Epoxidation of -2-butene

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. 

DMDO epoxidation of cyclohexene (Table 5) is rednced by 4.1 kcalmoD when a single water molecule is hydrogen-bonded to the distal oxygen of DMDO (a bimolecular process relative to a prereaction clnster of DMDO, H2O) and by 6.3 kcalmoD with two complexed water molecules [B3LYP/6-311+G(d,p)]. The H-bonded DMDO-CH3OH prereaction cluster has a stabilization energy of —6.9 kcalmoD. The calculated barriers for the DMDO epoxidation of -2-butene with and without water catalysis are 11.0 and... 

FIGURE 19. B3LYP/6-31 H-G(d,p)-optimized transition stmctures for the epoxidation of cyclohexene with DMDO in the presence of one (a) and two (h) water molecules. The transition structure for the epoxidation of -2-butene (c) is optimized at the same level of theory in the presence of one water molecule. The classical barriers are estimated using total electronic energies of the transition stmctures, cyclohexene (—234.71316 au), ii-2-butene (—157.27453 au), DMDO with one water molecule (—344.81523 au) and DMDO with two water molecules (—421.28672 au)... 

FIGURE 28. Effect of substitution in peracids on the activation barriers (kcal mol-1) and charge distribution (electrons) for the epoxidation of -2-butene. Charge distributions in B3LYP/6-31+G(d,p) optimized transition structures are calculated using NBO, B3LYP/6-31+G(d,p)... 

Stereospecific Epoxidation of 2-Butene. The hydroperoxide epoxidation reaction is stereospecific. Pure cis- and trans-2-butene were epoxi-dized separately by cumene hydroperoxide. The cis olefin gave exclusively cis epoxide, and the trans olefin gave exclusively trans epoxide. In both cases, the epoxide was the sole product formed from the olefin. They can be distinguished easily by their different retention times on a gas chromatography column of 20% diisodecyl phthalate on Chromosorb W(60-80 mesh). They were also identified by comparing their infrared spectra with authentic samples. 

Epoxidation of ( >2-butene gives a racemic mixture of two enantiomeric epoxides. 

The synthesis of butadiene dioxide with air at 250° has been described. The epoxidation of 2-butene takes place partly stereospecifically to trans-2,3-epoxybutane. ... 

As another example, epoxidation of -2-butene gives fran.y-2,3-dimethyloxirane, whereas Z-2-butene gives cw-2,3-dimethyloxirane. 

In one method of production via petrochemical means, n-butenes can be separated by distillation from hydrocarbons. Treatment with hydrogen peroxide converts butanes such as 1-butene or 2-butene to their epoxide. A glycol such as 2,3-BD is then derived from the epoxide of 2-butene (Szmant 1989). 

Diperoxo(oxo)molybdenum(IV) complex bearing (S)-lacdc acid piperidineamide as a chiral ligand has been used for the epoxidation of -2-butene (Scheme 6B.8) and moderate enantiose-lectivity (49%) is achieved wherein the reaction is stoichiometric [16]. TWo possible mechanisms have been proposed for this reaction. One mechanism includes coordination of an olefin prior to epoxidation, which makes the olefin electrophilic and facilitates the nucleophilic attack of the proximal oxygen atom of the pooxide on the olefin. The other one is that an olefin nucleophilically attacks the peroxo group of the molybdenum complex. 

Epoxidation of alkenes is a stereospecific syn addition Which stereoisomer of 2 butene reacts with peroxyacetic acid to give meso 2 3 epoxybu tane Which one gives a racemic mixture of (2/ 3/ ) and (25 35) 2 3 epoxybutane ... 

Reactions of the epoxide of 1-butene with CH3Li gives a 90% yield of 3-pentanol. In contrast, reaction with CH3MgBr under similar conditions gives an array of products, as indicated below. What is the basis for the difference in reactivity of these two organometallic compounds toward this epoxide ... 

Reaction of the epoxide of 1-butene with methyllithium gives 3-pentanol in 90% yield. In contrast, methylmagnesium bromide under similar conditions gives the array of products shown below. Explain the difference in the reactivity of the two organomet-allic compounds toward this epoxide. 

TABLE 11. Calculated activation barriers (AE, kcal mol-1), H-bonding energies (/in-bonding, kcal mol-1) in the peroxy acid" and exothermicities (AErcatiinii, kcal mol-1) of the epoxidation reactions of -2-butene with substituted peroxy acids at the B3LYP//B3LYP/6-31+G(d,p) level of... 

Oxidation of Bis (1-methyl-2-acetoxypropyl) selenide in the Presence of 2-Butene. The only product of the reaction was 3-acetoxy-l-butene. No epoxides and only traces of diols were detected in the reaction product. Approximately 0.85 mole of 3-acetoxy-l-butene was produced per mole of peracetic acid consumed, and approximately 90% of the original selenide was recovered unchanged. 

The sequence of reactivity for the butenes is ds-2-butene (16) > 1-butene (6) > isobutylene (4.7) > trans-2-butene (1.0). A higher reaction rate for the cis isomer was also observed in the epoxidation of 2-hexenes, as was retention of stereochemical configuration (Tatsumi et al., 1990a). 

Spirolactones result from the reaction of epoxides with (2-buten-1,4-diyl) magnesium complexes and subsequent carbonation (95JOC5143). 

Fig. 2. Activation parameters vs number of HFIP molecules for the epoxidation of Z-butene within a solution model at 298K (RB3LYP/6-311++G(d,p)//RB3LYP/6-31+G(d,p)). Dashed lines refer to values in parentheses which include a correction for the dispersion interaction from a BSSE-corrected MP2/6-31+G(2d,p)//B3LYP/6-31+G(d,p) single-point calculation on the corresponding initial aggregates. AG (cyclooctene) and -TAS (cyclooctene) correspond to the experimentally determined activation parameters for the epoxidation of Z-cyclooctene at 298 K...

Problem 28.9 The following reactions have all been found to yield a mixture of pinacol and pinacolone, and in the same proportions treatment of 3-amino-2,3-dimethyl-2-butanol with nitrous acid treatment of 3-chloro-2,3-dimethyl-2-butanol with aqueous silver ion and acid-catalyzed hydrolysis of the epoxide of 2,3-dimethyl-2-butene. What does this finding indicate about the mechanism of the pinacol rearrangement ... 

The products of the ozonizotion of 2-butene in acetic acid and of 2,3-dimethyl-2-butene in isopropyl alcohol are compared with known substances. The monomeric ozonides of methyl trimethylacrylate and of trimethylacrolein are described. Some unsymmetri-cally disubstituted ethylenes give epoxides instead of ozonides, when ozonized in inert solvents. 

In studies with cis and tram isomers of 2-butene epoxide,26 it was found that in aqueous perchloric acid solution the cis isomer gave the dl glycol whereas the meso glycol was formed from the tram isomer. Consequently, inversion must have occurred during the reaction and the carbonium ion could have had no completely separate existence. For the cis isomer this transformation can be illustrated as follows ... 

Epoxidation of 2-methyl-3-buten-2-ol, la, catalysed by "titanium alkoxide or tungsten or... 

The Ti-Al-Beta catalyzed epoxidation of 2,3-dimethyl-2-butene 1 with H2O2 (30 wt% aqueous molar ratio 1 H2O2 = 2.4 1), via the epoxide 2 to pinacol 3 (Scheme 3), using different types of solvents, i.e. methyl-/er/-butylether (MTBE), acetone, r-BuOH, /-PrOH, diethyleneglycoldimethylether (diglyme) and 1,4-dioxane was studied in detail (Table 1). 

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