Electrochemical Coupling of Biomass-Derived Acids: New C8 Platforms for Renewable Polymers and Fuels

Article abstract of DOI:10.1002/cssc.201601271

Electrolysis of biomass-derived carbonyl compounds is an alternative to condensation chemistry for supplying products with chain length >C₆for biofuels and renewable materials production. Kolbe coupling of biomass-derived levulinic acid is used to obtain 2,7-octanedione, a new platform molecule only two low process-intensity steps removed from raw biomass. Hydrogenation to 2,7-octanediol provides a chiral secondary diol largely unknown to polymer chemistry, whereas intramolecular aldol condensation followed by hydrogenation yields branched cycloalkanes suitable for use as high-octane, cellulosic gasoline. Analogous electrolysis of an itaconic acid-derived methylsuccinic monoester yields a chiral 2,5-dimethyladipic acid diester, another underutilized monomer owing to lack of availability.

Full text of DOI:10.1002/cssc.201601271

Accepted Article
Title: 2,7-Octanedione and 2,5-Dimethyladipic Acid From the
Electrochemical Coupling of Biomass-derived Carboxylic Acids:
C8 Platforms for Renewable Polymers and Fuels
Authors: Linglin Wu, Mark Mascal, Thomas Farmer, Sacha Pérocheau
Arnaud, and Maria Angelica Wong Chang
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To be cited as: ChemSusChem 10.1002/cssc.201601271
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ChemSusChem
2,7-Octanedione and 2,5-Dimethyladipic Acid From the Electrochemical Coupling of Biomass-derived
Carboxylic Acids: C8 Platforms for Renewable Polymers and Fuels
Linglin Wu,[a] Mark Mascal,* [a] Thomas J. Farmer,[b] Sacha Pérocheau Arnaud[b] and Maria-Angelica Wong
Chang[a]
[a] Dr. L. Wu, Prof. M. Mascal, Ms. M.-A. Wong Chang
Department of Chemistry
University of California Davis
1 Shields Avenue
Davis, CA 95616 (USA)
E-mail: mjmascal@ucdavis.edu
[b] Dr. T. J. Farmer, Mr. S. Pérocheau Arnaud
Green Chemistry Centre of Excellence
Department of Chemistry
University of York
Heslington, York, YO10 5DD (UK)
Abstract: Electrolysis of biomass-derived carbonyl compounds is an alternative to condensation
chemistry for supplying products with chain length >C6 for biofuel and renewable material production.
Kolbe coupling of biomass-derived levulinic acid gives 2,7-octanedione, a new platform molecule only
two low process-intensity steps removed from raw biomass. Hydrogenation to 2,7-octanediol provides a
chiral secondary diol largely unknown to polymer chemistry, while intramolecular aldol condensation
followed by hydrogenation yields branched cycloalkanes suitable for use as high-octane, cellulosic
gasoline. Analogous electrolysis of an itaconic acid-derived methylsuccinic monoester gives chiral 2,5-
dimethyladipic acid, another underutilized monomer due to lack of availability.
Introduction
Biofuels and renewable polymers play an undisputed role in the green technology movement, and their
production from biomass-derived carbohydrates has been investigated by multiple research groups. In
the former case, since common monosaccharides are C6 or less, a C–C coupling step is essential to
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eventually achieve the hydrocarbon volatility range required for automotive fuels. In the case of
polymers, virtually any platform molecule that can be rendered bifunctional may potentially serve as a
monomer, and C–C coupling reactions can also be of value here, likewise offering products not limited
to six carbons.
