Production of Free Radicals in Organic Solids by Hydrogen-Atom Bombardment

A beam of hydrogen (or deuterium) atoms, produced by a microwave electrodeless discharge, has been found capable of producing free radicals upon striking polycrystalline samples of malonic acid, malonamide, methyl malonic acid, and methyl malonamide. The radicals produced in these compounds, identified by means of their electron magnetic resonance signals, arise from the removal of a methylene hydrogen of the parent molecule. Only one radical species is produced in each compound, in contrast to x irradiation which often produces several types of radicals. The present study strongly suggests that the impinging hydrogen atoms (a) abstract methylene hydrogens from the organic molecules to form radicals and H2 and (b) penetrate several molecular layers of the crystallites before they react. Radicals were also formed by impinging hydrogen atoms in naphthalene, hexamethylene tetramine, calcium malonate, calcium formate, and aluminum acetyl acetonate. However, no positive identification of these radicals could be made on the basis of their powder EMR spectra. On the other hand, several other organic powders gave no radicals by the hydrogen-bombardment technique.