Olefins, epoxidation hydrogenation

The primary determinant of catalyst surface area is the support surface area, except in the case of certain catalysts where extremely fine dispersions of active material are obtained. As a rule, catalysts intended for catalytic conversions utilizing hydrogen, eg, hydrogenation, hydrodesulfurization, and hydrodenitrogenation, can utilize high surface area supports, whereas those intended for selective oxidation, eg, olefin epoxidation, require low surface area supports to avoid troublesome side reactions. 

The observation that addition of imidazoles and carboxylic acids significantly improved the epoxidation reaction resulted in the development of Mn-porphyrin complexes containing these groups covalently linked to the porphyrin platform as attached pendant arms (11) [63]. When these catalysts were employed in the epoxidation of simple olefins with hydrogen peroxide, enhanced oxidation rates were obtained in combination with perfect product selectivity (Table 6.6, Entry 3). In contrast with epoxidations catalyzed by other metals, the Mn-porphyrin system yields products with scrambled stereochemistry the epoxidation of cis-stilbene with Mn(TPP)Cl (TPP = tetraphenylporphyrin) and iodosylbenzene, for example, generated cis- and trans-stilbene oxide in a ratio of 35 65. The low stereospecificity was improved by use of heterocyclic additives such as pyridines or imidazoles. The epoxidation system, with hydrogen peroxide as terminal oxidant, was reported to be stereospecific for ris-olefins, whereas trans-olefins are poor substrates with these catalysts. 

In conclusion, the above summary of oxidation methods shows that there is still room for further improvements in the field of selective olefin epoxidation. The development of active and selective catalysts capable of oxidizing a broad range of olefin substrates with aqueous hydrogen peroxide as terminal oxidant in inexpensive and environmentally benign solvents remains a continuing challenge. 

Micellar catalysis to enhance or diminish the rate of chemical reactions is well known [97]. Of somewhat greater interest is the influence of micelles on competing reactions, e.g., proton-catalyzed reactions. An example related to the effect of alkanesulfonates is the epoxidation of simple aliphatic olefins. The reaction of olefins and hydrogen peroxide catalyzed by strongly acidic Mo(VI)... 

A. Berkessel and J. A. Adrio, Dramatic acceleration of olefin epoxidation in fluorinated alcohols Activation of hydrogen peroxide by multiple H bond networks. J. Am. Chem. Soc. 128, 13412 13420 (2006). 

Clerid, M.G. and Ingallina, P. (1993) Epoxidation of lower olefins with hydrogen peroxide and titanium silicate. J. Catal., 140, 71-83. 

Dramatic Acceleration of Olefin Epoxidation in Fluorinated Alcohols Activation of Hydrogen Peroxide by Multiple Hydrogen Bond Networks... 

As a third example for an organocatalytic reaction, based on multiple hydrogen bonding and mechanistically investigated by DFT, we selected olefin epoxidation with hydrogen peroxide in fluorinated alcohol solvents, such as 1,1,1,3,3,3-hex-afluoro-2-propanol (HFIP) (Scheme 8). Here we encounter a new type of catalytic hydrogen bond the cooperative hydrogen bond. 

Therefore, the following mechanistic investigation of the epoxidation of olefins with hydrogen peroxide is constrained to reaction pathways which (1) involve HFIP in an sc or even sp conformation and (2) to hydrogen bonded HFIP aggregates comprising up to four alcohol monomers. 

Although hydrogen peroxide and aUcyl hydroperoxides in general are not snfliciently reactive to epoxidize alkenes, there are some exceptions. Experimental observations show that direct olefin epoxidation by H2O2, which is extremely sluggish otherwise, occurs in fluorinated alcohol (RfOH) solutions under mild conditions requiring no additional... 

TABLE 24. Manganese-catalyzed epoxidation of olefins using hydrogen peroxide as oxygen source... 

Berkessel and Andreae reported that the catalytic activity of benzenearsonic acid in the epoxidation of olefins with hydrogen peroxide is potentiated in fluorinated alcohols such as Since Brpnsted acids do not effect epoxidation under these conditions, the... 

SCHEME 98. Arsonic acid-catalyzed epoxidation of olefins with hydrogen peroxide in ionic Mquids... 

Platinum(II) and ruthenium(II) complexes with chiral modified diphosphines like 47 or tetradentate P2N2 ligands like 48 have been used for the asymmetric epoxidation of olefins with hydrogen peroxide with ee values of 18-23%, which increased up to 41% when cationic solvato derivatives such as P2Pt(CF3)(CH2Cl2)(BF4) are used . Similar chiral inductions were reported for Ru derivatives, although the nature of the active intermediate was still in question. ... 

Bromopyrogallol Red, hydrogen peroxide determination, 628-9 Bronchial epithehal cells, IR spectrophotometry, 683 Br0nsted acids, olefin epoxidation, 471 BSA see Bovine semm albumin BTSP see Bis(trimethylsilyl) peroxide 2-Butanone peroxide, hydroperoxide determination, 686, 688, 689 -2-Butene, final ozonide, 721 t-Butoxy free radical, a-methylstyrene dimer reaction, 697... 

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