Aerobic flow oxidation of alcohols in water catalyzed by platinum nanoparticles dispersed in an amphiphilic polymer

Article abstract of DOI:10.1039/c4ra14947e

We have developed a technique for the aqueous aerobic flow oxidation of alcohols in a continuous-flow reactor containing platinum nanoparticles dispersed on an amphiphilic polystyrene-poly(ethylene glycol) resin (ARP-Pt). Various primary and secondary alcohols including aliphatic, aromatic and heteroaromatic alcohols were efficiently oxidized within 73 seconds in a flowing aqueous system at 100-120°C under 40-70 bar of the system pressure to give the corresponding carboxylic acids and ketones, respectively, in up to 99% yield. Benzaldehydes could be also prepared selectively from benzyl alcohols by conducting the flow oxidation under the standard conditions in the presence of triethylamine. Moreover, a practical gram-scale synthesis of surfactants was realized in the aqueous aerobic continuous flow oxidation for 36-116 hours. This aerobic flow oxidation system provides a safe, clean, green, rapid and efficient practical method for oxidizing alcohols.

Full text of DOI:10.1039/c4ra14947e

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Aerobic flow oxidation of alcohols in water
catalyzed by platinum nanoparticles dispersed in an
Cite this: RSC Adv., 2015, 5, 2647
amphiphilic polymer†
a
a
ab
*
Takao Osako, Kaoru Torii and Yasuhiro Uozumi
We have developed a technique for the aqueous aerobic flow oxidation of alcohols in a continuous-flow
reactor containing platinum nanoparticles dispersed on an amphiphilic polystyrene–poly(ethylene glycol)
resin (ARP-Pt). Various primary and secondary alcohols including aliphatic, aromatic and heteroaromatic
alcohols were efficiently oxidized within 73 seconds in a flowing aqueous system at 100–120 ꢀC under
40–70 bar of the system pressure to give the corresponding carboxylic acids and ketones, respectively,
in up to 99% yield. Benzaldehydes could be also prepared selectively from benzyl alcohols by
conducting the flow oxidation under the standard conditions in the presence of triethylamine. Moreover,
a practical gram-scale synthesis of surfactants was realized in the aqueous aerobic continuous flow
oxidation for 36–116 hours. This aerobic flow oxidation system provides a safe, clean, green, rapid and
efficient practical method for oxidizing alcohols.
Received 20th October 2014
Accepted 1st December 2014
DOI: 10.1039/c4ra14947e
www.rsc.org/advances
continuous-ow systems for the aerobic oxidation of a wide
range of alcohols (including less-active aliphatic alcohols),
Introduction
realizing safe, green, and efficient preparation of a variety of
carbonyl compounds, would be an eagerly-awaited device.
We have previously developed novel supported palladium
and platinum catalysts for the aerobic oxidation of alcohols in
water.3a–d Dispersions of platinum nanoparticles in amphiphilic
polystyrene–poly(ethylene glycol) resin (PS–PEG),10 prepared by
treatment of a PS–PEG resin-supported dichloro(ethene)plat-
inum complex with benzyl alcohol (Scheme 1),11 catalyze the
aerobic oxidation of various alcohols, including less-reactive
primary aliphatic alcohols, in water under mild conditions
Although the oxidation of alcohols to the corresponding
carbonyl compounds is among the most fundamental and most
important processes in organic chemistry, conducting the
reaction in a safe and green manner remains a major challenge
because conventional protocols for the oxidation of alcohols
oen require stoichiometric amounts of harmful and toxic
oxidants, as well as the use of halogenated organic solvents.1
Indeed, although a variety of heterogeneous catalysts that
promote the aerobic oxidation of alcohols have been developed
in the last decade,2–4 there are only a few isolated reports on
aerobic oxidations of less-active aliphatic alcohols.5
ꢀ
(oxygen or air at 1 atm, 60 C, 8–36 h). Furthermore, the cata-
lysts are stable and can be readily recycled.3b,c These ndings
prompted us to apply these catalysts in a continuous-ow
system for the oxidation of alcohols. Here, we report the
aerobic oxidation of a wide range of alcohols, including less-
reactive primary aliphatic alcohols, in water in a continuous-
The development of organic transformations under condi-
tions of continuous ow is becoming an increasingly important
eld of research in synthetic organic chemistry.6 However, the
catalytic aerobic oxidation of alcohols in continuous-ow
systems with heterogeneous catalysts are yet immature.7,8
Previously reported catalytic aerobic ow oxidations of alcohols
were generally performed in toxic and/or explosive organic
solvents.7g–i,8b,9 In addition, the applicable substrates were
usually limited to highly reactive (e.g., benzylic) alcohols, and
the reaction efficiency was not on a satisfactory level of practical
synthetic processes.7,8 Thus, it is not surprising that the
ow reactor containing
a PS–PEG resin dispersion of
aInstitute for Molecular Science (IMS) Myodaiji, Okazaki, Aichi 444-8787, Japan.
