AQUEOUS HIGH-TEMPERATURE CHEMISTRY OF CARBOCYCLES AND HETEROCYCLES .18. 6-MEMBERED HETEROCYCLES WITH ONE NITROGEN ATOM - PYRIDINE, QUINOLINE, ACRIDINE, AND PHENANTHRIDINE SYSTEMS

Seven nitrogen-containing heterocycles were chosen as model compounds: pyridine, 2-picoline, acridine, phenanthridine, quinoline, isoquinoline, and 2-methylquinoline. They were heated in eight different sets of conditions: (i) cyclohexane, (ii) water alone, (iii) aqueous formic acid, (iv) aqueous phosphoric acid (v) aqueous sulfuric acid, (vi) water and nontronite clay, (vii) water and Al-pillared clay, and (viii) water and calcium montmorillonite clay. Aquathermolyses under conditions (ii)-(viii) could thus be compared with purely thermal reactions under condition (i). Pyridine is almost unreactive under both thermolysis and aquathermolysis conditions, but in the presence of 10% H3PO4 almost 10% conversion was observed. 2-Picoline is more reactive toward heteroatom removal affording phenol (5.2%) as the major product. Acridine showed much higher conversions than phenanthridine; however, no nitrogen removal was observed and both compounds showed only hydrogenation and/or oxidation products. Quinoline, isoquinoline, and 2-methylquinoline are much more reactive than pyridine and 2-picoline, especially in the presence of 10% HCO2H, H3PO4, or H2SO4, and yield a large variety of products including phenol and aniline. Structures of the products have been elucidated and reaction sequences for their formation suggested.