Alkanoic Acids and Esters

SUBSECTION 5Esterification is a naturally occurring process which can be performed in the laboratory

Methanoic acid (formic acid)

Ethanioic acid (acetic acid)

Acetyl salicylic acid (aspirin)

Functional group

C

O

O H

-COOH

The carboxyl acid group

IUPAC Systematic Naming• count no. carbons in straight chain • select prefix for parent alkane(carbon 1

from –COOH)• drop “e” and add ending –oic acid• formic acid and acetic acid are IUPAC

preferred names for methanoic and ethanoic acids

Ester functional group

CO

O

C

RC

O

O 1

RR = H or alkyl group

R1 = alkyl group

Naming Esters

• 1st part of name comes from the alkanol– e.g. methanol produces methyl-, ethanol

produces ethyl- etc...• 2nd part of name comes from alkanoic acid

– e.g. methanoic acid produces –methanoate, ethanoic acid produces –ethanoate etc...

CH O

CH

H HOH

HC C H

H

ethyl

ethyl ethanoate

ethanoate

Name this ester

C C C

O

O C C C C

H

H

H

H

HH

H H H H

H

HH H

Practice• Name the esters produced from...

– Butanol and pentanoic acid– Heptanoic acid and ethanol

• Name the alkanols and alkanoic acids used to produce...– Pentyl butanoate– Methyl octanoate

5.2.3• explain the difference in melting and

boiling point caused by straight-chained alkanoic acids and straight-chained primary alkanol structures

Reactions• alkanoic acids react with alkanols to

produce esters (alkyl alkanoates).

Producing Esters

• a condensation reaction where two molecules combine with the elimination of a small molecule like water.

Alkanol + Alkanoic acid D

Ester + Water

Example

CH

OCH

H H

OCH

OCH

HH

H

H

+ OH H+C

H OC

H

H HOH

HC C H

H

• The –OH is removed from the ACID• The –H is removed from the

ALCOHOL

CH3CH2CH2OH + HOOCCH2CH3 CH3CH2CH2OOCCH2CH3

• The C with H atoms attached is from the alcohol

• The C without H atoms attached is from the acid

Problem• Use structural formulae to illustrate the

reaction of:– Methanol with butanoic acid;– Propanoic acid with ethanol.

Properties of Esters• have pleasant fruity smells• colourless liquids (lower molecular

weight are more volatile)• polar molecules • short chain soluble in water

– solubility i with h in length of carbon chain

• good organic solvents• neutral to Litmus

• flavours & fragrances– contribute to the tastes and smells of fresh

fruits and flowers– used as fragrances in body care products

and cosmetics– methyl salicylate used in “Deep Heat” as an emollient to soothe sore muscles

Esters - Uses

• lubricants– used as jet engine lubricants for many

decades due to their low viscosity– polar molecules – stronger intermolecular

forces so lower rates of evaporation and higher flash points

Esters - Uses

• solvents– used in wood lacquers and thinners– esters of acetic acid used in personal care

products and cosmetics– ethyl acetate in nail polish remover

Esters - Uses

• plasticisers– phthalate esters are oily liquids used to

soften hard plastics like PVC– plasticised PVC used to make medical

tubing, gloves, shower curtains, toys

Esters - Uses

ASPIRIN (acetyl salicylic acid)an ester of acetic acid and salicylic acid

Triglycerides

Triesters of glycerol and fatty acids

The reverse reaction• The formation of esters is a reversible

reaction.

• This means that an alkanol and alkanoic acid can be produced from an ester.

Alkanol + Alkanoic acid

Ester + Water

This breakdown using water is called a “hydrolysis” reaction.

Hydrolysis of Esters

CH O

CH

H HOH

HC C H

H

COH

CHH O H

Ethanoic acid

CO

H

CHH

H

H H

Ethanol

CH3COOCH2CH2CH3

CH3COOHEthanoic acid

CH3CH2CH2OHPropan –1- ol

Esterification• slow reaction at room temperature that

reaches equilibrium• heating increases the reaction rate, but• the reactants and products with lower

boiling points will vaporise readily and be lost

ethanol bp 78oCethanoic acid 114ethyl ethanoate 77water 100

Esterification• slow reaction at room temperature that

reaches equilibrium• heating increases the reaction rate, but• the reactants and products with lower

boiling points will vaporise readily and be lost

• heat under reflux – use a cooling condenser vertically over reaction vessel so vapours condense and run back down into reaction flask

Esterification• add conc. H2SO4 as

– catalyst to improve reaction rate– dehydrating agent as it removes water

so not available for reverse reaction - drives the equilibrium to the right

• excess of alkanol shifts equilibrium to the right

Separation of Ester - Fractional DistillationComponent Boiling point (oC)methanol 64.7propanoic acid 140.8water 100methyl propanoate 79.9

Separation of Ester - Aqueous Separation

Mixture placed into separating funnel

Draining off the aqueous layer