Improved preparation of 3,3′,4,4′-tetramethyldiphenylethane by self coupling reaciton in aqueous media

Article abstract of DOI:10.1002/jccs.200900153

In this article, 3,3′,4,4′-tetramethyldiphenylethane was obtained in 86.5% total yield by self coupling reaction of 3,4-dimethylbenzyl chloride catalyzed by Cu/Cu/₂/Cl/₂//PEG-600 and promoted by iron in aqueous media and the starting

Full text of DOI:10.1002/jccs.200900153

1056
Journal of the Chinese Chemical Society, 2009, 56, 1056-1063
Improved Preparation of 3,3¢,4,4¢-tetramethyldiphenylethane by Self
Coupling Reaciton in Aqueous Media
Yu-Lin Hu (
Qi-Fa Liu (
Chemical Engineering College, Nanjing University of Science and Technology, Nanjing 210094, P. R. China
), Ming Lu* (
),
) and Qiang Ge (
)
In this article, 3,3¢,4,4¢-tetramethyldiphenylethane was obtained in 86.5% total yield by self coupling
reaction of 3,4-dimethylbenzyl chloride catalyzed by Cu/Cu2Cl2/PEG-600 and promoted by iron in aque-
ous media and the starting material 3,4-dimethylbenzyl chloride was prepared by chloromethylation of
o-xylene in CTAB micellar catalytic system. Compared to other synthetic methods, the improved method
not only enhanced the yield, but also made the operating units easy workup. The mechanisms of the
chloromethylation and the self coupling were proposed. The structures of the products were confirmed by
Elemental analysis, 1H NMR and 13C NMR or compared with authentic samples.
Keywords: 3,3¢,4,4¢-tetramethyldiphenylethane; Micellar catalysis; Phase transfer catalysis;
Chloromethylation; Self coupling reaciton.
INTRODUCTION
3,3¢,4,4¢-tetramethyldiphenylethane (TMDE) is an
tants, so that the reaction interface area between oil phase
reactants and water phase reactants is enlarged greatly. The
interface magnifying effect as well as electrostatic interac-
tion and concentrating effect result in dramatic increases of
reaction rates.10,11 In addition, micellar catalysis can make
reaction conditions gentle, can effectively avoid side reac-
tions to occur, and enhance the efficiency of organic syn-
thesis. In our previous paper, we had successfully applied
surfactant micelles for the chloromethylation of 2-bromo-
ethylbenzene and found that cetyltrimethylammonium bro-
mide (CTAB) was the most active surfactant.12 Phase trans-
fer catalysis (PTC) is an another versatile synthetic tech-
nique that has been widely applied to intensify otherwise
slow heterogeneous reactions involving an organic sub-
strate and an ionic reactant, either dissolved in water (liq-
uid–liquid) or present in solid state (liquid–solid).13 Be-
cause PTC can decrease the reaction activation energy, ac-
celerate reaction speed, make conditions gentle and avoid
side reaction to occur, it has been applied in various organic
synthesis.14-16 The reductive coupling of organic halides
with active metals is an important method for the formation
of carbon-carbon bonds and a number of these methods
have been developed to obtain diphenylethanes from ben-
zyl halogenation.17-21
important intermediate in the synthesis of a variety of fine
or special chemicals such as dyes, flavors, polymers, etc.
Moreover, it is known as an important thermosensitive pa-
per sensitizer and has been becoming the primary sensitizer
throughout the market because of its excellent properties
such as damp-resistant, oil-resistant, light-resistant, etc.1-4
Generally, 3,3¢,4,4¢-tetramethyldiphenylethane is pre-
pared by Friedel-Crafts alkylation reaction between o-xy-
lene and 1,2-dichloroethane.5-8 However, this procedure is
invariably associated with certain limitations such as low
yield, poor selectivity, special anhydrous condition opera-
tion and the use of virulent 1,2-dichloroethane. Another
procedure starting from o-xylene and acetaldehyde via a
isomerization reaction has been reported recently,9 which,
however, requires high reaction temperature, expensive
and special apparatus and troublesome work-up proce-
dures. Consequently, there is a great desire to develop an
efficient and improved procedure for the synthesis of
3,3¢,4,4¢-tetramethyldiphenylethane.
