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the formation of a-hydroxyketones (acyloins), which contain the—CH(OH)CO— group, from two aldehyde molecules:
2RCHO → RCOCH(OH)R
The CN ion (for example, from NaCN or KCN) serves as a specific catalyst of the condensation. This reaction is characteristic mainly for aromatic aldehydes, as well as for certain heterocyclic aldehydes of aromatic character (for example, furfural); it is used to obtain benzoin from benzoic aldehyde (hence its name).
Benzoin, the organic compound C6 H5 COCH(OH)C6 H5 , is a white crystalline substance; Tm = 133°–137°C, Tb = 343°-344° C. Benzoin is used in organic synthesis, as a standard in calorimetry, and so on.