To an ice cooled suspension of 5.29 g (0.02 mol) 1-(4-chlorophenyl)-1,4-dihydro-4-oxo-6-methyl pyridazine-3-carboxylic Acid (see Example 12) and 2.02 g (0.02 mol) of triethylamine in 125 mol of toluene there is added dropwise 3.13 g (0.02 mol) of phenyl chloroformate. The suspension formed is stirred at room temperature for 15 minutes and to it there is added 1.88 g (0.02 mol) of phenol in 25 ml of toluene. The mixture is stirred at room temperature for 18 hrs. and to it there is added 100 ml of water. The suspension is stirred at room temperature for 2 hrs. and is poured into 800 ml of hexane. The suspension formed is stirred at room temperature for 3 hrs. and is vacuum filtered. The filter cake is slurried in 25 ml of toluene and is filtered. The filtrate is added to 150 ml of hexane and the suspension formed is stirred at room temperature for 2 hrs. The suspension is vacuum filtered and the filter cake air dried to afford 1.3 g (19% yield) of product, mp 140°-146° C.
