ABSTRACT
Sulfur is ubiquitous in plants as it is a component of vitamins, coenzymes, and proteins which are essential in intermediary metabolism. In addition, some plants contain secondary organic sulfur compounds, usually in small amounts, which often are of interest because of their powerful and characteristic odors. Many of these have been shown to be simple aliphatic sulfur compounds including thiols (mercaptans),1 sulfides, and disulfides. Other aliphatic sulfur compounds from plants include sulfonium compounds, sulfoxides, and sulfones. The general structures of these compounds are illustrated in Figure 1. Derivatives in which sulfur is found in a higher oxidation state include sulfonic acids and sulfates, however, these types appear to be found mainly in lower plants. A noteworthy class consists of thiophene derivatives containing substituent groups in the 2-and 5-positions (Figure 1 ) which include highly unsaturated moieties (e.g., 1 -propynyl, R = -C=C-CH3). One of the most important types of sulfur compound is that of glucosinolates. Their general structure is shown in Figure 1 and R may include simple alkyl groups, various aromatic substituents, or more complex groups. These anionic compounds are normally found as potassium salts, however salts of organic bases also occur, e.g., the basic compound sinapine found in sinalbin. Recently, many thiazole (Figure 1 ) derivatives have been identified as volatile aromatic constituents of foods.2 These are generally fairly simple derivatives containing one, two, or three alkyl groups attached to the ring carbons. Benzothiazole, the 2-phenyl derivative, also occurs naturally. Various other sulfur compounds have also been reported, including thioketones and sulfur-containing alkaloids.
