Summary
The use of catalytic hydrogenation as a quantitative method for the measurement of total unsaturation in tung oil and related products containing conjugated unsaturation, has been investigated.
The apparatus, which comprises essentially a gas burette, manometer, and reaction vessel, is relatively simple, is constructed entirely of glass, and employs an externally mounted magnetic agitator. The weighed sample and platinum catalyst are suspended in glacial acetic acid during hydrogenation. In the case of tung oil and partially hydrogenated tung oil, heating of the reaction vessel is necessary to complete the hydrogenation.
Hydrogen iodine values representing the total unsaturation in domestic and imported oils, alpha‐ and beta‐eleostearic acids, the residual unsaturation in partially hydrogenated tung oils, and the unsaturation of other organic materials are reported. Tung oil and eleostearic acid gave hydrogen iodine values of approximately 240 and 271, respectively.
Analytical hydrogenation, as described, is particularly well suited for the determination of unsaturation in conjugated systems.
Summary
A procedure has been described which extends the scope of the spectrophotometric method for polyun‐saturated acids to the determination of linoleic and conjugated acids in the presence of large quantities of conjugated trienoic acids.
Basis for the proposed method rests on equations which are offered to correct the “end” or “back‐ground” absorption of the highly absorbing triene conjugated acids at 233 mμ, the position of maximum absorption of conjugated dienoic acids and alkali isomerized linoleic acids. The method is limited to samples which do not contain nonconjugated trienoic acids (linolenic acids).
The method has been tested by the analysis of several mixtures of cottonseed and dehydrated castor oils of known composition, to which varying amounts of alpha, beta, and mixtures of alpha‐ and beta‐eleostearic acids have been added. These samples have been used to demonstrate the application of the proposed method for the determination of dienoic conjugated acids, alpha‐eleostearic acid, beta‐eleostearic acid linoleic acid, oleic acid, and total saturated fatty acids.
Comparisons of the results obtained with similar values, calculated from the known composition of the mixtures, prove that the proposed method gives reasonable results. Standard deviations between determined and calculated results vary from 0.36 for diene conjugated acids to 1.40 for oleic acid.
The method has been applied to the analysis of foreign and domestic tung oils.
SummaryMethyl alpha‐eleostearate has been reacted with mercuric acetate in acetic acid solution. Carrying out the reaction below room temperature gave products having the highest mercury content. Even these products were relatively unstable, gradually decomposing to produce mercury or mercurous acetate or both at room temperature. A typical product obtained at 10°C. is a viscous, pale yellow oil, insoluble in petroleum ether but soluble in alcohol, ether, and chloroform. Each C18 chain contained, on the average, 1.4 acetoxymercuri‐groups (CH3COOHg−), 1.5 acetoxyl groups attached directly to the carbon chain and 0.4 double bonds. For each mole of mercuric acetate added to the methyl eleostearate approximately one mole of mercuric acetate was reduced to mercurous acetate and a double bond in the ester chain was oxidized to an oxygen‐containing group of undetermined structure. Treatment of the acetoxymercuri‐, acetoxy‐ester with aqueous chlorides or bases yielded the corresponding chloromercuri‐ or hydroxymercuri‐derivative. Refluxing the acetoxymercuri‐, acetoxy‐ester in alcoholic potassium hydroxide saponified all the ester linkages and removed the acetoxymercuri‐groups with the formation of an equal number of double bonds, most of which are present in conjugatedtrans‐trans systems. The Marvel‐Rands chromatographic procedure was modified to permit determination of total acetoxyl groups and of acetoxyl groups attached to mercury atoms. Acetoxyl groups of the latter kind can also be determined by direct titration with standard base.
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