Deoxydehydration of glycols catalyzed by carbon-supported perrhenate

Article abstract of DOI:10.1002/cctc.201300545

Support group: The first heterogeneous catalyst for the deoxydehydration (DODH) of glycols into olefins is reported. A carbon-supported perrhenate material was found to catalyze the reductive conversions of styrene diol, tetradecane diol, and diethyl tartrate into their respective olefins with high chemo-, regio-, and stereoselectivity. Effective reductants for this DODH reaction include H₂, alcohols, and tetralin. Copyright

Full text of DOI:10.1002/cctc.201300545

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DOI: 10.1002/cctc.201300545
Deoxydehydration of Glycols Catalyzed by Carbon-
Supported Perrhenate
Alana L. Denning,[a] Huong Dang,[b] Zhimin Liu,[a] Kenneth M. Nicholas,*[b] and
Friederike C. Jentoft*[a]
Growing recognition that the Earth’s fossil-based, non-renewa-
ble resources are becoming depleted has sparked interest in
the development of new chemical processes for the conver-
sion of renewable biomass into chemicals and fuels.[1] The high
oxygen content of biomass feedstocks, such as carbohydrates
and triglycerides, requires the development of selective
oxygen-removal processes for the production of most chemi-
cals and fuels. Traditionally, dehydration has been the primary
research focus for the conversion of polyoxygenates.[1,2] Reduc-
tive processes have also been under investigation and the par-
tial hydrodeoxygenation (hydrogenolysis) of sugars and polyols
has been achieved with various selectivities and efficiencies by
using both heterogeneous[3] and homogeneous[4] transition-
metal catalysts.
(dehydration) sequence to produce a reduced metallo-O,O-gly-
colate, which undergoes fragmentation (retrocyclization) to
produce the olefin.
All of the effective DODH reactions that have been reported
to date have employed homogeneous (soluble) rhenium cata-
lysts. The practical advantages of heterogeneous (solid) cata-
lysts for large-scale commercial processes motivated us to seek
supported-rhenium catalysts for DODH reactions. Herein, we
report our initial findings that demonstrate the ability of a new
carbon-supported perrhenate catalyst to promote the DODH
of glycols into olefins.
The catalyst was prepared by the equilibrium adsorption of
perrhenate onto activated carbon by using aqueous NH4ReO4.
The rhenium content was typically 3–4 mass% Re. Figure 1
shows attenuated total reflectance (ATR)-IR spectra of an as-
Recently, a reaction that involves the reductive conversion of
glycols into olefins, termed “deoxydehydration” (DODH), has
received increasing attention (Scheme 1). The first catalytic
Scheme 1. The reductive conversion of glycols to olefins.
DODH reaction was reported by Cook and Andrews, who em-
ployed arylphosphines (PR3) as reductants and [Cp*ReO3] as
a catalyst.[5] Recently, a number of groups have expanded the
range of effective reductants and rhenium catalysts to include
the following combinations: H2/[MeReO3],[6] Na2SO3/[ZReO3,4],[7]
and secondary alcohols/[Re2(CO)10], [MeReO3], or [NH4ReO4].[8]
Mechanistic studies of DODH reactions that are driven by
phosphines with [(tris-pyrazolylborate)ReO3] catalysts[9] and
a recent computational study[10] have suggested the operation
of a catalytic cycle that involves a deoxygenation/condensation
Figure 1. ATR-IR spectra of ReOx-C, the carbon support, and solid NH4ReO4.
prepared ReOx-C catalyst and reference samples. NH4ReO4 ex-
hibits three vibrations at 3200, 1407, and 900 cmÀ1. The band
at 900 cmÀ1 is assigned to the ReÀO stretching of the ReO4
À
ion;[11] the bands at 3200 and 1407 cmÀ1 arise from antisym-
+
metric stretching and asymmetric bending of the NH4 ion, re-
[a] A. L. Denning, Dr. Z. Liu, Prof. Dr. F. C. Jentoft
Chemical, Biological and Materials Engineering
University of Oklahoma
spectively. In addition to characteristic bands of the activated
carbon support, ReOx-C shows an IR band at 900 cmÀ1, consis-
Norman, OK 73019 (USA)
Fax: (+1)4053255813
E-mail: fcjentoft@ou.edu
À
tent with the antisymmetric stretching of ReO4 ions. The
bands at 3200 and 1407 cmÀ1 are absent in the IR spectrum of
the ReOx-C sample, thus suggesting that, under the prepara-
tion conditions, the carbon support does not present suitable
[b] H. Dang, Prof. Dr. K. M. Nicholas
Department of Chemistry and Biochemistry
University of Oklahoma
+
adsorption sites for NH4 .
