The possibility of chemical transformation of glucose in choline chloride/glucose deep eutectic solvent with thermal instability.

Deep eutectic solvents (DESs), characterized by their low volatility, non-toxicity, and biodegradability, have gained attention as green solvents due to their minimal environmental impact and sustainability. The choline chloride/glucose DES, composed solely of biomass, is notable for its high biocompatibility and ability to be prepared at low cost. However, it is also known for its low thermal stability and tendency to denature when heated. In this study, we approached the choline chloride/glucose DES, with its thermal denaturation properties, as a unique chemical conversion medium entirely constituted from biomass. We investigated the thermal denaturation and reaction behaviors of the DES when subjected to prolonged heating. It was found that the choline chloride/glucose DES was relatively thermally stable at around 100 °C, but underwent thermal denaturation at 130 °C, enabling the production of 5-HMF and seven types of rare sugars derived from glucose. The yield of disaccharides containing seven types of rare sugars and 5-HMF relative to the weight of glucose was as high as approximately 70% and 5%, respectively. This study thus reveals that simply heating a liquid composed exclusively of biomass under mild conditions can generate a range of high-value compounds.

CO formation from glucose and cellulose as treated in ionic liquids.

The formation of carbon monoxide (CO) from glucose and cellulose by the treatment with various ionic liquids was studied. Ionic liquids with an imidazolium structure as cation and the chloride or acetate as anion were used. Additionally, 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) was employed as an additive. CO was generated from glucose with a maximum yield of 0.57 mol% after 90 min of treatment at 120 °C in the reaction system in which DBU was added to the ionic liquid. Pyrolysis above 600 °C has been commonly employed for the gasification of lignocellullosics to produce useful gases such as CO. However, this study has revealed that gasification of lignocellullosics to produce CO can occur at significantly lower temperature, specifically at 120 °C.

Vanillin Production Pathways in Alkaline Nitrobenzene Oxidation of Guaiacylglycerol-ß-guaiacyl Ether.

Alkaline nitrobenzene oxidation (AN oxidation) is a significant method for chemical analysis of lignin. Despite its importance in lignin chemistry, the detailed chemical reactions involved in AN oxidation are not yet fully understood. Surprisingly, there is almost no experimentally supported information available regarding the reaction pathways in the AN oxidation of guaiacyl glycerol-ß-guaiacyl ether (GG), a common model compound in lignin chemistry. This study reports the results of our investigation into the formation pathway of vanillin (4-hydroxy-3-methoxybenzaldehyde) in the AN oxidation of GG. Our series of experiments proposed a vanillin formation pathway involving an enol ether with a C2 side chain, 2-methoxy-4-[2-(2-methoxyphenoxy)-ethenyl]-phenol C2EE, as an intermediate, in which C2EE is produced by the non-oxidative degradation of GG by alkali. Another enol ether with a C3 side-chain, Z-4-[3-hydroxy-2-(2-methoxyphenoxy)-1-propen-1-yl]-2-methoxyphenol (C3EE), and the condensation products formed under alkaline conditions were found to be insignificant as vanillin sources. On the other hand, the comparison of the vanillin yields from GG and isolated C2EE (80.7 and 86.5 mol %, respectively) in their AN oxidation to the C2EE yield from GG in the absence of nitrobenzene (69.9 mol %) also suggested that the vanillin formation from GG involved unknown pathways in which C2EE is not an intermediate.

Synthesis of Bridged Indigos and Their Thermoisomerization and Photoisomerization Behaviors.

Bridged indigos were synthesized by bridging the two nitrogen atoms in the indigo structure with a carbon chain, and their properties were carefully examined. These bridged indigos have intrinsic planar chirality, and the enantiomers were separated using chiral high-performance liquid chromatography. When the chiral bridged indigos were subjected to thermo- and photoisomerization, the corresponding (Z)-indigo was not observed at all, and racemization was observed. This phenomenon is caused by the low activation energy of inversion due to the 1.5 bond order of the double bond of the indigo skeleton and the large energy difference between the ground states of (E)-indigo and (Z)-indigo.

Selective production of bio-based aromatics by aerobic oxidation of native soft wood lignin in tetrabutylammonium hydroxide.

