Article

Standard molar enthalpies of formation for crystalline vanillic acid, methyl vanillate and acetovanillone by bomb calorimetry method

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Abstract

The massic energies of combustion for three crystalline monosubstituted guaiacols such as vanillic acid, methyl vanillate and acetovanillone were determined by using bomb calorimeter method and were found to be − (21,070.3 ± 8.6), − (23,352.3 ± 7.4) and − (26,732.2 ± 5.2) J g⁻¹, respectively. The standard molar enthalpy of combustion and standard molar enthalpy of formation in the crystalline state at 298.15 K were calculated. They are − (3542.9 ± 1.5) and − (748.5 ± 1.8) kJ mol⁻¹ for vanillic acid, − (4255.4 ± 1.7) and − (715.3 ± 2.1) kJ mol⁻¹ for methyl vanillate, − (4444.7 ± 0.9) and − (526.1 ± 1.5) kJ mol⁻¹ for acetovanillone, respectively. The basic contribution in a value of standard molar enthalpy of formation for oxygen-containing aromatic compounds provides the replacement of the hydrogen atom in the benzene ring to the oxygen-containing group. The calculation of these contributions gives the following values for the crystalline state at 298.15 K for substituents CHO − (150 ± 6), COCH3 − (201 ± 4), COOCH3 − (392 ± 6) and COOH − (428 ± 4) kJ mol⁻¹. The differences in contributions for crystalline and gaseous states were estimated for groups CHO, COOCH3, COCH3 − (26 ± 3) kJ mol⁻¹ in monosubstitute benzene derivatives, 4-substituted anisoles and guaiacols, − (35 ± 4) kJ mol⁻¹ in 4-substituted phenols and for group COOH − (50 ± 3) kJ mol⁻¹ in all abovementioned groups of compounds. More higher differences in contributions found for 4-substituted phenols and benzenecarboxylic acids are attributed to the hydrogen bonds formation in crystalline state of these derivatives.

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Article
Cisplatin induced nephrotoxicity is primarily caused by ROS (Reactive Oxygen Species) induced proximal tubular cell death . NADPH oxidase is major source of ROS production by cisplatin. Here, we reported that pharmacological inhibition of NADPH oxidase by acetovanillone (obtained from medicinal herb Picrorhiza kurroa) led to reduced cisplatin nephrotoxicity in mice. In this study we used various molecular biology and biochemistry methods a clinically relevant model of nephropathy, induced by an important chemotherapeutic drug cisplatin. Cisplatin-induced nephrotoxicity was evident by histological damage from loss of the tubular structure. The damage was also marked by the increase in blood urea nitrogen, creatinine, protein nitration as well as cell death markers such as caspase 3/7 activity and DNA fragmentation. Tubular cell death by cisplatin led to pro-inflammatory response by production of TNFα and IL1β followed by leukocyte/neutrophil infiltration which resulted in new wave of ROS involving more NADPH oxidases. Cisplatin-induced markers of kidney damage such as oxidative stress, cell death, inflammatory cytokine production and nephrotoxicity were attenuated by acetovanillone. In addition to that, acetovanillone enhanced cancer cell killing efficacy of cisplatin CONCLUSION: Thus, pharmacological inhibition of NADPH oxidase can be protective for cisplatin-induced nephrotoxicity in mice. Copyright © 2015. Published by Elsevier Ltd.
Article
Molar sublimation enthalpies of the methyl- and methoxybenzoic acids were derived from the transpiration method, static method, and TGA. Thermochemical data available in the literature were collected, evaluated, and combined with own experimental results. This collection together with the new experimental results reported here has helped to resolve contradictions in the available enthalpy data and to recommend sets of sublimation and formation enthalpies for the benzoic acid derivatives. Gas-phase enthalpies of formation calculated with the G4 quantum-chemical method were in agreement with the experiment. Pairwise interactions of the methyl, methoxy, and carboxyl substituents on the benzene ring were derived and used for the development of simple group-additivity procedures for estimation of the vaporization enthalpies, gas-phase, and liquid-phase enthalpies of formation of substituted benzenes.
