Prediction of the Thermodynamic Properties of Key Products and

Combustion Pathways of Biofuel Model Compounds. Carrigan J. Hayes , Donald R. Burgess , Jeffrey A. Manion. 2015,103-187 ...
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Prediction of the Thermodynamic Properties of Key Products and Intermediates from Biomass. II Monica Vasiliu, Andrew J. Jones, Kurt Guynn, and David A. Dixon* Chemistry Department, The University of Alabama, Shelby Hall, Box 870336, Tuscaloosa, Alabama 35487-0336, United States S Supporting Information *

ABSTRACT: The thermodynamic properties of a wide range of chemical compounds relevant to the conversion of biomass-derived oxygenated feedstocks into fuels or chemical feedstocks were predicted using the correlated G3MP2 computational chemistry approach. The energetics of a range of reactions starting from 2,5-furandicarboxylic acid, 3-hydroxypropionic acid, aspartic acid, glucaric acid, glutamic acid, itaconic acid, malic acid, lactic acid, 3-hydroxybutyrolactone, furfural, and xylitol/arabinitol were calculated. The calculated G3MP2 gas phase heats of formation are mostly within ±2 kcal/mol of the available experimental values. Heats of formation of the liquid were obtained from calculations of the boiling point combined with the rule of Pictet and Trouton using modified values for ΔSvap. Reaction energies in the aqueous phase at 298 K were estimated from self-consistent reaction field calculations of the solvation energy using the COSMO parametrization. Most of the reactions are exothermic, and the reaction products are stabilized by aqueous solvation. Endothermic processes include dehydrogenation, deamination, and dehydration reactions.



INTRODUCTION Biomass is a renewable source of fixed carbon, and the development of this resource is necessary as a substitute for fossil resources such as coal, natural gas, or petroleum, as these resources eventually will become unsustainable as they are consumed. A second issue with fossil fuels is that they are transformed into energy through combustion reactions with CO2 gas emissions into the atmosphere, which can impact climate change.1 Biofuels derived from biomass are a promising alternative energy source due to the potential for such fuels to be carbon neutral and the fact that liquid hydrocarbon fuels can be generated, which requires no major changes to the existing fuel distribution infrastructure.2−5 The environmental, economic, and energetic benefits of biofuels (ethanol and biodiesel) remain a challenge as a fuel replacement technology as they exhibit inefficiencies that are hard to overcome.6−8 Biomass, under catalytic, thermal, and/or biochemical conversion, can be broken down into different components that can be used in conventional combustion engines.9−14 Glucose, written as the hydrate of carbon ((C(H2O))6), is a key component of biomass or its derivatives. There is significant interest in the development of low cost processing methods to convert glucose to different chemical compounds that can serve as fuels or as feedstocks for the chemical industry. A challenge is that there are many potential biobased targets, and the optimization of which one to choose and how to produce it can be difficult given a lack of data. Computational chemistry using high level molecular orbital theory methods can be used to predict accurate thermodynamic properties for these types of chemicals compounds which are needed for the design of new, clean, and more efficient synthetic routes of such biomass derivatives. © 2012 American Chemical Society

A U.S. Department of Energy report listed a series of target structures that can be produced from biorefinery carbohydrates as important biomass building blocks.11,12 Previously, we reported the thermodynamic properties of seven of these target glucose-derived chemical compounds.15 In the current study, we provide thermodynamic data for the remaining compounds: 2,5-furandicarboxylic acid (FDCA), 3-hydroxypropionic acid (3HPA), aspartic acid, glucaric acid, glutamic acid, itaconic acid, malic acid, lactic acid, 3-hydroxybutyrolactone (3-HBL), furfural and xylitol/arabinitol, many of which can be produced in biofermentation processes. It will probably be necessary to combine biological and chemical processes and develop novel enzymatic and heterogeneous catalysts to achieve the cost-effective production of a large number of building blocks and intermediates from biomass.16−20 FDCA is suggested as an important renewable building block because it can be a green replacement for terephthalic acid, a component of polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT),21 leading to completely biomass-derived polyester materials. A new class of nylons can be prepared as a result of the reaction of FDCA with amines or from the synthesis of derived FDCA amines.11 In addition, the previously studied succinic acid15 can be prepared from FDCA. Acrylic acid and acrylate esters can be produced from 3-HPA if appropriate fermentation processes can be developed on an industrial scale.22,23 Aspartic acid, mainly used to produce Received: July 3, 2012 Revised: August 26, 2012 Published: August 28, 2012 20738

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approach described below. These calculations were done with the Gaussian 09 program system.37 The heats of formation of the pure liquid phase were estimated using the fact that the free energy is zero at a phase change so that ΔHvap = TBPΔSvap, where ΔHvap is the enthalpy of vaporization, TBP is the boiling point in degrees Kelvin (K), and ΔSvap is the entropy of vaporization. As noted by Pictet and Trouton,38 ΔSvap is approximately constant for many compounds, and thus, for a given boiling point value, ΔHvap can be estimated. The heat of formation of the pure liquid phase is obtained as the difference between the gas heat of formation and the enthalpy of vaporization: ΔHliq = ΔHgas − ΔHvap. The COSMO-RS39−41 approach as implemented in the ADF42 program was used to estimate TBP from DFT results at the B88P86/TZ2P level.43 For small molecules, a value of ΔSvap = 0.022 kcal/(mol K) is appropriate, but we have shown44 for larger molecules that a value of ΔSvap = 0.025 kcal/ (mol K) provides better agreement with experiment. However, the presence of substantial intermolecular hydrogen bonding in the liquid gives values of ΔSvap that are substantially higher than 0.025 kcal/(mol K).15 Thus, to predict the heats of formation of compounds, we used the previous approach, and we modified ΔSvap for different classes of compounds: ΔSvap = 0.031 kcal/(mol K) for acids, 0.035 kcal/(mol K) for dialcohols, and 0.040 kcal/(mol K) for higher polyalcohols based on our glycerin result.15 From the gas phase geometries, the solvation free energies in water at 298 K were calculated using the self-consistent reaction field approach45 with the COSMO parameters40,46 as implemented in the Gaussian 0347 and ADF.42 For the COSMO (B3LYP/DZVP2) calculations in Gaussian 03, the radii developed by Klamt and co-workers were used to define the cavity.46 For the COSMO calculations at the B88P86/TZ2P level43 in ADF, the default MM3 radii from Allinger and coworkers48 were used to define the cavity. The aqueous Gibbs free energy (free energy in aqueous solution) (ΔGaq) was calculated from eq 1:

