Synthesis of 7- Hydroxy -4- Methyl Coumarin

Aim

To Synthesis and submit Synthesis of 7- Hydroxy -4- methyl coumarin.

Principle

A general synthesis of coumarins involves the interaction of a phenol with a β- ketoester in presence of an acid condensing agent (Pechmann
reaction). Concentrated sulphuric acid is usually used as the condensing agent for simple monohydric phenols and β- ketoesters, although phenol itself reacts better in the presence of aluminium chloride. The mechanism of the reaction involves the initial formation of a β- hydroxy ester, which then cycles and dehydrates to yield the coumarin. Polyhydric phenols, particularly here the two hydroxy groups are meta oriented, react with great ease and sulphuric acid is used as the condensing agent with careful temperature control to ensure a good yield.

Reaction

Requirements

• Conc. Sulphuric acid -7.5 ml
• Resorcinol – 1.2 g
• Ethylacetoacetate – 2.4 ml
• Ice – q.s
• Sodium Hydroxide – q.s
• Ethanol – q.s

Procedure

Take 1 litre of concentrated sulphuric acid in 3 litres capacity 3 necked flask fitted with a thermometer, mechanical stirrer and a dropping funnel. Immerse the flask in an ice bath. When the temperature falls below 100C, add a solution of 100 g (0.91 mol) of resorcinol in 134 g (130.5 ml, 1.03 mol) of redistilled ethyl acetoacetate dropwise and with stirring. Maintain the temperature below 100C by means of an ice bath during the addition (2h). Keep the mixture at room temperature for 18 hr and then pour it into a mixture of 2 kg of crushed ice with vigours stirring and add 3 litres of water. Collect the precipitate by suction filtration and wash it with three 25 ml portions of cold water. Dissolve the solid in 1500 ml of 5 per cent sodium hydroxide solution, filter and add dilute 2 M sulphuric acid (about 550 ml) with vigorous stirring until the solution is acid to litmus. Filter the crude 4-methyl-7-hydroxy coumarin at the pump, wash with four 25 ml portions of cold water and dry at 1000C. The yield is 155g (97%). Recrystallise from 95 per cent ethanol: the pure compound separate in colourless needles, m.p. 1850C.

Use

• Laser dye.
• Starting material for production of the insecticide ‘ hymecromone’.

Report

7- hydroxy -4- methyl coumarin was synthesized and the percentage yield was found to be …….. %.