Substitution in barbituric acids

Aromatic and aliphatic aldehydes readily condense with thiobarbituric acid to form 5-arylidenethiobarbituric acids or 5-arylidenebis(thiobarbituric acid)s. A longer time is required for condensation with ketones. The UV spectra of the arylidene derivatives have two absorption bands, with maxima at 240–275 and 280–405 nm, while the spectra of the alkylidene derivatives only one absorption band, with a maximum at 280–295 nm.For part I, see 1].