Thermocatalytic transformations of wood and cellulose in the presence of HCl, HBr, and H2SO4

The compositions of the liquid organic products formed from aspen wood and cellulose at 150, 200, and 250° C in the presence of 1, 3, and 5% of HCl, HBr, and H₂SO₄ have been studied. The yield of levulinic acid from wood reached 13.0–15.5%, and from cellulose 28.8%.Institute of the Chemistry of Natural Organic Raw Material, Siberian Division of the Russian Academy of Sciences, Krasnoyarsk, fax (3912) 43 93 42. Translated from Khimiya Prirodnykh Soedinenii, Vol. 33, No. 1, pp. 107–112, January–February, 1997.     

Electrically conducting,thermally stable,and mechanically strong CuS-poly(parabanic acid) composite films and their shielding effect of electromagnetic wave

Poly(parabanic acid)-CuS composite film (wt-% of CuS=20–50) prepared by using organosol of CuS (=1500 Å) showed electrical conductivity of 0.1–70 S cm^–1, high thermal stability up to 250°C, high mechanical strength (breaking stress=7.0–12 × 10⁷ Pa), and good shielding effect of electromagnetic wave.     

Ionization constants of benzoic acid from 25 to 250°C and to 2000 bar

The ionization constant of benzoic acid has been determined by conductivity measurements of dilute aqueous solutions and found to vary from 6.27×10^–5 at 25°C to 0.39×10^–5 at 250°C. The pressure effect to 2000 bar has been measured, and the ratio of ionization constants K₂₀₀₀/K₁ is 2.26 at 25°C and 7.3 at 250°C. V°₁, the standard partial molar volume change for the ionization at 1 bar, varies from –11.7 cm³-mol^–1 at 25°C to –60 cm³-mol^–1 at 250°C. The volume changes are smaller at higher pressures.     

Dissociation constant of aqueous trifluoroacetic acid by cryoscopy and conductivity

The dissociation constant of trifluoroacetic acid in aqueous solution has been determined at 25°C by electrical conductivity (0.65 mol-l^–1) and at 0°C by cryoscopy (1.05 mol-l^–1) and electrical conductivity (0.98 mol-l^–1). The good agreement between the values of the constant determined by cryoscopy and conductivity at 0°C lends confidence to the value at 25°C determined by electrical conductivity. The constant determined at 25°C is in reasonable agreement with values determined by differential refractometry (0.92 mol-l^–1) and from acidity function data (0.80 mol-l^–1) reported by other workers. This work renews confidence in the electrical conductivity method for determining dissociation constants of moderately strong acids.     

Heteroaromatization of substituted aromatic amidines upon reaction with perfluorohexanecarboxylic acid nitrile

Conclusions Heteroaromatization was carried out under mild conditions at 20°C to obtain 2-phenyl-4, 6 diperfluorohexyl-1, 3, 5-triazine from N-alkylbenzamidines with the nitrile of perfluorohexane-carboxylic acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1194–1195, May, 1989.     

On the polymorphism of dicarboxylic acids: I pimelic acid

The results of solid-state analytical studies on pimelic acid demonstrate that the compound occurs in three polymorphic modifications. The modifications have been characterized by means of thermal analysis (videosupported thermomicroscopy, DSC, TGA), temperature-controlled FTIR microscopy and X-ray powder diffractometry, FT Raman and¹³C NMR spectroscopy, as well as pycnometry. The thermodynamic relationships are illustrated in a semi-schematic energy/temperature-diagram, which gives information about the relative stabilities and physical properties of the three modifications. Mod. III (commercial product, density 1.315 g cm^–3) is the thermodynamically stable form between absolute zero and nearly 57 °C (transition point with mod. II 55 to 59 °C). Mod. II (density 1.276 g cm^–3) is thermodynamically metastable in ambient conditions, but resistant. The transition point of mod. II with I (m.p. 105 °C) was determined to be 97.0 to 97.6 °C.Part of this work was presented at the 8th Österreichische Chemietage, Graz, Austria, September 28–30, 1994     

Analogs of D(+)-pantothenic acid. V. Synthesis and investigation of the structure of N-pantoyl derivatives of proline

