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Standard molar enthalpies of formation for crystalline vanillic acid, methyl vanillate and acetovanillone by bomb calorimetry method
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.
... β-D-idoseptanose C6H12O6 oxepane-2(S),3(R),4(S),5(R),6(S)-pentaol 41847-28-3 13 C NMR studies showed that aqueous D-idose (I) at 37°C contains 1.6% of a septanose anomer in addn. to the furanose and pyranose anomers. ...
In this paper, we continue to review the phonetic similarity of trivial names of chemical substances and the names of the elements in the periodic table. Thermochemical properties are explicitly considered. We review elements from potassium (K) through xenon (Xe) (Z = 19 to 54).
... A comparison of the value of ε calor of some combustion calorimeters found in the literature was made (see table 4 [36][37][38][39][40][41][42][43][44][45][46][47][48]). This scheme shows heat capacities for traditional combustion calorimeters and some with semi-micro combustion bombs. ...
... III. Vanillic Acid: (Fig. 5) Name: Vanillic acid Class: Polyphenols Chemical name: 4-Hydroxy-3-methoxybenzoic acid [86]. Structural chemistry: The ester and hydroxyl groups present and their position affects the antioxidant capacity in the body [87]. ...
... III. Vanillic Acid: (Fig. 5) Name: Vanillic acid Class: Polyphenols Chemical name: 4-Hydroxy-3-methoxybenzoic acid [86]. Structural chemistry: The ester and hydroxyl groups present and their position affects the antioxidant capacity in the body [87]. ...
... III. Vanillic Acid: (Fig. 5) Name: Vanillic acid Class: Polyphenols Chemical name: 4-Hydroxy-3-methoxybenzoic acid [86]. Structural chemistry: The ester and hydroxyl groups present and their position affects the antioxidant capacity in the body [87]. ...
... Lamprecht [2] states that combustion calorimeters are widely used in almost all fields of human activity. Combustion calorimetry is also irreplaceable in waste management and the food and feed industry, but is also one of the important scientific research methods for basic research in the area of natural sciences [3][4][5][6][7]. Hansen et al. [8] states that calorimetry can be used to develop models for biological growth. ...
Combustion calorimetry is one of the methodological possibilities in biological science disciplines. Using calorimetry, interspecies and interorgan organ differences in the rate of primary and secondary metabolism can be determined. Generally, the lower energy content is usually that of vegetative organs in comparison with the generative organs, whereas stems or leaves have a similar composition of organic matter and a relatively high proportion of ash matter; therefore, their calorific content fluctuates less than in the reproductive organs. The said effect is mainly due to solar energy plant leaves, as the calorific value reflects the utilization of sunlight, water and other natural sources of plants. Most commonly reported values of solar radiation utilization in the field crops range from 1 to 2.5%, but the natural reed vegetation in central Europe during the vegetation utilizes solar radiation from 4 to 7%. The combustion calorimetry method is therefore a suitable method for monitoring the development and stability of natural but also agroforestry ecosystems.
... Lamprecht [2] states that combustion calorimeters are widely used in almost all fields of human activity. Combustion calorimetry is also irreplaceable in waste management and the food and feed industry, but is also one of the important scientific research methods for basic research in the area of natural sciences [3][4][5][6][7]. Hansen et al. [8] states that calorimetry can be used to develop models for biological growth. ...
Combustion calorimetry is one of the methodological possibilities in biological science disciplines. Using calorimetry, interspecies and interorgan organ differences in the rate of primary and secondary metabolism can be determined. Generally, the lower energy content is usually that of vegetative organs in comparison with the generative organs, whereas stems or leaves have a similar composition of organic matter and a relatively high proportion of ash matter; therefore, their calorific content fluctuates less than in the reproductive organs. The said effect is mainly due to solar energy plant leaves, as the calorific value reflects the utilization of sunlight, water and other natural sources of plants. Most commonly reported values of solar radiation utilization in the field crops range from 1 to 2.5%, but the natural reed vegetation in central Europe during the vegetation utilizes solar radiation from 4 to 7%. The combustion calorimetry method is therefore a suitable method for monitoring the development and stability of natural but also agroforestry ecosystems.
