Synthesis of arylazopyrazolo[1,5‐ a ]pyrimidines and their application to synthetic fibres

4‐Phenyl‐5‐aminopyrazole 2 obtained from phenylcyanoacetaldehyde 1 and hydrazine hydrate reacted with diethyl malonate to give 3‐phenyl‐5,7‐dioxopyrazolo[1,5‐ a ]pyrimidine 3 , used as the key compound in the synthesis of arylazo dyes. The key compound 3 was coupled with various aryldiazonium salts 4 to yield 3‐phenyl‐7‐hydroxy‐6‐arylazopyrazolo[1,5‐a]pyrimid‐5‐ones 5. The resulting arylazo dyes (5) were refluxed in phosphorus oxychloride to give 3‐phenyl‐5,7‐dichloro‐6‐arylazo‐pyrazolo[1,5‐ a ]pyrimidines 6 , which subsequently reacted with refluxing morpholine and piperidine to yield 3‐phenyl‐5,7‐bis(morpholino and piperidino)‐6‐aryiazopyrazolo[1,5‐ a ]pyrimidines 7. The arylazo dyes 5 and 7 were applied to polyester fibres as disperse dyes and the arylazo dyes 6 were applied to polyamide fibres as disperse reactive dyes. The spectral and dyeing properties of the dyes were studied.