Preparation of .beta.-carotene products with a high 9 (Z) content

A process for preparing .beta.-carotene products with a high content of 9(Z)-.beta.-carotene of formula I:

• ##STR7## from a mother liquor from the industrial preparation of C.sub.15 -triarylphosphonium salts, comprising:
• (a) extracting a mother liquor comprising a 9(Z)-C.sub.15 -triarylphosphonium salt of formula (II) and an all-(E)-C.sub.15 -triarylphosphonium salt of formula (VI):
• ##STR8## with water to produce an aqueous solution containing the salts, wherein X is halogen or HSO.sub.4 and Ar is an unsubstituted or substituted phenyl group;
• (b) precipitating the all-(E)-C.sub.15 -triarylphosphonium salt of formula (VI) by
• either
• (1) concentrating the aqueous solution containing the salts to produce the salts as an oil, followed by dissolving the oil in a lower alkanol, or
• (2) concentrating the aqueous solution containing the salts while changing the solvent from water to a lower alkanol;
• (c) removing the precipitated all-(E)-C.sub.15 -triarylphosphonium salt to produce a C.sub.15 -triarylphosphonium salt enriched in the 9(Z)-isomer of formula (II);
• (d) reacting the C.sub.15 -triarylphosphonium salt enriched in the 9(Z)-isomer of formula (II) in the presence of a base in a solvent suitable for a Wittig reaction with either
• (1) all-(E)-.beta.-apo-12'-carotenal of formula (III):
• ##STR9## or (2) a symmetrical C.sub.10 -dialdehyde of formula (IV):
• ##STR10## followed by reacting the resulting 9(Z)-.beta.-apo-12'-carotenal of formula (V):
• ##STR11## in the presence of a base in a solvent suitable for a Wittig reaction with said all-(E)-.beta.-C.sub.15 -triarylphosphonium salt of formula (VI),
• to produce a .beta.-carotene product enriched in the 9(Z) isomer;
• and
• (e) optionally, isomerizing the (Z) double bond at the 11 or 11' position of the .beta.-carotene product by heating.