Synthesis and Aroma Properties of Bis 1,1 and 2,2 (Methylthio) Alkanes

AIiphatic carbonyl compounds can be found in the volatile essence of most foods. Similarly, methylmercaptan is a predominant sulfur-containing odorant in many foods such as coffee, meat, and miIk. Since aliphatic carbonyls and methyl mercaptan possess interesting flavor notes in themselves, we investigated the organoleptic properties of the compounds formed by the reaction of figure 1 or, in the more general case herein studied of figure 2.

Bis (methylthio) methane has been reported to occur in boiled beef as well as in cheese, and bis (methylthio) ethane has been reported in beef. These occurrences provided additional impetus to study this series of flavorants.

Experimental--General Synthesis

To a round-bottom flask fitted with a magnetic stirrer and ice water bath is added 10 ml of methylene chloride, 2 ml of starting aldehyde or ketone, and a small quantity of molecular sieve to remove water formed during the reaction. To this stirred solution is added 4 ml of methyl mercaptan and (cautiously) 0.2 ml of BF3 etherate. The mixture is allowed to stir at room temperature for 4 hours. Finally, the reaction is washed with saturated NaCl solution, dried over NaSO4 and purified by preparative scale gas chromatography (SP-2100). The purified products were analyzed by IR and GC/MS as proof of their identity. Representative spectral information is indicated for 1,1 bis (methylthio) hexane. Infrared spectra indicated loss of all carbonyl (1730 cm-l) and aldehydic protons (2830, 2720 cm-1 ). Mass spectral analysis shows loss of methylthio groups and typical n-alkyl fragmentation patterns.

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