Maleic Anhydride → HCID 178516299, Verbindung

Beteiligte Stoffe

Reaktionsbedingungen

Reaktionsschritte

The substituted pyridazinones of the formula (III), to be used as starting materials for the preparation of the compounds of the formula (I), could be prepared, for example, as follows: ##STR7## A solution of 68.3 g of sodium nitrite in 135 ml of water was added dropwise, at 0°-5° C., to a solution of 133 g (0.75 mol) of 4-trifluoromethoxyaniline in 300 ml of concentrated hydrochloric acid and 300 ml of water. After the end of the addition, the reaction mixture was allowed to run, at 5°-10° C., into a solution of 450 g of tin chloride hydrate in 450 ml of hydrochloric acid. After half an hour the salt which had precipitated was filtered off and dissolved in 900 ml of hot water, and the solution was filtered. 73.5 g (0.75 mol) of maleic anhydride were then added to the filtrate at 95°-100° C. and the mixture was stirred for a further hour at 100° C. The product which had precipitated was filtered off at 80° C., rinsed with warm water and then dissolved in dilute sodium hydroxide solution. The filtered solution was acidified with hydrochloric acid and the product which had crystallized out was then filtered off and rinsed with water. 99 g (49% of theory) of 1-(4-trifluoromethoxyphenyl)-3-hydroxy-1,6-dihydropyridazin-6-one were thus obtained in the form of a beige powder of melting point 243° C.

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