Regioselectivity of aniline and toluidine nitration with HNO 3 and H 2 SO 4 in acetic acid

Content Provider	Semantic Scholar
Author	Sousa, Ângelo F. Telo, João P. Santos, Pedro Paim Ângelo
Copyright Year	2016
Abstract	The goal of this work is to study how the regioselectivity in aniline and toluidine nitration is affected by the resonance and induction effects of N-acetyl and N-succinimidil groups. Starting materials were protected with acetic and succinic anhydride, and nitration occured via SEAr with a HNO3/H2SO4 mixture in AcOH. Nitrated products were hydrolyzed and a sample of each experiment was analysed by HPLC. Aniline results show product distribution is controlled by both functional groups’ ortho/para directing and +R effects, yielding similar percentages of 2-nitroaniline (23%) and 4-nitroaniline (76%). For 4-methylacetanilide, regioselectivity control is once again established by the +R effect, favoring the ortho-substituted product (97%). Since succinimide group is less activating than the acetamide group, reaction control is taken over by the methyl group, yielding 94% 4methyl-3-nitroaniline. 3-methylacetanilide nitration yielded 91% 3-methyl-4-nitroaniline, which is a product favored by both +R effect of the acetamide group and +I effect of the methyl group. For N-(3-methylphenyl)succinimide, the yield of 3-methyl-6-nitroaniline increased to 62% since the succinimide group has a weaker activating effect due to the electronic pull of its two carbonyl groups. For the N-(2-methylphenyl)-succinimide, product distribution was controlled by the alkyl group, with the main products being ortho/meta substituted, yielding 29% 2-methyl-3-nitroaniline and 55% 2-methyl-5-nitroaniline. This is due to the non-planar position between the succinimide group and the aromatic ring, nullifying its +R effect. For the acetanilide derivative, regioselectivity is controlled by its +R effect (45% 2-methyl-4-nitroaniline) and by the +I effect of the methyl group (33% 2-methyl-5-nitroaniline). Overall it was shown that the +R effect of the acetamide groups is stronger than that of the succinimide group. This is due to the presence of one more carbonyl group in the latter, which pulls electrons away from the aromatic ring by induction (-I effect) and by resonance (-R effect) deactivating the starting material to an EAS reaction. Experiments with the N-acetyl derivative also showed that +R effect is more important to regioselectivity control than the +I of the alkyl group. This was an expected result, as the nonshared electron pair of the nitrogen atom has a greater importance to the stabilization of the aromatic ring than the electron-donating role of the CH3.
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