O-Tolidine Dihydrochloride

Make a thin paste of 21 5 g. of finely-powdered o-tolidine (a commercial product) with 300 ml. of water in a 1-litre beaker, add 25 g. (21 ml.) of concentrated hydrochloric acid, and warm until dissolved. Cool the solution to 10° with ice, stir mechanically, and add a further 25 g. (21 ml.) of concentrated hydrochloric acid (1) partial separation of o tolidine dihydrochloride will occur. Add a solution of 15 g, of sodium nitrite in 30 ml. of water as rapidly as possible, but keep the temperature below 15° a slight excess of nitrous acid is not harmful in this preparation. Add the clear, orange tetrazonium solution to 175 ml. of 30 per cent, hypophosphorous acid (2), and allow the mixture to stand, loosely stoppered, at room temperature for 16-18 hours. Transfer to a separatory funnel, and remove the upper red oily layer. Extract the aqueous layer with 50 ml, of benzene. Dry the combined upper layer and benzene extract with anhydrous magnesium sulphate, and remove the benzene by distillation (compare Fig. II, 13, 4) from a Widmer or similar flask (Figs. II, 24, 3-5) heat in an oil bath to 150° to ensure the removal of the last traces of benzene. Distil the residue at ca. 3 mm. pressure and a temperature of 155°. Collect the 3 3 -dimethyldiphenyl as a pale yellow liquid at 114-115°/3 mm. raise the bath temperature to about 170° when the temperature of the thermometer in the flask commences to fall. The yield is 14 g. 

TOLIDINE (CH3(NH2)C6H3-)2 and o-TOLIDINE DIHYDROCHLORIDE (CH3(NH2)C6H3-)2)2HC1... 

SYNS 4,4 -DIAMINO-3,3 -DIMETHYLBIPHENYL DIHYDROCHLORIDE 3,3 -DIMETHYLBIPHENYI 4,4 -BIPHENYLDIAMINE DIHYDROCHLORIDE 2,3 -DIMETHYLBIPHENYL-4,4 -DLANnXE DIHYDROCHLORIDE o-TOLIDINE DIHYDROCHLORIDE... 

In a i-l. beaker 21.2 g. (o.i mole) of d-tolidine is made into a thin paste with 300 cc. of water and dissolved by the addition of 20 cc. (23.6 g., 0.23 mole) of concentrated hydrochloric acid (sp. gr. 1.18), warming a little if necessary. The solution is cooled to 10° with ice, mechanical agitation is started, and 21 cc. (35 g., 0.24 mole) more of concentrated hydrochloric acid added (Note i). This causes partial separation of o-tolidine dihydrochloride. Keeping the temperature at 10-15°, a solution of 14.5 g. (0.2 mole) of gs per cent sodium nitrite in 40 cc. of water is run in rapidly, holding back the last 10 per cent which is added slowly and only as needed to give a distinct positive test for nitrous acid on starch-iodide paper. This excess is maintained for one-half hour. Throughout the diazotization an excess of hydrochloric acid should be present as shown by a strong test... 

If the hydrochloric acid is added all at once instead of in two portions as detailed, a solid will be obtained consisting of o-tolidine coated with its dihydrochloride, and the diazotisation will proceed slowly. 

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