Kinetic features

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

The kinetic features of this reaction, including the solvent isotope effect, are consistent with a rate-determining protonation to form a vinyl cation. ... 

All the reactions discussed in this review are aromatic nucleophilic substitutions in the ordinary sense. These reactions are briefiy described in the following sections with respect to their general kinetic features and mainly involve aza-activated six-membered ring systems, although a few studies of other heteroaromatic compounds are also available. 

As a conclusion, the basic kinetic features of the emulsion polymerization system may be summarized as follows ... 

Kinetic features of phase separation under alloy ordering ... 

Initially it was necessary to devise an improved method for the preparation of 2-hydroxyglycal esters, because the standard procedure (treatment of an acylglycosyl bromide with diethylamine in benzene or chloroform solution) was inconveniently lengthy in time and frequently afforded only a moderate yield of product (5). As a result of their recent thorough investigation of the kinetic features of the dehydrobromination of tetra-O-acetyl-a-D-glucopyranosyl bromide Lemieux and Lineback... 

Other aspects of these copolymerizations were studied including some kinetic features, molecular weights (which were low), the extent of branching due to side reactions on the furan ring, and the characterization of the complex formed between 2-furaldehyde and BF3 Et20. 

Polymer Flexibility as a Decisive Parameter of the Thermodynamic and Kinetic Features of Orientation Processes... 

To explain the observed magnitude of E and other kinetic features of reaction, a homogeneous bimolecular interaction between neighbouring CIO4 ions in the crystal structure was postulated and application of the activated complex theory to this model gave good agreement with the experimental observations. 

The parameter aH is positive for electropositive (electron donor) adsorbates and negative for electronegative (electron acceptor) adsorbates. Even when deviations from linearity exist, the main feature of Eq. (2.23) remain valid and form the basis for understanding the main kinetic features of classical and electrochemical promotion ... 

Although the activation parameters corresponding to steps and are given, there is some doubt over the correct value for (and the accompanying under the conditions employed. There seems to be no special kinetic feature about the oxygen ligand in since the rates of reaction of the latter oxocation... 

The kinetics are the same in sulphuric and phosphoric acid media as in perchloric acid. The main kinetic features are reproduced in a nitric acid medium although a term, k[Ag(II)]V[Ag(I)], is also involved. Both terms include a strong inverse acidity dependence however, the role of the nitrate ions obscures this. 

Typical non-enolising aldehydes are formaldehyde and benzaldehyde, which are oxidised by Co(III) Ce(IV) perchlorate and sulphate , and Mn(III) . The main kinetic features and the primary kinetic isotope effects are the same as for the analogous cyclohexanol oxidations (section 4.3.5) and it is highly probable that the same general mechanism operates. kif olko20 for Co(III) oxidation of formaldehyde is 1.81 (ref. 141), a value in agreement with the observed acid-retardation, i.e. not in accordance with abstraction of a hydroxylic hydrogen atom from H2C(OH)2-The V(V) perchlorate oxidations of formaldehyde and chloral hydrate display an unusual rate expression, viz. 

The V(V) oxidation has some interesting kinetic features. The dependence of rate upon acidity shows a sharp minimum in the region of 3 and the... 

In a number of cases, electrochemical reactions involving adsorbed substances exhibit special kinetic features. For instance, when the reactant bulk concentration is... 

This great variety of pathways makes it difficult to decide which of the steps is the rate-determining step. It is most likely that at intermediate current densities the overall reaction rate is determined by the special kinetic features of step (15.24) producing the oxygen-containing species. The slopes of = 0.12 V observed experimentally are readily explained with the aid of this concept. Under different conditions, one of the steps in which these species react further may be the slow step, or several of the consecutive steps may occur with similar kinetic parameters. 

Previous kinetic investigations dealing with the NO + H2 reaction over supported noble metal-based catalysts showed different kinetic features according to the nature of the support [29,53-58], Initially, this reaction has been described in the absence of oxygen on Rh deposited on silica and alumina by the following mechanism [29],... 

Structural and Kinetic Features of Alcohol and Aldehyde Dehydrogenase I 421... 

Finally, a discussion of the kinetic features of the macrocyclic effect (the kinetic macrocyclic effect ) mentioned in Chapter 1 is deferred until the next chapter. 

A brief overview on why most of the autoxidation reactions develop complicated kinetic patterns is given in Section II. A preliminary survey of the literature revealed that the majority of autoxidation studies were published on a small number of substrates such as L-ascor-bic acid, catechols, cysteine and sulfite ions. The results for each of these substrates will be discussed in a separate section. Results on other metal ion mediated autoxidation reactions are collected in Section VII. In recent years, non-linear kinetic features were discovered in some systems containing dioxygen. These reactions form the basis of a new exciting domain of autoxidation chemistry and will be covered in Section VIII. 

A review by Brandt and van Eldik provides insight into the basic kinetic features and mechanistic details of transition metal-catalyzed autoxidation reactions of sulfur(IV) species on the basis of literature data reported up to the early 1990s (78). Earlier results confirmed that these reactions may occur via non-radical, radical and combinations of non-radical and radical mechanisms. More recent studies have shown evidence mainly for the radical mechanisms, although a non-radical, two-electron decomposition was reported for the HgSC>3 complex recently (79). The possiblity of various redox paths combined with protolytic and complex-formation reactions are the sources of manifest complexity in the kinetic characteristics of these systems. Nevertheless, the predominant sulfur containing product is always the sulfate ion. In spite of extensive studies on this topic for well over a century, important aspects of the mechanisms remain to be clarified and the interpretation of some of the reactions is still controversial. Recent studies were... 

Essentially the same mechanism was proposed for the [CuI(FLA) (PPh3)] (127) and [Cun(FLA)(IDPA)]+ (IDPA = 3,3 -iminobis(Al,Al-di-methylpropylamine) (128) catalyzed reactions. In the former case, composite kinetic features were found in the initial phase of the reaction indicating a slow transformation of the complex presumably to the same catalytically active species which was postulated in the Cu(FLA)2 system. 

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