P - Nitrosodimethylaniline hydrochloride

Dissolve 30 g (31.5 ml, 0.25 mol) of Af,/V-dimethylaniline in 105 ml of concentrated hydrochloric acid contained in a 600-ml beaker, and add finely crushed ice until the temperature falls below 5°C. Stir the contents of the beaker mechanically (or, less satisfactorily, with a thermometer) and slowly add (c. 10 minutes) a solution of 18 g (0.26 mol) of sodium nitrite in 30 ml of water from a separatory funnel, the stem of which dips beneath the surface of the liquid. Maintain the temperature below 8°C by the addition of ice, if necessary. When all the nitrite solution has been added, allow the mixture to stand for 1 hour, filter the yellow crystalline p-nitrosodimethylaniline hydrochloride at the pump, wash it with 40 ml of dilute hydrochloric acid (1 1), drain well and finally wash with a little alcohol. The yield is good and depends upon the purity of the original dimethylaniline. If the pure hydrochloride is required, it may be recrystallised from hot water in the presence of a little dilute hydrochloric acid yellow needles, m.p. 177 °C. Recrystallisation is, however, unnecessary if the free base is to be prepared. 

Dinitrobenzaldehyde. CfHjN.O mol wt 196.12. C 42,87%, H 2.06%, N 14.29%, O 40.79%. Prepn P-Nitrosodimethylaniline hydrochloride, obtained by reacting dimethylaniline and sodium nitrite, is condensed with 2,4-dinitrotolUene in the presence of sodium carbonate. The product, dinitrobenzylidene-p-aminodimethylaniline is split under steam agitation with HCl Bennett, Bell, Org. Syn. 

Transfer 30 g. of the hydrochloride to a 500 ml. separatory funnel, add 100 ml. of water and shake until a thin paste of uniform consistency is obtained add 10 per cent, aqueous sodium hydroxide solution in the cold with shaking until the whole mass has become bright green (the colour of the free base) and the mixture has an alkaline reaction. Extract the free base by shaking with two 60 ml. portions of benzene (1). Dry the combined benzene extracts with a little anhydrous potassium carbonate, and filter into a distilling fiask fitted with a water condenser. Distil off about half of the benzene, and pour the residual hot benzene solution into a beaker. Upon cooling, the p-nitrosodimethylaniline crystallises in deep green leaflets. Filter these off and dry them in the air. The yield of p-nitrosodimethylanihne, m.p. 85°, from the hydrochloride is almost quantitative. 

The salts of p-nitrosodimethylaniline, on the other hand, are yellow. Moreover, since they are neutral-—test this with the pure salt—and since dimethylaniline hydrochloride is add to litmus paper, they cannot have resulted from the simple addition of the acid to the tertiary dimethylamino-group. It is therefore assumed that the salts are formed by the addition of H and acid ion in the 1 7-positions, so that a quinonoid system results through a rearrangement ... 

This dyestuff is obtained by the action of nitrosodimethylaniline chlorhydrate on the ditolylnaphthylenediamine obtained by heating a-dioxynaphthalene (M.P. 180°) with paratoluidine and parato-luidine hydrochloride. The dyestuff forms a brownish crystalline powder, soluble in water with a bluish-violet colour. It dissolves in concentrated sulphuric acid with a greenish-blue colour, which on dilution changes through green to violet, a bluish-violet precipitate being formed. Basle blue is a basic dyestuff and is best dyed on cotton prepared with tannic acid and tartar emetic. 

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