Synthesis of an active quaternary phosphonium salt and its application to the Wittig reaction: Kinetic study

Abstract

The synthesis of liquid crystal methyl [4-(nonyloxy) styryl] benzoate was achieved in four stages. First, toluic acid [1] was brominated with N-bromosuccinimide in refluxing CCl₄ to form 4-bromotoluic acid [2] (BTA); second, BTA was esterified with methanol in SOCl₂/CH₂Cl₂ to afford methyl (4-bromomethyl) benzoate [3] (BME); third, BME was condensed with triphenylphosphine (PPh₃) in CH₂Cl₂ to produce the active Wittig reagent methyl (4-methylbenzoate) triphenylphosphonium bromide [4] (MBPB) and fourth, MBPB reacted with 4-nonyloxybenzaldehyde to produce MNSB in high yield. Each of these four reactions was carried out in a separate homogeneous organic solution and the effects of the reaction conditions in each reaction as well as a kinetic model for each individual reaction were studied. Furthermore, the active reagent was applied to the reaction of 4-nonyloxybenzaldehyde (n-C₉H₁₉O(C₆H₄)CHO) to synthesise cis-(E) and trans-(Z)methyl[4-(nonyloxy)styryl]benzoate (n-C₉H₁₉(C₆H₄)CHCH(C₆H₄)COOCH₃) from a two-phase medium alkaline solution of NaOH/organic solvent. High conversion and high selectivity were obtained via this reaction.