CHEMSUSCHEM
COMMUNICATIONS
DOI: 10.1002/cssc.201200781
Catalytic Deoxydehydration of Glycols with Alcohol
Reductants
[
a]
Camille Boucher-Jacobs and Kenneth M. Nicholas*
The complex, highly oxygenated nature of biomass materials,
including cellulose-derived carbohydrates and plant oil-based
glycerides, challenges chemists to develop new, selective
methods of oxygen removal for producing diverse classes of
secondary alcohols to form unsaturated alcohols, unsaturated
[10]
ethers, and polyenes (as well as the associated ketones).
Additionally, Abu Omar and Liu reported the MeReO -catalyzed
3
redox disproportionation of glycerol to distillable products,
that is, allyl alcohol, acrolein, and propanal (as well as non-
[
1]
value-added chemicals from renewable resources. Primary
[
2]
[3]
[11]
efforts focused on dehydration and hydrodeoxygenation
volatile dihydroxyacetone). Herein, DODH reactions catalyzed
processes; recently significant advances have been achieved
with both approaches. More recent research has focused on
selective oxygen removal through deoxydehydration (DODH),
in which vicinal hydroxyl groups are eliminated to form un-
saturated carbon–carbon bonds, see Scheme 1. Ellman et al.
by ammonium perrhenate with primary benzylic alcohols as re-
ductants are presented for the efficient and economical
production of olefins.
To develop DODH catalyst/reductant systems with optimum
efficiency, selectivity, economy, and simplicity we used
NH ReO (APR; ammonium perrhenate) as the catalyst because
4
4
[12]
of its relatively low cost, proven DODH ability with other re-
[13]
ductants, greater hydrolytic stability relative to MeReO3, and
its ionic nature and solubility properties that might facilitate its
recovery after use. A primary alcohol was the preferred DODH
reductant because the resulting aldehyde co-product could be
separated and used or recycled more easily than the ketones
produced in DODH with secondary alcohols. After screening
and reaction optimization studies using benzyl alcohol in com-
bination with the APR catalyst, we determined that the repre-
sentative glycols were converted to the corresponding olefins
(and benzaldehyde) in good to excellent yields when heated
for 5–24 h at 140–1758C with 1.0 equivalent of benzyl alcohol
in aromatic solvents [Scheme 2, Table 1].
[
5]
Scheme 1. The first reported metal-catalyzed DODH reaction.
reported high temperature, formic acid-driven DODH of several
[4]
polyols, which afforded unsaturated products and CO2. The
olefinic products from such reactions have diverse applications
in the manufacture of chemical intermediates such as polymers
and lubricants.
The first metal-catalyzed DODH reaction reported by
Andrews and Cook used aryl phosphine reductants [Scheme 1,
[
5]
Red=PR ] and (C Me )ReO as the catalyst. Gable et al.
3
5
5
3
probed the mechanism of the Re-catalyzed, phosphine-driven
DODH reaction and developed (tris-pyrazolylborate)ReO com-
3
[
6]
plexes as more robust catalysts. More recently, others have
demonstrated the ability of more economical and benign re-
agents to serve as DODH reductants. Abu Omar et al. de-
Scheme 2. Optimized DODH reaction scheme for glycol conversion to the
corresponding olefins.
scribed the MeReO -catalyzed DODH of glycols and epoxides
3
[
7]
by using hydrogen, and Nicholas et al. reported that MeReO
3
+
+
+
and perrhenate salts, such as ZReO (Z=Na , NH , Bu N ),
4
4
4
[
8]
catalyze the sulfite-driven DODH of glycols. Alcohols have
also been established as effective reductants for the glycol to
olefin conversion, again with rhenium-based catalysts. Berg-
man et al. first reported that the DODH of glycols by secondary
alcohols can be promoted by using Re (CO) under aerobic
The efficient conversion of several glycols to olefins with the
formation of benzaldehyde in comparable quantities are
shown in Table 1, entries 1–5. The olefins were formed regio-
selectively (i.e., no C=C isomers were detected); also, the acid-
or water-sensitive ether and ester linkages were well tolerated
as evidenced by the glycerol derivatives in entries 2–4. DODH
reactions of polyols that produce low-boiling olefins are best
conducted in a high-boiling solvent, for example, dichloro-
benzene (entry 2). The stereoselective conversion of (+)-diethyl
tartrate (entry 5) to diethyl fumarate indicated a syn-diol elimi-
nation, consistent with a concerted fragmentation of the pre-
2
10
conditions; producing both olefins and the corresponding ke-
[
9]
tones as by-products. Toste and Shiramizu demonstrated that
MeReO catalyzed the efficient conversion of higher polyols by
3
[
a] C. Boucher-Jacobs, Dr. K. M. Nicholas
Department of Chemistry and Biochemistry
University of Oklahoma, 101 Stephenson Pkwy.
Norman, OK 73019 (USA)
sumed Re–glycolate intermediate. The APR/PhCH OH reaction
2
of glycerol (as solvent), an important biomass resource, result-
ed in only a moderate yield of allyl alcohol (entry 7). The Toste
E-mail: knicholas@ou.edu
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201200781.
system of MeReO /3-octanol performed considerably better
3
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2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2013, 6, 597 – 599 597