Sulfides functional group

Treatment of any of these compounds with strong base produces an anion (or a lithium derivative if BuLi is used) on what was the methyl group. How does the sulfur stabilize the anion This question has been the subject of many debates and we have not got space to go into the details of all of them. There are at least two factors involved, and the first is evident from this chart of pKa values for protons next to sulfone, sulfoxide and sulfide functional groups. 

Yet the attached oxygen atoms cannot be the sole reason for the stability of anions next to sulfur because the sulfide functional group also acidifies an adjacent proton quite significantly. There is some controversy over exactly why this should be, but the usual explanation is that polarization of the sulfur s 3s and 3p electrons (which are more diffuse, and therefore more polarizable, than the 2s and 2p electrons of oxygen) contributes to the stabilization. 

Lignin is a major component of plants where it serves as a binding agent for cellulose and other materials, and the kraft process of paper production, heating with alkali and sulfide, produces polyhydroxy phenolic, carboxylic acid, and sulfide functional groups in a soluble black liquor mixture [5]. Acidification precipitates this modified lignin as a powder, hereafter referred to as limin, a 20630% by product in the manufacture of paper. 

Examples are known (22-25) of the oxidation of macromolecular substrates containing sulfide functional groups, with chiral polysulfoxides being prepared by different synthetic approaches ( 6,27.). However, the asymmetric oxidation of polymeric precursors was only performed with very limited degrees of chemoselectivity and enantioselectivity (27). The asymmetric oxidation reaction employed in this work is accomplished with a moderate enantioselectivity, which is nevertheless on the order of magnitude as those obtained with low molecular weight substrates (11.28.29). 

Bridges between aromatic rings of calixarenes and resorcinarenes are commonly considered chemically inert. Therefore, substitution of the bridges is the least common among modifications due to synthetic difficulties. However, in some cases, the modifications can be introduced prior to the cyclization step, as in 49 (Fig. 2.13) [55, 56]. Another possibility involves using thiacalixarenes. Oxidation of the adjacent sulfide functional groups in an a/ifi-relationship leads to an inherently chiral structure 50 [57]. It should be noted however, that inherent chirality in this case is inextricably boimd to stereogenic centers at the sulfur atoms. 

The limitations of this reagent are several. It caimot be used to replace a single unactivated halogen atom with the exception of the chloromethyl ether (eq. 5) to form difluoromethyl fluoromethyl ether [461 -63-2]. It also caimot be used to replace a halogen attached to a carbon—carbon double bond. Fluorination of functional group compounds, eg, esters, sulfides, ketones, acids, and aldehydes, produces decomposition products caused by scission of the carbon chains. 

Numerous diamines and aromatic dianhydrides have been investigated. WhoUy aromatic Pis have been stmctiirally modified by incorporating various functional groups, such as ether, carbonyl, sulfide, sulfone, methylene, isopropjlidene, perfluoroisopropyUdene, bipyridyls, sdoxane, methyl phosphine oxide, or various combinations of these, into the polymer backbone to achieve improved properties. The chemistry and apphcations of Pis have been described in several review articles (4). 

The functional group ia collectors for nonsulfide minerals is characterized by the presence of either a N (amines) or an O (carboxyUc acids, sulfonates, etc) as the donor atoms. In addition to these, straight hydrocarbons, such as fuel oil, diesel, kerosene, etc, are also used extensively either as auxiUary or secondary collectors, or as primary collectors for coal and molybdenite flotation. The chain length of the hydrocarbon group is generally short (2—8 C) for the sulfide collectors, and long (10—20 C) for nonsulfide collectors, because sulfides are generally more hydrophobic than most nonsulfide minerals (10). 

Sulfides are sulfur analogs of ethers they contain the C—S—C functional group. They are named as alkylthio derivatives of alkanes in substitutive lUPAC nomenclature. The functional class lUPAC nmnes of sulfides are derived in the same manner as those of ethers, but the concluding word is sulfide. 

Thiols (R—S—H) and sulfides (R—S—R ) are sulfur analogs of alcohols and ethers, respectively. Both functional groups are found in various biomolecules, although not as commonly as their oxygen-containing relatives. 

This chapter finishes the coverage of functional groups with C-O and C—S single bonds that was begun in Chapter 17. We ll focus primarily on ethers and take only a brief look at thiols and sulfides before going on to an extensive coverage of compounds with C=0 bonds in Chapters 19 through 23. 

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