Aerobic oxidation of native soft wood lignin in an aqueous solution of Bu4NOH facilitates efficient production of vanillin (4-hydroxy-3-methoxybenzaldehyde), which is one of the platform chemicals in industry. Oxidation of Japanese cedar (Cryptomeria japonica) wood flour at 120 °C for 4 h under O2 in Bu4NOH-based aqueous solutions produced vanillin in 23.2 wt% yield based on the Klason lignin content of the starting material. This yield was comparable to that in alkaline nitrobenzene oxidation of the same material (27.2%), which indicated that our aerobic oxidation exploited the full potential of the wood flour for vanillin production. Further mechanical investigation with lignin model compounds suggested that the vanillin formation occurred mainly through following successive reactions: alkaline-catalyzed degradation of ß-ether linkages in middle units of lignin polymer to form a glycerol end group, oxidation of the glycerol end group by O2 to a HCα[double bond, length as m-dash]O moiety, and release of vanillin from the HCα[double bond, length as m-dash]O end. One of the reasons for the high performance of Bu4NOH for the vanillin production was explained by the general understanding in organic chemistry that Bu4OH is a stronger base than simple alkali, e.g. NaOH. The other more fundamental mechanical aspect was that Bu4N+ suppressed disproportionation of the vanillin precursor (the CαHO end group) probably due to strong interaction between the cation and the HCα[double bond, length as m-dash]O end group.

Degradation of the Cellulosic Key Chromophore 5,8-Dihydroxy-[1,4]-naphthoquinone by Hydrogen Peroxide under Alkaline Conditions.

5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores in cellulosic materials. Its almost ubiquitous presence in cellulosic materials makes it a target molecule of the pulp and paper industry's bleaching efforts. In the presented study, DHNQ was treated with hydrogen peroxide under alkaline conditions at pH 10, resembling the conditions of industrial hydrogen peroxide bleaching (P stage). The reaction mechanism, reaction intermediates, and final degradation products were analyzed by UV/vis, NMR, GC-MS, and EPR. The degradation reaction yielded C1-C4 carboxylic acids as the final products. Highly relevant for pulp bleaching are the findings on intermediates of the reaction, as two of them, 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) and 1,4,5,8-naphthalenetetrone, are potent chromophores themselves. While DHBQ is one of the three key cellulosic chromophores and its degradation by H2O2 is well-established, the second intermediate, 1,4,5,8-naphthalenetetrone, is reported for the first time in the context of cellulose discoloration.

Paleoseismic study of the Kamishiro Fault on the northern segment of the Itoigawa-Shizuoka Tectonic Line, Japan.

The Mw 6.2 (Mj 6.8) Nagano (Japan) earthquake of 22 November 2014 produced a 9.3-km long surface rupture zone with a thrust-dominated displacement of up to 1.5 m, which duplicated the pre-existing Kamishiro Fault along the Itoigawa-Shizuoka Tectonic Line (ISTL), the plate-boundary between the Eurasian and North American plates, northern Nagano Prefecture, central Japan. To characterize the activity of the seismogenic fault zone, we conducted a paleoseismic study of the Kamishiro Fault. Field investigations and trench excavations revealed that seven morphogenic paleohistorical earthquakes (E2-E8) prior to the 2014 Mw 6.2 Nagano earthquake (E1) have occurred on the Kamishiro Fault during the last ca. 6000 years. Three of these events (E2-E4) are well constrained and correspond to historical earthquakes occurring in the last ca. 1200 years. This suggests an average recurrence interval of ca. 300-400 years on the seismogenic fault of the 2014 Kamishiro earthquake in the past 1200 years. The most recent event prior to the 2014 earthquakes (E1) is E2 and the penultimate and antepenultimate faulting events are E3 and E4, respectively. The penultimate faulting event (E3) occurred during the period of AD 1800-1400 and is associated with the 1791 Mw 6.8 earthquake. The antepenultimate faulting event (E4) is inferred to have occurred during the period of ca. AD 1000-700, likely corresponding to the AD 841 Mw 6.5 earthquake. The oldest faulting event (E8) in the study area is thought to have occurred during the period of ca. 5600-6000 years. The throw rate during the early Holocene is estimated to be 1.2-3.3 mm/a (average, 2.2 mm/a) with an average amount of characteristic offset of 0.7-1.1 m produced by individual event. When compared with active intraplate faults on Honshu Island, Japan, these slip rates and recurrence interval estimated for morphogenic earthquakes on the Kamishiro Fault along the ISTL appear high and short, respectively. This indicates that present activity on this fault is closely related to seismic faulting along the plate boundary between the Eurasian and North American plates.

