Benzils aldehydes 2 molecules

Potassium cyanide (s. a. under K [Fe(CN)g]) Benzils from 2 aldehyde molecules... 

Beckett, A., A. D. Osborne, and G. Porter Primary Photochemical Processes in Aromatic Molecules. Part II. Radicals and Radical Anions Derived from Benz-aldehyde. Acetophenone and Benzil. Trans. Faraday Soc. 60, 873 (1964). 

PEG 400 was foxmd to be a good solvent for the syntiiesis of imidazoles 70 in the multicomponent condensation of benzil and aldehydes with two equivalents of ammonium acetate (Scheme 39) [63]. The replacement of one of the reaction-involved ammonium acetate molecules by anilines afforded 1-aryl-substituted imidazoles 71. Imidazoles 70 and 71 were also obtained when benzoin was used instead of benzil in this reaction [64]. This reaction in PEG 400 upon heating xmder reflux provided 70 and 71 with good yields (89-96%). It was proposed tixat benzoin converted to benzil xmder these conditions. 

Mukhopadhyay and Tapaswi have carried out the reaction of several benzils 86, aromatic aldehydes 51, and ammonium acetate in the presence of crown ether DB18C6 and potassimn hydrogen sulfate in water to obtain trisubstituted imidazoles 87 (Scheme 28) [64]. Tetrasubstituted imidazoles 88 are obtained by adding anilines in the reaction mixtiu-e (Scheme 29). The formation of trisubstituted imidazoles 87 involves protonation of the aldehyde carbonyl, formation of diamine intermediate 89 with two molecules of ammonia from ammonium acetate, and condensation with one molecule of benzil to form an intermediate 90, which aromatizes (Scheme 30). The formation of tetrasubstituted imidazoles 88 is explained through the formation of imines 91 from aldehydes and anilines. The imines subsequently form the diamine intermediate 92, which leads to the final product in same way via intermediate 93 as in trisubstituted imidazoles. 

---