Styrene oxidation, solvent effect

Fig. 51. Correlation between the intensity of Ti-superoxo ([A + A] and [B + C]) signals and selectivity for styrene oxide and non-selective products in the styrene epoxidation reaction. The effects of titanosilicates, oxidants, and solvent on the correlation are depicted [from Srinivas et al. (52)].

Gold-catalyzed oxidation of styrene was firstly reported by Choudhary and coworkers for Au NPs supported on metal oxides in the presence of an excess amount of radical initiator, t-butyl hydroperoxide (TBHP), to afford styrene oxide, while benzaldehyde and benzoic acid were formed in the presence of supports without Au NPs [199]. Subsequently, Hutchings and coworkers demonstrated the selective oxidation of cyclohexene over Au/C with a catalytic amount of TBHP to yield cyclohexene oxide with a selectivity of 50% and cyclohexenone (26%) as a by-product [2]. Product selectivity was significantly changed by solvents. Cyclohexene oxide was obtained as a major product with a selectivity of 50% in 1,2,3,5-tetramethylbenzene while cyclohexenone and cyclohexenol were formed with selectivities of 35 and 25%, respectively, in toluene. A promoting effect of Bi addition to Au was also reported for the epoxidation of cyclooctene under solvent-free conditions. 

Small but significant effects of solvent polarity were found in the autoxidation of a variety of alkenes and aralkyl hydrocarbons [216-220] (styrene [216, 218, 219], ethyl methyl ketone [217], cyclohexene [218], cumene [218, 219], tetralin [219], etc.). An extensive study on solvent effects in the azobisisobutyronitrile (AIBN)-initiated oxidation of tetralin in a great variety of solvents and binary solvent mixtures was made by Kamiya et al. [220],... 

These mechanistic possibilities require further investigation. Some examples of how the reaction is influenced by the structure of the olefin, the catalyst, and the solvent are given. In the presence of MX(CO)(PPh3)2 (M = Rh, Ir X = Cl, I), the oxidation of a-and /3-methylstyrenes and cis- and frans-stilbenes permitted the establishment of an activity sequence dependent on the catalyst and the stucture of the olefin. The solvent effect has been studied in the Ru complex-catalyzed oxidation of styrene and methylstyrene. In the presence of a Rh or Ir complex, the oxidation of tetramethylthylene is very selective" and takes place at a faster rate than those of the less-substituted olefins. It emerges from this that a significant role is not played by the coordinative linkage between the metal center and the olefin. Examinations have also been made on the oxidation activities of metallo-porphyrins, for example, the oxidation of cyclohexene with Co and Rh porphyrins. ... 

Embedded quantum/classical calculations were used to study the epoxidation reaction of styrene catalyzed by Mn-porphyrins. Optimized geometries were obtained for the Mn-porphyrin, reaction intermediates, and transition state structures along the proposed reaction path. A polarizable continuum model (PCM) was used to study solvent effects, with dichloromethane as the solvent. While it has been shown previously that the concerted intermediate between the oxidized porphyrin and the alkene is the lowest energy configuration, a transition state to directly form the concerted intermediate without the prior formation of a radical could not be found. A stepwise mechanism, in which a radical intermediate is formed before the concerted intermediate, is proposed. 

The Effect of Solvent on the Styrene Oxidation with CrS-1 and H2O2... 

Benzylic oxidation. Dihydroisobenzofuran and isochroman are readily converted to the lactones. Solvent effects are manifested in the cleavage of styrenes, since EtOAc favors the formation of aldehydes, whereas in THF, the major products are the benzoic acids. 

Similar solvent effects influence the morphology of block polymers of a crystallizable and a noncrystallizable component also. In principle, the poly(ethylene oxide) blocks of the biblock polymer, poly(styrene-Z -ethylene... 