Micellar catalysis is an effective means to accelerate
organic reactions between oil phase and water phase reac-
tants. In micellar catalysis system, lipophilic reactants are
solubilized in the surfactant micelles, and the swelling mi-
celles disperse in water phase containing hydrophilic reac-
The objectives of the present work are to report an im-
proved and economic procedure for synthesis of 3,3¢,4,4¢-
* Corresponding author. Tel: +86-025-84315030; Fax: +86-025-84315030; E-mail: luming1963@163.com

Preparation of TMDE by Self Coupling Reaciton
J. Chin. Chem. Soc., Vol. 56, No. 5, 2009 1057
Scheme I Two-step synthesis of 3,3¢,4,4¢-tetramethyldiphenylethane
tetramethyldiphenylethane by self coupling reaction of
3,4-dimethylbenzyl chloride catalyzed by Cu/Cu2Cl2/PEG-
600 and promoted by iron in aqueous media under PTC
conditions and the starting material 3,4-dimethylbenzyl
chloride was prepared by chloromethylation of o-xylene in
CTAB micellar catalytic system (Scheme I).
the conversion was increased to 94%. After that, the con-
version and the yield became level off.
Fig. 2 shows the influences of CTAB concentration
on the chloromethylation. When CTAB concentration was
below CMC, the yield after 4 h was only 25.4%, the con-
version was about 78%, and hardly varied with surfactant
concentration. However, the yield and the conversion in-
creased with an increase in the surfactant concentration
higher than CMC, and leveled off after the surfactant con-
centration reaching to 18CMC. The experimental facts dis-
play distinctly the advantage of high efficiency of micellar
catalysis system. When no surfactant was used or surfactant
concentration was below CMC, the reaction system is a
suspension (under stirring) with two phases, and the inter-
face between oil phase and water phase is very small, so the
reaction rate is very slow. However, when surfactant mi-
celles were formed, o-xylene was solubilized into the mi-
celles, the interface area of oil phase/water phasewas mag-
nified suddenly and the rate of chloromethylation reaction
occurred at the interface was accelerated abruptly, so the
conversion showed a break point at CMC. Above CMC, the
RESULTS AND DISCUSSION
Preparation of 3,4-dimethylbenzyl chloride (a)
In a preliminary study, the chloromethylation was
carried out in oil-water biphasic system in the presence and
absence of CTAB. As shown in Fig. 1, in the absence of
surfactant (CTAB), the chloromethylation reaction pro-
ceeded very slowly, the yield was less than 20% after 7 h,
and the conversion was only 73%. Reaction performed
with CTAB (its critical micelle concentration, CMC, in
pure water at 25 °C is 9.20 ´ 10-4 mol/L 22) at a concentra-
tion of 2.57 ´ 10-2 mol·L-1 (18 CMC) proceeded very rap-
idly and the yield reached 89.7% in a shorter time (4 h), and
Fig. 1. Plot of the chloromethylation degree of o-xy-
lene vs. time in presence and in absence of
CTAB. Reaction conditions: O-xylene, 10.6 g
(0.1 mol); paraformaldehyde, 3.15 g (0.105
mol); 20% H2SO4, 60 mL; AcOH, 30 mL; anhy-
drous hydrogen chloride gas, 60 mL/min; con-
centrations of CTAB, 18-fold CMC; tempera-
ture, 45 °C.
