Rate coefficients of decomposition of azoethane and azoisopropane

The thermal decompositions of azoethane and azoisopropane were studied in a large excess of ethylene in the temperature interval of 523–623 K. It was demonstrated that under such conditions, the bulk of the alkyl radicals react with ethylene. Via measurements on the consumption of the azo compound and on the formation of gaseous nitrogen, it was possible to determine the rate coefficients of the initiation reactions: . The resulting data were as follows: For azoethane, . For azoisopropane,      

Very low-pressure pyrolysis. IX. The decomposition of azoethane,azoisopropane, and 2,2′-azoisobutane

The very low-pressure (VLPP) technique was used to study the pyrolysis of azoethane (AE), azoisopropane (AIP), and 2,2′-azoisobutane (AIB). The low pressure rate constants were related to the high-pressure Arrhenius parameters by means of the RRKM theory. This procedure in itself does not yield an unambiguous set of parameters. However, thermochemical and kinetic arguments are given which support the following values of log k∞ for the pyrolysis of AE, AIP, and AIB, respectively: 16.4–49.7/θ 16.6–47.9/θ, and 16.4–42.8/θ, where θ = 2.303RT in kcal/mole. The flow dependence of k_uni was used to estimate the collisional efficiencies of the azo compounds relative to the wall.     

Excited-state kinetics in the photolysis of azoethane and hexafluoroazomethane at 366 nm,up to one atmosphere pressure,and from room temperature to 150°C

The photochemistry of azoethane and hexafluoroazomethane at 366 nm has been reinvestigated up to 1 atm pressure, and over a range of temperature from 27 to 150°C. The Stern-Volmer type quenching plots primarily demonstrate the decomposition of a single electronic and vibrationally excited state for azoethane, but competitive photodissociation from two different electronic and vibrationally excited states, which was previously postulated for hexafluoroazomethane and azoisopropane, is confirmed for hexafluoroazomethane. It is concluded, however, that two different electronic and vibrationally excited photodissociating states are present in azoethane photolysis, but that one of them is difficult to detect, at least by the present approach Photosensitization with biacetyl at 436 nm also causes the dissociation of azoethane, and this is probably from the vibrationally equilibrated first triplet state. The energy barrier for this process was found to be 5.0 kcal/mol.     

Ionization potentials of some azoalkanes by photoelectron spectroscopy

Photoelectron spectra have been obtained for a set of azo compounds consisting of three pairs of cis, trans isomers, seven bridgehead substituted 2,3-diazabicyclo[2.2.2]oct-2-enes (DBO's), and one arylazoalkane. The lowest ionization potentials, which range from 7.83 to 9.21 eV, do not correlate with cis ground state energy or photolability of the DBO derivatives. Vibrational fine structure was observed in three DBO's, allowing verification that the lowest ionization takes place from the antibonding combination of nitrogen lone pairs.     

Excited-state proton transfer kinetics of carbazole

Rate constants for the excited-state proton transfer reaction of carbazole in aqueous alkaline solution have been determined using picosecond single photon counting. Fluorescence decay measurements show that the back reaction is slow compared to the fluorescence decay time and therefore equilibrium is not attained in the excited state. The validity of a pK value for the lowest excited state determined from steady-state fluorescence measurements assuming equilibrium is discussed. It is concluded that the thermodynamic pK^* value for carbazole is 10.98.     

Pyrolyses of azoalkanes. photoelectron spectra of some hydrocarbon radicals

The pyrolyses of azocyclobutane (=1)and azocyclopropylmethane (=2) have been used to generate C₄H₇ radicals. The photoelectron spectra at various temperatures are presented and the results compared with the data obtained by pyrolyses of the corresponding methylnitrites.     

Synthesis and further reactivity studies of some transition metal gallyl complexes

Reactions of the anionic gallium(I) heterocycle salt, [K(tmeda)][Ga(DAB)] (DAB = {N(Dip)C(H)}₂; Dip = C₆H₃Prⁱ₂-2,6), with a series of groups 6-9 and 11 metal halide complexes have given rise to the metal gallyl complexes, [CpCr(IMes){Ga(DAB)}] (IMes = :C{(Mes)NC(H)}₂; Mes = mesityl), [M(tmeda){Ga(DAB)}₂] (M = Mn, Fe or Co) and [Cu(dppe){Ga(DAB)}] (dppe = 1,2-bis(diphenylphosphino)ethane). The majority of the complexes have been crystallographically characterized. The reactivity of the previously reported copper(I) gallyl complex, [(IPr)Cu{Ga(DAB)}] (IPr = :C{(Dip)NC(H)}₂), towards a variety of unsaturated substrates has been explored. Three crystallographically characterized complexes have arisen from this phase of the study, viz. [(IPr)CuCCPh], [(IPr)Cu{Ga(DAB)}(CNBu^t)] and [(IPr)Cu{κ¹-OC(O)C(CNHDip)(NHDip)}]. The results of these investigations show that the reactivity of [(IPr)Cu{Ga(DAB)}] is significantly different to that of related copper boryl complexes.     

