The ozonization of model lignin compounds in aqueous solutions catalyzed by Mn(II) ions

The influence of Mn(II) ions on the rate of the reaction between ozone and model lignin compounds, guaiacol and veratrole, was studied. The catalyst did not influence the rate of the destruction of the aromatic ring and intermediate ozonolysis products, compounds with conjugated double bonds, in acid media but substantially increased the rate of oxidation of saturated carboxylic acids, ketoacids, and aldehydes. Ozone consumption then increased from 2 to 5 moles per mole of the transformed substrate. A mechanism of the catalytic action of Mn(II) in reactions between ozone and the compounds studied was suggested.     

Thermal decomposition of poly(vinyl chloride) and chlorinated poly(vinyl chloride). II. Organic analysis

A concerted study of poly(vinyl chloride), chlorinated poly(vinyl chloride), and poly(vinylidene chloride) polymers by spectroscopy, thermal analysis, and pyrolysis-gas chromatography resulted in a proposed mechanism for their thermal degradation. Polymer structure with respect to total chlorine content and position was determined, and the influence of these polymer units on certain of the decomposition parameters is presented. Distinguishing differences were obtained for the kinetics of decomposition, reactive macroradical intermediates, and pyrolysis product distributions for these systems. It was determined that chlorinated poly(vinyl chloride) systems with long-chain ? CHCI? units were more thermally stable than the unchlorinated precursor, exhibited increasing activation energy for the dehydrochlorination, and produced chlorine-containing macroradical intermediates and chlorinated aromatic pyrolysis products. The poly(vinyl chloride) polymer was relatively less thermally stable, exhibited decreasing activation energy during dehydrochlorination, and produced polyenyl macro-radical intermediates and aromatic pyrolysis products.     

Synthesis of new α-chloroacryl-amides,thioamides and amidines from saturated amides

Chorination of saturated amide-chlorides followed by hydrolysis, thiolysis, aminolysis and catalysed dehydrochlorination leads to α-chloro acrylamide derivatives in high yield. The reaction sequence is applied to lactames and can also be extended to the synthesis of α-chloro acrylthioamide and amidine.     

Polymeric p-benzoquinone–tin derivatives as thermal stabilizers for rigid poly(vinyl chloride). II. Evaluation of the stabilizing efficiency

The polymeric p-benzoquinone-tin derivatives obtained from the reaction of p-benzoquinone with tin tetrachloride in the absence of solvent have been investigated as thermal stabilizers for rigid PVC at 200°C by measuring the rate of dehydrochlorination. The results reveal the greater stabilizing efficiency of the investigated products in relation to dibutyltin maleate and the basic lead stabilizers commonly used in industry. Evidence has been accumulated that the quinone and metallic elements (Sn? Sn bonds) of the stabilizer participate in the stabilization process by trapping the radical intermediates of degradation and blocking the odd electron sites formed on the polymer chains. Although stabilizers with high quinone content provide greater stabilization in the early stages of degradation, their efficiency sharply decreases in subsequent stages. On the other hand, stabilizers of high tin content effectively prohibit the dehydrochlorination reaction at all stages of degradation. On an equivalent basis of metal content, the results clearly demonstrate the greater stabilizing efficiency of tin atoms when found in direct contact in the stabilizer molecule. The mechanism of stabilization suggested to account for the results obtained may be considered as additional evidence in support of the radical nature of the dehydrochlorination reaction.     

Continuous dehydrochlorination of 1,3-dichloropropan-2-ol to epichlorohydrin: process parameters and by-products formation

The influence of pre-reactor and reactor temperatures on the conversion of 1,3-dichloropropan-2-ol and the selectivity of its transformation to epichlorohydrin in continuous dehydrochlorination for two modes of the reaction product collection was studied. The dehydrochlorination process and mechanism of diglycidyl ether formation are described.     

Stabilization of vinylidene chloride barrier resins

Vinylidene chloride copolymers have a number of superior properties, most notably a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. Unsaturation generated via interaction of the polymer with a variety of agents commonly encountered during polymerization or processing introduces an allylic dichloromethylene unit which may function as a major defect (labile) site for the initiation of degradation. Three approaches to the potential stabilization of these materials have been examined. The first involved the addition of agents, e.g. metal formates, capable of converting labile dichlormethylene units into non-reactive groups which would interrupt propagation of the degradative dehydrochlorination. The second involved the incorporation into the polymer of a commoner capable of scavenging free chlorine atoms. The third involved the preparation of copolymers which contains units capable of reaction with (consumption of) a mole of hydrogen chloride to expose a good free radical stabilizer to scavenge chlorine atoms.     

