octanal was obtained during the oxidation of 1-octanol. We are
now investigating this methodology for the oxidation of more
complex substrates.
Experimental
The following materials were used without purification: CO
SFC grade, >99.99%, BOC Gases), O (BOC), He (CP Grade,
9.999%, BOC Gases), H (99.995%, BOC Gases), air (BOC
Gases), Ar (BOC Gases), 2-octanol (97%, Alfa Aesar), 1-octanol
2
(
2
9
2
(
(
>99%, Aldrich), 2-propanol (reagent grade, Fisher), acetone
reagent grade, Fisher), ±-2-pentanol (99%, Alfa Aesar), 3-
pentanol (98+%, Alfa Aesar), 2-butanol (99%, Alfa Aesar),
-decanol (98%, Aldrich), ±-1-phenylethanol (96%, Fluka), 1-
phenyl-1-propanol, 3-heptanol, 2-heptanol, 5 wt% Pt + 1 wt%
Bi on Al (batches M01620C/D, Johnson Matthey), 5 wt%
Pt + 1.5 wt% Bi on Al (batch M04432, Johnson Matthey),
2
2
O
3
Fig. 7 Variation in yields in the oxidation of 1-octanol with varying
temperature, using a 5% Pt + 1.5% Bi/Al catalyst. Trace quantities of
the ester octyl octanoate were observed, but no octenes were detected by
2
O
3
2
O
3
sodium borohydride (Fisher), ethanol (reagent grade, Fisher),
40–60 petroleum ether (reagent grade, Fisher), sodium sulfate
-1
2
GC. Conditions: pressure: 100 bar, CO flow rate: 1 mL min , 1-octanol:
(
Fisher). Water was obtained from an in-house deionisation and
1
.96 mol%, O :1-octanol ratio: 0.5.
2
purification system (Elga PureLab Option S). 4-Heptanol was
not readily available commercially so was synthesised according
to a modified literature preparation, and its identity confirmed
could possibly increase the partitioning of the aldehyde and/or
water into the vapour phase, thereby decreasing the likelihood
of the aldehyde being hydrated by a water-rich liquid phase
covering the catalyst surface. Although challenging because of
the high temperatures, investigations into the phase behaviour
of this system would prove interesting.
1
13
by H and C NMR (Jeol EX-270).
The 2-octanol experiments used the 5% Pt + 1% Bi/Al O cat-
2
3
alyst, and the 1-octanol experiments the 1.5% Bi analogue. In a
typical reaction, the tubular reactor (78 mm long, 3.05 mm I.D.,
volume 0.57 mL) was filled with catalyst (typically ~300 mg),
2
The behaviour of 1-octanol with increasing O
2
concentration
largely echoes that of 2-octanol, although the maximum conver-
and then pressurised and heated with CO at the desired flow
sion is shifted to significantly lower O
in Fig. 8.
2
concentrations, as shown
rate. The substrate and O were then introduced, and this was
defined to be the beginning of the experiment.
2
Gas analysis was performed with a Varian CP 4900 Micro-Gas
Chromatograph (microGC), fitted with 20 m M5A molecular
sieve and 0.4 m HSA porous polymer columns for analysing low
molecular weight gases and heavier components, respectively.
The carrier gas was Ar and detection was with a Thermal
Conductivity Detector (TCD).
Reactions were analysed by Gas Chromatography (GC) using
a Shimadzu GC-2010 fitted with RTX-5 (Restek, 10 m ¥ 0.1 mm
I.D. ¥ 0.20 mm film thickness) or BETADEX 110 (Supelco, 30
m ¥ 0.25 mm I.D. ¥ 0.25 mm film thickness) columns. He was used
as the carrier gas, and appropriate temperature programming
was used to separate the components before detection with
a Flame Ionisation Detector (FID). Samples were prepared
by dilution of the BPR effluent in acetone or methanol, and
compared with external standards to determine concentrations.
Analysis was quantitative for the mass balance experiments, but
qualitative for others.
Fig. 8 Variation in the yield of octanal; with O
2
concentration.
flow rate:
◦
Conditions: pressure: 100 bar, temperature: 135 C, CO
2
-1
1
mL min , 1-octanol: 1.96 mol%.
Acknowledgements
We are grateful to the EPSRC and DICE for support (grant no.
EP/FO15275/1), and Johnson Matthey for the kind donation of
catalysts. We thank Xue Han for her assistance and M. Guyler,
P. Fields and R. Wilson for technical support.
Conclusions
In this paper we have described a miniature reactor which can be
successfully used for the continuous oxidation of primary and
secondary alcohols with O
2
in scCO
2
. In the case of 2-octanol,
Notes and references
we have shown that a 75% yield of 2-octanone can be achieved
with a >90% mass balance. The oxidation of a series of other
secondary alcohols was also investigated. High selectivity to
1
X. G. Wang, H. Kawanami, S. E. Dapurkar, N. S. Venkataramanan,
M. Chatterjee, T. Yokoyama and Y. Ikushima, Appl. Catal., A, 2008,
349, 86–90.
3
14 | Green Chem., 2010, 12, 310–315
This journal is © The Royal Society of Chemistry 2010