The carbonyl group by itself does not produce colour, but when two adjacent groups occur in the molecule, as for example in the a-diketones (such as di-acetyl and benzil), a yellow colour is produced.
Azoximes can also be produced from a-benzil dioxime by the "Beckmann" change.
The carbon disulphide and salicylic aldehyde products have also been used as means of distinction, as has also the formation of the stilbazonium bases obtained by condensing ortho-semidines with benzil (0.
The a-acid on oxidation yields benzoic acid, whilst the 1 3-acid yields benzil in addition.
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