Abstract

Viedma deracemization is the attrition-induced asymmetric amplification of a conglomerate crystal mixture of achiral or racemizing compounds. There are 13 reported crystalline systems that undergo Viedma deracemization that can be classified as having: (i) achirality in solution, (ii) a racemizing state in solution or (iii) a reversible racemizing reaction in solution. This phenomenon is based on an autocatalytic attrition-enhanced Ostwald ripening process with a requirement for an achiral, or rapidly racemizing state in solution. The concepts of ‘chiral amnesia’, where a molecule’s chiral memory is lost in solution, and ‘the common ancestor effect’, where the chirality of daughter crystals is the same as the mother crystal, can be used to rationalize the generation of a homochiral solid-state. The involvement of chiral clusters in the overall deracemization mechanism is critical. This research explores the generality of Viedma deracemization for an additional 5 achiral organic molecules: benzil, diphenyl disulfide, benzophenone, butylated hydroxytoluene and tetraphenylethylene. Stochastic chiral crystallization was observed for benzil, however chiral crystallization for butylated hydroxytoluene, diphenyl disulfide, tetraphenylethylene and benzophenone was non-stochastic, likely resulting from a cryptochiral environment. Under standard Veidma deracemization conditions, each system reached homochirality within 2 to 30 hours. A shaking mechanism and liquid assisted grinding conditions were also examined and yielded homochiral benzil crystals as little as 10 minutes. Chiral methylbenzylamine was used to direct the chiral amplification of benzil as an example of implementing ‘the rule of reversal’ under attrition conditions, where (R)-methylbenzylamine yielded M-form benzil and (S)-methylbenzylamine yielded P-form benzil.