Phosphorus oxychloride → 2-Butylamino-5-chloro-pyrido[2,3-d]pyridazine-3-carboxylic acid, ethyl ester

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Reaction Steps

5.8 g of 2-butylamino-5-hydroxy-pyrido[2,3-d]pyridazine-3-carboxylic acid, ethyl ester (0.02 mol) are treated with 20 ml of phosphorous oxychloride for 5 days at room temperature with permanent stirring. The excess of phosphorous oxychloride in distilled off in vacuo and the remaining residue is extracted with 20 ml of hot ethyl acetate. 2-butylamino-5-chloro-pyrido[2,3-d]pyridazine-3-carboxylic acid, ethyl ester crystallizes on cooling. Yield 5.5 g (83%); m.p. 126.7° C. (ligroin).

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