Chapter 20, Problem 20.68P

Interpretation Introduction

Interpretation:

It is to be shown how to synthesize $\text{2, 4-diphenylbut-2-ene}$ using phenylethanoic acid (phenylacetic acid) as the only source of carbon atoms.

Concept introduction:

Lithium aluminum hydride (${\text{LiAlH}}_{\text{4}}$) is the strong reducing agent and reduces carboxylic to corresponding alcohol. Alcohol on heating with a strong acid (either Conc. ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ or ${\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}$) produces the corresponding alkene. Alkene on treatment with dilute acid, the water molecule adds to the double bond according to Markovnikov’s rule. When an unsymmetrical reagent treated with an unsymmetrical alkene, the negative part of the reagent adds to the carbon of double bond which possesses less number of hydrogen atom is nothing but the Markovnikov’s rule. Pyridinium chlorochromate (PCC) is the molder oxidizing agent and used to oxidize primary alcohol to the corresponding aldehyde and secondary alcohol is oxidized to the ketone. Alcohol can be converted to corresponding alkyl halide by the treatment of either ${\text{PBr}}_{\text{3}}{\text{or PCl}}_{\text{3}}$. The back to back ${\text{S}}_{\text{N}}\text{2}$ reaction occurs to form the corresponding alkyl halide. The alkyl halide on treatment with triphenylphosphine followed by treatment of the strong base especially, $\text{BuLi}$, corresponding phosphonium ylide is formed which is used in Wittig reaction. A Wittig reaction is useful for the conversion of $\text{C=O}$ the bond of a ketone or aldehyde into a $\text{C=C}$ bond.