Chemical polarization of nuclei. PMR spectra of decomposition products of dimethyl peroxydiphthalate

Chemical polarization of protons was observed in methyl benzoate formed during the thermal decomposition of dimethyl ester of peroxydiphthalic acid. The polarization pattern of methyl benzoate aromatic protons was very different in this case from that observed during the thermal decomposition of acetyl benzoyl peroxide. The unpolarized products formed from the methoxy radical, CH₂O and CH₃OH, were found in the mixture of decomposition products of this peroxide and were identified by means of PMR spectroscopy.     

The thermal decomposition of fluorinated esters

The kinetics of thermal decomposition of ethyl, isopropyl, and t-butyl trifluoroacetates have been studied in the gas phase. In each case initial decomposition follows the normal ester route to give an olefin and trifluoroacetic acid, and elimination of hydrogen fluoride does not occur. However, trifluoroacetic acid is thermally unstable at ethyl and isopropyl ester decomposition temperatures, and further products result, including those from the difluorocarbene produced by decomposing trifluoroacetic acid. Placing a CF₃ group at an ester's γ carbon increases the polarity of its transition state and decreases its thermal stability. The activation energies of the ethyl and isopropyl esters are lowered by 3.8 and 4.7 kcal/mol compared to the corresponding acetates, and the primary decomposition kinetics, which are homogeneous and of the first order, are expressed by α-Methylation enhances the reactivity of the trifluoroacetates, and the t-butyl ester, the transition state for which is sufficiently polar for heterogeneous decomposition to occur, shows signs of thermal instability at room temperature. The equilibrium was also investigated and gave ΔH° = +13,580 cal/mol and ΔS° = +31.07 gibbs/mol in the forward direction. The results obtained extend and support the known structure–rate correlations in the gas-phase elimination of esters.     

McLafferty-type rearrangement in the collision-induced dissociation of Li+, Na+ and Ag+ cationized esters of N-acetylated peptides

In this study we investigated the multi-stage collision-induced dissociation (CID) of N-terminally acetylated di-, tri- and tetrapeptides in the form of C-terminal ethyl, n-propyl, isopropyl, n-butyl and tert-butyl esters and cationized by the attachment of Li(+), Na(+) and Ag(+). While methyl ester versions of the metal cationized peptides primarily eliminate H(2)O following collisional activation and dissociation, the ethyl, propyl and butyl ester versions of the peptides exhibit a dissociation pathway consistent with gamma-hydrogen transfer to the C-terminal carbonyl group, with associated elimination of an alkene, in a McLafferty-type rearrangement. The rearrangement leaves a metal cationized, free-acid form of the peptide, as confirmed by comparing the multi-stage CID of rearrangement products generated from peptide esters with the CID of corresponding metal cationized free-acid peptides. The transfer of a gamma-hydrogen in the rearrangement reaction was confirmed by investigating the CID of ethyl esters for which the terminal methyl group was labeled with deuterium. We found that the rearrangement product was significantly more abundant, relative to other product ions, when derived from isopropyl and tert-butyl esters than from ethyl, n-propyl or n-butyl ester analogues.     

The effect of water on the rate and direction of the oxidation of organic substances

The effect of the polarity of the medium on the rate and direction of oxidation processes has been studied. It has been shown that the rate of oxidation of methyl ethyl ketone in aqueous solutions diminishes with increase in the water concentration. A considerably greater reduction in the rate of decomposition of the RO ₂ ^. radical is observed than in the rate of the interaction of this radical with methyl ethyl ketone, which results in an increase in the selectivity of the oxidation process. When methyl ethyl ketone is diluted with water in the molar ratio C₄H₈O H₂O=120, the quantity of acetic acid in the reaction products amounts to 98–99% of the methyl ethyl ketone consumed. The suggestion is made that the high selectivity of the oxidation of methyl ethyl ketone in aqueous solutions is due to the effect of the dielectric constant of the medium on the ratio between the two parallel reactions of the peroxide radical RO ₂ ^. .     