The synthesis of pantothenic acid analogs is described. Boiling the Na salt of L-proline (L-I) with D-(–)-pantolactone (D-II) in MeONa Yielded 53.91% of N-D-pantoyl-L-proline (III), [] _D ² ° –52° (c 2; MeOH), and 19.18% of cyclo(N-D-pantoyl-L-proline) (IV), mp 119–121°C (ethanol), [] _D ² ° –68.9° (c 2; MeOH). The following were obtained similarly: N-L-pantoyl-L-proline, cyclo(N-L-pantoyl-L-proline), N-D-pantoyl-D-proline, cyclo(N-D-pantoyl-D-proline), N-L-pantoyl-D-proline, cyclo(N-D-pantoyl-hydroxyproline), and N--hydroxybutyryl-L-proline. By fusing D-II and DL-I at 140°C cyclo(N-D-pantoyl-DL-proline) and prolylproline anhydride (V) were obtained. Compound (V) with mp 136–138°C was synthesized from DL-1 by heating at 140°C. The PMR spectra of compounds (III-V) are given. The IR spectra of compounds (III and IV) are discussed.All-Union Scientific-Research Vitamin Institute, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 378–383, May–June, 1979.     

Degradation of benzoic acid and its derivatives in subcritical water

In this research, the stability of benzoic acid and three of its derivatives (anthranilic acid, salicylic acid, and syringic acid) under subcritical water conditions was investigated. The stability studies were carried out at temperatures ranging from 50 to 350 °C with heating times of 10–630 min. The degradation of the benzoic acid derivatives increased with rising temperature and the acids became less stable with longer heating time. The three benzoic acid derivatives showed very mild degradation at 150 °C. Severe degradation of benzoic acid derivatives was observed at 200 °C while their complete degradation occurred at 250 °C. However, benzoic acid remained stable at temperatures up to 300 °C. The degradation products of benzoic acid and the three derivatives were identified and quantified by HPLC and confirmed by GC/MS. Anthranilic acid, salicylic acid, syringic acid, and benzoic acid in high-temperature water underwent decarboxylation to form aniline, phenol, syringol, and benzene, respectively.     

Electrical conductivity measurements of hyaluronic acid and collagen

Electrical properties of hyaluronic acid (HYA) and collagen in the temperature range from –90°C (resp. –50°C for collagen) to 40°C are described. The value and type of electrical conductivity, temperature stability, and processes arising in the investigated samples during continual stress heating are determined by the measurements of temperature dependence of the electrical conductivity (both d.c. and a.c.).     

Ionization constants of aqueous ammonia from 25 to 250°C and to 2000 bar

The ionization constant of ammonia has been determined by conductivity measurements and found to vary from 1.77×10^–5 at 25°C to 1.3×10^–6mol-kg^–1 at 250°C. The pressure effect to 2000 bar has been measured and the ratio K₂₀₀₀/K₁ is 6.8 at 25°C and 11 at 250°C. The standard molar volume change for the ionization at 1 bar, V ₁ ^o , changes from –28.8 at 25°C to –67 cm³-mol^–1 at 250°C.     

Thiyl radicals in gas-phase thermolysis of xanthic acid esters

Gas-phase thermolysis of xanthic acid esters and their reaction with acetylene at 250–600°C have been studied for the first time. The direction of the thermolysis is determined by the nature of the substituents at the oxygen and sulfur atoms. The main products of the thermolysis are gaseous hydrocarbons, carbon monoxide and hydrogen sulfide. The yields of liquid products of the thermolysis and of the reactions with acetylene are 4–46%. The role of thiyl radicals in thiophene molecule formation and reaction routes to carbon disulfide, dithiocarbonates, and stilbene are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 150–153, January, 1996.     

TG and autoignition studies on forest fuels

The autoignition delay times of some important Mediterranean forest species: Arbutus adrachne, Abies cephallonica, Pinus brutia, Pinus halepensis, Pistacia lentiscus, Cupressus semprevirens, Olea europaea, Cistus incanus were determined in the range 460–600°C under precisely controlled temperature and airflow conditions. Based on these data the forest fuels examined were classified into two groups: the least and the most flammable species. The autoignition delay data were related to the thermal analysis measurements. The themogravimetric analysis in an inert (nitrogen) atmosphere showed that the thermal decomposition of cellulose in the range of 300–400°C as well as the mass residue at 600°C are directly related to the ignition behavior.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nitrosation of ascorbic acid by nitrite ion in unbuffered neutral and moderately acidic aqueous solutions

The kinetics of nitrosation of ascorbic acid by nitrite in unbuffered aqueous solutions was measured in the pH range from 6.7 to 4.0 at 25°C. The reaction order with respect to the proton is reliably lower than 2, especially in a more acidic solution. This means that under the studied conditions unprotonated nitrous acid may be involved directly in nitrosation of ascorbic acid.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1540–1544, July, 1992.     

