Olefin epoxidation study

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

The similarity of olefin epoxidation by TM peroxo and hydroperoxo complexes with epoxidation by dioxirane derivatives R2CO2 and percar-boxylic acids RCO(OOH) was confirmed by computational studies [73-79]. This similarity holds in particular for the spiro-type transition structure. 

An important improvement in the catalysis of olefin epoxidation arose with the discovery of methyltrioxorhenium (MTO) and its derivatives as efficient catalysts for olefin epoxidation by Herrmann and coworkers [16-18]. Since then a broad variety of substituted olefins has been successfully used as substrates [103] and the reaction mechanism was studied theoretically [67, 68, 80]. 

Such stability is only relative, however, given the possibility of the acid-catalyzed 1,2-shift of a proton observed in some olefin epoxides of general structure 10.10 (Fig. 10.3) [12], Such a reaction occurs in the in vivo metabolism of styrene to phenylacetic acid the first metabolite formed is styrene oxide (10.10, R = Ph, Fig. 10.3, also 10.6), whose isomerization to phenyl-acetaldehyde (10.11, R = Ph, Fig. 10.3) and further dehydrogenation to phenylacetic acid has been demonstrated by deuterium-labeling studies. A com-... 

Several years later, the group of Corma reported on a successful study on stereoselective olefin epoxidation with MTO using various chiral nitrogen bases. Although the conversion is low (10%), an enantiomeric excess (ee) of up to 36% can be obtained with cA-p-methylstyrene as the substrate and R-(+)-1 -phenylethylamine as base (Fig. 3b) [34], Also, the groups of Saladino and Crucianelli used /f-(+)- -phenylethylamine as chiral base in a 1 1 ratio with MTO, forming the corresponding perrhenate salt, but also here, very low conversion is obtained. In the same report, the use of Lrans-( R,2R)-, 2-diaminocyclohexane (Fig. 3c) in combination with MTO as... 

Berkessel A, Adrio JA (2004) Kinetic studies of olefin epoxidation with hydrogen peroxide in l,l,l,3,3,3-hexafluoro-2-propanol reveal a crucial catalytic role for solvent clusters. Adv Synth Catal 346 275-280 Berkessel A, Adrio JA (2006) Dramatic acceleration of olefin epoxidation in fluorinated alcohols activation of hydrogen peroxide by multiple H-bond networks. J Am Chem Soc 128 13412-13420 Berkessel A, Adrio JA, Huttenhain D, Neudorfl JM (2006a) Unveiling the booster effect of fluorinated alcohol solvents aggregation-induced conformational changes, and cooperatively enhanced H-bonding. J Am Chem Soc 128 8421-8426... 

Various combinations of metal catalyst and single oxygen donor have been used to effect different oxidative transformations of olefins epoxidation, dihydroxyla-tion, oxidative cleavage, ketonization and allylic oxidation. The most extensively studied example is undoubtedly olefin epoxidation [39]. 

A number of new oxaziridinium epoxidation reagents have been reported. A new axially chiral epoxidation catalyst 4 has been reported <070BC501>. These catalysts, as are others, are converted to an oxaziridinium with Oxone, which then epoxidizes the olefin. This study examined several chiral groups on the nitrogen as well as both atropisomers. The (S,F)-isomer 4 provided the (1R,2R) epoxide with moderate enantioselectivity and 82% conversion. The (.V,A/)-isomcr of 4 provided the (lS,2S)-epoxide in slightly lower enantiomeric excess (76%) and lower conversion as well. 

Yudanov, I. V., Gisdakis, P., Di Valentin, C., Rosch, N. Activity of peroxo and hydroperoxo complexes of Ti(IV) in olefin epoxidation. A density functional model study of energetics and mechanism. Eur. J. Inorg. Chem. 1999, 2135-2145. 

Although, as stated above, olefin epoxidation is commonly referred to as an electrophilic oxidation, recent theoretical calculations suggest that the electronic character of the oxygen transfer step needs to be considered to fully understand the mechanism [451]. The electronic character, that is, whether the oxidant acts as an electrophile or a nucleophile is studied by charge decomposition analysis (CDA) [452,453]. This analysis is a quantitative interpretation of the Dewar-Chatt-Dimcanson model and evaluates the relative importance of the orbital interactions between the olefin (donor) and the oxidant (acceptor) and vice versa [451]. For example, dimethyldioxirane (DMD) is described as a chameleon oxidant because in the oxidations of acrolein and acrylonitrile, it acts as a nucleophile [454]. In most cases though, epoxidation with peroxides occurs predominantly by electron donation from the 7t orbital of the olefin into the a orbital of the 0-0 bond in the transition state [455,456] (Fig. 1.10), so the oxidation is justifiably called an electrophilic process. 

A. Berkessel, J. A. Adrio, Kinetic studies of olefin epoxidation with hydrogen peroxide in l,l,l,3,3,3-hexafluoro-2-propanol reveal a crucial catalytic role for solvent clusters, Adv. Synth. Catal. 346 (2004) 275. 

P. Gisdakis, 1. V. Yudanov, N. Rdsch, Olefin epoxidation by molybdenum and rhenium peroxo and hydroperoxo compounds A density functional study of energetics and mechanisms, Inorg. Chem. 40 (2001) 3755. 

P. Gisdakis, N. Rosch, Solvent effects on the activation barriers of olefin epoxidation - A density functional study, Eur. J. Org. Chem. (2001) 719. 

P. Gisdakis, W. Antonczak, S. Kostlmeier, W. A. Herrmann, N. Rosch, Olefin epoxidation by methyltrioxorhenium A density functional study on energetics and mechanisms, Angew. Chem. Int. Ed. Engl. 37 (1998) 2211. 

As stated above, czs-stilbene is a frequently used substrate for the study of olefin epoxidation mechanisms [100] because of mechanistic information associated with the ratio of the cis- and frazzs-isomers in the stilbene oxide product. Catalytic f-BuOOH epoxidation of czs-stilbene was performed, with our Mn (Me2EBC)Cl2 catalyst, under and product analysis shows that czs-stilbene oxide contains 25 0.3% incorporation of from atmospheric 02 versus 1.7 0.3% in a control experiment using ordinary air, whereas frzzzzs-stilbene oxide contains 55.1 1% incorporation of O from O2 versus 2.6 1% incorporation in a control experiment. Similar incorporation ratios are expected for the cis- and frzzzzs-stilbene oxides if all epoxidation products result from only one reaction pathway and a single reactive intermediate. However, the incorporation of in czs-stilbene oxide (25 0.3%) is definitely different from that in frzzzzs-stilbene oxide (55.1 1%). This result leads to the conclusion that, at least two distinct reactive intermediates occur in these epoxidation reactions. This is also consistent with the results described above for norbomylene epoxidation. 

R. Prabhakar, K. Morokuma, C. L. Hill, D. G. Musaev, Insights into the mechanism of selective olefin epoxidation catalyzed by [7-(SiO4)VVii,O 2H . A computational study, Inorg. Chem. 45 (2006) 5703. 

H. Munakata, Y. Oumi, A. Miyamoto, A DET study on peroxo-complex in titanosilicate catalyst Hydrogen peroxide activation on titanosilicalite-1 catalyst and reaction mechanisms for catalytic olefin epoxidation and for hydroxylamine formation from ammonia, J. Phys. Chem. B 105 (2001) 3493. 

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