Benzyltrimethylammonium hydroxide Elimination

Preparation. The reagent is readily prepared by the condensation of benzil with dibenzyl ketone in the presence of a basic catalyst. Dilthey s original procedure, adopted by Organic Syntheses specifies ethanol as solvent and a solution of potassium hydroxide in ethanol as the base. This procedure suffers from the low boiling point of the alcohol and the limited solubility of both potassium hydroxide and the reaction product in ethanol. In an improved procedure - use of the better solvent triethylene glycol permits operation at a higher temperature, and use of the readily soluble benzyltrimethylammonium hydroxide as base eliminates the step of dissolving potassium hydroxide in ethanol, A mixture of 0.2 mole each of benzil and... 

Hauser et were able to isolate the intermediate dimeric halide when 9-chlorofluorene was allowed to react with only one equivalent of sodium amide in liquid ammonia. In t-butyl alcohol containing its potassium salt or a dilute aqueous solution of benzyltrimethylammonium hydroxide, the rate of formation of bifluorenylidene is second-order in 9-bromofluorene and first-order in the basicity of the reaction medium as measured by the ionisation of nitroaniline indicators . Under the same reaction conditions, protium exchange of 9-deutero-9-bromofluorene and elimination from 9-bromo-9,9 -bifluorenyl are much faster reactions than the conversion of 9-bromofluorene into bifluorenylidene. These facts are consistent with the displacement mechanism. 

Racemization via a reversible addition/elimination process under mild conditions can be used, with for example cyanohydrins, hemiacetals, hemiaminals and hemithioacetals. SiUca-supported benzyltrimethylammonium hydroxide (BTAH) was used to racemize cyanohydrins and effected an efficient DKR process in tandem with porous ceramic-immobilized lipase (lipase PS-C II) (Scheme 4.22) [57]. 

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