Epoxides, reaction with reside

The nature of the Lewis acid and the residence time in the reactor drastically affect the ratio exo/endo of these terminal unsaturations. AICI3-based initiation leads to about 10% of vinylidenes with respect to total unsaturations, whereas the use of BF3-based catalysts, allowing a shorter contact time between the acid and the polymer and thus limiting isomerization, increases this exo structure to 70% or more [25,29]. The vinylidene double bond is much more reactive than the endo one, and favors considerably the furt her terminal functionalization of the oligomers for example, maleination, epoxidation, ozonolysis, reaction with phosphorus pentasul-fide, etc. (Fig. 2). 

The results of studies described above have eliminated water from the solvent and O2 from the air as the source of the oxygen in the product of the main epoxidation reaction, and strongly indicated that the oxygen is derived from the oxidant directly. Closure is foimd in the complementary experiment in which the label resides on the peroxide. Epoxidation of cis- stilbene with 2% H2 O2 (90% enrichment of used as received due to cost) and open to the air resulted in 89.9 0.8% incorporation of in czs-stilbene oxide and 72.5 2.4% incorporation in frzzzzs-stilbene oxide (Scheme 3.11). The reproducibility is encouraging,... 

Turnover numbers after 24 h, epoxide yield (mmol) and product distribution (%) for the epoxidation of 1-octene with Ti-MCM-41 using aqueous hydrogen peroxide as oxidant. (B = blank reaction P = catalyst as powder M = membrcme resident catalyst)... 

Employing a silicon micro reactor [channel dimensions = 500 or 1000 pm (width) x 250 pm (depth)], wall-coated with the acidic zeolite titanium silicate-1 (TS-1, Si Ti ratio = 17) (83) (3 pm), Gavrilidis and co-workers [52] demonstrated a facile method for the epoxidation of 1-pentene (84) (Scheme 6.23). Using H202 (85) (0.18 M, 30wt%) as the oxidant and 84 (0.90 M) in MeOH, the effect of reactant residence time on the formation of epoxypentane (86) was evaluated at room temperature. The authors observed increased productivity within the 500 pm reaction channel compared with the 1000 pm channel, a feature that is attributed to an increase in the surface-to-volume ratio and thus a higher effective catalyst loading. 

Heterogenization of catalytic nanoparticles stabilized by block copolymers can be carried out by their incorporahon into porous membranes based on poly(acrylic acid) crosslinked with a difunctional epoxide [20-22]. Membranes with defined porosities and amounts of palladium were studied in the selective hydrogenahon of propyne to propene as a model reaction. The porosity of the polymer membrane, the content of catalyst, and the residence time of the reaction mixture were found to influence the conversion and selectivity. The main advantage of these membranes compared to other heterogeneous catalysts is simple adjustment to reaction conditions and fadhtated mass transfer. 

In this reaction, the catalytic role of the tertiaiy amine resides in the intensification of the nucleophihc activity of the proton-donor molecule, i.e., the phenol, by the withdrawal of a proton. The o Qrgen of the epoxide ring can form a hydrogen bond with the -proton of the ammonium in which there is polarization of the bond in the ring. The reaction proceeds through a cyclic transition state in which there is an alternation of charges. 

The first step reaction example involves the preparation of water-based epoxy resins via ring-opening polymerizations of different epoxides with various diamines, dithiols or diols residing in the miniemulsion droplets at 60°C [75]. The basic requirement for successful miniemulsion polymerization is that both reactive components exhibit relatively low solubility in the continuous aqueous phase. The diepoxide Epikote E828, triepoxide Decanol EX-314, and tetraepoxide EX-411 are potential candidates for this purpose. Furthermore, incorporation of conventional costabilizers such as hexadecane into the... 

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