aspartame, a synthetic sweetener, can be used as the precursor in the synthesis of new biodegradable polymers such as polyaspartic acid and polyaspartanes, which have applications as superabsorbent polymers, detergents, water treatment systems, and corrosion inhibitors.11 Another N-containing chemical, glutamic acid, has the potential to be used to build five-carbon polymeric structures as polyesters and polyamides from biomass.11 Glucaric acid and its esters have been proposed in the synthesis of a new class of nylons and other new polymer materials as detergent surfactants.11 The C5 building block, itaconic acid, as well the C4 building block diacids, succinic acid, malic acid, and fumaric acid, show a significant market opportunity for the development of biobased products if the cost of fermentation can be reduced.11 Lactic acid is mainly used to synthesize polylactic acid via direct polymerization or more effectively through a lactide in the presence of a catalyst.24,25 A polylactic acid polymer has been developed that shows properties similar to or even better than those of polystyrene. This polymer could be a substitute for PET for the storage resistance of fatty foods and dairy products, as it has good heat stability and barrier properties for flavors and aromas.26 Due to these promising properties, polylactic acid was intensively studied by Cargill-Dow, and an extensive life cycle analysis has been reported.27 Lactate esters show promising interest as “green” solvents.28 Through electrospinning techniques, lactic acid is used in preparing novel nanostructural materials for neutral tissue engineering,29 and also can be used in making biodegradable fibers for apparel, furniture, and biomedical materials such as dissolving sutures.30 3-HBL, currently used in pharmaceutical syntheses, could also be a starting material for the synthesis of new polymers.11 Furfural, similar to hydroxymethylfurfural (HMF), is a potential platform chemical in a biorefinery.12 Xylitol and arabinitol are hydrogenated products of xylose and arabinose, respectively. The C5 sugars are possible building blocks for commodity chemicals. Xylitol is a non-nutritive sweetener with a low current commercial production, and, for arabinitol, there is no current commercial production.11 The conversion of biomass to biofuels and useful chemical feedstocks involves various types of reaction types including hydrolysis, dehydration, reforming, C−C or C−O hydrogenolysis, isomerization, selective oxidation, and hydrogenation/ dehydrogenation. As the conversion processes may take place in the gas phase or in solution, we calculated the heats of formation for the pure gas and liquid phases. We also estimated the reaction energies in gas, liquid, and aqueous phases.

ΔGaq = ΔGgas + ΔΔGsolv

(1)

where ΔGgas is the gas phase free energy and ΔΔGsolv is the aqueous solvation free energy. A dielectric constant of 78.39 corresponding to that of bulk water was used in the COSMO calculations. The solvation energy is reported as the electrostatic energy (polarized solute − solvent). The calculations were performed on a Xeon-based Dell Linux cluster at the University of Alabama, and a local AMD Opteronbased and Intel Xeon-based Linux cluster from Penguin Computing.



COMPUTATIONAL METHODS The geometries were optimized using density functional theory (DFT);31 the DFT calculations were done with the hybrid B3LYP exchange-correlation functional32,33 and the DZVP2 basis set.34 Vibrational frequencies were predicted to ensure that the optimized structures were minima. A number of conformers of each species were sampled, and the optimized B3LYP/ DZVP2 geometries of the lowest energy conformer were then used as starting points for G3MP235 to predict the heats of formation (ΔHgas) in the gas phase. The G3MP2 method was chosen as it represents a good compromise between cost and accuracy. Although the use of a single conformer can lead to small errors in the calculated energetics,36 the errors due to conformational changes are probably smaller than errors in the energy calculations, especially for the energies in solution using the



RESULTS AND DISCUSSION

The computational studies were performed for the reaction schemes shown in Figures 1−11. The optimized Cartesian coordinates for all of the compounds reported in this work together with the appropriate total energies in a.u. are given in the Supporting Information. For each reaction scheme, the computational thermodynamic predictions are divided into two parts: (1) the gas and liquid heats of formation and (2) the reaction energies and solvation effects. Heats of Formation: Benchmarks. The heats of formation of all of the compounds are given in Table 1 at the G3MP2 level of theory for the gas phase values and in the liquid phase using the methods described above. A comparison with 20739

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Figure 1. Conversion of FDCA. The complete reactions including the reagents and the byproducts are given in Table 2.

Figure 2. Conversion of 3-HPA. The complete reactions, including the reagents and the byproducts, are given in Table 3.

the appropriate conformation for FDCA is important. The lowest energy conformer of FDCA is planar with the OH groups from the carboxylic acids on the same side of the plane with the O atom of the furan ring, and the H atoms from the carboxylic OH’s are hydrogen bonded to the carbonyl group of the carboxyl and not toward the O atom of the furan. For acrylonitrile, both the gas and liquid phase heats of formation are in good agreement with experiment. There are a number of reported gas and liquid phase heats of formation53−57 which range from 41.3 kcal/mol53 to 44.0 kcal/mol57 for the gas phase and 33.553 kcal/mol to 35.75 kcal/mol56 for the liquid phase heats of formation. Our calculated heats of formation are in very good agreement, within 0.5 kcal/mol, of the more positive reported values. The calculated gas and liquid phase heats of formation for β-propiolactone are in very good agreement with the experimental values.58−60 The calculated liquid heats of formation of β-propiolactone estimated using either the experimental or calculated boiling points are in agreement with the experiment within 0.5 kcal/mol.58−60 The calculated gas heat of formation of acrylamide is in good agreement with the experiment.61 The heat of the formation of the liquid is reported49,53 to be ∼3 kcal/mol more negative

experiment is possible only for some of the studied compounds. Where the experimental boiling points were available, we calculated the heats of vaporization and the heats of formation for the liquid phase, respectively, using both the calculated and the experimental49−51 values of the boiling points. Our calculated G3MP2 gas phase heats of formation are usually within ±2 kcal/mol of the experimental data. The overall good agreement with experiment for the gas phase values suggests that our use of only the lowest energy conformer for the prediction of the gas phase heats of formation is a reasonable approximation. The heats of formation of some compounds are not given in Table 1 as they were previously reported and discussed.15 The gas phase heats of formation of FDCA and furfuryl alcohol were previously calculated at the G4MP2 and G4 levels.52 Our G3MP2 gas phase heat of formation for FDCA is in good agreement with the respective G4MP2 and G4 values of −184.4 and −186.3 kcal/mol as is the G3MP2 gas phase heat of formation for furfuryl alcohol with the respective G4MP2 and G4 values of −52.3 and −52.6 kcal/mol. Although energy differences due to the use of different conformations are usually smaller than errors in the energy calculations,36 the choice of 20740

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Figure 3. Conversion of aspartic acid. The complete reactions including the reagents and the byproducts are given in Table 4.

Figure 4. Conversion of glucaric acid. The complete reactions including the reagents and the byproducts are given in Table 5.

than that of the solid, which is not possible. Thus, we calculated the experimental heat of formation of the liquid from the experimental heat of formation of the solid (−50.688 ± 0.072 kcal/ mol)54,61 and the heat of fusion (3.66 kcal/mol).49,61 Using ΔS = 0.025 kcal/(mol K) leads to heats of formation for the liquid (−42.8 kcal/mol using the calculated TBP and −40.3 kcal/mol using the experimental TBP), which are 4−7 kcal/mol too positive. This suggests that a value of ΔS = 0.035 kcal/(mol K) is

more appropriate for use with this amide, and reasonable agreement with experiment is now found for the liquid. The calculated and experimental62−64 gas heats of formation of 1,5pentanediol are in good agreement. The calculated liquid phase heat of formation of 1,5-pentanediol is about 2 kcal/mol more positive as compared to experiment.62,63,65 The calculated gas phase heat of formation of proline is in very good agreement with the experimental value.66 Only the heat of formation of the 20741

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Figure 5. Conversion of glutamic acid. The complete reactions including the reagents and the byproducts are given in Table 6.

