o-Phenylenediamine has been prepared by the reduction of o-nitroaniline by means of tin and hydrochloric acid,1 stannous chloride and hydrochloric acid,2 sodium stannite,3 zinc dust and water,4 sodium hydrosulfite and sodium hydroxide,5 and zinc dust and alcoholic alkali;6 by electrolytic reduction in aqueous alcohol.
o-Phenylenediamine mainly functions as a dye substance in oxidative hair dye products. The substance can be found in cosmetic products* such as hair dyes, hair colors, hair tints and rinses.
The zinc dust should be at least 80 per cent pure, and the amount used should be equivalent to 130 g. of 100 per cent material. A large excess of zinc dust has been used without changing the yield.
Great care must be taken not to add too much zinc dust at first as the reaction becomes very vigorous. It is well to have a bath of ice and wet towels at hand in order to control the reaction if it should become too violent.
Occasionally the reaction suddenly stops and it is necessary to add an additional 10 cc. of 20 per cent sodium hydroxide solution, which causes the reaction to proceed.
