Mechanism of Debromination of 1-Aryl-1,2-dibromo-2-nitropropanes Promoted by Secondary Amines in Acetonitrile

Article abstract of DOI:10.1021/jo00112a030

Debromination reactions of erythro-dl-1-aryl-1,2-dibromo-2-nitropropanes with secondary amines in MeCN have been investigated kinetically.Reactions of erythro-dl-1-aryl-1,2-dibromo-2-nitropropanes with secondary amines in MeCN are stereospecific, producing (E)-1-aryl-2-nitropropenes quantitatively.The rate equation for the reaction is k_obs = k₂ + k₃², indicating that the reactions proceed by both uncatalyzed and base-catalyzed pathways.The Hammett ?, Broensted β, ΔH(excit.), and ΔS(excit.) values for the k₂ and k₃ processes are 1.22 +/- 0.04 and 1.20 +/- 0.02, 0.77 +/- 0.05 and 1.05 +/- 0.13, 5.6 +/- 0.3 and 1.7 +/- 0.1 kcal/mol, and -49.1 +/- 4.5 and -60.7 +/- 204 eu, respectively.For dehalogenation reactions from vicinal dibromo and bromochloro compounds, the element effect of the leaving group k_Br/k_Cl = 7.8 and 25 have been determined for the k₂ and k₃ processes.From these results, the mechanism and the trasition-state character of these reactions are assessed.