Dictionary of Chemistry [6th Ed.]

cohol with an acid to produce an

ester and water; e.g.

CH 3 OH + C 6 H 5 COOH ˆ

CH 3 OOCC 6 H 5 + H 2 O

The reaction is an equilibrium and is

slow under normal conditions, but

can be speeded up by addition of a

strong acid catalyst. The ester can

often be distilled off so that the reac-

tion can proceed to completion. The

reverse reaction is ester hydrolysis or

*saponiÜcation. See also labelling.

estersOrganic compounds formed

by reaction between alcohols and

acids (see illustration). Esters formed

from carboxylic acids have the gen-

eral formula RCOOR′. Examples are

ethyl ethanoate, CH 3 COOC 2 H 5 , and

methyl propanoate, C 2 H 5 COOCH 3. Es-

ters containing simple hydrocarbon

groups are volatile fragrant sub-

stances used asÛavourings in the

food industry. Triesters, molecules

containing three ester groups, occur

in nature as oils and fats. See also dep-

sides; glycerides.

A

• Information about IUPAC nomenclature

ethanal(acetaldehyde)A colourless

highlyÛammable liquid aldehyde,

CH 3 CHO; r.d. 0.78; m.p. –121°C; b.p.

20.8°C. It is made from ethene by the

*Wacker process and used as a start-

ing material for making many or-

ganic compounds. The compound

polymerizes if dilute acid is added to

give ethanal trimer (or paraldehyde),

which contains a six-membered ring

of alternating carbon and oxygen

atoms with a hydrogen atom and a

methyl group attached to each car-

bon atom. It is used as a drug for in-

ducing sleep. Addition of dilute acid

below 0°C gives ethanal tetramer (or

metaldehyde), which has a similar

structure to the trimer but with an

eight-membered ring. It is used as a

solid fuel in portable stoves and in

slug pellets.

ethanamide(acetamide)A colour-

less solid crystallizing in the form of

long white crystals with a character-

istic smell of mice, CH 3 CONH 2 ; r.d.

1.159; m.p. 82.3°C; b.p. 221.25°C. It is

made by the dehydration of ammo-

nium ethanoate or by the action of

ammonia on ethanoyl chloride,

ethanoic anhydride, or ethyl

ethanoate.

ethaneA colourlessÛammable

gaseous hydrocarbon, C 2 H 6 ; m.p.

–183°C; b.p. –89°C. It is the second

member of the *alkane series of hy-

drocarbons and occurs in natural gas.

ethanedialSee glyoxal.

ethanedioic acidSee oxalic acid.

ethane-1,2-diol(ethylene glycol;

glycol)A colourless viscous hygro-

scopic liquid, CH 2 OHCH 2 OH; m.p.

–11.5°C; b.p. 198°C. It is made by hy-

drolysis of epoxyethane (from

ethene) and used as an antifreeze

and a raw material for making *poly-

esters (e.g. Terylene).

ethanenitrile(acetonitrile, methyl

cyanide)A poisonous liquid, CH 3 CN;

b.p. 82°C. It is made by dehydrating

ethanamide or from ammonia and

ethyne. It is a good polar solvent and

esters 212

e

CH 3 OHHO

O

C C 2 H 5

CH 3 O

C C 2 H 5

O

+H 2 O

methanol propanoic acid

methyl propanoate water

Esters