Replacement of an oxygen atom by chlorine atoms in the reaction of pentafluorobenzaldehyde with CCl3-substituted compounds in the presence of AlCl3

Article abstract of DOI:10.1023/A:1015537125084

The interaction of pentafluorobenzaldehyde with RCCl3 (R = Cl, Ph, C6F5) in the presence of threefold molar excess of AlCl3 proceeds with replacing the oxygen atom of the aldehyde group by two chlorine atoms from the CCl3 group and results in the formatio

Full text of DOI:10.1023/A:1015537125084

544
Russian Chemical Bulletin, International Edition, Vol. 51, No. 3, pp. 544—546, March, 2002
Replacement of an oxygen atom by chlorine atoms
in the reaction of pentafluorobenzaldehyde with
CCl3ꢀsubstituted compounds in the presence of AlCl3
ꢀ
T. D. Petrova, V. E. Platonov, and L. M. Pokrovskii
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry,
Siberian Branch of the Russian Academy of Sciences,
9 prosp. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383 2) 34 4752. Eꢀmail: petrova@nioch.nsc.ru
The interaction of pentafluorobenzaldehyde with RCCl3 (R = Cl, Ph, C6F5) in the presꢀ
ence of threefold molar excess of AlCl3 proceeds with replacing the oxygen atom of the
aldehyde group by two chlorine atoms from the CCl3 group and results in the formation of
pentafluorobenzylidene chloride. The electrophilic mechanism of the reaction is proposed.
Key words: pentafluorobenzaldehyde, CCl4, AlCl3, benzotrichloride, pentafluorobenzoꢀ
trichloride, pentafluorobenzylidene chloride, electrophilic mechanism.
The reactions of pentafluorobenzaldehyde (1), pentaꢀ
The interaction of aldehyde 1 with CCl4 and excess of
fluoroacetophenone and decafluorobenzophenone with
CCl4 (2a), benzotrichloride (2b), and pentafluorobenzoꢀ
trichloride (2c) in the presence of excess AlCl3 as a conꢀ
tinuation of our investigations into the electrophilic
polyhaloalkylation of polyfluoroaromatic Nꢀ, Sꢀ, and
Oꢀfunctional derivatives by R—CX3 (X = Cl, F;
R = alkyl, aryl) compounds1—5 were studied in the present
paper.
It was established that on the interaction of aldehyde 1
with CCl4 and trihalomethyl derivatives 2b,c in the presꢀ
ence of threefold molar excess of AlCl3 in respect to 1 the
replacement of the oxygen atom from the aldehyde
group by two chlorine atoms resulting in pentafluoroꢀ
benzylidene chloride (3) and of benzoyl and pentaꢀ
fluorobenzoyl chlorides (4b,c, respectively) takes place
(Scheme 1).
AlCl3 proceeds at the boiling point of the reaction mixꢀ
ture and causes dichloride 3 formation in 54% yield (the
known procedure for obtaining 3 from 1 in 80% yield
includes heating 1 in the presence of PCl5 7). The reacꢀ
tion does not take place at room temperature, in the presꢀ
ence of catalytic amounts of AlCl3 or at heating 1 together
with AlCl3 in the absence of ССl4. On the contrary, aldeꢀ
hyde 1 and benzotrichloride 2b begin to interact already
at 0 °C, and almost fully convert into dichloride 3 at room
temperature. The reaction of 1 with 2c also proceeds
at room temperature. By GC/MS analysis αꢀchloroꢀ
2,3,4,5,6ꢀpentafluorobenzyl benzoate (5) as well
as isomeric trichloromethyldiphenyldichloromethanes
PhCCl2C6H4CCl3 (6) and the products of their hydrolyꢀ
sis, viz., trichloromethylbenzophenones PhCOC6H4CCl3
(7), which are likely resulted from a transformation of the
initial benzotrichloride 2b, were found in the products of
the reaction of aldehyde 1 with benzotrichloride 2b. Acꢀ
cording to 19F NMR analysis, the proportion of the comꢀ
pounds 3 and 5 is equal to ∼4.7 : 1.
Scheme 1
Pentafluoroacetophenone and decafluorobenzopheꢀ
none give no fluorineꢀcontaining products in their reacꢀ
tions with CCl4 or with 2b. In the case of 2b, the reaction
mixtures contain besides unreacted initial ketone comꢀ
pounds 6 and 7 as well.
R = Cl (a); Ph (b); C6F5 (c)
In the case of benzaldehyde, this reaction is realized
only in the course of its interaction with benzotrichloride
2b (but not with CCl4) in the presence of Lewis acid in
catalytic amounts (0.2 wt.%).6
Taking into account the data about electrophilic propꢀ
erties of polyhalomethanes in the presence of Lewis acids
and about the generation of the cationoid intermediates
8—12
on the interaction of CCl4 with SbF5
and of comꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 504—506, March, 2002.
1066ꢀ5285/02/5103ꢀ544 $27.00 © 2002 Plenum Publishing Corporation

