Triethylamine → 7-Fluoro-1-methyl-4-oxo-1,4-dihydro-quinol-3-yl ethanesulphonate

Ethanesulphonyl chloride (1.5 ml) was added to a stirred mixture of 7-fluoro-3-hydroxy-1-methyl-4quinolone (3.0 g), obtained as described in Example 3a-f, triethylamine (4.35 ml) and dry dichloromethane (100 ml) at ambient temperature and the resultant solution stirred for 5 minutes then kept at ambient temperature overnight. Further ethanesulphonyl chloride (0.2 ml) was added and the solution stirred at ambient temperature for 4 hours and then kept at this temperature for 3 days. The mixture was filtered and the filtrate was washed with water (2×150 ml). The dichloromethane solution was dried over magnesium sulphate and the solvent evaporated to give a residue which was crystallised from industrial methylated spirit (100 ml). The solid was triturated with diethyl ether (100 ml) and then water (500 ml) to give the novel compound 7-fluoro-1-methyl-4-oxo-1,4-dihydro-quinol-3-yl ethanesulphonate, m.p. 154°-156.5°.