S. Le Guenic et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 72–77
73
Scheme 1. Extraction of aldehyde 2 from water to the organic phase.
ran, toluene and ethyl acetate) and from Acros (cyclopentyl methyl
ether and methyl-tetrahydrofuran). All materials were used with-
product yield (Y ), the conversion (X), the selectivity (S ) and the
i i
ratio 2/(2 + 3) were calculated by the following equations:
out further purification. Distilled H O was used for preparation of
all aqueous solutions.
2
Final amount of product i (mol)
Product yield Y =
× 100
Initial amount of reactant (mol)
i
Conversion X = (
Initial reactant amount (mol) − Final reactant amount (mol))
2.2. General procedure for the synthesis of phenylacetaldehyde in
Initial amount of reactant (mol)
water-CPME as biphasic media from 1-phenylethan-1,2-diol
Yield of product i
Conversion of reactant
Selectivity Si =
× 100%
In a typical experiment, a 10 mL glass vessel was charged with
water (0.5 mL), CPME (1.4 mL), 1-phenylethan-1,2-diol (1, 100 mg,
0
.725 mmol) and a catalyst (20 mol%). The vessel was sealed with a
septum, placed in the microwave apparatus (AntonPaar Monowave
00) and heated to the desired temperature under magnetic stir-
Final amount of product 2 (mol)
Final amounts of product 2 + product 3 (mol)
Ratio 2/(2 + 3) =
× 100%
3
ring (600 rpm) for the desired time. Temperature in the vessel was
measured by means of an IR sensor. At the end of the reaction, the
vessel was cooled down to 40 C using compressed air. Then, the
reaction mixture was diluted in 100 mL of acetonitrile. An aliquot
of the diluted solution was taken (ca. 1.5 mL) and filtered prior to
analysis through a syringe filter (PTFE, 0.45 m, VWR).
3
. Results and discussion
.1. Effect of the nature of organic solvent
Cyclopentyl methyl ether (CPME), ethyl acetate, toluene,
◦
3
methyltetrahydrofuran (Me-THF) and tetrahydrofuran (THF) as
organic solvents were tested in the presence of different selected
acids (AlCl , FeCl , HCl or H SO ) in water under microwave irra-
3
3
2
4
2.3. General procedure for the synthesis of phenylacetaldehyde in
diation to investigate their effect on aldehyde 2 yield. The ratio
between the organic solvent and water was 1:1, v/v (Table 1). It
should be noted that, whatever the solvent used, reactions per-
formed without acid catalyst afforded no conversion of the starting
diol 1. With ethyl acetate, a large amount of aldehyde 3 (9–25%)
was detected. In our conditions, ethyl acetate was degraded during
the process and only one phase was obtained at the end of reaction
preventing the transfer of aldehyde 2 in the organic phase. With
Me-THF and THF, yields of the target compound 2 were comprised
between 47% and 86% yields and formation of enal 3 was observed
whatever the acid. In contrast, toluene gave selectively the alde-
hyde 2 with good yield for the four acids. However substitution of
toluene as fossil solvent was recommended. The ether CPME gave
excellent yield (>86%) in presence of FeCl , HCl or H SO and low
water-CPME as biphasic media from styrene oxide
In a typical experiment, a 10 mL glass vessel was charged
with water (0.5 mL), CPME (1.4 mL), styrene oxide (4, 87 mg,
0
.725 mmol) and a catalyst (20 mol%). The vessel was sealed with a
septum, placed in the microwave apparatus (AntonPaar Monowave
00) and heated to the desired temperature under magnetic stir-
3
ring (600 rpm) for the desired time. Temperature in the vessel was
measured by means of an IR sensor. At the end of the reaction, the
◦
vessel was cooled down to 40 C using compressed air. Then, the
reaction mixture was diluted in 100 mL of acetonitrile. An aliquot
of the diluted solution was taken (ca. 1.5 mL) and filtered prior to
analysis through a syringe filter (PTFE, 0.45 m, VWR).
3
2
4
amount of compound 3 (<2%). Even if CPME is industrially produced
from fossil carbon, it is considered as green solvent and as an alter-
native to ethereal solvents [19,20]. For these reasons, a mixture of
CPME and water for the dehydration of diol 1 to aldehyde 2 was
chosen.
2
.4. Product analysis
1H and 13C NMR spectra were recorded on a 400 MHz Bruker
UltraShield 400 MHz/54 mm Ultra long hold. Chemical shifts (d)
are quoted in ppm and are referenced to TMS as an internal stan-
dard. Coupling constants (J) are quoted in Hz. All reactions were
monitored by HPLC. The column used is a GRACE Prevail C18.
The detector used is a SPD-M20A photo diode array detector (Shi-
madzu). The mobile phase is a mixture of water and MeOH (20:80).
Reactant and product concentrations were determined using cal-
ibration curves that were obtained from references samples. The
3.2. Effect of the ratio water/CPME on the phenylacetaldehyde
yield
Variation of the ratio between water and CPME was realized to
optimize the selectivity of aldehyde 2 and the selectivity between
the aldehyde 2 and the enal 3 (Table 2). Five ratios were tested
(water-CPME, 3:1; 2:1; 1:1; 1:2; 1:3, v/v) in presence of AlCl , FeCl ,
3
3