Nitrosodimethylaniline hydrochloride

A solution of 25 g. of sodium hydroxide in 500 c.c. of water is heated to boiling (porous pot ) in a distilling flask (capacity 1 1.) connected to a downward condenser which is provided with a receiver containing 60 c.c. of 2 A-hydrochloric acid. Through the corked neck of the flask 18-6 g. of nitrosodimethylaniline hydrochloride—preferably the moist reaction product—are added in portions. Each addition is only made after most of the oily drops of the base from the preceding portion have dissolved, and finally the liquid is boiled until it has become reddish-brown. The dimethylamine produced is trapped in the hydrochloric acid in the receiver at the conclusion of the distillation the contents of the receiver must still be acid. They are evaporated to dryness on the wateT bath in a small porcelain or glass basin, and finally the completely anhydrous salt can be recrystallised from a very small amount of absolute alcohol. Yield 5-6 g. 

A solution of 300 g. (2.4 moles) of technical dimethyl aniline in 1050 cc. of concentrated hydrochloric acid is placed in a large jar or crock and finely divided ice added until the temperature has fallen to 5 °. The contents of the jar are then stirred mechanically, and a solution of 180 g. (2.6 moles) of sodium nitrite in 300 cc. of water is slowly added from a separating funnel, the stem of which dips beneath the surface of the liquid. The addition takes one hour, and the temperature is kept below 8° by the addition of ice if necessary. When all the nitrite has been added the mixture is allowed to stand one hour and then filtered. The solid -nitrosodimethylaniline hydrochloride is washed with 400 cc. of 1 1 hydrochloric acid and then with 100 cc. of alcohol. After drying in air, it weighs 370-410 g. (80-go per cent of the theoretical amount). 

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. 

It should be mentioned in passing that the first oxazine to attain technical importance was Meldola blue (naphthol blue, Bengal blue), prepared from nitrosodimethylaniline hydrochloride and naphthol. It is a very fast dye but does not give pure shades. Furthermore, its dust irritates the mucuous membranes so severely that many persons cannot work with it. Despite these disadvantages, however, Meldola blue is still rather widely used. 

Toluylene blue may be obtained by mixing solutions of equivalent quantities of nitrosodimethylaniline hydrochloride and metatoluylenediamine, and also by oxidation of the latter base with dimethylparaphenylenediamine. It is an amido-indamine characterised by a greater degree of stability than the previous ones. The monoacid salts are blue, and the diacid salts are colourless. 

Malta Grey and Nigrisine are bodies of unknown constitution prepared by heating nitrosodimethylaniline hydrochloride in aqueous or alcoholic solution. 

Freshly prepared />-nitrosodimethylaniline hydrochloride was used without further purification. 

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. 

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