Methyl sulfide groups, determination

The methyl sulfide-containing alkaloids, varamines A (123) and B (124) were isolated from L. vareau. Their structures were determined by interpretation of NMR spectral data and by comparison with related alkaloids. The varamines were cytotoxic towards L1210 murine leukaemia cells with IC50 values of 0.03 and 0.05 Xg/mL, respectively [138], The varamines (123-124), lissoclins (110-111) and diplamine (112) all contain a methyl sulfide group linked to a pyridoacridine ring system [22],... 

The second, even more convenient, method to determine double-bond positions in unsaturated hydrocarbons is the use of dimethyldisulfide derivatives (Francis and Veland, 1981 Carlson et al, 1989 Howard, 1993). In this approach, alkenes are dissolved in a carbon disulfide and iodine solution and kept overnight. The reaction yields a derivative with methyl sulfide substituents on each of the carbons that comprised the double bond. If the double bonds are separated by four or more methylene groups, the reaction proceeds... 

Ideally, Q1 should be determined via Eq. (10-2) or (10-2aX from a value for the simplest possible derivative of i e.g., above compounds for i equal —S—. The use of more complex compounds in this connection is often complicated by deviations from Eq. (10-1), as discu ed in Section 0-2B and Chapter 11. In the absence of a X value fOr a simple derivative of i, somewhat less reliable values of 2 can be calculated from poly-functional molecules, or even from AT values for gas-solid adsorption I Eq. (9-2)]. As discussed in Section 10-3B, it is also possible to estimate for a given group (e.g., —S— in dimethyl sulfide) from a Value of 0 for the same group with different substituents (e.g.,—S in phenyl methyl sulfide). Likewise, it is possible to estimate for a group adsorbed... 

Methyl sulfide (CHi-S) groups arise from methionine and may be determined by the method of Baemstein (39) or colorimetrically (40). 

The concentration of zinc accelerator-thiolate complexes in the rubber is not the only factor determining the balance of the two reactions in NR. Both the rate of desulfuration of polysulfide crosslinks and the rate of their thermal decomposition depend upon the positions of attachment of the sulfur chains to the backbone rubber chains and the detailed structure of the hydrocarbon at the ends of the crosslinks. In the course of normal accelerated vulcanization there are three different positions of attack on the polyisoprene backbone two of these are methylene groups in the main chain (labelled d and a in 3), and the third is the side chain methyl group (labelled b in 3). Direct analysis of the distribution of the sites of attack cannot yet be made on actual rubber vulcanizates, and information has had to be obtained solely by sulfuration of the model alkene 2-methyl-2-pentene and, more recently, 2,6-dimethyl-2,6-octadiene. The former (4) models the a-methylic site but only one of the two a-methylenic sites of polyisoprene the latter (5) models all three sites, but at the present time these are not all supported by the synthesis of relevant sulfides. Because allylic rearrangements are common in subsequent reactions of the sulfurated rubber, sulfur substituents appear not only on allylic carbon atoms but on isoallylic carbon atoms. Thus, from 2-methyl-2-pentene, the groups shown in Scheme 2 are formed. 

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