Primuline (Green),

Chloramine Yellow FF (Naphthamine Yellow NN) and Thiazole Yellow, from p-Toluidine.

Generally speaking sulphur reacts with aromatic amines to give substitution products, two aromatic nuclei being joined together by a sulphur atom to give a thio-compound. A number of different bodies are, however, always produced simultaneously, and it is quite impossible to obtain homogeneous reaction products. Even by acting upon p-toluidine with sulphur four products are formed which may be easily recognized, in spite of various views which have been expressed to the contrary. These are in the first place unchanged p-toluidine, then thiotoluidine, dehydrothiotoluidine, and bis-dehydrothiotoluidine. The following formulae indicate the constitution of the above substances:

p-Toluidine.

Thio - p - Toluidine. I.

Dehydro thio-p - Toluidine. II.

"Bis"-dehydrothio-p-Toluidine, or Primuline base.

III.

214 Gms. (2 mols.) of p-toluidine are heated with 140 gms. powdered sulphur {not flowers of sulphur) and 2 gms. dehydrated sodium carbonate 1 to 1800 in a stirring pot provided with a reflux condenser as shown on Plate XIV. (Fig. 36). Hydrogen sulphide is evolved which is absorbed either in caustic soda lye or by a tower filled with moist lumps of caustic soda.

After about 8 hours the evolution of hydrogen sulphide slackens and the temperature is then raised slowly to 2200, and kept there for 5 hours. There is practically no further evolution of hydrogen sulphide, and the melt is then transferred to a flat tin tray where it solidifies to a light yellow crystalline cake. Yield 235 gms.

214 gms. p-Toluidine.

140 gms. S. 2 gms. Na2Co3.

Separation of the Melt.

Method 1. - The cold, hard melt is finely powdered and intimately mixed with 1 % of its weight of dehydrated sodium carbonate, the purpose of which is to prevent the formation of lumps on sulphona-tion. 100 Gms. of the melt are added to 300 gms. monohydrate, the temperature being allowed to rise freely. As soon as all is in solution, which will occupy about an hour, the mixture is cooled to 25° with continuous stirring, and 200 gms. of 66 % oleum are allowed to drop in during an hour with good cooling and stirring, the temperature being kept below 300. After stirring for 5 hours at 300, the temperature is raised to 400, and kept there until a small test portion of the mixture dissolves readily in dilute ammonia. Complete solution is usually attained in 10 hours, but it is advisable not to stop the operation at this point as, for the subsequent filtration, the mass must be thoroughly sulphonated (cf. also sulphonation of β-naphthylamine on p. 37). The mixture is now poured on to 500 gms. ice and 500 c.cs. water, and filtered off after standing for 12 hours. The sulphonic acid is thoroughly washed out with cold water, by which means the greater part of the toluidine sulphonic acid and the thiotoluidine sulphonic acid is washed away. As soon as the washings show only a faint mineral acid reaction, the cakes are dissolved in about 50 gms. ammonia (20 % Nh3) and 800 c.cs. water, the whole being made up to 1200 c.cs. at 80°. The sparingly soluble ammonium salt of dehydro-thiotoluidine sulphonic acid separates out completely in the course of 2 days, when it is filtered and washed with a little 5 % ammonia. The mother-liquor contains the Primu-line, which is precipitated at the boil with 15 % of common salt.

100 gms. Malt. 1 gm. Na2Co3. 100 gms. 100 % H2So4. 200 gms. 60% Oleum.

1 The addition of soda is necessary in order to neutralize the traces of acidic substances which are always found in sulphur. If this is omitted, dark-coloured to black primuline melts are obtained almost invariably.

The yield of dry ammonium salt is about 25 gms., and that of Primuline about 80 gms. of concentrated product.

Method 2. - The finely powdered melt is extracted with alcohol of not less than 90 % strength. By this treatment the toluidine, thiotoluidine, and dehydrothiotoluidine go into solution whilst a pure Primuline base remains behind. The alcoholic extract is evaporated down to dryness, and the toluidine and part of the thiotoluidine are finally driven off by heating to 2500. The product so obtained is sulphonated with 25 % oleum.

Method3. - The sulphonation is effected as before, and the washed sulphonic acid is dissolved at 8o° in twenty times its volume of water and the necessary quantity of caustic soda lye, after which sufficient salt is added to give an 8 % solution, and the whole is filtered at 75°. The Primuline remains behind, whilst the dehydrothiotoluidine sulphonic acid is dissolved in the form of its easily soluble sodium salt, which may subsequently be salted out.

Primuline, discovered by A. G. Green, was the first artificial direct yellow dye which could be diazotized on the fibre and developed by means of phenols or amines to give dyeings fast to washing. On treatment with β-naphthol, Primuline Red is formed, which was at one time made use of to a very large extent. The fastness to washing is good, but the fastness to light is insufficient; further, it cannot be discharged to a white, but only to a yellow, as the Primuline base withstands the action of all discharging agents.

500 gms. Ice and 500 gms. H2O.

About 50 gms. 20 % Nh3 + 800 gms. H2O.

Naphthamine Yellow NN (and FF) and Thiazole Yellow.

Originally dehydrothiotoluidine was a by-product, and in the early days of Primuline manufacture was melted up with sulphur to Primuline base. Nowadays this relationship has quite altered as the originally worthless dehydrothiotoluidine has now become the chief product. Unfortunately it is not possible so to conduct the melt that only the simple dehydrothiotoluidine is formed, and statements to the contrary are incorrect. At the present time Primuline is the by-product, and is sold for what it will fetch. The dyes which are manufactured from dehydrothiotoluidine are of various kinds. The free base or its sulphonic acid is diazotized and then combined with various naphthol sulphonic acids, e.g. with the so-called є-acid (= naphthol disulphonic acid 1:3:8). This colour is distinguished by its great purity, and can be discharged completely to a pure white. Direct red dyes of this kind come into the market under various names and are referred to usually as dyes of the Erika Red type.1 Besides the actual azo colours derived from dehydrothiotoluidine, two other products are prepared which are important yellow dyes. The first of these is Naphthamine Yellow NN or Chloramine Yellow (Kalle & Co.), formed by oxidizing dehydrothiotoluidine-sulphonic acid with sodium hypochloride, whilst the other is Thiazole Yellow or Clayton Yellow, which is produced by combining diazotized dehydrothiotoluidine-sulphonic acid with a second molecule of the same compound; by this means a diazo-amino compound is formed which is further described below.