vegetable) oil/ lessens need to dispose of (vegetable) oil

Could lessen use of (non-renewable/nonsustainable) crude oil/fossil fuels

vegetable oil/biodiesel/reactants renewable/ sustainable

Plants grown for vegetable oil could offset some CO2 emissions

BIOFUELSBIOFUELS

DisadvantagesDisadvantages • poor availability - very few outlets & manufacturers

• more expensive to produce• poorly made biodiesel can cause engine problems

FutureFutureproblemsproblems • there isn’t enough food waste to produce large amounts

• crops grown for biodiesel use land for food crops• a suitable climate is needed to grow most crops• some countries have limited water resources

POLYESTERPOLYESTER

Polyesters are polymers in which the monomers are liked together by ester groups

POLYESTERPOLYESTER

POLYESTERPOLYESTER

Hydrolysis of polyester

Polymer + Acid Hydrolysis/ Break down to monomers

Simple esters are easily hydrolysed by reaction with dilute acids or alkalis.

contents structure of carboxylic acids nomenclature physical properties of carboxylic acids...

Documents

cooh group

carboxyl functional

o absorption c

longest chain of c atoms

carbonyl c

chain positions

standard iupac rules

o absorptionacids