Abstract
The condensation of 1,3-dialkylbarbituric acids with ethyl orthoacetate to give coloured products, is described. The reaction products, are shown by elemental analysis, proton magnetic resonance and mass spectrometric measurements to be derivatives of 7H-pyrano[2,3-d] pyrimidine. Investigations into the condensations of these dyes with various reagents, are outlined, and the results confirm the assigned structures. The preparation of a number of non-ionic tri-nuclear dyes containing the pyrano[2,3-d]pyrimidine nucleus, and the light absorption properties of the dyes containing this nucleus, are discussed. The condensation of ethyl 3-hydrazino-5-methyl-pyrazole-4-carboxylate with various aldehydes and acid chlorides, is outlined. The cyclisation of the resulting hydrazones and hydrazides, under oxidative and dehydrative conditions, respectively, to give ethyl 1H-pyrazolo [3,2-c]-s-triazole-7-carboxylates, is described. The hydrolysis of these esters, and the decarboxylation of the corresponding acids to give 1H-pyrazolo[3,2-c]-s-triazoles, are discussed. Another method of synthesis of 1H-pyrazolo[3,2-c]-s-triazoles, involving the condensation of S-methylisothio-carbohydrazide hydriodide with beta-keto-esters, is described. The synthesis of a range of azamethine and other dyes, related to cyanines, containing the pyrazolo[3,2-c]-s-triazole nucleus, is outlined. The light absorption properties of these dyes are discussed. The applications of the dyes to photographic systems are mentioned.