Oxirane oxygen

Typical Lewis acids like BF3 and SbCls coordinate with oxirane oxygen to give (presumably) a cyclic oxonium ion (41) which reacts further (Scheme 28) (64HC 19-1)446, B-67MI50505). 

Anchimeric assistance by oxirane oxygen may accelerate the solvolysis of (44 Scheme 33) (by a factor of ca. 10 -l6 ) compared to the exo isomer (45 Scheme 34) (81JOC3512). 

The methylene protons that are very close to the oxirane oxygen atom are deshielded and appear as a broader signal near 8 = 4.2. This deshielding appears to be due to both van der Waals interactions between protons and the oxygen atom 331 and the effect of the unshared electron pair at the heteroatom 34). 

Potassium selenocyanate with 2 (or the c-ido isomer) yieldsss l,2-0-isopropylidene-a-D-xy(o-hex-5-enofuranose (65) by elimination of the oxirane oxygen atom. A similar elimination had earlier been... 

The dipole moments of oxepin and benzene oxide have been calculated to be in the range 0.76-1.36 D and >1.5 D respectively using the ab initio SCF and MINDO/3 methods (80JA1255). The lower calculated dipole moment would be in accord with experimental observations where the equilibrium was found to favor oxepin (7) in less polar solvents. Coordination between the oxirane oxygen atom and polar solvent molecules would also strengthen the C—C bond of the epoxide and thus lead to a preference for the benzene oxide isomer <72AG(E)825). Thus the proportion of oxepin (7) was found by UV spectral analysis to be higher in isooctane solvent (70%) than in water-methanol (10%). 

In concomitance with the displacement observed by i.r., an evolution of the catalytic activity has been observed while studying the liquid-phase epoxidation of cyclohexene in the presence of (EGDA)- Mo(VI), freshly prepared or after four months of conditioning at room temperature under inert atmosphere. As usual, the appearance of epoxide was followed by gas chromatographic analyses or by direct titration of oxirane oxygen and the disappearance of hydroperoxide was monitored by iodometric titration. In figure we report concentration-time for typical runs in ethylbenzene at 80°C obtained with the experimental procedure already described (ref. 9). It may be seen that with a freshly prepared catalyst an induction period is observed which lowers the initial catalytic activity. Our modified Michaelis-Menten type model equation (ref. 9) cannot adequately fit the kinetic curves obtained due to the absence of kinetic parameters which account for the apparent initial induction period (see Figure). 

Substituted aryloxiranes undergo a quantitative ring opening at the least substituted carbon when treated with Bi(OTf)3 and substituted phenols in dichloromethane at room temperature.27 In the proposed mechanism, the Bi(OTf)3 coordinates with the oxirane oxygen. This intermediate is the substrate in the S 2 reaction at the least substituted carbon. 

Ring opening occurs in the presence of iodine in an SnI process, the oxirane oxygen being initially complexed with the iodine. The two oxygen atoms bound to C-l serve to destabilize positive charge formation at C-2, rendering nucleophilic attack to C-3 more favorable. This accounts for the diequatorial product observed. 

Viscosities of the terpolymers were measured in toluene at 20°C. in an Oswald-Fenske viscometer. Analyses for oxirane oxygen were carried out by titrating with HBr in acetic acid (19). 

PROP Iodine number maximum of 6, oxirane oxygen minimum of 6.0 percent. SAFETY PROFILE When heated to decomposition it emits acrid smoke and irritating fumes. 

The hydroxy function may originate from the reduction of an a-halogenated carbonyl compound or a Grignard reaction. The oxirane oxygen is not always incorporated directly from a hydroxy group for instance, in the case of a carboxylic acid ester, it is derived with neighboring-group participation from an ortho-monoester intermediate. 

Starting from oxiranes, oxygen-containing macrocycles can also be prepared a good example of this is the formation of the ten-membered oxygen-containing heterocycle 126 via the condensation of chloral hydrate and oxirane using the phase-transfer technique. 

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