Mechanochemical Metathesis between AgNO and NaX (X = Cl, Br, I) and AgXNO Double-Salt Formation.

Here we describe real-time, monitoring of mechanochemical solid-state metathesis between silver nitrate and the entire series of sodium halides, on the basis of tandem powder X-ray diffraction and Raman spectroscopy monitoring. The mechanistic monitoring reveals that reactions of AgNO with NaX (X = Cl, Br, I) differ in reaction paths, with only the reaction with NaBr providing the NaNO and AgX products directly. The reaction with NaI revealed the presence of a novel, short-lived intermediate phase, while the reaction with NaCl progressed the slowest through the well-defined AgClNO intermediate double salt. While the corresponding iodide and bromide double salts were not observed as intermediates, all three are readily prepared as pure compounds by milling equimolar mixtures of AgX and AgNO. The observation of reactive intermediates in these simple metathesis reactions reveals a surprising resemblance of reactions involving purely ionic components to those of molecular organic solids and cocrystals. This study demonstrates the potential of reaction monitoring for mechanochemical reactions of ionic compounds as well as completes the application of these techniques to all major compound classes.