... A comparison of the value of ε calor of some combustion calorimeters found in the literature was made (see table 4 [36][37][38][39][40][41][42][43][44][45][46][47][48]). This scheme shows heat capacities for traditional combustion calorimeters and some with semi-micro combustion bombs. ...
The enthalpy of formation can be determined indirectly with different calorimetric techniques; one of the most used is combustion calorimetry. During a combustion process, there are multiple energy variables that can significantly influence the overall result of the measurement. One of these variables is the energy exchange that exists between the calorimeter and the surroundings. To reduce this energy contribution and obtain more precise measurements of combustion energies of compounds containing the elements C, H, O and N, a combustion calorimeter in isoperibolic operation was designed, constructed and calibrated. The measurements made with this instrument show good precision; the results obtained for internal energy and the combustion enthalpy of succinic acid (solid sample) and for glycidol, glycidyl isopropyl ether, glycidyl butyrate and glycidyl methacrylate (liquid samples) are presented. The error percentage for the -calor of the calorimetric system proposed was compared with a commercial calorimeter and published results in the literature.
For effective and reliable ignition of ammonium perchlorate and hydroxyl-terminated polybutadiene (AP/HTPB) solid composite propellant base bleed (BB) grain a simple, reproducible and high-energy igniter composition were studied. Zirconium and potassium perchlorate (ZPP)-based compositions were developed with and without nitrocellulose (NC) lacquer as binder. The effects of different ratios of Zr/KClO4 were investigated by using fuse wire technique for burning rates, bomb calorimeter for calorific value and high-pressure closed vessel (CV) for pressure–time (P–t) curve, pressure maximum (Pmax), time to reach Pmax (tPmax), and rate of change of pressure change (dP/dt). It was observed that composition K-8 with fuel, oxidizer, and binder ratio of 1:1:0.02 gave reliable burning rate, calorific value, Pmax, and dP/dt. After careful analysis of combustion performance, composition K-8 was further investigated for burning rate and P–t data after 10 h of temperature conditioning at − 40 °C, + 21 °C and + 50 °C, respectively. Selected composition was then press-filled in specially designed steel igniter cups which were press-fitted in base bleed kit igniter bodies. Several static firings were performed by initiating igniter with electric squib for recording the burning time, igniter mass burning behavior, and reproducibility of successful ignition results. ZPP igniter was finally fitted in base bleed kit equipped with AP/HTPB composite propellant BB grain and tested on static as well as dynamic level by firing with 155-mm artillery projectile. Dynamic testing after temperature conditioning of complete projectile equipped with BB kit at + 21 °C, + 50 °C and − 40 °C for 24 h. Igniter provided successful ignition to base bleed grain until it achieved stable burning. All fired rounds achieved enhanced range of 30% approximately, with controlled uniform muzzle velocity and chamber pressure. ZPP igniter is recommended to be used for AP/HTPB solid composite propellant base bleed grain.
A properties model was developed for use in commercial process simulators to model pyrolysis of lignocellulosic biomass. The component list was chosen to enable process simulations based on a recently published lumped pyrolysis kinetics model. Since many of the compounds involved in pyrolysis are not found in simulator databanks, estimation based on available literature data was used to establish missing parameters. Standard solid enthalpy of formation, solid heat capacity, and solid density estimates calculated from the limited experimental data available were prepared for six biomass constituents and nine intermediate and end products of their pyrolysis. Ideal gas enthalpy of formation and heat capacity, critical property, and vapor pressure estimates were prepared for another four pyrolysis end-products and one biomass component. The estimates were all validated against the closest available experimental data in the literature. Addition of these new components and properties allows thermodynamically rigorous simulation of lumped biomass pyrolysis reactions with accurate energy balances. Enthalpies of reaction calculated from the properties model were compared with reported reaction enthalpies for the same lumped biomass pyrolysis reactions and found to be in general agreement.