Fig. 2. Influences of concentration of CTAB on the
chloromethylation. Reaction conditions: O-xy-
lene, 10.6 g (0.1 mol); paraformaldehyde, 3.15
g (0.105 mol); 20% H2SO4, 60 mL; AcOH, 30
mL; anhydrous hydrogen chloride gas, 60
mL/min; temperature, 45 °C; time, 4 h.

1058 J. Chin. Chem. Soc., Vol. 56, No. 5, 2009
Hu et al
number of micelles increased with the increasing surfactant
concentration, so the rate of chloromethylation reaction
speeded up and a higher conversion can be obtained. The
further increase of the surfactant concentration could in-
duce micelles to expand, which could cause slow increase
of oil/water interfacial area. Therefore, at high CTAB con-
centration, the rate increase became gradually slow and the
conversion of o-xylene did not change significantly. Be-
sides CTAB, we also tried to use another types of surfac-
tants such as SDS, NP-10 and TTAB as catalysts in the re-
action. As shown in Fig. 3, it was observed that the yield
was highest for the CTAB system, higher for the TTAB,
lower for the NP-10 and much lower for the SDS. The dif-
ferent catalytic abilities of surfactants should be attributed
to their different solubilization abilities. CTAB, TTAB,
NP-10 and SDS have various CMC, the lower CMC leads
to more micelles at the same concentration causing more
o-xylene to be solubilized into micelles and greater en-
counter probability between o-xylene and reactive species.
Thus, the observed rate and yield of the reaction is CTAB >
TTAB > NP-10 > SDS.
45 °C are shown in Fig. 5. No reaction occurred in the ab-
sence of sulfuric acid, and the increase in the concentration
of sulfuric acid enhanced the catalysis. The yield reached
maximum at the 20% sulfuric acid, however, it decreased
with further increase of the concentration of sulfuric acid.
Fig. 6 shows the influences of the volume ratio of AcOH
and 20% H2SO4 at 45 °C. In the absence of acetic acid, the
chloromethylation reaction proceeded badly, only 67.7%
yield was obtained and the conversion decreased to 87%,
and the increase in the amount of acetic acid (i.e. the vol-
ume ratio increased) enhanced the catalysis, the yield
Fig. 4 shows the influences of reaction temperature
on the chloromethylation. The catalytic activity increased
with the temperature to 45 °C, however, the yield was de-
creased with the further increase of the temperature. The
yield reached maximum at 45 °C, under such temperature
the conversion can be kept at the highest. These results
show that the moderate temperature, such as 45 °C en-
hanced the chloromethylation.
Fig. 4. Influences of temperature on the chloromethyl-
ation. Reaction conditions: O-xylene, 10.6 g
(0.1 mol); paraformaldehyde, 3.15 g (0.105
mol); 20% H2SO4, 60 mL; AcOH, 30 mL; anhy-
drous hydrogen chloride gas, 60 mL/min; con-
centrations of CTAB: 18-fold CMC; time, 4 h.
The influences of the concentration of sulfuric acid at
Fig. 5. Influences of concentration of sulfuric acid on
the chloromethylation. Reaction conditions:
O-xylene, 10.6 g (0.1 mol); paraformaldehyde,
3.15 g (0.105 mol); AcOH, 30 mL; anhydrous
hydrogen chloride gas, 60 mL/min; concentra-
tions of CTAB: 18-fold CMC; temperature, 45
°C; time, 4 h.
Fig. 3. Influences of different types of surfactants on
the chloromethylation. Reaction conditions:
O-xylene, 10.6 g (0.1 mol); paraformaldehyde,
3.15 g (0.105 mol); 20% H2SO4, 60 mL; AcOH,
30 mL; anhydrous hydrogen chloride gas, 60
mL/min; concentrations of surfactants: 18-fold;
temperature, 45 °C; time, 4 h.

