Bond cleavage, ranking

Formation of asphaltenes during solubilization of low-rank bituminous coals has been attributed to cleavage of open ether-bridges (6). But while the presence of such configurations in high- and medium-rank bituminous coals is well established (7), their existence in less mature coals remains to be demonstrated. From reactions of low-rank bituminous coals with sodium in liquid ammonia or potassium in tetrahydrofuran, it has, in fact, been concluded that open ether-bonds are absent (8) or only present in negligible concentrations (9). 

The most interesting outcome of this work is the observation that low-rank vitrinites can be rendered substantially soluble in chloroform and pyridine by alkylating coal salts formed in a non-reducing medium and under conditions that appear to preclude cleavage of covalent bonds. 

The protic cleavage of the carbon-metal a-bond ranks among the simplest of all electrophilic substitution processes. As organomercurials are readily prepared in high purity, can be manipulated with ease and are monomeric in solution, most mechanistic studies of the protonolysis of carbon-metal o-bonds have focused on the protic cleavage of organomercurials. Reviews and a book have been published on this subject. 

A diverse number of techniques has been employed to characterize the iron sulfides under coal liquefaction conditions. It is observed that the stoichiometry of the iron sulfides is determined by the H2S partial pressure and that greater activity is observed when the surface is rich in vacancies. All the iron sulfides show great affinity toward oxygen-containing compounds. This activity was demonstrated both with low rank coals as well as model compounds. It is proposed that pyrrhotites can act as catalysts for the cleavage of oxygen bonds in coal. 

The t-butoxycarbonyl group also ranks as an important amino-protecting group. The introduction by N-acylation is usually accomplished using t-butoxycarbonyl azide. Removal is based on the relative stability of the t-butyl cation. Acidic conditions (anhydrous trifluoroacetic acid is often used) result in cleavage of the C-O bond, and decarboxylation follows. ... 

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