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 100 ml of toluene there is added dropwise 2.17 g (0.02 mol) of ethyl chlorofomate. The suspension formed is stirred at room temperature for 15 min. and is cooled to 5° C. To the suspension is added 2.59 g (0.02 mol) di-n-butylamine and the mixture is stirred at room temperature for 18 hrs. To the mixture is added 100 ml of water and the suspension formed is stirred at room temperature for 1 hr. The toluene layer is isolated, dried over magnesium sulfate and concentrated in vacuo. The residue oil is dissolved in 25 ml of ether and to it there is added 25 ml of hexane. The mixture is allowed to stand at room temperature for 30 minutes and is vacuum filtered. The filter cake is washed with hexane and air dried to afford 5.5 g (73% yield) of product, mp 101°-105° C.
