Rate laws decarboxylation

At the other end of the reaction, deviations from idealized rate laws are attributed to secondary reactions such as degradations of acids, alcohols, and amines through decarboxylation, dehydration, and deamination, respectively. The step-growth polymers which have been most widely studied are simple... 

The overall rate law is, however, found to contain a term involving [ketoacid] (47) as well as the term involving [ketoacid anion]. The ready decarboxylation of the (3-ketoacid itself is probably due to incipient proton transfer to 0=0 through hydrogen-bonding in (47) ... 

The kinetics and mechanisms of gas-phase elimination of ethyl 1-piperidinecarboxyl-ate, ethyl pipecolinate, and ethyl 1-methylpipecolinate has been determined in a static reaction system.9 The reactions proved to be homogeneous, unimolecular, and obey a first-order rate law. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene. The acid intermediate undergoes a very fast decarboxylation process. The mechanism of these elimination reactions has been suggested on the basis of the kinetic and thermodynamic parameters. 

It was shown many years ago that the decarboxylation of acids that meet these requirements are first-order in the acid - ". However, part of the decarboxylation arises from the anion of the acid without violation of first-order kinetics . The rate law for decarboxylation of )S-ketoacids has the form " ... 

A comparison of the relative rates of decarboxylation according to this rate law are given in Table 42 . For dicarboxylic acids, it appears that the dianion makes only a small contribution to the overall rate of decarboxylation. This conclusion was reached from the effect of pH on the rate of decarboxylation of dimethyl-... 

The anion (R ), which is generated in reaction (12), may be a carbanion or an enolate anion. It was found that dibromomalonate monoanion decarboxylation obeys a first-order rate law and that in the presence of bromine, the rate of decarboxylation equals the rate of bromine uptake . This indicates the formation of an enolate anion in the rate-determining step (12). 

The intermediacy of a lactone (276) would seem reasonable, but the predominance of the tra/is-alkene is not explicable in this case. As long as the acid was completely ionised, the rate of dehalogenative decarboxylation was independent of pH (in aqueous solution). However, in more strongly alkaline solution (pH > II), the E2 dehydrohalogenation becomes competitive, but the rate coefficient for the dehalogenative decarboxylation also increases . An initial attack of hydroxide on the acid, giving (277) and a second-order term in the rate law, has been suggested. 

The gas-phase elimination kinetics of several ethyl esters of 2-oxocarboxylic acid have been found to be homogeneous, unimolecular, and follow a first-order rate law. ° Ethyl oxalyl chloride undergoes only decarboxylation, while both ethyl piperidinegly-oxilate and ethyl benzoyl formate exhibit parallel decarboxylation and decarbonylation reactions. The mechanisms of these decomposition reactions were described in terms of concerted discrete polar cyclic TS structures. 

Several studies have been made using Pb as an oxidant. The reaction with methanol yields formaldehyde with rupture of a C—H bond as the rate-limiting step. Whereas the product is reportedly stable in the presence of Pb(OAc)4, fact further reaction takes place to yield methyl formate. The mechanism of decarboxylation of 2-hydroxycarboxylic acids, ROH, in anhydrous acetic acid has been investigated using several techniques. The rate law is of the form... 

The rates of oxidative decarboxylation of amino acids by the cop-per(III) complex [Cu(I06)2] increase with increasing pKb of the substrate. " Periodate inhibition in the rate law suggests formation of a complex between the amino acid and [CuflOe)] , which decomposes in... 

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