Microwave-Assisted Hydrogenation of Codeine in Aqueous Media

An efficient one-pot microwave-assisted hydrogenation of codeine was achieved in aqueous solution. This technique is simple, fast, environmentally friendly, and highly efficient. Structure of produced dihydrocodeine was approved by using FT-IR, 1H NMR, 13C NMR, EIMS, and elemental analysis technique. Its purity analysis was performed by using HPLC and assay analysis was performed by using potentiometric titration methods. 1. Introduction Dihydrocodeine is a semisynthetic alkaloid that has preventive effects of shortness of breath and cough, as well as used extensively in killing postoperative pain [1]. Importance of dihydrocodeine is increasing day by day as second step of the “analgesic ladder” proposed for the treatment of cancer pain [2–4]. By extending the duration of action of the drug, since dihydrocodeine became available as a slow-release preparation, in this regard, it has begun to replace codeine [5]. Dihydrocodeine is also an important intermediate used in synthesis of other alkaloids such as hydrocodone [6]. A number of methods have been reported to prepare dihydrocodeine. Grew and coworkers have prepared dihydrocodeine by hydrogenation of hydrocodone [7, 8]. However, when compared with the hydrogenation process from codeine, additional steps are incorporated into the process and this ultimately increases the cost for obtaining dihydrocodeine. For hydrogenation of codeine palladium supported on carbon, catalysts are generally studied [6, 9]. In these methods, generally there is a need for excessive amounts of organic solvent for hydrogenation these processes bear risks in terms of health as well as causing environmental pollution. Therefore, Rapoport and Lithotworik used water as a solvent in the hydrogenation process of codeine [10, 11]. Disadvantages of some of these methods are a number of side reactions difficult to control, undesirable side products, long reaction times, and necessity of using a deactivating agent which is connected to the surface of catalytic metal that can minimize isomerisation side reactions of codeine. Microwave-assisted organic synthesis is an invaluable technology for drug synthesis because it often reduces reaction times, typically from days or hours to minutes or even seconds [12–14]. On the other hand, the use of microwave irradiation to accelerate catalytic reactions can be used to obtain good results from low-yielding reactions [15, 16]. With the employment of microwaves in metal catalysed reaction are reduced other unwanted side reactions [17–19]. Here, we describe the microwave-assisted synthesis of