Acid-catalyzed condensation with urea preparation

Heterocycles. Base-catalyzed condensation of urea with diethyl oxalate gives parabanic acid (Murray ) condensation with diethyl malonate gives barbituric acid (Dickey and Gray ). The first procedure uses a solution prepared from sodium... 

The glycosyl ureide and thioureide obtained through the isocyanate and isothiocyanate routes were prepared from tetra-O-acetyl-a-D-glucopyranosyl bromide. The glycosyl ureides derived from this source are identical with those prepared by the acid-catalyzed condensation of D-glu-cose with urea and with thiourea. 

A cationic starch can be prepared by blending a condensate of formaldehyde plus an inorganic ammonium salt with starch and heating at 80 °C for up to 1 h.1316 A great interest was developed with urea-formaldehyde resins that were made to react with such polyalcohols as starch.1317-1319 It was reported that the reaction of starch with urea-formaldehyde resin required an acidic catalyst592,1320-1325 and the use of such dispersants as polyphosphates.1326 Ammonium metaphosphate catalyzed the reaction without the addition of any other acid catalyst.1327 A product that formed a paste was produced by controlling the proportion of starch to aldehyde (either up to 20% of formaldehyde or up to 30% of acetaldehyde) and urea (up to 15%) at pH 2 1.1328... 

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