Styrene oxide, from benzaldehyde

Optically pure (S)-benzyl methyl sulfoxide 139 can be converted to the corresponding a-lithio-derivative, which upon reaction with acetone gave a diastereomeric mixture (15 1) of the /S-hydroxysulfoxide 140. This addition reaction gave preferentially the product in which the configuration of the original carbanion is maintained. By this reaction, an optically active epoxy compound 142 was prepared from the cyclohexanone adduct 141181. Johnson and Schroeck188,189 succeeded in obtaining optically active styrene oxide by recrystallization of the condensation product of (+ )-(S)-n-butyl methyl sulfoxide 143 with benzaldehyde. 

Johnson et al. were the first to prepare enantiomerically pure aminosulfoxonium ylide 3.73 from 3.72, which on reaction with benzaldehyde gave (P)-styrene oxide (3.69) in 20% ee. The reaction of aminosulfoxonium ylide 3.74 with heptaldehyde gave the corresponding epoxide 3.75 with opposite enantioselectivity (39% ee, S) as expected. 

The 4,5-corane (84) is obtained in SOX yield on photo-decarbonylation of the pentacyclic ketone (85). Photochemical decomposition of the carbonate (86), by the loss of carbon dioxide, affords a mixture of products containing oxirane. styrene oxide, bibenzyl and phenylacetaldehyde. Triplet sensitized irradiation yields products solely from benzyl radicals. - An earlier study of the irradiation (at 254 nm) of the carbonate (87) reported that benzaldehyde, phenyl carbene, and carbon dioxide were produced. A reinvestigation of the irradiation of this compound (at 254 nm in acetonitrile) has provided evidence that the cis- and trans-stilbene oxides (88) and (89) are formed as well as deoxybenzoin and smaller amounts of diphenylacetaldehyde and bibenzyl. When methanol is used as the solvent the same products are produced accompanied by benzylmethyl ether, 1,2-diphenylethanol, and 2,2-diphenylethanol. These authors suggest that the oxiranes (88) and (89) are formed by way of... 

The highly distorted Ru(DPP)(0)2 (X-Ray data revealed that its precursor, Ru(DPP)(CO)(py), also exhibits both saddle and ruffle distortion)catalyzes in benzene-MeCN (9 1) some epoxidation of norbornene, styrene, cyclohexene, cyclooctene and cA-stilbene under 1 atm O2 with turnovers of 8 - 40 in 4 h before deactivation of catalyst the numbers are comparable with those for Ru(TMP)(0)2 and greater than for Ru(0EP) 0)2 and Ru(TPP)(0)2. There were also co-oxidation products benzaldehyde (7 turnovers) and trace phenylacetylaldehyde were formed from styrene, cyclohex-2-en-l-ol (20 turnovers) and cyclohex-2-en-l-one (11 turnovers) from cyclohexene, and trace benzaldehyde and trans-stilbene... 

Fig. 6. 13 Kinetics of products formation in the oxidative carboxylation of styrene at 393 K under metal oxides catalysis. Styrene oxide is formed in a slight excess with respect to benzaldehyde with a selectivity of ca. 55-60 % with respect to styrene. Reprinted with permission from [107]. Copyright (2002) Elsevier...

The kinetics shown in Figure 2.2 has been rationalized proposing that the formation of styrene oxide requires the generation of peroxy radicals derived from benzaldehyde. According to this, benzaldehyde should evolve at initial stages of the reaction and, when present in sufficient concentrations, can become oxidized to peroxyl radicals by the PINO radical present in NHPI-FeBTC. Experimental support to this proposal was obtained by performing a series of experiments in which increasing concentrations of benzaldehyde... 

Chromyl chloride oxidation of alkenes proceeds via the formation of adducts at a rate necessitating stopped-flow techniques. At 15 °C the formation of 1 1 adduct from styrene and oxidant in CCI4 solution is simple second-order with 2 = 37.0 l.mole .sec . Measurements with substituted styrenes yielded = — 1.99. E = 9.0 kcal.mole and = —23.8eu for styrene itself. Hydrolysis of the styrene adduct yields mostly phenylacetaldehyde (76.5 %)and benzaldehyde (21.1 %). Essentially similar results were obtained with a set of 15 alkenes and... 

In some cases, oxidation of double bonds does not stop at the epoxide, but proceeds further to oxidative cleavage of the double bond. It was reported that the reaction of a-methyl styrene with H2O2 in the presence of TS-1 or TS-2 produces a-methyl styrene epoxide (15%), a-methyl styrene diol (10-40%) and acetophenone (40-60%) (Reddy, J. S. et al., 1992). However, results similar to those obtained with titanium silicates were obtained for many other catalysts, such as HZSM-5, H-mordenite, HY, A1203, HGa-silicalite-2, and fumed Si02. These materials have much different properties and differ significantly from titanium silicates thus, the results cast some doubt on the role of the catalyst in this reaction. Furthermore, the oxidation of styrene is reported to proceed with C=C cleavage and formation of benzaldehyde, in contrast to previous reports of the formation of phenylacetaldehyde with 85% selectivity (Neri et al., 1986). 

A PEG-SCCO2 system has also been used in the aerobic oxidation of styrene (Figure 8.7). In the presence of cuprous chloride co-catalyst the reaction favours acetophenone formation, whereas in the absence of copper benzaldehyde is favoured. The catalyst could be recycled five times and it was suggested that the PEG acts to prevent the palladium catalyst from decomposing and also assists in product separation. 

C7 by-products derive from reactions in oxidation, and, to a lesser extent, epoxidation, with the radical decomposition of EBHP to benzaldehyde being the major route. Benzaldehyde, like phenol, is an undesirable component in the recycle EB to oxidation. Most of the benzaldehyde enters the dehydration reactors with the MPC and is removed from styrene by distillation. 

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