Regeneration of Aqueous Periodate Solutions by Ozone Treatment: A Sustainable Approach for Dialdehyde Cellulose Production.

A method for easy and fast regeneration of aqueous periodate solutions from dialdehyde cellulose (DAC) production by ozone treatment is presented, along with a direct and reliable simultaneous quantification of iodate and periodate by reversed-phase HPLC. The influence of iodate and ozone concentration, solution pH, and reaction time on the regeneration efficiency was studied, as well as the reaction kinetics. Regeneration of spent periodate solutions by ozone was successfully performed in alkaline medium, which favors the formation of free (.) OH radicals, as supported by the addition of radical scavengers and quantum mechanical calculations. At pH 13 and an ozone concentration of approximately 150 mg L(-1) , periodate was completely regenerated from a 100 mm solution of iodate within 1 h at room temperature. A cyclic process of cellulose oxidation and subsequent regeneration of spent periodate with 90 % efficiency has been developed. So far, commercial applications of DAC have been hampered by difficulties in reusing the costly periodate. This work overcomes this hurdle and presents a highly efficient, clean, and low-cost protocol for the preparation of DAC with integrated periodate recycling, with the possibility of scaling the process up.

Theoretical study on the effects of a 4,6-O-diacetal protecting group on the stability of ion pairs from D-mannopyranosyl and D-glucopyranosyl triflates.

Ion pair formation from 2,3-di-O-methyl-4,6-O-formylidene-α-D-mannopyranosyl triflate αTMan and its D-glucopyranosyl counterpart αTGlc was investigated at the DFT(M06-2X) level of theory, for the purpose of clarifying the effects of the 4,6-tethering on the structure and stability of α- and ß-contact ion pairs and solvent-separated ion pairs at -78 °C. In both mannopyranosyl and glucopyranosyl triflates, the 4,6-O-formylidene group destabilized (4)H3-type conformers of the α-contact ion pairs, rendering B2,5-types the exclusive conformers for this species. The B2,5-like α-contact ion pair from αTMan was 3.5 kcal/mol more stable than that from αTGlc, probably due to the stabilizing effect by the planar O-5-C-1-C-2-O-2 dihedral angle of the former. This difference in stability of the α-contact ion pair between the mannopyranosyl and glucopyranosyl series gives insights into the mechanisms underlying the reported experimental observation that highly ß-selective mannosylation can be achieved with 4,6-O-diacetal mannopyranosyl donors.

Contact ion pairs and solvent-separated ion pairs from D-mannopyranosyl and D-glucopyranosyl triflates.

The chemical nature of contact ion pairs and solvent-separated ion pairs from 2,3,4,6-tetra-O-methyl-α-D-mannopyranosyl triflate was investigated at the DFT(M06-2X) level of theory. Comparison of the present results to those obtained for the D-glucopyranosyl counterpart in our previous study indicated that the ion pairs from the D-mannopyranosyl triflate adopt B2,5-like conformations more preferably than those from the D-glucopyranosyl triflate. Similarly, 1,6-anhydro-D-mannopyranosyl dioxacarbenium ions bearing a (1)C4 conformation were shown to be more stable than the D-glucopyranosyl counterparts.

Theoretical foundation for the presence of oxacarbenium ions in chemical glycoside synthesis.

Glycoside formation in organic synthesis is believed to occur along a reaction path involving an activated glycosyl donor with a covalent bond between the glycosyl moiety and the leaving group, followed by formation of contact ion pairs with the glycosyl moiety loosely bound to the leaving group, and eventually solvent-separated ion pairs with the glycosyl moiety and the leaving group being separated by solvent molecules. However, these ion pairs have never been experimentally observed. This study investigates the formation of the ion pairs from a covalent intermediate, 2,3,4,6-tetra-O-methyl-α-d-glucopyranosyl triflate, by means of computational chemistry. Geometry optimization of the ion pairs without solvent molecules resulted in re-formation of the covalent α- and ß-triflates but was successful when four solvent (dichloromethane) molecules were taken into account. The DFT(M06-2X) computations indicated interconversion between the α- and ß-covalent intermediates via the α- and ß-contact ion pairs and the solvent-separated ion pairs. The calculated activation Gibbs energy of this interconversion was quite small (10.4-13.5 kcal/mol). Conformational analyses of the ion pairs indicated that the oxacarbenium ion adopts (4)H3, (2)H3/E3, (2)H3/(2)S0, E3, (2,5)B, and B2,5 pyranosyl ring conformations, with the stability of the conformers being strongly dependent on the relative location of the counteranion.

