Regioselective nitration of phenols and anisols in microemulsion

A nitration reaction was performed in a cationic surfactant-based microemul sion system with four different aromatic compounds, and the ortho-to-para r atio was examined. The results have been compared with a reference reaction performed in a two-phase system without surfactant and with previous work done with reactions in microemulsions. We report almost selective para-nitr ation of the chosen compounds when the reactions were performed in the micr oemulsion. Reaction in a two-phase system gave approximately equal ortho- a nd para nitration. The difference in reaction rate between the microemulsio n system and the two-phase system was examined as well. Using diluted HNO3 the reaction in microemulsion went to completion in 30 min. The two-phase s ystem demanded concentrated HNO3; with dilute HNO3, there was almost no rea ction after 24 h. H-1-NMR techniques were used to characterise the microemu lsion and to determine the ortho-to-para ratio of the reaction products. (C ) 2001 Elsevier Science B.V. All rights reserved.