Acetic anhydride
efficient. The method adopted by the manufacturers in this case is outlined below.
The Manufacturing Process Acetone is placed in a boiling flask and heated to boiling. The resulting vapour passes into a glass chamber and comes into contact with a filament (nichrome wire) which is connected to leads sealed in a glass stopper. The filament is heated electrically to a dull red heat and controlled by a variable trans- former. The acetone vapour is pyrolys- ed on contact with the filament and forms ketene. The ketene then passes through a cooling system (condenser) where any "unchanged' acetone vapour will condense and return to the boiling flask. The ketene vapour continues to pass through a trap and is then passed into glacial acetic acid contained in a conical flask. Ketene reacts with glacial acetic acid to form acetic anhydride. An alternative method of manufacture which has also been used in Hong Kong is as follows:
Phosphorus trichloride in a separat- ing funnel is allowed to drop on to an excess of sodium acetate in a reaction flask which is subject to constant shaking and cooling to give acetic anhydride. When the reaction has subsided, the resultant mixture is subjected to fractional distillation to separate acetic an- hydride from the mixture.
Equipment set up for the illicit manufacture of acetic anhydride. (LMC/CCB/40/75)
Introduction
An acetylating substance is essential in the conversion of morphine to heroin and, in Hong Kong, acetic anhydride is the chemical normally used in the illicit manufacture of heroin. There is little legitimate use for this chemical locally, and the majority of the acetic anhydride found in Hong Kong is illegally imported from Japan, Taiwan and Thailand.
Three cases have been detected by the police of the illicit manufacture of acetic anhydride in Hong Kong. The most recent of these was in August 1975, on a New Territories farm where acetic anhydride was being manu- factured for use in the manufacture of heroin on the same premises. Although the process was being carried out in a very small shed, the equipment and method were both sophisticated and
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