Figure 6. Conversion of itaconic acid. The complete reactions including the reagents and the byproducts are given in Table 7.

crystal proline is reported experimentally.67,68 The calculated heat of formation of pyrrolidine in the gas phase is in good agreement with the experiment69,70 within 1.5 kcal/mol. Use of the calculated and experimental boiling points and ΔSvap = 0.025 kcal/(mol K) leads to calculated heats of formation for the liquid phase that are too positive by about 2.5 and 1.2 kcal/ mol, respectively, as compared to experiment.69−71 The calculated gas and liquid phase heats of formation for propylene oxide are in very good agreement with experiment.72,73 For furfural64,74−76 and furan,64,77,78 the calculated gas and liquid

phase heats of formation are in very good agreement with the experiment, the latter being obtained with a value of ΔSvap = 0.025 kcal/(mol K). The calculated gas phase heat of formation of furfuryl alcohol is in good agreement with the experimental values.64,65,72,76,79 The calculated liquid phase heats of formation of furfuryl alcohol (−62.1 kcal/mol using the calculated TBP and −62.0 kcal/mol using the experimental TBP) are about 4 kcal/mol more positive than the experiment64,65,72,76,79 when a value of ΔSvap = 0.025 kcal/(mol K) is used. Use of ΔSvap = 0.035 kcal/(mol K) as found for the dialcohols gives much 20742

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Figure 7. Conversion of malic acid. The complete reactions including the reagents and the byproducts are given in Table 8.

Figure 8. Conversion of lactic acid. The complete reactions including the reagents and the byproducts are given in Table 9.

values. Thus, we believe that our estimates using a value of ΔSvap = 0.031 kcal/(mol K) for the heats of formation of the liquids of fumaric and maleic acid, which are about 12 and 8 kcal/mol, respectively, more positive then the reported experimental72,83 values, are more reliable than the experimental ones. The experimental liquid phase heats of formation for fumaric and maleic acid are too negative. The calculated gas phase heat of formation for methyl acrylate is about 7 kcal/mol more positive than the reported experimental value.54,64 In order to determine whether there is an error in our approach, we used the G3,84 G4,85 and G4MP286 methods starting from the optimized B3LYP/DZVP2 geometry of methyl acrylate to predict the gas phase heat of formation; we

better agreement with the experimental liquid value for furfuryl alcohol. For fumaric and maleic acid, there is reasonable agreement between the calculated and the experimental64 gas phase heats of formation if the error estimates for both are included. We note that the calculated stability of these cis and trans isomers is reversed from that of experiment, with maleic being more stable experimentally and fumaric more stable computationally. There is a clear issue with the experimental heats of formation in the liquid in that they are the same as in the solid, which is not possible. Using the heat of sublimation80 plus the heat of formation of the solid64,89,81,82 gives calculated heats of formation of the gas phase in good agreement with our calculated 20743

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Figure 9. Conversion of 3-HBL. The complete reactions including the reagents and the byproducts are given in Table 10.

Figure 10. Conversion of furfural. The complete reactions including the reagents and the byproducts are given in Table 11.

ΔHf298(expt) = 44.088) are within 0.5 kcal/mol of experiment. This strongly suggests that the heat of formation determined from the heat of combustion experiment54 is in error. The calculated heat of formation of the liquid phase for methyl acrylate is about 5 kcal/mol more positive than the reported experimental value from both calculated and experimental boiling point values as well. As the experimental heat of vaporization54 of 6.98 kcal/mol does not differ substantially from our values, this suggests that the actual issue with the experiment is the determination of the heat of formation of the liquid.

obtained comparable values of −73.8, −73.1, and −72.5 kcal/ mol, respectively. The isodesmic reaction (eq 2) acrylic acid + dimethyl ether → methyl acrylate + methanol (2)

gives a gas phase heat of formation for methyl acrylate of −72.9 kcal/mol. The calculated G3MP2 heats of formation in kcal/mol for acrylic acid (ΔHf298(calc) = −47.8, ΔHf298(expt) = −48.264), dimethyl ether (ΔHf298(calc) = −77.3, ΔHf298(expt) = −77.6,15,87), and methanol (ΔHf298(calc) = −43.8, 20744

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Figure 11. Conversion of xylitol (arabinol). The complete reactions including the reagents and the byproducts are given in Table 12.

For malonic,89 aspartic,72,90 glutamic,72,90,91 glutaric89,92 and malic89 acids and for xylitol,64,93 only the heats of formation of a crystal are reported experimentally, and we give them for completeness when there is no other data. Reaction Energies and Solvation Effects. The reaction enthalpies in the gas and liquid phases (Tables 2−12) were predicted using the calculated heats of formation. Tables 2−12 also contain the gas phase free energies at 298 K and the free energies including the aqueous solvation effects at 298 K. The free energies of solvation are reported in the Supporting Information for each compound using the approaches in the Gaussian03 (G03) and ADF programs. The electrostatic free energies of solvation in water calculated from both G03 and ADF (see Supporting Information) differ by less than 3 kcal/mol between the two different implementations of COSMO. FDCA can be obtained from glucose via HMF by dehydration and oxidation processes. A wide range of catalysts have been studied to improve either the oxidation of HMF to FDCA or both dehydration and oxidation in a single pot.94 The dehydration processes are mostly nonselective and, thus, the unstable intermediate is immediately transformed into more stable chemicals. Both the gas and liquid phase enthalpies for reaction 1 are calculated to be exothermic. From the freeenergy perspective, 1 is not thermodynamically favorable. Inclusion of solvation effects leads to 2,5-furandicaraldehyde (DFF) being slightly stabilized in water. Through selective reduction, hydrogenated products such as 2,5-dihydroxymethyl furan (DHMF) and 2,5-dihydroxymethyl tetrahydrofuran (DHMTHF) are formed, and reactions 2 and 3 are exothermic processes in both the gas and liquid phases (Table 2). In terms of the free energies, the hydrogenation of a CC bond as in reaction 3 to DHM-THF is thermodynamically more favorable as compared to the hydrogenation of a CO bond as in reaction 2 to DHMF as previously observed for HMF.15 Reaction 4 to form 2,5-bis(aminomethyl)-tetrahydrofuran from FDCA is also highly exothermic, and the product is stabilized by aqueous solvation by more than 10 kcal/mol (Table 2). The formation

of succinic acid from FDCA is highly exothermic in the gas phase and is an endothermic process in the liquid phase (Table 2, 5). From the gas phase free energies, 5 is predicted to be a thermodynamically favorable process and the product is destabilized by aqueous solvation. In order to test a computationally more efficient method, the reaction energies (ΔHgas) in Figure 1 were calculated at the DFT B3LYP/DZVP2 level (Table 2). The B3LYP/DZVP2 reaction energies values differ by up to 4 kcal/mol as compared to G3MP2 values, so the DFT results can be considered to be semiquantitative for the reaction energies. 3-HPA can be obtained from glycerol in a fermentation process via 3-hydroxypropionaldehyde.95,96 Dehydration of 3-HPA leads to acrylic acid (6) and acrylate esters. Experimentally, acrylate production has low yields, and research has been conducted to find improved metabolic pathways.97,98 Reaction 6 is calculated to be endothermic in both gas and liquid phases, but the gas phase free energy shows that this is a thermodynamically favorable reaction (Table 3). There is a slight stabilization of acrylic acid as compared to 3-HPA in aqueous solution. Methyl acrylate is formed in an esterification process after dehydration of 3-HPA (7). For reactions 7 and 8, the gas phase reaction enthalpies are calculated to be nearly thermoneutral and slightly endothermic, respectively, and in the liquid phase, the reaction enthalpy is exothermic for both reactions. Reactions 7 and 8 are thermodynamically favorable in terms of ΔG, and solvation in aqueous solution is predicted to stabilize the methyl acrylate and acrylamide products by more than 10 kcal/mol. Reactions 9 and 10, the acrylonitrile and propiolactone syntheses, respectively, are endothermic processes in both gas and liquid phases, and the positive values of the Gibbs free energy shows that these are not thermodynamically favorable. The esterification of 3-HPA (11) leading to the formation of ethyl-3-hydroxypropionate is calculated to be slightly exothermic in both the gas and liquid phases. Reaction 11 is thermodynamically allowed from the negative value of the gas free energy, and water solvation does not affect the products stability. The oxidation reaction of 3-HPA to malonic acid (12) 20745

