Preparation of phosphonium salts

#The present invention relates to a process for preparing 3,7,11-trimethyldodeca-2,4,6, 10-tetraen-1-ylphosphonium salts, to the corresponding phosphonium salts, and to a process for preparing lycopene.

#As a rule, the C15-phosphonium salts for synthesizing carotenoids are prepared from vinylcarbinols by reaction with triphenylphosphine and a strong acid such as HC1 or H2SO4 in protic solvents (see, for example, J. Chem. Soc., 1965, 2019-2026). Unlike vinyl-β-ionol, which is a precursor used for synthesizing vitamin A and β-carotene, it is possible to react vinylpseudoionol as precursor for preparing lycopene under these standard conditions only with poor yields and with low E/Z selectivities to give the corresponding C15-phosphonium salts.

#EP 382 067 describes a process in which C15-phosphonium salts of lower alkanoic acids are prepared as intermediates because the salts which are mentioned of strong acids always give poor E/Z selectivities and, in the subsequent preparation of lycopene, low yields (byproducts). The salts of the alkanoic acids must be converted back into the chlorides (anion exchange) in an elaborate procedure before the subsequent Wittig reaction. In addition, to obtain a high E/Z ratio in the lycopene, it is necessary to remove (Z) contributions to the phosphonium salt by crystallization.

#A mixture of 41.9 g of triphenylphosphine, 13.7 g of methanesulfonic acid (70% strength) and 100 ml of acetic acid was heated to 80° C. and then, over the course of 10 minutes, 24.2 g of 3,7,11-trimethyldodeca-1,4E,6E,10-tetraen-3-ol (91% pure) were added. The mixture was then stirred for 30 minutes before distilling off the acetic acid under 50 mbar. The residue, consisting of 3,7,11-trimethyldodeca-2,4,6,10-tetraen- 1-yltriphenyliphosphonium methanesulfonate, was taken up in 100 ml of toluene, which was then likewise distilled off under 50 mbar, to remove the last residues of acetic acid. This procedure was then repeated once more. The residue was taken up in 25 ml of methanol and extracted once with 100 ml, and four times with 50 ml each time, of heptane. The methanolic solution containing the required product was investigated by HPLC with an internal standard. Analysis revealed 50.7 g (90.4%) of 3,7,11-trimethyldodeca-2,4,6,10-tetraen-1-yltriphenylphosphonium methanesulfonate consisting of 39.8 g (71.0%) of all-E isomer, 5.69 g (10.1%) of 6Z isomer and 5.22 g (9.3%) of 2Z isomer. The ratio of the E isomer to the Z isomers is accordingly 3.71.

#A mixture of 39.3 g of triphenylphosphine, 15.1 g of trifluoromethanesulfonic acid and 100 ml of acetic acid was heated to 80° C. and then, over the course of 10 minutes, 23.2 g of (95% pure) 3,7,11-trimethyldodeca-1,4E,6E,10-tetraen-3-ol were added. The mixture was then stirred for 30 minutes before the reaction solution was analyzed by HPLC with an internal standard for content and selectivity. The solution contained 56.7 g (92.2%) of 3,7,11-trimethyldodeca-2,4,6,10-tetraen-1-triphenylphosphonium trifluoromethanesulfonate consisting of 43.7 g (71.1%) of all-E isomer, 6.33 g (10.3%) of 6Z isomer and 6.64 g (0O.8%) of 2Z isomer. The E isomer/Z isomers ratio is accordingly 3.4:1.

#A mixture of 39.3 g of triphenylphosphine, 19.0 g of p-toluenesulfonic acid and 100 ml of acetic acid was heated to 80° C. and then, over the course of 10 minutes, 23.2 g of (95% pure) 3,7,11-trimethyldodeca-1,4E,6E,10-tetraen-3-ol were added. The mixture was then stirred for 30 minutes before the reaction solution was analyzed by HPLC with an internal standard for content and selectivity. The solution contained 53.5 g (84.0%) of 3,7,11-trimethyldodeca-2,4,6,10-tetraen-1-yl-triphenylphosphonium p-toluenesulfonate consisting of 41.5 g (65.2%) of all-E isomer, 6.39 g (10.0%) of 6Z isomer and 5.59 g (8.8%) of 2Z isomer. The E isomer/Z isomers ratio is accordingly 3.5:1.