Dehydrochlorination reactions in polymers. Part II. Chlorinated polystyrene

The dehydrochlorination of chlorinated polystyrene was studied in the temperature range 120–220°C., when HCl was the sole volatile product. The dehydrochlorination was accompanied by the slow development of color and chain scission. The elimination rate fell too rapidly with reaction extent to be accounted for by reduction of reagent. Solution studies in o-dichlorobenzene indicated that the reaction was initially first-order in polymer concentration but was retarded by the polyene reaction products. The overall elimination was interpreted as a radical process in which the product was an active retarder. These observations are also valid for the elimination of HBr from brominated polystyrene.     

Mechanism of action of some stabilizers in the thermal degradation of poly(vinyl chloride)

The dehydrochlorination of PVC under vaccum has been studied at 170–200°C by a volumetric method. The accelerating effect of HCl is related to its interaction with the forming polyene units of macromolecules. A mechanism is proposed. The effects of various stabilizers, such as organic salts of Ca, Ba, Cd, trialkyl- and dialkyltin, trialkyl phosphites, and mixtures of phosphites with metal salts upon the rate of dehydrochlorination, polymer crosslinking, and electron absorption spectra of PVC during degradation in evacuated ampoules were investigated. The stabilizing activity of these compounds depends primarily on the effectivity of absorption of HCl and destruction of polyene units by these compounds.     

Mechanism of the thermal dehydrochlorination of poly(vinyl chloride) models in the liquid phase

The thermal dehydrochlorination of model compounds of PVC has been investigated in the liquid phase in an inert atmosphere. Electrophilic catalysis and the effect of various solvents on this reaction have been studied. It has been found that the electron-accepting power of the reaction medium is the decisive rate-determining factor, while the dielectric constant comes second. A mechanism of thermal dehydrochlorination has been suggested, in which a reaction between the substrate and the proton giving rise to the carbonium ion is the rate-determining step for the whole process.     

Synthesis of some α-fluoroacryl esters

Russian Journal of Applied Chemistry - A possibility of producing α-fluoroacrylic esters by dehydrochlorination of the products of reaction of α-fluoro-β-chloropropanoic acid or...     

Degradation of polymer mixtures. VI. Blends of poly(vinyl chloride) with polystyrene

The degradation of films containing both PS and PVC has been examined by TVA and TG. Stabilization of both polymers, more notably PS, is observed, but the degradation products are the same as when the polymers are degraded alone. Molecular weight measurements indicate a more rapid decrease in the molecular weight of PS when PVC is present. The possibility of grafting or other processes leading to chlorine incorporation in PS has been excluded by the results of experiments using ³⁶Cl-labeled PVC. The mechanisms of possible interactions between the degrading polymers are discussed. Processes involving reaction of chlorine radicals with PS at lower temperatures and reaction of PS radicals with the residue of PVC dehydrochlorination or its decomposition products at higher temperatures appear probable.     

Kinetics of phenol oxidation with ozone in a thin layer on a solid surface

Ozone has been reacted with phenol in thin supported layers, and the dynamics of this reaction has been investigated. The stoichiometry of this reaction coincides with the stoichiometry of the same reaction in solution. Specific reaction rate (β) has been determined for various phenol conversions. The effective rate constant of the reaction, estimated by extrapolating β to zero reaction time, is significantly higher than the rate constant of the reaction in solution. The reaction between ozone and phenol is diffusion-controlled. The reaction products form a barrier layer, which protects the deeper phenol layers against ozone. The barrier layer is as thick as 8–15 phenol monolayers.     

氯化天然橡胶的等速升温热降解动力学

天然胶乳;氯化天然橡胶的等速升温热降解动力学     

The simplest mathematical model of the process of the thermal dehydrochlorination of poly(vinyl chloride)

The dehydrochlorination of PVC under vacuum (～ 10^?4 mm Hg), with continuous removal of volatile products by freezing out, has been studied at 180–250°. The equation has been deduced and solved to describe the thermal degradation of PVC. The rate constants of separate steps of polymer dehydrochlorination and the dependence of concentrations of polyenes on time of degradation are calculated.     

Reaction of a phospholipid monolayer with gas-phase ozone at the air-water interface: measurement of surface excess and surface pressure in real time

The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known about the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface, suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of (1)H-POPC on D(2)O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air-water interface leading to the formation of OH radicals. The highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation of oxidized lipids with shorter alkyl tails.     

