A facile synthesis of long chain acyclic alkanols via kolbe coupling: 1-docosanol and 1-triacontanol

摘要

A convenient synthesis of long chain acyclic alkanols viz., 1-docosanol and 1-triacontanol has been devised via Kolbe radical coupling of mono-methyl azelate 2, which has been synthesized from azelaic acid 1. The dimer viz. dimethyl thapsate 3, on Ba(OH)_2 hydrolysis affords mono-methyl thapsate 4, which upon mixed Kolbe coupling with appropriate alkanoic acid [CH_3(CH)_2)_n COOH, n = 6 for 1-docosanol and n = 14 for 1-tri-acontanol] gives the cross coupled products mthyl docosanoate 7 and methyl triacontanoate 8 along with the radical dimers dimethyl triacontanedioate 4' and tetradecane 5'/triacontane 6' as byproducts. Compounds 7 and 8 on LAH reduction in dry THF yield 1-docosanol 9 and 1-triacontanol 10, respectively in high yields. The mixed anodic coupling has been studied by varying parameters viz. degree of neutralization and molar ratio of compounds 4 and C_8/C_(16) alkanoic acid, current density, anode material etc.