Mechanochemical Metathesis between AgNO3and NaX (X = Cl, Br, I) and Ag2XNO3Double-Salt Formation

Here we describe real-time, in situmonitoring 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 AgNO3with NaX (X = Cl, Br, I) differ in reaction paths, with only the reaction with NaBr providing the NaNO3and 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 Ag2ClNO3intermediate 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 AgNO3. The in situobservation 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 in situreaction monitoring for mechanochemical reactions of ionic compounds as well as completes the application of these techniques to all major compound classes.