Primuline base

The dye component with the structure 125 is obtained through so-called primu-line fusion p-toluidine is heated with sulfur to 200 to 280°C. Subsequent distillation affords not only the primuline base ... 

The yellow crust is then finely ground and extracted with 95% alcohol. This dissolves the toluidine, thiotoluidine, and the dehydrothiotoluidine, leaving the insoluble primuline base (p. 389). The extract is evaporated to dryness and heated to 250°, which removes the toluidine and part of the thiotoluidine. The mixture is then sulphonated with 25% oleum and poured on to ice, filtered, and well washed with water until the washings give only a faint acid reaction. The toluidine and thiotoluidine sulphonic acids pass into solution. The residue is dissolved in 50 gms. of 20% ammonia solution and 800 c.cs. water, and heated to 80°, other 100 c.cs. of water being then added. The solution is filtered hot, if necessary, and the ammonium salt of dehydrothiotoluidine sulphonic acid separates out in the course of 2 days. Primuline can be obtained from the mother liquor by saturating with common salt at the boiling point. 

The mass, after cooling, is powdered and heated with 4 times its weight of fuming sulphuric acid (30% S03) to 70°—80° for a few minutes until a sample dissolves in caustic soda. The sulphonation mixture is poured into ice-water, and the sulphonic acid of the primuline base which is precipitated filtered and washed free of acid. 

Research by Zerweck et al. [2] suggests that many bake dyes contain thiazole rings. It was already known that dehydrothio-p-toluidine, which can be made by sulfur baking of />-toluidinc, and primulin bases, which are formed at higher temperatures, are both thiazole derivatives. 

Acetoacetic acid arylides and pyrazolone derivatives are the coupling components mainly used. Naphtbolsulfonic acids are of only minor importance here. Dehydrothio- p-toluidine sulfonic acid (2) and the sulfonated primulin base are also used as diazo components for certain orange disazo direct dyes. 

Coupling the diazotized monosulfonic acid of the primulin base to acetoacetic acid anilide produces the clear, greenish yellow C. I. Direct Yellow 22, 13925 [.10190-69-9] (21). 

Substantive yellow monoazo dyes with very good light fastness are also obtained by oxidation of dehydrothio-p-toluidine and its derivatives. Oxidation of the sodium salt of the monosulfonic acid of the primulin base in the alkaline pH range with sodium hypochlorite results, for example, in C. I. Direct Yellow29, 19556 [6537-66-2] (22). 

Method 2. The finely pulverized melt is extracted with alcohol of at least 90 per cent strength. The toluidine, thiotoluidine, and dehydrothiotoluidine go into solution leaving a pure primuline base behind. The alcoholic extract is evaporated to dryness, and the toluidine and part of the thiotoluidine are driven off by heating to 2M°C. Sulfonation of the primuline base is done with 25 per cent oleum. 

In the early days of primuline manufacture, dehydrothiotoluidine was a by-product and was remelted with sulfur to make primuline base. Today, the situation is reversed, and the previously worthless dehydrothiotoluidine has become the main product, while primuline is the byproduct. The dehydrothiotoluidine can be obtained pure by vacuum distillation. Unfortunately, it is not possible to conduct the fusion so that only the simple dehydrothiotoluidine is formed statements to the contrary are incorrect. 

Derivation By heating p-toluidine and primuline base with sulfur and separation from the primuline base by distillation in vacuo. 

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