Synthesis of 4-deoxy-4-nitrosialic acid

The synthesis of 4-deoxy-4-nitrosialic acid (3,4,5-trideoxy-4-nitro-D-glycero-beta-D-galacto-non-2-ulopyranosonic acid, 5), was completed in seven steps starting from D-arabinose. Coupling of the 6-carbon fragment, 2-acetamido-1,2-dideoxy-1-nitro-D-mannitol (6) with ethyl alpha-(bromomethyl)acrylate afforded a 2 : 1 mixture of ethyl 5-acetamido-2,3,4,5-tetradeoxy-2-methylene-4-nitro-D-glycero-D-galacto-nononate (9a-S) and ethyl 5-acetamido-2,3,4,5-tetradeoxy-2-methylene-4-nitro-D-glycero-D-talo-nononate (9a-R). This mixture of enones was subjected to ozonolysis, and following reduction of the ozonide, the resultant products cyclised to the pyranosides. The target compound, ethyl 4-deoxy-4-nitrosialate (11a) was isolated by fractional crystallisation. Hydrolysis of the ethyl ester proved problematic; thus, the synthesis was modified by using tert-butyl alpha-(bromomethyl)acrylate. Following ozonolysis of the corresponding tert-butyl enoate esters and diastereomer separation, the tert-butyl ester of 4-nitrosialic acid (11b) could be deprotected under acidic conditions to afford . The target compound is a useful intermediate for synthesis of a variety of C-4 substituted sialic acid derivatives, and it is synthesised by a modular route.     

Thermal decomposition of perfluoro-di-t-butyl peroxide

The thermal decomposition of perfluoro-di-t-butyl peroxide has been studied for the first time. The reaction was carried out in the gas phase between 5 and 600 torr in the 108-149°C temperature region. The products consisted solely of C₂F₆ and CF₃COCF₃. The decomposition was found to be first order and homogeneous. The rate constant is given by log k_decomp(sec^?1) = (16.2 ± 1.2) - (148.7 4.4)/2.3RT where R is 0.008314kJ/mol · °K. These Arrhenius parameters are consistent with those determined for the decomposition of di-t-butyl peroxide.     

Enantiomeric separations using polymeric L-glutamate surfactant derivatives: effect of increasing steric factors

This study examines the role of steric hindrance near the stereogenic centers of four glutamic acid based polymeric surfactants. The single amino acid surfactants of glutamic acid, glutamic acid methyl ester, glutamic ethyl ester, and glutamic acid tert-butyl ester were investigated. The micellar electrokinetic chromatography (MEKC) separation of three binaphthyl derivatives and three benzodiazepines were used to study these steric factors. In addition, the hydrophobicity of these polymers as a function of pH was investigated by use of fluorescence measurements.     

TiO2 photocatalytic degradation of dimethyl- and diethyl- methylphosphonate, effects of catalyst and environmental factors

Dimethyl methylphosphonate (DMMP) and diethyl methylphosphonate (DEMP) are readily mineralized by photoexcited titanium dioxide (TiO₂). Intermediate products include low molecular weight organic acids and methylphosphonic acid. Complete mineralization yields phosphate and carbon dioxide. The photoactivities of different types of TiO₂ were investigated. The decomposition kinetics of DMMP and effects of DMMP and catalyst concentration, sonication, solar irradiation, oxygen concentration, temperature, and hydrogen peroxide on the rate of decomposition are reported. The degradation rates increase with simultaneous sonication, addition of hydrogen peroxide, and at higher temperatures.     

