SU50530A1 - Method for isolating rhodamine bases - Google Patents

Description

When producing rhodamines by fusing (mono-or-di) alkylaminophenols with phthalic anhydride in the presence of water-removing agents (SnClj, ZnCb, etc.), it is extremely important to release the dye base, which further, without special labor is converted to hydrochloric salt.

Acrid caustic soda or soda was usually used to separate the base from the melt. Under such conditions, the base is obtained, for the most part, in a form that is difficult to filter, poorly washed and noticeably soluble. These circumstances significantly impede manufacturing operations, make it difficult to obtain a dye of proper purity and reduce the yield.

The author of the present invention has found that all these difficulties are resolved if the base is isolated in crystalline form, which can easily be achieved if the raw melt is treated with an aqueous solution of ammonia and stirred until the base of the rhodamine is obtained in a crystalline form. The base obtained (green crystals) is poorly soluble in cold water, when heated, loses water of crystallization, the transition to the amorphous form, which is significantly soluble in water.

The formation of the base of rhodamine in crystalline form was described by E. Noelting and Dziewanski-Berichte, 38, 3519, 1905, who obtained it by the action of diluted (1-2%) caustic soda on hydrochloride. Treatment of the water with aqueous ammonia at ordinary temperature, followed by extraction of the resulting free base with benzene is suggested to be germs. pat No. 44002. However, the possibility of isolating a crystalline base directly from melt (representing phthalate mixed with phthalic anhydride and products of side reactions) and the use of ammonia for this purpose has not been proven.

The application of the proposed method provides significant technical advantages. When the free base of the dye is obtained, permanent and good results are obtained, even with the use of crude diethyl-meta-amidophenol, the crystalline base is well filtered, easily and completely washed off from impurities. The poor solubility of the crystalline form in water, together with the possibility of obtaining it by this method, in a particularly pure form (which allows the dye to be regenerated from the filtrates after separation of the hydrochloride) gives a 90% theoretical yield of dyes.

Example 1 10 kg of diethyl meta-amidophenol was fused with 12 hg phthalic anhydride. The resulting melt is crushed, kneaded with water and, using external cooling, an aqueous solution of ammonia is poured in and the reaction mass is maintained for the necessary time. Well-formed base crystals are filtered and washed (eg, with a cold solution of 5% NaOH and (, NaCl). The pressed base paste is poured into a mixture of 90 l of water and 8 g of hydrochloric acid heated to 50 ° C with good stirring. While cooling the solution Rhodamine hydrochloride precipitates as a green crystalline precipitate, which is filtered and dried. The yield is 80-86% of theoretical.

Example 2 10 / cg diethyl meta-amidophenol was fused with 12 kg of phthalic anhydride. The resulting melt is treated as in Example 1, and the excreted base is poured into a filtrate heated to 50 °, obtained by filtering the dye of the previous operation with the addition of the required amount of hydrochloric acid and made up with water (volume up to 95 L).

Then proceed according to example 1. Output 90% of theoretical and higher.

The subject matter of the invention.

1. A method for isolating rhodamine bases from conventional rhodamine melts, characterized in that the crude melts are treated with aqueous ammonia solutions, mixing until the rhodamine base is obtained in crystalline form and the precipitated base is separated by conventional methods.

2. With the method indicated in paragraph 1, the use of filtrates obtained after the separation of the bases of rhodamines in previous operations is used instead of fresh ammonia solutions.