Reaction between 8-Hydroxyquinoline and Salicylic Acid in Solid State and Solution

Abstract

8-Hydroxyquinoline reacts with salicylic acid both in solid state and solution forming a yellow coloured compound. Phase diagram studies have shown the formation of a 1:1 addition compound stable in solid state and dissociated in solution. Differential thermal studies have shown that the reaction products obtained from solution and solid state reaction are almost identical except that there is a possibility of entrapped solvent molecules when the product was prepared from benzene. Also the reaction product shows a thermochromic effect. X-ray diffraction studies have revealed some structural difference between the reaction product obtained from solution and solid state reaction. Spectroscopic studies show the possibility of hydrogen bonding in the reaction product.The reaction in the solid state is slow and once a thin layer of reaction product is formed at the surface of salicylic acid crystals, the reaction rate becomes practically negligible. This may be due to the compactness of the product layer and unfavourable crystal packing in to the crystal lattice of salicylic acid. Microstructural studies have shown that there are structural changes during solid state reaction.