Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

ESTERS. 207

well cooled, since otherwise an energetic, sometimes explosive

oxidation may occur according to the equation

SO 2 + 2 HN0 3 = H 2 SO 4 + 2 NO 2.

This last reaction is more likely to take place if the nitric acid

has not been diluted with acetic acid as recommended above.

Drain the thick crystalline paste, wash it with a little cold, glacial

acetic acid, then freely with carbon tetrachloride, and dry the

product in a vacuum desiccator over sulphuric acid. The crys-

tals obtained in this manner can be preserved in a well-stoppered

flask for a long time unchanged. Yield, about 80 to 90 g.

ESTERS.

Esters are derived from acids by the replacement of the acid hydrogen

atoms by hydrocarbon radicals; they are often called "etherial salts," but are

to be distinguished from ordinary salts by their inability to dissociate elec-

trolytically.

HNO 3 CH 3 NO 3

Nitric Acid. Methyl nitrate (methylester of nitric acid).

Of the methods of forming such substances the following three will be con-

sidered here:

1. From an acid and an alcohol with elimination of water:
   C 2 H 6 OH + HNO 3 = H 2 O + C 2 H 5 NO 3 (No. 153)
   Ethyl Alcohol Ethyl Nitrate


2. From an acid chloride and an alcohol with elimination of hydrogen,
   chloride:
   SOC1 2 + 2 C 2 H 5 OH = 2 HC1 + SO^GJI,;), (No. 155)
   Thionyl Chloride Ethyl Alcohol Diethyl Sulphite


3. From the silver salt of an acid and an alkyl halide:
   Ag2SO 3 + 2 C 2 H 5 I = 2 Agl + SO 3 (C 2 H 5 ) 2 (No. 156)
   Silver Sulphite Ethyl Iodide Diethyl Sulphite

The first method of formation is reversible; the opposed reaction, by which
the ester is broken down, is termed saponification and is in its nature quite
identical with the hydrolysis of salts. Since the saponification of esters
takes place much more slowly than the hydrolysis of salts, it is admirably
adapted for the study of reaction velocities (see text books on Physical Chem-
istry). Inasmuch as the two opposed reactions — esterification and saponi-
fication — often lead to an equilibrium in which all four of the reacting
substances are present in finite determinable concentrations, this so-called
"ester equilibrium" is used with great success in demonstrating the law of