E-mail: uo@ims.ac.jp
bRIKEN, Wako, Saitama, 351-0198, Japan
† Electronic supplementary information (ESI) available: Fig. S1 and
characterization data and NMR charts for the products. See DOI:
10.1039/c4ra14947e
Scheme 1 Preparation of ARP-Pt.
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platinum nanoparticles (amphiphilic resin-supported nano-
particles of platinum (ARP-Pt)) (Scheme 1). Oxidation of various
primary and secondary alcohols, including aliphatic, alicyclic,
benzylic, and allylic alcohols, was achieved within 73 seconds of
the residence time to give the corresponding carboxylic acids
and ketones in up to 99% isolated yield with a practical level of
the productivity (substrate concentration ¼ 10–100 mM, ow
rate ¼ 0.6–0.8 mL minꢁ1). Moreover, >50 gram-scale synthesis
of surfactants was realized via a continuous-ow of 116 h.
Scheme 2 Continuous-flow aerobic oxidation of 1-phenylethanol to
1-phenylethanone.
(entry 1D). Aerobic ow oxidation of 1a at a system pressure of
30 bar was also examined at various temperatures with ow
rates of 0.8 and 0.4 mL minꢁ1, corresponding to contact times
of 55 and 110 seconds, respectively (entries 2A–D, 3A–D). At
each temperature, the conversion of 1-phenylethanol was
higher for the longer contact time. 1-Phenylethanol (1a) was
quantitatively oxidized to 1-phenylethanone (>99%) at 100 ꢀC
within 55 seconds at a system pressure of 30 bar (entry 2D),
although traces of unreacted 1a could still be detected by
Results and discussion
The ARP-Pt-catalyzed aerobic oxidation of alcohols in water was
performed in a ow reactor (Fig. 1a).12,13 The reactor was capable
of producing controlled ow rates of up to 3.0 mL minꢁ1 at
temperatures of up to 200 ꢀC and system pressures of up to 150
bar, while supplying a constant volume (5 vol%) of nanosize
bubbles of O2 to the continuously owing solution through a
gas mixer equipped with a titanium frit (pore size 50 nm).14
We selected 1-phenylethanol (1a) as a substrate for opti-
mizing the conditions for the aerobic ow oxidation (Scheme 2).
A 1.0 M aqueous solution of 1-phenylethanol (1a) was intro-
duced into the reactor at a ow rate of 1.0 mL minꢁ1, and
passed sequentially through two catalyst cartridges (internal
diameter 4 mm, length 70 mm; Fig. 1b), each charged with ARP-
Pt (0.17 mmol Pt for the two cartridges). Under these condi-
tions, the total contact time of the solution with the catalyst was
44 seconds. Flow oxidation of 1a at 25 ꢀC and a system pressure
of 30 bar gave 1-phenylethanone (2a) in 7% conversion (Fig. 2,
entry 1A). Raising the temperature improved the conversion
(entries 1A–D), and we were pleased to nd that the aerobic
oxidation proceeded smoothly in water at 100 ꢀC to give 1-
phenylethanone (2a) in 98% conversion within 44 seconds
ꢀ
GC/MS analysis. Complete conversion was observed at 100 C
and a contact time of 110 seconds (ow rate ¼ 0.4 mL minꢁ1
)
(entry 3D).
