Лако-красочные материалы — производство

A solution is made by dissolving 36.6 grams of pure toluylenediamine in 1 liter water at 40°C., and to this solution, after cooling, is added

16.5 grams of 100 per cent sodium nitrite. The volume is brought to 1600 cc. by adding ice, and a mixture of 60 grams of concentrated hydrochloric acid and 40 cc. water is added, with continuous stirring, over a period of 20 minutes. The acid should be introduced below the surface of the liquid. The solution immediately becomes deep brown in color and considerable nitrogen is evolved. The final temperature is

about 10°. After 8 hours, the dye is salted out with 300 grams of salt and filtered off after 3 hours more. The extremely soluble dye is rinsed onto the filter with the mother liquor. The dye is dried at a low tempera­ture (in vacuum in the plant) and weighs, when it is dry, about 40 grams.

The dyes are applied to cotton using a tannin-tartar emetic mordant. They are cheap dyes, giving full shades which are fast to washing but not fast to light. Despite their instability to light, both dyes are widely used for cotton, silk, paper, and especially leather. Mixed with azo yel­low, they give brown tints on furniture leather which have good fast­ness to light and rubbing. The G brand is prepared in exactly the same way, but it generally does not precipitate well and is difficult to filter. This difficulty can be overcome in part by using a larger excess of nitrite.

Chrysophenine G

NH, N =N / <DH N=N<f o-CaH,

0. 1 mole (37 grams) of diaminostilbenedisulfonic acid is dissolved in a solution of 11 grams of soda ash in 200 cc. water. The solution is cooled, and the disulfonic acid is precipitated by the addition of 50 cc. (about 60 grams) 30 per cent hydrochloric acid. Ice is added to bring the temperature to 5°C., and diazotization is carried out by adding 14 grams of sodium nitrite over a period of 2 hours. At the end of the re­action, a small but definite excess of nitrous acid should be present. More ice is added to bring the temperature to 0°, and 20 grams of phenol, liquified with a small amount of water, is added. The mixture of tetrazo compound and phenol is stirred well, and a solution of 50 grams of soda ash in 200 grams of water is poured in rapidly.[57] Ice is added in
sufficient quantity to keep the mixture at about 8°. A clear solution is formed at first and after a short time, part of the brilliant yellow pre­cipitates. After 2 hours, the mixture is heated to 70°, 100 grams of salt is added, and the amount of hydrochloric acid is added which will pre­cipitate the dye completely but not cause the color to change from yel­low to blue. The mixture is then cooled, and the dye is filtered off with suction and sucked as dry as possible. The material weighs about 180 grams.

Ethylation. The moist press cake is made up to 200 grams with water, and 50 grams of soda ash and 30 grams of 35 per cent sodium hydroxide are added. The pasty mixture is transferred to a stirring or rotating autoclave along with 250 grams of 90 per cent alcohol, and 40 grams of ethyl chloride is added in the manner described on page 148. The reaction mixture is heated with continuous stirring for 10 hours at 100°C. (maximum pressure, 6 atmospheres). The autoclave is then cooled and opened. The mixture is treated with twice its volume of 10 per cent salt solution, and the nicely crystalline dye is filtered off. If the diaminostilbenedisulfonic acid was free from diaminodibenzyldi — sulfonic acid, the dye obtained is about 20 per cent stronger than the strongest commercial product. The yield is about 70 grams of dry, con­centrated dye.

Technical Observations. Chrysophenine is the most important yellow direct dye, being practically unrivaled because of its light fastness on wool, silk, and cot­ton, and because of its low cost. The ethylation reaction can also be carried out in aqueous solution in the presence of lime, instead of in alcohol. In either case, it is essential to precipitate the alkyl derivative immediately. The prevailing cost of alcohol determines which of the two methods is preferable. The procedure using alcohol is given here because it involves pressures of not greater than 6 atmospheres. The lime ethylation, on the other hand, requires pressures of 25 atmospheres or higher.

Chrysophcnine shows a characteristic reaction with mineral acids with which it turns a beautiful blue. It is of interest, theoretically, that chrysophcnine is an extra­ordinarily strong dye even though it contains no auxochroiue groups of the type required by the Witt color theory.

The endpoint of the ethylation reaction is recognizable in the following way. A small test portion of the reaction mixture is dissolved in water and treated with a few drops of acetic acid. A few drops of this weakly acid solution are placed on a filter paper, and the yellow flecks are spotted with 10 per cent soda solution. If the ethylation is complete, no change of color to reddish yellow or red is observed. In large scale prep;irations, samples are withdrawn from time to time through a test cock. The ethyl chloride is added in portions of 10 to 15 kilograms, never all at once. Heat­ing is done by means of a steam jacket. The reaction is carried out in a horizontal cylindrical boiler with a horizonfcd stirring mechanism whose stuffing-box must be kept cooled to prevent the alcohol from dissolving the lubricant. The ethyl chloride used amounts to about 180 per cent of that required theoretically.