In the majority of cases, the approach to accessing suitable biofuel precursors from biomass-derived
carbonyl compounds involves aldol or related condensation reactions, which are catalyzed,
thermodynamically driven processes resulting in C–C bond formation.[1] We however became attracted
to the proposition of carrying out electrochemical coupling of such molecules to accomplish the
necessary chain elongation for the following reasons: 1) the electrochemical dimerization of sugar
derivatives is an inexpensive, non process-intensive method where the driving force for the reaction
essentially comes from the power grid, 2) novel structures may be accessed which are not available via
condensation chemistry, and 3) coupled products can be obtained in a more advanced state of
reduction, thus avoiding extensive hydrodeoxygenation. Comparison of a condensation reaction versus
the Kolbe electrolysis serves as an illustration (Scheme 1). Using the same substituted acetic acid as a
hypothetical model, Claisen-type condensation/decarboxylation gives a ketone, whereas the electrolysis
gives a substituted ethane. In both cases, oxygen is carried away in the form of CO2, although in the
latter H2 is co-generated, reminiscent of the production of hydrogen and CO2 from hydrocarbons by a
combination of steam reforming and the water-gas shift reaction.
Herein, we will demonstrate that electrolysis of biomass-derived carbonyl compounds has disruptive
potential to deliver >C6 biorefinery outputs of value both in materials and fuels markets.
Scheme 1. Comparison of products derived by a condensation reaction versus electrochemical coupling.
Claisen chemistry, while feasible with carboxylic acids,[2] is routinely carried out with the corresponding
esters, in which case the condensate is an alcohol instead of water.
2
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Results and Discussion
Looking to the literature, there has been little activity around the direct coupling of sugars, although
it was interesting to find that glucose itself has been made to undergo a cathodic process whereby it
was transformed into a dodecitol, presumably via its aldehyde form.[3] The electrolysis however of sugar
derivatives presents a viable alternative, and we were drawn to reports of the dimerization of levulinic
acid (LA) 1 to 2,7-octanedione 2 (Scheme 2).[4-6] The recent upsurge of interest in LA 1 as a renewable,
carbohydrate-derived platform molecule, and the continuing development of technologies to produce it
on an industrial scale,[7] advance dione 2 as a potential "second-generation" platform only two steps
removed from biomass. The electrolysis reaction is straightforward, providing 65% yield of 2 at 90%
conversion using platinum plate electrodes in an undivided cell under constant current conditions (see
Supporting Information for details).
Scheme 2. Cellulose to 2,7-octanedione via levulinic acid.
The only substantive account of the use of 2 in materials applications was published by Joshi and
Limaye, who in the 1980s reported the conversion of 2 into 2,7-octanediamine via reduction of the
corresponding dioxime and subsequent production of a terephthalate polymer.[8] Another
straightforward approach to monomer synthesis would be to simply reduce 2 to corresponding diol 3.
Due to the (historically) limited access to 2, compound 3 is largely unknown to polymer chemistry, the
only reference to our knowledge being its use as one of a series of diols to test the concept of iterative
tandem catalysis by polymerization with adipic esters.[9] In that case, 3 was prepared via the
corresponding ,-diene. It has also been previously made from 2 using Meerwein-Pondorff-Verley
reduction.[10] However, we opted for more industrially relevant hydrogenation, which proceeded
smoothly and in high (94%) yield (Scheme 3).
Scheme 3. Preparation of 2,7-octanediol 3 and its polyesters.
3
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While a range of bio-derived diols have been investigated for polyester synthesis, both via chemo-
and enzyme-catalyzed reactions, most are primary diols, typically 1,3-propanediol, 1,4-butanediol and
1,6-hexanediol.[11] Polymerization of secondary alcohols and high molecular weight monomers is known
to be more challenging as a result of steric issues and high boiling points, respectively. In the standard
esterification/transesterification procedure for polyester synthesis, the diol is generally used in excess
relative to the diacid or diester component and high temperatures are applied to remove the excess diol
and drive the polymer to high chain lengths. Attempts have been made to circumvent both the reactivity
and volatility issues by using diacid chlorides in a 1:1 stoichiometric ratio with the diol.[12] In the first
instance we applied this approach to reaction of terephthaloyl chloride with diol 3 to obtain a 63% yield
of poly(2,7-octanediol)terephthalate 4, which was found to have a good chain length (Mn >8500 Da) and
low polydispersity (Pdi <1.5). Another motivation for using diacid chlorides was our facile, two-step
preparation of 2,5-furandicarbonyl chloride (FDCC) from 5-(chloromethyl)furfural (CMF), which itself is
one step removed from raw biomass.[13] Since levulinic acid 1, the precursor to 3 (via 2) is also a single
step from CMF,[14] this provides us an opportunity to showcase the synthesis of a novel polyester with
both monomers ultimately derived from a single platform molecule. The resultant poly(2,7-octanediol)-
2,5-furanoate polymer 5 from the reaction between FDCC and diol 3 was also isolated in good yield
(54%) and with a reasonable chain length and low Pdi. The data for these polymers are presented in
Table 1.