Norman, OK 73019 (USA)
Fax: (+1)4053256111
E-mail: knicholas@ou.edu
To confirm that the IR data are representative of all of the
rhenium in the sample, X-ray absorption near-edge structure
(XANES) spectroscopy was used. Normalized Re L3-edge XANES
spectra of fresh ReOx-C catalyst and NH4ReO4 as a reference
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300545.
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Table 1. Deoxydehydration of glycols catalyzed by ReOx-C.
Entry
R1
R2
T
[8C]
P
t
[h]
Olefin yield[a]
[%]
[MPa]
1
2
3
4
5
6
7
8
9[d]
10[e]
11[f]
12
13
14
Ph
C12H25
H
H
150
150
1.4
1.4
24
25
48
72
72
72
48
24
24
24
24
73
73
24
39
12
23
42
30
23
95[c]
36
23
20
10
43 (42)[g]
31 (30)[g]
56 (48)[h]
C12H25
C12H25
CO2Et
C12H25
C12H25
C12H25
C12H25
C12H25
C12H25
C12H25
H
H
175
175
150
175
175
175
175
150
150
175
1.4
0.7
1.4
1.4
1.4
1.4
1.4
1.4
1.4
1.4
CO2Et[b]
H
H
H
H
H
H
H
Figure 2. Re L3-edge XANES spectra of fresh ReOx-C catalyst and NH4ReO4.
[a] Yield determined by GC analysis with naphthalene as an internal stan-
dard. [b] (+)-Diethyl tartrate. [c] Yield determined by integration of the
1H NMR spectrum with DMSO as an internal standard. [d] Recovered cata-
lyst from run 8 was recharged with reactants. [e] Recovered catalyst from
run 9 was recharged with reactants. [f] Recovered catalyst from run 10
was recharged with reactants. [g] Cumulative yield after charging the fil-
trate with new reactants; yield in parentheses corresponds to the preced-
ing run with ReOx-C; room-temperature filtration. [h] Same as [g], but
with hot filtration.
(Figure 2) show very similar positions and shapes, thus imply-
ing that the rhenium valence and local environment in these
two materials are similar. Initial observations by high-resolution
electron microscopy indicate that the rhenium species are
highly dispersed, consistent with perrhenate ions as the pre-
dominant species.
The ReOx-C material was evaluated for its catalytic activity
with a representative set of glycols, as models of biomass-de-
rived carbohydrates and polyols, with H2 as the reductant
(Scheme 2).
Scheme 2. Deoxydehydration of Glycols Catalyzed by ReOx-C.
Scheme 3. Product distribution in preparative scale DODH reaction.
As summarized in Table 1, styrene glycol, 1,2-tetradecane-
diol, and (+)-diethyl tartrate were each converted into their
corresponding olefins in moderate-to-excellent yields. Little or
none (<2%) of the respective alkanes, which would arise from
over-reduction, were detected (at 1508C). A control reaction
under the same conditions with non-metalated activated
carbon and 1,2-tetradecanediol showed no conversion of the
glycol. As has been reported for homogeneous rhenium-cata-
lyzed DODH reactions,[5–9] styrene diol (Table 1, entry 1) was
more reactive than aliphatic glycols (Table 1, entries 2–6). Small
amounts of ethyl benzene, PhCH2CHO, PhCH2CH2OH, and di-
meric ethers were detected, presumably owing to competing
acid-catalyzed rearrangement, condensation, and hydrogenoly-
sis.[12] Notably, with the slower-reacting C14-glycol (Table 1, en-
tries 2–4), the terminal olefin was produced regioselectively
(>98%), with no apparent isomerization. To assess the mass
balance and to identify the non-olefinic products, a prepara-
tive-scale (2 mmol) reaction of the C14-glycol was performed
and the products were isolated by column chromatography
(Scheme 3).
85%. These latter products were likely formed through an
acid-catalyzed pathway.[11] Initial tests on the effects of the op-
erating parameters on the conversion rate showed significant
retardation at lower H2 pressures (Table 1, entry 6 versus
entry 5) and substantial acceleration at higher temperature
(Table 1, entry 2 versus entry 8).
The lifetime of the ReOx-C catalyst was evaluated by deter-
mining the yield of tetradecene in four consecutive runs by re-
cycling the recovered catalyst (about 90%) and recharging
with fresh glycol, solvent, and hydrogen (Table 1, entries 8–11).