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C3H5NO

C4H6O2

C5H10O3 C3H4O4 C4H7NO4 C4H4O4(Z)

C4H4O4(E)

acrylamide

methyl acrylate

ethyl-3-hydroxypropionate malonic acid aspartic acid fumaric acid

maleic acid

C4H5NO3 C4H9NO C4H11NO2 C4H7NO2 C4H7NO2 C4H8N2O C4H8N2O C7H13NO4 C6H10O8 C8H14O8 C6H8O8 C6H6O6 C6H8O7 C6H8O7 C5H9NO4 C5H12O2

C4H11NO C5H13NO2 C5H8O4

C5H11NO3 C5H9NO2

aspartic anhydride 3-aminotetrahydrofuran 2-amino-1,4-butanediol 3-amino-γ-butyrolactone 4-amino-γ-butyrolactone 3-amino-2-pyrrolidone 4-amino-2-pyrrolidone 2-isopropylamino succinic acid glucaric acid dimethyl glucarate α-ketoglucaric acid glucarodilactone glucaro-δ-lactone glucaro-γ-lactone glutamic acid 1,5-pentanediol

5-amino-1-pentanol glutaminol glutaric acid

norvoline proline

−162.4 ± 0.664

−161.6

20746

706.6 501.2

−146.3 −89.2

−87.5 ± 1.066

472.4 585.8 637.3

615.9 433.4 552.4 634.6 557.4 615.4 580.7 752.3 888.9 778.5 797.7 775.6 811.7 785.3 627.5 525.7

598.9

482.3 573.9 669.8 558.5

373.6

500.4

−56.4 −100.9 −201.0

−105.6 ± 1.4,62 −107.7 ± 1.664,63

−161.5 ± 1.564

−147.3 −186.0 −189.0 −164.4

−118.1 −37.2 −97.1 −81.8 −81.5 −40.3 −40.8 −203.3 −361.2 −352.8 −336.4 −216.9 −295.0 −300.0 −194.5 −106.2

−79.59 ± 0.264

−72.6

−30.3

464.0

C3H4O2

β-propiolactone

−67.6

496.3 349.8

−143.2 44.4

C3H6O3 C3H3N 41.3,53 42.95,54 43.7,55 43.6,56 44.057 −68.4 ± 0.3,58 −67.6 ± 0.259,60 −31.12 ± 0.4154,61

561.9 547.1

−185.9 −44.5

C6H4O5 C6H14N2O

BP (K) calc

FDCA 2,5-bis(aminomethyl)tetrahydrofuran 3-HPA acrylonitrile

ΔHf(gas) exp

ΔHf(gas) calc

compound

molecular formula

473.2

512 ± 7

353.15

398.2

435.15

350.15

BP (K) exp49−51

0.031 0.031

0.025 0.035 0.031

0.025 0.025 0.035 0.025 0.025 0.025 0.025 0.031 0.040 0.040 0.040 0.035 0.040 0.040 0.031 0.035

0.031

0.025 0.031 0.031 0.031

0.025

0.035

0.025

0.031 0.025

0.031 0.025

ΔSvap

11.8 20.5 19.8a 14.7b 21.9 15.5

15.4 10.8 19.3 15.9 13.9 15.4 14.5 23.3 35.6 31.1 31.9 27.1 32.5 31.4 19.5 18.4a 17.9b

18.6

11.6a 10.9b 17.5a 14.0b 9.3a 8.8b 12.1 17.8 20.8 17.3

15.4 8.7

17.4 13.7

ΔHvap,BP

−212.95 ± 0.1(cr)89 −232.6 ± 0.2(cr)72,90 −193.6 ± 0.3,72,83 −194.0 ± 0.2(cr)64 −188.2 ± 0.4,72,83 −188.7 ± 0.2(cr)64

−79.6 ± 0.3,58 −78.8 ± 0.259,60 −47.0 ± 0.4,49,53 −50.7 ± 0.4(cr)54,61 −86.57 ± 0.264

33.5,53 35.2,54 35.7556

ΔHliq exp

−133.5 −48.1 −116.4 −97.7 −95.4 −55.7 −55.3 −226.6 −396.8 −383.9 −368.3 −244.0 −327.5 −331.4 −214.0 −239.8 ± 0.3(cr),91 −240.2 ± 0.3(cr),72,90 −241.3 ± 0.2(cr)90 −124.6a −126.4 ± 1.4,62 b −124.1 −126.9 ± 0.7,63 −125.865 −68.2 −121.4 −220.8a −229.4 ± 0.389,92 b −215.7 −168.2 −104.7 −121.3 ± 0.6(cr),67

−180.2

−79.2a −78.5b −47.8a −44.3b −82.0a −81.4b −159.3 −203.8 −209.8 −181.7

−158.6 35.6

−203.3 −58.2

ΔHliq calc

Table 1. Heats of Formation at 298 K in kcal/mol and Boiling Points (BPs) in Kelvins (K) for Compounds in Figures 1−11

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C3H6O

C4H6O3 C4H4O2 C4H4O3 C7H8O4 C4H9NO2 C4H9NO C4H8O2

C5H4O2

C4H4O

propylene oxide

3-hydroxy butyrolactone γ-butenyl-lactone epoxy-lactone acrylate-lactone 2-amino-3-hydroxy-THF 3-amino-THF 3-hydroxy-THF

furfural

furan

C5H10O3

ethyl lactate

C4H6O2

C6H8O4 C4H8O3

lactide methyl lactate

methyl acrylate

C5H11N

C5H11NO C5H7NO3 C5H9NO2 C5H6O4 C5H14N2 C5H8N2O2 C5H11N C6H11NO C6H11NO C6H11NO C5H12O2 C5H10O C5H8O2 C5H8O2 C4H6O5 C6H12O C4H9N

molecular formula

N-methyl pyrrolidine

prolinol pyroglutamic acid pyroglutaminol itaconic acid 2-methyl-1,4-butanediamine itaconic diamide 3-methylpryrrolidine 3-methyl NMP 4-methyl NMP 5-methyl NMP 2-methyl-1,4-butanediol 3-methyl THF 3-methyl GBL 4-methyl-GBL malic acid 2,5-dimethyl THF pyrrolidine

compound

Table 1. continued

−8.4

275.5

410.9

−35.8,74 −36.1 ± 1.1,64,75 −34.5,65 −36.276 −6.6,77 −7.1,76

−36.9

280.9 574.4 494.0 515.2 769.4 510.3 394.6 437.9

−22.63 ± 0.1572,73

−22.2

373.6

−125.8 −62.4 −81.9 −141.6 −83.7 −37.2 −82.5

−79.5954,64

459.1

−150.7 −72.6

602.7 425.0

−168.7 −142.5

483.1 688.9 599.9 545.4 438.7 669.7 337.3 488.7 495.1 493.0 494.5 333.5 489.6 501.5 638.2 359.6 308.9

BP (K) calc

298.3

−0.81 ± 0.2,69 −0.86 ± 0.270

ΔHf(gas) exp

−3.0

−44.7 −134.4 −91.8 −170.9 −121.2 −86.0 −6.6 −57.7 −57.4 −59.1 −108.2 −50.4 −95.7 −95.5 −230.2 −63.2 0.5