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Lignin is a carbon-rich renewable source owning aromatic structure units, which is an important constituent in biomass. Hydrothermal conversion of lignin is widely studied as a promising method to produce not only bioenergy but also value-added useful chemicals. Fuel gas, aromatic aldehydes and phenolic products can be obtained from lignin hydrothermal gasification, wet oxidation and hydrothermal liquefaction, respectively. This article discusses and compares the three methods of lignin hydrothermal conversion, including their process parameters, possible conversion routes, catalysts, application of products. Effects of hot-compressed organic solvent-water mixture solution on conversion of lignin and effects of lignin in biomass hydrothermal conversion are commented. Wet oxidation of lignin is an efficient mean of recovering value-added aromatic aldehydes, especially vanillin. Hydrothermal liquefaction of lignin is a promising way of recovering phenolics-rich bio-oils. Both aromatic aldehyde and phenolic compound are important chemical intermediates. There are strict requirements of process conditions and relative high costs to get fuel gas from direct hydrothermal gasification of lignin. However, further studies on improving gasification of lignin seem necessary in order to get fuel gas from hydrothermal gasification of the whole biomass.
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Systematic and thorough investigation of the structure and antioxidant properties of different technical lignins, high molecular polyphenols of natural origin, which are formed in large amounts as by-product of pulp-and-paper industry and other lignocellulosics chemical processing, was made. Py-GC/MS was the main method used to quantitatively determine the structural descriptors needed for rationalization of lignin antioxidant activity. Size-exclusion chromatography (SEC), electron paramagnetic resonance (EPR) spectroscopy and wet chemistry tests were also used as complementary methods. Antioxidant properties of lignin samples under study were evaluated as their capacity to scavenge the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. The use of Py-GC/MS in combination with some other experimental and chemometric methods allowed for the first time quantitatively characterize lignin structure-antioxidant activity relationship, which can significantly favor the rational use of lignin.
Chapter
The inevitability of transition toward a biobased economy is fueled by the problems related to fossil fuel utilization such as climate change due to greenhouse gas emissions. Lignin is a renewable feedstock that can be used to produce hydrocarbons in a sustainable manner. Lignin is obtained as a by-product of several conversion processes when it is isolated from the lignocellulosic biomass matrix. It is the major fraction that contributes to the organic hydrocarbons such as aromatics, phenolics, and platform chemicals that are presently produced from fossil resources. Lignin exhibits different physicochemical characteristics depending on the isolation process used. Lignin, over the years, has been converted to various value-added hydrocarbons (bioenergy, biofuels, biochemicals, and petrochemical feedstocks) using several thermochemical methods of conversion such as pyrolysis, gasification, and liquefaction. Challenges in the valorization of lignin include understanding the effect of source on the lignin structure, development of novel catalysts for conversion, increased selectivity and yield from processes, and effective separation processes.
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Our severe dependence on fossil resources for the production of fuels and chemicals is responsible for two major global challenges: declining the fuel supply and increasing the anthropogenic greenhouse gas emissions. Conversion of biomass to fuels and chemicals can be a part of the low-carbon solution to both issues. Among various biomass species, inedible biomass such as lignocellulosics is the preferred choice for such applications due to their minimal impact on the food security. While technologies for the conversion of carbohydrates to value-added materials such as pulp, sugar monomers, and ethanol are well-established, lignin upgrading and valorization processes are significantly less-developed, and technical lignins are almost entirely burnt to generate heat and steam. The economic viability of biorefineries - which will receive significant amounts of lignin in future - can potentially improve significantly when advanced technologies are available that aid the conversion of lignin to value-added compounds. In this paper we assess how thermochemical processes can be used to isolate lignin from the lignocellulosic biomass, and subsequently convert it to liquid fuels, hydrogen, and aromatic monomers. To this end, different depolymerization, gasification and upgrading technologies for lignin conversion will be considered. Finally, the foreseeable applications of lignin-based products, the future directions for development, and the potential supportive interventions from policy makers are critically assessed.
