Chemical Education Today
Letters Coulometric Titrations in Wine Samples In the article by Lowinsohn and Bertotti (1), the discussion can be enriched by taking into account the following: • White wines to which a sulfite is added as preservative probably contain diethyl sulfite, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide in addition to the sulfur species considered by the authors (2). • Volatile sulfur compounds present in wine have been determined by GC using the S-sensitive flame photometric detector(s) by entrainment in a nitrogen stream, adsorption on porous polymer, and desorption directly onto the GC column. • Sulfur dioxide adds to conjugated dienes and simple alkenes yielding 2,5-dihydrothiophene-1,1-dioxides (sulfolenes) and thiiran-1,1-dioxides (episulfones), respectively (3, 4) . However, neither sulfolenes nor episulfones are S(IV) species although both eliminate sulfur dioxide when heated and the latter when treated with base as well (4). • In general, there is no relation between the thermodynamic stability and kinetic lability of two different chemical species such as the bisulfite addition complexes of acetaldehyde and formaldehyde.
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Differential solvation (5) is probably more important than inductive effects in explaining why “the adduct formed between acetaldehyde and hydrogen sulfite is a less stable compound” (than the one derived from formaldehyde). Literature Cited 1. Lowinsohn, Denise; Bertotti, Mauro. J. Chem. Educ. 2002, 79, 103–105. 2. Chem. Abstr. 1983, 99, 37993w. 3. Leppanen, O. et al. J. Inst. Brew. 1979, 85(6), 350–353; Chem. Abstr. 1980, 93, 68569t. 4. Durst, T. Sulphones. In Comprehensive Organic Chemistry, Vol. 3; Barton, D.; Ollis, W. D., Eds.; Pergamon: Oxford, 1979; pp 178–180, 187–193. 5. March, J. Advanced Organic Chemistry, 4th ed.; Wiley: New York, 1992; p 270. Gabriel Gojon Reactimex, S.A. de C.V. Av. Industrias #1200-C Pte., Col. Bella Vista Monterrey, N.L. 64410, Mexico
[email protected] Vol. 81 No. 1 January 2004
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