ΔHf(gas) calc

304.7 ± 0.6

434.7 ± 0.4

454.15

307.9 ± 0.5

353.15

427.15

417.15

353.15

360 ± 3

BP (K) exp49−51

0.025

0.025

0.025 0.025 0.025 0.025 0.025 0.025 0.025

0.025

0.025

0.025

0.025 0.025

0.025

0.031 0.031 0.025 0.031 0.025 0.025 0.025 0.025 0.025 0.025 0.035 0.025 0.025 0.025 0.031 0.025 0.025

ΔSvap

6.9a

15.0 21.4 15.0 16.9 11.0 16.7 8.4 12.2 12.4 12.3 17.3 8.3 12.2 12.5 22.3 9.0 7.7a 9.0b 7.5a 8.8b 15.1 10.6a 10.4b 11.5a 10.7b 9.3a 8.8b 7.0a 7.7b 14.4 12.4 12.9 19.2 12.8 9.9 10.9a 11.4b 10.3a 10.9b

ΔHvap,BP

−15.3a

−59.7 −155.8 −106.8 −187.8 −132.2 −102.7 −15.1 −70.0 −69.7 −71.5 −125.5 −58.8 −107.9 −108.1 −252.6 −72.2 −7.2a −8.5b −10.4a −11.8b −183.7 −153.1a −152.9b −162.2a −161.4b −81.9a −81.4b −29.2a −29.9b −140.2 −74.7 −94.8 −160.8 −96.5 −47.1 −93.5a −93.9b −47.2a −47.8b

ΔHliq calc ΔHliq exp

−13.2,77 −13.7,76

−47.8,74 −46.6,65 −48.2 ± 1.164,76

−29.30 ± 0.1572,73

−86.5754,64

−9.80 ± 0.2,69,71 −9.85 ± 0.270,71

−264.3 ± 0.2(cr)89

−123.1 ± 0.1(cr)68

The Journal of Physical Chemistry C Article

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Article

Calculated ΔHvap,BP (ΔHvap = TBPΔSvap) or ΔHliq,298K (ΔHliq = ΔHgas − ΔHvap) using the calculated BP value. bCalculated ΔHvap,BP or ΔHliq,298K using the experimental BP value.

is calculated to be highly exothermic for both gas and liquid phases and also has a negative free energy, and aqueous solvation stabilizes the product (Table 3). 1,3-Propandiol has been studied by DuPont as a potential monomer that may be useful in fibers for carpets because of properties such as improved dye ability and elasticity.11 The synthesis of 1,3-propandiol (13) is calculated to be an exothermic process in gas and liquid phases, and the 1,3-propandiol product is stabilized by water solvation (Table 3). There are different known ways to produce aspartic acid including chemical synthesis, protein extraction, fermentation, and enzymatic conversion; the latter approach is the most used. A wide range of chemicals such as 1,4-butanediol, tetrahydrofurans, or γ-butyrolactones can be produced from aspartic acid for use in polymer chemistry and solvent applications. Reactions 14−16 are calculated to be exothermic in the gas and liquid phases; they are thermodynamically allowed in the gas phase, and reaction products are stabilized by aqueous solvation by more than 10 kcal/mol (Table 4). Reaction of aspartic acid with secondary alcohols such as isopropanol leads to various substituted amino-diacids. Reaction 17 is calculated to be exothermic and thermodynamically allowed in terms of ΔG. Anhydride synthesis via a dehydration process (18) is an exothermic process and is not thermodynamically favorable (positive value of the gas phase free energy) (Table 4). By reduction/ dehydration reactions, cyclic oxygenated products such as amino γ-butyrolactones and tetrahydrofuran can be obtained (19−21). These reactions 19−21 are exothermic, thermodynamically allowed in terms of ΔG, and the products are stabilized by water solvation. Syntheses of the unsaturated diacids, fumaric and maleic acid, are endothermic reactions and not thermodynamically favorable in terms of ΔG (22 and 24), whereas the synthesis of the saturated diacid, succinic acid, from aspartic acid is an exothermic process and thermodynamically allowed (23) in terms of ΔG. Solvation does not significantly affect the formation of these diacid products (Table 4). Glucaric acid is an oxidized sugar which can be prepared in high yield from glucose via oxidation in the presence of chemical or biochemical catalysts, but the process is difficult to scale up. The cyclization reaction 25 with the formation of glucarodilactone is an endothermic process and is not thermodynamically allowed (positive ΔG) (Table 5). The synthesis of glucaro-δ-lactone (26) is calculated to be slightly endothermic in the gas phase and close to thermoneutral in the liquid phase. The gas free energy is calculated to be ∼0.5 kcal/mol, and solvation in water slightly stabilizes the glucaro-δ-lactone product by up to 4 kcal/mol. The enthalpies for the cyclization reaction 27, with the formation of glucaro-γ-lactone are calculated to be to be slightly endothermic in the gas phase (3.7 kcal/mol) and slightly exothermic in the liquid (−2.9 kcal/mol) (Table 5). From the free energy perspective, reaction 27 is thermodynamically favorable and solvation does not significantly affect the stability of the products. The esterification reaction of glucaric acid (28) is an exothermic process and from the calculated free energies, this reaction is favorable thermodynamically and not affected by water solvation. Reaction 29 to form α-ketoglucaric acid from glucaric acid is a highly endothermic process, not allowed thermodynamically in terms of ΔG, and the stability of the products is not influenced by aqueous solvation. The main issue with the production of glutamic acid as a building block is due to its production by a fermentation route. The challenge is to develop an organism that can make free

a

C5H12O5 C5H10O4 C5H8O7 xylitol mixture of hydroxy furans xylaric acid

−227.5 −165.6 −314.3

−50.7,79-50.8,65 −50.6 ± 0.564,76

703.5 612.4 722.7

430 ± 70

0.040 0.040 0.040

0.025 0.025 0.035 749.3 749.3 434.6 C13H10O3 C13H24O3 C5H6O2

−8.3 ± 0.264,78

fufural dimer furfural reduced dimer furfuryl alcohol

−20.1 −152.9 −51.2

ΔHliq exp BP (K) calc ΔHf(gas) exp ΔHf(gas) calc molecular formula compound

Table 1. continued

−66.1,79 −66.2,65 −66.0 ± 0.364,72,76 −267.35 ± 0.15(cr)64,93

−16.0b −38.1 −171.7 −66.4a −66.2b −255.6 −190.1 −343.2 7.6b 18.0 18.7 15.2a 15.0b 28.1 24.5 28.9

ΔHliq calc BP (K) exp49−51

ΔSvap

ΔHvap,BP

−14.9 ± 0.264,78

The Journal of Physical Chemistry C

20748

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The Journal of Physical Chemistry C

Article

Table 2. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 1 ΔGsol‑aqueous no. 1 2 3 4 5 a

ΔHgas

reaction FDCA FDCA FDCA FDCA FDCA

+ + + + +

2H2 → 2,5-furandicarbaldehyde + 2H2O 4H2 → 2,5-DHMF + 2H2O 6H2 → 2,5-DHM-THF + 2H2O 2NH3 + 6H2 → 2,5-bis(aminomethyl)-tetrahydrofuran +4H2O 3H2O → succinic acid +2CO2 + 2H2

4.8 −26.5 −66.3 −67.8 −24.1

a

(4.4) (−25.6)a (−64.9)a (−63.9)a (−22.1)a

ΔGgas

ΔHliq

G03

ADF

2.3 −10.7 −30.5 −32.9 −37.3

−10.9 −45.4 −83.4 −94.1 10.6

−10.3 −24.7 −42.8 −61.6 −15.0

−8.4 −24.2 −38.4 −54.4 −15.2

Values at B3LYP/DZVP2 level for comparison.