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A group contribution method is used to predict the standard net heat of combustion of pure hydrocarbons from their molecular structures. A multivariable nonlinear regression based on the least square method was used to arrive at a set of 32 atom-type structural groups that can best represent the standard net heat of combustion for about 452 pure hydrocarbon substances. The proposed method is very simple, requires no experimental data, and can predict the standard net heat of combustion from the knowledge of the molecular structure alone with an average absolute error of 0.71% and a correlation coefficient of 0.9982. The method can predict the standard net heat of combustion of hydrocarbon isomers as well.
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Cisplatin is one of the extensively used anticancer drugs against various cancers. Dosage dependent nephrotoxicity is the major problem in cisplatin chemotherapy. Cisplatin induced nephrotoxicity results in the depletion of renal antioxidant defence system. Our present study is aimed to investigate the nephroprotective effect of vanilic acid to against cisplatin induced nephrotoxicity in male wistar rats. Elevated levels of serum creatinine, blood urea nitrogen, serum uric acid and reduced antioxidant status were observed as indicatives of nephrotoxicity in cisplatin (7 mg/kg bw) alone administered rats. Animals which are pre-treated with vanillic acid (50 mg/kg and 100 mg/kg) restored the elevated levels of renal function markers and reduced antioxidant status to near normalcy when compared to cisplatin alone treated animals. Cisplatin induced lipid peroxidation was markedly reduced by oral administration of vanillic acid at a high dose. The findings in the present study suggest that vanillic acid is a potential antioxidant that reduce cisplatin nephrotoxicity and can be as a combinatorial regimen in cancer chemotherapy.
Article
The present work is dedicated to investigate the effect of pyrolysis temperature on the products distribution and the yield of monophenols producing from lignin fast pyrolysis. The bio-oils obtained at different pyrolysis temperatures were first qualitatively identified and then quantified by using external standards with mainly focus on the major monophenols. The results showed that the yield and identity of the phenolic products were strongly correlated to the pyrolysis temperature as well as the chemical structure and thermochemical properties of lignin. The highest yield of bio-oil (54.17%) was obtained at a pyrolysis temperature of 600 °C. The major individual monophenols were phenol, p-methylguaiacol, p-ethylphenol, and vanillin etc., and their associated yields (mg monophenol/g lignin) determined from the optimal pyrolysis conditions were 28.47 mg g−1, 24.84 mg g−1, 20.42 mg g−1, and 15.01 mg g−1, respectively.
Article
Significant discrepancies in the literature data for the enthalpy of formation of gaseous anisole, ΔfHº(PhOCH3, g), have fueled an ongoing controversy regarding the most reliable enthalpy of formation of the phenoxy radical and of the gas phase O-H bond dissociation enthalpy, DHº(PhO-H), in phenol. In the present work ΔfHº(PhOCH3, g) was reassessed using a combination of calorimetric determinations and high-level (W2-F12 ) ab initio calculations. Static-bomb combustion calorimetry led to the standard molar enthalpy of formation of liquid anisole at 298.15 K, ΔfHº(PhOCH3, l) = -(117.1±1.4) kJ.mol-1. The corresponding enthalpy of vaporization was obtained as, ΔvapHº(PhOCH3, g)= (46.41±0.26) kJ.mol-1, by Calvet-drop microcalorimetry. These results give ΔfHº(PhOCH3, g)= -(70.7±1.4) kJ.mol-1, in excellent agreement with ΔfHº(PhOCH3, g)= -(70.8±3.2) kJ.mol-1, obtained from the W2-F12 calculations. The ΔfHº(PhOCH3, g) here recommended leads to ΔfHº(PhO•, g) = 55.5±2.4 kJ.mol-1 and DHº(PhO-H) = 368.1±2.6 kJ.mol-1.
