Carbon-13 Kinetic Isotope Effects in the Decarbonylation Of Liquid Formic Acid in Water Solution

Abstract

Carbon-13 kinetic isotope effects (¹³C KIEs) in the decarbonylation of formic acid diluted with water 1:1 (V:V) has been studied in the 130–181°C temperature interval in sealed vacuum all glass reactions vessels. The experimental ¹³C KIEs are higher than the ¹³C KIEs values extrapolated from low 50–100°C temperature interval ¹³C KIEs observed in the decarbonylation of water free liquid formic acid but less than ¹³C KIEs expected theoretically assuming the complete carbon—oxygen (¹³C[sbnd]¹⁶O) bond rupture in the transition state. For instance the (k₁₂/k₁₃) KIE found in this study is 1.0375 at 170.2°C while the “full” ¹³C KIE is expected to be 1.0429 at this temperature. The ¹³C KIE extrapolated to 170.2°C from the low temperature data published earlier is 1.0299. - The Arrhenius activation energy for the decarbonylation of formic acid in 1:1 water solution E = 31.3 kcal/mol is by 6 kcal/mol higher than that which was obtained with 99,9% pure formic acid (E = 25,660 kcal/mol). The entropy of activation ΔS ^≠ increased from -21.4 e.u. (pure formic acid) to -15.3 e.u. in the decarbonylation of formic acid diluted with water 1:1. The increases of the enthalpy of activation, of the entropy of activation and partly of the carbon-13 kinetic isotope effect observed in the decarbonylation of formic acid in water solution have been rationalized by suggesting isotopic equilibria interfering the pure kinetic fractionation of ¹³C and intervention of the water molecules into the process of transfer of protons to the formic acid molecules lowering the absolute rate of their decomposition.     

18O/16O and 13C/12C Fractionation During the Reaction of Carbonates with Phosphoric Acid: Effects of Cationic Substitution and Reaction Temperature

Abstract

The factors for ¹⁸O/¹⁶O fractionation between carbonates and CO₂ gas produced by the dissolution of the carbonates in phosphoric acid (sealed vessel method) have been investigated as a function of reaction temperature (20–90°C) and cationic substitution in the solid. Synthetic CaCO₃, Ca_0.75 Mn_0.25 CO₃, MnCO₃, BaCO₃ and SrCO₃ powders, and a natural kutnahorite sample were used as solids. The δ¹⁸O values of the gaseous CO₂ liberated by the reaction with phosphoric acid decrease with increasing temperature and seem to be a linear function of T(°K)^?2. The slopes are specific for different carbonates. No temperature-depended ¹³C/¹²C fractionation seems to exist.     

Carbon Isotope Fractionation in the Decarboxylation of Phenylpropiolic Acid in Hydrogen Donating Media

Abstract

¹³C kinetic isotope effect (KIE) in the decarboxylation of phenylpropiolic acid (PPA) in tetralin medium (Tn) has been determined at 409–432 K and found to be of magnitude similar to the ¹³C KIE observed in the decarboxylation of malonic acid where the rupture of the C-C bond is the rate determining step. ¹³C KIE equals 1.0318/at 136°C in the decarboxylation of PPA in Tn medium. Intramolecular ¹³C KIE in the decarboxylation of malonic acid equals 1.0316 at this temperature. Thus it has been shown that the nearly “full” ¹³C KIE can be achieved by providing the excess hydrogen to C _x of PPA (or to triple acetylene bond) using not only strong mineral acids as the source of protons but also by carrying out the decarboxylation in organic medium like tetralin. A mechanism of decarboxylation of PPA in Tn is suggested.     

