By heating nitroso-dialkylamines with gallic acid or its amide, well-defined compounds are obtained which are termed Oxazines. The gallic acid is obtained exclusively from natural tannin.

Reaction: 2

p-Nitrosodimethylaniline.

Gallamide.

Gallamine Blue (R. Geigy).

(a) Nitroso-dimethylaniline.

100 Gms. dimethyl aniline are mixed with 200 gms. 30 % hydrochloric acid and, after cooling, 300 gms. of ice are added. A concentrated solution of 60 gms. of 100 % sodium nitrite are then dropped in during 5 hours, the beaker being placed in ice-water. It is not possible to test for free nitrous acid with nitrite paper, as nitroso-dimethylaniline hydrochloride itself reacts with it. The excess, therefore, can only be recognized by its odour. The reaction to Congo paper should, of course, be shown the whole time. After standing for 6 hours, the product is filtered off, rinsed out into the filter by means of the mother-liquor, and the precipitate sucked as dry as possible. Finally, it is squeezed in a screw-press, and the moist nitroso-dimethylaniline powdered as much as possible. The salt

100 gms. Dimethyl-aniline.

200 gms. Hc1.

300 gms. Ice.

60 gms. 100 %

NaNO,.

1 The caustic lye must be free from chlorate so that electrolytic caustic cannot be used or else oxidation occurs on hydrolysis and acidification.

2 One molecule of nitroso-dimethylaniline is used up as the oxidizing agent.

must not be dried, but is used in the fresh moist condition. On the large scale it is obtained in a sufficiently dry condition merely by centrifuging.

Para-nitroso-diethylaniline is obtained in a similar manner, except that, owing to the very great solubility of the hydrochloride, no water is used for the nitrosation but only concentrated hydrochloric acid and saturated sodium nitrite solution, with external cooling. In the works the process is carried out in enamelled vessels, as in the case of the Tropaeoline coupling.

(b) Gallamine Blue,

20 Gms. gallamide of 92 % purity 1 are dissolved in 500 c.cs. of 90 % alcohol contained in a glass bolthead provided with reflux condenser and stirrer (6ee Figs. 9 and 18a), and nitroso-dimethyl-aniline obtained from 75 gms. dimethlaniline are added in three portions to the boiling mixture. Preferably the additions are made at intervals of 15 minutes, so that the mixture is completed in three-quarters of an hour. The product is boiled up under reflux for a further 4 hours, and is then allowed to stand for 12 hours. The Gallamine Blue is obtained as a brilliant, glistening, bronzed precipitate which is filtered off and washed with water. The alcohol is redistilled. The yield of pure Gallamine Blue is about 40 gms. A grey dye similar to Nigrosine is obtained from the alcoholic mother-liquor, which gives fast grey shades with chrome acetate on cotton under the name of Methylene Grey.

Gallamine Blue is practically insoluble in water and can therefore not be used in this form. By means of various reactions, however, it may be converted into an easily soluble form.

One part Gallamine Blue is warmed up to 500 on the water-bath with six parts of sodium bisulphite solution containing 25 % So2, until the evolution of sulphurous acid has ceased. If this is the case, after about an hour the product is heated up to 85o for 1-3 days until the colour of the mixture has become pure greyish-green. The dye obtained is a sulphonic acid of the leuco-compound (or possibly a complex sulphonic salt), and dyes wool, mordanted with chrome acetate, a beautiful and fast navy blue. It may also be used for printing cotton, but is overshadowed in importance by another colouring matter belonging to this group, namely, the Modern Violet of Durand and Hugenin, which is obtained as a leuco-compound

20 gms. Gallamide.

500 gms. Alcohol. Nitroso-dimethyl-aniline from 75 gms. dimethyl-aniline.

1 part

Gallamine

Blue.

6 parts

25% Bisulphite.

1 The purity is determined by distilling off the ammonia with caustic soda solution and titrating.

by the reduction of Gallamine Blue with hydrogen sulphide, and affords extremely pure and fast chrome lakes on cotton:

Modern Violet (Durand and Hugenin).

50 Gms. Gallamine Blue are dissolved in about 40 gms. of 30 % caustic soda solution and 400 c.cs. water, and to the clear solution are added 50 gms. crystallized sodium sulphide. The liquid is acidified at 6o° during one hour with about 100 gms. strong hydrochloric acid until a permanent reaction is given with Congo paper. The blue colour will have disappeared by this time, leaving a practically colourless solution, which is filtered from the precipitated sulphur, and the hydrochloride of the leuco compound salted out with 150 gms. common salt. It is then filtered off, washed with a little saturated salt solution, and well pressed out. The dye is dried in vacuo at 6o° as it rapidly reoxidizes. Yield about 55 gms.

Notes on Works Technique and Practice. - The oxazines are printing colours par excellence. In addition to the dimethylaniline derivatives the corresponding diethyl derivatives are also prepared, which are characterized by their very pure greenish shades (Celestine Blue). If gallic acid be used in place of gallamide, the Gallocyanines are produced which were accidentally discovered by Horace Kochlin; he attempted to fix nitroso-dimethylaniline on cotton by means of tannin and tartar emetic, and so obtained blue colours which he recognized to be oxazines. The Gallocyanines cannot be manufactured conveniently in ethyl alcoholic solution, methyl alcohol being used instead, which is, however, less pleasant to work with owing to its poisonous nature and its volatility. Besides the simple oxazines there are also a number of more complex condensation products known, but we cannot enter into these here.

We may recall the fact that the first oxazine to attain to technical importance was Meldola's Blue, Naphthol Blue, or Bengal Blue, which is obtained from nitroso-dimethylaniline hydrochloride and β-naphthol. It is very fast, but does not give beautiful shades, and

50 gms.

Gallamine

Blue.

40 gms.

30%

NaOH.

400 c.cs. H2O.

50 gms. Na2S+Aq.

About 100 gms. conc. Hc1. 150 gms. NaCl.

its dust attacks the mucous membranes so strongly that many people cannot work with it. In spite of this, however, it is still fairly widely used.

The large-scale plant is constructed of enamelled cast-iron with a reflux condenser made from lead tubing. A charge of 40 kilos, gallamide is used, the operation lasting about 12 hours.

Owing to its oxidizability Modern Violet must be ground up in the cold as otherwise spontaneous combustion may occur. The presence of finely divided sulphur is obviously the cause of this undesirable phenomenon.