Decarboxylation data

Results obtained for two mixed plastics are summarized in Table 4. A balance exists between process temperature, plastics feed rate, and product yields (67). For example, lower temperatures increase wax formation due to incomplete depolymerization. Slower feed rates and increased residence times reduce wax formation and increase the yield of Hquids. The data summarized in Table 4 illustrate that the addition of PET to a HDPE PP PS mixture changes the performance of the Conrad process. Compared to the reference HDPE PP PS mixture, increased amounts of soHds ate formed. These are 95% terephthahc acid and 5% mono- and bis-hydroxyethyl esters. At higher temperatures, apparentiy enough water remains to promote decarboxylation. 

The latter on hydrolysis and decarboxylation yielded womicotyrine (II, above], rosettes of flattened needles, m.p. 98-9°, picrate, m.p. 203-4° dec.), in good agreement with the data of previous authors. 

Little data is available, but methyl groups a and y to ring nitrogens appear to be activated. 2-Methyl and 6-methyl substituents in pyrido[3,2-d]pyrimidines undergo bromination 38.79,12.9 oxidative decarboxylation, and form styryl compounds.The 6-methyl group in pyrido[2,3-d]pyrimidines could not be brominated. ... 

The current-potential relationship indicates that the rate determining step for the Kolbe reaction in aqueous solution is most probably an irreversible 1 e-transfer to the carboxylate with simultaneous bond breaking leading to the alkyl radical and carbon dioxide [8]. However, also other rate determining steps have been proposed [10]. When the acyloxy radical is assumed as intermediate it would be very shortlived and decompose with a half life of t 10" to carbon dioxide and an alkyl radical [89]. From the thermochemical data it has been concluded that the rate of carbon dioxide elimination effects the product distribution. Olefin formation is assumed to be due to reaction of the carboxylate radical with the alkyl radical and the higher olefin ratio for propionate and butyrate is argued to be the result of the slower decarboxylation of these carboxylates [90]. 

The tertiary structure of glutamate racemase has already been resolved and it has also been shown that a substrate analog glutamine binds between two cysteine residues. These data enabled us to predict that the new proton-donating amino acid residue should be introduced at position 74 instead of Gly for the inversion of enantioselectivity of the decarboxylation reaction. 

Tableir.Surmary Data on Decarboxylation of Kevlar and its Ra of Oxygen (as a Constituent in 44c02 °C°2 anli °C°2)...

Data are deduced from pseudo first order decarboxylations at 196°C for 20 m1n from the top surface layer of the photolyzed Kevlar ... 

The results presented by Cramer and Kampe are amplified by the data in Table XII which correspond to a recent investigation of the cyclohepta-amylose-catalyzed decarboxylation of a series of substituted phenylcyanoacetic acid anions (Straub and Bender, 1972). These data differ strikingly... 

Beck et al. (1997) used GC-MS to monitor the increase in the proportion of retene in pine tars with increasing temperature, and 13C-NMR to monitor the increased aromatic signal resulting from dehydrogenation and decarboxylation reactions. These data allow approximate determinations of the production temperature of a tar from the molecular composition. Diterpenoid molecules of probable pine origin have been detected in many archaeological contexts and some detailed compositional studies have appeared (Robinson et al, 1987 Heron and Pollard, 1988 Beck et al., 1989 Reunanen et al., 1989 Beck et al, 1994). 

With respect to the biosynthesis of the solvents it has been speculated on the basis of quantitative data and the identification of (3,y-unsaturated acids in primitive oxytelid beetles that pairs of 1-alkenes and y-lactones are synthesized from corresponding 3-alkenoic acids by either lactonization or by decarboxylation [118]. 

There are two mechanistic possibilities left, either hydride transfer precedes decarboxylation, or vice versa. These two possibilities can be distinguished using Equations 11.51 and 11.53. Within experimental error only Equation 11.51 is consistent with the isotope effect data collected in Table 11.1, thus confirming that the reaction proceeds via a stepwise mechanism with hydride transfer to triphosphate nucleotide (NADP+) and intermediate formation of oxalacetate preceding decarboxylation ... 

Biocatalytk decarboxylation is a imique reaction, in the sense that it can be considered to be a protonation reaction to a carbanion equivalent intermediate in aqueous medimn. Thus, if optically active compoimds can be prepared via this type of reaction, it would be a very characteristic biotransformation, as compared to ordinary organic reactions. An enzyme isolated from a specific strain of Alcaligenes bronchisepticus catalyzes the asymmetric decarboxylation of a-aryl-a-methyhnalonic acid to give optically active a-arylpropionic acids. The effect of additives revealed that this enzyme requires no biotin, no co-enzyme A, and no ATP, as ordinary decarboxylases and transcarboxylases do. Studies on inhibitors of this enzyme and spectroscopic analysis made it clear that the Cys residue plays an essential role in the present reaction. The imique reaction mechanism based on these results and kinetic data in its support are presented. 

Patel et al. [40] found that moismre and the pH of the micro-environment influenced degradation the most. They identified the best diluent for tablet manufacture as being dibasic calcium phosphate, with a basic modifier (sodium carbonate, sodium bicarbonate or magnesium oxide). The authors indicated that the degradation pathways observed were deiodination, deamination and decarboxylation. The data are shown in Table 2.4. 

Similarly, vesicular reactivity is dependent on bilayer fluidity and Arrhenius (or Eyring) plots for the decarboxylation of 6-NBIC show a break around Tm. " For the Kemp elimination in different bilayers, it was found that the bilayer for which kinetic data had been gathered below its was least effective as a catalyst. Ester hydrolysis has also been found to be faster above r. For the decarboxylation of 6-NBIC, the increase in catalytic efficiency was attributed to different aggregate surface dynamics based on the observation that vesicles above showed intermediate activation parameters between vesicles below and micelles. One could, of course, discuss causality here considering the fact that many of the bilayer... 

Decarboxylase reaction Kinetic constants The optimum pH of the decarboxylase reaction was determined with the natural substrates of both enzymes, pyruvate (PDC) and benzoylformate (BFD). Both enzymes show a pH optimum at pH 6.0-6.5 for the decarboxylation reaction [4, 5] and investigation of the kinetic parameters gave hyperbolic v/[S] plots. The kinetic constants are given in Table 2.2.3.1. The catalytic activity of both enzymes increases with the temperature up to about 60 °C. From these data activation energies of 34 kj moT (PDC) and 38 kJ mol (BFD) were calculated using the Arrhenius equation [4, 6-8]. 

Figure 8.10a is an example of some data in which the effect of added salt is more than a competitive ion-binding phenomenon. The reaction involved is the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate, catalyzed by hexadecyl trimethyl ammonium bromide micelles ... 

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