Laser enrichment of carbon-14

An experimental study has been performed of the carbon-14 enrichment achievable in the ultraviolet laser dissociation of mixtures of¹⁴CH₂O and¹²CH₂O. The¹⁴C:¹²C enrichment factor in the CO product has been measured at 352.2 nm as a function of laser linewidth, formaldehyde temperature and pressure, and degree of carbon-14 depletion. The enrichment decreases with an increase in each of these parameters; the highest enrichment, 1190, was measured at 0.02 cm^–1, 303 K, 1 Torr and a¹⁴C depletion of 10%. The results are assessed in terms of their application to radiocarbon dating, in particular for groundwater dating required for nuclear waste disposal, and to the enrichment of¹⁴C operating wastes extracted from nuclear reactors to a level suitable for commercial sale.This work was supported in part by Atomic Energy of Canada Limited     

Influence of high intensity ultrasound on wet process phosphoric acid

High intensity ultrasound (800 kHz and 80 Wcm^-2) is passed through phosphoric acid of different origins and concentrations. Its influence on fluorine content, viscosity, density, colour and tendency to form sludge on ageing is observed. The quantity of fluorine in all samples of acid goes on decreasing with the time of exposure to ultrasound. Due to removal of fluorine by the ultrasound, the tendency of the acids to form sludge also decreases. The evolution of fluorine from the wet process phosphoric acid may be due to the decomposition of H₂SiF₆ present in the acid to HF and SiF₄ by the enormous amount of energy released due to cavitation. The exposed acid thus becomes purer, and can be concentrated and transported easily without sludge formation.     

Corrosion behaviour of steel in concentrated phosphoric acid solutions

The corrosion rates of steel in concentrated phosphoric acid (1.0-11.0 M) were determined by the weight loss method, at three temperatures 298, 308 and 323 K. Results obtained show that corrosion rate increases with both acid concentration and temperature. The logarithm of corrosion rate was fitted against the acid concentration, values of Hammett H_o and Strehlow R_o(H) functions. The activation energies, enthalpies and entropies of the dissolution process were determined.     

N.M.R. relaxation time studies in liquid methyl iodide

The spin-lattice relaxation times of the various nuclei in methyl iodide, methyl iodide-d ₃, and carbon-13 methyl iodide (¹³C, ¹H, ²D) were measured between 210 and 350 K. The separation of the proton-proton intermolecular relaxation was accomplished by a dilution study in methyl iodide-d ₃; the resulting intermolecular contribution agreed well with the existing theories for this mechanism. It was found that the spin-rotation interaction contributed significantly to the intramolecular relaxation of both the protons and the carbon-13. For both nuclei the separation of the spin-rotation interaction from the intramolecular dipole-dipole interaction was accomplished without making any assumptions about the temperature dependence of the spin-rotation relaxation time. The resulting spin-rotation relaxation times for both carbon-13 and protons offer evidence that the large spin-rotation effects are due to the methyl group reorientation.     

Ultrasound-assisted conversion of tannic acid to gallic acid as a strategy to obtain value-added products

In this work, ultrasound was applied for the conversion of tannic acid into gallic acid using only diluted H₂O₂ as reagent. Experiments were carried out using several types of ultrasonic horns operating at 20 kHz (VC750W processor). The following experimental conditions were evaluated: H₂O₂ concentration (0.2 to 8.5 mol L⁻¹), horn type (10 to 25 mm of diameter), ultrasound amplitude (20 to 70%), sonication time (10 to 45 min), tannic acid concentration (170 to 1360 mg L⁻¹), and reaction temperature (50 to 90 °C). Gallic acid production was monitored with ultra-performance liquid chromatography with high-resolution time-of-flight mass spectrometry (UPLC-ToF-MS). The isolated gallic acid was confirmed with nuclear magnetic resonance (¹H and ¹³C NMR). It is important to emphasize that this study was developed as a proof of concept to demonstrate the potential of ultrasound for tannic acid conversion into gallic acid using just diluted H₂O₂. Under selected conditions gallic acid production yield was 128 ± 4 mg g⁻¹ of initial tannic acid (using 170 mg L⁻¹ of tannic acid as starting material). Reaction time was set as 30 min, which was carried out using 1 mol L⁻¹ H₂O₂ and ultrasound amplitude of 50% at 90 °C. At silent conditions (mechanical stirring, from 100 to 1000 rpm), gallic acid production was halved (less than 78 ± 4 mg g⁻¹ of initial tannic acid).     