A moderate loss in activity was detected over the four runs,
thus suggesting that some catalyst deactivation or leaching
into the solvent had occurred. Therefore, a key question is
whether the active catalyst species is homogeneous (through
the leaching of rhenium into the solvent) or heterogeneous. To
address this point, three post-reaction mixtures from the C14-
glycol were filtered to remove the solid catalyst and the fil-
trates were tested for catalytic activity with additional glycol
under the same conditions as in the preceding experiment
with solid ReOx-C (Table 1, entries 12–14). If the filtration was
performed at room temperature, no appreciable increase in
the yield of the olefin was detected (Table 1, entries 12 and
13). However, if the filtration was performed while the reaction
In addition to 1,2-tetradecene (57% yield), 2-tetradecanone
(13%) and a mixture of isomeric cyclic ethers and acetals
(10%) were identified with a total mass recovery of about
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mixture was hot, further reaction was observed and the yield
increased from 48 to 56% (Table 1, entry 14). Thus, at high
temperatures, some leaching occurs and the catalysis is partly
performed by soluble rhenium species. However, the re-depo-
sition of soluble Re species at room temperature allows the re-
use of the recovered catalyst for batch applications. To exclude
the theory that these reactions are entirely the result of homo-
geneous catalysis, the yields that were obtained with the ReOx-
C catalyst were compared with those from reference com-
pounds that were able to produce dissolved oxorhenium spe-
cies. NH4ReO4 catalyzes the DODH reaction of tetradecanediol,
but with lower yields than ReOx-C, likely as a result of its poor
solubility in benzene. Re2O7 dissolved and showed high initial
DODH rates, but quickly became deactivated. Overall, the
yields of tetradecene were much lower than with the hetero-
geneous catalyst (17–19% versus 36% in Table 1, entry 8). The
lower productivity with the oxorhenium reference compounds
Figure 3. Concentrations of the reactant and the product, as determined by
in situ ATR-IR spectroscopy, and the pressure during the DODH of diethyl
tartrate catalyzed by ReOx-C at 1508C.
support the notion that
a
stabilized, catalytically active
The change in total pressure, which can be largely ascribed
to H2 consumption under these conditions, follows the profile
of the tartrate consumption, as would be expected from the
reaction stoichiometry (Scheme 4). An induction period of 2 h
was found when the ReOx-C sample was pre-reduced for only
10 min prior to the addition of diethyl tartrate, whereas the in-
duction period was shorter when the catalyst was reduced for
a longer time. These results indicate that the catalyst first has
to be transformed into a reduced active state.
perrhenate species exists on the carbon support. Interestingly,
the solubility of both reference compounds increased in the
presence of diols, thus suggesting complexation of the rheni-
um by the diol.
The deoxydehydration of (+)-diethyl tartrate by ReOx-C re-
sulted in an efficient and highly selective conversion into the
trans olefin, diethyl fumarate, in excellent yield (>95%)
(Scheme 4), with no detectable reduction or hydrolysis of the
Finally, we also assessed the ability of ReOx-C to catalyze hy-
drogen-transfer DODH reactions of glycols. Heating a mixture
of the C14-glycol and diisopropyl carbinol with ReOx-C (about
10 mol%, 1508C, benzene) over a few days cleanly afforded
1,2-tetradecene (43% yield, 165 h, Scheme 5). With benzyl alco-
Scheme 4. The deoxydehydration of (+)-diethyl tartrate by ReOx-C.
carboxy groups. Diethyl fumarate is the expected product if
the catalytic reaction proceeds through stereoselective syn
elimination of the vicinal hydroxy groups, which can be realiz-
ed through the formation and concerted retrocyclization of
a Re-O,O-glycolate intermediate, as proposed for the homoge-
neous rhenium-catalyzed DODH reaction.[5–10] Some caution
must be applied to this result, because diethyl maleate (cis)
was partially converted into diethyl fumarate under catalytic
conditions (ReOx-C, 1.4 MPa H2, 1508C, 24 h).
Scheme 5. Yields of the olefin in the DODH reaction with various hydrogen-
transfer reagents.
