Z. Xiong et al.
of wastes. So, it is necessary to search out a less-polluting and more environmen-
tally friendly synthetic route for ADM.
Dimethyl carbonate(DMC), widely used in the fields of pesticides, medicine,
polymer synthesis, and some other fields, is a new type of organic synthesis
intermediates, which is non-toxic as well as pollution free [4–6]. It has been reported
that DMC has a good biological activity for the presence of methyl, methoxyl,
carbonyl, etc.[7–10], and, therefore, it can react with phenol, alcohol, amine,
hydrazine, and ester compounds [11, 12], producing many important chemical
products. The reaction of catechol with DMC on alumina was studied, and the
conversion of catechol was 68 % at a time on-stream of 1 h at 553 K [13]. A series of
meso- and microporous materials, previously described and characterised, were tested
in the catechol O-alkylation process using methanol and DMC as alkylating reagents,
and it was confirmed that DMC is a better methylating agent than methanol with
respect to the conversion ratio of catechol and guaiacol [14]. It has also been reported
that veratrole was obtained in a high yield by the vapor phase methylation of catechol
with DMC when alumina was loaded with various alkali metal compounds [15].
In this work, ADM was prepared from ADH in the presence of K2CO3 and PTC
[16], using DMC as methylating agent instead of conventional toxic reagents (such
as haloalkane and dimethyl sulfate, etc.). The optimum reaction conditions were
obtained considering these influencing factors such as kinds of PTC, reaction time,
reaction temperature, reactant ratio, and so on. The results show that the synthesis
conditions are mild and easy to control. Moreover, both the reactant and the final
products are non-toxic and less corrosive, overcoming the deficiencies of the
traditional synthetic methods. The synthetic route we reported was more effective,
economical and ecofriendly, in accordance with the development direction of green
chemistry.
Experimental
Materials and instrumentation
All the chemicals used were from commercial sources without further purification.
All reagents were of analytical grade apart from those used as mobile phase for high
performance liquid chromatography (HPLC) use, such as methanol and acetonitrile,
which were chromatographically pure. HPLC experiments were performed on a
liquid chromatograph (Shimadzu, Japan), consisting of a reversed C18 column,
ø4.6 9 250 mm and ultraviolet–visible light detector (UVD) system.
Preparation of ADM
ADH (3.5 g, 27.6 mmol), K2CO3 (11.4 g, 82.7 mmol), and TBAB (0.9 g, 2.8 mmol)
were dissolved in 40 ml DMF in a 100-ml four-necked flask equipped with stirring
bar, a reflux condenser, a thermometer, and a 50-ml dropping funnel. Then, DMC was
slowly added to the reaction flask under 150 °C over a period of 30 min, and the
reaction mixer was stirred for another 10 h under 150 °C. The obtained product was
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