Polarizing Microscopic and 31P NMR Studies of Decylammonium Chloride/Potassium Chloride/Water System. Containing Phosphoric Acid Monodecyl Ester and H3PO4

The decylammonium chloride (DACl), KCl and D₂O system forms two phases(N_c+N_d) in the nematic range. The N_d phase was ca. 15% by volume and exhibited extinct appearance. From conoscopic measurements it was inferred that the optical axis of the N_d phase was tilted. The lamellar phase of the DACl-KCl-D₂O system as well as the lamellar phase obtained by adding phosphoric acid decylester/phosphoric acid (PDE/H₃PO₄) showed the following phase sequence: L_α + N_d 35°C H_α + N_d 40°C N_c + N_d 45°C N_c 50°C isotropic The line shapes of ³¹P NMR of PDE/H₃PO₄ were found to be sensitive to micelle size and dynamics occuring in the lyotropic system, but they do not differentiate between different micelle shapes.     

31P AND 2H NMR Spectra of A Lyomesophase Containing Phosphoric Acid Monodecylester and H3PO4

This is a report on ³¹P nmr spectra of phosphoric acid monodecylester, PDE, and ²H quadrupolar splitting of D₂O in a lyomesophase developed from n-decylammonium chloride, PDE/H₃PO₄ and D₂O.Polarizing microcopic and ²H nmr studies showed that the mesophase was of lamellar-like structure but alignes as the temperature is increased. As the mesophase contained a minute amount of free H₃PO₄, the ³¹P nmr spectra gave a sharp peak and a hump. The latter was interpreted to arise from a slow tumbling process of PDE between different agglomerates in this system.     

A High-Precision Carbon-13 Shift Thermometer for the Temperature Range 100–300 K

The first carbon-13 shift thermometer for the temperature range of 100–300 K is based on the very rapid equilibration of a pair of semibullvalene valence tautomers. The temperature dependence of the equilibrium constant is reflected in strongly temperature-dependent shift differences Δδ between averaged signals, e.g.,d(Δδ)/dT= 0.051 ppm K⁻¹at 300, 0.087 ppm K⁻¹at 200, and 0.175 ppm K⁻¹at 110 K for the quaternary carbon atoms C2 and C6. At 37 temperaturesT, which were measured with calibrated platinum resistance thermometers, shift differences Δδ were taken from nondecoupled carbon-13 spectra recorded from solutions of 1 in mixtures of chlorodifluoromethane and deuterated dimethyl ether without spinning. The least-squares fit of these Δδ vsTdata to a polynomial equation of the fourth degree (Eq. [5],r²= 0.9999) allows the calculation of temperatures from measured shift differences with a standard deviation of 0.46 K and an estimated error of about 1 K. The heating effects of WALTZ-16 decoupling and the influence of solvents on Δδ are investigated. A comparison with existing NMR thermometers demonstrates the superior performance of the new carbon-13 shift thermometer with respect to precision and the accessible temperature range.     

Ultrasound-assisted acid hydrolysis of cellulose to chemical building blocks: Application to furfural synthesis

In this work, the use of ultrasound energy for the production of furanic platforms from cellulose was investigated and the synthesis of furfural was demonstrated. Several systems were evaluated, as ultrasound bath, cup horn and probe, in order to investigate microcrystalline cellulose conversion using simply a diluted acid solution and ultrasound. Several acid mixtures were evaluated for hydrolysis, as diluted solutions of HNO₃, H₂SO₄, HCl and H₂C₂O₄. The influence of the following parameters in the ultrasound-assisted acid hydrolysis (UAAH) were studied: sonication temperature (30 to 70 °C) and ultrasound amplitude (30 to 70% for a cup horn system) for 4 to 8 mol L⁻¹ HNO₃ solutions. For each evaluated condition, the products were identified by ultra-performance liquid chromatography with high-resolution time-of-flight mass spectrometry (UPLC-ToF-MS), which provide accurate information regarding the products obtained from biomass conversion. The furfural structure was confirmed by nuclear magnetic resonance (¹H and ¹³C NMR) spectroscopy. In addition, cellulosic residues from hydrolysis reaction were characterized using scanning electron microscopy (SEM), which contributed for a better understanding of physical-chemical effects caused by ultrasound. After process optimization, a 4 mol L⁻¹ HNO₃ solution, sonicated for 60 min at 30 °C in a cup horn system at 50% of amplitude, lead to 78% of conversion to furfural. This mild temperature condition combined to the use of a diluted acid solution represents an important contribution for the selective production of chemical building blocks using ultrasound energy.     

