A comparison of homogeneous and heterogeneous platinum as catalysts for the deuteration of condensed polycyclic aromatic hydrocarbons

Abstract

A comparison has been made of homogeneous sodium chloroplatinate(II) with heterogeneous platinum metal as catalysts for the exchange in D₂O of naphthalene, anthracene and pyrene, three representative condensed polycyclic aromatic hydrocarbons. For this purpose, very careful detailed experiments have been designed so that the progressive deuteration of the aromatics could be followed with time especially in both catalytic systems. Initial isotope orientation is similar for both catalysts although specificity is better with homogeneous platinum. Naphthalene during the initial stages of exchange yields ,&orientation with an M value of 1, ultimately giving naphthalene[β-D₄]. Only with heterogeneous platinum does prolonged exchange yield naphthalene[D₈]. A unique scrambling reaction of naphthalene[β-D₄] has been observed only with heterogeneous platinum. The reactivities of anthracene and pyrene are similar to naphthalene. Present data have been interpreted in terms of bond localization concepts, in particular the role of π-olefin type complexes in both catalytic systems. The results also indicate that π- dissociative, as compared with π-associative, mechanisms predominate both homogeneously and heterogeneously.