Dariusz Bogdal*, Izabela Stêpieñ, Micha³ Pajda
Department of Polymer Chemistry and Technology,
Krakow University of Technology,
ul. Warszawska 24, 31-155 Krakow, Poland

* e-mail: pcbogdal@cyf-kr.edu.pl

Abstract
Coumarines are compounds originating from the nature that can be used in industry. They are common in cosmetics, seasonings, pharmaceutics, and photochemistry. Through years many methods of coumarine synthesis were developed such as Pechman, Perkin or Knoevenagel reactions and many others. Since compounds having optical active groups have been studied in our laboratory, we have been interested in coumarines. First we have investigated their derivatives synthesis through Pechmann reaction than by Knoevenagel condensation. All compounds were characterised and most of them gave satisfactory results in comparison with authentic samples. Than series of coumarines methacrylates were synthesised, and copolymerised to give photo- and electroluminescent polymers.

Keywords
Knoevenagel reaction, microwave irradiation, methacrylates, coumarines

Introduction
Coumarines are one of compounds originating from the nature and smell nicely. They occur in ethereal oils of many plants, e.g. cinnamon (Cinnamonum zeylanicum). They attracted a significant attention as compounds that can be used in industry, they are broadly used in cosmetics, in food and drinks as a flavouring (1), as a as materials for enzymes synthesis in pharmacy (2). Their derivatives present also fluorescence properties and it was proved that they can be used in optoelectronics thin films or laser dyes (3).

Discusion
Through years, many methods of coumarine synthesis were developed such as Pechman, Perkin or Knoevenagel reactions and many others (4-13). Since coumarine derivatives have been studied in our laboratory, we have investigated their synthesis through Knoevenagel condensation under microwave irradiation (14), (15). In this paper we present usage of Knoevenagel condensation leading to several 3-carboxycoumarine derivatives under microwave irradiation. Synthetised 3-carboxycoumarine derivatives were converted into methacrylate monomers that were copolymerised with methacrylates containing carbazolyl groups to give photo- and electroluminescent polymeric materials, which has been described in our previous papers (19). The application of microwave irradiation during Knoevenagel condensation and hydrolysis of 3- carboxycoumarine esters resulted in substantial reduction of reaction times as compared to traditional ones (16-18). Moreover, it allows eliminating long lasting and difficult process of precipitation and purification. At the stage of monomer synthesis, the use of N,N'-dicyclohexylcarbodiimide (DCC) enabled decrease of reaction temperature and time. During this reaction there is almost unnoticeable part of side-polymerisation, which allows eliminating usage of polymerisation inhibitors, and benefits by higher purity of synthesised monomers. Eventually, application of microwave irradiation, as well as DCC, results in reduced reaction times, easiness of synthetic preparation and substantial purity of crude products.

Experimental

General procedure of synthesis of coumarin conteining methacrylate monomers through Knoevenagel condensation (Fig. 1).
3- Carboxycoumarines were synthesised from appropriate hydroxybenzealdehydes (0.1 mol), diethyl malonate (0,1 mol) and piperidine (0,01 mol) as catalyst. They were stirred in a flask in the temperature of 190oC under microwave irradiation for 20 minutes in. Then product was hydrolysed to give acid, which was conducted still in the same vessel. The solution of sodium base (50ml; 0,1 mol/l) and 50ml of methyl alcohol was used as a hydrolysis agent. The reaction mixture was stirred for 25 minutes under microwave irradiation in the temperature of slight boiling. Appropriate 3-carboxycumarine was precipitated by addition of water and HCl to pH = 2, then filtered, dried and recrystallised from ethanol.
To synthesise 3-ethacryloyloxyethoxycarbonylcoumarin derivatives a mixture of 3-carboxycoumarine derivative (0,1 mol), 2- hydroxyethyl methacrylate (0,11 mol) and 4 - pyrrolidino - pyridine (5% of total substrates weight ) as catalyst in THF was stirred at ambient temperature for 24 hours, during the first 30 min. of the reaction, DCC (0,11 mol) in a THF solution was added dropwise. After completing the reaction N,N'-dicyclohexylurea (DCH) was filtered off from the solution, and the solvent was evaporated under reduced pressure to give crude product., which was recrystallised from ethanol, and then dried. All compounds were identified by GC-MS and IR and gave satisfactory results in comparison with authentic samples.

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