Excited state kinetics and stern-Volmer quenching plots in the photolysis of azoisopropane at 366 nm

The photochemistry of azoisopropane is reinvestigated at 366 nm over an extended pressure range by using n-butane as an added bath gas, and over a range of temperature from 277° to 180°C. The Stern-Volmer type plot of the N₂ product quantum yield is interpreted in terms of the decomposition of the vibrationally excited upper singlet and triplet states, with the onset of the dissociation of the vibrationally equilibrated triplet state as the temperature is increased. The energy barrier for the dissociation of the vibrationally equilibrated first triplet state is found to be 8.8 kcal/mole. Triplet sensitization experiments with biacetyl correlate with our observations, and it is suggested that the proposed mechanism is generally applicable to the photodissociation of acyclic azoalkanes at 366 nm, based on a comparison of our data with those of Wu and Rice on hexafluoroazomethane.     

Thermal, phase transition, and thermal kinetics studies of carbamazepine

The thermal, phase transition of carbamazepine dihydrate and the solid-state transformation of carbamazepine from form III to form I were performed by Differential scanning calorimetry (DSC), Thermo gravimetry (TG–DTA), and X-ray powder diffraction.The non-thermal kinetic analysis of carbamazepine dihydrate and form III was carried out by DSC at different heating rates in dynamic nitrogen atmosphere. The model-free model, the Kissinger method, was used to give the Arrhenius parameters. Arrhenius plots from the kinetic model yielded activation energies corresponding to dehydration of dihydrate and melting of anhydrate CBZ form I were 95.28, 966.06 kJ mol^?1, the pre-exponential factors were 8.34E+11 and 1.41E+149, respectively. For the transformation of carbamazepine from form III to form I, activation energies corresponding to the melting of CBZ form III, recrystallization of form I, and melting of form I were 1160.81, 710.89, 1265.89 kJ mol^?1, the pre-exponential factors were 2.29E+144, 4.43E+91, and 1.61E+151, respectively. As a comparison, Ozawa method was used to verify the activation energy values obtained by Kissinger method. The result shows a close activation energy values between two methods.     

On some errors committed in the studies of kinetics of thermal dissociation of solids

The methods of preparing the samples for kinetic studies are critically discussed with particular consideration to the effect of granulometric characteristics and structure of the material, conditions of performing the measurements, and choice of proper kinetic equation on the reliability of the results obtained.     

Excited-state Acidity of Bifunctional Compounds. 7. Long Distance, Solvent-assisted Excited-state Proton Transfer in Olivacine

Abstract— By use of fluorescence spectroscopy and time-correlated single photon counting, solvent-assisted excited-state proton transfer (ESPT) has been observed for olivacine in two organic solvents, 1,4-dioxane and methanol. Because of spectral overlap, factor analysis was used to determine the emission spectrum of the proton-transferred (PT) species. The ESPT is not observed in the nonpolar solvent n -hexane. For the first time in a system of this type, the individual excited-state rate constants have been calculated exactly from time-resolved single photon counting results. Because the PT process involves a path of more than 6 Å, its individual rate constant is extremely low, approximately 10⁷ s⁻¹.     

Cyclic voltammetric and electrochemical impedance studies on the structure,adsorption kinetics,and barrier properties of some organic dithiol self-assembled monolayers on gold

We have studied the orientation and barrier properties of self-assembled monolayers (SAMs) of two alkanedithiols, hexanedithiol, octanedithiol, and an aromatic dithiol, 1,4-benzene dimethanethiol (BDMT), on gold in acetonitrile. From our studies, we conclude that BDMT molecules can form more organized monolayers on gold than aliphatic dithiol SAMs due to extremely strong lateral van der Waals interaction among the phenyl rings in the former. A study of the adsorption kinetics of octanedithiol in ethanol indicates that the adsorption rate law is concentration dependent just as for alkanethiols. However, the rate of adsorption is considerably faster than for simple alkanethiols.     

Synthesis,characterization, and kinetics studies of organic soluble photosensitive copolyimide

A copolyimide synthesized from 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, 3,5-diaminobenzoic acid, and 2,3,5,6-tetramethyl-p-phenylene diamine was found to be soluble in N-alkyl substituted amides. An organic soluble photosensitive polyimide was obtained by further reaction of the copolyimide with methacrylic acid glycidyl ester. After adding Michler's ketone, the UV spectra absorbance near 360 nm of the copolyimide decreased rapidly upon the irradiation of mercury lamp. Using benzoic acid and methacrylic acid glycidyl ester as model compounds and N, N-dimethylbenzylamine as catalyst, the mechanism of reaction between the carboxylic group of the copolyimide and epoxy group of methacrylic acid glycidyl ester in N-methyl-2-pyrrolidone was found to have two competitive reactions, namely the auto-catalytic and the catalytic reactions. The apparent rate constants of each reaction were determined. Comparison of apparent rate constants between the model compound and the polymer reaction system are also reported.     