Ligustrazine-vanillic acid derivatives had been reported to exhibit promising neuroprotective activities. In our continuous effort to develop new ligustrazine derivatives with neuroprotective effects, we attempted the synthesis of several ligustrazine-vanillic acid amide derivatives and screened their protective effect on the injured PC12 cells damaged by CoCl2. The results showed that most of the newly synthesized derivatives exhibited higher activity than ligustrazine, of which, compound VA-06 displayed the highest potency with EC50 values of 17.39 ± 1.34 μM. Structure-activity relationships were briefly discussed.Open image in new windowGraphical abstractNew series of ligustrazine-vanillic acid amide derivatives were synthesized and evaluated for their protective effect on the injured PC12 cells damaged by CoCl2. VA-06 was found to be the most active one
As the most abundant source of renewable aromatic compounds on the planet, lignin is gaining growing interest in replacing petroleum-based chemicals and products. Value-added applications of lignin are also essential for economic viability for future bio-refineries. It is however an under-utilized natural resource due to its structural heterogeneities. Lignin nanoparticles offer many opportunities for value-added applications of lignin. The solution structures of lignin were proposed as one of the key elements in controlling lignin nano-/micro-particle preparation. Fundamental understanding of solution structures of lignin aid in designing better fabrication of lignin nanoparticles. A deeper understanding of the observed experimental results also points to the need for detailed studies of lignin in solution. This review consists of two major topics, the solution structures of lignin and lignin nano-/micro-particle preparation. Suggestions for future studies regarding these two topics were also put forward.
As the attraction of creating biofuels and bio-based chemicals from lignocellulosic biomass has increased, researchers have been challenged with developing a better understanding of lignin structure, quantity and potential uses. Lignin has frequently been considered a waste-product from the deconstruction of plant cell walls, in attempts to isolate polysaccharides that can be hydrolyzed and fermented into fuel or other valuable commodities. In order to develop useful applications for lignin, accurate analytical instrumentation and methodologies are required to qualitatively and quantitatively assess, for example, what the structure of lignin looks like or how much lignin comprises a specific feedstock׳s cellular composition. During the past decade, various diverse strategies have been employed to elucidate the structure and composition of lignin. These techniques include using two-dimensional nuclear magnetic resonance to resolve overlapping spectral data, measuring biomass with vibrational spectroscopy to enable modeling of lignin content or monomeric ratios, methods to probe and quantify the linkages between lignin and polysaccharides, or refinements of established methods to provide higher throughput analyses, less use of consumables, etc. This review seeks to provide a comprehensive overview of many of the advancements achieved in evaluating key lignin attributes. Emphasis is placed on research endeavored in the last decade.
Context:
Vanillic acid (VA), a flavoring agent used in food and drug products, obtained naturally from the plant Angelica sinensis (Oliv.) Diels (Apiaceae), used in the traditional Chinese medicine. It is reported to possess strong antioxidant, anti-inflammatory, and neuroprotective effects. However, the pharmacological effects on oxidative stress-induced neurodegeneration are not well investigated.
Objective:
This study investigates the neuroprotective effect of VA on streptozotocin (STZ)-induced neurodegeneration in mice through behavioral and biochemical parameters.
Materials and methods:
The behavioral effects were determined using the Y-maze and open-field habituation memory. In biochemical parameters, acetylcholinesterase (AChE), corticosterone, tumor necrosis factor (TNF)-α, and antioxidants (superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase) were measured. Five groups of animals used were of control, negative control, and three separate groups treated with 25, 50, and 100 mg/kg of VA, respectively, for 28 d. Intracerebroventricular (ICV) injections of STZ were performed for all groups except control on 14th and 16th of 28 d of VA treatment.
Results:
VA improved spatial learning and memory retention by preventing oxidative stress compared with control animals. VA at 50 and 100 mg/kg dose significantly (p < 0.001) improved the habituation memory, decreased the AChE, corticosterone, TNF-α, and increased the antioxidants (p < 0.001). VA (100 mg/kg) exhibited dose-dependent effect in all parameters with p < 0.001 except antioxidants in which VA showed the significance of p < 0.01.
Discussion and conclusion:
VA exhibited reduction in AChE, TNF-α, and corticosterone with improved antioxidants to contribute neuroprotection and could be an effective therapeutic agent for treating neurodegenerative disorders.
