The Electrochemical Method Developed By Salicylaldehyde

Salicylaldehyde, another scientific name is Hydroxy-benzaldehyde. is a useful fine chemical intermediate. It is used in the production of pesticide, medicine, and flavor etc. Salicylaldehyde, as a fine chemical intermediate in reaction, play an important role in all kinds of production. For example, in the process of production Salicylaldehyde from salicylic acid, based on the market price, salicylic acid is about ten thousand yuan a kilogram. Salicylaldehyde is about thirty thousand yuan a kilogram and coumarin is about eighty-five thousand yuan a kilogram, so the economic benefit is uncountable and the production of Salicylaldehyde has very good benefit of economic and society. Recently, salicyaldehyde is in dire need of in our country and any other countries of the world, as a result the production of Salicylaldehyde has wide prospect.A great deal of research has proved that carboxyl is very difficult to be electrochemical reduced and only those acids with carboxyl groups directly attached to an aromatic ring or directly attached to strongly acceptable electron groups can be reduced. Though the carboxyl group of salicylaldehyde(hydroxy-benzaldehyde) is directly attached to the aromatic ring, from the result of voltammetric behavior that the E|: value noticed on Hg electrode is -1.6V vs SCE and on GCE(Glass Carbon Electrode) the voltammertic peak is noticed around -1.2V which indicate that salicylic acid is difficult to be reduced and cause the low current efficiency. Therefore, this dissertation is to solve this problem about this difficulty by the theoretical guidance.Electrochemical-reduction method has been adopted in this dissertation to reduce salicylic acid to the flavor of Salicylaldehyde. Themain studies in the dissertation are as follows:inOn the basis of lots of references and experiments, the reaction system has been selected. Voltammetric behaviour of salicylic acid on glass carbon electrode has been studied. The effects of a series of influence factors such as current density, total electric charge circulated. material concentration, electrolyte concentration on material conversation and product's yield have been optimized in detail. The electrode material has been chosen. The structure was tested with IR and the high-performance liquid chromatographic method which determine the content of salicylic acid and salicylaldehyde in the electrolyte has been established. A simple and rapid spectrophotometric method for the determination of salicylic acid in the electrolyte has been developed.The results of high-performance liquid chromatography and cyclic voltammetric curves has showed that there is no byproduct in the electro-reduction of salicylic acid to form salicylaldehyde, which takes advantage to chemical method.Salicylaldehyde was synthesized by electro-reduction of salicylic acid by using Hg cathode and Pb alloy anode in membranous electrolyzer. The best conditions were deduced as follows, the cathode electrolyte(350ml) contained 14g salicylic acid.25g NaHSO-,.30y H3BO3,27.5g KC1 and 5.6g KOH, the anode electrolyte contained 10%(W/W) Na2SC>4, the current density and the passed charge were 18A/dm2 and 1.8F/mol respectively, and pH=6.0 + 0.2, and the temperature in the reaction was controlled between 13"C and 18C. The material was added successively. The yield of salicylaldehyde can exceed 80%.