Replacement of oxygen by deuterium

Catalytic hydrogenolysis of C—O bonds of benzyl esters and similar compounds by deuterium has rarely been used for preparation of labeled compounds, whereas predeuterated Pd in D20 is recommended for formation of deuterated alcohols from epoxides.63 

Since it is rarely satisfactory to reduce simple hydroxyl groups, the diversion by way of the bromide and Grignard reagent is usually chosen for replacement of OH by D (see Section 2.2, I), or the ester obtained by using a sulfonyl 

A different complex metal hydride, namely, the water-soluble NaBD4, has been used for conversion of D-glucuronic acid 5-lactone in more than 90% yield into D-tl-DJglucose,68 a product that was previously synthesized by reduction of glucuronic acid y-lactone by sodium amalgam and D20.68b 

In principle, such consideration apply of course also to the reverse reaction. Indeed, labile deuterium atoms must be washed out of a labeled compound by water because use of such a compound requires that it can be purified to constant isotopic composition by distillation, 

In contrast to the above, it is very difficult to replace hydrogen bound to carbon. It is possible only after complete or partial fission of a C-H bond — a process that naturally requires a considerable activation energy.70,71 

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