A Simple and Convenient Strategy for the Synthesis of Novel Ten,Twelve, and Fourteen‐membered Phosphorus Macrocyclic Compounds

Synthesis of the title compounds 4(a – i) was accomplished through a two‐step process. The synthetic route involves the cyclization of equimolar quantities of 2,2′‐methylene(methyl)bis(4,6‐di‐tert‐butyl‐phenol) ( 1 ) with tris‐(2‐chloro‐ethyl) phosphite ( 2a ), tris‐(2‐bromo‐ethyl) phosphine ( 2b ), and tris‐bromo methyl phosphine ( 2c ) in the presence of sodium hydride in dry tetrahydrofuran at 45–50°C. They were further converted to the corresponding oxides, sulfides, and selenides under N₂ atmosphere by reacting them with hydrogen peroxide, sulfur, and selenium, respectively ( 4a – c , 4d – f, and 4g – i ). But the compounds 6a , b were prepared by the direct cyclocondensation of equimolar quantities of 1 with (2‐chloro‐ethyl)‐phosphonic acid dibromomethyl ester ( 5a ) and (2‐chloro‐ethyl)‐phosphonic acid bis(2‐bromo‐ethyl) ester ( 5b ) in the presence of sodium hydride in dry tetrahydrofuran at 45–50°C in moderate yields. All the newly synthesized compounds 4 ( a – i ) and 6 ( a – b ) exhibited moderate in vitro antibacterial and antifungal activities.     

Thermal decomposition of 2‐ethylhexyl nitrate (2‐EHN)

The decomposition mechanism of 2‐ethyl‐hexylnitrate (2‐EHN), an important additive to diesel fuel to improve the cetane number, was investigated in solution and in the gas phase. In trans‐decalin as solvent, an activation barrier for the thermal decomposition of 39 kcal/mol was determined, and thus the decomposition is slow at temperatures below 100°C. Under high pressure conditions (2.4 kbar) the decomposition rates decrease, in accordance with a radical mechanism. Flash vacuum pyrolysis with subsequent detection of the products via mass spectroscopy or matrix IR spectroscopy allows to identify NO₂, formaldehyde, and several olefins as the major decomposition products. These data allow proposing a consistent mechanistic scheme for the 2‐EHN decay. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 34–38, 2002     

Polymerization initiated by ylide: Polymerization of ethyl methacrylate with the use of 4-picolinium p-chloro phenacylide as initiator

The ylide 4-picolinium, p-chloro phenacylide-initiated thermal polymerization of ethyl methacrylate (EMA) was studied. 4-Picolinium p-chloro phenacylide induces the thermal polymerization of ethyl methacrylate at 65°C. The rate of polymerization (R_p) rose as the initiator concentration increased from 2 × 10^?3 to 4 × 10^?3 M and the initiating exponent was computed as 1.9. The R_p decreased as the concentration of ylide increased from 6 × 10^?2 to 1M. The greater initiator concentration also affected the molecular weight inversely. The polymerization was carried out at different temperatures and the overall activation energy was computed as 4.08 Kcal/mol. Polymerization was inhibited in the presence of hydroquinone as a radical scavenger. Kinetic studies and other data show that the overall polymerization takes place in a radical mechanism. The various kinetic parameters, such as the rate and average degree of polymerization, molecular weight, and energy of activation of the present system, were evaluated.     

环状三过氧烷引发剂热分解和引发苯乙烯聚合

用气相色谱质谱联用仪 (GC MS) ,分析新型环状三过氧基团引发剂 (3,6 ,9 triethyl 3,6 ,9 trimethyl 1,4 ,7 triperoxonane ,简称TETMTPA)在乙苯和苯中的分解产物 .根据产物的分子结构 ,提出了涉及氧氧、碳碳和碳氧断键的分解机理 ;考察该引发剂引发苯乙烯本体聚合的速率和分子量 ,并与单过氧基团的过氧化二特丁基引发和热引发进行比较 ,发现用TETMTPA可以使分子量增加 ,对形成高分子量聚苯乙烯的原因作了解释 ;通过差示扫描量热仪 (DSC)和核磁共振仪 (NMR)聚合产物进行分析 ,验证了所提出的TETMTPA引发机理     

Thermal decomposition of tert-butyl ester of triethylsilylperacetic acid

Conclusions A study was made of the decomposition products of the tert-butyl ester of triethylsilylperacetic acid in cumene, n-nonane and tetraethylstannane. In the latter case the processes of generating the free radicals (C₂H₅)₃SiCH₂COO and (CH₃)₃CO, and their subsequent decomposition, are markedly suppressed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1542–1544, July, 1971.     