Preparation of TMDE by Self Coupling Reaciton
J. Chin. Chem. Soc., Vol. 56, No. 5, 2009 1059
reached maximum at 0.5 of the ratio. However, the yield
decreased slowly with further increase in the amount of
acetic acid although the conversion seem stable. One possi-
bility for the role of acetic acid may be due to the enhance-
ment of solubility to prompt the contact of paraformalde-
hyde with o-xylene by the solvation, however, further
studies are necessary for the clarification of the mecha-
nism.
Table 1. PTC catalyzed self coupling of 3,4-dimethylbenzyl
chloride with Fe and Cu/Cu2Cl2 in aqueous mediaa
Phase transfer
Entry
Amount (mmol)
Yield (%)b
catalyst
1
2
3
4
5
6
90.0
96.5
94.5
93.0
92.7
92.2
PEG-600
CTAB
TTAB
1.2
1.2
1.2
1.2
1.2
TBAB
TEAB
a Reaction conditions: 3,4-dimethylbenzyl chloride, 15.4 g (0.1
mol); Fe, 3.37 g (0.06 mol); Cu2Cl2, 0.2 g (0.001 mol); Cu, 0.15
g (0.0024 mol); H2O, 100 mL; temperature, 80 °C; time: 2 h.
b Isolated yield.
Preparation of 3,3¢,4,4¢-tetramethyldiphenylethane (b)
In the process of reductive coupling, 3,4-dimethyl-
benzyl chloride was initially carried out by vigorously stir-
ring the two phase system (a and 100 mL H2O) at 80 °C in
the absence of phase transfer catalyst (PTC) and the yield
was only 90% (Table 1, entry 1) after 2 h. Using PEG-600
(1.2 mmol) as phase transfer catalyst under the same condi-
tions, b was obtained in a higher yield 96.5% (Table 1, en-
try 2). Besides PEG-600, we also tried to use CTAB, TTAB,
TBAB and TEAB as phase transfer catalysts in this cou-
pling reaciton. However, the yields were 94.5%, 93%,
92.7% and 92.2%, respectively (Table 1, entries 3-6). Thus,
based on the results obtained, the best phase transfer cata-
lyst is PEG-600.
Table 2. Cu/Cu2Cl2 catalyzed self coupling of 3,4-dimethyl-
benzyl chloride with Fe and PEG-600 in aqueous
mediaa
Entry
Cu (g)
Cu2Cl2 (g)
Yield (%)b
1
2
3
4
5
6
7
8
17.5
45.2
96.5
96.6
96.7
43.0
96.5
96.6
0.15
0.15
0.15
0.15
0.2
00.25
0.3
0.2
Table 2 shows the influences of Cu and Cu2Cl2 on the
reaction. In the absence of Cu and Cu2Cl2, the reaction pro-
ceeded very slowly, only 17.5% yield was obtained (Table
2, entry 1) after 4 h, and the addition of Cu (0.15 g) or
Cu2Cl2 (0.2 g) to it resulted in the increase of the yield, b
could be obtained in a higher yield 45.2% (Table 2, entry 2)
0.20
0.25
0.2
0.2
a Reaction conditions: 3,4-dimethylbenzyl chloride, 15.4 g (0.1
mol); Fe, 3.37 g (0.06 mol); PEG-600, 0.73 g (1.2 mmol); H2O,
100 mL; temperature, 80 °C; time: 2 h.
b Isolated yield.
or 43.0% (Table 2, entry 6) under the same conditions. The
yield can be greatly improved when the combined use of
Cu and Cu2Cl2, and it reached maximum (96.5%) in a
shorter time (2 h) when the addition of Cu (0.15 g) and
Cu2Cl2 (0.2 g) (Table 2, entry 3). However, further addition
the amount of Cu (Table 2, entries 7, 8) or Cu2Cl2 (Table 2,
entries 4, 5), under the same conditions, the yield was not
enhanced significantly. Therefore, the optimal reaction
conditions were observed in Table 2, entry 3.
