114
LEBEDEV et al.
Mono- and polyfluoroanilines XIIa XIIk are si-
excess of phosgene in toluene 15 20 C gives rise to
isocyanates XIVa XIVk. The yields and spectral and
physicochemical characteristics of the latter are given
in the table.
lylated in high yields when refluxed with a 20% ex-
cess of HMDS (procedure c) to form N-trimethylsilyl
derivatives XIIIa XIIIk whose treatment with a 10%
R5
R4
R5
R5
R4
R4
(Me3Si)2NH
NH3
COCl2
R3
NCO
R3
NH2
R3
NHSiMe3
Me3SiCl, HCl
R1
R2
R1
R1
R2
R2
XIIa XIIk
XIIIa XIIIk
XIVa XIVk
Unspecified R = H; R1 = F (a); R2 = F (b); R3 = F (c); R1 = R3 = F (d); R1 = R4 = F (e); R1 = R2 = R4 = R5 = F (f); R2 =
F, R3 = CH3 (g); R2 = Cl, R3 = F (h); R1 = F, R3 = Br (i); R1 = CF3 (j); R2 = CF3 (k).
As seen from the table, the yields of isocyanates
decreases in the presence of fluorine ortho to the
amino group, which is probably explained by intra-
molecular Si F bonding which hinders reaction of
the amino group with COCl2; as a result, isocyanates
react with unreacted starting amines after removal of
phospene from the reaction mixture, forming the
corresponding ureas.
dropwise with stirring a mixture of 22.78 g of chloro-
trimethylsilane and 21.2 g of dry triethylamine. The
mixture was stirred for 1 h at 80 C and then diluted, if
required, with 100 ml of dry toluene to obtain a fluid
suspension, and cooled to 10 C. The triethylammo-
nium salt that precipitated was filtered off, and the
mother liquor was distilled in a vacuum to obtain
silylamines Va Ve and X in yields of 88 94%.
Given are compound number and melting point, C:
Va, 38; Vb, 50; Vc, 53 55; Vd, 65; Ve, 45 50; and
X, 25.
Generally, with fluroanilines, too, phosgenation of
their N-silyl derivatives provides a convenient syn-
thetic route to isocyanates.
Exhaustive silylation of amines Ia and Ib. To
0.2 mol of amine Ia or Ib we added 39 g of HMDS
and 2 drops of conc. H2SO4. The mixture was slowly
heated to 160 C, kept for 1 h, cooled, and distilled in
a vacuum to isolate compounds VIIa and VIIb in
yields of 87 and 90%, respectively.
It should be noted that 2,3,5,6-tetrafluorophenyl
isocyanate (XIVf) could only be isolated as a short-
lived (no more than 2 days) 5% toluene solution
stable below 5 C, which is explained by an exceptio-
nally strong tendency of compound XIVf for poly-
merization.
Silylation of amines XIIa XIIk with HMDS.
c. To 0.2 mol of amine XIIa XIIk we added 19.4 g
of HMDS and 2 drops of conc. H2SO4. The mixture
was slowly heated to 170 175 C, kept for 1 h, cooled,
and distilled in a vacuum to isolate silylamines
XIIIa XIIIk. Given are compound number and n2D0:
XIIIa, 1.5008; XIIIb, 1.5005; XIIIc, 1.4980; XIIId,
1.4795; XIIIe, 1.4802; XIIIg, 1.5031; XIIIh, 1.5102;
XIIIi, 1.5470; XIIIj, 1.4605; XIIIk, 1.4560.
EXPERIMENTAL
1
The H NMR spectra were measured on a Bruker
AM-360 spectrometer at 360.14 MHz in CDCl3 solu-
tions.
The mass spectra were obtained on a QP-5000
instrument at an ionizing energy of 70 eV.
Silylation of amines I and IV with HMDS. a. To
0.2 mol of amine Ia, Ib, or IVa IVe we added 16.9 g
of HMDS and 2 drops of conc. H2SO4. The mixture
was slowly heated to 160 C, kept for 30 min, cooled,
and distilled to isolate silylamine IIa, IIb, or Va Ve.
The yield of compounds Va Ve was 48 55%.
Synthesis of isocyanates IIIa, IIIb, VIa VIf, XI,
and XIVa XIVk. To a solution of 21.8 g of phos-
gene in 75 ml of toluene at 5 15 C (for compounds
II, V, VII, and X) or 15 20 C (for amines XIII) we
added slowly, by maintaining the temperature range,
dropwise a solution of 0.2 mol of silylamine in 30
50 ml of toluene (for compounds IIa, IIb, Vb, Vc,
VIIa, VIIb, and XIIIa XIIIk) or 75 ml of dry di-
methyl ether of diethylene glycol (for amines Va, Vd,
Silylation of amines IV and IX with chlorotri-
methylsilane. b. To a solution of 0.2 mol of amine
IVa IVe or IX in 200 ml of dry toluene we added
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 1 2006