Exchange reactions in acid media

D30+ ions are, however, normally insufficiently powerful deuteron-donors for labeling aromatic hydrocarbons but as early as 1936 Ingold and his colleagues94 found that deuterium sulfate constituted a suitable reagent for preparation of labeled compounds. A concentration of 65 mole-% of acid caused side reactions as well as exchange, and at a concentration of 40 mole-% exchange is very slow, so experiments are carried out at add concentrations of 51-52 mole-% in D20. 

Pure benzene is carefully dried over P205, then distilled into deuterium sulfate, and the mixture is shaken for 3-4 days, after which the benzene is distilled off in a vacuum into a fresh batch of D2SO4. After four repetitions of these operations the benzene is transferred to a flask containing roasted barium oxide, after 12 hours to a flask containing P205, and after a further 15 min to a storage flask. The [D6]benzene obtained contains 99.8% of deuterium. 

Brullmann, H.-J. Gerber, and D. Meier, Helv. Chim. Acta9 41, 1831 (1958). 

Liquid deuterium bromide has proved a solvent well suited for isotope exchange and it is also a powerful deuteron-donor.106 The hydrogen of polycyclic aromatic hydrocarbons is rapidly exchanged at 20° the hydrogen of 

Melander and S. Olsson, Acta Chem. Scand., 10, 879 (1956) Arkiv Kemi, 14, 85 (1959). 

---