A Study of Factors Influencing the Stability of Five-Membered Lactone Rings

Abstract

An attempt has been made to study the effect of substituents on the ability of five-membered lactone rings. Lactones are cyclic esters found by heating the open chain hydroxyl acids. These compounds are of much importance from the pharmacological point of view. So it was considered worth-while to study the stability of the lactone rings in detail. One of the special properties of the lactones in the establishment of equilibrium between the ring form and the open chain form in the presence of acid. If the equilibrium is more towards the right hand side the ring form is more stable and if the equilibrium is more towards the left hand side, open chain form is more stable. Thus by the position of equilibrium, stability of the ring can be found. For this purpose nine different lactones having different substituents at different positions in the ring were synthesized and their equilibrium constants were determined using the method of direct titration of the open chain –hydroxy acid formed against standard sodium hydroxide. It was found that the electron donating groups stabilize the ring while the electron attracting groups destabilize it. There are evidences that mechanism of hydrolysis if lactone depends on the number and the type of substituents present in the ring. The hydrolysis i.e. ring opening can take place in two ways a i.e. acyl-oxygen cleavage or b i.e. alkyl oxygen cleavage. So far the mechanism of hydrolysis of only butyrolactone has been studied which involves acyl-oxygen cleavage. Similarly mechanism of hydrolysis of other –lactones which have been synthesized can be found,