Carboxylate decompositions, mechanisms

Though salt dehydration was not accompanied [27] by particle disintegration, the anhydrous pseudomorph was shown by X-ray diffiaction measurements to be very poorly crystallized (a characteristic feature of many nickel carboxylates). Decomposition in air (554 to 631 K) proceeded at a constant rate (0.1 < nr < 0.8 and = 96 kJ mol" ), ascribed to the operation of an autocatalytic mechanism. The reaction in vacuum (562 to 610 K) gave a sigmoid ar-time curve which was fitted by the Prout-Tompkins equation. Because the activation energy was the same as that for reaction in air, it was concluded that the same mechanism operated. The reaction in air yielded residual nickel oxide, while reaction in vacuum gave the carbide with excess carbon and some oxide. In addition to carbon dioxide, the volatile products of decomposition included water and acetic acid. 

For the decompositions of the metal carboxylates, alternative mechanisms involving breaking of each of the different principal linkages in the R-CO-O-M group have been proposed as rate controlling (reference [40] p.210), in addition to mechanisms based on charge transfer, interface strain and catalysis by an active product. 

Scheme 1735. Decomposition mechanisms for a lithium adduct of a 1,2-diglyceride. (Adapted with permission from Ref. 162.) (a) Lx)ss of lithium carboxylate (b) loss of long-chain fcetene.

Similar decomposition mechanisms have been found with other Pseudomonas strains (including P. multivorans) and with monomethyl and dimethyl naphthalenes, for example to methyl salicylic acids and to dimethyl salicylic acids (if both methyl groups were present in the same nucleus of the naphthalene), or to methyl naphthalene carboxylic acids [51]. On the other hand, Cunninghamella el-egans metabolizes naphthalene to trans-l,2-dihydrodiol, from which 1-naphthol, 1,4-naphthoquinone and 4-hydroxy-1-tetralone are formed as intermediates for further decomposition [126, 127]. 

The tetrazinc [Zn4(/r4-0)(/i-C02CR)6] can be prepared by a variety of methods with short straight chain carboxylic acids and this structural type identified by characteristic IR bands. The formation process and influence of water were monitored by IR spectroscopy and a mechanism of formation and decomposition proposed.375 Further evidence for the validity of the mechanism,... 

Abstract In this chapter, the depression mechanism of five kinds of depressants is introduced respectively. The principle of depression by hydroxyl ion and hydrosulphide is explained which regulates the pH to make the given mineral float or not. And so the critical pH for certain minerals is determined. Thereafter, the depression by cyanide and hydrogen peroxide is narrated respectively which are that for cyanide the formation of metal cyanide complex results in depression of minerals while for hydrogen peroxide the decomposition of xanthate salts gives rise to the inhibitation of flotation. Lastly, the depression by the thio-organic such as polyhydroxyl and poly carboxylic xanthate is accounted for in detail including die flotation behavior, effect of pulp potential, adsorption mechanism and structure-property relation. 

Bromine-atom atomic resonance absorption spectrometry (ARAS) has been applied to measure the thermal decomposition rate constants of CF3Br in Kr over the temperature range 1222-1624 K. The results were found to be consistent with recently published theory. The formation of cyclopent[a]indene and acenaphthylene from alkyl esters of biphenyl-mono- and -di-carboxylic acids has been observed in flash vacuum pyrolyses at 1000-1100 °C. The kinetics and mechanisms of free-radical generation in the ternary system containing styrene epoxide, / -TsOH, and i-PrOH have been examined in both the presence and absence of O2. ... 

The presence of various types of Au sites and carbonate/carboxylate species as well as variation in the OH intensity of Ti02 (not shown here) during the reaction suggests that CO oxidation over AuCb catalyst could follow the carboxylate mechanism which involves the reaction of adsorbed CO with OH to produce a carbonate/carboxylate species on Au cations and the decomposition of carboxylate to COz-iS, 10) Transient infrared study needs to be employed to further verily the role of carbonate/carboxylate species in the reaction pathway. (13)... 

A further mechanism of decomposition which was observed up to date only for M = Cu(II) (101,102) is the -elimination of carboxylates ... 

This mechanism is of importance in radical induced amino acid damage catalyzed by copper ions. The study of the decomposition of transients with a metal-carbon -bond containing two potential leaving groups (both an amine and a carboxylate group) at the p position of the carbon centered radical is of special interest. It was reported that the intermediate formed with the amino acid 2-methylalanine with cupric ions decomposes via p-carboxyl elimination whereas the intermediate formed with cuprous ions decomposes via p-amine elimination (102). 

The catalysis of the selective oxidation of alkanes is a commercially important process that utilizes cobalt carboxylate catalysts at elevated (165°C, 10 atm air) temperatures and pressures (98). Recently, it has been demonstrated that [Co(NCCH3)4][(PF6)2], prepared in situ from CoCl2 and AgPF6 in acetonitrile, was active in the selective oxidation of alkanes (adamantane and cyclohexane) under somewhat milder conditions (75°C, 3 atm air) (99). Further, under these milder conditions, the commercial catalyst system exhibited no measurable activity. Experiments were reported that indicated that the mechanism of the reaction involves a free radical chain mechanism in which the cobalt complex acts both as a chain initiator and as a hydroperoxide decomposition catalyst. 

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