Table 3. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 2

Table 5. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 4

ΔGsol‑aqueous no. 6 7 8 9 10 11 12 13

reaction

ΔHgas

ΔGgas

ΔHliq

G03

ΔGsol‑aqueous

ADF

8.6 −2.3 7.3 −7.4 −5.8 3-HPA → acrylic acid + H2O 3-HPA + MeOH → 2.3 −7.0 −4.1 −19.1 −15.7 methyl acrylate +2H2O 8.4 −3.5 −8.7 −15.6 −13.4 3-HPA + NH3 → acrylamide +2H2O 3-HPA + NH3 → 25.2 3.1 6.4 −12.4 −9.2 acrylonitrile +3H2O 3-HPA → propiolactone 17.9 8.4 11.2 1.1 3.7 + H2O 3-HPA + EtOH → −6.0 −4.8 −3.0 −5.5 −4.2 ethyl-3-hp + H2O 3-HPA + O2 → malonic −100.5 −102.2 −113.5 −113.3 −114.1 acid + H2O 3-HPA + 2H2 → −9.8 −1.5 −16.2 −10.1 −7.3 1,3-propanediol + H2O

no.

reaction

ΔHgas

ΔGgas

ΔHliq

G03

ADF

25

glucaric acid → glucarodilactone +2H2O glucaric acid → glucaroδ-lactone + H2O glucaric acid → glucaroγ-lactone + H2O glucaric acid +2MeOH → dimethyl glucarate +2H2O glucaric acid → α-ketoglucaric acid + H2

28.7

11.2

16.2

1.0

3.2

8.7

0.5

1.0

−3.4

−2.4

3.7

−4.9

−2.9

−6.9

−6.4

−10.7

−8.5

−11.3

−7.3

−8.6

24.8

15.1

28.5

16.4

13.4

26 27 28 29

Table 6. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 5 ΔGsol‑aqueous

Table 4. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 3

no.

reaction

30

glutamic acid + H2 → glutaric acid + NH3 glutamic acid +5 H2 → 1,5pentanediol + NH3 + 2H2O glutamic acid +2 H2 → 5-amino-1-pentanol + CO2 + H2O glutamic acid → pyroglutamic acid + H2O glutamic acid +4H2 → prolinol +3H2O glutamic acid +2H2 → proline +2H2O glutamic acid +2H2 → pyroglutaminol +2H2O glutamic acid +2H2 → norvoline + H2O glutamic acid +4H2 → glutaminol +2H2O

31

ΔGsol‑aqueous no.

reaction

ΔHgas

ΔGgas

ΔHliq

G03

ADF

14

aspartic acid +4H2 → 2-amino1,4-butanediol +2H2O aspartic acid + NH3 + 2H2 → 3-amino-2-pyrrolidone +3H2O aspartic acid + NH3 + 2H2 → 4-amino-2-pyrrolidone +3H2O aspartic acid + isopropanol → 2-isopropylamino succinic acid + H2O aspartic acid → aspartic anhydride + H2O aspartic acid +2H2 → 3-aminoγ-butyrolactone +2H2O aspartic acid +2H2 → 4-aminoγ-butyrolactone +2H2O aspartic acid +4H2 → 3aminotetrahydrofuran +3H2O aspartic acid → fumaric acid + NH3 aspartic acid + H2 → succinic acid + NH3 aspartic acid → maleic acid + NH3

−23.7

−6.4

−43.2

−19.4

−19.2

−13.6

−15.1

−33.8

−31.7

−29.4

15

16

17

18 19 20 21 22 23 24

32 33 34

−14.1

−15.6

−33.4

−30.8

−28.5

−6.9

−4.8

−10.4

−7.6

−6.9

13.2

3.6

8.0

−2.0

−1.0

−8.4

−9.0

−24.5

−24.2

−21.6

−8.1

−8.8

−22.2

−20.8

−18.5

−21.6

−14.0

−43.2

−29.2

−25.9

13.6

3.4

11.1

1.7

−0.4

−17.3

−19.0

−18.0

−21.2

−21.0

16.4

6.2

12.6

2.5

0.8

35 36 37 38

ΔHgas ΔGgas ΔHliq

G03

ADF

−17.2 −17.2 −23.5 −23.9 −20.6 −37.9 −21.3 −63.9 −40.1 −34.1 −13.4 −16.6 −16.3 −22.0 −17.8 9.3

−6.4

−9.7

−16.2 −12.8

−23.2 −14.8 −50.3 −31.9 −22.8 −10.0 −10.4 −27.0 −21.4 −18.9 −13.2 −12.6 −29.1 −29.8 −26.8 −9.2

−0.5

−22.2 −12.3

−8.2

−21.6

−4.8

−43.7 −20.5 −15.3

terms of ΔG (Table 6). Inclusion of solvation leads to the products of reaction 31 being stabilized in water by more than 15 kcal/mol. For reactions 30 and 32, solvation does not significantly affect the stability of the products. The cyclodehydration reaction with the formation of pyroglutamic acid (33) is an endothermic process in the gas phase and exothermic in the liquid phase. From the calculated free energies, this reaction 33 is favorable thermodynamically, and the products are stabilized by aqueous solvation. Reactions 34−38 are calculated to be highly exothermic for both the gas and liquid phases, and, because they are dehydration processes, water solvation stabilizes the products. Itaconic acid (methyl succinic acid) is usually synthesized via fungal fermentation. The chemistry of itaconic acid, a C5

glutamic acid, not a salt, which involves costly neutralization and purification steps.11 From the reaction enthalpies, reactions 30−32 are calculated to be exothermic processes in both the gas and liquid phases, and are thermodynamically favorable in 20749

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Article

Table 7. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 6 ΔGsol‑aqueous no. 39 40 41 42 43 44 45 46 47 48

reaction itaconic itaconic itaconic itaconic itaconic itaconic itaconic itaconic itaconic itaconic

acid acid acid acid acid acid acid acid acid acid

+5H2 + 2NH3 → 2-methyl-1,4-butanediamine +4H2O +2NH3 → itaconic diamide +2H2O +5H2 + NH3 → 3-methylpryrrolidine +4H2O + CH3OH + 3H2 + NH3 → 3-methyl NMP + 4H2O + CH3OH + 3H2 + NH3 → 4-methyl NMP + 4H2O + CH3OH + 3H2 + NH3 → 5-methyl NMP + 4H2O +5H2 → 2-methyl-1,4-BDO + 2H2O +5H2 → 3-methyl THF + 3H2O +3H2 → 3-methyl-GBL + 2H2O +3H2 → 4-methyl-GBL + 2H2O

ΔHgas

ΔGgas

ΔHliq

G03

ADF

−59.5 −8.7 −55.9 −58.8 −58.5 −60.2 −52.9 −52.9 −40.4 −40.2

−29.9 −3.9 −37.9 −48.0 −47.6 −49.2 −26.2 −34.1 −29.8 −29.6

−183.6 −17.5 −83.5 −81.2 −80.9 −82.7 −74.3 −75.9 −56.7 −56.9

−45.0 −12.0 −54.5 −64.3 −64.4 −65.8 −37.2 −48.5 −42.4 −42.5

−43.3 −14.5 −52.2 −63.6 −63.7 −64.7 −36.3 −46.4 −41.9 −41.5

Table 8. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 7

Table 10. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 9

ΔGsol‑aqueous

ΔGsol‑aqueous

no.

reaction

ΔHgas

ΔGgas

ΔHliq

G03

ADF

no.