The influences of iron powder on the reaction are
shown in Table 3. In this reaciton, the role of iron powder is
as an inevitable reductant, we found its physical and chemi-
cal forms have great influences on the reaction. Using soft
gray iron powder (0.06 mol) as reductant, b could be ob-
tained in a high yield 96.5% (Table 3, entry 5), however,
when we use wrought iron powder and steel powder as
reductant, under the same conditions, the yields were
Fig. 6. Influences of volume ratio of acetic acid and
sulfuric acid on the chloromethylation. Reac-
tion conditions: O-xylene, 10.6 g (0.1 mol);
paraformaldehyde, 3.15 g (0.105 mol); anhy-
drous hydrogen chloride gas, 60 mL/min; con-
centrations of CTAB: 18-fold CMC; tempera-
ture: 45 °C; time: 4 h.

1060 J. Chin. Chem. Soc., Vol. 56, No. 5, 2009
Hu et al
yield was obtained. The yield reached the maximum at 80
°C and then, decreased when at higher temperature. The in-
fluences of the reaction time are shown in Fig. 8. The yield
increased with the increase of the reaction time, and reached
maximum at 2 h.
Table 3. Fe reduced self coupling of 3,4-dimethylbenzyl chloride
catalyzed by Cu/Cu2Cl2/PEG-600 in aqueous mediaa
Ratio (mol
Entry
Reductant (Fe)
Yield (%)b
Fe/mol a)
1
2
3
4
5
6
7
Wrought Iron Powder
Steel Powder
0.6
0.6
74.0
78.3
65.0
87.5
96.5
96.6
96.7
Soft Gray Iron Powder
Soft Gray Iron Powder
Soft Gray Iron Powder
Soft Gray Iron Powder
Soft Gray Iron Powder
0.4
Mechanism of reaction
0.5
It can be observed that the reaction for the formation
of 3,3¢,4,4¢-tetramethyldiphenylethane consists of multiple
reaction steps, and they can be divided basically into two
types of reactions: chloromethylation of o-xylene and re-
ductive coupling of 3,4-dimethylbenzyl chloride. Despite
the absence of any supporting evidence and the detailed
pathways is not clear, we envision a plausible mechanism
that explains the peculiar effectiveness of the excellent pro-
cedure, key steps are proposed on the basis of the related
literatures,12,23-26 our observations and obtained results
(Scheme II). Accordingly, CTAB micellar-catalyzed chlo-
romethylation of o-xylene proceed by a similar mechanism
as shown in a reported literature12 and possibly consists of
four steps: the electrophilic substitution reaction (steps 1
and 2) to form 3,4-dimethylphenyl methanol (II) and then
the nucleophilic substitution reaction (steps 3 and 4) to
form 3,4-dimethylbenzyl chloride (V). The self coupling of
3,4-dimethylbenzyl chloride possibly consists of five steps
(steps 5-9).23-26 Initially, Cu2Cl2 act as a source of Cu+, V
reacts with Cu+ to form transition state (VI) and then, the
VI eliminated Cu+ to yield benzyl free radical (VII), then
VII reacts with each other through self coupling to from the
0.6
00.65
0.7
a Reaction conditions: 3,4-dimethylbenzyl chloride, 15.4 g (0.1
mol); Cu2Cl2, 0.2 g (0.001 mol); Cu, 0.15 g (0.0024 mol); PEG-
600, 0.73 g (1.2 mmol); H2O, 100 mL; temperature, 80 °C;
time: 2 h.
b Isolated yield.
merely 74.0% and 78.3%, respectively (Table 3, entries 1,
2). From these results, it was observed that the best re-
ductant is soft gray iron powder. Also, the amount of iron
powder has great influences on the reaction. The yield in-
creased with the ratio of Fe and a (i.e. the amount of Fe in-
creased) and reached maximum at 0.6 of the ratio (Table 3,
entry 5), and further addition the amount of Fe, under the
same conditions, the yield was not enhanced significantly
(Table 3, entries 6, 7).