Polymerization products of p-benzoquinone as thermal stabilizers for rigid poly(vinyl chloride). Part II—Evaluation of the stabilizing efficiency

Quinone-tin polymers prepared by the cationic polymerization of p-benzoquinone with tin(II)chloride in the absence of solvent have been investigated as thermal stabilizers for rigid PVC at 180°C in air by measuring the rate of dehydrochlorination. The results reveal the higher stabilizing efficiency of these products relative to dibutyltin maleate, basic lead carbonate and barium-cadmium stearate stabilizers commonly used in industry. The induction period in the early stages of the dehydrochlorination process increases as a function of the metal content in the stabilizer molecule. The evidence indicates that the quinone and the metal part (

) of the stabilizer participate in the stabilization process by trapping the radical intermediates, as well as blocking the odd electron sites formed on the PVC chains. The mechanism of stabilization suggested to account for the results obtained supports a radical mechanism for the dehydrochlorination reaction.     

Dehydrochlorination of Poly(vinyl Chloride) in Pyridine. 1. Effect of Conditions

Poly(viny1 chloride) (PVC) was dehydrochlorinated thermally in pyridine solution under N₂ atmosphere and the effect of variation of reaction time, temperature, and concentration of PVC in pyridine was studied. The extent of dehydrochlorination (or conversion, x%) increases with an increase in reaction time and temperature, and with a decrease in the concentration of PVC. Incomplete precipitation of dehydrochlorinated PVC (DHPVC) occurs by nonsolvent (methanol). During dehydrochlorination there is no HCl evolution as it forms a pyridine hydrochloride complex which is supposed to act as a catalyst for dehydrochlorination. A possible mechanism has been proposed. Chain scission and cross-linking reactions are responsible for the molecular weight changes that take place during the reaction.     

Chlorinated long-chain fatty acids. Their properties and reactions—VI : Kinetics and mechanisms of base-catalyzed dehydrochlorination of sodium threo,threo-9,10,12,13-tetrachlorooctadecanoate

The base-catalyzed dehydrochlorination of sodium threo,threo-9,10,12,13-tetra-chlorooctadecanoate has been carried out in aqueous ethylene glycol solutions. During the first reaction step two chlorine atoms are eliminated nearly simultaneously as hydrogen chloride whereas the third and fourth chlorine atoms are released separately. The relative rates of these three reaction steps at 130°C are 497,41 and 1, respectively. The possible reaction mechanisms have been discussed in light of the kinetic results and product analyses which showed that the dehydrochlorination results mainly in conjugated diene-yne systems.     

CH2 CHF与臭氧反应机理的量子化学研究

用量子化学MP2方法,在6-311+ +G(d,p)基组水平上研究了烯烃CH2CHF与臭氧反应的机理,对氟代乙烯臭氧化反应Criegee机理进行了系统的计算,全参数优化了反应过程中反应物、中间体、过渡态和产物的几何构型,在QCISD(T)/6-311+ +G(d,p)水平上计算了它们的能量.并对它们进行了频率分析,以确定中间体和过渡态的真实性.研究结果表明,氟代乙烯与臭氧反应沿Criegee机理是可信的、合理的.同时研究还发现,就氟代乙烯与臭氧反应活性而言,其控制步骤的位垒较低,可以说氟代乙烯与臭氧反应活性较强,也就是说氟代乙烯对臭氧的损耗较大.     

Disturbance of the determination of aldehydes and ketones: Structural elucidation of degradation products derived from the reaction of 2,4-dinitrophenylhydrazine (DNPH) with ozone

None of the reaction products of ozone and DNPH immobilized on solid phase support have been identified yet. However, they can interfere with the determination of carbonyl compounds in ozone containing air when analysis is performed by sampling and derivatization with DNPH coated silica cartridges. To elucidate the structure of these compounds, DNPH silica cartridges were treated with synthetic air containing defined concentrations of ozone and eluted with acetonitrile. The products were characterized by HPLC-UV/Vis and nuclear magnetic resonance (NMR) spectroscopy. Three of the degradation products were identified as 2,4-dinitrophenol, 2,4-dinitroaniline and 1,3-dinitrobenzene. The identification was confirmed by comparison with commercially available standard compounds. The other elutable products were characterized as substituted aromatic compounds. The formation of all characterized products is consistent with a radical mechanism which has been previously discussed in the literature. Received: 9 September 1998 / Revised: 9 February 1999 / Accepted: 11 February 1999