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Chiral resolution in stereochemistry is a process for the separation of racemic compounds into their enantiomers. It is an important tool in the production of optically active drugs. Other terms with the same meaning are optical resolution and mechanical resolution. One disadvantage of chiral resolution of racemates compared to direct asymmetric synthesis of one of the enantiomers is that only 50% of a desired enantiomer is obtained. Several methods exist. ==Resolution by crystallization== 5-10% of all racemates are known to crystallize as mixtures of enantiopure crystals, so-called conglomerates.〔''Enantiomers, racemates, and resolutions'' Jean Jacques, André Collet, Samuel H Wilen 1981 ISBN 0-471-08058-6〕 Louis Pasteur was the first to conduct chiral resolution when he discovered the concept of optical activity by the manual separation of left-handed and right-handed tartaric acid crystals in 1849. In 1882 he went on to demonstrate that by seeding a supersaturated solution of sodium ammonium tartrate with a d-crystal on one side of the reactor and a l-crystal on the opposite side, crystals of opposite handedness will form on the opposite sides of the reactor. This type of resolution, called spontaneous resolution, has also been demonstrated with racemic methadone. In a typical setup 50 grams dl-methadone is dissolved in petroleum ether and concentrated. Two millimeter-sized d- and l-crystals are added and after stirring for 125 hours at 40°C two large d- and l-crystals are recovered in 50% yield. Another form of direct crystallization is preferential crystallization also called resolution by entrainment of one of the enantiomers. For example an added seed of (−)-hydrobenzoin to an ethanol solution of (±)-hydrobenzoin will have the (−)-enantiomer crystallizing out and after 15 cycles 97% optical purity can be obtained. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「chiral resolution」の詳細全文を読む スポンサード リンク
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