Lignin can be converted into value-added products that could significantly improve the economics of a biorefinery. The polymeric lignin can be converted into low molecular weight and monomeric aromatic forms that serve as the building block for chemical syntheses of high-value products. This chapter presents the utilization of lignin to derive value-added products and their applications.
Specific energy of combustion of vanillin was determined using the bomb calorimeter BIC 100 with high degree of thermal protection from environment impact. The standard deviation of mean for energy equivalent was 0.01%. Based on the specific energy of combustion −(25,072.1 ± 7.4) J g⁻¹, the standard molar enthalpy of combustion and standard molar enthalpy of formation for vanillin in the crystalline state at 298.15 K were calculated to be −(3815.9 ± 1.1) and −(475.5 ± 1.5) kJ mol⁻¹, respectively. Standard molar enthalpy of formation of vanillin in the gaseous state was determined to be −(375.8 ± 2.1) kJ mol⁻¹ from ab initio calculations using density functional theory and G3 methods. The enthalpy of sublimation of vanillin at 298.15 K, determined as difference between standard molar enthalpies of formation of vanillin in crystalline and gaseous states, was found to be 100 ± 3 kJ mol⁻¹.
Vanillic acid grafted chitosan (Va-g-Ch) was evaluated as a new antioxidant wall material for
microencapsulation of polyunsaturated fatty acid rich sardine oil. A high grafting ratio of 305
mg vanillic acid equivalent/g of polymer was achieved using a free radical mediated grafting
reaction. Oil in water emulsion was prepared with an optimised combination of Va-g-Ch and
Tween 20 (3.2:1). Sardine oil loaded microparticles (SO-M) were produced (~75% yield) by
spray drying. The average diameter and polydispersity Index (PDI) of the particles were
found to be 2.3 μ and 0.345. XRD spectra of SO-M showed reduction in crystallinity due to
microencapsulation. After four weeks of storage, a moderate (~12%) decrease in the EPA and
DHA content and a low PV of 5.5±0.51 meq/kg oil in SO-M demonstrated good oxidative
stability. Satisfactory encapsulation efficiency (84±0.84%) and loading efficiency
(67±0.51%) values, also demonstrated the suitability of Va-g-Ch for microencapsulation of
sardine oil.
Vine shoots, considered a residue from winery operations, possess valuable antioxidant and antimicrobial activities that can be potentially obtained under the scheme of biorefinery. In this framework, we evaluated the autohydrolysis of vine shoots combined with a further stage of extraction with ethyl acetate as viable valorization process. The extraction yield ranged from 0.95 to 3.80 g extract/100 g vine shoots. Moderately high temperature (215 °C) was required for the maximum recovery of phenolics, flavonoids and antioxidant activities. The major phenolic compounds identified were derived from lignin: vanillin, acetovanillone, guaiacylacetone, syringaldehyde and acetosyringone. The ethyl acetate extract from the liquors obtained at 200 °C was assayed for antimicrobial activity against Gram positive and negative bacteria showing values of MIC and MBC in the range of 5–20 mg/mL. This work showed that the antioxidant extracts could be used as cheap source of natural compounds, with potential applications in the food and pharmaceutical industries.
Commercial sodium lignosulfonate from conifer black liquor (RSL) was used in our study to investigate acid-catalyzed hydrolysis of lignosulfonate (LS) by inorganic acids in aqueous solution. Before the hydrolysis process, RSL was purified by alcohol-water solution. Combustion method and gel permeation chromatography (GPC) of the high performance liquid chromatography system (HPLC) were used to detect the purification efficiency. The results showed that methanol-water solution had better purification effect. In addition, for the purified RSL (PSL-M), 0.5 mol/L NaOH solution was chosen as the best dissolving medium through the comparison of aggregation behaviors of PSL-M in deionized water and various concentrations of NaOH solutions. In the following acid-catalyzed hydrolysis process, the experimental results proved that the three kinds of inorganic acids (HCl, H2SO4 and H3PO4) could catalytically hydrolyze PSL-M to lower molecular weight fractions and other organic chemicals, but HCl had the best efficiency. Moreover, in 0.5 mol/L NaOH solution, PSL-M (solid-liquid ratio, 50 g/L) catalytically hydrolyzed by 0.68 mol/L HCl at 50 °C for 10 min could produce 1.729 g/kg isovanillic acid, 0.088 g/kg vanillin, 0.007 g/kg syringaldehyde, 0.056 g/kg acetosyringone and 0.024 g/kg acetovanillone respectively.
