Phosphotungstic Acid: An Efficient Catalyst for the Aqueous Phase Synthesis of Bis-(4-hydroxycoumarin-3-yl)methanes
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Phosphotungstic Acid: An Efficient Catalyst for the Aqueous Phase Synthesis of Bis-(4-hydroxycoumarin-3-yl)methanes Prashant Singh • Pradeep Kumar • Anju Katyal • Rashmi Kalra • Sujata K. Dass • Satya Prakash • Ramesh Chandra
Received: 6 October 2009 / Accepted: 29 November 2009 / Published online: 16 December 2009 Ó Springer Science+Business Media, LLC 2009
Abstract In this present work, we report that phosphotungstic acid provides a simple, efficient and environmentally benign route is a two-component one-pot domino Knoevenagel-type condensation/Michael reaction between 4-coumarin derivative and an aldehyde in water as a solvent in shorter duration with high yields.
O
O
+ Ar-CHO
Phosphotungstic acid, Water, 80 °C
O
O O
OH
O
OH
OH
P. Singh A. R. S. D. Collage, University of Delhi, Delhi 110007, India P. Kumar R. Chandra (&) Department of Chemistry, University of Delhi, Delhi 110007, India e-mail: [email protected] P. Singh A. Katyal R. Chandra Dr. B. R. Ambedkar Center for Biomedical Research, University of Delhi, Delhi 110007, India R. Kalra A. N. D. Collage, University of Delhi, Delhi 110007, India S. K. Dass V.P.C. Institute, University of Delhi, Delhi 110007, India S. Prakash Department of Biomedical Engineering, McGill University, Montreal, QC H3A 2B4, Canada
Keywords 4-Hydroxycoumarin Phosphotungstic acid Green chemistry
1 Introduction Coumarin is a biological active chemical compound found in many plants, notably in high concentration in the tonka bean, woodruff, and bison grass [1]. It has a sweet scent, readily recognised as the scent of newly-mown hay. It has clinical value as the precursor for several anti-coagulants, notably warfarin. It is also used as a gain medium in some dye lasers [2, 3]. Coumarin is often found in tobacco products and artificial vanilla substitutes, though it has been banned as a food additive in numerous countries since the mid-twentieth century because it is moderately toxic to the liver and kidneys, with an LD50 of 275 mg/kg—low compared to related compounds [4–7]. Although only moderately dangerous to humans, coumarin is a potent rodenticide: rats and other rodents largely metabolize it to 3,4-coumarin epoxide, a toxic compound that can cause internal hemorrhage and death. Humans largely metabolize it to 7-hydroxycoumarin, a compound of low toxicity [8–10]. A number of coumarins exhibit interesting pharmacological activities and are therefore of therapeutic use. Along with these, coumarin derivatives have recently revealed new biological activities with interesting potential in therapeutic application besides their traditional employment as anticoagulant (anti-vitamin K activity) and sustaining agents, they have yielded important results as antibiotics and antitumor drug [11–13]. Heteropoly acids (HPAs) are promising materials having strong acidity as well as oxidizing ability and used as catalyst for various organic transformation [14–16] like phopshotungstic acid. Catalysis by HPAs is an expanding field of active research
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