Aromatic Nitration with KNO3/H2SO4 in Dichloromethane

This could be useful for 2-CN and it would bee very useful in cheapskates quualude synthesis because it adds to substituted benzenes with fairly high ortho selectivity, I belive this will hold for toluene although they did not test it specifically. This will also make it easier for OTC bee's to get nitric acid as the DCM/HNO3 can be extracted with water to get any concentration of nitric acid desired.

Abstract

Pure dry HNO3 can be liberated from KNO3 with 96% H2SO4 directly into CH2Cl2 to yield solutions of variable concentration for use in a number of organic reactions. The present method efficiently replaces the employment of 100% HNO3 in some synthetic applications, avoiding the problems associated in storage and handling the acid.

Procedure

Unless otherwise specified, finely powdered KNO3 (50.0 mmol) was treated with the appropriate amount of 96% H2SO4 (47.5 mmol) and the mixture stirred for 15 min at room temperature; CH2Cl2 (25.0 mL) was added to the homogeneous slurry so obtained and the mixture cooled at 0°C with vigorous stirring. A solution of the substrate 1 (5.0 mmol) in CH2Cl2 (8.0 mL) was added dropwise and the stirring continued at room temperature for the required time. The reaction mixture was then poured into 10% aqueous Na2SO4 (30 mL) and the separated organic phase washed with 10% aqueous Na2SO4 (2×20 mL), dried over anhydrous Na2SO4, concentrated to dryness and the products obtained conveniently purified.

Nitration of phenylacetaldehyde had 97% conversion and 84% ortho selectivity, in a reaction time of 2 hours. Nitration of P2P had 98% conversion and 85% ortho selectivity, reaction time 2 hours.

The others showed similar trends although they reacted them for 24 hours, that does not appear to bee necessary.

The HNO3 in DCM is not stable and they reference possible explosions but state that they had no such problems. Be careful and only make this reagent when you need it, and dispose of extra.

Reference: Tetrahedron Letters, Vol 42(7), 1387-1389 (2001)