Jet turbine fuels have not been completely replaced by biomass-derived fuels due, in part, to the lack of the aromatic and cycloalkane hydrocarbons in bio-jet fuels. Such molecules play a critical role in traditional jet fuels for combustion characteristics and material compatibility. To date, this problem has been addressed by blending bio-jet fuel with traditional petroleum-based oils. In order to produce a 100% biomass-derived jet fuel, a suitable bioresource is needed for synthesizing aromatic and cycloalkane fuel compounds. Lignin, the only biomass component rich in aromatic benzene ring structures, is currently underutilized for low-value heat or treated as process waste because of its high chemical resistance. In this review, a four-step pathway of pretreatment, depolymerization, hydrodeoxygenation (HDO), and alkylation to convert lignin into jet-fuel-range aromatic hydrocarbons and cycloalkanes is explored. While many studies about these processes can be found in the literature for biomass and bio-derived molecules, the purposes of those studies were often for something other than lignin valorization. For example, pretreatment processes focus on cellulose and hemicellulose as desired products while lignin is handled as a waste. Most HDO studies focus on the upper phase of bio-oil which contains primarily water and phenolic monomers, ignoring the bottom phase which contains the larger, main components from depolymerization. Many alkylation studies used single, pure components; by comparison, the feedstocks from HDO of lignin-derived bio-oil are mixtures of varying complexity. This review of each process can be used to guide pathway integration and optimization.
The review describes the natural biopolymer lignin, which is second in plant biomass abundance. It is evident now that lignin is considerably undervalued and insufficiently studied in the applied area. The review focuses on the history of the lignin discovery, methods for its extraction from plant objects, its biodegradation by fungi, the enzymes degrading lignin, and the prospects of its application in current biotechnology.
Lignin and lignin derivatives biopolymers have several properties, such as high thermal stability, antioxidant, biodegradability, antimicrobial actions, adhesive properties, etc., and thus they can be extensively used in wide range of areas. Although human history mostly depend on the biopolymers, however derivatives of lignin such as sulfonate, phenolic, organosolv, Kraft and sodium sulfonate lignin have good mechanical and physicochemical properties. Well-designed materials such as coatings and paints, manufacturing of plastics and resins, for rubber packaging, for fuel production etc., can be obtained by the functionalizations of chemically modified lignin. Considering multi purposes properties of the lignin and lignin derivatives and extensive industrial applications of derivatives, this review sheds a light on lignin derivatives based materials with their prospective applications. All the technical scientific issues have been addressed highlighting the recent advancement.
In this work, energetic and structural studies concerning vanillyl alcohol, based both on experimental and computational studies, were developed. The massic energy of combustion and the vapour pressures at different temperatures were measured by static bomb combustion calorimetry and Knudsen mass-loss effusion techniques, respectively. The computational studies were performed using the G3(MP2)//B3LYP method. The combination of experimental and computational data enabled the determination of the enthalpies, entropies and Gibbs energies of sublimation and formation of this compound both in the crystal and gas phase. The intramolecular hydrogen bond energy present in vanillyl alcohol was evaluated, together with the O–H homolytic bond dissociation enthalpy. The new data are very useful for process design and development in the biorefinery.
Dissolution thermodynamics of vanillic acid (VA) in eight pure solvents, namely, ethanol, methanol, 2-butanol, ethylene glycol, ethyl acetate, triethyl orthoformate, 1,4 dioxane and cyclohexanone were studied. The solubility of vanillic acid in the above solvents was measured over the temperature range from (293.15 to 318.15) K at atmosphere pressure using a thermostatted reactor and UV/vis spectrophotometer analysis. It is observed that the solubility increases with the increase of temperature. All these data were regressed by van't Hoff model, the modified Apelblat equation and λh equation. The results show that three equations may well correlate the measured information. Moreover, thermodynamic studies obtained the dissolution process for vanillic acid in the selected solvents is endergonic, not spontaneous. Therefore, the experimental figures and typical parameters would provide essential support for industrial design and further theoretical studies.
