TWO-PHASE WITTIG REACTION OF SYNTHESIZING LIQUID CRYSTAL INTERMEDIATE BY ACTIVE QUATERNARY PHOSPHONIUM SALT

Abstract

In this work, (4-methyl)methyl benzoatyltriphenylphosphonium bromide (BrPPh₃CH₂C₆H₄COOCH₃, MBPB), which was prepared from the reaction of (4-bromomethyl)methyl benzoate BrCH₂(C₆H₄)COOCH₃ and triphenyl phosphine (PPh₃) in a CH₂Cl₂/H₂O two-phase medium in the laboratory, acted as the active reagent to synthesize methyl {4-[4-(nonyloxy)-styryl]} benzoate in Z- and E-form (n-C₉H₁₉O(C₆H₄)CH=CH(C₆H₄)COOCH₃, MNSB). The product is a useful liquid crystal intermediate used in industries. Through the active reagent, MNSB is synthesized from the reaction of 4-nonyloxybenzoic aldehyde (n-C₉H₁₉O(C₆H₄)CHO, NAOD) in an alkaline solution of NaOH/organic solvent two-phase medium. The reaction is largely enhanced in the presence of MBPB compound as the active reagent in the Wittig reaction. Under most reaction conditions, this reaction is favorable for the production of E-form MNSB product rather than forming the Z-form MNSB product. A kinetic model was developed and a pseudo-first-order rate law was found to be sufficient to express the kinetic behaviors of the reaction. Effects of the reaction conditions, including the agitation speed, the temperature, the reactant concentration, the organic solvents, the sodium hydroxide concentration, and the 4-nonyloxybenzoic aldehyde concentration on the conversion of NAOD and the reaction rate were investigated in detail. Rational explanations to the observed results have been made.

Keywords:

• Active quaternary phosphonium salt
• Methyl {4-[4-(nonyloxy)-styryl}benzoate]
• Synthesis and kinetics
• Two-phase reaction

Acknowledgment

The authors thank National Science Council (NSC) for the financial support (NSC83-0402-E-007-004) for this work.