Hydrochloric Acid → Valproic Acid

Participants

Reaction Conditions

Reaction Steps

A 2-L flask is charged with 21.6 g (200 mmol) of lithium valerate, 9.5 g (100 mmol) of anhydrous magnesium chloride and 250 mL anhydrous tetrahydrofuran (freshly distilled from sodium, benzophenone). The stirred mixture is warmed to 50° C. allowing the metathetical exchange to occur and a homogeneous solution is produced within 5-15 minutes. The slightly hazy solution is cooled and 5.1 g (200/4 mmol) of diisopropylamine is added. Some precipitate forms and continued stirring fails to effect solution. Finally, 120 mL of a standard solution (1.67M; 200 mmol) of n-butyllithium in heptane is added in four portions at 15-minute intervals at 25°-30° C. After addition of the first portion, a homogeneous solution is produced but addition of the remaining portions yields a turbid mixture. After addition of the final portion, the mixture is permitted to stir for 2 hours at ambient temperature. Then the heterogeneous mixture is cooled to 0° C. and 24.6 g (200 mmol) of 1-bromopropane is added over 10 minutes. Finally, the mixture is warmed to 50° C. for 12 hours overnight. At the conclusion of the reaction period, the mixture is cooled and 200 mL of 6N hydrochloric acid solution is added at a temperature <15° C. followed by 100 mL of water. The phases are separated and the aqueous layer is back-extracted with 100 mL of diethyl ether. The organic layers are combined and the solution is washed with brine, dried (magnesium sulfate), evaporated and the residue is distilled through a 6" heated helices packed column to afford 6.5 g of 2 -propylpentanoic acid; bp 89°-92° C./2 mm.

Provenance & Evidence