Table 1. Co-polyesters of diol 3.
c
Polymer
Ar
%recovery
63%
Mn (Da)a
8531
Mw (Da) b
12220
Pdi
4
1.43
5
54%
3978
5079
1.28
aNumber average molecular weight. bWeight average molecular weight. cPolydispersity index.
Thermogravimetric analysis under an N2 atmosphere was used to determine the stability of 4 and 5
(Table 2), which showed that little mass loss occurs in either prior to 290 °C. The terephthalate polyester
4 was shown to have a slightly higher thermal stability than furandioate 5, with both its TD10 and TD50
being roughly 20 °C higher than the furan equivalent. Likewise the glass transition temperature (Tg) of 4
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was found to be higher than of 5. In comparison to literature values for analogous aromatic-aliphatic
polyesters (Table S3 in the Supporting Information), it can be seen that both 4 and 5 conform to the
previously observed trend whereby extending the length of the diol reduces the Tg while diols of
secondary alcohols show increased Tg relative to their primary alcohol regioisomers. This highlights the
potential value of 3 as a new bio-based monomer that allows further control of characteristics that have
a direct impact on the processability and applications of the final product. For example, the near room
temperature Tg of 5 may point to potential thermoresponsive polymer applications where changes from
the glassy to rubbery state of a plastic between ambient temperature and body temperature is desired.
Table 2. Thermal analysis of polymers 4 and 5.
d
Polymer
TD10 (°C)a
312.4
TD50 (°C)b
330.5
Tg (°C)c
62.6
Tm
4
5
n.d.
n.d.
289.5
301.6
26.0
aTemperature at 10% mass loss. bTemperature at 50% mass loss. cTg = glass transition temperature as
determined by differential scanning calorimetry (DSC). dTm = melt point as determined by DSC. n.d. =
none detected.
To date, the only application of 2 directed towards biofuels involved complete reduction to n-
octane,[15,16] a compound of no use in gasoline (RON = -19) and too volatile for diesel fuel.[17] We
recognized an opportunity to use dione 2 to much better advantage in the production of fuels by
employing intramolecular condensation chemistry, leading ultimately to branched, cyclic alkanes. Thus,
2 could be made to undergo aldol condensation by treatment with either acid or base. The ,-
unsaturated ketone product mixture was however prone to side reactions under these conditions which
made it difficult to achieve good selectivity, a result also noted by Bouillon et al.[18] We therefore
performed the aldol reaction in tandem with hydrogenation of the double bond to provide mainly
methyl 2-methylcyclopentyl ketone 6 alongside small amounts of the alternative cyclization product 3-
methylcycloheptanone 7 (Scheme 4). This product mixture could be isolated and characterized, but the
best yield of hydrocarbon was obtained by introducing additional Pd/C and the hydrodeoxygenation
catalyst Al(OTf)3[19] at this point, then increasing the reaction temperature and H2 pressure to 220 °C and
50 atm, respectively. Using this approach, the total yield of cycloalkanes 8-11 starting from 2 was 85%,
with the relative ratios as determined by GC-MS shown. The observation of dimethylcyclohexanes 9 and
10 is the result of carbocation rearrangements, and since commercial gasoline is a mixture of hundreds
of hydrocarbons,[20] the lack of selectivity to 8 presents no problems.
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Scheme 4. Production of cycloalkane biofuels from 2,7-octanedione.