Fig. 7 shows the influences of reaction temperature
on the yield. The catalytic activity increased with the in-
crease in the temperature to 80 °C, at lower temperatures
such as 50 °C, the reaction proceeded slowly and only 36%
Fig. 7. Influences of temperature on the coupling. Re-
action conditions: 3,4-dimethylbenzyl chlo-
ride, 15.4 g (0.1 mol); Fe, 3.37 g (0.06 mol);
Cu2Cl2, 0.2 g (0.001 mol); Cu, 0.15 g (0.0024
mol); PEG-600, 0.73 g (1.2 mmol); H2O, 100
mL; time: 2 h.
Fig. 8. Influences of reaction time on the coupling. Re-
action conditions: 3,4-dimethylbenzyl chlo-
ride, 15.4 g (0.1 mol); Fe, 3.37 g (0.06 mol);
Cu2Cl2, 0.2 g (0.001 mol); Cu, 0.15 g (0.0024
mol); PEG-600, 0.73 g (1.2 mmol); H2O, 100
mL; temperature, 80 °C.

Preparation of TMDE by Self Coupling Reaciton
J. Chin. Chem. Soc., Vol. 56, No. 5, 2009 1061
Scheme II A possible reaction mechanism
desired product VIII. The self coupling of complex VII oc-
curs continuously via the oxidation-reduction reactions
(steps 8 and 9) and the reduction of Cu2+ by iron (step 9)
likely initiates the catalytic reaction.
CTAB micellar-catalyzed chloromethylation of o-xylene
was carried out successfully. The conversion for a in the
micellar solutions could be remarkably improved to 94%
contrast to other procedures catalyzed by lewis acids, ionic
liquids or rare-earth metal triflates whose conversion for a
was usually 72~80%,27-32 which demonstrated the high ef-
ficiency for the chloromethylation of o-xylene. Another
glittery point in our paper was that we have developed a
new and efficient procedure for the preparation of b from a
via a self coupling catalyzed by Cu/Cu2Cl2/PEG-600 and
promoted by iron in aqueous media under PTC conditions.
The good yields obtained in all cases, makes this self cou-
pling procedure very attractive.
CONCLUSION
A facile and improved procedure for the synthesis of
3,3¢,4,4¢-tetramethyldiphenylethane has been developed in
this paper, which is prepared by CTAB micellar-catalyzed
chloromethylation with o-xylene as starting material for
the first time with subsequent self coupling reaciton cata-
lyzed by Cu/Cu2Cl2/PEG-600 and promoted by iron in
aqueous media.
One of the noticeable points in our paper was that the
In conclusion, we have developed an excellent proce-

1062 J. Chin. Chem. Soc., Vol. 56, No. 5, 2009
Hu et al
dure for the preparation of 3,3¢,4,4¢-tetramethyldiphenyl-
ethane in two steps in a 86.5% total yield. Judging from the
conditions employed, this method showed has great pros-
pects in industrial applications.
7.04-7.13 (m, 3H, Ar-H), 13C NMR (400 MHz, d in ppm
from TMS in CDCl3): 21.9, 22.5, 46.8, 126.1, 129.7, 130.5,
135.8, 137.1, 137.5. Anal. Calcd for C9H11Cl: C, 69.86; H,
7.18; Cl, 22.96. Found: C, 69.90; H, 7.17; Cl, 22.93.
Preparation of 3,3¢,4,4¢-tetramethyldiphenylethane (b)
A mixture of Fe (3.37 g, 0.06 mol), Cu2Cl2 (0.2 g,
0.001 mol), Cu (0.15 g, 0.0024 mol), PEG-600 (0.73 g, 1.2
mmol) and H2O 100 mL was stirred in 250 mL round flask.
Then 3,4-dimethylbenzyl chloride (15.4 g, 0.1 mol) was
added dropwise when the temperature reached to 80 °C.
