Methyl oxygen exchange with

The operation of the nitronium ion in these media was later proved conclusively. "- The rates of nitration of 2-phenylethanesulphonate anion ([Aromatic] < c. 0-5 mol l i), toluene-(U-sulphonate anion, p-nitrophenol, A(-methyl-2,4-dinitroaniline and A(-methyl-iV,2,4-trinitro-aniline in aqueous solutions of nitric acid depend on the first power of the concentration of the aromatic. The dependence on acidity of the rate of 0-exchange between nitric acid and water was measured, " and formal first-order rate constants for oxygen exchange were defined by dividing the rates of exchange by the concentration of water. Comparison of these constants with the corresponding results for the reactions of the aromatic compounds yielded the scale of relative reactivities sho-wn in table 2.1. 

Metal alkoxides undergo alkoxide exchange with alcoholic compounds such as alcohols, hydro-xamic acids, and alkyl hydroperoxides. Alkyl hydroperoxides themselves do not epoxidize olefins. However, hydroperoxides coordinated to a metal ion are activated by coordination of the distal oxygen (O2) and undergo epoxidation (Scheme 1). When the olefin is an allylic alcohol, both hydroperoxide and olefin are coordinated to the metal ion and the epoxidation occurs swiftly in an intramolecular manner.22 Thus, the epoxidation of an allylic alcohol proceeds selectively in the presence of an isolated olefin.23,24 In this metal-mediated epoxidation of allylic alcohols, some alkoxide(s) (—OR) do not participate in the epoxidation. Therefore, if such bystander alkoxide(s) are replaced with optically active ones, the epoxidation is expected to be enantioselective. Indeed, Yamada et al.25 and Sharp less et al.26 independently reported the epoxidation of allylic alcohols using Mo02(acac)2 modified with V-methyl-ephedrine and VO (acac)2 modified with an optically active hydroxamic acid as the catalyst, respectively, albeit with modest enantioselectivity. 

Another example is tetrameric methoxy(methyl)zinc, (MeZnOMe)4. The mechanism can be treated both as an aggregative process as well as a ligand coordination exchange process. It reveals aggregation due solely to oxygen bridging, with no direct participation of the C—Zn bond, and will be mentioned only briefly. 

Clearly with ratios of khyJkt.yeh in the region observed for ethyl benzoate under these conditions, the rates and activation parameters are largely determined by the addition step. And in this case at least the small rate decrease due to the breakdown step is entirely an entropy effect. In several instances, notably the hydrolyses of methyl and substituted benzyl benzoates, phthalide and y-butyrolactone. kh>rt > kcsch. since no concurrent oxygen exchange could be detected on alkaline hydrolysis212-3". ... 

Lithiation of dibenzofuran with butyllithium and mercuration both occur at the 4-position. Thallation occurs at the 2-position, however (57IZV1391). The mercury and thallium derivatives serve as a source of the iodo compounds by reaction with iodine. Bromodibenzofurans undergo bromine/lithium exchange with butyllithium and the derived lithio compounds may be converted into phenols by reaction with molecular oxygen in the presence of a Grignard reagent, into amines by reaction with O-methylhydroxylamine, into sulfinic acids by reaction with sulfur dioxide, into carboxylic acids by reaction with carbon dioxide and into methyl derivatives by reaction with methyl sulfate (Scheme 100). This last reaction... 

The rates of hydrolysis and carbonyl-oxygen exchange carried out at 27°C with potassium hydroxide (1.5 N) on labeled N-benzyl-M-methyl derivatives of formamide (21 ), acetamide (22), and propionantide (23) have been reported (14). 

The isotopic exchange reactions between a secondary alcohol and water were further investigated by Goering and Josephson (1962) in connection with the oxygen exchange accompanying the acid-catalysed allylic rearrangement of cis- (7) and fraws-5-methyl-2-cyclohexenol (8) in aqueous acetone. 

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