Indicator
Method for preparing an N,N'-diphenylbenzidine indicator solution: Dissolve 1.0 g of N,N'-diphenylbenzidine in 100 mL of sulphuric acid (96%). This redox indicator has an E₀ (pH 0) of +0.76. At the titration endpoint, the colour changes from violet (oxidised state) to colourless (reduced state).
Chemical Properties
GREY TO BROWNISH FINE CRYSTALLINE POWDER
Uses
N,N'-Diphenylbenzidine is an indicator suitable for redox titrations, e.g. with dichromate or cerium(IV) sulfate 1,2. It is also used as intermediates in organic synthesis.
Synthesis
The synthesis of N,N'-Diphenylbenzidine is as follows:
3.12 g (10mmol) of 4,4'-dibromodiphenyl, 2.3 mL (25 mmol) of aniline, 2.9 g (30 mmol) of t-BuONa, 183 mg (0.2 mmol) of Pd2(dba)3, and 20 mg (0.1 mmol) of P(t-Bu)3 were dissolved in 30 mL of toluene, and then stirred at 90°C for 3 hrs. The reaction mixture was cooled to room temperature and three times extracted with distilled water and diethyl ether. Precipitates in an organic layer were filtered, washed with acetone and diethyl ether, and then dried in vacuum to obtain 0.3g of the intermediate compound C (yield: 90%).
Purification Methods
Crystallise the benzidine from toluene or ethyl acetate. Store it in the dark. [Beilstein 13 H 223, 13 IV 368.]
