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2786
GAZIZOV et al.
Scheme 5.
ArCHBr2 + ZnCl2
ArCH Br ZnCl2
DAA
Br
ArCHBr [ZnCl2BrH]
ArCHBr // ZnCl2Br
13a
13b
XHC(OR)2,
X = OR (2), Ph (9)
Br X(RO)CH
O
R
CHBrAr
ArCH(OR)Br + X(RO)CHBr
_ZnCl2
14
11
X = Ph (11), RO (12).
atom in 13a or 13b leads to the formation of new ion
pair 14 with liberation of zinc chloride, and ion pair 14
decomposes to α-bromo ether 11 and bromo acetal 12.
The latter is readily converted to alkyl formate and
alkyl bromide (Scheme 5).
mixture of 2.00 g (0.0072 mol) of compound 1 and
3.06 g (0.0288 mol) of trimethyl orthoformate (2a).
The reaction was accompanied by heat evolution. The
mixture was left to stand for 24 h at room temperature,
and volatile components were removed under reduced
pressure to obtain 2.22 g (98%) of 1-(dibromomethyl)-
In summary, 4-(dibromomethyl)benzaldehyde reacts
with trialkyl orthoformates in the presence of sulfuric
acid (Brønsted acid) to give the corresponding acetal
as the only product. Analogous reaction in the presence
of a soft Lewis acid (anhydrous zinc chloride) also
involves initial acetalization of the aldehyde group,
and the subsequent reaction at the dibromomethyl
group leads to the formation of terephthalaldehyde and
its mono- and bis-acetals, depending on the reactant
ratio and conditions. The obtained results are of
fundamental significance for organic chemistry.
1
4-(dimethoxymethyl)benzene (4a) as colorless oil. H
NMR spectrum, δ, ppm: 3.28 s (6H, Me), 5.40 s (1H,
3
CHO2), 6.62 s (1H, CHBr2), 7.42 d (2H, C6H4, JHH
=
8.4 Hz), 7.55 d (2H, C6H4, JHH = 8.4 Hz). 13C NMR
spectrum, δC, ppm: 40.77 (CHBr2), 52.81 (OMe),
102.37 (CHO2), 126.48 (CHarom), 127.11 (CHarom),
139.94 (Carom), 142.02 (Carom). Mass spectrum, m/z (Irel,
%): 247 (0.26) [M – CH(OMe)2]+, 199 (96.5) [M –
OMe – Me – Br]+, 168 (8.6) [M – CH(OMe)2Br]+, 89
(100.0) [C7H5]+, 63 (80.9) [C5H3]+, 50 (21.7) [C4H2]+.
Found, %: C 36.84; H 3.65; Br 49.21. C10H12Br2O2.
Calculated, %: C 37.06; H 3.74; Br 49.32.
3
The key intermediate in the transformation of
dibromomethylarene to the corresponding aldehyde by
the action of 1 equiv of trialkyl orthoformate is α-
bromo ether which is formed via direct reaction of the
dibromide with ortho ester or intermediate acetal.
b. Following an analogous procedure, from 1.00 g
(0.0036 mol) of aldehyde 1 and 3.20 g (0.0216 mol) of
triethyl orthoformate (2b) we obtained 1.23 g (97%) of
1-(dibromomethyl)-4-(diethoxymethyl)benzene (4b) as
1
EXPERIMENTAL
colorless oil. H NMR spectrum, δ, ppm: 1.23 t (6H,
3
3
CH2Me, JHH = 7.1 Hz), 3.54 q (4H, CH2Me, JHH
=
1
The H and 13C NMR spectra were recorded on
7.1 Hz), 5.50 s (1H, CHO2), 6.63 s (1H, CHBr2), 7.60
1
Tesla BS-567A (100 MHz for H) and Bruker Avance
3
d and 7.69 d (2H each, C6H4, JHH = 8.7 Hz). Found,
400WB spectrometers (400.13 MHz for 1H and 100.61
MHz for 13C) using CDCl3 as solvent and reference.
The mass spectra were obtained on a Thermo Electron
DFS GC/MS instrument (Germany); electron impact,
70 eV; ion source temperature 250°C; BPX5 SGE
capillary column, 50 m×0.32 mm; carrier gas helium.
Ion peaks for most abundant isotopes are given (79Br).
%: C 40.71; H 4.43; Br 45.31. C12H16Br2O2. Cal-
culated, %: C 40.91; H 4.55; Br 45.45.
Reaction of 4-(dibromomethyl)benzaldehyde (1)
with trimethyl orthoformate (2a) in the presence of
ZnCl2. a. Reactant ratio 1:1. A mixture of 1.00 g
(0.0036 mol) of compound 1, 0.38 g (0.0036 mol) of
ortho ester 2a, and 0.05 g (0.36 mmol) of zinc chloride
was heated for 5 min at 80°C. The mixture was
extracted with hot isooctane to isolate 0.47 g (98%) of
Reaction of 4-(dibromomethyl)benzaldehyde (1)
with trialkyl orthoformates in the presence of
sulfuric acid. a. A drop of sulfuric acid was added to a
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 12 2017