Monocarboxy acids

The course of hydrocarboxylation was studied further by sequential analyses of reaction mixtures and by detailed characterization of the purified carboxy acid products. Figure 1 plots kinetic runs with linoleic acid and methyl linoleate at 120°C. Analysis by GLC shows the rapid disappearance of diene followed successively by initial conjugation of the diene system, monocarboxylation, and then dicarboxylation. Cyclic ketones and other unidentified materials (not shown) are formed in minor amounts. Conjugated dienes (mixture of cis,trans and trans,trans) peak at 1 hr and then rapidly disappear. Monocarboxy acids peak around 6-8 hrs and disappear at later stages of the reaction. At 140°C, the carboxylation follows the same course (Figure 2A). Formation of conjugated dienes reach a maximum around 0.5 hr. Monocarboxy acids peak around 1 hr, decrease, and then level at 3-4 hrs. 

Further characterization showed that the monocarboxy acids from both linoleate and its conjugated diene isomers are unsaturated. These unsaturated carboxy acids to a great extent are carboxylated further. However the GLC and kinetic results indicate that a small amount becomes saturated at 140°C (5 to 10%). Conversion to dicarboxy acids reaches a maximum (75-83%) because of the formation of these saturated monocarboxy acids and byproducts. 

To elucidate further the reaction sequence, competitive catalytic carboxylation was studied with mixtures of methyl linoleate and conjugated linoleate. At 120 °C methyl linoleate carboxylates initially more rapidly than conjugated linoleate (Figure 3). With this mixture, monocarboxy acids are formed in larger amounts than the dicarboxy acids. 

Product characterization provides further insight on the course of diene carboxylation. The monocarboxy acids were identified as methyl carboxyoctadecenoate (1) from chromatographic, IR, mass spectral, and selective hydrogenation studies. The double bond of 1 from carboxylated linoleate is 40% trans in configuration (IR), and its carboxy group is located mainly on carbon-10 and -12 positions (Table II). In contrast,... 

The methyl ester of carboxyoctadecenoate 1 was also identified (about 10% by GLC) in the neutral ether extract from the salts of car-boxylated linoleate. Apparently some methanol is formed from H20 and CO under the conditions of hydrocarboxylation, and esterification of the monocarboxy acids occurs to a small extent. Double bond hydrogenation is another minor side reaction observed. Small amounts of carboxyocta-decanoate la detected in final hydrocarboxylation mixtures would arise from H2 produced by the water-gas reaction (CO + H20 = C02 + H2). 

Figure 8 shows kinetic data on the catalytic hydrocarboxylation of methyl linolenate. There is initial conjugation of the triene system. Monocarboxy acids formed as initial products peak after 2 hrs and disappear almost completely. The dicarboxy acids are important intermediates and carboxylate further to give tricarboxy acids. The conversion to tricarboxy acids at 140°C does not exceed 50 to 53% (Runs 9 and 11, Table I). Cyclic ketones are formed as in linoleate in small but significant amounts. 

Analysis of aqueous obidoxime (250 mg ml ) stored at approximately 20°C for 19 years yielded 92% obidoxime, 2.5% of the presumed monocarboxy derivative, 0.16% formaldehyde and only traces (0.7 fig ml. ) of cyanide, while the pH had dropped to about 3.5 (Spohrer and Eyer, 1995). Formation of free formaldehyde may accelerate the decomposition of obidoxime and it has been argued that formaldehyde reacting with the liberated hydroxylamine may shift the equilibrium in favour of the aldehyde and eventually to the carboxylic acid (Rubnov et al.,... 

The acid salts of dicarboxy-acids so far described have compositions in the ratio of MHY. But just as monocarboxy-adds sometimes form salts of anomalous composition, such as AfHAj, so also do dicarboxylic acids. We have already mentioned the superacid succinate, KHgYj. A variety of such compositions is known, and examples are certain to multiply as seeirch is turned in that direction. 

Driers, also referred as siccatives, are compounds used to catalyze the autoxidation process in drying or semidrying oil based resins at ambient or elevated temperatures. They are typically organometallic compounds, most commonly metal soaps of long chain monocarboxy-lic acids, supplied in a suitable solvent (carrier). These metal soaps are synthesized from a variety of metals and acids. Although the metal, being the active part of the compound, effects the drying reaction, the monocarboxylic acid component confers solubility and compatibility of the drier in solvents and resin. 

Ultra-violet absorption spectroscopy applied to the pyridine monocarboxy-lic acids, their methyl esters and N-methylbetaines shows that in aqueous solutions near the isoelectric points the acids are present predominantly in the zwitterionic forms. On the other hand, in ethanol the neutral non-dipolar form is favoured. ... 

A reducing disaccharide on oxidation yields a monocarboxy bionic acid, the —CHO becoming —COOH. These acids, like all hydroxy acids with hydroxyl in the 3, 4, 5, or 6 position, readily close up to form a lactone, or ring compound made by condensation between —COOH and one of the —OH groups of the same carbon chain. 

Dipolai Form of the Amino Acids.—The monoamino-monocarboxy acids are neutral in solution, and are very weak electrolytes. At the same time they are able to neutralise either acids or bases. This property, termed amphotericity, is due to the presence of an acid and a basic group in the same molecule. In aqueous solutions amino acids ionise to form a dipolar or zwitter-ion, having two equal charges of opposite electric sign, and tending to migrate neither to anode nor cathode when a current is passed through the solution. 

The neutral group of monocarboxy-monoamino acids. No complete qualitative method of separation is known. On concentration, tyrosine, leucine, and cystine, the least soluble of the acids, crystallise out. 

AO represents a specific amino acceptor, such as an a-keto acid. In the reverse reaction, AH.NH2 represents a suitable amino donor, which may be one of the natural amino acids. That is to say, the aminopherase system, working in one direction, can convert monocarboxy keto acids such as pyruvic, into amino acids by donation of — NH2 and working in the reverse direction, aminopherases can deaminate amino acids to keto acids by removal of — NHg. Such systems are of obvious importance in the natural synthesis of amino acids from carbohydrate residues and products. 

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