Article
An empirical study of the solubility of pharmaceuticals in supercritical carbon dioxide has been performed by using a modified enhancement factor and a group contribution method. According to the results, polar solids with similar sublimation enthalpies, and at similar experimental conditions, show similar solubility in terms of the proposed modified enhancement factor. Several equations to estimate that modified enhancement factor (depending on the experimental conditions and the sublimation enthalpies) with a deviation less than 5% have been determined. These equations can be used as a tool to identify if experimental data follow the common solubility tendency. However, they cannot be used with other type of solids, such as inorganic compounds.
Article
The vapor pressures of crystalline and liquid phases of methyl p-hydroxybenzoate and of methyl p-methoxybenzoate were measured over the temperature ranges (338.9 to 423.7) K and (292.0 to 355.7) K respectively, using a static method based on diaphragm capacitance gauges. The vapor pressures of the crystalline phase of the former compound were also measured in the temperature range (323.1 to 345.2) K using a Knudsen mass-loss effusion technique. The results enabled the determination of the standard molar enthalpies, entropies and Gibbs free energies of sublimation and of vaporization, at T = 298.15 K, as well as phase diagram representations of the (p, T) experimental data, including the triple point. The temperatures and molar enthalpies of fusion of both compounds were determined using differential scanning calorimetry and were compared with the results indirectly derived from the vapor pressure measurements. The standard (p degrees = 10(5) Pa) molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, of the compounds studied were derived from their standard massic energies of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpies of formation, in the gaseous phase at T = 298.15 K, were calculated and compared with the values estimated by employing quantum chemical computational calculations. A good agreement between experimental and theoretical results is observed. To analyze the thermodynamic stability of the two compounds studied, the standard Gibbs free energies of formation in crystalline and gaseous phases were undertaken. The standard molar enthalpies of formation of the title compounds were also estimated from two different computational approaches using density functional theory-based B3LYP and the multilevel G3 methodologies.
Article
Values of the standard (po = 0.1 MPa) molar enthalpy of formation of 2’-, 3’- and 4’-methoxyacetophenones were derived from their standard molar energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of sublimation/vaporization of the compounds studied. The standard molar enthalpies of formation of the three compounds, in the gaseous phase, at T = 298.15 K, have been derived from the corresponding standard molar enthalpies of formation in the condensed phase and the standard molar enthalpies for the phase transition. The results obtained are −(232.0 ± 2.5) kJ·mol-1, −(237.7 ± 2.7) kJcmol-1 and −(241.1 ± 2.1) kJ·mol-1 for 2’-, 3’- and 4’-methoxyacetophenone, respectively. Standard molar enthalpies of formation were also estimated from different methodologies: the Cox scheme as well as two different computational approaches using density functional theory-based B3LYP and the multilevel G3 methodologies.
Article
Comparing to the case without alkaline additive, the addition of 20 wt.% hydroxide or carbonate greatly varied the production of major phenolic chemicals. Because the liquid yield only slightly decreased by the additives, the content in the produced tar represents also the total production rates of all the plotted chemicals. In general, the use of alkaline additives resulted in higher production of phenols. The carbonates obviously promoted the production of methoxy-phenols, while the hydroxides greatly increased the alkyl-phenol production. All the tested additives reduced the production of vanillin. At the same additive amount, the sodium alkalis exhibited the higher effect than the potassium alkalis because the former had actually more moles due to its lower molecular weight.
Article
A new group-contribution approach involving systematic corrections for 1,4-non-bonded carbon-carbon and carbon-oxygen interactions has been proposed. Limits of the applicability of the method, associated with the highly branched structures, were established. Experimental data for enthalpies of formation in the liquid phase, enthalpies of vaporization, and enthalpies of formation in the gas phase for alkanes, alkenes, alkynes, alkylbenzenes, alkanols, ethers, ketones and aldehydes, carboxylic acids, esters, and carbonates were collected and critically evaluated through dynamic data evaluation as implemented in the NIST ThermoData Engine. An automatic procedure for molecular structure “decomposition” was developed, and algorithms for the assessment of expanded uncertainties for the predicted property values were implemented. The combination of these software tools allows for ongoing improvements of the group-contribution parameter set as new experimental data become available. Fifty-two group-contribution parameters and their variances were evaluated for the proposed schema. Based on comparison of critically evaluated and predicted data for all classes of compounds studied, the performance of the new group formulation and associated parameters is superior to that originally suggested by Benson and the update by Cohen without an increase in the number of required parameters.