In a seminal paper in Nature in 2005, Hughes et al. [165] reported catalytic activity of supported Au nanoparticles in the epoxidation of aUcenes using small amounts of peroxide initiators. Strong solvent effects were estabhshed, yet, wide particle size distributions (5-50 nm) did not allow pinpointing any size effects. Medium-to-high selectivity toward epoxide formation was achieved by careful tuning. For example, in the case of styrene as substrate with a 1% Au/C catalyst, a selectivity toward partial oxidation products (cf. the complete oxidation product, COj) of 97% was achieved with an epoxide selectivity of about 23%. 

Magnetically separable catalysts synthesised by Saikia that show effective utilisation of Fe304 impregnated chromium-based MOF have been used for the solvent-free oxidation of benzyl alcohol in the presence of TBHP. Sulfonic acid functionalised chromium MILlOl can be used as an efficient catalyst for the vapour-phase dehydration of butanol by oleic acid. Also, bimetallic MOF catalysts of iron and chromium (Fe(Cr)-MIL-lOl) have received attention for epoxidation of styrene to styrene oxide with excellent selectivity and catalytic recyclability. ... 

A detailed kinetic study using UV-vis, FTIR (Fourier-transform infrared), and NMR spectroscopy a Hammett plot with /0 = -h1.98 using para-substituted styrene oxides an inverse solvent kinetic isotope effect (KIE) (fcnHp/ HHP-d2) = 0.86 and nonlinear effects studies" have all shown that the (salen)Co- (J) and amidine-co-catalysed enantioselective ring opening of terminal- and mew-epoxides by fluoride ion (forming trans- -ttuoTO alcohols in a 42-89% yield with 84-99% ee) occurs by the mechanism shown in Scheme 5. /-BuOOH oxidizes the Co(H) to Co(III) in the (salen)Co(III) catalyst. PhCOF provides the fluorine for the reaction. 

A detailed kinetic study, a Hammett plot with /0 = h-1.98 using para-substituted styrene oxides, an inverse solvent KIE (fcjjpjp/A jjp[p.(i2) = 0.86, and studies on nonlinear effects" indicating the mechanism of the (salen)Co- and amine-co-catalysed... 

Liu, G., Hou, M Song, J Zhang, Z., Wu, T and Han, B. (2010) Ni -containing ionic liquid immobilized on silica effective catalyst for styrene oxidation with H2O2 at solvent-free condition. /, Mol. Catal. A, 316, 90-94. 

A mixture of monolauryl phosphate sodium salt and triethylamine in H20 was treated with glycidol at 80°C for 8 h to give 98% lauryl 2,3-dihydro-xypropyl phosphate sodium salt [304]. Dyeing aids for polyester fibers exist of triethanolamine salts of ethoxylated phenol-styrene adduct phosphate esters [294], Fatty ethanolamide phosphate surfactant are obtained from the reaction of fatty alcohols and fatty ethanolamides with phosphorus pentoxide and neutralization of the product [295]. A double bond in the alkyl group of phosphoric acid esters alter the properties of the molecule. Diethylethanolamine salt of oleyl phosphate is effectively used as a dispersant for antimony oxide in a mixture of xylene-type solvent and water. The composition is useful as an additive for preventing functional deterioration of fluid catalytic cracking catalysts for heavy petroleum fractions. When it was allowed to stand at room temperature for 1 month it shows almost no precipitation [241]. 

The remarkably high isotope effects found in Reactions 10 and 10a are almost as embarrassing as was our discovery of an isotope effect of about 15 in the reaction with phenols referred to above. [For 2,6-di-tert-butyl-4-methylphenol in oxidizing styrene at 65°C. we obtained an isotope effect kH/kD = 10.6 (11). We have since carefully measured the isotope effect for 2,4,6-tri-ferf-butylphenol under the same conditions and have obtained a value 15. In these cases, hydrogen bonding to the solvent is relatively unimportant (6, 12). Similarly, DaRooge and Mahoney (9) have reported that for the reaction of 2,4,6-tri-tert-butylphenoxy radicals with 4-phenylphenol kH/kD 7.5.] Although... 

Effect of Temperature and Solvent on Co-Oxidation of Styrene and Butadiene... 

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