By means of G4 theory and the M06-2X calculations we investigated the thermochemistry and C-OH bond ruptures of quercetin, fistein, lutelin, caffeic acid, pinocembrin and p-coumaric acid. Notwithstanding the fact that we observed a good agreement for the prediction of the weakest O-H bond, the mean absolute deviation (MAD) between the bond dissociation energies (BDE) computed at the G4 and M06-2X/6-311+G(3df,2p) levels was 5.0 kcal/mol. With regard to the ΔHof,0 computed at the M06-2X/6-311+G(3df,2p) level, the MAD was 10.0 kcal/mol. Therefore, thanks to error cancellation the error found for the O-H BDE was smaller. Intramolecular hydrogen bond is one of the key factors stabilizing the oxygen radicals formed when the CO-H bonds are broken. Finally, we propose the following enthalpies of formation at 0 K: -222.0, -174.5, -180.2, -134.4, -109.7 and -91.9 kcal/mol for quercetin, fistein, lutelin, caffeic acid, pinocembrin and p-coumaric acid, respectively.
A phosphinated biphenol, 6-(1-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl)ethyl)-6H-dibenzo[c,e] [1,2]oxaphosphinine 6-oxide (1), was synthesized from a sustainable phenol, acetovanillone. A methoxy-substituted poly(ether sulfone), methoxy-PES-1, was successfully prepared by the nucleophilic substitution of (1) and difluorodiphenyl sulfone in the presence of potassium carbonate. Another phosphinated biphenol, 6-((4-hydroxy-3-methoxyphenyl)(4-hydroxyphenyl)methyl)-6H-dibenzo[c,e] [1,2]oxaphosphinine 6-oxide (2), was prepared from another sustainable phenol, vanillin. However, the preparation of the methoxy-substituted poly(ether sulfone) based on biphenol (2) is not successful due to the biphenol (2) being unstable in an alkaline condition. After demethylation of the methoxy-PES-1, a phenolic hydroxyl poly(ether sulfone), hydroxyl-PES-1, was obtained. The phenolic hydroxyl linkages of the hydroxyl-PES-1 act as reacting sites for the epoxy resins. High-performance, bendable, flame retardant, and unexpectedly transparent cured epoxy film can be achieved through the curing of hydroxyl-PES-1 with commercially-available epoxy resins.
Lignin is a primary component of lignocellulosic biomass that is an underutilized feedstock in the growing biofuels industry. Despite the fact that lignin depolymerization has long been studied, the intrinsic heterogeneity of lignin typically leads to heterogeneous streams of aromatic compounds, which in turn present significant technical challenges when attempting to produce lignin-derived chemicals where purity is often a concern. In Nature, microorganisms often encounter this same problem during biomass turnover wherein powerful oxidative enzymes produce heterogeneous slates of aromatics compounds. Some microbes have evolved metabolic pathways to convert these aromatic species via ‘upper pathways’ into central intermediates, which can then be funneled through ‘lower pathways’ into central carbon metabolism in a process we dubbed ‘biological funneling’. This funneling approach offers a direct, biological solution to overcome heterogeneity problems in lignin valorization for the modern biorefinery. Coupled to targeted separations and downstream chemical catalysis, this concept offers the ability to produce a wide range of molecules from lignin. This perspective describes research opportunities and challenges ahead for this new field of research, which holds significant promise towards a biorefinery concept wherein polysaccharides and lignin are treated as equally valuable feedstocks. In particular, we discuss tailoring the lignin substrate for microbial utilization, host selection for biological funneling, ligninolytic enzyme–microbe synergy, metabolic engineering, expanding substrate specificity for biological funneling, and process integration, each of which presents key challenges. Ultimately, for biological solutions to lignin valorization to be viable, multiple questions in each of these areas will need to be addressed, making biological lignin valorization a multidisciplinary, co-design problem.
