Members of the class of anhydrous N-(3-chloro-2-hydroxypropyl)trialkyl ammonium salts, such as the N-(3-chloro-2-hydroxypropyl)trimethyl ammonium chloride (CHPTMAC), are reactive chemical intermediates and are used in industrial operations for the modification of both natural and synthetic polymers. Particularly, extensive is their use for the production of cationic polysaccharides entailing reaction with starch and cellulose.
It is known that CHPTMAC can be obtained by reaction of epichlorohydrin with trimethylamine hydrochloride. According to U.S. Pat. No. 2,876,217, this reaction is conducted in an aqueous system and the CHPTMAC reaction product is obtained in the form of an aqueous solution. A disadvantageous consequence of conducting the reaction in an aqueous medium, according to U.S. Pat. No. 2,876,217, is the occurrence of a series of side reactions which, for instance, result in the formation of structures such as 1,3-bis(trimethylammonium)-2-hydroxypropane dichloride, which if not removed will contaminate any subsequent reaction product. A further potential and very undesirable by-product of this process is the 1,3-dichloropropanol-2 which may cause crosslinking in subsequent reactions.
Formation of undesirable by-products characterizes also a known process which entails hypochlorination of allyl quaternary ammonium salts. This process is also conducted in an aqueous medium and may be carried out according to the disclosures found in U.S. Pat. Nos. 3,532,751 and 3,558,501. In addition to the by-products mentioned above, this process results in a mixture of N-(2-chloro-3-hydroxypropyl)- and N-(3-chloro-2-hydroxypropyl)trimethylammonium chlorides, and appreciable quantities of the chlorination product N(2,3-dichloropropyl)trimethylammonium chloride (I&EC Product Res. & Dev. 8,279 (1969)). Therefore, the known approaches of the prior art result in aqueous solutions that, in most cases, require careful purification, such as described by Paschell in U.S. Pat. No. 2,876,217 prior to further use. It has, therefore, been proposed that the N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride be prepared in an anhydrous crystalline form. According to European Pat. No. 0,005,223, this product is obtained by a process that entails use and reaction of both gaseous trimethylamine and tetrachloroethane. Disadvantages of this process are the need to operate with gaseous trimethylamine and the formation of the by-product trichloroethylene according to the reaction: ##STR1##
According to European Patent Application No. 0,055,796, the undesirable use of the toxic trimethylamine for the production of a solid product is circumvented by use of an aqueous trimethylamine hydrochloride solution for the reaction with epichlorohydrin, and subsequent removal of water by azeotropic distillation. Since however, in this process the principal reaction is conducted in an aqueous medium, this approach also is characterized by all the disadvantageous consequences arising from the operation in an aqueous system as discussed earlier. Furthermore, the additional process steps necessitated by the azeotropic distillation affect unfavorably the economics of the process, particularly when a truly anhydrous crystalline product is desired.
It is, accordingly, apparent that a need exists for an improved method for the preparation of anhydrous, pure, crystalline N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride wherein the product can be produced conveniently by a simple process that does not entail an aqueous medium or the use of gaseous trimethylamine.