Nitration of 2,3′‐bithienyl

Abstract

AbstractThe nitration of 2,3′‐bithienyl (1) with fuming nitric acid in acetic anhydride at 0° gives a mixture of 3‐nitro‐ (2), 2′ ‐nitro‐ (3) and 5‐nitro‐2,3′‐bithienyl (4) with relative percentages of 38.7%, 34.8% and 26.5%. When the nitration of 1 was carried out with fuming nitric acid in acetic acid at 20°, the same compounds 2, 3 and 4 were obtained, but with different relative percentages: 20.4%, 36.5% and 43.1% respectively. The results of the mononitration of 1 are compared with those obtained in other electrophilic substitutions and with the theoretical predictions. The further nitrations of 2, 3 and 4 with nitric acid in acetic anhydride at room temperature lead to the formation of five dinitro‐2,3′‐bithienyl isomers. Compound 2 gives a mixture of 2′,3‐dinitro‐ (5) and 3,5′‐dinitro‐2,3′‐bithienyl (6); compound 3 gives a mixture of 5, 2′,5‐dinitro‐ (7) and 2′,4‐dinitro‐2,3′‐bithienyl (8); compound 4 gives 7 and 5,5′‐dinitro‐2,3′‐bithienyl (9). The possible reasons of the formation of the various dinitro‐2,3′‐bithienyl isomers are discussed.