Sulfur—carbon bonds halogens

The overall transformation is the conversion of the carbon-sulfur bonds bond to a carbon-carbon double bond. The original procedure involved halogenation of a sulfide, followed by oxidation to the sulfone. Recently, the preferred method has reversed the order of the steps. After the oxidation, which is normally done with a peroxy acid, halogenation is done under basic conditions by use CBr2F2 or related polyhalomethanes for the halogen transfer step.92 This method was used, for example, to synthesize 1,8-diphenyl-1,3,5,7-octatetraene. 

The different reactivities of the two substituents on C-l allow selective replacement and conversion of them. Alkyl monothio-acetals [proposed as intermediates in mercury(II)-catalyzed demer-captalation reactions—see Section IV,l,b] have been prepared from a-bromothioethers by the combined action of an alcohol and silver(I) carbonate the introduction of S-nucleophiles is discussed in Section 11,6. Reduction of 81 by lithium aluminum hydride effects hydrogen-olysis of the carbon-halogen bond, whereas the action of Raney nickel on the derived S-ethyl O-methyl monothioacetal specifically cleaves the carbon-sulfur bond to afford the pentaacetate of 1-0-methyl-D-galactitol.327... 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

Codeposition of silver vapor with perfluoroalkyl iodides at -196 °C provides an alternative route to nonsolvated primary perfluoroalkylsilvers [272] Phosphine complexes of trifluaromethylsilver are formed from the reaction of trimethyl-phosphme, silver acetate, and bis(trifluoromethyl)cadmium glyme [755] The per-fluoroalkylsilver compounds react with halogens [270], carbon dioxide [274], allyl halides [270, 274], mineral acids and water [275], and nitrosyl chloride [276] to give the expected products Oxidation with dioxygen gives ketones [270] or acyl halides [270] Sulfur reacts via insertion of sulfur into the carbon-silver bond [270] (equation 188)... 

The most widely used method for the synthesis of iminoboranes involves the 1,2-addition of boron-element bonds such as boron-hydrogen, boron-halogen, boron-carbon, or boron-sulfur bonds across the C=N bond of nitriles thereby producing variously substituted iminoboranes (Eq. (2)). The formation of iminoboranes as well as the stability of the products depends on the substituent on the nitrile group, the nature of the boron-element bond to be cleaved during the 1,2-addition across the C N bond, and to a lesser extent on the non-reacting boron substituents 26T... 

The fingerprint region (1500-500 cm 1), where all single bonds between carbon and elements such as nitrogen, oxygen, sulfur and halogens absorb... 

Substitutions such as alkylation (Chapter 5) and oxygenation (Chapter 9) are fundamental transformations essential to the chemistry of hydrocarbons. Other heterosubstitutions (i.e., formation of carbon-heteroatom bonds), such as halogenation, nitration, or sulfuration (sulfonation), are also widely used reactions. It is outside the aim of our book to discuss comprehensively the wide variety of substitution reactions (for a scope, see, e.g., March s Advanced Organic Chemistry), but it is considered useful to briefly review some of the most typical selected heterosubstitutions of hydrocarbons. 

Examples of electrophilic reagents that normally add to carbon-carbon double bonds of alkenes to give saturated compounds include halogens (Cl2, Br2, and I2), hydrogen halides (HC1 and HBr), bypohalous acids (HOC1 and HOBr), water, and sulfuric acid ... 

While carbon and oxygen radicals add irreversibly to carbon-carbon double bonds, the fragmentation reaction is rapid (and often reversible) for elements like tin, sulfur, selenium and the halogens (Scheme 36). This elimination reaction can be very useful in synthesis if the eliminated radical Y- can either directly or indirectly react with a radical precursor to propagate a chain. Given this prerequisite, an addition chain can be devised with either an allylic or a vinylic precursor, as illustrated in Scheme 37. Carbon radicals are generated by the direct or indirect reaction with Y- and are removed by the -elimination of Y-. Selectivity is determined by the concentration of the alkene acceptor and the rate of -elimination... 

This review summarizes some earlier qualitative work as well as recent quantitative studies of redistribution equilibria and describes the principles underlying the mathematical treatment of such equilibria as well as the general implications of these equilibria with respect to general chemistry. In line with the general objective of the Advances in Organometallic Chemistry series, this article is limited to carbon-metal-bonded systems, metal hydrides, metal carbonyl compounds, metallocenes, and similar complexes. Excluded therefore are halogen-, sulfur-, nitrogen, and phosphorus-based systems.Various aspects of redistribution reactions were reviewed previously (42, 74, 87, 88,150,186, 285, 286, 288). 

Unlike many other type of radical addition reactions, the product is most often an alkyl-cobalt(III) species capable of further manipulation. These product Co—C bonds have been converted in good yields to carbon-oxygen (alcohol, acetate), carbon-nitrogen (oxime, amine), carbon-halogen, carbon-sulfur (sulfide, sulfinic acid) and carbon-selenium bonds (equations 179 and 180)354. Exceptions to this rule are the intermolecular additions to electron-deficient olefins, in which the putative organocobalt(III) species eliminates to form an a,/ -unsaturated carbonyl compound or styrene353 or is reduced (under electrochemical conditions) to the alkane (equation 181)355. 

Heterocumulenes undergo insertion reactions with numerous substrates. In general, carbodiimides react faster than isocyanates and isothiocyanates, in that order. Insertions of carbodiimides into metal-hydrogen, metal-halogen, metal-mitrogen, metal-oxygen and metal-sulfur bonds are reported. Also insertions of carbodiimides into carbon-hydrogen bonds are known. 

---