In this work we applied experimental and theoretical thermodynamics to methyl ferulate hydrolysis, a model biological reaction, in order to calculate the equilibrium constant and reaction enthalpy. In the first step, reaction data was collected. Temperature-dependent equilibrium concentrations of methyl ferulate hydrolysis have been measured. These were combined with activity coefficients predicted with electrolyte PC-SAFT in order to derive thermodynamic equilibriums constants Ka as a function of temperature.
In a second step, thermochemical properties of the highly pure reaction participants methyl ferulate and ferulic acid were measured by complementary thermochemical methods including combustion and differential scanning calorimetry. Vapor pressures and sublimation enthalpies of these compounds were measured by transpiration and TGA methods over a broad temperature range. Thermodynamic data on methyl ferulate and ferulic acid available in the literature were evaluated and combined with our own experimental results. Further, the standard molar enthalpy of methyl ferulate hydrolysis reaction calculated according to the Hess's Law applied to the reaction participants was found to be in agreement with the experimental reaction enthalpy from the equilibrium study.
In a final step, the gas-phase equilibrium constant of methyl ferulate hydrolysis at 298.15 K was calculated with the G3MP2 method. This value was adjusted to the liquid phase using the experimental vapor pressures of the reaction participants. As a result, the liquid phase Ka value calculated by quantum chemistry with additional data on the pure reaction participants was in good agreement with the experimental Ka reported in the literature for the aqueous phase. The thermodynamic procedure based on the quantum-chemical calculations is found to be a valuable option for assessment of thermodynamic properties of biologically relevant chemical reactions.
The majority of commodity plastics and materials are derived from petroleum-based chemicals, illustrating the strong dependence on products derived from non-renewable energy sources. As the most accessible, renewable form of carbon (in comparison to CO2), lignocellulosic biomass (defined as organic matter available on a renewable basis) has been acknowledged as the most logical carbon-based feedstock for a variety of materials such as biofuels and chemicals. This Review focuses on methods developed to synthesize polymers derived from lignin, monolignols, and lignin-derived chemicals. Major topics include the structure and processing of lignocellulosic biomass to lignin, polymers utilizing lignin as a macromonomer, synthesis of monomers and polymers from monolignols, and polymers from lignin-derived chemicals, such as vanillin.
Introduction: Scope and Definitions ThermochemistryDefinition of Phenols and Arenols: Comparisons with Related CompoundsArenols Unsubstituted Arenols The OH/H Increment Exchange Energies: δ(OH/H) and δ&(OH/H)Comparison of Phenol with AlkanolsNaphthols and AnthrolsCarbon-bonded Substituents Monoalkylated Phenols: Methyl and tert-butyl SubstituentsThe Amino Acid Tyrosine and Its DerivativesCarboxylic Acids and Their DerivativesAcylphenols and Their DerivativesCyanophenolsNitrogen-bonded Substituents AminophenolsNitrosophenolsNitrophenolsOxygen-bonded Substituents Hydroxy DerivativesAlkoxy DerivativesSulfur-bonded SubstituentsHalogen Substituents MonohalophenolsDihalophenolsPolyhalophenolsArenediols Unsubstituted BenzenediolsAlkylated BenzenediolsOtherwise Substituted BenzenediolsNaphthalenediols and Other ArenediolsArenetriolsArenolquinonesTautomeric Arenols Obstacles and OpportunitiesUnsubstituted ArenolsNitrosophenols and Nitrosonaphthols (Quinone Oximes)Arylazo Derivatives of Phenol and the NaphtholsAmbiguous ArenepolyolsReferences and Notes ThermochemistryDefinition of Phenols and Arenols: Comparisons with Related Compounds Unsubstituted Arenols The OH/H Increment Exchange Energies: δ(OH/H) and δ&(OH/H)Comparison of Phenol with AlkanolsNaphthols and AnthrolsCarbon-bonded Substituents Monoalkylated Phenols: Methyl and tert-butyl SubstituentsThe Amino Acid Tyrosine and Its DerivativesCarboxylic Acids and Their DerivativesAcylphenols and Their DerivativesCyanophenolsNitrogen-bonded Substituents AminophenolsNitrosophenolsNitrophenolsOxygen-bonded Substituents Hydroxy DerivativesAlkoxy DerivativesSulfur-bonded SubstituentsHalogen Substituents MonohalophenolsDihalophenolsPolyhalophenols The OH/H Increment Exchange Energies: δ(OH/H) and δ&(OH/H)Comparison of Phenol with AlkanolsNaphthols and Anthrols Monoalkylated Phenols: Methyl and tert-butyl SubstituentsThe Amino Acid Tyrosine and Its DerivativesCarboxylic Acids and Their DerivativesAcylphenols and Their DerivativesCyanophenols AminophenolsNitrosophenolsNitrophenols Hydroxy DerivativesAlkoxy Derivatives MonohalophenolsDihalophenolsPolyhalophenols Unsubstituted BenzenediolsAlkylated BenzenediolsOtherwise Substituted BenzenediolsNaphthalenediols and Other Arenediols Obstacles and OpportunitiesUnsubstituted ArenolsNitrosophenols and Nitrosonaphthols (Quinone Oximes)Arylazo Derivatives of Phenol and the NaphtholsAmbiguous Arenepolyols
