In the absence of a photocatalyst and other additives, the radical arylation of diverse arenes and heteroarenes has been achieved with aryldiazonium salts under visible-light irradiation from a blue light-emitting diode (LED). Although the course of some reactions can be rationalized by the formation of strongly light-absorbing charge-transfer (CT) complexes between the diazonium ion and the aromatic substrate, several further examples indicated that the simple presence of an aromatic substrate, showing only weak interactions to the diazonium ion, is fully sufficient to enable product formation.

The radical arylation of anilines and pyrroles can be achieved under transition-metal- and catalyst-free conditions by using aryldiazotates in strongly alkaline aqueous solutions. The aryldiazotates act as protected diazonium ions, which do not undergo azo coupling with electron-rich aromatic substrates, but can still serve as an aryl radical source at slightly elevated temperatures. Based on an improved preparation of aryldiazotates in aqueous solution, homolytic aromatic substitutions of anilines and pyrroles were conducted with good overall yields and high regioselectivity. Moreover, DFT calculations provided further mechanistic insights.

Low concentrations of nitrogen dioxide, which arises as a side product from a range of industrial processes, can effectively be recycled through the diazotization of anilines. The studies reported herein now demonstrate that the removal of nitrogen dioxide from gas streams is even more effective when hydrophilic anilines are used as starting materials. The diazonium salts, which are obtained in this way in up to quantitative yields, can directly be employed in azo coupling reactions, thus opening up an attractive route to the industrially important group of azo compounds.

Aryl radicals generated in the aqueous phase of biphasic mixtures haveregardless of a comparably low polarity a strong preference to react with aromatic substrates in the aqueous phase and not to undergo phase-transfer into a lipophilic phase, independent from the presence of a surfactant. These results represent an important prerequisite toward future studies in biological systems, which typically consist of various compartments of either hydrophilic or lipophilic character.

The tracer diffusion of deuterium and tritium in the P-phase of PdH, has been measured by means of special techniques, the time lag method with mass spectrometer or counter tube as detector, and the decay function of isotope exchange. It has been found that D atoms as tracer in P-PdH,, i.e. surrounded by H atoms, reveal a smaller mobility than in PdD,, where they are surrounded by their own species. T atoms in the P-phase of PdH, showed about the same mobility as can be estimated-from results of a-phase measurements-for PdT,. An explanation of this unexpected bevavior can be givenby the assumption of displacement jumps as a particular type of correlation effect; by this the mobility of the tracer atoms becomes dependent on the mobility of the surrounding isotope species in the lattice.Die Tracerdiffusion von Deuterium und Tritium in der !3-Phase von PdH, wurde mit Hilfe spezieller Methoden gemessen. d. h. der Durchbruchsmethode mit Massenspektrometer oder Zahlrohr als Detektor sowie mit der Methode der Abklingfunktion des Isotopenaustauschs. Es wurde festgestellt, daO die D-Atome als Tracer in 8-PdH,, d. h. umgeben von H-Atomen, eine geringere Beweglichkeit aufweisen als in PdD., wo sic von Atomen ihrer eigenen Art umgeben sind. T-Atome zeigten in der P-Phase von PdH. etwa dieselbe Beweglichkeit, wie sie aus Ergebnissen von Messungen in der a-Phase fur PdT, abgeschatzt werden konnte. Eine Deutung fur dieses unerwartete Verhalten kann in der Annahme von Verdrangungsspriingen als besondere Art eines Korrelationseffektes gefundcn werden; hierdurch wird die Beweglichkeit der Traceratome abhangig von der Beweglichkeit der sie im Gitter umgebenden IsotoDensorte.