Reactions of C6F5CHO with RCCl3/AlCl3
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 3, March, 2002
545
ture of ion source was 173 °C. The scanning velocity was
1.2 scan s–1 in the mass interval 30—650 amu.
pound 2b with AlCl3 under Friedel—Crafts reaction conꢀ
ditions,13 as well as our data about electrophilic character
of interaction of the RCCl3—AlCl3 system with polyꢀ
fluoroaromatic functional derivatives1—4, one can proꢀ
pose the following scheme of the transformation of aldeꢀ
hyde 1 into dichloride 3 in the presence of AlCl3 excess
(Scheme 2).
Interaction of polyfluoroaromatic carbonyl compounds with
RCCl3 in the presence of AlCl3. А. The polyfluorinated carbonyl
compound (2 mmol), fresh sublimated AlCl3 (6 mmol), and
4 mL of anhydrous CCl4 (2 g of 2b or 2c) were stirred for 6 h at
the corresponding temperature. The reaction mixture was deꢀ
composed with cold water, extracted with ether. The ether
layer was dried over CaCl2, and then the ether was evapoꢀ
rated. The residue was analyzed by 19F NMR and GC/MS techꢀ
niques.
Scheme 2
B. Pentafluorobenzylidene chloride 3. Aldehyde 1 (1.2 g,
6 mmol), AlCl3 (2.4 g, 18 mmol), and CCl4 (10 mL) were heated
at 80 °C for 6 h. After the reaction mixture was treated as
described above, the residue was distilled in vacuo. The yield of 3
was 0.81 g (54%), b.p. 77 °C (25 Torr) (cf. Ref. 7: 82—84 °C
b.p. (30 Torr)).
In the experiments with benzotrichloride (2b) the formaꢀ
tion of presumably αꢀchloroꢀ2,3,4,5,6ꢀpentafluorobenzyl benꢀ
zoate (5) and two isomeric trichloromethyldiphenyldichloroꢀ
methanes 6 and trichloromethylbenzophenones 7 along
with unreacted initial compounds was detected by GC/MS techꢀ
nique
In MS of compound 5 fragment ions with m/z (Irel (%)):
336 [M]+ (0.05), 301 [M – Cl]+ (13.9), 215 [M – OCOC6H5]+
(6.72), 195 [M – COC6H5—HCl]+ (6.47), 167 [C6F5]+ (2.66),
105 [C6H5CO]+ (100), 77 [C6H5]+ (24.13) were observed. The
values of chemical shifts of fluorine atoms in the 19F NMR
spectrum of this compound (2Fо 21.58 ppm, Fp 11.18 ppm,
2Fm 1.62 ppm) were close to the corresponding values for dichloꢀ
ride 3 (2Fo 21.72 ppm, Fp 11.32 ppm, 2Fm 1.63 ppm).
For major isomer 6 m/z (Irel (%)): 319 (100), 317 [М – Cl]+
(77.82), 282 [M – 2 Cl]+ (5.78), 247 [M – 3 Cl]+ (20.53), 212
[M – 4 Cl]+ (36.19), 176 [M – 4 Cl – HCl]+ (35.40), 165
[M – 2 Сl – CCl3]+ (65.33); for 7, respectively: 298 [M]+
(6.74), 263 [M – Cl]+ (100), 165 [M – 3 Cl – CO]+ (16.07), 158
[M – Cl – C6H5CO]+ (10.40), 123 [M – Cl2 – C6H5CO]+
(23.77), 105 [C6H5CO]+ (88.93), 77 [C6H5]+ (56.98).
Experiments with polyfluorinated ketones were carried out
at 80 °C. In the reactions with CCl4 the obtained reaction mixꢀ
tures contained only initial ketone.
The conversion 8 → 9 seems to be occur more easily
when R = Ph or C6F5, than when R = Cl, because in
former two cases the relatively stable intermediates with
cationic centers in benzyl position are generated. This
can explain the fact that compound 3 is formed from
aldehyde 1 in the course of its interaction with triꢀ
chloromethyl derivatives 2b and 2c under milder condiꢀ
tions than with CCl4.
Electrophilic character of the processes under study is
confirmed by the formation of diphenyldichloromethane
derivatives 6 which seem to be the products of alkylation
of the initial 2b by phenyldichloromethyl cationoid interꢀ
mediate formed from 2b in the presence of AlCl3.
Interaction of benzotrichloride 2b with AlCl3. Aluminum chloꢀ
ride (0.4 g, 3 mmol) was added to benzotrichloride 2b (1 g,
5 mmol) and the mixture was stirred for 6 h at ∼20 °C. Then the
reaction mixture was decomposed as described above. After ether
evaporation, 0.88 g of the residue was obtained. According to
the GC/MS analysis, the residue contained compounds 6 and 7
along with initial benzotrichloride 2b.
Experimental
The compositions of the reaction mixtures were deterꢀ
mined by 19F NMR spectrometry and GC/MS techniques. The
19F NMR spectra were recorded with a Bruker WPꢀ200SY
spectrometer (188.28 MHz), hexaflourobenzene (+162.9 ppm
from CCl3F) was used as the internal standard. The GC/MS
analysis was carried out on a HewlettꢀPackard G 1081A instruꢀ
ment with a HP 5890 series II gas chromatograph and an
HP 5971 massꢀselective detector (EI, 70 eV) with the HP5
capillary column (diphenyl (5%)—dimethylsiloxane (95%)):
30 m × 0.25 mm × 0.25 µm. The He flow (1 mL min–1) was used
as a carrier gas. The following temperature regime program was
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Received July 19, 2001;
in revised form December 29, 2001