N,N'-bis(4-fluorophenyl)-thiourea has been previously synthesized in the literature:

S. Hüunig, H. Lehman, G. Grimmer, Liebigs Ann. Chem., 579, 77-86 (1953) H.P Buu-Hou, N.D. Xuong, N.H. Nam, J. Chem. Soc., 1573-1581 (1955)

We performed the synthesis of N,N'-bis(4-fluorophenyl)-thiourea according to the procedure of Fry as modified by Raiford and McNulty and with a modified work-up procedure we ourselves developed:

H.S. Fry, J. Am. Chem. Soc., 35, 1539-1546 (1913) L.C. Raiford, G.M. McNulty, J. Am. Chem. Soc., 56, 680-681 (1934) On The Synthesis and Reactivity of N'-Haloarylalkoxycarbimidoyl Nitrenes M. Tellez, Ph.D. Dissertation, New Mexico State University, Las Cruces, NM (1995) (RP259)

To 4-fluoroaniline (22.2g, 0.2 moles) and pyridine (31.62 g, 0.4 moles) in carbon disulfide (250 mL) was added iodine (25.4 g, 0.1 moles) in carbon disulfide (150 mL). The solution was then brought to reflux and stirred for three hours. Most of the solvent was recovered through distillation, and the remainder removed under reduced pressure. The solid was then washed with water (2 X 40 mL) and 1M hydrochloric acid (2 X 50 mL) and filtered off. The filter funnel was transfered to a different filtration flask and the solid washed with cold chloroform (3 X 35 mL) to afford the desired product in 97.7% yield (25.8 g, 0.098 moles) as a greyish-white solid. If no reflux is used,the yield is 77%. Recrystallization from acetone affords the thiourea with m.p. 189-190.5 degrees Celsius (lit.<53LA77> 145 degrees Celsius, lit. <55JCS1573> 208 degrees Celsius "All these thioureas undergo thermal decomposition on prolonged heating below their m.p.s; the m.p.s therefore depend to a great extent on the rate of heating. This accounts for the wide discrepancies recorded at times in the literature" <55JCS1573>). 1H-NMR(DMSO) 9.81 (s, 2H), 7.49 (dd, 4H), 7.18 (t, 4H); IR(KBr) 3218, 3017, 1550, 1509, 1333, 1239, 843, 720, 673; 13C-NMR(DMSO)(H-decoupled) 180.30 (s), 159.12 (d, 241 Hz), 135.55 (d, 2 Hz), 126.21 (d, 8 Hz), 114.97 (d, 22 Hz). G.C./M.S. affords two sharp G.C. peaks which correspond to the decomposition of the thiourea into the corresponding aniline and isothiocyanate:

The spectrum of the first G.C. peak belongs to that of the aniline and affords the following M.S.pattern:
					    % of base
				m/e		 peak
	parent peak(p)		111		5.30
	base peak		43		100.00
	other peaks of interest
	p-HCN			84		3.01
	p-(H & HCN)		83		1.84

The spectrum of the second G.C. peak belongs to that of the isothiocyanate and affords the following M.S. pattern:
					    % of base	
				m/e		 peak
	parent peak(p)		153		48.27        
	base peak		43		100.00
	other peaks of interest
	p-HF			133		3.21
	p-S			121		2.80
	p-CS			109		4.42
	p-NCS			95		26.06
	p-(HF&NCS)		75		21.80

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