Levoglucosan formation from crystalline cellulose: importance of a hydrogen bonding network in the reaction.

Levoglucosan (1,6-anhydro-ß-D-glucopyranose) formation by the thermal degradation of native cellulose was investigated by MP4(SDQ)//DFT(B3LYP) and DFT(M06-2X)//DFT(B3LYP) level computations. The computational results of dimer models lead to the conclusion that the degradation occurs by a concerted mechanism similar to the degradation of methyl ß-D-glucoside reported in our previous study. One-chain models of glucose hexamer, in which the interchain hydrogen bonds of real cellulose crystals are absent, do not exhibit the correct reaction behavior of levoglucosan formation; for instance, the activation enthalpy (Ea =≈38 kcal mol(-1) ) is considerably underestimated compared to the experimental value (48-60 kcal mol(-1) ). This problem is solved with the use of two-chain models that contain interchain hydrogen bonds. The theoretical study of this model clearly shows that the degradation of the internal glucosyl residue leads to the formation of a levoglucosan precursor at the chain end and levoglucosan is selectively formed from this levoglucosan end. The calculated Ea (56-62 kcal mol(-1) ) agrees well with the experimental value. The computational results of three-chain models indicate that this degradation occurs selectively on the crystalline surface. All these computational results provide a comprehensive understanding of several experimental facts, the mechanisms of which have not yet been elucidated.

Degradation of 2,5-dihydroxy-1,4-benzoquinone by hydrogen peroxide under moderately alkaline conditions resembling pulp bleaching: a combined kinetic and computational study.

2,5-Dihydroxy-1,4-benzoquinone (DHBQ) is one of the key chromophores occurring in all types of aged cellulosics. This study investigates the mechanism of H2O2 degradation of DHBQ under conditions relevant to pulp bleaching (3.0% H2O2, NaOH, pH 10), to obtain insights useful for improved pulp processing. DHBQ is degraded quantitatively into malonic acid with an activation energy (E(a)) of 16.1 kcal/mol and activation entropy (Δ(‡)S°) of ~28 cal/mol·K. Higher concentrations of sodium cations increase the reaction rate. Theoretical computations indicate the formation of an intermediate I(O) having an O-O bridge between C-2 and C-5 of the 1,4-cyclohexadione structure. I(O) undergoes O-O homolysis to form a biradical Bt, which is fragmented into malonate anions. The calculated E(a) (17.8 kcal/mol) agrees well with the experimental one. Coordination of Na(+) to I(O) and Bt decreases their energies and enhances the O-O homolysis rate, which is consistent with the acceleration by sodium cation and the negative Δ(‡)S°. The homolysis of I(O) is much favored over that of the neutral counterpart, with the unpaired electrons of Bt being stabilized by the geminal anionic oxygen. This difference in the stability of the intermediates translates into significant variations in the reaction rate and the product distribution between pH 10 and neutral/acidic conditions.

Ammoxidation of lignocellulosic materials: formation of nonheterocyclic nitrogenous compounds from monosaccharides.

Ammoxidized technical lignins are valuable soil-improving materials that share many similarities with native terrestrial humic substances. In contrast to lignins, the chemical fate of carbohydrates as typical minor constituents of technical lignins during the ammoxidation processes has not been thoroughly investigated. Recently, we reported the formation of N-heterocyclic, ecotoxic compounds (OECD test 201) from both monosaccharides (D-glucose, D-xylose) and polysaccharides (cellulose, xylan) under ammoxidation conditions and showed that monosaccharides are a source more critical than polysaccharides in this respect. GC/MS-derivatization analysis of the crude product mixtures revealed that ammoxidation of carbohydrates which resembles the conditions encountered in nonenzymatical browning of foodstuff affords also a multitude of nonheterocyclic nitrogenous compounds such as aminosugars, glycosylamines, ammonium salts of aldonic, deoxyaldonic, oxalic and carbaminic acids, urea, acetamide, α-hydroxyamides, and even minor amounts of α-amino acids. D-glucose and D-xylose afforded largely similar product patterns which differed from each other only for those products that were formed under preservation of the chain integrity and stereoconfiguration of the respective monosaccharide. The kinetics and reaction pathways involved in the formation of the different classes of nitrogenous compounds under ammoxidation conditions are discussed.

