 Furthermore, the type of solvent used is very important to ensuring high yields of the 4-hydroxyquinoline product.In the early work, the cyclization was accomplished by heating the Schiff base without a solvent and the yields were very moderate (below 30%).Limpach reported many years later that the yields in the cyclization were raised to 95% in many cases when an inert solvent, such as mineral oil, was used for the reaction.