(primary and second alcohols) is defined as the ratio of the
number of moles of PGME produced in the reaction to the
total number of moles of PO initially added. The selectivity for
1-methoxy-2-propanol is defined as the ratio of the number of
moles of 1-methoxy-2-propanol to the number of moles of the
two isomers.
Yield ¼
moles of ð1-methoxy-2-propanol þ 2-methoxy-1-propanolÞ produced
moles of propylene oxide initially added
Selectivity ¼
Scheme 2 The synthesis of the 1,1,3,3-tetramethylguanidine-based
molð1-methoxy-2-propanolÞ
ILs.
molð1-methoxy-2-propanolÞ þ molð2-methoxy-1-propanolÞ
toxic isomer 1-methoxy-2-propanol can be obtained. Moreover,
after the reaction, [TMG][Ac] can be easily recovered and
recycled without any considerably decrease in the yield
or selectivity. This protocol provides a green and effective
alternative for the synthesis of PGME at low temperature.
The authors are grateful for the financial support of the
National Natural Science Foundation of China (20932002,
20733010, 20633080) and the Chinese Academy of Sciences
(KJCX2.YW.H16).
Notes and references
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Experimental
1,1,3,3-Tetramethylguanidine was purchased from the Baigui
Chemical Company (Shijiazhuang, China). All acids and
solvents (analytical grade) were purchased from the Beijing
Chemical Reagent Plant (Beijing, China).
We have only described the procedure to synthesize 1,1,3,3-
tetramethylguanidinium acetate ([TMG][Ac]) because those to
prepare 1,1,3,3-tetramethylguanidium lactate ([TMG][Lac])
and 1,1,3,3-tetramethylguanidium trifluoroacetate ([TMG][Tfa])
are similar. The main difference is that the corresponding acids
are used (Scheme 2). In a typical experiment, 100 mL of
ethanol and 2.30 g of TMG (20.0 mmol) were loaded into a
250 mL flask in a water bath at 0 1C. Then, 20.0 mmol of
CH3COOH in 35 mL of ethanol was slowly charged into the
flask with stirring. The reaction lasted for 2 h. The reaction
mixture was evaporated under reduced pressure at 333 K. The
crude oily residue was dissolved in 100 mL of ethanol, treated
with active carbon, filtered and evaporated under vacuum.
The catalytic performance of the ILs was evaluated in a
6.5 mL batch reactor with a molar ratio of methanol to PO
from 1 : 1 to 5 : 1. After running at the desired temperature for
a suitable time under magnetic stirring, the reactor was cooled
to room temperature. The products were analyzed by a GC
(Agilent 6820) equipped with an FID detector and a capillary
column (SUPELCOWAX 10, 30 m in length, 0.25 mm in
diameter). n-Propanol was used as the internal standard to
calculate the amount of the products. The yield of PGME
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2536 New J. Chem., 2010, 34, 2534–2536 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010