Tocopheramines and tocotrienamines as antioxidants: ESR spectroscopy, rapid kinetics and DFT calculations.

Tocopheramines (TNH2) and tocotrienamines (T3NH2) are analogues of tocopherols (TOH) and tocotrienols in which phenolic OH is replaced by NH2. It was shown in previous studies that TNH2 and T3NH2 act as potent antioxidants. In this study we compared the one-electron oxidation of TNH2/T3NH2 by diphenyl picryl hydrazyl (DPPH) and galvinoxyl (GOX) radicals with the one of α-TOH as a reference compound using ESR spectroscopy, stopped flow spectrophotometry and density functional theory (DFT) calculations. ESR spectroscopy revealed the presence of tocopheramine radicals during electrochemical oxidation of α-TNH2. Kinetic measurements demonstrated that in apolar n-hexane TNH2/T3NH2 derivatives reacted two to three orders of magnitude slower than α-TOH with the model radicals. DFT calculations indicated that this correlates well with the higher bond dissociation energy (BDE) for N-H in TNH2 than for O-H in α-TOH in pure H-atom transfer (HAT). In the more polar medium ethanol TNH2/T3NH2 derivatives partially reacted faster than α-TOH depending on the reaction partner. DFT calculations suggest that this is due to reaction mechanisms alternative to HAT. According to thermochemistry data sequential proton loss and electron transfer (SPLET) is more favored for α-TOH in ethanol than for TNH2. Therefore, for TNH2 a contribution of the alternative mechanism of sequential electron transfer-proton transfer (SET-PT) could be a possible explanation. These data show that the antioxidant reactivity strongly depends on the structure, reaction partners and environment. According to these findings TNH2/T3NH2 should be superior as antioxidants over α-TOH in polar head group regions of membranes but not in the apolar core of lipid bilayers.

Preparation and physicochemical properties of surfactant-free emulsions using electrolytic-reduction ion water containing lithium magnesium sodium silicate.

Surfactant-free emulsions by adding jojoba oil, squalane, olive oil, or glyceryl trioctanoate (medium chain fatty acid triglycerides, MCT) to electrolytic-reduction ion water containing lithium magnesium sodium silicate (GE-100) were prepared, and their physiochemical properties (thixotropy, zeta potential, and mean particle diameter) were evaluated. At an oil concentration of 10%, the zeta potential was ‒22.3 ‒ ‒26.8 mV, showing no marked differences among the emulsions of various types of oil, but the mean particle diameters in the olive oil emulsion (327 nm) and MCT emulsion (295 nm) were smaller than those in the other oil emulsions (452-471 nm). In addition, measurement of the hysteresis loop area of each type of emulsion revealed extremely high thixotropy of the emulsion containing MCT at a low concentration and the olive emulsion. Based on these results, since surfactants and antiseptic agents markedly damage sensitive skin tissue such as that with atopic dermatitis, surfactant- and antiseptic-free emulsions are expected to be new bases for drugs for external use.

A 3D-RISM-SCF method with dual solvent boxes for a highly polarized system: application to 1,6-anhydrosugar formation reaction of phenyl α- and ß-D-glucosides under basic conditions.

One of the difficulties in application of the usual reference interaction site model self-consistent field (RISM-SCF) method to a highly polarized and bulky system arises from the approximate evaluation of electrostatic potential (ESP) with pure point charges. To improve this ESP evaluation, the ESP near a solute is directly calculated with a solute electronic wavefunction, that distant from a solute is approximately calculated with solute point charges, and they are connected with a switching function. To evaluate the fine solvation structure near the solute by incorporating the long-range solute-solvent Coulombic interaction with low computational cost, we introduced the dual solvent box protocol; one small box with the fine spacing is employed for the first and the second solvation shells and the other large box with the normal spacing is employed for long-range solute-solvent interaction. The levoglucosan formation from phenyl α- and ß-d-glucosides under basic conditions is successfully inspected by this 3D-RISM-SCF method at the MP2 and SCS-MP2 levels, though the 1D-RISM-SCF could not be applied to this reaction due to the presence of highly polarized and bulky species. This 3D-RISM-SCF calculation reproduces the experimentally reported higher reactivity of the ß-anomer. The 3D-RISM-SCF-calculated activation free energy for the ß-anomer is closer to the experimental value than the PCM-calculated one. Interestingly, the solvation effect increases the difference in reactivity between these two anomers. The reason is successfully elucidated with 3D-RISM-SCF-calculated microscopic solvation structure and decomposition analysis of solute-solvent interaction.

