Reaction mechanism of hydrogen-tritium exchange reactions between several organic and HTO molecules: a role of the second HTO.

Taro Udagawa,Masanori Tachikawa

doi:10.1039/c7ra13110k

Taro Udagawa, Masanori Tachikawa

Open Access

https://doi.org/10.1039/c7ra13110k

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Abstract

The mechanism of hydrogen-tritium (H-T) exchange reactions between several small organic and HTO molecules have been investigated using M06-2X/6-311++G(d,p) method. The second HTO molecule is taken into account for both direct and addition–elimination H-T exchange reactions. The reactivity of small organic molecules for H-T exchange reactions is in the order of CH3COOH > CH3CH2OH > CH3CHO ≈ CH3COCH3 ≈ C2H4 and C3H6 > CH4, C2H6, and C3H8. In particular, the energies of activation in addition–elimination H-T exchange reactions of alkene with two HTO molecules become lower than those of direct H-T exchange ones. Our study reveals that (i) the reactivity of alkene with HTO molecules is comparable to that of aldehyde and ketone when the effect of the second HTO molecule is taken into account and (ii) the H-T exchange reactions between alkene and HTO molecules prefer addition–elimination H-T exchange mechanism, whereas other organic molecules favor a direct one.

Highlights

Tritiated water, HTO molecule, is known as a toxic and radioactive molecule and is considered as one of the components of tritium-containing waste oils.[1]
For the direct H-T exchange reactions, our results are consistent with the Dong's conclusion from the zero-point vibrational energy (ZPVE)-corrected energetic point of view,[5] that is, the reactivity of small organic molecules for direct H-T exchange reaction is in the order of CH3COOH > CH3CH2OH > CH3CHO z CH3COCH3 > C2H4 and C3H6 > CH4, C2H6, and C3H8
Addition–elimination H-T exchange mechanism is favored for the reactions between alkene and two HTO molecules, and the reactivity of small organic molecules for H-T exchange reaction is in the order of CH3COOH > CH3CH2OH > CH3CHO z CH3COCH3 z C2H4 and C3H6 > CH4, C2H6, and C3H8

Summary

Introduction

HTO molecule, is known as a toxic and radioactive molecule and is considered as one of the components of tritium-containing waste oils.[1]. The above results of DEa values are basically consistent with the previous Dong's study.[5] Based on the DEa values, the reactivity of small organic molecules for H-T exchange reaction with HTO molecules is in the order of CH3COOH (carboxylic acid) > CH3CH2OH (alcohol) > CH3CHO (aldehyde) z CH3COCH3 (ketone) > C2H4 and C3H6 (alkene) > CH4, C2H6, and C3H8 (alkane).

Results

Conclusion