We next examined the effect of the system pressure (15–50
bar) on the aerobic oxidation of 1-phenylethanol (1a) at 100 ꢀC
at a ow rate of 0.8 mL minꢁ1 (Scheme 3). The ow oxidation of
Fig. 2 Optimization of conditions for the aerobic oxidation of an
aqueous solution of 1-phenylethanol (1a) in a flow reactor equipped
with ARP-Pt cartridges. Top: three dimension bar graph. Bottom: table
for the results. Reaction conditions: 0.1 M aq. 1-phenylethanol, APR-Pt
(0.17 mmol Pt). O2 (5 vol%) was introduced into the solution as
nanosized bubbles at a system pressure of 30 bar (back pressure). The
Fig. 1 (a) Schematic diagram of the flow-oxidation reactor. P: pres- conversion (%) of 1-phenylethanol was determined by GC analysis. a44
sure sensor, G: gas buffer area, V: valve, N: nanobubble generator, B: s: flow rate ¼ 1.0 mL minꢁ1, 55 s: flow rate ¼ 0.8 mL minꢁ1, 110 s: flow
bubble detector. (b) View of the catalyst cartridge.
rate ¼ 0.4 mL minꢁ1
.
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various para substituents, such as methoxy, methyl, chloro or
triuoromethyl, underwent aerobic ow oxidation in a mixture
of water and tert-butyl alcohol (8 : 2 to 7 : 3)15 at a system
pressure of 50–70 bar to give the corresponding ketones 2b–e in
91 to 95% isolated yield (100% conversion). Cyclopropyl(phenyl)
methanol (1f) also underwent aerobic ow oxidation to give
cyclopropyl(phenyl)methanone (2f) in 87% yield, without the
formation of any ring-opening products. Aliphatic, acyclic and
cyclic secondary alcohols 1g–n were also fully oxidized (100%
conversion) in water or a mixture of water and tert-butyl alcohol
(7 : 3) at a system pressure of 50 bar with 55–73 seconds of
Scheme 3 Optimization of the pressure dependence.
1a at a system pressure of 15 bar provided 2a in 74% conversion.
When the system pressure increased to 50 bar, 1-phenylethanol
(1a) was fully converted into 1-phenylethanone (2a) in 55
seconds.
ꢀ
contact time at 100–120 C to give the corresponding ketones
We then examined the aerobic ow oxidation of a range of
benzylic and aliphatic secondary alcohols in water in the
continuous-ow reactor containing ARP-Pt under the optimized
conditions (Scheme 4). Oxidation of 1-phenylethanol (1a) under
2g–n in 83–99% isolated yield. The ow oxidation of borneol
(1o) proceeded efficiently at a system pressure of 70 bar to give
camphor (2o) in 84% yield with 10% recovery of the starting
alcohol.
the optimal conditions (50 bar O2, 100 ꢀC, 0.8 mL minꢁ1
;
The scope of the reaction for various primary alcohols was
also investigated under the aerobic ow oxidation conditions
(Scheme 5). Aerobic ow oxidation of benzyl alcohol (3a) in
water at 100 ꢀC at a system pressure of 70 bar and a contact time
of 73 seconds (ow rate ¼ 0.6 mL minꢁ1) gave benzoic acid (4a)
in 95% isolated yield (100% conversion). Various para-
substituted benzyl alcohols bearing methoxy, methyl, chloro,
nitro or triuoromethyl groups underwent aerobic ow oxida-
tion in the presence of one equivalent of sodium carbonate to
give the corresponding para-substituted benzoic acids 4b–f in
74–91% isolated yield (100% conversion). 1,4-Phenyl-
enedimethanol (3g) was similarly converted into terephthalic
acid (4g, 91%) in the presence of two equivalents of Na2CO3.
Benzyl alcohols bearing methyl or chloro groups in the ortho- or
meta-positions 3h–k were tolerated and gave the corresponding
benzoic acids 4h–k in 74–98% isolated yield. Benzyl alcohols
bearing an ester group (3l) or an ether group (3m) were oxidized
in a mixture of water and tert-butyl alcohol (7 : 3)15 at 120 ꢀC to
give the corresponding benzoic acids 4l and 4m without
undergoing hydrolysis. [4-(Methylsulfanyl)phenyl]methanol
(3n) was converted exclusively into 4-(methylsulfanyl)benzoic
acid (4n) in 74% yield without oxidation of the sulfur atom.
Interestingly, the aerobic oxidation of 4-aminophenol (3o)
and hydroquinone (3p) at a system pressure of 70 bar gave the
corresponding benzaldehydes 5o and 5p in good yields without
formation of the benzoic acids. It is possible that the catalytic
activity of the platinum nanoparticles might have been reduced
by coordination to the NH2 and OH groups of the aniline and
phenol derivatives, respectively.16 In fact, protection of the
hydroxy and amino groups with tert-butoxycarbonyl and acetyl
groups, respectively, led to full conversion into the corre-
sponding benzoic acids 4q and 4r in 93% and 84% yield,
respectively. Aerobic oxidation of heteroaromatic primary
alcohols (2-pyridyl-, 2-thienyl- and 2-furylmethanol) proceeded
efficiently to give the corresponding carboxylic acids 4s–u in 63–
87% yield. Cinnamyl alcohol (3v) was also tolerated in the
aerobic ow oxidation and gave cinnamic acid (4v) in 77% yield.