To gain an initial insight into the reaction kinetics, the DODH
of diethyl tartrate was spectroscopically monitored in an auto-
clave with an integrated ATR-IR probe in the reactor wall. The
specific IR bands of the reactant (diethyl tartrate) and product
(diethyl fumarate) were used to calculate their respective con-
centrations (for details of the reactor and calibration proce-
dures, see the Supporting Information). No other products
except for diethyl fumarate were observed by in situ IR spec-
troscopy, consistent with the high selectivity that was ob-
served by GC and NMR spectroscopy. Figure 3 shows excellent
correlation between the rate of conversion of the tartrate and
the rate of formation of fumarate.
hol as the co-reactant under the same conditions, a faster reac-
tion ensued with 52% of the olefin detected after 70 h, along
with benzaldehyde as a co-product. The H-donor tetrahydro-
naphthalene, which is abundant in petroleum, was also effec-
tive under the same conditions in the DODH reaction catalyzed
by ReOx-C, thereby affording 40% of tetradecene (and naph-
thalene) after 161 h. In all cases, no alkane product was
detected.
Herein, we have reported the first polyol-into-olefin DODH
reactions catalyzed by supported ReOx, by employing both H2
and hydrogen-transfer reductants. It appears that DODH catal-
ysis is promoted by both soluble and surface-bound Re spe-
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cies. Efforts to expand the scope of the reaction, to improve
the activity, selectivity, and longevity of the catalyst, and to
identify the active catalytic species are underway.
by the DOE (DE-AC02-06CH11357), at MR-CAT beamline 10 ID
(GU-25815). We thank T. Shibata, T. Wu, and J. T. Miller for their
support. We also thank R. E. Jentoft and G. Chapman for provid-
ing technical and training assistance.
Experimental Section
Keywords: alkenes
·
chemoselectivity
·
heterogeneous
ReOx-C was synthesized according to a modified literature proce-
dure.[13] Activated carbon (granular, Darco, 20–40 mesh) was dried
at 1508C. A 1 mm solution of NH4ReO4 (Alfa Aesar, >99%) in water
was used as prepared or adjusted to pH 3 by adding HCl, which re-
sulted in a higher overall rhenium content. Then, the hot, dry
carbon was added and the resulting suspension was stirred for
5 h; in some of the preparations, H2 was bubbled through the
liquid, but this step was found not to be essential. The solid mate-
rial was allowed to settle overnight and the supernatant was re-
moved by using a cannula. The remaining damp solid was dried
under a flow of N2 at 1108C.
catalysis · regioselectivity · supported catalysts
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The rhenium content was determined by photometric analysis of
the recovered solution. Quantitative analysis of the characteristic
absorption band of perrhenate at a wavelength of 227 nm gave
the residual concentration and the difference from the initial con-
centration was used to calculate the amount of adsorbed material;
typical analyses gave 3–4 mass% Re. A “spot-check” on a ReOx-C
sample by ICP-MS (Galbraith Laboratories) was found to contain
4.2 mass% Re (4.2 mass% by photometric analysis).
In a typical reaction, the glycol (1.0 mmol) and ReOx-C (about
30 mmol) were combined with benzene (5 mL) in a glass-lined
stainless-steel reactor, which was pressurized with H2 up to a total
pressure of 0.7–1.4 MPa and then heated to 150–1758C for the
time period indicated (i.e., 1–3 days). Samples were withdrawn
from the reactor and analyzed by GC (after the addition of
1
0.5 mmol naphthalene as an internal standard), GCMS, and H NMR
spectroscopy.
ATR spectra of the solid samples were collected by using a PIKE ac-
cessory with a ZnSe crystal and a FTIR spectrometer. In situ ATR-IR
spectra were recorded on a Mettler-Toledo ReactIR iC10, with a K4
conduit diamond integrated into the wall of a custom-design auto-
clave (see the Supporting Information). The ReOx-C sample was
pretreated in benzene at 1508C in 1.4 MPa H2 prior to the addition
of diethyl tartrate.
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Acknowledgements
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nol. 2010, 44, 4716.
This work was, in part, supported by NSF EPSCoR award EPS
0814361 (F.C.J. and A.L.D.), NSF award 0923247 (instrumentation),
DOE EPSCOR grant DE-SC0004600 (Z.L.), and the U.S. Department
of Energy (K.M.N.). XAS data were collected at the APS, supported
Received: July 6, 2013
Published online on && &&, 0000
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Support group: The first heterogeneous
catalyst for the deoxydehydration
A. L. Denning, H. Dang, Z. Liu,
K. M. Nicholas,* F. C. Jentoft*
(DODH) of glycols into olefins is report-
ed. A carbon-supported perrhenate
material was found to catalyze the
reductive conversions of styrene diol,
tetradecane diol, and diethyl tartrate
into their respective olefins with high
chemo-, regio-, and stereoselectivity.
Effective reductants for this DODH reac-
tion include H2, alcohols, and tetralin.
&& – &&
Deoxydehydration of Glycols
Catalyzed by Carbon-Supported
Perrhenate
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