Kinetics and mechanism of the photochemical hydrolysis of phosphoenolpyruvic acid

It was established that phosphoenolpyruvic acid, photoexcited by UV light at 20°C, loses its phosphoryl group under the action of acids and bases. Raising the temperature to 50°C induces dissociation of the photoexcited molecule into enolpyruvate and metaphosphate, which in turn phosphorylates HPO₄ ^2– and H₂P₂O₇ ^2– ions and AMP.Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya St., 253094 Kiev-94, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 5, pp. 287–290, September–October, 1996. Original article submitted December 1, 1995.     

Carbon-13 kinetic isotope effects in the decarbonylation of formic acid of natural isotopic composition in phosphoric acid media

The¹³C kinetic isotope effect (K.I.E.) in the decarbonylation of formic acid of natural isotopic composition in 85% orthophosphoric acid, in 100% H₃PO₄, and in pyrophosphoric acid has been measured in different temperature intervals ranging from 19 to 133 °C. In 85% H₃PO₄ the carbon-13 K.I.E. is determined by the fractionation of carbon isotopes expected for C–O bond rupture (k ₁₂/k ₁₃=1.0531 at 70°C). In 100% H₃PO₄ the¹³C K.I.E. indicates that C–H bond rupture is the major component of the reaction coordinate motion (thek ₁₂/k ₁₃ lay in the range of 1.026–1.017 over the range 30–70 °C). In pyrophosphoric acid the fractionation factor for¹³C equals 1.010 at 19 °C. Activation parameters for the decarbonylation of H¹²COOH in phosphoric acid media have been determined also and suggestions concerning the intimate mechanisms of decarbonylation of formic acid in dilute and concentrated phosphoric acids are made.     

Phase Diagram of the Xe–H2O System up to 15 kbar

The phase equilibria in the Xe–H2O system have been studied by the DTA technique under hydrostatic pressures up to 15 000 bar in a temperature range from -25 °C to 100 °C. We have shown that the cubic structure I xenon hydrate forming at ambient pressure does not undergo any phase transitions under the conditions studied. The temperature of its decomposition into water solution and gas (fluid) increases from 27 °C at 25 bar to 78.2 °C at 6150 bar. At higher pressures the hydrate decomposes into water solution and solid xenon. In the temperature range from 6800 to 9500 bar the decomposition temperature (79.0–79.5 °C) is practically independent of pressure, while further pressure increase results in a slow decrease to 67 °C at 15 000 bar.     

Kinetics of the thermal decomposition of cellulose nitrate over a wide range of nitrogen contents

We have studied the kinetics of the thermal decomposition of cellulose nitrate at 167.4°C in a vacuum for the range of nitrogen contents from 0.09 to 13.45%. The rate constants of the initial and autocatalytic stages have been determined. The method of nitrating cellulose with a mixture of the vapors of water and nitric acid in a previously evacuated sealed vessel has no special effect on the thermal kinetic properties of the cellulose nitrate produced. It is shown from the experimental results that at 167.4°C the rate constant for the loss of NO₂ groups in the primary position is about 14 times less than for those in the secondary position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1273–1279, June, 1990.     

The first ionization constant from 25 to 200°C and 2000 bar for orthophosphoric acid

The ionization constant of orthophosphoric acid, determined by conductivity measurements, decreased from 7.11×10^–3 at 25°C to 6.2×10^–4 mol-kg^–1 at 200°C. The pressure effect to 2000 bar was also measured and the ratio K₂₀₀₀/K₁ is 2.7 at 25°C and 3.7 at 200°C. The standard partial molar volume change for the ionization at 1 bar, , changes from –16.1 at 25°C to –33.3 cm³-mol^–1 at 200°C. The partial molar compressibility change for the ionization, , varies from –3.8×10^–3 to –8.3×10^–3 cm³-mol^–1 bar^–1 over the same temperature range.     

Thermal properties of oxidized cellulose

Three series of oxidized celluloses – 2,3-dialdehyde celluloses (DACs), 2,3-dicarboxycelluloses (DCCs) and sodium 2,3-dicarboxycelluloses (NaDCCs) — were prepared, having incremental changes in their degrees of oxidation. Their thermogravimetric analysis (TG) and differential thermal analysis (DTA) were studied. It was found that oxidation generally destabilized cellulose at lower temperatures (below 250 °C), but at higher temperatures the oxidized products were found to be more stable. Cellulose, DACs, and DCCs all showed final weight losses in the region of 80–85%. However, 80% NaDCC and 98% NaDCC showed weight losses of only 30 and 37%, respectively.NCL Communication No. 6051.