49

malic acid +2CH3OH +5H2 → dimethyl THF + 6H2O malic acid + CH3OH + 5H2 → methyl THF + 5H2O malic acid + NH3 + 5H2 → pyrrolidine +5H2O malic acid + NH3 + CH3OH + 5H2 → N-methyl pyrrolidine +6H2O malic acid + NH3 + CH3OH + 3H2 → N-methyl pyrrolidone +5H2O

−83.4

−72.4

−115.0

−97.4

−90.7

61

−63.8

−53.5

−94.3

−76.3

−70.0

−47.3

−39.2

−79.1

−62.2

−56.1

62 63

−60.4

−50.5

−93.4

−73.7

−67.7

−49.6

−48.5

−77.3

−71.7

−67.3

50 51 52

53

64 65 66

Table 9. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 8 reaction

ΔHgas

ΔGgas

ΔHliq

G03

ADF

54

lactic acid → acrylic acid + H2O lactic acid + CH3OH → methyl acrylate +2H2O lactic acid + CH3OH → methyl lactate + H2O lactic acid + C2H5OH → ethyl lactate + H2O 2(lactic acid) → lactide +2H2O lactic acid +2H2 → propylene glycol + H2O propylene glycol → propylene oxide + H2O

7.0

2.4

0.4

−4.7

−3.7

55 56 57 58 59 60

ΔHgas ΔGgas ΔHliq

G03

ADF

−2.8 −11.1 −10.8 45.4 −1.5

36.8 −2.0

35.3 −1.3

−7.6

4.6

4.8

−26.5 −12.0 −10.9 −21.6 −8.6

−7.6

Table 11. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 10

ΔGsol‑aqueous no.

reaction

3-HBL → γ-butenyl-lactone + 5.7 −4.9 H2O 43.9 35.1 3-HBL → epoxy-lactone + H2 3-HBL + acrylic acid → 3.8 4.7 acrylate-lactone + H2O 3-HBL + NH3 + H2→ 2-amino −4.7 4.3 -3-hydroxytetrahydrofuran + H2O −16.0 −8.2 3-HBL + NH3 + 2H2 → 3-aminotetrahydrofuran + 2H2O −14.5 −6.2 3-HBL + 2H2 → 3-hydroxytetrahydrofuran + H2O

ΔGsol‑aqueous no.

reaction

ΔHgas

ΔGgas

ΔHliq

G03

ADF

furfural + H2 → furfuryl alcohol furfuryl alcohol + H2O → levulinic acid 2(furfural) + acetone → furfural dimer +2H2O furfural dimer +7H2 → furfural reduced dimer furfural +4H2 → 2-methyl THF + H2O furfural +4H2 → THF + CH3OH furfural +2H2 → furan + CH3OH

−14.3

−4.4

−4.0

−4.2

−3.4

−35.9

−28.0

−24.2

−24.2

−23.8

−10.0

−4.3

−19.8

−12.5

−11.2

−132.8

−63.8

−114.8

−60.9

−58.3

−74.1

−45.6

−74.3

−49.2

−46.8

−54.6

−27.4

−61.2

−29.0

−26.3

−19.7

−11.3

−18.4

−12.4

−10.7

1.9

−1.8

−9.9

−9.6

−8.4

67

−10.2

−3.8

−8.1

−4.3

−3.9

68

−10.7

−3.9

−8.4

−4.5

−3.8

69

−0.5

4.4

−8.1

−7.1

−5.5

70

−18.1

−3.5

−29.8

−11.6

−9.8

71

22.2

12.1

20.0

−0.5

1.2

72 73

dicarboxylic acid, is considered to be similar to that of maleic acid or maleic anhydride.11 The company Itaconix is interested in producing itaconic acid from biomass in order to polymerize itaconic acid into super absorbents and dispersants. The polymers derived from itaconic acid show promising properties, but further evaluations are necessary.11 The hydrogenation/reduction and/or cyclization reactions to synthesize 2-methyl-1,4-butanediamine (39), 2-methyl-1,4-butanediol (2-methyl-1,4-BDO) (45), 3-methyl-THF (46), 3- and 4-methyl-γ-butyrolactone (3and 4-GBL) (47 and 48) are highly exothermic in both the gas and liquid phases and thermodynamically allowed in terms of ΔG (Table 7). The reaction products are stabilized by aqueous solvation by more than 10 kcal/mol (Table 7). These reactions 45−48 should be similar to the hydrogenation reactions of

maleic anhydride to produce BDO, THF and GBL. Synthesis of itaconic diamide is also an exothermic reaction stabilized by water solvation (40). 3-Methylpyrrolidine and N-methyl pyrrolidones (41−44) can be obtained from itaconic acid. Reactions 41−44 are calculated to be highly exothermic processes, thermodynamically favored in terms of ΔG, and the cyclic products are stabilized by aqueous solvation (Table 7). Malic acid, a C4 dicarboxylic acid, shows chemistry similar to that of succinic acid. Of interest is the synthesis of substituted THF and pyrrolidine/pyrrolidone derivatives from malic acid. Reactions 49 and 50 to dimethyl and methyl from malic acid are highly exothermic, and the products are stabilized by 20750

dx.doi.org/10.1021/jp306596d | J. Phys. Chem. C 2012, 116, 20738−20754

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61 and 63 by about 6 kcal/mol. The epoxy-lactone synthesis (62) is calculated to be a highly endothermic process, not thermodynamically allowed in terms of ΔG, and the stability of the epoxide product is not influenced by solvation (Table 10). THF derivatives can be prepared from 3-HBL, and these processes are calculated to be exothermic (65 and 66) or just slightly exothermic (64). The gas phase Gibbs free energy of reaction 64 is calculated to be positive, and for reactions 65 and 66 negative; the reaction free energies are not strongly affected by aqueous solvation (Table 10). Furfural is produced by Avantium by dehydrating 5C-sugars as xylose and arabinose; it is a promising substitute for diesel fuel. The conversion to THF and THF derivatives is one of the largest applications of furfural. Reactions 71−73 are calculated to be exothermic processes, and solvation does not influence the stability of the products. Selective hydrogenation of furfural leads to furfuryl alcohol (67). From the calculated gas and liquid reaction enthalpies, reaction 67 is exothermic, and the furfuryl alcohol product is not affected by aqueous solvation (Table 11). Levulinic acid can be prepared from furfuryl alcohol through acid catalyzed rehydration99 (68). Reaction 68, levulinic acid synthesis, is calculated to be highly exothermic in both the gas and liquid phases, and solvation does really affect the stability of the product. A furfural dimer can be synthesized in a condensation reaction of furfural with acetone, and the dimer can be further reduced (69 and 70). Both 69 and 70 are calculated to be exothermic or even highly exothermic for the reduction, as previously predicted,15 and thermodynamically allowed in terms of ΔG. The furfural dimer (69) is slightly stabilized by aqueous solvation, but the reduced dimer product is not really affected by water solvation (Table 11). Xylitol and arabinitol are C5 hydrogenated sugars which, similar to glucose, can be transformed to important products for the biofuel industry. Thus, propylene glycol, ethylene glycol, glycerol, and lactic acid can be obtained from xylitol (74−76). Reaction 74, propylene glycol synthesis, is calculated to be exothermic in both gas and liquid phases, thermodynamically allowed in terms of ΔG, and aqueous solvation slightly stabilizes the products by not more than 8 kcal/mol. Reactions 75−77 are slightly exothermic processes, and water solvation slightly stabilizes the products of reactions 75 and 77 and does not affect the products stability of 76 (Table 12). The cyclization reaction 78 is calculated to be close to thermoneutral, slightly endothermic in the gas phase and slightly exothermic for the liquid phase, thermodynamically favored in terms of ΔG, and the stability of the products is not much affected by water solvation. Xylaric acid can be prepared in a selective oxidation of the terminal primary alcoholic groups from xylitol (79). Reaction 79 is a highly exothermic process as previously predicted for glucose oxidation,15 and aqueous solvation does not affect the product stability (Table 12). General Reaction Trends. Most of the reactions that were studied are thermodynamically allowed with a negative ΔG, and the products are stabilized by aqueous solvation with the exception of some reactions where solvation does really affect the stability of the product, as in 11, 17, 23, 28, 56, 57, 64, 66−68, 70−73, 76, and 79, which are mostly esterification and hydrogenation reactions. The processes that are endothermic in both gas and liquid phases include the dehydrogenation reactions 29 and 62, the deaminations 22 and 24, the dehydration reactions 6, 10, 18, 26, 54, and 60 where only one mole of water is eliminated and 25 where two mole of water are eliminated, and reaction 9 with acrylonitrile formation from 3-HPA.

