A study of odor stability of commercial stearic acid through isolation and identification of its volatile odoriferous compounds

Abstract

AbstractCommercial stearic acid may have an iodine value of less than 0.5. However, it develops a characteristic objectionable odor quite rapidly, sometimes before a shipment has reached its destination. The present investigation is an identification of the volatile odoriferous compounds which are responsible for this undesirable odor. Volatile compounds were isolated from commercial stearic acid and separated into acidic and nonacidic compounds. The acidic fraction did not have the characteristic off‐odor of the commercial stearic acid and was discarded. The nonacidic fraction was fractionated into pure compounds by repeated gas chromatography, which then were identified by a combination of gas chromatographic retention time and IR and mass spectrometry. A total of 52 compounds was identified positively. They contained a relatively large number of lactones, viz, 7 γ‐lactones, 4 δ‐lactones, and 2 γ‐2‐ene lactones. The other identified compounds were 11 saturated hydrocarbons, 7 saturated primary alcohols, 6 saturated methyl ketones, 10 saturated normal aldehydes, 4 saturated esters, and 1 diphenyl ether. In addition, 2 saturated aldehydes and 1 γ‐3‐ene lactone were identified tentatively. The odors of the saturated and unsaturated lactones were reminiscent of the objectionable odor characteristic of commercial stearic acid. Quantitative estimation indicated that commercial stearic acid contained: 0.47 ppm of 4‐hydroxy‐hexanoic acid, lactone; 0.06 ppm of 4‐hydroxy‐heptanoic acid, lactone; 0.31 ppm of 4‐hydroxy‐octanoic acid, lactone; 0.06 ppm of 4‐hydroxy‐nonanoic acid, lactone; and 0.53 ppm of 4‐hydroxy‐undecanoic acid, lactone.