Лако-красочные материалы — производство

The product from (b) is dissolved in 1 liter water and treated with 50 grams of concentrated sulfuric acid, previously somewhat diluted. 40 grams of flowers of sulfur is added and the mixture is stirred for 3 hours at 95°C., adding water from time to time. The resulting dye is allowed to settle, and is then filtered off, washed with water, and dried at about 80°. The yield of thioindigo is about 25 grams, or 70 per cent of the theoretical amount based on the О acid. The product contains some sulfur and can be purified by alkaline reduction and reoxidation.