PURPOSE: To obtain a sulfoisophthalic acid derivative useful for the modification of dyeability of polyester, polyamide, etc., in high purity and quality by reacting a metal salt of a 5-sulfoisophthalic acid dialkyl ester with a phosphonium salt.
CONSTITUTION: This 5-sulfoisophthalic acid dialkyl ester phosphonium salt can be produced by reacting a compound of formula I (R1 and R2 each is a 1-4C alkyl; Mn+ is an n-valent metal ion or ammonium ion; (n) is 1 or 2) with a compound of formula II (X1 to X4 each is a 1-20C alkyl; Y is a halide anion) in a mixture of water and a scarcely water-soluble organic solvent (e.g. water- toluene) at 15-95°C. The phosphonium salt having extremely low content of inorganic materials and by-products such as metal halide salt or ammonium salt is easily producible by this process in the state of an alkylene glycol solution which is easily handleable in use.
HORIKAWA YASUHIKO
TAKAHASHI SHIGENOBU
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