Understanding solid/solid organic reactions

The concept of an organic reaction between two macroscopic solid particles is investigated. Thus, we study several reactions that have been recently r eported to proceed "in the solid phase" and clearly show that, in most case s, grinding the two solid reactants together results in the formation of a liquid phase. This is true both for catalytic transformations (e.g., aldol condensations and oligomerization of benzylic compounds) and for noncatalyt ic reactions (Baeyer-Villiger oxidations, oxidative coupling of naphthols u sing iron chloride, condensation of amines and aldehydes to form azomethine s, homo-etherification of benzylic alcohols using p-toluenesulfonic acid, a nd nuclear aromatic bromination with NBS). This liquefaction implies the ex istence of a eutectic mixture with T-fusion below ambient temperature (alth ough both reagents have higher than ambient melting points). In cases where heating is required, it is again clear that a phase change (from solid to liquid) occurs, explaining the observed reaction kinetics. On the basis of 19 experimental examples, we discuss the possibility of solid-phase organic reactions and the implications of these findings to the reaction between t wo solid reagents. A general description of such reactive systems is propos ed. based on a consideration of the potential for eutectic (or peritectic) formation between the constituents of the liquid phases that arise during t he process of mechanical mixing of the solid reagents and products.