Since we propose the conversion of 2 to 8-11 as a new approach to cellulosic gasoline, we
undertook to determine the fuel properties of these products. Existing biomass to biofuel processes
generally target linear hydrocarbons appropriate to diesel or jet fuel applications.[1] Efficient, renewable
methods that lead to the branched and cycloalkanes found in gasoline therefore fill a commercial
void.[21] 8-11 are all previously described compounds with boiling points between 118-134 °C, thus well
within the volatility range of motor gasoline (ca. 40-200 °C).[20] The key measure of fuel performance in
spark ignition engines is the antiknock index, commonly referred to as octane number. For individual
molecules, a value for the research octane number (RON) will either have been measured or can be
calculated using various algorithms. The experimental RON value for 9 is 69 and for 10 is 81.[22]
modeled value for 8 = 93 has been reported.[23] As for the minor component 11, the RON of
A
cycloheptane itself is 38.8. Methyl branching generally increases octane numbers, and the index value
for this molecule has been calculated at RON = 68 using the model of Dahmen and Marquardt.[24] An
estimated RON of the blend of 8-11 in the proportions observed in the hydrogenation reaction would be
86.8. In combination with 10% ethanol as an oxygenate, the calculated RON is 89.
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Finally, our success in processing levulinic acid into useful biofuel and polymer components
prompted us to consider the electrochemical dimerization of other bio-derived acids. Itaconic acid 12 is
another up and coming biorefinery platform molecule,[25] and its applications to heterocycle and
polymer chemistry have recently been reviewed.[26,27] Like levulinic acid, it appears on the NREL list of
the top 12 value added chemicals from biomass.[28] Although the electrolysis of itaconic acid has been
investigated,[29] no Kolbe coupling of 12 or its monoesters has been reported to date. However, Hancock
and Linstead reported that a methylsuccinic acid monoester 13, derived by the methanolysis of
methylsuccinic anhydride, underwent electrolytic dimerization to 2,5-dimethyladipic ester 14. In that
work, a poorly defined mixture of half-esters was used and the reported yield of 14 was 30%. We set out
to improve access to 14 by optimization of the electrochemical reaction. Thus, ester 13 was prepared
from itaconic acid 12 using a published method, wherein the diester of 12 was selectively hydrolyzed
and the double bond asymmetrically hydrogenated.[30] While a stereodefined form of 13 presents an
attractive option for future work, for the purposes of this study, the racemate was used. Subjecting 13
to the same conditions as in the conversion of 1 to 2, i.e. constant current electrolysis at a current
density of 180 mA cm-2 across platinum electrodes in an undivided cell, gave diester 14 in 60% yield at
85% conversion.
Scheme 5. Production of dimethyl 2,5-dimethyladipate by electrolysis of itaconate-derived succinic acid
monoester 13.
Despite being a simple analogue of one of the highest volume monomers used in industry, limited
access has meant that very little in the way of polymer chemistry has been described for 14, as was also
the case for 3. The only systematic study of materials derived from 14 involved the production of
stereoisomeric polyamides from hexamethylene diamine and meso-, d-, and dl-14, all of which showed
considerably less crystallinity than the parent polymer.[31] The development of new applications for 14
would be stimulated by improved availability. Of particular interest would be a study of the properties of
polyesters of 3 with 14, and we will report on such materials in a separate paper.
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Conclusions
The purpose of this work is to showcase the opportunities for accessing novel platform molecules via
the electrochemical processing of primary biomass derivatives. The diversity of >C6 structures attainable
using this approach points to future materials and fuels markets comprising a range of novel products.
Here, we have presented levulinic acid 1 as a precursor to branched C8 monomers and cycloalkane
components that embody a high-octane, cellulosic gasoline, both via 2,7-octanedione 2. The monomer
2,7-octanediol 3 was used to prepare novel polyesters with terephthalic and 2,5-furandicarboxylic acids.
An analogous renewable monomer synthesis was demonstrated in 2,5-dimethyladipic diester 14. Novel
access to 3 and 14 by means of electrochemical C-C coupling chemistry opens up new opportunities for
products that were formerly both limited in their availability and produced from unsustainable feeds.
