Methylation of Isobutyrophenone Using Potassium Triphenylmethide: An Advanced Organic Chemistry Laboratory Experiment

Abstract

Formation of carbon-carbon bonds is of fundamental importance in the syntheses of a variety of organic compounds, including terpenes and steroids. One of the methods available to produce this transformation is the alkylation of ketones, a reaction that is well documented in the chemical literature (1-4). A survey of experiments in organic laboratory texts and this Journal indicates a void in the area of alkylation reactions of simple ketones. This experiment provides a relatively simple procedure to fill this vacancy in the undergraduate organic chemistry laboratory literature.A variety of bases (5-7) have been used to convert ketones into their corresponding enolate anions that may then undergo an S N 2 alkylation reaction with alkyl halides to produce new carbon-carbon bonds. Potassium triphenylmethide (tritylpotassium, 1) is a useful base in these reactions for several reasons: it is a strong base with a pK a value of 31.5, it is soluble in inert solvents, it reacts quickly to avoid aldol condensations and is not nucleophilic nor a reducing agent, and the red anion of 1 can be used as an indicator to determine when equivalent amounts of base and ketone have reacted to produce the enolate anion and colorless triphenylmethane. KH 1) DMSO/Ar or He (g) 2) (C 6 H5)3CH/DME 3) 40 °C/30 min (C 6 H 5

A Practical New Chiral Controller for Asymmetric Diels−Alder and Alkylation Reactions

“…The best alkylation results were obtained via the potassium enolate which was formed with triphenylmethylpotassium as the base. Tritylpotassium was readily prepared in quantity in dimethoxyethane (DME) solution by the procedure of House or more conveniently by reaction of potassium hydride, triphenylmethane, and a catalytic amount of dimethyl sulfoxide (DMSO) …”