Article
An estimation method, which was developed by S. W. Benson and coworkers for calculating the thermodynamic properties of organic compounds in the gas phase, has been extended to the liquid and solid phases for organic compounds at 298.15 K and 101,325 Pa. As with a previous paper dealing with hydrocarbon compounds, comparisons of estimated enthalpies of formation, heat capacities, and entropies with literature values show that extension of the Benson’s group additivity approach to the condensed phase is easy to apply and gives satisfactory agreement. Corresponding values for the entropy of formation, Gibbs energy of formation and natural logarithm of the equilibrium constant for the formation reaction are also calculated provided necessary auxiliary data are available. This work covers 1512 compounds containing the elements: carbon, hydrogen, oxygen, nitrogen, sulfur, and halogens in the gas, liquid, and solid phases. About 1000 references are provided for the literature values which are cited. §
Article
Molar enthalpies of sublimation of 1,2-di-hydroxybenzene, 1,3-di-hydroxybenzene, and 1,4-di-hydroxybenzene were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The molar enthalpies of fusion of 1,2- and 1,4-isomers were measured by differential scanning calorimetry (DSC). A large number of the primary experimental results on the temperature dependences of vapor pressure and phase transitions have been collected from the literature and have been treated in a uniform manner in order to derive sublimation, vaporization and fusion enthalpies of di-hydroxybenzenes at the reference temperature 298.15 K. The data sets on phase transitions were checked for internal consistency. This collection together with the new experimental results reported here has helped to resolve contradictions in the available thermochemical data and to recommend consistent and reliable sublimation, vaporization and fusion enthalpies for all three isomers under study.
Article
The heat capacities between T = 5 K andT = 320 K and the enthalpies of phase transitions of methyl benzoate, methyl o -toluate, methyl m -toluate, and methyl p -toluate in the condensed state were measured in a vacuum adiabatic calorimeter. It was found that liquid methyl m -toluate supercooled by cooling it from T = 300 K at a rate of 0.02 K · s − 1to 0.03 K · s − 1, formed a glass. The crystalline phase of methyl m -toluate was obtained and the residual entropy of the glass at T → 0 was evaluated. Methyl o -toluate had two solid-to-solid transitions before fusion. Thermodynamic parameters of fusion for the compounds and solid-to-solid transitions for methyl o -toluate were determined and the molar thermodynamic functions in the condensed state were derived for the methyl esters under study. The enthalpy of formation of holes in liquid methyl m -toluate at the glass transition temperature was estimated on the basis of the heat capacity jump at the glass transition and the enthalpy of vaporization. The temperature dependencies of the configurational entropy and the number of molecules in a cooperative domain according to the Adam–Gibbs theory were evaluated for liquid methyl m -toluate. The residual entropy of the glassy methyl m -toluate was shown to be mainly caused by the orientational disorder of domains.
Article
(Solid + liquid) phase equilibria for N,N-dimethylacetamide + tetrachloromethane) have been obtained from time-against-temperature warming curves. Standard enthalpies of melting of three pure components and standard molar enthalpies of formation of 14 solid intermolecular compounds have been calculated from the corresponding (solid + liquid) equilibria reported in this paper and from previous results obtained in our laboratory.
Article
The standard (po = 101.325 kPa) molar enthalpies of combustion in oxygen at 298.15 K were measured by static-bomb calorimetry and the standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry for each of the three trihydroxybenzenes, 3-methoxycatechol, and 4-nitrocatechol: View Within ArticleThe derived standard molar enthalpies of formation of the gaseous compounds were compared with values estimated assuming that each group, when substituted into the benzene ring, produces a characteristic increment in the enthalpy of formation, with additional corrections for adjacent substituents.