Octanoic acid, decarboxylation

In octanoic acid solvent, alkyl substitution of malonic acids causes a small decrease in AG and thus an increase in rate as seen from Table 47. This is in contrast to the alkyl substituent effect in water (Table 46). The enthalpy of activation is clearly more favorable for decarboxylation of alkyl malonic acids than malonic acid in octanoic acid. Both Ai/ and AG are less favorable for decarboxylation of malonic acid in octanoic acid compared to water. This is expected on the basis of either the concerted (2) or the zwitterion mechanism (3) and (4). Association of the carboxyl groups of malonic acid with the octanoic acid solvent would thwart the attainment of the concerted transition state. Also generation of the zwitterion would be suppressed in octanoic acid. It is clear that additional work is required... 

Alkyl and aryl nitriles readily hydrolyze when submitted to NCW conditions. The hydrolysis is a multistep sequence as shown in Fig. 9.26. For instance, Katritzky et al. have reported that benzonitrile is converted to benzamide and benzoic acid at 250°C over a period of 5 days, and they conclude that the amide and the acid were in equilibrium. Under these conditions some decarboxylation can also occur. An et al. have reported the product distribution for the hydrolysis of benzonitrile as a function of time and temperature. Specifically, the ratio of benzamide to benzoic acid varied as follows after 1 h at 250°C, the distribution was 5 4. However, at 280°C after 1 h, the ratio was 1 1, and became 1 25 when the reaction time was extended to 6 h. Alkylnitriles exhibit similar behaviors Siskin et ah reported that at 250°C for 2.5 days decanonitrile quantitatively yields two major products, decanoic acid and decanoamide. When octanenitrile was hydrolyzed to octanoic acid amide and octanoic acid, the reaction was slightly slower than that ofbenzonitrile. Only 29% conversion took place in 1 h at 290°C. The limited solubility of octanenitrile in water, even in NCW conditions, was suggested as a possible factor for the slow reaction. Again the product distribution was dependent on the residence time and the temperature. 

Volatile fatty acid homologs higher than acetic acid have not been found as natural products of woody plants, although such acids and their esters are important components that contribute to the organoleptic properties of fruits. Nevertheless, propionic, butyric, valeric, and caproic acids occur in wetwood, in addition to elevated levels of acetic acid, as anaerobic fermentation products of starch (34, 36, 37, 43). For example, the concentration of acetic, propionic, and butyric acids of 0 to 3 mM in normal sapwood of white fir increases to as much as 38, 55, and 23 mM, respectively, in the wetwood of some fir species (38). The volatile fatty acids in gum turpentine and in the low wine (the aqueous phase of turpentine distillation) and turpentine tailings (24) also are likely the product of anaerobic fermentation. However, it should be noted that the oleoresin turpentine from Pinus sabiniana consists primarily of -heptane (22), and the turpentine from R jeffreyi contains a significant proportion of -heptane (22) and smaller amounts of A2-pentane, nonane, and undecane (39). The -heptane is derived not through the mevalonate pathway but rather by decarboxylation of octanoic acid (32). Presumably, the other hydrocarbons are also formed by decarboxylation. 

Scytalidin. This is the name proposed for a new fungitoxic metabolite isolated from a culture medium which has supported growth of Scytalidium sp., an imperfect fungus. Structure (148), which is similar to those determined for the nonadride metabolites (131) and (132), was established for this compound on the basis of spectroscopic and chemical investigations. Its biosynthesis, by analogy with the nonadrides, is considered to involve coupling of two Cu units (147), probably formed by decarboxylation of the condensation product from an octanoic acid derivative and oxaloacetate. 

Lipoic acid, or 6,8-dithiolane octanoic acid, is widely distributed in living organisms, intervening in hydrogen transport and acyl radicals by acting as a necesssary coenzyme in the oxidative decarboxylation of pyruvate. If one considers the electrochemical oxidation of the lipoic acid at the surface of the carbon paste electrode (EPC), in contrast to cystine, the molecule is electroactive at potentials less positive than +1.0 V vs SCE. The voltammetric recordings show a perfectly defined oxidation peak which indicates a fast kinetic reaction Ep - Ep/2 = 50 mV. 

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