Chirality recognition in solvent-free solid-state crystallization: chiral adduct formation by bis-beta-naphthol derivatives and benzoquinone crystals

New adduct crystals were obtained by simply mixing/grinding component crystals of bis-beta-naphthol (BN) derivatives with benzoquinone (BQ) under solvent-free conditions. Chiral recognition was found to operate during this process and either a racemic or a chiral crystal of a BN derivative produced an adduct crystal with BQ by solid-state crystallization. The chirality preference changed subtly according to the molecular structure of the BN derivative. Even in circumstances in which no adduct was formed, addition of a third component, such as crystals of naphthalene, to the grinding mixture yielded an adduct crystal. Remarkably, these adduct crystals were found to decompose spontaneously with time and revert to the starting crystal of the BN derivative by losing BQ molecules from the crystal lattice. Local melting of crystals by the grinding pressure was found unlikely to be the mechanism of adduct formation. Overall, these results demonstrate that molecules in the solid state could change their relative location and hydrogen bonding partners, thereby exerting chiral discrimination.