Experimental Section
Electrolysis of levulinic acid
Levulinic acid (464 mg, 4.00 mmol) was subjected to constant current electrolysis (178 mA/cm2) on
platinum plate electrodes (1.5 x 1.5 cm2; distance between electrodes = 12 mm) in 0.075 M methanolic
KOH (10 mL) using an undivided cell with magnetic stirring at 22 ˚C. The reaction was terminated after
the consumption of 1.0 F/mol of charge (16 min). The mixture was acidified to pH 3 with 1M HCl and the
volatiles were evaporated under vacuum. The conversion (90%) and yield of 2,7-octanedione 2 (65%)
were determined by NMR using 1,4-dioxane as an internal standard. To the residue was added 1M
NaOH (50 mL) and the mixture was extracted with dichloromethane (50 ml x 3). The combined organic
extract was washed with brine and dried over sodium sulfate. The solution was filtered and
concentrated under vacuum, and the residue was passed through a short plug of silica using ethyl
acetate as eluent. The solvent was evaporated to give 2,7-octanedione 2 as a pale yellow solid (178 mg,
63%). 1H NMR (600 MHz, CDCl3) δ 2.44-2.42 (m, 4H), 2.12 (s, 6H), 1.55-1.53 (m, 4H); 13C NMR (150 MHz,
CDCl3) δ 208.63, 43.38, 29.90, 23.14.
Hydrogenation of 2,7-octanedione
2,7-Octanedione (994 mg, 6.99 mmol), 5% palladium on carbon (280 mg), potassium hydroxide (140 mg,
2.1 mmol) and water (35 mL) were introduced into a Parr hydrogenator. The vessel was sealed, flushed
three times with hydrogen and pressurized to 12 bar H2. The mixture was heated at 80 ˚C with stirring
for 140 min, then allowed to cool to rt. The pressure was released and the reaction was filtered through
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a short pad of Celite. The filtrate was concentrated under vacuum and the residue was filtered through a
short plug of silica gel using acetone as eluent. Evaporation of the solvent gave 2,7-octanediol 3 as a
colorless oil (962 mg, 94%). 1H NMR (400 MHz, D2O) δ 3.78-3.71 (m, 2H), 1.39-1.26 (m, 8H), 1.08 (d, J =
6.3 Hz, 3H); 13C NMR (100 MHz, D2O) δ 67.87, 37.78, 24.84, 21.82.
Tandem intramolecular aldol condensation and catalytic hydrogenation of 2,7-octanedione
2,7-Octanedione (284 mg, 2.00 mmol), 10% palladium on carbon (42 mg), p-toluenesulfonic acid
monohydrate (38 mg) and hexanes (10 ml) were introduced into a Parr hydrogenator. The vessel was
sealed, flushed three times with hydrogen and pressurized to 5 bar H2. The reaction was heated at 80 ˚C
with stirring for 3.5 h and allowed to cool to rt followed by further cooling to 10 ˚C in an ice-water bath.
The reaction mixture was filtered through silica gel and further eluted with an ethyl acetate/hexane
(1:5) solvent mixture. Evaporation of the solvent gave a mixture of isomeric ketones 6 (major) and 7
(minor) (227 mg, 90%). The above reaction was repeated but instead of isolating 6 and 7, the reactor
was opened and Al(OTf)3 (95 mg), additional 10% palladium on carbon (168 mg), and hexanes (30 ml)
were added. The vessel was sealed, flushed three times with hydrogen and pressurized to 50 bar H2. The
reaction was heated to 220 ˚C, which increased the internal pressure to ca. 95 bar. After 24 h at this
temperature, the reactor was allowed to cool to rt and then further to 0 ˚C in an ice-water bath. The
interior walls of the vessel were washed down with acetone. The catalyst was removed by filtration
through Celite and the yields of 8-11 (85% total) were determined by GC-MS analysis with a dodecane
internal standard and data matching against the National Institute of Standards and Technology (NIST)
mass spectral library.
1-Ethyl-2-methylcyclopentane 8. MS (EI): m/z (% of max intensity) 41.2 (58), 55.1 (100), 70.2 (55), 83.2
(95), 97.2 (11), 112.1 (24). Retention time in GC-MS: 3.42 min (trans) and 3.85 min (cis). Trans/cis ratio is
2.1:1.
