GB903717A - Improvements in or relating to the chlorination of naphthoquinone - Google Patents

Abstract

2,3 - Dichloro - 1,4 - naphthoquinone is prepared by the action of chlorine gas on 1,4-naphthoquinone in the presence of hydrated ferric chloride as catalyst, the chlorination being carried out in a series of reaction-cycles in which the mother-liquor separated from a batch of dichloronapthoquinone is used as a reaction medium for making a further batch of product, the first stage of each cycle being conducted at a temperature not greater than 45 DEG C. and the subsequent stages of the cycle being carried out at a temperature of at least 60 DEG C. The catalyst is preferably dispersed in a reaction-medium such as nitrobenzene or nitrotoluene. In Example 1, chlorine gas is passed into a slurry of naphthoquinone in nitrobenzene, which contains dissolved FeCl3, 6H2O; the temperature being maintained at 20 DEG -25 DEG C. for 4 hours. The temperature is then raised to 70 DEG C., and the chlorination is continued for about another 4 hours. The chlorination is finally completed at 85 DEG C. for 1 hour. The reaction-mixture is then cooled to ambient temperature; and 2,3-dichloro-1,4-naphthoquinone is precipitated, and filtered off. The mother-liquor is used as reaction-medium for making another batch of dichloronaphthoquinone; and 19 further batches are made in the same manner. In Example 3, FeCl3,6H2O is formed in situ from iron powder, water and chlorine. Specification 854,977 is referred to.