Use of Phosphoantimonic Acid for Arsenic Determination by Activation Analysi

A methed was elaborated to determine arsenic amount in skin samples by neutron activation analysis and high-resolution gamma spectrometry including sample preparation after mineralization by sorption on silicagel saturated with phosphoantimonic acid. The samples were irradiated in the VVR-S reactor core in a flux of 10¹³ neutrons · cm^?2 · s^?1, mineralized with a mixture of nitric and sulphuric acids, the gamma spectrum was measured after passing through an ion-exchanger containing 0.5 mol P₂O₅ to 1 mol Sb₂O₅ (SP-2) by a gamma-spectroscopy system PLURIMAT 20 with a Ge(Li) detector, and the ⁷⁶As photopeak of E_γ = 0.559 MeV was measured. The values of the results obtained varied in the range of (4?5 )× 10^?1 ppm arsenic. The sensitivity of the proposed determination method is l×10^?3 μg arsenic.     

Measurement of surface resistivity and surface conductivity of anodised aluminium by optical interferometry techniques

Optical interferometry techniques were used for the first time to measure the surface resistivity and surface conductivity of anodised aluminium samples in aqueous solution, without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out in different sulphuric acid solutions (1.0–2.5% H₂SO₄), by the technique of electrochemical impedance spectroscopy (EIS), at room temperature. In the mean time, the real-time holographic interferometric was carried out to measure the thickness of anodised (oxide) film of the aluminium samples during the anodization process. Then, the alternating current (AC) impedance (resistance) of the anodised aluminium samples was determined by the technique of electrochemical impedance spectroscopy (EIS) in different sulphuric acid solutions (1.0–2.5% H₂SO₄) at room temperature. In addition, a mathematical model was derived in order to correlate between the AC impedance (resistance) and to the surface (orthogonal) displacement of the samples in solutions. In other words, a proportionality constant (surface resistivity or surface conductivity=1/surface resistivity) between the determined AC impedance (by EIS technique) and the orthogonal displacement (by the optical interferometry techniques) was obtained. Consequently the surface resistivity (ρ) and surface conductivity (σ) of the aluminium samples in solutions were obtained. Also, electrical resistivity values (ρ) from other source were used for comparison sake with the calculated values of this investigation. This study revealed that the measured values of the resistivity for the anodised aluminium samples were 2.8×10⁹, 7×10¹², 2.5×10¹³, and 1.4×10¹²  Ω cm in 1.0%, 1.5%, 2.0%, and 2.5% H₂SO₄ solutions, respectively. In fact, the determined value range of the resistivity is in a good agreement with the one found in literature for the aluminium oxide, 85% Al₂O₃ (5×10¹⁰ Ω cm in air at temperature 30 °C), 96% Al₂O₃ (1×10¹⁴  Ω cm in air at temperature 30 °C), and 99.7% Al₂O₃ (>1×10¹⁴ Ω cm in air at temperature 30 °C).     

Carbon-13 Isotopic Species of H2C3, H2C4, and H2C5: High-Resolution Rotational Spectra

The microwave rotational spectra of the carbon-13 isotopic species of H₂C₃, H₂C₄, and H₂C₅ have been observed in a pulsed supersonic molecular beam by Fourier transform microwave spectroscopy. At high resolution all of the rotational lines exhibit hyperfine structure produced by the magnetic interaction between the nuclear spin of ¹³C and the overall rotation of the molecule. The component of the nuclear spin-rotation tensor along the a-inertial axis is large for most isotopic species, especially at the carbene carbon; at this position C_aa is two to three times larger than at other substituted positions along the chain. In contrast to both H₂C₃ and H₂C₃, in H₂C₄C_aa exhibits a pronounced alternation along the carbon chain backbone. Following detection of the five carbon-13 isotopic species and D₂C₅, an experimental structure (r₀) has been determined to high accuracy for H₂C₅.     