Nowadays, the synthesis of (semi)aromatic polymers from lignin derivatives is of major interest, as aromatic compounds are key intermediates in the manufacture of polymers and lignin is the main source of aromatic biobased substrates. Phenols with a variety of chemical structures can be obtained from lignin deconstruction; among them, vanillin and ferulic acid are the main ones. Depending on the phenol substrates, different chemical modifications and polymerization pathways are developed, leading to (semi)aromatic polymers covering a wide range of thermomechanical properties. This review discusses the synthesis and properties of thermosets (vinyl ester resins, cyanate ester, epoxy, and benzoxazine resins) and thermoplastic polymers (polyesters, polyanhydrides, Schiff base polymers, polyacetals, polyoxalates, polycarbonates, acrylate polymers) prepared from vanillin, ferulic acid, guaiacol, syringaldehyde, or 4-hydroxybenzoic acid.
Phenolic acid is a very important class of allelochemicals with allelopathic weed control activity. In this study, three benzoic acid derivatives (syringic, 4-hydroxybenzoic, and vanillic acids), three cinnamic acid derivatives (cinnamic, 4-hydroxycinnamic, and ferulic acids) were tested, and high-performance liquid chromatography was used to conduct a dynamic analysis on the changes in the concentration of phenolic acids in a bioassay based on the initial concentration and test time. The results showed that the concentration of individual phenolic acids and a solution of mixed phenolic acids decreased to a certain extent irrespective of environment, i.e., bioassay (4–7 days) or a rice-growing environment, and a significant decrease in concentration was measured after 48 h. Based on the above results, the laboratory bioassay was conducted using a fresh solution of phenolic acids every 48 h. The results showed that the instability of phenolic acid could affect its weed control activity, and this effect was more significant for high concentrations of phenolic acids. On the other hand, changing the solution did not have a significant impact on the weed control activity of phenolic acids in the natural environment (pH 6.50), in which allelopathic rice release phenolic acids. These results reveal the instability of phenolic acids could significantly reduce the inhibition rate on the growth index for receptor plants in an indoor bioassay.
High level density functional theory calculations have been carried out for a benchmark set of benzene derivatives, including methyl, ethyl, n-propyl, i-propyl, tert-butyl, phenyl, and benzyl groups as substituents. Geometries were obtained using the B3LYP method and three basis set expansions, namely 6-31G(d), 6-311G(d,p), and 6-311++G(d,p). Final energies were calculated in B3LYP/6-311+G(3df,2p) single-point calculations. Based on these calculations the performance of different theoretical schemes aiming at reproducing substituent effects on enthalpies of formation has been assessed. The poorest performance is obtained when atomization energies or isodesmic reactions are used. No significant improvement is found when using homodesmotic processes. A significant improvement is achieved when the isodesmic processes used involve the unsubstituted parent compound. That means that this procedure can be a good alternative to explore substituent effects on the enthalpies of formation, although the absolute values of this thermodynamical magnitude have still a significant error. The best performance is obtained when different atom equivalent schemes are used, the correlation coefficient of the linear relationship between calculated and experimental values being greater than 0.999.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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. §
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.
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.
(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.
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.