A mild and practical preparation of trifluoromethaneselenenyl chloride

Article abstract of DOI:10.1135/cccc20021262

Trifluoromethaneselenenyl chloride is prepared by a two-step procedure with an 85% overall yield. Benzyl trifluoromethyl selenide is formed from dibenzyl diselenide and trifluoromethyl iodide in the presence of sodium hydroxymethanesulfinate. The benzyl-s

Full text of DOI:10.1135/cccc20021262

1262
Magnier, Wakselman:
A MILD AND PRACTICAL PREPARATION OF
TRIFLUOROMETHANESELENENYL CHLORIDE
1
2,
Emmanuel MAGNIER and Claude WAKSELMAN *
Laboratoire SIRCOB, ESA CNRS 8086, Equipe Fluor, Université de Versailles-Saint-Quentin
en Yvelines, 45, avenue des Etats-Unis, 78035 Versailles cedex, France;
1
2
e-mail: magnier@chimie.uvsq.fr, wakselma@chimie.uvsq.fr
Received March 19, 2002
Accepted Jun e 6, 2002
Dedicated to the memory of Professor Miloš Hudlický.
Trifluorom eth an eselen en yl ch loride is prepared by a two-step procedure with an 85% overall
yield. Ben zyl trifluorom eth yl selen ide is form ed from diben zyl diselen ide an d trifluoro-
m eth yl iodide in th e presen ce of sodium h ydroxym eth an esulfin ate. Th e ben zyl–selen ium
bon d is th en cleaved with sulfuryl ch loride to give th e correspon din g selen en yl ch loride.
Keyw ord s: Selen ium ; Fluorin e; Radical ion s; Electron tran sfer; Cleavage reaction s.
Trifluorom eth an eselen en yl ch loride, CF3SeCl, is a useful syn th on for th e
in troduction of th e trifluorom eth ylselen o group in to organ ic m olecules1,2
.
Th is ch loride is classically obtain ed by reaction of a lim ited am oun t of
chlorine with bis(trifluoromethyl) diselenide3, CF3SeSeCF3. The latter is formed,
as a m ixture with bis(trifluorom eth yl) selen ide, CF3SeCF3, by treatment of
3
trifluorom eth yl iodide with selen ium un der pressu re at 260–280 °C .
Followin g th is m eth od, th e yield of th e diselen ide is lim ited to 10–15%.
Altern atively, th is com poun d is form ed wh en a glass tube con tain in g m er-
curic or silver trifluoroacetate an d selen ium is gradually h eated in an open
flam e. In th is case, yields are 16 an d 28%, respectively4. Obviously, th ese
h arsh con dition s an d poor yields h ave lim ited th e use of th is fluorin ated
diselen ide an d con sequen tly of its selen en yl ch loride derivative.
Recen tly, we reported th at perfluorooctan eselen en yl ch loride, C8F17SeCl,
can be obtain ed in a two-step procedure: form ation of ben zyl perfluoro-
octyl selen ide from diben zyl diselen ide an d perfluorooctyl iodide in th e
presen ce of sodium h ydroxym eth an esulfin ate (Ron galite), followed by
cleavage of th e ben zyl–selen ium bon d with ch lorin e or sulfuryl ch loride
(Sch em e 1)5. In itially, application of th is m eth od to th e preparation of
Collect. Czech. Chem. Commun. (Vol. 67) (2002)
doi:10.1135/cccc20021262