It is noteworthy that the less-reactive primary aliphatic alcohols
3w–3aa all underwent aerobic ow oxidation under similar
conditions to give the corresponding acids 4w–4aa in 77–92%
isolated yield. When alcohols bearing terminal or internal
contact time ¼ 55 s) gave a 95% isolated (100% conversion)
yield of 1-phenylethanone (2a). 1-Phenylethanols bearing
Scheme 4 Scope of secondary alcohols for aerobic flow oxidation in
water. Isolated yields are reported. aIsolated yield. bO2 (70 bar).
cContact time 73 s (flow rate 0.6 mL minꢁ1), 120 ꢀC. dNMR yield using
an internal standard.
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with a contact time of 44 seconds (ow rate ¼ 1.0 mL minꢁ1
)
gave benzaldehyde (5a) in 90% yield with no formation of
benzoic acid (Scheme 6).17 The oxidation of aldehydes to
carboxylic acids is suppressed by deactivation of the platinum
nanoparticles by the amine.
In the presence of triethylamine, (4-methoxyphenyl)meth-
anol (3b) and (4-methylphenyl)methanol (3c) were converted
into benzaldehydes 5b and 5c, respectively, in 86 and 72% yield
without formation of the carboxylic acids.17 When (4-chlor-
ophenyl)methanol was subjected to the ow-reaction condi-
tions, 4-chlorobenzaldehyde was obtained as the major product
in 62% yield, together with 14% of the carboxylic acid 4d (14%).
Cinnamyl alcohol (3v) was also tolerated and it gave cinna-
maldehyde (5v) in 80% yield as the sole product. However,
oxidation of aliphatic alcohols in the presence of triethylamine
was sluggish and gave low conversions of the alcohols.
To demonstrate the practical utility of this process, we per-
formed a gram-scale oxidation of oligo(ethylene glycol) mono-
dodecyl ethers 7 in the aqueous aerobic ow oxidation system to
give the corresponding dodecyl{oligo(oxyethylene)}acetic
acids.18 A 0.05 M aqueous solution of tetra(ethylene glycol)
dodecyl ether (7a; n ¼ 4) was introduced into the ow reactor
containing ARP-Pt cartridges (0.17 mmol Pt for the two catalyst
cartridges) and subjected to ow oxidation at 100 ꢀC and 60 bar
at a ow-rate of 0.6 mL minꢁ1 (contact time 73 s) for 26 hours.
The collected aqueous eluent was freeze dried to give 40 g
(100%) of the desired detergent carboxylic acid 8a (n ¼ 4) with a
high catalyst turnover number (TON ¼ 624) (Scheme 7). Deter-
gent 8a was obtained in a highly pure state without further
purication. The ow oxidation of a 0.25 M aqueous solution of
a mixture of oligo(ethylene glycol) ethers 7b (n ¼ 3–6) also
proceeded efficiently under similar conditions at a ow-rate of
0.8 mL minꢁ1 (contact time 55 s) for 113 hours to give 57 g of 8b
(n ¼ 3–6) at a TON of 890 (100% conversion). These results
showed that the catalytic activity was retained during the
continuous ow oxidation at 100 ꢀC for long period (113 hours).
Scheme
5 Aerobic flow oxidation of primary alcohols in water.
aIsolated yield. bWithout Na2CO3. cNa2CO3 (2 equiv.) was used. dIn
H2O/tBuOH (7 : 3). At 120 ꢀC. The yield was determined by H NMR
with an internal standard. gContact time 55 s (flow rate 0.8 mL minꢁ1).
hO2 (50 bar). iContact time 88 s (flow rate 0.5 mL minꢁ1).
e
f
1
alkyne groups were used as substrates, the aerobic ow oxida-
tion was sluggish, possibly because the reaction was inhibited
by strong coordination of the alkyne to the platinum species.
