Acid retardation mechanism

This mechanism is supported by these facts (1) the kinetics are second order (first order in each reactant) (2) added acetic acid retards the reaction (drives the equilibrium to the left) and (3) cis glycols react much more rapidly than trans glycols. For periodic acid the mechanism is similar, with the intermediate ... 

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 flame retardant mechanism for phosphorus compounds varies with the phosphorus compound, the polymer and the combustion conditions (5). For example, some phosphorus compounds decompose to phosphoric acids and polyphosphates. A viscous surface glass forms and shields the polymer from the flame. If the phosphoric acid reacts with the polymer, e.g., to form a phosphate ester with subsequent decomposition, a dense surface char may form. These coatings serve as a physical barrier to heat transfer from the flame to the polymer and to diffusion of gases in other words, fuel (the polymer) is isolated from heat and oxygen. 

Organic acids retard the formation of nitroxyl radicals via the reaction of the peroxyl radical with the aminyl radical [10], Apparently, the formation of a hydrogen bond of the >N H0C(0)R type leads to the shielding of nitrogen, which precludes the addition of dioxygen to it, yielding the nitroxyl radical. Thus, the products of the oxidation of alcohols, namely, acids have an influence on the mechanism of the cyclic chain termination. 

Role of Ascorbates At low levels 100 ppm) ascorbic acid has been shown to catalyze development of WOF as shown by increased TBA values 0> 3). At higher levels (>1,000 ppm), however, ascorbic acid retards oxidation (3). Although the mechanism of retardation is not known, it Was been suggested that high levels of ascorbates may upset the balance between... 

KEY WORDS citric acid, gypsum, mechanical properties, mechanism of sel retardation, microstnicture of retarded gypsum mortars, texture index, strength, creep properties... 

The object of this research work is the investigation of the mechanism of retardation of gypsum plaster by the addition of citric acid and its influence on the properties of the fresh and hardened mortar. The significance of this work lies in the explanation of the retardation mechanism and its close connection with the microstructure and hence with the mortar properties. 

Co", Cr", Cu", Pd" and Pt" accelerate the racemization rates of amino acids. The mechanisms are not always as simple as that outlined above for Co". Thus, with [Cu(L-AlaO)2] it has been known for some time that the rate of racemization was faster than that for H-D exchange under the same conditions. It was subsequently shown that at high pH, with O2 present, pyruvate was formed from an oxidative deamination reaction which further catalyzed the racemization rate through formation of a Schiff base intermediate (16). This combination of carbanion and Schiff base intermediates was further confirmed by studies on the Zn" complex. Contrary to earlier reports it has now been shovra that Ni" actually retards the racemization rates of amino acids. ... 

Concerning the mechanism of acid retardation. Hatch and Dillon [115] note that various ideas or their combinations may be offered to explain the absorption of strong acids on anion-exchange resins ... 

The above-discussed acid retardation and base retardation in the immobiUzed Uquid phase could be compared with the so-called salting-out effects. However, this term is hardly applicable to the case of salt retardation, the first example of which was demonstrated by a successful removal of small amounts of NH4CI from a concentrated brine of (NH4)2S04. This practically important problem arises in the manufacture of caprolactam, where large amounts of sulfuric acid are converted into ammonium sulfate used for the preparation of the crystalline fertilizer. The new process of ISE on nanoporous NN-381 resin allowed an effective purification of very large volumes of concentrated sulfate brine, due to the fact that small ions of NH and Cl are efficiently squeezed into and retained in the finest pores of the sorbent [172]. We consider this salt retardation process as a convincing proof of our interpretation of the mechanisms of the new electrolyte separation process. 

It has been suggested that materials, which decompose to give Lewis acids, fall into this category of flame-retardant mechanisms [19]. 

The flame retardant mechanism operates in the solid state. Ammonium polyphosphate decomposes endothermically on heating to 275 °C, liberating polyphosphoric acid and... 

The crosslinking is very rapid at first with the benzoyl peroxide-amine system, unless the concentration of tertiary amine (N,N-dimethyl aniline or N,N-dimethyl para-toluidine) is very low. But the reaction fades early, probably because of the retarding effect of the benzoic acid. The mechanical properties of the finished product tend not to match those obtained with the cobalt system. Also there is a yellowing of the resin as cure proceeds. Consequently, the hydroxide-cobalt(n) system is more widely used. One proposed mechanism is ... 

As regards sulphuric acid, there is here again an increase in polarity and an increase in rates of nitration when comparison is made with other solvents in the series. This gross fact would be difficult to reconcile with any mechanism, such as the one, which contains an essential forward step which would be retarded by increased polarity of the solvent. 

Alkyl diphenyl phosphate plasticizers can exert flame-retardant action in vinyl plastics by a condensed-phase mechanism, which is probably some sort of phosphoms acid coating on the char. Triaryl phosphates appear to have a vapor-phase action (29). 

The question as to whether a flame retardant operates mainly by a condensed-phase mechanism or mainly by a vapor-phase mechanism is especially comphcated in the case of the haloalkyl phosphoms esters. A number of these compounds can volatilize undecomposed or undergo some thermal degradation to release volatile halogenated hydrocarbons (37). The intact compounds or these halogenated hydrocarbons are plausible flame inhibitors. At the same time, thek phosphoms content may remain at least in part as relatively nonvolatile phosphoms acids which are plausible condensed-phase flame retardants (38). There is no evidence for the occasionally postulated formation of phosphoms haUdes. Some evidence has been presented that the endothermic vaporization and heat capacity of the intact chloroalkyl phosphates may be a main part of thek action (39,40). 

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