Eqn. (a) represents the interaction between 2-bromo-6-methoxy naphthalene and cadmium chloride in the presence of fresh magnesium turnings and tetrahydrofuran (THF) followed by reflux to give rise to the formation of one mole of di-(6-methoxy-2-naphthyl) cadmium
- (b) shows the interaction between (I) and two moles of ethyl-2-bromopropionate in the presence of THF, at 20°C for 24 hours followed by hydrolysis in the presence of methanolic NaOH to yield the desired product naproxen with the elimination of one mole of CdBr2 and two moles of ethanol.
- 8.29.4 Chemicals Required. 2-Bromo-6-methoxynaphthalene : 24 g ; Tetrahydrofuran (THF) : 450 ml ; Magnesium turnings (Fresh) : 2.5 g ; Cadmium chloride : 20 g ; Ethyl-2-bromopropionate : 18 g ; Methanolic NaOH solution [5% (w/v)] : 200 ml ; Ether : q.s. ; Acetone : Hexane (1 : 1) : q.s.
- 8.29.5 Procedure. The different steps followed sequentially are as stated below* :
- 1) A solution of 24 g 2-bromo-6-methoxynaphthalene in 300 ml THF is poured gradually to 2.5 g fresh magnesium turnings and 100 ml THF at reflux temperature (~ 66°C).
- 2) Once the addition is complete, 20 g cadmium chloride is added ; and the resultant mixture is refluxed for 10 minutes to yield a solution of di-(6-methoxy-2-naphthyl) cadmium (I).**
- 3) A solution of 18 g ethyl-2-bromopropionate in 20 ml THF is now added to the previously cooled reaction mixture obtained in step (2). After allowing to keep the resulting mixture at 20°C for a duration of 24 hours, the product is subjected to hydrolysis by adding carefully 200 ml of methanolic NaOH solution, followed by heating to reflux for 60 minutes.
- 4) The resulting mixture is then diluted with excess of sulphuric acid (1 N) to acidic condition ; and extracted with ether successively. The ethereal layer is separated, evaporated to dryness.
- 5) The residue is recrystallized from a mixture of acetone and hexane (1 : 1) to give rise to the ultimate yield of the desired product, naproxen, to the extent of 16.66 g, mp
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