Sulphuric acid, decarboxylation

If only the monocarboxybc acid is required, the ester after hydrolysis with potash may be strongly acidified with sulphuric acid and the mixture heated under reflux the mineral acid promotes decarboxylation at a temperature just above 100°. The net result is the replacement of the halogen atom of the alkyl halide by —CH COOH thus in the above example ... 

The kinetics of the sulphuric acid-catalysed decarboxylation of a range of alkyl substituted benzoic acids have been measured by Schubert et a/.634,635. The variation of rate coefficient with temperature for mesitoic acid is given in Table 206 and the value for the methyl ester shows that, at this acid concentration, the... 

The rates of decarboxylation of a range of 3-substituted mesitoic acids in 82.1 wt. % phosphoric and 83.0 wt. % sulphuric acids have been measured636 over a range of temperatures as indicated in Table 209, which gives the first-order rate coefficients together with the log A values and the energies, enthalpies, and entropies of activation calculated at 80 °C for sulphuric acid, and 119 °C for phosphoric acid these kinetic parameters are somewhat different from those... 

The decarboxylation of 2,4-dimethoxybenzoic acid by 2.5-8.0 M sulphuric acid at 60.5 °C has also been studied and division of the first-order rate coefficient by the molar concentration of sulphuric acid gave constant values (2.94+0.25 x 10 6) throughout the acid range so that the A-SE2 reaction was again indicated643. 

The kinetics of the decarboxylation of anthranilic acid have recently been examined. Earlier, an investigation of the decarboxylation of anthranilic acid in aqueous or acidic solution at 100 °C gave a C12 C13 value of 108.02 after 72 % reaction in 1.0 M sulphuric acid compared with 108.5 from complete decarboxylation, so that there is virtually no kinetic isotope effect for this compound646. First-order rate coefficients are given in Table 218 and from the variation of rate... 

Oxidation of the dihydropyridine derivative is most conveniently carried out with an aqueous nitric-sulphuric acid mixture. Removal of the ethoxycarbonyl groups may be achieved by a stepwise hydrolysis and decarboxylation sequence, but the one-step reaction described in Expt 8.29 using soda-lime is convenient. 

Unsymmetrical phenylpentafluorophenyl and methylpentafluorophenyl compounds are obtained from the appropriate mercury(ll) halide [45], or by decarboxylation procedures [69], and these mixed derivatives are particularly susceptible to attack. Nevertheless, bis(pentafluorophenyl)mercury is very resistant to acid cleavage for example, it can be recrystallised from concentrated sulphuric acid, but the well-known ligand-exchange process, e.g. with mercury(ll) chloride, occurs very rapidly and presumably by a four-centre process [45] (Figure 10.23). 

Tetrahydropyran-2-carboxylic acids are decarboxylated by concentrated sulphuric acid and the resulting carbonium ions, such as (14), are relatively stable this was demonstrated by n.m.r. spectroscopy. Qneolic acid (15), which was known to produce the lactone (17), also yielded the oxonium ion... 

Treatment of the alcohol derived from 3-methyltriazolpyridine 72 with aqueous sulphuric acid gave the alcohol 78 (60%) as a diaster-eoisomeric mixture, d.e. 5% (determined by NMR), and with acetic acid, acetate 80 (75%, d.e. 5%) was obtained. The chiral fenchyl group is too far from the triazolopyridine 3-position for chiral induction. In both cases small quantities of the elimination product, vinylpyridine 79, is formed. Under the usual conditions for treatment with selenium dioxide (i.e. 2,5M sulphuric acid, 80 °C, 24 h) (85JP12719) no reaction was observed. However, in p-xylene at reflux temperature, known pyridine 81 was obtained (97TA1869), probably due to a total oxidation followed by decarboxylation of the first-formed ketone 82 (Scheme 16). 

A method has been developed for the measurement of D-glucuronic acid in urine based on a reaction with tetraborate in the presence of sulphuric acid and 3-hydroxydiphenyl. ° Both free and bound acids can be determined more accurately than by the commonly used decarboxylation and resorcinol methods. 

Synthesis of compound 68 by oxidative decarboxylation of adamantane carboxylic acid is described in [25], Initially, for the synthesis of 2-(l-adamantyl)benzimidazole (68), adamantan radical was obtained in sulphuric acid diluted by silver nitrate in the presence of ammonia persulfate. Then, the synthesized radical was inserted directly into the heterocycle. After N-methylation, 2-(l-adamantyl)benzimidazole (68) was transferred in l-methyl-2-(l-adamantyl)-benzimidazole (79). The experiments carried out on chicken embryo revealed high antiviral activity of both obtained compounds [25] ... 

This study was extended to decarboxylation of 2,4,6-trimethoxybenzoic acid in aqueous sulphuric, perchloric and hydrochloric acids, the average values of the first-order rate coefficients obtained at 10 °C being listed in Table 213642. In the... 

Di-(l-naphthylmethyl)sulphone forms an excimer but does not react to give an intramolecular cycloaddition product like the corresponding ether but rather fragments to give sulphur dioxide and (l-naphthyl)methyl radicals (Amiri and Mellor, 1978). I-Naphthylacetyl chloride has a very low quantum yield of fluorescence and this is possibly due to exciplex formation between the acyl group and the naphthalene nucleus (Tamaki, 1979). Irradiation leads to decarbonylation. It is known that acyl chlorides quench the fluorescence of aromatic hydrocarbons and that this process leads to acylation of the aromatic hydrocarbon (Tamaki, 1978a). The decarboxylation of anhydrides of phenylacetic acids [171] has been interpreted as shown in (53), involving... 

The proposed catalytic mechanism of the ferredoxin oxidoreductase [32] is shown in Fig. 4, a similar mechanism existing for the analogous citric acid cycle enzyme, 2-oxoglutarate oxidoreductase. In outline, the 2-oxoacid is decarboxylated in a TPP-dependent reaction to give an hydroxyalkyl-TPP. From this, one electron is abstracted and transferred to the enzyme-bound iron-sulphur cluster, generating a free-radical-TPP species. This intermediate can then interact direct with coenzyme-A to form acyl-CoA, the iron-cluster receiving the second electron. In each case, ferredoxin serves to re-oxidise the enzyme s redox centre. 

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