N,N'-bis(4-fluorophenyl)-thiourea
N,N'-bis(4-fluorophenyl)-thiourea has been previously synthesized in the literature. S. Hüunig, H. Lehman, G. Grimmer, Liebigs Ann. Chem., 579, 77, (1953) and H.P Buu-Hou, N.D. Xuong, N.H. Nam, J. Chem. Soc., 1573, (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, (1913); L.C. Raiford, G.M. McNulty, J. Am. Chem. Soc., 56, 680, (1934)
On The Synthesis and Reactivity of N'-Haloarylalkoxycarbimidoyl Nitrenes M. Tellez, PhD Dissertation, New Mexico State University, Las Cruces, NM (1995) (RP259)
Experimental
To 4-fluoroaniline (22.2 g, 0.2 mol) and pyridine (31.62 g, 0.4 mol) in carbon disulfide (250 mL) was added iodine (25.4 g, 0.1 mol) in carbon disulfide (150 mL). The solution was then brought to reflux and stirred for 3 h. 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 1 M 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 mol) 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 celsius (lit.<53LA77> 145 celsius, lit. <55JCS1573> 208 celsius "All these thioureas undergo thermal decomposition on prolonged heating below their mps; the mps 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). GC/MS affords two sharp GC peaks which correspond to the decomposition of the thiourea into the corresponding aniline and isothiocyanate:
The spectrum of the first GC peak belongs to that of the aniline and affords the following MS pattern (Table 1)
Table 1
|
|
|
% of base
|
|
m/z |
peak |
| parent peak(p) |
111 |
5.30 |
| base peak |
43 |
100.00 |
| p-HCN |
84 |
3.01 |
| p-(H & HCN)
|
83 |
1.84 |
The spectrum of the second GC peak belongs to that of the isothiocyanate and affords the following MS pattern (Table 2)
Table 2
|
|
|
% of base
|
|
m/z |
peak |
| parent peak(p) |
153 |
48.27 |
| base peak |
43 |
100.00 |
| 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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