In a
12-l. flask fitted with
stirrer and
reflux condenser are placed
600 g. (3.8 moles) of potassium permanganate, 7 l. of water, and
200 g. (1.6 moles) of o-chlorotoluene (Org. Syn. Coll. Vol. I, 1941, 170). The mixture is slowly heated to boiling
(Note 1) with continual stirring until the permanganate color has disappeared. This requires three to four hours. The condenser is now set downward for distillation, and the mixture is distilled, with constant stirring, until no more oil passes over with the water. The unattacked
o-chlorotoluene thus obtained amounts to 25–30 g. The hot mixture is filtered with suction and the cake of hydrated
manganese dioxide washed with two 500-cc. portions of hot water. The combined filtrate is concentrated
(Note 2) to about 3.5 l.; if it is not entirely clear it may be clarified by the use of
1–2 g. of decolorizing carbon. It is now, while still hot, acidified by cautiously adding
250 cc. of concentrated hydrochloric acid (sp. gr. 1.19) with continual agitation. When the mixture is cool the white precipitate of
o-chlorobenzoic acid is filtered and washed with cold water. The dry weight is
163–167 g. (
76–78 per cent of the theoretical amount, based on the amount of
o-chlorotoluene actually oxidized) of a very nearly pure
(Note 3) product melting at
137–138°. For purification this may be recrystallized from
600 cc. of toluene, when
135–140 g. of a product melting at
139–140° is obtained. Further crops can be obtained by concentrating the mother liquor.