Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

CHAPTBE II
CARBOXYLIC ACIDS AND THEIR SIMPLE DERIVATIVES
1. ACID CHLORIDES
(a) ACETYL CHLORIDE 1
PHOSPHORUS TRICHLORIDE (72 g.) is run from a dropping funnel into
a distilling flask containing 90 g. (1-5 mole) of anhydrous glacial
acetic acid and cooled in water. The flask is fitted with a downward
condenser, and next warmed in a porcelain basin of moderate
size containing water at 40°-50°, until the vigorous evolution of
hydrogen chloride slackens and the originally homogeneous liquid
has separated into two layers. The acetyl chloride is then distilled
from the lower layer of phosphorous acid by means of a vigorously
boiling water bath. A small filter flask attached to the lower end
of the condenser by a cork serves as a receiver and its contents are
protected against atmospheric moisture by a calcium chloride tube
connected by means of a rubber tube. The substance is purified by
repeated distillation with the use of a thermometer. The fraction
boiling between 48° and 53° is collected separately. (Boiling point
of pure acetyl chloride 51°). Yield 70-80 g. Use in the preparation
of acetic anhydride, see p. 126, and of acetophenone, p. 346.
The product is tested for the presence of phosphorus (PC13) by decomposing
a few drops with a little warm water and evaporating the
solution in a porcelain capsule. The residue is twice evaporated with
concentrated nitric acid or with bromine water and is finally tested
for phosphoric acid in the usual way. If phosphorus is detected, the
material should again be distilled with a few drops of glacial acetic acid.
(6) BENZOYL CHLORIDE
Into a round-bottomed flask (capacity 0-25 1.) fitted if possible
with a ground-in condenser and containing 40 g. (0-33 mole) of dry
1 Bechamp, Compt. rend., 1855, 40, 946 ; 1856, 42, 226.
121