Sulfur reactions with alkenes

Metallacyclopentadienes undergo a range of synthetically versatile reactions which proceed with extrusion of the metal atom and attendant ligands. Thus, reactions with alkenes and alkynes afford cyclohexa-1,3-dienes and arenes (Scheme 6), and thiophenes, selena-cyclopentadienes, pyrroles and cyclopentadienones (indenones, fluorenones) can be obtained by treatment with sulfur, selenium, nitroso compounds and CO, respectively. The best studied substrates for such reactions are cobaltacyclopentadienes of the type (24a), which have been converted into a wide variety of arenes, cyclohexadienes and five-membered heterocycles, many of which would be very difficult to obtain by conventional organic procedures (74TL4549, 77JOM(139)169, 80JCS(P2)1344). 

Several detailed theoretical studies have been conducted on the reaction of sulfur trioxide with alkenes to afford /3-sultones. The first publication <1998JA6468> details the reaction of sulfur trioxide with ethylene to afford /3-sultone 9 via transition state 8 (Scheme 1). Important bond lengths are shown (pm). Density functional and correlated ab initio calculations indicate that the reaction proceeds by a concerted [2+2] pathway. 

Their kinetic and product analysis is consistent with the working hypothesis indicated previously for insertions the singlet process is stereospecific, while the triplet process is at best only selective. Here, as in the reaction of sulfur atoms with alkenes, (217), some progress has been made in separating the problem of the reacting species and their reaction rates from the observed SS in the product (Gunning and Strausz, 1966). In general, however, interconversion rates of triplet cisoid and transoid diradicals are uncertain, and deductions from overall stereoselectivity are also uncertain. 

Explosive reaction with alkenes + diiodomethane, sulfur dioxide. Reacts violently with bromine, water, nitro compounds. Ignites on contact with air, ozone, methanol, or hydrazine. Reacts violently with nonmetal halides (e.g., arsenic trichloride or phosphorus trichloride) to produce pyrophoric triethyl arsine or triethyl phosphine. To fight fire, do not use water, foam, or halogenated extinguishing agents. Use dty materials, such as graphite, sand, etc. When heated to decomposition it emits toxic fumes of ZnO. See also ZINC COMPOUNDS. 

Other retrocycloadditions may occur in the decomposition of /3-sultines, obtained by reaction of triplet sulfur dioxide with alkenes, to ketones and sulfines (or a carbene and sulfur monoxide) and in the decomposition of 1,2-oxathietane-4-one 2-oxides to carbon dioxide and a sulfine. The mass spectrum of 1,2-oxathietane 2-oxide shows a fragment attributed to sulfine. ... 

In the presence of bases, mild thiolation of organic compounds by treatment with sulfur provides an efficient route to organosulfur compounds. The reaction with alkenes is of great industrial importance in the vulcanisation of rubber. Many common reactions of... 

Saturated hydrocarbons are dehydrogenated when heated with sulfur, and further reaction with alkenes occurs. An application of this reaction is in the vulcanization of rubber, in which soft rubber is toughened by cross-linking of the poly-isoprene chains, making it suitable for use in, for example, t)Tes. The reactions of sulfur with CO or [CN] )deld OCS (16.13) or the thiocyanate ion (16.14), while treatment with sulfites gives thiosulfates (equation 16.21). 

Some specific reactions of this type that we shall study in this chapter include addition of hydrogen halides, sulfuric acid, water (in the presence of an acid catalyst), and halogens. Later we shall also study some specialized reagents that undergo addition reactions with alkenes. 

For reactions in H2O an analogous discussion applies as for reactions with the protonated sulfuric acid form. The reactive intermediate now, however, is H3O+. H3O+ has a much stronger OH bond than H3SO4 +, and hence its reactivity is much less. The species that is formed by reaction with alkene in an aqueous solution can best be compared with protonated alcohols forms typically known as alkyl oxonimn ionsl l Protonated alkene is hydrated in aqueous media. The formation of alkyloxonimn ions instead of the carbenium ions in H2O can be viewed as due to the basicity of water. The major difference between solid acids and acidic solutions arises because the hydrogen atoms in solid acids are part of strong covalent bonds and are not present as protons that are present in in the solution phase. In a solution there is a equilibrium between non-dissociated acid molecules and the... 

Acid-Gatalyzed Synthesis. The acid-catalysed reaction of alkenes with hydrogen sulfide to prepare thiols can be accompHshed using a strong acid (sulfuric or phosphoric acid) catalyst. Thiols can also be prepared continuously over a variety of soHd acid catalysts, such as seoHtes, sulfonic acid-containing resin catalysts, or aluminas (22). The continuous process is utilised commercially to manufacture the more important thiols (23,24). The acid-catalysed reaction is commonly classed as a Markownikoff addition. Examples of two important industrial processes are 2-methyl-2-propanethiol and 2-propanethiol, given in equations 1 and 2, respectively. 

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