Electron spin resonance investigation of carbon-13 hyperfine interactions in nitrobenzene anion radical

Synthesis of carbon-13 enriched nitrobenzene which contains 22·5 mole per cent of nitrobenzene-1-¹³C and an equal amount of nitrobenzene-4-¹³C has been accomplished. We report the carbon-13 hyperfine interactions in the corresponding anion radicals in a variety of solvent media. In hexamethylphosphoramide a _C1 = -7·05 gauss and a _C4 = 6·14 gauss. These couplings change to -9·03 gauss and 5·31 gauss, respectively, when the solvent medium is dimethylformamide containing 0·598 mole fraction of water. The solvent dependence of a _C1 is consistent with the radical remaining planar as opposed to adopting a pyramidal conformation at the nitrogen when hydrogen bonds form between the radical anion and protic solvents. Data reported here provide an experimental means to estimate the spin density distribution in nitrobenzene anion.     

Investigation of the dynamical behaviour of the FH(CN−) centre in KCl with temperature dependent endor spectroscopy

Abstract

The temperature dependence of the electron nuclear double resonance (ENDOR) spectra of F_H(CN^?) centres in KCl was investigated in the temperature range between 10–220 K. At the lowest temperature of 10 K only one CN^? orientation with respect to the F centre electron is present, in which the nitrogen is thought to be nearer to the F-electron than the carbon. With the very small thermal activation energy of 2.9 meV the opposite orientation is occupied. The superhyperfine interactions of those first shell K nuclei nearest to CN^? and of the ¹³C interaction of the CN^? molecule are strongly temperature dependent between 10 and 60 K, following an exponential law with a thermal activation energy of 4.2 meV. It is assumed that a soft local mode involving those two nearest K nuclei and the CN^? is causing the strong temperature dependence. The shf interactions of ¹⁴N nuclei have not been seen, probably because of the dynamical effects.     

E.P.R. study of Mn2+ in lithium potassium tartrate (LPT) and its isomorphism with lithium ammonium tartrate (LAT)

An E.P.R. study of Mn²⁺ in single crystals of LiKC₄H₄O₆. H₂O (LPT) was carried out from ～300 K to 77 K and four magnetically differently oriented but symmetry related triclinic complexes of Mn²⁺ were observed. Spin hamiltonian parameters were obtained at ～ 300 K. The E.P.R. results suggest that LPT is not only isomorphous but also isostructural to LiNH₄C₄H₄O₆ . H₂O (LAT). In LPT no structural phase transition could be detected in the temperature range 300 K to 77 K. The observed small magnitude of the low symmetry effect is attributed to the small contribution of fourth order crystal field terms relative to that of the second order crystal field terms, to the zero-field splittings of the ⁶ S ground state of Mn²⁺. A temperature dependent anomalous behaviour is observed in the low field region of the E.P.R. spectrum for B//[010] and its neighbourhood.     

Optimum parameters to etch Nd:YAG crystals with orthophosphoric acid H3PO4

Subsurface flaws, which determine the fracture strength of crystals, can be removed by the aid of chemical etching. Above a temperature of 200°C orthophosphoric acid H₃PO₄ is an efficient etchant for yttrium aluminium garnets. However, at these temperatures the etchant decomposes into its related phosphoric acids which show negligible etching rates for garnets. It takes a long time to warm up a large volume of acid and the etchant is decomposed for the most part already before the optimum temperature is reached. We show that efficient etching is achieved when the samples are in the bath already during the warm-up phase and specify the parameters for the optimum etch process.     

Preparation and Mössbauer spectra of CoV2O4 spinel doped with Fe2+ on tetrahedral sites

Co²⁺_0.98Fe²⁺_0.02Fe³⁺_?V³⁺_2-? 04 (?? 0.001) was obtained from a sample containing the iron dope mainly in the trivalent state, by reducing it at 910°C in a CO₂/CO atmosphere. Mössbauer spectra of ⁵⁷Fe at the tetrahedral site were taken between 5 and 300 K. Below the Curie temperature (143 K) there is a magnetically induced electric field gradient eQV_zz and a reduction of the hyperfine field H_hf. Values at 5 K are H_hf=141 kG and eQV_zz=5.74 mm/s. The effective splitting of the Fe²⁺⁵E ground-state doublet, as estimated from the temperature dependence of eQV_zz and H_hf, is $\text{2q}\text{δ}\text{/k = 28 K}$. It is derived that in these oxides the coupling of the electronic ⁵E states to local Jahn-Teller active E-modes of vibration is stronger than in comparable sulphides.