Deuterium-exchange Reactions with Substituted Aromatics. IV. The Poisoning Effect of Molecules Containing Nitrogen, Sulphur, or Arsenic

The catalytic exchange properties of a number of organic compounds containing nitrogen, sulphur, or arsenic have been studied in the presence of benzene and heavy water. The results confirm a charge-transfer-no-bond adsorption mechanism previously proposed for the deuteration of aromatic polycyclic hydrocarbons. For aromatic nitrogen compounds an increase in ionization potential of substrate leads to an increase in deuterium incorporation and a decrease in catalyst poisoning. Some aromatic amines deuterate faster than expected by theory and this is attributed to rapid exchange of the amino hydrogens in heavy water with a consequential increase in D-H ratio at the catalyst; surface. Sulphur and arsenic, even in their saturated valency states, extensively poison benzene exchange as does triethylamine. p-Benzoquinone, 2,6-dichloroquinone, and NN-dimethyl benzylamine exhibit catalytic side reactions which poison benzene exchange. With tritium oxide, the technique is suitable for the synthesis of tritiated aromatic amines and heterocycles to high specific activity.