ISSN 0023ꢀ1584, Kinetics and Catalysis, 2011, Vol. 52, No. 3, pp. 386–390. © Pleiades Publishing, Ltd., 2011.
Tunable Synthesis of Propylene Glycol Ether from Methanol
and Propylene Oxide under Ambient Pressure1
Yu Bai, Qinghai Cai, Xiaoguang Wang, and Bin Lu
Key Lab for Design and Synthesis of Functionalized materials and Green Catalysis,
School of Chemistry and Chemical Engineering, Harbin Normal University, Harbin, P.R. China
eꢀmail: qinghaic@yahoo.com.cn
Received June 2, 2010
Abstract—A series of basic and acidic ionic liquids, 1ꢀbutylꢀ3ꢀmethylimidazolium hydroxide (BMIMOH),
1ꢀacetylꢀ3ꢀmethylimidazolium chloride (AcMIMCl) and AcMIMClꢀFeCl3, or analogues of AcMIMCl,
namely 1ꢀpotassium acetateꢀ3ꢀmethylimidazolium chloride (KAcMIMCl), 1ꢀpotassium (sodium, ammoꢀ
nium) acetateꢀ3ꢀmethylimidazolium hydroxides (KAcMIMOH, NaAcMIMOH and NH4AcMIMOH),
were prepared and used as catalysts for catalytic synthesis of propylene glycol ether via reaction of propylene
oxide (PO) with methanol under mild reaction conditions. KAcMIMOH exhibited outstanding catalytic perꢀ
formance with 94.2% of conversion of PO and 99.1% of selectivity to 1ꢀmethoxyꢀ2ꢀpropanol (MPꢀ2) at 60°C
and ambient pressure for 4 h. However, AcMIMClꢀFeCl3 showed a good catalysis performance with high
selectivity to 2ꢀmethoxyꢀ1ꢀpropanol (MPꢀ1). The tunable synthesis of MPꢀ2 or MPꢀ1 catalyzed by basic
compound KAcMIMOH or acidic ionic liquid AcMIMClꢀFeCl3 was realized.
DOI: 10.1134/S0023158411030025
As an important solvent, glycol ether is widely used in under atmospheric pressure. High selectivity to 1ꢀmetoxyꢀ
various industries such as coating, printing ink, leather dyeꢀ 2ꢀpropanol (MPꢀ2) or 2ꢀmetoxyꢀ1ꢀpropanol (MPꢀ1) was
achieved by the catalysis of KAcMIMOH or KAcMIMClꢀ
FeCl3, respectively. This phenomenon is very rare in glycol
ether synthesis to our knowledge. Moreover, highly selecꢀ
tive processes of manufacture are among the most imporꢀ
tant targets pursued in green chemistry.
ing and so on. Propylene glycol ether is expected to be a safe
substitute for toxic ethylene glycol ether due to its negligible
toxicity [1]. There are several methods for synthesis of proꢀ
pylene glycol ether. Among them, the propylene oxide
route is the most convenient and industrially feasible. In this
synthetic process, propylene oxide (PO) reacts with fatty
alcohols to form propylene glycol ether, and the reaction
catalyzed by acid or base catalysts, including at first homoꢀ
geneous acids or bases, such as NaOH, alcoholic sodium,
H2SO4 and BF3 etc [2–4], and later solid acids and bases,
namely acidic zeolites, CaO, MgO and amine modified
porous silica [1, 5–7] etc. Although the catalysis of the solid
acids or bases can help to avoid separation of the catalysts,
liquid waste treatment and corrosion problems, they also
suffer from some drawbacks such as lower activity and
selectivity to target ether, high reaction temperature and
pressure. Hence, there is still a need to develop a new cataꢀ
lytic system and/or an easyꢀclean technology more suitable
for the synthesis of the ether and its derivatives. In light of
this idea, a series of basic and acidic ionic liquids, 1ꢀbutylꢀ
EXPERIMENTAL
Preparation of the Basic Compound
Ionic liquid AcMIMCl was prepared by previously
reported method [8]: in a threeꢀneck flask equipped
with a condenser and a magnetic stirrer, 47.25 g
(0.5 mol) of chloroacetic acid was dissolved in 100 ml
of chloroform under stirring. 40 ml (0.5 mol) of
methylimidazole was dropped in the solution at 40°C
Nꢀ
,
followed by reaction for 50 h. After cooling to room
temperature, the reaction mixture was washed by ethꢀ
anol, filtered and dried under vacuum to afford a white
solid AcMIMCl with yield of 36.8%.
8.8 g (0.05 mol) of AcMIMCl was slowly added to
3ꢀmethylimidazolium hydroxide (BMIMOH), 1ꢀacetylꢀ3ꢀ a solution of KOH (0.1 mol dissolved in 40 ml H2O) in
methylimidazolium chloride (AcMIMCl) and AcMIMClꢀ
FeCl3, or analogues, namely KAcMIMCl, KAcMIMOH,
NaAcMIMOH and NH4AcMIMOH (see Scheme below
as an example), were prepared and used as catalysts for the
synthesis of propylene glycol ether from PO and methanol
a threeꢀneck flask with iceꢀwater bath and retained for
5 h under stirring. After the reaction, the mixture soluꢀ
tion was evaporated under reduced pressure and the
remainder was dissolved in dehydrated methanol, and
then filtered to remove precipitated KCl. The filtrate was
again evaporated under reduced pressure to eliminate
methanol. After drying a white solid KAcMIMOH was
1
The article is published in the original.
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