Ester decomposition

Table 3 summarizes the scope and limitation of substrates for this hydrogenation. Complex 5 acts as a highly effective catalyst for functionalized olefins with unprotected amines (the order of activity tertiary > secondary primary), ethers, esters, fluorinated aryl groups, and others [27, 30]. However, in contrast to the reduction of a,p-unsaturated esters decomposition of 5 was observed when a,p-unsaturated ketones (e.g., trans-chalcone, trans-4-hexen-3-one, tra s-4-phenyl-3-buten-2-one, 2-cyclohexanone, carvone) were used (Fig. 3) [30],... 

Fig. 22 Initial reaction steps for fatty acid ester decomposition, represented by ethyl butanoate, which can decompose via thermolysis (pyrolysis), oxidation, or hydrolysis.

While complex nitrate esters, such as nitrocellulose and nitroglycerin, were the first to find application as explosives, understanding the mechanisms of nitrate ester decomposition was accomplished through the study of simpler compounds [11-16]. Ethanol nitrate was examhed by numerous researchers, and they conceded the first, and rate-determining, step was reversible loss of... 

The temperature dependence of the rate coefficient was given by the following Arrhenius equation kx = 10(1394 02)exp [(-174,000 2000)/8.3147] s 1. The relative rate ratio isopropyl chloroformate ethyl chloroformate was 160 at 280 °C. The enhanced rate due to an a-substitution was associated with the degree of polarity of the alkyl halides7. Therefore, the transition state for chloroformate ester decomposition must also be polar. The mechanism was believed to involve a cyclic six-membered transition state in which formation of HC1 is assisted, as shown below. 

This retro-ene reaction is accepted as the primary mode of ester decomposition. For olefins, it has been investigated both directly (8) and via the reverse reaction, the ene reaction (9). The best estimates for 1-hexene and 1-heptene are that the reaction proceeds with an activation energy of about 54 kcal/mol and a preexponential factor of 1012 sec-1. 

The relative importance of charge polarization stabilization as opposed to resonance stabilization in the transition states of the alkyl ester decompositions has been... 

The consistancy of the observed /4-factors, the magnitude of the activation entropies, the a correlations in the substituent effects at the a- and /8-carbon positions, the collective influence of all three substitutable centers on the reaction rates, the importance of charge stabilization in the transition state, and the primary deuterium isotope effects on the alkyl acetic acid ester decomposition, all favor the concerted polar 6-center transition state shown below (IV). However, an alternative possibility involving intimate ion-pair formation has been proposed by Scheer et al.. ... 

Cr produced by reaction of lower-valence states with hydroperoxides, can react with alcohols to produce chromate esters. These esters will, of course, decompose heterolytically, in the manner described above, to produce carbonyls and, for example, H2C1O3 [79]. A similar but somewhat altered mechanism of het-erolytic chromate ester decomposition has been proposed to explain differences noted among several alcohols in the oxidation of alcohols with Cr [81]. The use of chromium-containing catalysts to decompose hydroperoxides to carbonyls in reactions conducted without autoxidation has been frequently noted [82-85]. 

Al(OH)j EEA PVC PBMA PVB TG, TVA, IR HCl absorption TG, GC-MS TG, GC-MS Retards thennal degradation (endothermic decomposition) Higher degradation rate for uncrosslinked Inhibits monomer evolution, promotes ester decomposition Reduces degradation temperature 61 44 65 64... 

Various explanations have been offered for the mechanism of the formation of the carbon dioxide and of the ethane which has also been obtained in certain cases. None of these are entirely free from objections. Aldehydes are known to condense to esters under certain conditions and the decarboxylation of such has been offered as one explanation. However, the presence of carbon dioxide by this mechanism has not been supported by the evidence of other products of ester decomposition. Methane formation has not been reported in all cases where carbon dioxide has been found and this, together with the fact that entirely inadequate amounts of carbon have been found, seems to point that the rupture of acetaldehyde to C -+- C02 instead of carbon monoxide does not occur. The decomposition of aldehyde alone in the presence of precipitated iron oxide at 400° C. gave 40 per cent carbon dioxide and a large quantity of resinous matter.70 In the presence of reduced nickel, however, no carbon dioxide was formed and no resinous matter or oil resulted although nickel is an active catalyst for aldehyde decomposition. 

Monomer production is a general reaction of the methacrylates. Ester decomposition yielding methacrylic acid and the corresponding olefin is possible when the alcohol residue has P hydrogen atoms it becomes the most important mechanism in the case of tertiary esters like poly-t-butylmethacrylate but is competitive with monomer formation in ethyl- and n-butylmethacrylates. 

On the other hand, the reaction of peracid ester decomposition has a low selectivity in either pair... 

The addition of 2-diazopropane or 3-diazopentane to (112) results in exo-endo mixtures of both the triazoline (113) and the bicyclo[2.1,0]pentane (114). However, with the 1,2,3,4-tetramethyl analogue of (112) no addition occurs, Surprisingly, the imide (115) incorporates two and three molar equivalents of methylene from diazomethane to give products of spirocyclopropanation at C-4. Monocyclopropana-tion of (116) at the least substituted double bond proceeds efficiently when diazo-acetic ester decomposition is catalysed by copperfn) and similar monoaddition to... 

PBMA TG, GC-MS Inhibits monomer evolution, promotes ester decomposition 65... 

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