Preparation of Trifluoromethaneselenenyl Chloride
1263
CF3SeCl did n ot appear to be viable given th at th e yield in a sim ilar reac-
tion between trifluorom eth yl iodide an d diph en yl diselen ide was rath er
lim ited (Sch em e 2).
(i)
C8F17–Se–Bn
Bn–Se–Se–Bn
+
C8F17I
1
2
3
(ii)
C8F17–Se–Bn
C8F17–Se–Cl
3
4
(i) HOCH2SO2Na, DMF, H2O, rt, 80%; (ii) Cl2, CCl4, 0 oC or SO2Cl2, 0 oC, 95%
SCHEME 1
However, we h ave observed very recen tly th at th e sam e reaction per-
form ed with th e m ore reactive diben zyl diselen ide gives a m uch better
yield. Th is m ild tran sform ation open s th e way to an easy access to th e very
first m em ber of th e perfluoroalkylselen en yl ch loride series (Sch em e 2). Our
m eth od, previously described, h as allowed us to produce th e ben zyl
trifluorom eth yl selen ide (9) in 90% yield in a straigh tforward m an n er. Th e
com poun d is obtain ed pure with out an y purification 6. Such fluorin ated
selen ides are also available by fluoride-catalysed n ucleoph ilic trifluoro-
m eth ylation of alkyl- or arylselen ocyan ate with trim eth yl(trifluorom eth yl)
silan e (Ruppert’s reagen t)7,8. To facilitate th e isolation of CF3SeCl wh ich h as
a very low boilin g poin t (b.p. 22 °C), th e secon d step was perform ed with -
out an y solven t. Cleavage of th e ben zyl–selen ium bon d was accom plish ed
by sulfuryl ch loride. Th e desired com poun d was directly distilled an d iso-
lated in an alm ost quan titative yield (>95%). NMR data of com poun ds 9
an d 10 were in total accordan ce with th e literature7,9
.
(i)
CF3–Se–R
R–Se–Se–R
+
CF3I
8, R = Ph 28%
9, R = Bn 90%
5, R = Ph
6, R = Bn
7
(ii)
CF3–Se–Bn
CF3–Se–Cl
9
10
(i) HOCH2SO2Na, DMF, H2O, rt; (ii) SO2Cl2, rt, 95%
SCHEME 2
Several m ech an ism s can be con sidered for th e form ation of th e ben zyl
trifluorom eth yl selen ide. It is kn own th at h ydroxym eth an esulfin ate salts
can beh ave as a source of th e sulfoxylate radical an ion SO •2– 10,11. Th e latter
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1264
Magnier, Wakselman:
is able to tran sfer an electron to trifluorom eth yl iodide an d to gen erate a
trifluorom eth yl radical11,12 (Sch em e 3). Owin g to th e susceptibility of th e
weak selen ium –selen ium bon d in diselen ide to radical attack13, ben zyl
trifluorom eth yl selen ide can be produced from diben zyl diselen ide. Th is
m ech an ism is sim ilar to th at proposed for th e reaction of disulfides14,15
.
CF3
+
I
+
SO2
CF3I
CF3
+
SO2
+
Bn–Se–Se–Bn
CF3–Se–Bn
+
Bn–Se
6
9
Bn–Se
+
Bn–Se
Bn–Se–Se–Bn
SCHEME 3
However, th e reduction of diph en yl diselen ide with sodium h ydroxy-
m eth an esulfin ate in alkalin e eth an ol h as been described16. A selen ide an -
ion , wh ich can also be form ed, in sm all quan tity, in th e aqueous DMF
m edium em ployed17, can react with trifluorom eth yl iodide by two differen t
m echanism s18: an SRN1 process involving a radical chain reaction (Schem e 4)
SO2
Bn–Se–Se–Bn
2 Bn–Se
6
Bn–Se
CF3
+
CF3I
Bn–Se
+
CF3
+
I
+
Bn–Se
CF3–Se–Bn
CF3–Se–Bn
+
CF3
+
I
+
CF3I
CF3–Se–Bn
9
SCHEME 4
SRN1 process
or a halogenophilic process occurring by interm ediate form ation of a trifluoro-
m eth yl carban ion 19 (Sch em e 5). However, th e presen ce of th is carban ion in
th e m edium is h igh ly im probable. It sh ould react with water to form
trifluorom eth an e or decom pose quickly to difluorocarben e. Perh aps, th e
form ation of th e correspon din g ate-com plex20 [Bn Se-I-CF3]–Na+ could stabi-
lize partially th e carban ion an d could be respon sible for th e ben zyl
trifluorom eth yl selen ide form ation 21. Th is an ion ic path way appears rath er
un likely. Eviden ce h as been presen ted in support of th e occurren ce of a
