Parabanic acid, alkylation with

The use of triflic acid in the alkylation with other dicarbonyl compounds, such as isatins,258 parabanic acid,259 and ninhydrin,260 has also been explored. A significant acidity dependence was found in the reaction of isatin with benzene.258 Alkylation does not take place in the presence of trifluoroacetic acid (Ho = —2.7) at 25°C in 12 h. Adding 22% of triflic acid (//0 10.6) brings about a 90% yield of the 3,3-... 

X 10 ) and have very little basic character. The compound acts as a dibasic acid which forms readily alkylated salts. There are a variety of analogues of parabanic acid in which one or more of the ketone functions is replaced by =S or =NH. Such compounds revert to the 0X0 compound when treated with peracetic acid. Even hydrolysis with aqueous ethanolic mineral acid serves to convert =NH into =0 (79JOC3858). 

The reaction of thionyl chloride with 1,3-disubstituted ureas affords either N-sulfinylamines and isocyanates (R = n-alkyl), or chloroformamidine hydrochlorides (R = sec-alkyl, t-alkyl) However, the reaction of oxalyl chloride with ureas does not produce chloroformamidines, parabanic acids being the sole reaction product (51.6 5,66 ... 

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