As mentioned above, aerobic ow oxidation of 4-amino-
phenol (3o) and hydroquinone (3p) gave the corresponding
benzaldehydes 5o and 5p exclusively. These results prompted us
to explore the conditions for the selective oxidation of primary
alcohols to aldehydes. We were pleased to nd that aerobic ow
oxidation of benzyl alcohol (3a) in the presence of one equiva-
lent of triethylamine at 100 ꢀC and a system pressure of 40 bar
Scheme 6 Selective synthesis of aldehydes by aerobic flow oxidation
of alcohols on ARP-Pt in the presence of Et3N. aIsolated yield. b3a (25
mM), H2O. c3b (25 mM), H2O/tBuOH (8 : 2). d3c (12.5 mM), H2O/tBuOH
(8 : 2), O2 (60 bar). eNMR yield using an internal standard. f3d (15 mM),
H2O/tBuOH (7 : 3).
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catalyst cartridges (f 4 ꢂ 70 mm) and gas mixer system; (3) the
touch screen panel where the reaction conditions (ow rate,
system pressure, and temperature) can be controlled and
monitored. The stainless steel tubing has an inner diameter of
500 mm. The system can be pressurized up to 150 bar. In the
nanobubble generator part, a constant volume (5 vol%) of the
gas passed through a titanium frit (pore size 50 nm) is provided
as nano bubbles to the solution.
Preparation of the catalyst cartridges and calculation of the
contact time
A preweighed catalyst cartridge was packed with ARP-Pt (300
mg, 0.085 mmol Pt)3b,c with water and sealed on either end with
8 mm lters. Aer wetting the cartridge with H2O, the wet
catalyst cartridge was weighed. The reaction volume was
determined from the weight difference between the dry and the
wet cartridges. The reaction volume was 0.36 mL. According to
eqn (1), when the ow rate was set as 1.0 mL minꢁ1, the contact
time per one cartridge was 22 second.
Scheme 7 Gram-scale syntheses of surfactants 8 by aerobic aqueous
flow oxidation of alcohols 7.
Conclusions
We have developed a technique for the aqueous aerobic ow
oxidation of alcohols in a continuous-ow reactor containing
platinum nanoparticles dispersed on a PS–PEG resin (ARP-Pt).
Various primary and secondary alcohols were efficiently
oxidized within 73 seconds in the owing aqueous system at
100–120 ꢀC and 40–70 bar to give the corresponding carboxylic
acids and ketones, respectively. Benzaldehydes were prepared
selectively from benzyl alcohols by conducting the ow oxida-
tion under the standard conditions in the presence of triethyl-
amine. Moreover, a practical gram-scale synthesis of surfactants
was realized in the aqueous aerobic ow system. This aerobic
ow oxidation system provides a safe, clean, green and efficient
practical method for oxidizing alcohols. Further investigations
on practical applications of the technique are underway in our
laboratory.
reaction volume ðmLÞ ꢂ 60
Contact time ðsÞ ¼
(1)
flow rate ðmL minꢁ1
Þ
Typical procedure for the catalytic aerobic ow oxidation of
secondary alcohols in water
An aqueous solution of 1-phenylethanol (1a, 100 mM) was
pumped into the X-Cube reactor system installed with two
catalyst cartridges (300 mg ꢂ 2; total 0.17 mmol Pt) at a ow rate
of 0.8 mL minꢁ1. The oxidation was conducted at 100 ꢀC under
50 bar of the system pressure. The resulting solution was
collected for 1 h (48 mL) and extracted with Et2O three times.
The combined organic phase was dried over Na2SO4 and the
solvent was removed by evaporation to afford acetophenone (2a,
548 mg, 95% yield).
Experimental section
General
Typical procedure for the catalytic aerobic ow oxidation of
primary alcohols in water
All chemicals were commercially available and used without
further purication. Water was deionized with a Millipore
system as a Milli-Q grade. An X-Cube™ reactor system was
purchased from ThalesNano Nanotechnology Inc, Hungary. 1H
and 13C{1H} NMR spectra were recorded on a JEOL JNM-A500 or
JNM-ECS 400. GC analysis was carried out on a Hewlett Packard
4890 system. Mass spectra were recorded on a JEOL AccuTOF
GC JMS-T100GC equipped with Agilent 6890N GC (GC TOF-MS),
a JEOL AccuTOF JMS-T100LC (ESI TOF-MS), or a JEOL JMS-777V
(EI and FAB-MS). ICP analysis was performed on a LEEMAN
LABS Prole plasma spectrometer.