After that the mixture was stirred for 2 additional hours at
80 °C, the reaction progress was monitored by TLC and
HPLC, then cooled to room temperature and filtered, the
filtrate obtained was extracted with dimethylbenzene (3 ´
10 mL), the residue was dissolved with ethanol and di-
methylbenzene and filtered. The combined organic phases
was dried over anhydrous Na2SO4. The solvent was re-
moved and the crude product was recrystallized from etha-
nol and dimethylbenzene afforded a white powder (b, 11.5
EXPERIMENTAL
Materials and apparatus
Cetyltrimethylammonium bromide (CTAB), tetraeth-
ylammonium bromide (TEAB), tetrabutylammonium bro-
mide (TBAB), tetradecyltrimethylammonium bromide
(TTAB), nonylphenol polyoxyethylene ether (NP-10), so-
dium dodecyl sulfonates (SDS) and (polyethylene glycol
600) PEG-600 purchased from Aldrich Chemical Co., Inc.
were of analytical grade and used without further purifica-
tion. Other reagents purchased from Chinese companies
were all of analytical or chemical grades. Distilled water
was used for all the reactions. NMR spectra were recorded
on a Bruker 400-MHz spectrometer using CDCl3 as the sol-
vent with tetramethylsilane (TMS) as an internal standard.
High performance liquid chromatography (HPLC) experi-
ments were performed on a liquid chromatograph (Dionex
Softron GmbH, America), consisting of a pump (P680) and
ultraviolet-visible light detector (UVD) system (170U).
The experiments were performed on Diacovery C18 col-
umn, Æ 4.6 ´ 150 mm. Elemental analysis were performed
on a Vario EL III instrument (Elmentar Anlalysensy Teme
GmbH, Germany).
1
g, yield 96.5%, m.p. 87-89 °C, lit.8 m.p. 88-90 °C). H
NMR (400 MHz, d in ppm from TMS in CDCl3): 2.55 (s,
3H, CH3), 2.83 (s, 2H, CH2), 6.94-7.08 (m, 3H, Ar-H), 13
C
NMR (400 MHz, d in ppm from TMS in CDC13): 22.1,
22.8, 38.6, 125.7, 130.2, 135.1, 135.7, 137.4, 140.1. Anal.
Calcd for C8H22: C, 90.68; H, 9.32. Found: C, 90.70; H,
9.30.
Preparation of 3,4-dimethylbenzyl chloride (a)
ACKNOWLEDGEMENTS
Amixture of o-xylene (10.6 g, 0.1 mol), CTAB (0.8 g,
2.3 mmol), 20% H2SO4 60 mL and HAc 30 mL was stirred
in 250 mL round flask for 2 h at room temperature in order
to solubilize fully o-xylene in the surfactant micelle solu-
tion. Then paraformaldehyde (3.15 g, 0.105 mol) was
added and anhydrous hydrogen chloride gas was bubbled
into the flask at the flow rate of 60 mL/min. The mixture
was stirred for 4 additional hours at 45 °C and then cooled
to room temperature, the reaction progress was monitored
by TLC and HPLC. The residue obtained was extracted
with methylene chloride (3 ´ 20 mL). The combined or-
ganic phases was washed to neutral with 20% NaHCO3 so-
lution (3 ´ 20 mL) and water (3 ´ 20 mL), then dried over
anhydrous Na2SO4. The solvent was evaporated and then
purified by column chromatography over silica gel (eluent:
hexane/methylene chloride = 4.5/1) to give pure 3,4-di-
methylbenzylchloride (a, a colorless liquid, 13.8 g, yield
89.7%). 1H NMR (400 MHz, d in ppm from TMS in CDCl3):
2.29 (s, 3H, CH3), 2.30 (s, 3H, CH3), 4.56 (s, 2H, CH2),
We thank the Ministry of Education of the Republic
of China and Natural Science Foundation of Jiangsu Prov-
ince for supporting this research.
Received May 2, 2009.
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