Лако-красочные материалы — производство

Tetramethyldiaminodiphenylmethane is oxidized in dilute acid solution with just the calculated amount of lead dioxide in paste form. Lead dioxide, once dried, cannot be used for such oxidations because it is not in a fine enough state of subdivision. The oxidizing strength of lead dioxide paste must be determined by titration (see Analytical Section). However, for use in the laboratory, a lead dioxide paste of known strength can be prepared by dissolving a weighed quantity of lead nitrate in water, heating to boiling, and adding a chloride of lime solution, which has been prepared in the cold and filtered, until all of the lead has been precipitated. (Chloride of lime is very soluble in water, just as is calcium chloride; the insoluble residue obtained when it is mixed with water is calcium carbonate and calcium hydroxide.) The endpoint is reached when a spot of the colorless solution on filter paper is not blackened by sodium or ammonium sulfide solution. The mixture is boiled for a short time until it no longer smells of chlorine, and the lead dioxide is filtered off with suction, washed thoroughly with water, and mixed, without drying, with water to form a uniform paste.

A solution is made of 24.5 grams (0.1 mole) of tetramethyldiamino — diphenylmethane in 1400 cc. water and 60 cc. nitric acid (40° Вё). To the solution is added 600 grams of ice and then, all at once and with very vigorous stirring, the lead dioxide paste from exactly 0.1 mole (33.1 grams) of lead nitrate. A completely clear, yellow solution is obtained in about 30 to 45 minutes. 20 grams of anhydrous sodium sulfate, or 40 grams of the crystalline salt, is then added to precipitate the lead as its insoluble sulfate, which is filtered off and washed with water. The clear filtrate is added slowly with stirring to a solution of 100 grams of soda ash in 800 cc. water. The oily material separating with the first few drops is made to crystallize by rubbing with a glass rod or by seeding with some solid hydrol, and then the hydrol separates as light gray, crys­talline flocks as the mixing proceeds. The precipitate is filtered off im­mediately, washed thoroughly with cold water, and dried at ordinary temperatures. The yield is 26 grams, or about 96 per cent of the theo­retical amount.

The light gray crude product obtained in this way melts at 90-92°C. and is generally usable directly for preparing dyes. The material may be purified by recrystallization from 20 parts of low boiling ligroin, and then forms almost colorless needles or prisms melting at 101—103°. It dissolves in acetic acid to give a deep blue color, and in excess mineral acid to give a colorless solution.

The chief impurity in the crude product is the dihydryl ether:

(CHS),N-C, H. — C4H4—N(CHj),

ch~o—CH<^

(CH,),N-C, h; CeHt—N(CHj),

which forms colorless prisms melting at 200-201 °С. and which is almost insoluble in cold ether. This impurity undergoes condensation reactions just like the hydrol and its presence Joes no harm.

The hydrol can also be prepared, although less satisfactorily, by al­kaline reduction of Michler’s ketone. The hydroxyl group in the hydrol is extremely reactive; it is alkylated, for example, merely by boiling with alcohol. The technical importance of the hydrol arises from the ease with which it condenses with various aromatic compounds to form leuco compounds of triphenylmethane dyes (see wool green S, page 307).