Thermal stability of tert-butyl peroxypivalate

The thermal stability of tert-butyl peroxypivalate (TBPP) has been investigated in relation to peroxide—diluent compositions in the range 100—10% by weight of peroxide. TBPP was selected because the simple decomposition pattern of the pure product facilitates an interpretation of the concentration dependence. Differential thermal analyses, isothermal and adiabatic storage tests have been used analysis of the decomposition. From the experimental results it is found that the total heat of decomposition is proportional to the peroxide concentration, the activation energy is independent of concentration, and the reaction order varies slightly with concentration. The type of diluent influences the reaction rate. The results are applicable in the 290—360 K temperature range. For the determination of decomposition characteristics, a modified first order equation which takes into account the fraction of diluent can bew used for TBPP—diluent compositions.     

Graft Copolymerization of Methyl Methacrylate onto Poly(Ethylene Terephthalate) Fibers Using Benzoyl Peroxide

Abstract

The graft copolymerization of methyl methacrylate onto poly(ethylene terephthalate) fibers has been studied using benzoyl peroxide as initiator. The grafting reactions were carried out within the 70 to 90°C temperature range, and the variations of graft yield with monomer and initiator concentrations were also investigated. The overall activation energy for grafting was calculated as 34.1 kcal/mol. The results of dyeability with the disperse dye suggested that diffusion into the fiber structure was moderately difficult when the graft yield reached 14?15%. The maximum graft yield was obtained at a benzoyl peroxide concentration of 4.00 × 10^?3 M. The decomposition temperature values obtained from thermogravimetric analysis show that the thermal stability of poly(ethylene terephthalate) fibers decreased as a result of grafting. Further, such change in the properties of methyl methacrylate grafted fibers as density, diameter, and moisture regain were also determined.     

Kinetic Study and Optimization of Catalytic Peroxide Delignification of Aspen Wood

It is established that the main regularities of the peroxide delignification of aspen wood in the temperature range of 70–100°С in the presence of dissolved (H₂SO₄) and solid (TiO₂) catalysts are similar. With an increase of the temperature, the concentration of hydrogen peroxide and acetic acid, and the hydromodule (HM) values, as well as the duration of the process and the content of cellulose in the cellulose products, increase, while the content of the residual lignin decreases. Simultaneously, the total yield of cellulose products decreases independently of the nature of the catalyst. Delignification processes are satisfactory described by the first-order equation. A sufficiently high activation energy (88 kJ/mol in the presence of H₂SO₄ and 75 kJ/mol in the presence of TiO₂) indicates the absence of significant external diffusion constraints in the selected conditions. The optimal conditions of obtaining cellulose products with a low content of residual lignin from aspen wood are found by the calculation methods. It is shown by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) that the structure of cellulose products obtained corresponds to the structure of industrial microcrystalline cellulose. In the optimal conditions, a high-quality cellulose product can be obtained in mild conditions (the temperature is 100°С, atmospheric pressure) by using a safer and technological TiO₂ catalyst instead of a sulfuric acid catalyst.     

Studies on the kinetics of decomposition of diacyl peroxides: III. Kinetics and mechanism of decomposition of 3, 5, 5-trimethylhexanoyl peroxide in benzene

The kinetics of decomposition of 3,5,5-trimethylhexanoyl peroxide (1) in benzene at 30, 40, and 50°C respectively have been studied and the cage effect, main products and the products obtained in scavenging experiment with galvinoxyl determined and characterized. The results show that the decomposition of 1, with initial concentration between 0.04 to 0.43 mol. L^?1, followed first plus three halves order kinetics with cage effect of 0.6, and the mechanism of decomposition is basically the same as previously proposed for lauroyl peroxide (2).⁴ In comparison with 2, the decomposition of 1 at the same temperature showed a faster rate for spontaneous decomposition, a larger cage effect and lesser induced decomposition, which is attributed to the branching in molecule of 1, especially to the presence of β-methyl group, which caused a larger entropy increase between the peroxide molecule and the transition state for decomposition.     

