4. It is essential that the temperature of the reaction mixture be maintained below 10°. If the oxidant is added so rapidly that this temperature is exceeded, the yield is lowered considerably. With a good ice-salt bath, the time required for the addition is forty-five to sixty minutes.
6. This procedure appears to be generally applicable to the preparation of those substituted benzaldehydes in which the substituent is not attacked in the oxidation reaction. Thus, the submitters report that
p-bromobenzaldehyde may be prepared by the same procedure, substituting
62 g. (0.37 mole) of p-bromotoluene for the
p-nitrotoluene and carrying out the oxidation and isolation in the same manner. The yield of crude
p-bromobenzaldiacetate is
51–64 g. (
48–60 per cent of the theoretical amount), m.p.
90–92°. The pure diacetate is obtained by dissolving the crude product in
150 cc. of hot alcohol, filtering through a fluted filter, and cooling. Filtration gives
39–52 g. of pure material, m.p.
94–95°. A second crop is obtained by diluting the filtrate. The total yield is
47–56 g. (
46–54 per cent of the theoretical amount, based on the
bromotoluene). The crude product is hydrolyzed to
p-bromobenzaldehyde by refluxing 45 g. (0.157 mole) with 100 cc. of water,
150 cc. of alcohol, and
10 cc. of concentrated sulfuric acid, filtering through a fluted filter, cooling, and filtering with suction. A second crop is obtained by diluting the filtrate with about 300 cc. of water. The product weighs
24–28 g. (
83–96 per cent of the theoretical amount), m.p.
55–57°.