Table 12. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 11 ΔGsol‑aqueous no.

reaction

74 xylitol +2H2 → propylene glycol + H2O + ethylene glycol 75 xylitol +2H2 → 2(ethylene glycol) + CH3OH 76 xylitol + H2 → glycerol + ethylene glycol 77 xylitol → lactic acid + ethylene glycol 78 xylitol → mixture of hydroxy furans + H2O 79 xylitol +2O2 → xylaric acid +2H2O

ΔHgas ΔGgas ΔHliq

G03

ADF

−25.3 −26.7 −29.6 −34.9 −32.9 −6.1

−6.5

−3.8

−4.2

−7.6 −13.4 −11.8 0.8

−6.2

−5.4

−7.1 −23.2 −4.0 −23.7 −23.7 4.1

−5.0

−2.8

−9.2

−8.4

−86.8 −95.8 −87.6 −95.8 −97.5

aqueous solvation (Table 8). Reactions 51−53 to pyrrolidine and pyrrolidone products are also calculated to be highly exothermic, and the products are stabilized by water solvation by more than 15 kcal/mol. Lactic acid, mainly used for preservation, acidification, and flavor enhancement in food, is produced by fermentation of glucose. Lactic acid is converted to acrylic acid (54) and acrylic esters such as methyl acrylate (55) by dehydration reactions. The synthesis of acrylic acid (54) is calculated to be a slightly endothermic process in the gas phase (7.0 kcal/mol), and in the liquid phase, it is thermoneutral (0.4 kcal/mol) (Table 9). Reaction 54 is not thermodynamically allowed from the calculated value of the gas phase free energy of 2.4 kcal/mol, and the acrylic acid product is stabilized by aqueous solvation by only about 6−7 kcal/mol. Reaction 55 is calculated to be very close to thermoneutral from the reaction enthalpy of 1.9 kcal/ mol for the gas phase and slightly exothermic from the reaction enthalpy of −9.9 kcal/mol for the liquid phase (Table 9); it is thermodynamically favored in terms of ΔG, and water solvation stabilizes the methyl acrylate product by more than 7 kcal/mol. The esterification reactions of lactic acid with methyl or ethyl lactate synthesis (56 and 57) are calculated to be slightly exothermic for both gas and liquid phases, and solvation does not affect the free energies. Lactide is formed as an intermediate in the synthesis of polylactic acid (58). Reaction 58 is a thermoneutral process in the gas phase leading to the formation of the starting monomer for polylactic acid and slightly exothermic in the liquid phase. From the calculated gas phase free energy values, reaction 58 is not thermodynamically allowed, and solvation stabilizes the lactide product by more than 10 kcal/mol (Table 9). Propylene glycol can be obtained from lactic acid in a reduction process, which can undergo further dehydration to get propylene oxide (59 and 60). The synthesis of propylene glycol (59) is calculated to be an exothermic process, and water solvation slightly stabilizes the product. By contrast, propylene oxide synthesis (60) is an endothermic process in both gas and liquid phases, not allowed thermodynamically (positive gas phase ΔG), and the product is stabilized by aqueous solvation by more than 10 kcal/mol (Table 9). The synthesis of 3-HBL involves many steps and is considered to be difficult.11 Lactones and THF derivatives can be prepared from 3-HBL (Figure 9). Dehydration of 3-HBL (61) and esterification of 3-HBL with acrylic acid (63) are calculated to be close to thermoneutral processes. The gas phase free energy is calculated to be −4.9 kcal/mol for 61 and +4.9 kcal/ mol for 63 (Table 10). Solvation stabilizes the products of both 20751

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thanks the Robert Ramsay Chair Fund of The University of Alabama for support.

The dehydration processes including 1, 27, 33, and 61 are calculated to be slightly endothermic in the gas phase and slightly exothermic in the liquid phase. Similarly, other chemical processes that involve water elimination such as the esterification reactions 7, 55, and 63 and the amination reaction 9 are slightly endothermic in the gas phase and slightly exothermic in the liquid phase. Aqueous solvation has no effect on the dehydrogenation reactions 29 and 62, or the reactants are stabilized over the products on the dehydrations reactions 25 and 60, but the products of the other endothermic reactions are stabilized by water solvation.



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CONCLUSIONS The thermodynamics for the conversion of FDCA, 3-HPA, aspartic acid, glucaric acid, glutamic acid, itaconic acid, malic acid, lactic acid, 3-HBL, furfural, and xylitol/arabinitol, which are biomass-derived starting materials leading to a number of biobased fuels and chemicals, were calculated at the correlated molecular orbital theory G3MP2 level. The heats of formation for a large number of compounds were calculated in both gas and liquid phases. Our calculated gas heats of formation are mostly within ±2 kcal/mol of the experimental values where the experimental values were available. The largest exception is the heat of formation for methyl acrylate, which is calculated to be about 7 kcal/mol more positive than the reported experimental gas phase value. We suggested that there is an error in the liquid heat of formation of this compound determined from a heat of combustion. Overall, most of the studied reactions are exothermic so they are thermodynamically allowed, and the products are stabilized by aqueous solvation. This paper continues our studies of the conversion of biomass to more useful fuels and chemical feedstocks. These results can be used in designing new synthetic or catalytic approaches for these reactions to improve the conversion of the biomass. A large number of reaction intermediates and pathways are possible for each of the detailed molecular mechanisms of each reaction. Thus computing the kinetics for these processes will be a significant challenge. The current work provides the thermodynamics so that one can pursue the kinetics of the appropriate conversions of these glucose-derived starting materials.



ASSOCIATED CONTENT

S Supporting Information *

Full citations for refs 3, 37, and 47. Thermochemical values at the G3MP2 level of theory in a.u. Aqueous solvation energy contributions in kcal/mol. Optimized B3LYP/DZVP2 Cartesian coordinates in angstroms for the various structures and their molecular structures. This material is available free of charge via the Internet at http://pubs.acs.org.



REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS This work was supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, U.S. Department of Energy (DOE) under Grant No. DE-FG02-03ER15481 (catalysis center program). D.A.D. also 20752

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