Synthesis of functionalised macrocyclic compounds as Na⁺ and K⁺ receptors: A mild and high yielding nitration in water of mono and bis 2-methoxyaniline functionalised crown ethers

The syntheses of the bis-aromatic 15-crown-5 and 18-crown-6-ether derivatives 1 and 2, for the selective recognition of intra- and extracellular concentrations of Na⁺ and K⁺, from o-anisidine are described. These compounds were made with the aim of incorporating them into luminescent sensors. To facilitate their incorporation into such sensors, the compounds were nitrated. Whereas the use of conventional nitration reagents such as HNO₃, HNO₃-H₂SO₄ or NO₂BF₄ only gave low yields of the desired products, both mono- and bis-nitration products were formed in good yield by one-pot synthesis using NaNO₂ in a mixture of water and acetic acid (10:1). The use of X-ray crystallography proved the presence of the nitro-substituted products. An investigation into this mild nitration method revealed that the substitution pattern on the aromatic ring governed the ability of the compounds to undergo nitration.