Sulfur reaction-selective

Norbomene reacts with elemental sulfur to give a mixture of 1,2,3-trithiolane 59 (R = H) and pentathiepane (Equation 20) <2005TL7077>. The use of Ni(NH3)6Cl2 in DMF as a catalytic system allowed the selective transformation of norbomene and its derivatives into -l,2,3-trithiolanes 59 in good yields (75-82%). The reaction selectivity was maximal at an alkene Ss ratio of 1 3/8 <2005TL7077>. 

Reaction selectivity depends on the nature of ionite functional groups and is determined by the length of complexing groups CIkble20). In the presence of AN-51/8, H2S is oxidized to elemental sulfur, whereas in the presence of AN-221, it is oxidized to SOj . 

Role of Crystal Structure on Reaction Selectivity. The question of selectivity of the HDS reaction and its control by the sulfide catalyst has been little studied. However, the existence of two active sites on M0S2 is well established throughout much of the literature, particularly in the work of Voorhoeve (16). One site is usually described as a direct sulfur removal site and the other as a hydrogenation site. 

The following example of hydrocarbon catalysis illustrates the consequences of competitive adsorption for the order of the reaction, and the optimum conditions under which the reaction is carried out. The selectivity of the transition-metal catalyzed conversion of n-hexane to i-hexane versus the hydrogenolysis to smaller hydrocarbons depends strongly on the structure of the surface. Hydrogenolysis requires an ensemble of several atoms. When sites become blocked by inert atoms, such as carbon or sulfur, the selectivity for reactions maintaining chain length is significantly enhanced. 

Profrock, D., Leonhard, R, and Prange, A. (2003) Determination of sulfur and selected trace elements in metallothionein-like proteins using capillary electrophoresis hyphenated to inductively coupled plasma mass spectrometry with an octopole reaction cell. Anal. Bioanal. Chem., 377,132-9. 

Conditions of hydrogenation also determine the composition of the product. The rate of reaction is increased by increases in temperature, pressure, agitation, and catalyst concentration. Selectivity is increased by increasing temperature and negatively affected by increases in pressure, agitation, and catalyst. Double-bond isomerization is enhanced by a temperature increase but decreased with increasing pressure, agitation, and catalyst. Trans isomers may also be favored by use of reused (deactivated) catalyst or sulfur-poisoned catalyst. 

Boron trifluoride catalyst may be recovered by distillation, chemical reactions, or a combination of these methods. Ammonia or amines are frequently added to the spent catalyst to form stable coordination compounds that can be separated from the reaction products. Subsequent treatment with sulfuric acid releases boron trifluoride. An organic compound may be added that forms an adduct more stable than that formed by the desired product and boron trifluoride. In another procedure, a fluoride is added to the reaction products to precipitate the boron trifluoride which is then released by heating. Selective solvents may also be employed in recovery procedures (see Catalysts,regeneration). 

Organic hydroperoxides can be prepared by Hquid-phase oxidation of selected hydrocarbons in relatively high yield. Several cycHc processes for hydrogen peroxide manufacture from hydroperoxides have been patented (84,85), and others (86—88) describe the reaction of tert-huty hydroperoxide with sulfuric acid to obtain hydrogen peroxide and coproduct tert-huty alcohol or tert-huty peroxide. 

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