Ethanol → Mandelic Acid

Participants

Reaction Steps

The resolution of a racemic mixture of a compound of the formula I to prepare the (+) enantiomer of such compound is generally carried out using methanol, ethanol, or isopropanol, preferably isopropanol, as the organic reaction inert solvent. Preferably, the resolution is carried out by combining a racemic mixture of a compound of the formula I and (R)-(-)-mandelic acid in isopropanol, and stirring the mixture to form an optically enriched mandelic acid salt precipitate. The optically enriched precipitate is then recrystallized twice from isopropanol, after which the recrystallized precipitate is converted to the free base of the optically pure compound of formula I by partitioning it between dichloromethane and an aqueous base such as sodium hydroxide, sodium bicarbonate or potassium bicarbonate, preferably sodium hydroxide, or by stirring an alcoholic solution of the salt with a basic ion exchange resin. The free base, which is dissolved in the methylene chloride, can then be converted to the corresponding hydrochloric acid salt. Isolation of the mandelate may be conducted at temperatures from about 0° C. to about 40° C. About 25° C. is preferred.

Provenance & Evidence