Epoxidation isobutylene

Song, J., Bodis, J., and Fhiskas, J.E. Direct functionalization of poly isobutylene by living initiation with alpha-methylstyrene epoxide, J. Polym. Set, Polym. Chem., 40, 1005, 2002. 

Chen, Y., Puskas, J.E., and Tomkins, M. Investigation of the effect of epoxide structure on the initiation efficiency in isobutylene pol3mierizations initiated by epoxide/TiCLt systems, Eur. Polym. J., 39, 2147-2153, 2003. 

Puskas, J.E., Brister, L.B., Michef A J., I-anzenddrfer, M.G., Jamieson, D., and Pattern, W.G. Novel substituted epoxide initiators for the carbocationic pol3mierization of isobutylene, 7. Polym. Set, 38,444-451, 2000. Puskas, J.E. and Michel, A.J. New epoxy initiators for the controlled synthesis of functionalized polyisobutylenes, Makromol. Chem., Macromol. Symp., 161, 141-148, 2000. 

B. 2,5-Dimethyl-2,4-hexanediol. Isobutylene oxide (7.2 g, 0.10 mol) (Note 7) is added dropwise from the pressure-equalizing funnel to the LDBB solution in THF at -78°C at such a rate (the addition lasts for 8-12 min) that the temperature inside the flask does not exceed -78°C. After all the epoxide has been added (8-11 min), the solution becomes deep red. After 5 more minutes of stirring, isobutyraldehyde (7.2 g,... 

The epoxidation of propylene is discussed in Chapter 10, Section 2. Some isobutane can be made by isomerizing -butane. The isomerization of -butenes to isobutylene is also being commercialized. 

In marked contrast to the generally accepted mechanism, the involvement of a radical pair produced by an alkene-induced 0—0 bond homolysis was suggested by Minisci and coworkers . In a combined experimental and theoretical study Curci, Houk and coworkers sought to differentiate between a radical pathway and the commonly accepted concerted mechanism. Both product and kinetic smdies tended to exclude a radical pathway. Computational studies at the B3LYP/6-31G level on the epoxidation of isobutylene with DMDO predicted an activation energy = 15.3 kcalmor ) significantly lower... 

The numbers in brackets for propylene, isobutylene, iJ-2-butene and 1,3-butadiene entries are at the QCISD(T)//QCISD/6-31G(d) level of theory QCISD(T)/6-31G(d)//B3LYP/6-311- -G(3df,2p) gas-phase intrinsic barriers (AE ) for the epoxidation of -2-butene with dimethyldioxirane (DMDO) and peroxyformic acid are 14.3 and 13.2 kcalmol respectively. 

These composite data strongly suggest that the presence of adventitious water or other hydrogen donors can markedly affect the observed rate of epoxidation. For example, Murray and Gu have reported AH = 5.0 kcalmol" for the DMDO epoxidation of cyclohexene in CDCI3 and 7.4 kcalmol" in acetone as solvent . Curci and coworkers also reported an a value of 9.3 kcalmol" for the DMDO epoxidation of isobutylene in acetone . These barriers are significantly lower than the 13-18 kcalmoD gas-phase barriers reported " at the B3LYP level of theory (Tables 3 and 4). Activation barriers of 12.6,... 

FIGURE 22. Selected geometrical parameters of the transition stmcture for the epoxidation of isobutylene with peroxyformic acid calculated at the QCISD/6-31G, CISD/6-31G (in parentheses), B3LYP/6-31G (in square brackets), B3LYP/6-311+G(3df,2p) (in italic in square brackets) and MP2/6-31G (in curly brackets) levels... 

The epoxidations of propylene and isobutylene with peroxyformic acid proceed in a concerted way via slightly unsymmetrical Markovnikov-type transition stmctnres where the differences in the bond distances between the donble-bond carbons and the spiro oxygen are only 0.021 and 0.044 A at the QCISD/6-31G level. In contrast, the more polarizable natnre of the carbon-carbon double bond of o ,/ -unsaturated systems results in a highly nnsymmetrical transition structure for the epoxidation of 1,3-butadiene with an order-of-magnitnde difference in the carbon-oxygen bond distances of 0.305 A at the QCISD/6-31G level. A highly unsymmetrical transition structure has been also found for the epoxidation of acrylonitrile. 

Methyl substitution leads to a decrease in the epoxidation barriers from 18.8 kcal moD for ethylene to 13.7 kcalmol" for isobutylene at the QCISD(T)/6-31G //QCISD/6-31G level. 

The mechanism most consistent with all the data is an ionic acid opening of the epoxide —apparently where the hydrocarbonyl is used as an acid to attack the epoxide— which is more sensitive to steric effects than to electronic factors. This conclusion may at first appear to be inconsistent with our previous finding that isobutylene reacted with cobalt hydrocarbonyl to give exclusively addition of the cobalt to the tertiary position. The inhibitory effect of carbon monoxide on that reaction, however, indicated that it was probably cobalt hydrotricarbonyl that was actually adding to the olefin and steric effects would be expected to be much less important with the tricarbonyl than with the tetracarbonyl (7) Apparently he feels now that the former reactions really involve the tricarbonyl, loss of CO being important to get the reaction running whereas epoxide attack perhaps involves a tetracarbonyl, steric factors are more important here. 

There is one last experimental result arguing for a high activation energy for internal ft—C—H abstraction. When Steps 11" and 12 compete, epoxidation (Step 11") always seems to be faster than olefin formation (Step 12). This is true in the HC1 catalyzed, chain decomposition of ter -Bu202 which produces isobutylene oxide and negligible isobutene (2) via a peroxyalkyl radical. Similar behavior is observed from the addition of H02 and R02 to olefins, which produce mainly ethers or epoxides at rapid rates (12). Note that although we estimate A12 — 1013 4 sec."1 and An" -— 10115 sec. 1, Step 12 is endothermic by -— 11 to 13 kcal., while Step 11" is exothermic by 10 to 17 kcal. A reasonable estimate for Ei2 is 20 kcal., while En" has an upper limit of 16 kcal., and some data (12) point to a value closer to 10 kcal. 

Among the many alkyl-substituted epoxides that have hi n reported to undergo hydration under various conditions are propylnm oxide, isobutylene oxide, 1,2-epoxybutone, trimethylethylene oxide, and others-. . . , jtf, i w. . shown in JSq, (50 ). 

Among alkyl-substituted ethylene oxides known to umletrn cleavage on treatment with sodium sulfite are propylene oxide, isobutylene oxide, 1,2-epoxybutane, 1,2-epoxyoctane, and 2,3-cpow-butane.1 75 These reactions with sodium sulfite constitute the bani-, ffrail analytical method developed by Swan1875 for the estimation <[Pg.179]

Atom (Eq. 791)- Epoxides investigated in this manner included ethylene oxide, propylene oxide, isobutylene oxide, cm- and lmtw-2,8-epoxybutane, 2.a-opoxy-2 methylbutane1 and 2,3-epoxy-2,a dimethvl butane l4s , ... 

Unaymmetrical epoxides were said to give rise to mixed products, although experimental details were not included. Eqs. (908) and (900) illustrate the action of diethyl phosphite in base on propylene oxide mid isobutylene oxide. The latter undergoes preliminary isomerisation to wobutyrsddehyde before yielding a conventional carbonyl adduct. 

Pritchard and Long1416-141 studied the distribution of lsO in products obtained on hydration of propylene oxide and isobutylene oxide in Hs180, both in alkaline and in acid solutions (Eqs. 611 and 612). Their results are consistent with the premise that attack by water occurs predominantly on the terminal epoxide carbon atom, unless an... 

---