Epoxidation hydroxylic solvents

Majetich and Hicks <96SL649> have reported on the epoxidation of isolated olefins (e.g., 61) using a combination of 30% aqueous hydrogen peroxide, a carbodiimide (e.g., DCC), and a mildly acidic or basic catalyst. This method works best in hydroxylic solvents and not at all in polar aprotic media. Type and ratios of reagents are substrate dependent, and steric demand about the alkene generally results in decreased yields. 

Cobalt tetracarbonyl anion in such hydroxylic solvents as water or methanol also reacts with epoxides at temperatures of 60—100 and at an elevated pressure of carbon monoxide (2000 Ib./in. ) to give esters of j8-hydroxy acids. Thus, ethylene oxide has been found to react with sodium cobalt tetracarbonyl and carbon monoxide in methanol solution at 65 and 2000 Ib./in. to give methyl 3-hydroxy-propionate in a yield of 55% the remainder of the product was acetaldehyde and an involatile oil. It was also shown that this reaction proceeds almost as well at a much lower pressure (three or four atmospheres of carbon monoxide). ... 

NaBHi is a much milder reducing agent than LiAlH,. In hydroxylic solvents it reduces aldehydes and ketones rapidly at 25° but is essentially inert to other functional groups epoxides, esters, lactones, carboxylic acids and salts, nitrile and nitro groups. Acid chlorides are reduced rapidly in diglyme or dioxane. 

The successful examples of epoxidation reactions using MMPP have so far been carried out using a hydroxylic solvent to dissolve the reagent. This has usually been a low molecular weight alcohol or, where the substrate to be epoxidised is... 

This alkoxycarbonylation reaction is also catalytic, if the alkylcobalt tetracarbonyl is formed from an epoxide and cobalt carbonyl anion in a hydroxylic solvent (9). A stoichiometric amount of base is not required in this reaction. The initial product, a derivative of the anion of 2-hydroxy-ethylcobalt tetracarbonyl, may undergo three reactions (a) react with more epoxide to give polymer, (b) undergo an internal hydride shift to form aldehyde or ketone, or (c) undergo protonation, carbon monoxide insertion, and alcoholoysis (or hydrolysis) to form ester (or acid). Varying amounts of... 

Effects of hydroxylic solvents on epoxidation of styrene with H2O2 have been studied. Consistent results were obtained when the impact of a single molecule of water, ethanol, and t-BuOH on the reaction was simulated using the discrete model. Reactivity was greatest for /-BuOH followed by ethanol protic solvent molecules promote the heterolytic cleavage of H2O2 and form active oxygen species that reduce the reaction barrier. ... 

The stereochemistry of epoxidation of 5j5-steroids is changed from to predominantly a by the presence of an a-oriented hydroxyl group. The magnitude of this hydroxyl effect is less in polar solvents, as shown by the... 

The presence of hydroxyl groups in the benzylidene sugars does not interfere with the reaction and by-products are usually minor. Suitable solvents other than carbon tetrachloride, include benzene and tetra-chloroethane. Epoxide, amide, and other commonly encountered functionalities in sugar derivatives are unaffected under the reaction conditions. The corresponding 6-bromo-4-benzoates are valuable intermediates... 

Figure 14.14 Additional hydroxyl-particle activation methods include bis-epoxide modification, tosyl activation, and tresyl activation methods. The tosyl chloride and tresyl chloride activation procedures must be done in dry organic solvent, but the coupling of an amine-containing ligand can be done in either organic solvent or aqueous buffer.

The competition between attack by solvent at C-6 (intermediate 78) and attack at C-5 by the hydroxyl group on C-2 (intermediate 77) explains these results, which show the extent to which closure of an oxolane ring is favored. In principle, a third (unobserved) possibility exists, namely, closure of a six-membered, oxygen-containing heterocycle as a result of opening of the epoxide at C-6 by the hydroxyl group on C-2. 

Aliphatic hydroxylation. As well as unsaturated aliphatic compounds such as vinyl chloride mentioned above, which are metabolized by epoxidation, saturated aliphatic compounds also undergo oxidation. The initial products will be primary and secondary alcohols. For example, the solvent n-hexane is known to be metabolized to the secondary alcohol hexan-2-ol and then further to hexane-2,5-dione (Fig. 4.9) in occupationally exposed humans. The latter metabolite is believed to be responsible for the neuropathy caused by the solvent. Other toxicologically important examples are the nephrotoxic petrol constituents, 2,2,4- and 2,3,4-trimethylpentane, which are hydroxylated to... 

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