Synthesis
The synthesis of benoxaprofen contains a lot of different steps. The Sandmeyer reaction of 4-aminophenyl-alpha-methylacetonitrile (I) with NaNO2, HCl and H2SO4 gives the compound 4-hydroxyphenyl-alpha-methylacetonitrile (II). The next step is nitration with nitric acid in acetic acid which will give 4-hydroxy-3-nitrophenyl-alpha-methylacetonitrile (III). This compound (III) can be reduced with SnCl2.2H2O and HCl in ethanol, or with H2 over Pd/C in the same solvent. The result of this reduction is the compound 4-hydroxy-3-aminophenyl-alpha-methylacetonitrile (IV), which, together with refluxing concentrated HCl, is hydrolyzed to 4-hydroxy-3-aminophenyl-alpha-methylacetic acid (V). When this compound (V) is esterificated with the use of ethanol and HCl, it gives the corresponding ethyl ester (VI). When p-chlorobenzoyl chloride (VII) is added to the previous compound (VI), they will cyclize to pyridine at 100 °C which will result in ethyl 2-(4-chlorophenyl)-alpha-methyl-5-benzoxazoleacetate(VIII). In the last step, this compound (VIII) is hydrolyzed with NaOH in ethanol, which gives benoxaprofen (IX).
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