Organic compounds containing the unsaturated group =C:N.NH.CO.NH2. They are formed when aldehydes or ketones react with a semicarbazide (H2N.NH.CO.NH2). Semicarbazones are crystalline compounds with relatively high melting points. They are used to identify aldehydes and ketones in quantitative analysis: the semicarbazone derivative is made and identified by its melting point. Semicarbazones are also used in separating ketones from reaction mixtures: the derivative is crystallized out and hydrolysed to give the ketone.
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