p-Fluorobenzyl chloride 14.458g (100mmol) was added to a slurry of thiourea 7.612g (100mmol) in anh. ethanol 150mL and the mixture was stirred at reflux (oil bath 110C) for 1 day. The obtained solution was cooled and evaporated to dryness. The obtained solid residue was suspended in ethyl acetate 200mL, stirred for 15 min, the solids were collected by filtration, washed with ethyl acetate and dried on highvac. Y=21.84g(99%) of a white cryst solid
1H(d6-DMSO, 400MHz): 9.350(br s, 2H), 9.288(br s, 2H), 7.487(m, 2H), 7.208(m, 2H), 4.536(s, 2H); 19F(d6-DMSO, 376.5 MHz): -114.26(m, 1F)
The thiuronium salt 21.84g was suspended in 1M HCl 800mL. The slurry was cooled to 0C and a stream chlorine gas was introduced first at 0-5C for 15 min, then the cooling bath was replaced with ambient water bath and the chlorine bubbling was continued for additional 30 min. (The starting material dissolved and a new solid formed.) The precipitated crude product was collected by filtration, washed with 1M HCl and partially dried by suction. The material was dissolved in benzene 250mL (with stirring for 20 min), the obtained cloudy solution was dried with MgSO4 (20 min), filtered and evaporated to a small volume (about 50mL). The obtained solidified mixture was gently heated until complete re-dissolution, hexane 400mL was gradually added with heating and the obtained mixture was allowed to cool to RT undisturbed. The resulting cloudy solution was gently filtered through a medium-porosity filter (to avoid premature crystallization), the filtrates were inoculated mechanically and the mixture was allowed to crystallize overnight (12h). The supernatants were decanted off, the obtained large crystals (10.329g) were washed with hexane and dried on highvac. Evaporating the supernatants and re-crystallizing the residue from a mixture of benzene 10mL and hexane 150mL provided the second crop of pure product (5.413g). A third crop of pure product (0.950g) was obtained from the second supernatans in the same fashion. Combined Y=16.692g (81%) of large beautiful white needles.
1H(CDCl3, 400MHz): 7.452(app dd, 8.6Hz, 5.1Hz, 2H), 7.129(app t, 8.6Hz, 2H), 4.823(s, 2H); 19F(CDCl3, 376.5MHz): -109.90(m, 1F)