Degradation of 2,5-dihydroxy-1,4-benzoquinone by hydrogen peroxide: a combined kinetic and theoretical study.

2,5-Dihydroxy-1,4-benzoquinone (DHBQ) is one of the key chromophores formed upon aging in cellulosic materials. This study addresses the degradation mechanism of DHBQ by hydrogen peroxide to provide a solid knowledge base for optimization of bleaching sequences aiming at DHBQ removal. Kinetic analysis provided an activation energy (E(a)) of 20.4 kcal/mol. Product analyses indicated the product mixture to contain malonic acid, acetic acid, and carbon dioxide. DFT(B3LYP) computation presented a plausible mechanism for the formation of these products from DHBQ. DHBQ forms intermediate I2k, having an intramolecular O-O bridge between C-2 and C-5 of the 1,4-cyclohexadione structure. This O-O bond is homolytically cleaved, and the subsequent ß-fragmentation of the resulting radical forms ketene and oxaloacetic acid. While ketene yields acetic acid, oxaloacetic acid then gives malonic acid and carbon dioxide through further attack of hydrogen peroxide via an intermediate that is oxidatively decarboxylated. The calculated E(a) value (23.3 kcal/mol) in the rate-determining step, i.e., the homolysis of I2k, agreed well with the experimental value. There is also a minor pathway in which the spin state changes to triplet during the homolysis of I2k; in this way two malonyl radicals are formed that are converted to two molecules of malonic acid.

Theoretical study of 1,6-anhydrosugar formation from phenyl D-glucosides under basic condition: reasons for higher reactivity of ß-anomer.

Degradation of anomeric phenyl d-glucosides to levoglucosan under basic condition is theoretically studied. MP4(SDQ)//DFT(B3LYP)-computational results indicate that the degradation of phenyl α-glucoside (R(α)) occurs via the S(N)icB mechanism. In this mechanism, the oxyanion at the C6, which is formed through deprotonation of the OH group, directly attacks the anomeric carbon. On the other hand, the degradation of phenyl ß-glucoside (R(ß)) occurs via the S(N)icB(2) mechanism. In this mechanism, the oxyanion at the C2 attacks the anomeric carbon in a nucleophilic manner to afford 1,2-anhydride intermediate and then the oxyanion at the C6 attacks the anomeric carbon to afford levoglucosan. The activation barrier is much lower in the reaction of R(ß) (ΔG(0++) = 25.6 kcal/mol and E(a) = 26.5 kcal/mol) than in the reaction of R(α) (ΔG(0++) = 38.1 kcal/mol and E(a) = 37.2 kcal/mol), which is consistent with the experimental observation that ß-glucoside is generally much more reactive than the corresponding α-glucoside. The lower activation barrier of the reaction of R(ß) arises from the stereoelectronic effect, which is induced by the charge transfer from the ring oxygen to the anomeric carbon, and the staggered conformation around the C1-C2 bond. When the stereoelectronic effect is absent, the degradation needs larger activation energy; for instance, the degradation of phenyl 5a-carba-ß-d-glucoside (R(Cß)) occurs with large ΔG(0++) and E(a) values like those of α-glucosides, because the methylene group of R(Cß) does not contribute to the stereoelectronic effect. Also, the conformation around the C1-C2 bond is staggered in the transition state of the R(ß) reaction but eclipsed in that of the R(α) reaction, which also leads to the larger reactivity of R(ß).

Thermal degradation of methyl beta-D-glucoside. a theoretical study of plausible reaction mechanisms.

Thermal conversion of methyl beta-d-glucoside to levoglucosan was studied with the MP4//DFT(B3LYP) method. The first step is conformational change of the reactant to (1)C(4) from (4)C(1). The second step is intramolecular nucleophilic substitution at the anomeric C1, which occurs via one step without oxacarbenium ion intermediate. The DeltaG(0)() value (52.5 kcal/mol) is smaller than the C1-O1 bond energy, indicating the direct homolysis mechanism is clearly ruled out. Bimolecular reaction also occurs with smaller activation energy via the similar transition state.