1,3-Dimethylcyclohexane 9. MS (EI): m/z (% of max intensity) 41.2 (21), 55.2 (70), 69.2 (19), 97.2 (100),
112.1 (31). Retention time in GC-MS: 3.26 min (trans) and 3.62 min (cis). Trans/cis ratio is 1.8:1.
1,2-Dimethylcyclohexane 10. MS (EI): m/z (% of max intensity) 41.1 (40), 55.2 (91), 70.2 (27), 83.1 (20),
97.2(100), 112.2 (36). Retention time in GC-MS: 3.54 min (trans) and 3.97 min (cis). Trans/cis ratio is
2.3:1.
Methylcycloheptane 11. MS (EI): m/z (% of max intensity) 41.1 (71), 55.1 (98), 69.1 (35), 83.1 (40),
97.2(100), 112.1 (20). Retention time in GC-MS: 4.37 min.
9
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Electrolysis of 2-methylsuccinic acid 1-methyl ester
2-Methylsuccinic acid 1-methyl ester 13 (1.17 g, 8.01 mmol) was subjected to constant current
electrolysis (178 mA/cm2) on platinum plate electrodes (1.5 x 1.5 cm2; distance between electrodes = 12
mm) in 0.10 M methanolic KOH (20 mL) using an undivided cell with magnetic stirring at 0 ˚C. The
reaction was terminated after the consumption of 2.0 F/mol of charge (64 min). A small sample of the
reaction was acidified to pH=3 with 1M HCl and evaporated under vacuum. The conversion was
determined by NMR (85%) using 1,4-dioxane as an internal standard. The reaction mixture was
evaporated under vacuum and to the residue was added 0.1M NaOH (70mL). The solution was extracted
with dichloromethane and the combined organic extract was washed with saturated brine and dried
over sodium sulfate. The solution was filtered and the solvent was evaporated to give dimethyl 2,5-
dimethyladipate 14 as a colorless oil (489 mg, 60%). 1H NMR (400 MHz, CDCl3) δ 3.64 (s, 6H), 2.43-2.37
(m, 2H), 1.65-1.56 (m, 2H), 1.44-1.32 (m, 2H), 1.12 (d, J = 7.0 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ
176.81, 176.75, 51.47, 39.37, 39.20, 31.32, 31.08, 17.06, 16.89.
Experimental details for the preparation of polyesters 4 and 5 are provided in the Supporting
Information.
Acknowledgements
MM acknowledges support from NSF-CBET grant 1335646 and Dr. Andrew Sutton at Los Alamos
National Laboratory for helpful discussions. TJF and SPA would like to thank the Engineering and Physical
Sciences Research Council (EPSRC) UK for funding their involvement in this research through the grant
EP/L017393/1.
Access Statement
All data used in the preparation of this manuscript for the sections funded by the EPSRC grant
EP/L017393/1 is contained within this document, the electronic supplementary information, or available
from DOI: 10.15124/93ff2cd7-9408-4c34-aac6-3baa4f50abff
Keywords: Biomass Conversion • Electrochemistry • Itaconic Acid • Kolbe Coupling • Levulinic Acid
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References
[1] L. Wu, T. Moteki, A. A. Gokhale, D. W. Flaherty, F. D. Toste, Chem 2016, 1, 32-58.
[2] For an example of a metal-oxide catalyzed version of this reaction, see: L. M. Orozco, M. Renz, A.
Corma, ChemSusChem 2016, 9, 2430-2442.
[3] M. L. Wolfrom, W. W. Binkley, C. C. Spencer, B. W. Lew, J. Am. Chem. Soc. 1951, 73, 3357-3358.
[4] H. Hofer, Berichte 1900, 33, 650-657.
[5] S. Shimizu, Nippon Nogei Kagaku Kaishi 1950, 23, 288-294.
[6] I. Cabasso, M. Li, Y. Yuan, RSC Advances 2012, 2, 9998–10006.
[7] The Biofine Process-Production of Levulinic Acid, Furfural, and Formic Acid from Lignocellulosic
Feedstocks: D. J. Hayes, S. W. Fitzpatrick, M. H. B. Hayes, J. R. H. Ross, in Biorefineries-Industrial
Processes and Products: Status Quo and Future Directions, Vol. 1 (Eds.: B. Kamm, P. R. Gruber, M.
