Applications of Oxygen Isotopes in Chemical Studies

Abstract

The choice of the general subject of this article requires no apology, but the choice of the specific material to fit to the space allotted does. The limita tions and research interests of the reviewer were a governing factor in mak ing the selection, but also the consideration entered that the effects of the major omissions are tempered by other recent reviews in which much of the material omitted is discussed. Thus the important work in geochemistry involving oxygen isotopes is discussed in excellent reviews by Dole (I), and more recently by Craig & Boata (2). The work on heterogenous systems is discussed more completely in the article by Dole. It is hoped in this connec tion that a general article on the application of isotopes in the study of heterogeneous catalysis, induding work with oxygen isotopes, will be forth coming. In the subjects chosen for review, an effort has been made to be com plete ; and earlier literature as well as the more recent has been referred to. When work which is within the scope of the subject matter is not cited, it is because of oversight or because the work is dealt with in a more general article by the same author.The present article stresses the application of oxygen isotopes to the study of chemical phenomena in homogeneous solution. Much of the work exploiting oxygen isotope effects has been done for such systems. For reac tions of oxygen-containing substances in an oxide-labile solvent such as water, isotope studies can answer important questions which no other method can answer as directly; and they have been of great help in defining the nature of the solvent and of the substances dissolved in it, and in exposing the mechanisms of reactions in solution. TECHNIQUESIn the work reviewed, mainly the oxygen isotopes of mass 18 and 16 come into question. The mass spectrometric method of measuring isotope ratios has almost completely supplanted that depending on the determination of density differences in water. With care, commercial instruments can measure differences to a precision of 1 part in 1000 in O2 or CO2 of normal oxygen isotopic composition. With specially designed instruments (3), a precision of one part in approximately 10,000 on CO2 can be attained.When the oxygen is available as water, an accurate method (4) of isotopic assay is equilibration of CO2 with the H20, followed by measurement of the isotopic ratio in the CO2• Dostrovsky & Klein (5) have described the high temperature equilibration of CO2 and H20, and have derived an equation 1 The survey of literature pertaining to this review was completed in January, 1956.

On the Recoil Chemistry of 15O in Oxoanion Salts

“…Isotopic oxygen exchange between O2 and Hj 0 does not take place under our experimental conditions [14,15].…”

“…The field has been reviewed many years ago; the report [15] still contains much of the pertinent information available to date. Almost invariably the oxygen exchange process was investigated using HjO enriched in "O.…”

“…Although measurable in principle, the oxygen exchange between H2O and the following oxoanions is sufficiently slow under our experimental conditions to be considered of little or no concern. The following ranking of the oxoanions is crudely according to increasing probability of oxygen-exchange: PO4" [15], SO5- [15], S2OI- [16], CIO4 [15,17], Br04 [18], NOi [15,19], NOJ [15], ClOj [15,17], BrOj [15,19,20], CrO^ [15],…”

Understanding the transition states of phosphodiester bond cleavage: Insights from heavy atom isotope effects

“…2.5% inverse in the direction of formation of the metal hydrate. 46,47 Thus, understanding whether upstream equilibria are part of the reaction mechanism is crucial since they can have an important influence on the observed isotope effect.…”

The Exchange of Oxygen-18 Between Cellulose, Adsorbed Water, and Water Vapor

“…Oxygen-18 generally does not exchange between alcohols and water (10). However, only one author (11) has studied the system cellulose/water and a critical study of his data showed that less than 6% of the cellulose oxygens reacted.…”