on e-electron tran sfer from th e selen ide an ion to perfluoroalkyl h alides22.
Neverth eless, in both m ech an ism s, th e form ation of diben zyl diselen ide
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Preparation of Trifluoromethaneselenenyl Chloride
1265
can occur, an alogously with th e beh aviour of aliph atic th iolates23 (Sch em es
3, 5). Th e diselen ide so produced is recycled an d can react furth er to give
ben zyl trifluorom eth yl selen ide (Sch em e 3). Con sequen tly, form ation of
th is selen ide from trifluorom eth yl iodide an d diben zyl diselen ide in th e
presen ce of sodium h ydroxym eth an esulfin ate can be th e result of a com pe-
tition of several processes (Sch em es 3, 4, 5). We assum e th at th e first on e
(Sch em e 3) is probably th e predom in an t on e.
Bn–Se–I
+
CF3
Bn–Se
+
+
CF3I
CF3
CF3–Se–Bn
Bn–Se–I
9
Bn–Se–I
+
Bn–Se
Bn–Se–Se–Bn
+
I
6
SCHEME 5
Halogen oph ilic process
In con clusion , we h ave developed an efficien t an d m ild preparation of
CF3SeCl in two steps startin g from a com m ercial product an d with 85%
overall yield.
EXPERIMENTAL
NMR spectra were recorded in CDCl3 solution s, on a Bruker AC-300 spectrom eter. Reported
couplin g con stan ts (J, Hz) an d ch em icals sh ifts (δ, ppm ) were based on a first-order an alysis.
In tern al referen ce was th e residual peak of CHCl3 (7.27 ppm ) for 1H NMR spectra (300 MHz),
cen tral peak of CDCl3 (77 ppm ) for 13C NMR spectra (75 MHz), in tern al CFCl3 (0 ppm ) for
19F NMR spectra (282 MHz) an d extern al Me2Se (0 ppm ) for 77Se NMR spectra (57 MHz).
CAUTION: All experim en ts with CF3SeCl m ust be carried out in well ven tilated fum e-
h ood with safety precaution s. As CF3SCl is kn own to be extrem ely toxic24, it m ust be an tici-
pated th at CF3SeCl is at least as toxic. Th is com poun d is stable an d can be kept pure or in
solution in th e fridge.
Ben zyl Trifluorom eth yl Selen ide (9)
Diben zyl diselen ide (5.13 g, 15.08 m m ol) was dissolved in DMF (65 m l) un der argon . Th en ,
trifluorom eth yl iodide CF3I (9 g, 45.24 m m ol) was bubbled in to th e solution . Lastly, water
(1.2 m l) was in troduced in to th e m edium an d sodium h ydroxym eth an esulfin ate (7.00 g,
45.24 m m ol) was added in portion s over 4 h . Th e solution was stirred at room tem perature
for 16 h . Th e m ixture was extracted th ree tim es with Et2O, th e organ ic layer wash ed with
NaHCO3 (5% in H2O) an d water, th en dried over MgSO4, an d con cen trated un der reduced
pressure. Th e product 9 (6.50 g; 90%) was obtain ed pure with out furth er purification as a
pale yellow liquid. 1H NMR: 7.36 m , 5 H (arom atic); 4.28 s, 2 H (ben zylic). 19F NMR: –34.0 s,
3 F. 13C NMR: 136.2 (CArH); 129.1 (2 CArH); 128.9 (2 CArH); 127.8 (CAr); 123.0 q (CF3, J =
331); 29.2 (CH2).
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Magnier, Wakselman:
Trifluorom eth an eselen en yl Ch loride 10
Ben zyl trifluorom eth yl selen ide (9; 2.00 g, 8.36 m m ol) was placed in
a
two-n ecked
roun d-bottom ed flask, equipped with a m agn etic stirrin g bar, a septum an d a bridge
connected to a series of two round bottom ed flasks cooled with liquid nitrogen. Sulfuryl chloride
(0.69 m l, 8.36 m m ol) was added slowly with a syrin ge at am bien t tem perature. After 10 m in ,
a flush of argon was applied. Trifluorom eth an eselen en yl ch loride (10; 1.75 g; 95%) was iso-
lated in th e two first traps (m ain ly in th e first on e) as an in ten sively red liquid. 19F NMR:
–41.6 s, 3 F. 13C NMR: 121.1 q (CF3, J = 335.7). 77Se NMR: 1 076.4 s.
This work was supported by the CNRS. The authors thank E. Vit who began this work.
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