Complex deuterium oxide

During the course of these mechanistic studies a wide range of possible applications of this reaction have been revealed. When the reduction is carried out with lithium aluminum deuteride and the anion complex decomposed with water, a monodeuterio compound (95) is obtained in which 70% of the deuterium is in the 3a-position. Reduction with lithium aluminum hydride followed by hydrolysis with deuterium oxide yields mainly (70 %) the 3j5-di-epimer (96), while for the preparation of dideuterio compounds (94) both steps have to be carried out with deuterated reagents. ... 

The well-known acid-catalyzed conversion of sugars into furan derivatives obviously consists of a complex sequence of reactions, and the industrial heterophasic conversion of pentosans in plant tissues has been discussed in detail.11 The reactions themselves are still not well understood, although xylose and glucuronic acid in deuterium oxide afford 2-furaldehyde without uptake of isotope thus limiting the mechanistic possibilities to those not permitting reversible enolization.12 The bacterial sugar streptose yields... 

Since the associative and dissociative tt complex substitution mechanisms are not mutually exclusive, both may participate simultaneously in exchange reactions where deuterium oxide is the second reagent. It is therefore of interest to distinguish between the relative importance of these two mechanisms. 

The importance of the strength of tt complex adsorption on the reaction rate through the operation of displacement effects is further demonstrated by naphthalene randomization reactions. Naphthalene exchanges very slowly with deuterium oxide. That this is due to the displacement of water by normal naphthalene and not due to a toxic side reaction, such as polymerization, is shown in randomization experiments with mono a-deuterated naphthalene. Randomization is completed within 24 hours at 120°, whereas no significant deuteration occurs under the same reaction conditions with water. This result furnishes additional proof for the dissociative exchange mechanism. 

The fact that an isotope effect of 1.7 0.1 is observed 38) in the benzene/deuterium oxide reaction at 30°C indicates that this reaction is the rate-determining step of the dissociative n complex substitution mechanism. In this respect the result agrees with the direct observations made by other investigators 41, 42), namely that unsaturated hydrocarbons chemisorb at a faster rate than their subsequent interactions with chemisorbed hydrogen. 

The reaction of the lithiated species with deuterium oxide proceeds with retention of configuration due to the coordination of the electrophile to the lithium cation. However, the corresponding ate complex is formed with inversion because no coordination of the Lewis acid is possible at the lithium cation and, therefore, the protonolysis of the ate complex proceeds with inversion of configuration. Among the Lewis acids examined, triethylaluminum gives the best result. 

A mechanism which is consistent with the various experimental results for olefin formation involves the initial abstraction of the hydrazone proton (103 - 106)82 In this case, however, expulsion of the tosylate anion is associated with the abstraction of a second hydrogen from C-16 instead of hydride attack on the C=N bond (compare 97 - 98 and 106 - 107). Expulsion of nitrogen from the resulting intermediate (107) yields an anion (108) which is most probably stabilized in the form of a metal complex and can be readily decomposed by water to give an olefin (109). This implies that 17-d1-androst-16-ene (104) can be prepared by using deuterium oxide as the sole deuterated reagent.82... 

A range of variously substituted piperidines, piperazines and dialkylamines have been conveniently deuterated in a single step by isotopic exchange with deuterium oxide in the presence of an appropriate ruthenium complex catalyst.154 The isotopic exchange has been carried out efficiently in dimethylsulfoxide at positions both a and P to the NH group. 

Oxidation of O-methyldeacetyllythramine (75) with chromic anhydride-pyridine complex yielded the ketone (79) which exchanged four hydrogens on treatment with sodium deuteroxide in deuterium oxide and deutero-methanol (12). 

In 2002, however, it was observed that water did substantially affect radical cyclizations mediated by Ti(III) complexes. Thus, for example, when epoxide 20 was treated with Cp2TiCl in dry THF, the exocyclic alkene 21 was obtained. When the same epoxide was treated with CpaTiCl in the presence of water, however, the corresponding reduction product 22 was formed. Moreover, with deuterium oxide instead of water, the deuterium labeled isotopomer 23 (Scheme 18) was isolated [72],... 

Early efforts to use p.m.r. spectroscopy to establish the configurations of diastereoisomeric quercitols were unsuccessful, with two exceptions,64 because of complex spin-spin coupling, and overlapping of multiplets at 60 and 100 MHz. However, in the p.m.r. spectrum of (-l-)-proto-quercitol (7) in deuterium oxide at 220 MHz (see Fig. 1),... 

Figure 5 shows (on ZSM-5 completely exchanged with deuterium oxide and dried at 800 C) that readdition of water (D20) gave two new bands, possibly arising from hydration of A10+ ions to form A1(0D)2+ ions. This suggests that either hydrated or anhydrous complex A1 cations, held outside the zeolitic framework can be active for ethylene oligomerization. 

To supplement the data on prolyl isomerization, I will draw on the literature describing rotation about the C-N bond in secondary amides. Early studies in this field were described by Stewart and Siddall in an excellent 1970 review. As we will see, these reactions are related to prolyl isomerization and support the mechanism to be proposed for prolyl isomerization. The mechanism is based on results from a variety of experimental approaches. In all cases, experiments employing kinetic-based probes will be used to obtain an accurate picture of the activated complex in the rate-limiting transition state. The experiments that will be described include thermodynamics, in which activation parameters (i.e., AG, AHt, and ASt) will be described solvent effects, in which the influence of organic solvents and deuterium oxide will be reviewed acid-base catalysis substituent effects and secondary deuterium isotope effects. 

PMR spectra cannot indicate the presence of amide hydrogen because of rapid exchange of the proton with deuterium oxide solvent. We have found that nitrogen-cobalt bonded complexes with infrared absorptions at 1575 cm. may be formed when N-bromo primary amides react with pentacyanocobaltate(II). Comparison with the spectrum of a complex formed from an N-bromo secondary amide, in which no acidic hydrogen would be present, should help resolve this problem. 

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