Sulfurization, of aromatic rings

Sulfurization of aromatic rings with thionyl chloride... 

The aromatic sulfone polymers are a group of high performance plastics, many of which have relatively closely related stmctures and similar properties (see Polymers containing sulfur, polysulfones). Chemically, all are polyethersulfones, ie, they have both aryl ether (ArOAr) and aryl sulfone (ArS02Ar) linkages in the polymer backbone. The simplest polyethersulfone (5) consists of aromatic rings linked alternately by ether and sulfone groups. 

Too little is known about the nature of these reactions, although possible overall reaction pathways, including dehydrogenation of tetrahydroaromatics, chlorination and sulfuration of aromatics and their conversion into SSCl derivatives, and the pentathiepin ring formation, were proposed. 

Sulfonation Substitution of a sulfonic acid group (-SO3H) for a ring hydrogen occurs when benzene reacts with concentrated sulfuric acid and sulfur trioxide. Aromatic-ring sulfonation is a key step in the synthesis of such compounds as aspirin and the sulfa-drug family of antibiotics. 

Most of the other products found in irradiated meat volatiles except those containing sulfur or aromatic rings may also be accounted for by mechanisms associated with alkyl free radical formation in the fat. Oxygenated compounds are far less abundant than hydrocarbons, but appreciable amounts of a homologous series of n-aliphatic alcohols up to hexanol are found. Of these, only ethanol is detected in the unirradiated controls. Since the water content of meat averages nearly 60%, the formation of alcohols may be thought to occur by reaction of the alkyl free radical with water. Such a mechanism is supported by the fact that only traces of alcohols are found in irradiated dry butterfat and were undetected in irradiated triglycerides or methyl esters of fatty acids. 

To conclude, in a manner complementary to the interactions of oxygens and sulfurs with the hydrogens of aromatic rings, amino group hydrogens can make enthalpically favorable, weak, polar interactions with the tt-electrons of aromatic rings. These interactions are of sufficient importance to cause a marked anisotropy in the distribution of N—H and NH3 groups in the vicinity of aromatic side chains. 

Important reactions have included sulfur as nucleophile and leaving group in the Sn2 reaction (illustrated here see also Chapter 17), sulfonation of aromatic rings (Chapter 22), formation and reduction of thioacetals (Chapter 24) and La wesson s reagent for converting carbonyl groups to thiocarbonyl groups (Chapter 44). 

Phosphorus has positive effects on isomerization and hydrogenolysis reactions, which require acidic properties. Phosphorus also improves activity for hydrogenation reactions of aromatic rings, especially on NiMoP/Al catalysts. Phosphorus shows minor effects in thiophene HDS, and it may improve the HDS activity of catalysts for heavier sulfur-containing molecules such as those in VGO, in which hydrogenation of aromatic rings may... 

Sulfuric acid, H2SO4, rarely acts as an oxidant. It can be used for the dehydrogenative coupling of aromatic rings [595]. Equally rare is the oxidation of a sulfide to a sulfoxide with sulfuryl chloride, SO2CI2 [506]. 

The electronic modification caused by a low coverage of the catalyst can sometimes be beneficial. An initial reaction of a catalyst with a small amount of a sulfur compound can prevent further reaction with additional quantities of sulfur compounds, within certain limits.These sulfided catalysts have been used for reactions run in the presence of impurities such as sulfur and for the hydrogenations of sulfur containing compounds. The relative inactivity of these catalysts for the hydrogenation of aromatic rings, ketones and nitriles can... 

Similar rearrangements also occur in the case of sulfur analogs. Since the product of a Sommelet-Hauser rearrangement is a benzylic tertiary amine (or sulfide), just as the starting material was a benzylic amine (or sulfide), the process can be repeated and is a unique method to move substituents around the periphery of aromatic rings (Scheme 109). 

Hydrogenation of Oxygen- and Sulfur-containing Aromatic Ring Systems... 

Several methods have been presented for the selective hydrogenation of aromatic rings. As industrial products become more complex, however, further methods are needed for the selective organic transformations required in the production of chemical intermediates and fine chemicals. Of special interest are sulfur-tolerant catalysts and catalysts for the synthesis of chiral complexes. Future research should focus on either of these areas. Much is expected from novel catalysts obtained by immobilizing homogeneous complexes. 

For selective saturation of one of several double bonds, palladium or Raney nickel can be used. Platinum is less selective but can nevertheless sometimes be used. The reaction is interrupted after consumption of the calculated amount of hydrogen. Sulfur must be completely absent during hydrogenation of aromatic rings with platinum metals derivatives of benzene such as benzoic acid and phenol, also naphthalene, are more easily hydrogenated than benzene itself but for such cases it is often advantageous to use nickel catalysts in an autoclave. 

Removal of water from certain compounds is often used for synthesis of aromatic rings. Adams and Hufferd977 obtained mesitylene from acetone by treatment with sulfuric acid, and Lyle et al.91s give the following generalized procedure for preparation of 1,3,5-triarylbenzenes ... 

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