The addition reaction between silylene and ethyne: further isotope studies, pressure dependence studies, and quantum chemical calculations

Time-resolved kinetic studies of the reaction of dideutero-silylene, SiD 2, generated by laser flash photolysis of phenylsilane-d 3, have been carried out to obtain rate constants for its bimolecular reaction with C 2H 2. The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF 6 bath gas, at five temperatures in the range 297-600 K. The second-order rate constants obtained by extrapolation to the high-pressure limits at each temperature fitted the Arrhenius equation log( k (infinity)/cm (3) molecule (-1) s (-1)) = (-10.05 +/- 0.05) + (3.43 +/- 0.36 kJ mol (-1))/ RT ln 10. The rate constants were used to obtain a comprehensive set of isotope effects by comparison with earlier obtained rate constants for the reactions of SiH 2 with C 2H 2 and C 2D 2. Additionally, pressure-dependent rate constants for the reaction of SiH 2 with C 2H 2 in the presence of He (1-100 Torr) were obtained at 300, 399, and 613 K. Quantum chemical (ab initio) calculations of the SiC 2H 4 reaction system at the G3 level support the initial formation of silirene, which rapidly isomerizes to ethynylsilane as the major pathway. Reversible formation of vinylsilylene is also an important process. The calculations also indicate the involvement of several other intermediates, not previously suggested in the mechanism. RRKM calculations are in semiquantitative agreement with the pressure dependences and isotope effects suggested by the ab initio calculations, but residual discrepancies suggest the possible involvement of the minor reaction channel, SiH 2 + C 2H 2 --> Si( (3)P 1) + C 2H 4. The results are compared and contrasted with previous studies of this reaction system.     

Equilibrium studies of some divalent metal ions complexes with pyridoxol,pyridoxal and pyridoxamine

The interaction of vitamin B₆ compounds, pyridoxol, pyridoxal and pyridoxamine with metal ions Mn²⁺, Co²⁺, Ni²⁺ and Hg²⁺ are studied. Values for stability constants are evaluated and the reaction stiochiometries are investigated in aqueous 0.50 M KCl at 25°C. It is shown that only pyridoxamine possesses a fairly good affinity to interact with metal ions. A linear relation holds between the stability constants of the first complex and the ionization potential of the divalent metal ions.     

Facile synthesis,characterization, and antimicrobial studies of some disubstituted 1,2,3-triazoles with sulfonamide functionality

An expedient synthesis of some 1,4-disubstituted 1,2,3-triazoles (3a–3x) having sulfonamide functionality from various terminal alkynes and aromatic azides through Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition has been reported. The structures of newly synthesized compounds were confirmed by IR, ¹H NMR, ¹³C NMR, high-resolution mass spectra and screened for in vitro antimicrobial activity against Staphylococcus aureus (Gram-positive bacteria), Escherichia coli, Klebsiella pneumoniae, Enterobacter aerogenes (Gram-negative bacteria), Candida albicans, and Aspergillus niger (fungi). Some of the synthesized compounds were found to exhibit good potency against above-tested microbial strains. Moreover, to study the binding interactions, docking simulation of broadly active compound 3x was also performed against E. coli dihydropteroate synthase enzyme.     

Cellulosic biomass biocomposites with polyaniline,polypyrrole and sodium alginate: Insecticide adsorption-desorption,equilibrium and kinetics studies

This work was designed to synthesize and characterize biocomposites for the adsorptive elimination of insecticide (nitenpyram). Different biocomposites were synthesized of polyaniline (PAN-PH), polypyrrole (PPY-PH) and sodium alginate (Na-Al-PH) with cellulosic biomass of peanut husk (PH), which was characterized fourier-transform infrared spectroscopy (FTIR), pH_pzc and scanning electron microscope (SEM). In batch mode, different variables, i.e., contact time, pH, temperature, NP (nitenpyram) concentration and adsorbent dose effects were investigated. The adsorption capacities of PH, PAN-PH, PPY-PH and Na-Al-PH were recorded to be 13.0, 14.43, 13.61 and 11.91 (mg/g), respectively at 30 °C, 60 min contact time, 0.05 g and 2.0 pH. Pseudo second order kinetic and Freundlich isotherm models best explained the NP adsorption data. An exothermic adsorption nature of NP adsorption was observed on to PH, PAN-PH, PPY-PH and Na-Al-PH. The NP desorption was efficient with NaOH and biocomposites are competent for the adsorptive removal of NP, which can utilized for NP remediation in effluents.