Лако-красочные материалы — производство

The condensation of dimethylaniline with phosgene yields, besides the p, p’ product, considerable quantites of the o, o’ and o, p’ compounds. The phosgene necessary for the reaction is taken from a phosgene cyl­inder,[27] and a small excess of dimethylaniline is used in order to be sure that all of the hydrogen chloride formed is taken up.

One mole (99 grams) of phosgene is run into 4.3 moles of pure, dry dimethylaniline in a flask with good stirring, keeping the temperature below 24°C. The amount of phosgene taken up is determined period­ically by weighing. When the phosgene addition is completed, the mix­ture is stirred at 24-28° for 24 hours, and then examined to see whether the odor of phosgene has disappeared. If not, an additional 10 grams of dimethylaniline is added and stirring is continued for several hours.

40 grams of pulverized zinc chloride is then added and stirring is continued for 2 to 3 hours, during which all of the zinc chloride goes into solution. The temperature is raised to 55° over a period of 2
hours, and the mixture is held at this point for 12 hours. It is finally stirred for 2 hours at 80°,

The reaction is now completed. The mixture is diluted with 5 liters of water, and concentrated hydrochloric acid (about 40 grams) is added until the odor of dimethylaniline disappears. Unchanged dimethylaniline and some of the by-products go into solution, while Michler’s ketone, being appreciably less basic, remains undissolved. The solid material is filtered off and washed, then heated with 5 parts of water. In case the odor of dimethylaniline again appears, a small amount of concentrated hydrochloric acid is added. The ketone is now filtered off and dried at 100°. The yield is 177 grams, or about 66 per cent of the theoretical amount.

If necessary, the technically pure ketone can be recrystallized from kerosene (b. p. 180°C.). In large scale operations, the product is heated to 140° with this solvent and is allowed to cool. Michler’s ketone, purified in this way, melts at 170-172°.

Tetraethyldiaminobenzophenone is prepared in an analogous man­ner. This ketone is purified through its acid sulfate which crystallizes beautifully.

Technical Observations. Michler’s ketone and its homologs are important starting materials for the preparation of valuable triphenylmethane dyes such as Victoria blue В and Victoria pure blue BO.