Abstract
Catalytic synthesis of warfarin acetals by using different heteropolyacid catalysts In this research, we report on the synthesis of warfarin acetals by using Preyssler's anion, [NaP5W30O110]-14 and heteropolyacids (HPAs) catalysts. This reaction was performed using methanol and ethanol at reflux temperature conditions. Under these conditions we have excellent yields and high selectivity. Preyssler heteropolyacid catalyst were easily recycled recovery and reused without the loss of its catalytic activities. The synthesis of warfarin acetals has been achieved using the catalytic amounts of green, inexpensive and eco-friendly Keggin types heteropolyacids. The products were obtained in high yields.
Highlights
Coumarin and its derivatives form an elite class of compounds; they represent the ring systems of several important groups of natural products
There is a mechanism of the synthesis of warfarin acetals (Scheme 2)
On the basis of the results obtained as shown in Scheme 1, 2, the reflux promoted intra-cyclodehydration reaction of warfarin with methanol and or ethanol, to the corresponding acetals 2 or 3, in the presence of Preyssler heteropolyacid as a catalyst is a better choice than the conventional methods in term of reaction temperature, reaction time and yield
Summary
Coumarin and its derivatives form an elite class of compounds; they represent the ring systems of several important groups of natural products They have been used as anticoagulants[1,2], additives in food and cosmetics[3], and in the preparation of insecticides, optical brighteners[4] and dispersed fluorescent and laser dyes[5]. The synthesis of acetals is carried out with catalysis by a strong proton acid, such as sulfuric acid[8,9] phosphoric or methanesulfonic acid[10] or by Lewis acids These methods are not entirely satisfactory, owing to drawbacks such as low yield, long reaction times, corrosive properties of catalysts and difficult workup. Most typical Keggin HPAs such as H3PW12O40, H4SiW12O40 and H3PMo12O40 are commercially available
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