Radical polymerization of alkyl crotonates as 1,2-disubstituted ethylenes leading to thermally stable substituted polymethylene

Radical polymerization of several alkyl crotonates (RCr) was carried out in bulk or in benzene in the presence of radical initiators. Homopolymerization of RCr bearing bulky ester alkyl groups, e.g. tert-butyl (tBCr), 1-adamantyl (AdCr), and 3,5-dimethyl-1-adamantyl crotonate (DMAdCr) proceeded to give a polymer with molecular weight of several thousands despite of the steric hindrance and chain transfer by the presence of the β-methyl group, while the methyl and ethyl esters gave no polymer. The kinetics of the polymerization was examined in detail and absolute rate constants were evaluated by means of electron spin resonance spectroscopy. The propagation rate constants of RCr were 0.41–1.0 L/mol s, being much smaller than those of the corresponding methacrylates (530–570 L/mol s). The termination rate constants were also determined from the analyses of steady state and non-steady state polymerizations. Radical copolymerizations of AdCr (M₂) with several vinyl monomers (M₁) were carried out in bulk at 60°C and the rate constants for cross propagations were calculated to examine reactivities of the monomer and its polymer radical. The structure and thermal properties of the resulting poly (AdCr) were also investigated. Onset temperature of decomposition and glass transition temperature of poly(AdCr) were revealed to be much high as 302 and 234°C, respectively. © 1994 John Wiley & Sons, Inc.     

Kinetics of the thermal decomposition of nitrocellulose after treatment with weak acids

The kinetics of the thermal decomposition of nitrocellulose, treated with weak acids after nitrationin a nitric-sulfuric acid mixture, have been studied in the temperature range 75–110°C. It was found by Chromatographic analysis of the gaseous decomposition products that to an extent of up to 10% the decomposition takes place according to second order autocatalysis kinetics, and the rate of decomposition can vary by a factor of approximately two with the duration of the preliminary treatment and with the nature of the original cellulose. The activation energy in the initial stages of the process, determined from the rate of evolution of N₂O, CO₂, CO, and NO amounted to 24 kcal/mole. It was concluded that thermal decomposition is determined by acid hydrolysis of nitrocellulose residues by sulfuric acid. The rate constant for the hydrolysis of nitrocellulose by sulfuric acid in a nitrate ester medium and the diffusion constant of H₂SO₄ in nitrocellulose have been estimated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2744–2750, December, 1991.     

Thermal Decomposition and Glass Transition Temperature of Poly(methyl Methacrylate) and Poly(isobutyl Methacrylate)

Abstract

The thermal decomposition and the glass transition temperatures of poly(methyl methacrylate) (PMMA) and poly(isobutyl methacrylate) (PiBuMA) were studied with a differential scanning calorimeter (DSC). The undecomposed and decomposed polymers were analyzed by gel permeation chromatography (GPC) for molecular weight distributions and by DSC for changes in the thermal properties and glass transition temperatures, T. In the isothermal decomposition of PMMA and PiBuMA, depolymerization reactions exclusively are operative. During low temperature decompositions, longer PMMA chains depolymerize first. These are followed by the shorter chains. In the case of PiBuMA, the shorter chains depolymerize first. Some of these undergo chain recombinations to yield very high molecular weight products. For identical values of weight loss, the respective decomposition temperatures for PiBuMA are 40 to 70 K lower than those for PMMA. The activation energies of decomposition (42 kJ/mol for PMMA and 67 kJ/mol for PiBuMA) have been found to be lower than those reported in the literature. Although T_g∞ of PiBuMA (331 K) agrees well with the literature value (326 K), T_g∞ of atactic PMMA (394 K) is higher than the reported value (378 K).