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

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

NAMING CARBOXYLIC ACIDSNAMING CARBOXYLIC ACIDS

BUTANOIC ACID 2-METHYLPROPANOIC ACID

EXERCISE

• Name the compounds at page 29

• Question 1a

CHEMICAL PROPERTIESCHEMICAL PROPERTIES

ACIDITY

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

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

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

PREPARATION OF CARBOXYLIC ACIDSPREPARATION OF CARBOXYLIC ACIDS

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

Hydrolysis of esters RCOOR + H2O RCOOH + ROH

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

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

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

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

acidic CH3COOCH3 + H2O CH3COOH + CH3OH

alkaline CH3COOCH3 + NaOH ——> CH3COO¯ Na+ + CH3OH

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

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

HCOOH + C2H5OHMETHANOIC ETHANOL ACID

CH3COOH + CH3OHETHANOIC METHANOL ACID

ETHYL METHANOATE

METHYL ETHANOATE

http://en.wikipedia.org/wiki/File:Benzyl_acetate.png

phenylmethylethanoate

http://upload.wikimedia.org/wikipedia/commons/0/04/Butyl_butyrate.png

butylbutanoate

http://upload.wikimedia.org/wikipedia/commons/3/3a/Ethyl-acetate-2D-skeletal.png

ethylethanoate

http://upload.wikimedia.org/wikipedia/commons/4/40/Ethyl_butyrate.png

ethylbutanoate

http://upload.wikimedia.org/wikipedia/en/3/37/Ethyl_hexanoate.png

ethylhexanoate

http://upload.wikimedia.org/wikipedia/commons/a/ae/Ethyl-formate-2D-skeletal-B.png

ethylmethanoate

ethylheptanoate

ethylnonanoate

ethylpentanoate

2-methylpropylmethanoate

methylethanoate

pentylbutanoate

1-methylethylethanoate