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W. Dmowski et al. / Journal of Fluorine Chemistry 130 (2009) 509–511
Scheme 1.
Compound 2 was found to be easily soluble in acetonitrile,
chloroform, benzene and ethyl acetate.
Elemental analysis and mass spectrum gave unequivocal
evidence that the molecule of 2 consists of two aromatic rings
coupled via a CHCF3 bridge. The presence of the CHCF3 moiety is
confirmed by quartets in the 1H and 13C NMR spectra
Scheme 2.
2
(3JHF = 11.8 Hz, JCF = 32.2 Hz) and a doublet in the 19F NMR
spectrum. The simplicity of the 1H and 13C NMR spectra (only two
signals of the OCH3 groups in both spectra) implies highly
symmetric structure of compound 2. Trifluoromethyl-bis(2,4,6-
trimethoxyphenyl)methane (2) forms small, plate-like crystals, the
structure of which, as proved by X-ray analysis (Fig. 1), is similar to
the previously reported structures of 5-(trifluoromethyl)dipyrro-
methanes [11].
Formation of compound 2 probably involves a free radical chain
mechanism, analogical to that previously suggested for the
formation of 5-(trifluoromethyl)-dipyrromethanes [11], as
depicted in Scheme 2. Perhaps, the driving force for the
substitution of both halogen atoms in CF3CHClBr by the aryl
groups, is rapid elimination of HCl from the primary aryl radical (i)
to form radical (ii) which is stabilized by the CF3 group and capable
of attacking the second molecule of trimethoxybenzene (1).
In summary, the present paper describes the third (in addition to
the previously reported [11]) example of rather unique sodium
dithionite initiated reaction of 1-bromo-chlorotrifluoroethane with
an aromatic molecule leading to diaryl(trifluoromethyl)methanes.
3.1. Trifluoromethyl-bis(2,4,6-trimethoxyphenyl)methane (2)
Sodium dithionite (2.0 g [85%], 10 mmol), sodium hydrogen
carbonate (1.7 g, 20 mmol), 1,3,5-trimethoxybenzene (1.68 g,
10 mmol) and CF3CHClBr (3.0 g, 15 mmol) were added one by
one to an acetonitrile–water solution (1:1, 20 ml) at ambient
temperature (22 8C). The reaction mixture was vigorously stirred
and after few minutes slow gas evolution (CO2, formed by the
reaction of SO2 with NaHCO3) began with a slight exothermic effect
(the temperature rised to 30 8C). The temperature was kept at 30 8C
for 3 h by external heating, after which time the reaction ceased
(no more gas evolution) and most of inorganic salts dissolved.
Stirring was continued overnight at ambient temperature, then the
reaction mixture was poured into water (100 ml) to form a white
oil which was extracted with diethyl ether, the extract was washed
with water and dried over MgSO4. Evaporation of the solvent gave
a soft, slightly pink coloured solid (1.75 g) which was found by the
TLC to consist mainly of the product and smaller amount of
unreacted 1,3,5-trimethoxybenzene. The crude product was
subjected to column chromagraphy (silica gel) to give two
fractions: the first eluent (hexanes) contained only unreacted 1
(0.65 g) and the second eluent (hexanes/CH2Cl2, 1:1), after removal
of the solvents, afforded pure compound 2 as white solid. Yield:
0.8 g (1.92 mmol, 38.4%). M.p. 181–182 8C. Analysis—found: C,
57.7; H, 5.8; F, 13.7%. Calculated for C20H23F3O6 (416.39): C, 57.7;
H, 5.6; F, 13.7%. 1H NMR: 3.73 (s, 4ꢁ CH3); 3.77 (s, 2ꢁ CH3); 5.65 (q,
3JHF = 11.8 Hz, 1H); 6.09 (s, 4Harom). 19F NMR: ꢂ64.8 (d,
3. Experimental
Melting point was determined in a capillary and is uncorrected.
1H NMR, and 19F NMR spectra were recorded with a Varian 400
spectrometer in CDCl3 solutions. Chemical shifts are quoted in
p.p.m. from internal TMS for 1H and 13C and from internal CFCl3 for
19F nuclei. Coupling constants (J) values are in Hz. Mass spectrum
was obtained with an AMD-604 spectrometer. X-ray diffraction
experiment was performed on a MACH3 diffractometer.
2
3JHF = 11.8 Hz, CF3). 13C NMR: 36.4 (q, JCF = 32.2 Hz); 55.1 (s,
OCH3); 56.0 (s, OCH3); 91.2 (s, aromatic C-3, C-5); 106.8 (s,
1
aromatic C-1); 127.1 (q, JCF = 279 Hz, CF3); 159.8 and 160.1 (s,
aromatic C-2, C-6 and C-4). MS (EI): m/z (rel. int., ion): 416 (50, M+);
396 [16, (MꢂHF)+]; 381 [22, (MꢂCH3)+]; 347 [97, (MꢂCF3)+]; 301
(11, C17H17O5+); 181 (100, C10H13O3+); 151 (10, C9H11O2+); 136 (10,
C8H8O2+); 121 (17, C7H5O2+); 69 (5, CF3+).
In the alternative separation procedure unreacted 1 and all tar-
like materials were removed from the crude product by washing
with warm hexanes (3ꢁ 30 ml): the insoluble residue was pure 2
(0.67 g, yield 32%).
3.2. Crystal structure of 2
A colorless plate-like specimen of C20H23F3O6, approximate
dimensions 0.01 mm ꢁ 0.10 mm ꢁ 0.10 mm, was used for the X-
ray crystallographic analysis. The X-ray intensity data of com-
pound 2 were measured using graphite monochromatised CuK
a
˚
radiation (
l
= 1.54178 A). A total of 4394 frames were collected.
The total data collection time was 12.21 h. The frames were
integrated with the Bruker SAINT software package using a
narrow-frame algorithm. The integration of the data using a
monoclinic unit cell yielded a total of 5298 reflections to a
Fig. 1. X-ray crystal structure of 2 with crystallographic numbering scheme.
Thermal ellipsoids shown at 20% probability level.
Dmowski
