Estimation of p-Phenylenediamine

The para-diamines cannot be estimated by means of the diazo reaction. The following estimation is based on the formation of benzoquinone dichloro-imide when p-phenylenediamine in hydrochloric acid solution is added to a solution containing excess of sodium hypochlorite and sodium carbonate. 

A solution of sodium hypochlorite is prepared by diluting 50 c.cs. of a commercial solution containing about 12—15% available chlorine to 1,000 c.cs. Or, a corresponding solution may be prepared by passing chlorine into caustic soda (p. 512). 50 c.cs. of this solution are titrated N 

of hypochlorite solution are then measured out, diluted with an equal volume of cold water, and about 1 gm. of solid sodium carbonate added. 10 c.cs. of the solution to be determined, containing 2—6% of p-phenylenediamine dissolved in slight excess of hydrochloric acid, are added slowly with stirring. The mixture should then give a strong reaction with starch-iodide paper, otherwise the experiment must be repeated, using either less diamine or more sodium hypochlorite solution. On the addition of the diamine solution, the dichloro-imide is rapidly precipitated as an almost colourless solid. 

The turbid solution is then titrated, without filtration, with — sodium 

The method gives good results, the error varying from 0-3—0-7%. (J. S. C. I., 38, 408.) 

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