An aqueous solution of p-methoxybenzyl alcohol (3b, 25 mM) in
the presence of Na2CO3 (25 mM) was pumped into the X-Cube
reactor system installed with two catalyst cartridges (ARP-Pt:
300 mg ꢂ 2; total 0.17 mmol Pt) at a ow rate of 0.6 mL
minꢁ1. The aerobic ow oxidation was conducted at 100 ꢀC
under 70 bar of the system pressure. The resulting solution was
collected for 32 min (19 mL) and acidied by addition of 5%
HCl aq. until the pH of the solution became 3–4. The resulting
precipitate was collected by ltration, washed with water, and
dried under vacuum to afford a white solid (4b, 62 mg, 85%
yield).
General information for the X-Cube reactor
Typical procedure for the selective synthesis of aldehydes
The picture and the schematic diagram of the X-Cube reactor
are shown in Fig. S1.† The X-Cube system consists of 3 units; (1) A solution of p-anisic alcohol (3b, 25 mM) in the presence of
t
the pump unit having two built-in HPLC pumps which can Et3N (25 mM) in a mixture of H2O and BuOH (8 : 2) was pum-
provide up to 3 mL minꢁ1 liquid ow; (2) the reactor unit ped into the X-Cube reactor system installed with two catalyst
ꢀ
including two heating units (up to 200 C) equipped with the cartridges (ARP-Pt: 300 mg ꢂ 2; total 0.17 mmol Pt) at a ow rate
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of 1.0 mL minꢁ1. The ow oxidation was conducted at 100 C
under 40 bar of the system pressure. The resulting solution was
collected for 18 min (17.7 mL) and extracted with EtOAc (20 mL
ꢂ 4). The combined organic phase was washed with brine
(20 mL ꢂ 3) and dried over Na2SO4. Aer removal of the solvent
by evaporation, a colorless oil was obtained in 86% yield
(p-anisic aldehyde, 5b, 52 mg).
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Typical procedure for gram-scale synthesis of the surfactant 8
An aqueous solution of tetraethylene glycol dodecyl ether (7a)
(0.05 M) was pumped into an X-Cube reactor system installed
with two catalyst cartridges (ARP-Pt: 300 mg ꢂ 2: total 0.017
mmol Pt) at a ow rate of 0.6 mL minꢁ1. The oxidation was
conducted at 100 ꢀC under 60 bar of the system pressure. Aer
the continuous ow for 36 h, 1290 mL of the product solution
was collected. The resulting solution was concentrated under
freeze-dry conditions to afford 8a (white solid, 40 g).
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Acknowledgements
This work was nancially supported by the METI/NEDO, the
JST-CREST (Creation of Innovative Functions of Intelligent
Materials on the Basis of Element Strategy) and the JSPS (Grant-
in-Aid for Scientic Research on Innovative Area no. 2105). We
appreciate the partial funding from Grant-in-Aid for young
scientists (B) no. 22750141, 26810099) and Shionogi & Co., Ltd.
(Shionogi Award in Synthetic Organic Chemistry). We are
grateful to Nihon Surfactant Kogyo for providing poly(ethylene
glycol)dodecyl ether 7.
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0.1
M in toluene, solution rate rate: 1 ,
mL minꢁ1
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¨
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ꢀ
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support.
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K. Niesz, I. Kovacs, Z. Szekelyhidi, Z. Bajko, L. Urge and
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Paper
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14 Ley and coworker have developed another efficient system of
gas introduction into liquid ow stream (tube-in-tube gas
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blocked without addition of tert-butyl alcohol. We used a
mixture of water and tert-butyl alcohols (8 : 2–7 : 3) to solve
the blocking issue. A mixture of water–alcohols is greener
than organic solvents. See the evaluation of water–alcohols
¨
for greenness: C. Capello, U. Fischer and K. Hungerbuhler,
supplied into the owing solution through
a
Green Chem., 2007, 9, 927–934.
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M. O'Brien, T. P. Petersen, I. R. Baxendale and S. V. Ley,
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triethylamine was conducted at a system pressure of 70
bar, the aldehydes were obtained exclusively without
formation of the carboxylic acids. Therefore the system
pressure did not affect the selectivity for formation of
aldehydes.
15 Because of low solubility of the resulting carbonyl 18 The target compounds 8 are known as a potential alternative
compounds in water, the continuous ow stream was
to peruoro carbon detergents for ne electronic devices.
2654 | RSC Adv., 2015, 5, 2647–2654
This journal is © The Royal Society of Chemistry 2015