Constantine Ricciuti

Formation of peroxides in fatty esters. II. Methyl linoleate: application of the polarographic and direct oxygen methods

SummaryThis study of the prolonged autoxidation of methyllinoleate at 80°C. has included polarographic identification and determination of hydroperoxides, the direct determination of oxygen contents, and catalytic micro-hydrogenation for the determination of unsaturation. The polarographic method has further substantiated the observations of other workers that the principal peroxidic substance formed during the autoxidation of methyl linoleate at 80°C. is a hydroperoxide. The direct oxygen measurements have shown that most of the oxygen absorbed in the initial stages of autoxidation can be accounted for as hydroperoxide. During the latter stages there was a continuous increase of oxygen uptake, half of which can be accounted for as free acid and half as forms other than hydroperoxide, ester, or free acid. By means of the catalytic micro-hydrogenation method it has further been shown that as the autoxidation progresses there is a continuous decrease in unsaturation.

Reactions of fatty materials with oxygen. XVI. Relation of hydroperoxide and chemical peroxide content to total oxygen absorbed in autoxidation of methyl oleate

SummaryMethyl oleate has been autoxidized at 100°, 80°, and 60° in the Barcroft-Warburg apparatus. Samples have been analyzed for total peroxide by the iodometric method and for hydroperoxide by the polarographic method. These peroxide values have been compared with each other and with total oxygen absorbed.The relation of chemical peroxide (yc) to oxygen uptake (x) is expressed by yc=1.09x0.936. This equation is equally valid at the three temperatures for the first 150 millimoles (15%) of oxygen absorbed per mole of methyl oleate.Similarly, the hydroperoxide content (yh) for the first 150 millimoles of oxygen absorbed at 80° and 100° is given by the equation yh=1.02x0.936.The ratio of hydroperoxide to chemically determined peroxide was, on the whole, constant throughout the entire range of oxidation (15–300 millimoles of oxygen absorbed per mole), and averaged about 95%.It has been shown unequivocally that the major portion of the peroxides formed in the autoxidation of methyl oleate are hydroperoxides, confirming conclusions of recent investigators. A small but significant amount of non-hydroperoxidic peroxide appears to be formed concurrently.

A polarographic investigation of the kinetics of epoxidation of unsaturated fatty acid esters

SummaryA polarographic technique which uses a nonaqueous electrolytic solution consisting of 0.25M ammonium acetate in glacial acetic acid is a suitable medium for the investigation of the kinetics of fatty acid ester epoxidations. From the polarographic data the specific reaction rate constants for the perlauric acid epoxidation of vinyl laurate, methyl oleate, and vinyl oleate in benzene at 25°C. were found to be 12, 232, and 270 × 10−3 l./mole−1 min−1. The Arrhenius equation for the epoxidations of methyl oleate and vinyl oleate by perlauric acid can be expressed as

Polarographic Studies of Oxygen-Containing Organic Compounds

k{\text{ = 5}}{\text{.53 x 10}}^{\text{7}} {\text{ e }}\frac{{{\text{ - 11,500}}}}{{{\text{RT}}}}{\text{ }}and{\text{ k = 8}}{\text{.61 x 10}}^{\text{6}} {\text{ e }}\frac{{{\text{ - 10,300}}}}{{{\text{RT}}}}.