Methyl isotopic exchange with

The Bilik reaction applied to 2-ketoses yield 2-hydroxymethyl aldoses in which the tertiary carbon originates from C2 of the ketose and the C2 hydroxyl is on the opposite side to the C3 hydroxyl of the ketose (in the Fischer projection). Thus, o-fructose yield o-hamamelose. The position of equilibrium, however, lies towards the straight-chain sugar, although it can be pulled over somewhat towards the branched-chain aldose by the addition of borate. The mechanism in Figure 6.9 again explains the main reaction, but not the formation of sorbose as a by-product, which probably arises from a metal ion-promoted hydride shift, as there is no isotope exchange with solvent. The Bilik reaction can be applied to the production of l-deoxy-o-xylulose from 2-C-methyl-D-erythrose the reaction is particularly clean and only the two... 

Solutions of the salt K2PtCU in aqueous acetic acid are more stable upon heating than aqueous solutions. A 50% aqueous solution of acetic acid is very convenient to use as a solvent. Furthermore, in aqueous solutions, the solubility of hydrocarbons is rather low. Besides, even with a consideration of a different solubility of the hydrocarbons, the rate of alkane isotope exchange with D2O in 50% acetic acid turns out to be about 30 times greater than in water. Since a methyl group of acetic acid also exchanges with D2O in the presence of Pt(II), a... 

Cya.nideExcha.nge, Acetone cyanohydrin and methyl isobutyl ketone cyanohydrin [4131 -68-4] dissolved in an organic solvent, such as diethyl ether or methyl isobutyl ketone, undergo cyanide exchange with aqueous cyanide ion to yield a significant cyanide carbon isotope separation. The two-phase system yields cyanohydrin enriched in carbon-13 and aqueous cyanide depleted in carbon-13. Fquilibrium is obtained in seconds. 

Wells and coworkers53 have prepared a series of deuterated tetramethyltin compounds, which they used to study the long-range deuterium isotope effects on the proton chemical shifts of tetramethyltin. The various deuterated tetramethyltin compounds, with one to four trideuteromethyl groups on the tin atom, were prepared by a series of methyl group exchanges beginning with tri-trideuteromethyltin chloride and undeuterated tetramethyltin (Scheme 12). 

Figure 5.5 Activition of an [NiFe] hydrogenase such as that from D.gigas, by incubation with H2, as measured by different assay methods.These are production of H2 with the low-potential donor methyl viologen consumption of H2 with the high-potential acceptor dlchlorolndophenol and Isotope exchange of H2 with H2O. The proportions of the enzyme in three different states, unready, ready and active, are indicated by the shading.

The formation of acyclic enediols is, apparently, the initial reaction that leads to dehydration products. Sugar enediols are transitory compounds that have never been isolated. However, because, when treated with either acid or base, an aldose gives rise to its 2-epimer, as well as to its 2-keto isomer, a persuasive argument is provided for the 1,2-enediol as the intermediate common to each of the products. The evidence in favor of these intermediates is based primarily on isotope-exchange experiments, on reactions that involve isomeriza-tions of O-methyl sugars, and on kinetic measurements.10... 

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