Kamm), Wiley-VCH, Weinheim, 2006, pp. 144–160; see also: B. Girisuta, L. P. B. M. Janssen, H. J. Heeres,
Ind. Eng. Chem. Res. 2007, 46, 1696.
[8] U. R. Joshi, P. A. Limaye, Biovigyanam 1985, 11, 101-103.
[9] B. A. C. van As, J. van Buijtenen, T. Mes, A. R. A. Palmans, E. W. Meijer, Chem. Eur. J. 2007, 13, 8325-
8332.
[10] U. R. Joshi, P. A. Limaye, Ind. J. Chem. 1986, 25B, 1176-1178.
[11] C. Vilela, A. F. Sousa, A. C. Fonseca, A. C. Serra, J. F. J. Coelho, C. S. R. Freire, A. J. D. Silvestre, Polym.
Chem., 2014, 5, 3119-3141.
[12] M. Gomes, A. Gandini, A. J. D. Silvestre, B. Reis, J. Polym. Sci., Part A: Polym. Chem., 2011, 49, 3759-
3768.
[13] S. Dutta, L. Wu, M. Mascal, Green Chem. 2015, 17, 3737-3739.
[14] M. Mascal, E. B. Nikitin, Green Chem. 2010, 12, 370-373.
[15] P. Nilges, T. R. dos Santos, F. Harnisch, U. Schröder, Energy Environ. Sci. 2012, 5, 5231-5235.
11
This article is protected by copyright. All rights reserved.

10.1002/cssc.201601271
ChemSusChem
[16] T. R. dos Santos, P. Nilges, W. Sauter, F. Harnisch, U. Schroder, RSC Adv. 2015, 5, 26634-26643.
[17] Diesel Fuels Technical Review, Chevron Corporation 2007, www.chevron.com/-
/media/chevron/operations/documents/diesel-fuel-tech-review.pdf
[18] J.-P. Bouillon, C. Portella, J. Bouquant, S. Humbel, J. Org. Chem. 2000, 65, 5823-5830.
[19] H.-J. Song, J. Deng, M.-S. Cui, X.-L. Li, X.-X. Liu, R. Zhu, W.-P. Wu, Y. Fu, ChemSusChem 2015, 8, 4250-
4255.
[20] Motor Gasolines Technical Review, Chevron Corporation 2009, www.chevron.com/-
/media/chevron/operations/documents/motor-gas-tech-review.pdf
[21] M. Mascal, S. Dutta, I. Gandarias, Angew. Chem. Int. Ed. 2014, 53, 1854-1857.
[22] Knocking characteristics of pure hydrocarbons (Knocking Characteristics of Pure Hydrocarbons,
STP225-EB, ASTM International, West Conshohocken, PA, 1958, http://dx.doi.org/10.1520/STP225-EB.
[23] A. L. Lapidus, E. A. Smolenskii, V. M. Bavykin, T. N. Myshenkova, and L. T. Kondrat'ev, Petroleum
Chem. 2008, 48, 277-286.
[24] M. Dahmen, W. Marquardt, Energy Fuels 2015, 29, 5781−5801.
[25] M. Okabe, D. Lies, S. Kanamasa, E. Y. Park, Enoch, Appl. Microbiol. Biotech. 2009, 84, 597-606.
[26] A. M. Medway, J. Sperry, Jonathan, Green Chem. 2014, 16, 2084-2101.
[27] T. Robert, S. Friebel, Green Chem. 2016, 18, 2922-2934.
[28] Top Value Added Chemicals From Biomass. Volume I: Results of Screening for Potential Candidates
from Sugars and Synthesis Gas, Technical report identifier PNNL-14804, Pacific Northwest National
Laboratory and the National Renewable Energy Laboratory, 2004 (http://www.nrel.gov/docs/fy04osti/
35523.pdf).
[29] G. Aarland, J. Prakt. Chem. 1873, 6, 256-272.
[30] K. Achiwa, J. Organomet.Chem. 1981, 218, 249-260.
[31] J. H. Brewster, J. Am. Chem. Soc. 1951, 73, 366-70.
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