The Radiolysis of CMPO: Effects of Acid, Metal Complexation and Alpha vs. Gamma Radiation

The organophosphorus amide octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) is proposed for use in fuel cycle separations as a group actinide/lanthanide extractant. Alternative compounds such as the monoamides and diglycolamides (DGAs) proposed for actinide and/or actinide/lanthanide extraction also contain the amidic functional group, but do not contain the CMPO aromatic or phosphoryl groups. Their radiation stability is in the order monoamides > CMPO > DGA for irradiation under similar conditions. Although they produce similar radiolysis products, the kinetics of degradation for CMPO are completely different than for the other amides. CMPO degradation occurs in a zero-order fashion, and the -G-value for the change in [CMPO] is much lower when in the presence of acid. The DGAs and monoamides degrade with pseudo-first-order kinetics and are not protected by acidity. Possible mechanistic reasons for the differences between CMPO and the other amides are discussed, as are the effects of the diluent and metal complexation on CMPO free radical reaction rates. Finally, it is also shown that α-irradiation has much less adverse effects on CMPO degradation than β/γ irradiation, both with respect to -G-values, and radiolysis product generation.