ACETYL CHLORIDE, Ethanoly chloride, CH3-CO-Cl.
According to the accepted abbreviation of an acetyl group, CH3CO-, as Ac, the formula of acetyl chloride may be written as AcCl.
In the laboratory, it is made by the action of phosphorus trichloride on glacial acetic acid in cold.
A distillation flask (250 ml) is fitted with a tap funnel and connected to a water-condenser leading to a receiver guarded by a calcium chloride tube to exclude moisture (Fig. 1.1). 50 g of glacial acetic acid are placed in the distillation flask which is cooled by immersion in cold water. Then 40 g (25 ml) of phosphorus trichloride is added dropwise from the tap-funnel. When all has been added, the flask is warmed on a water bath to 40-50ºC. As the evolution of hydrogen chloride slackens, the temperature is raised to boiling.
The acetyl chloride that distills over is collected in the receiver cooled by ice water. It is again purified by distilling from the receiver flask in the usual way. The fraction distilling between 50-54ºC is collected.
Acetyl chloride is a colorless liquid, bp 52ºC. It has a very pungent smell and fumes strongly in moist air. It is soluble in ether, acetone, and acetic acid.
Its chemical reaction with various nucleophilic agents such as alcohols, ammonia, and amines have been discussed under the general treatment of acid halides. In these reactions, an H atom of the functional group OH or NH2 is replaced by the acetyl group (CH3CO-). This process is known as Acetylation i.e., the introduction of an acetyl group, which is very useful in synthetic organic chemistry.
The chief use of acetyl chloride is an acetylating agent in the preparation of several derivatives, dye-stuffs, and pharmaceuticals. It is also used to determine the number of OH groups in organic molecules.