Title:Understanding Nucleophilicity of Pyridine-N-oxides Towards
2,4,6-Trinitrophenylbenzoate Through Simple Absorption Spectroscopic
Studies
Volume: 11
Issue: 1
Author(s): Ladapborlang Mawrie, Fazlur Rahman and Sarifuddin Gazi*
Affiliation:
- Department of Chemistry, School of Applied Sciences, University of Science & Technology Meghalaya, Techno City,
Kling Road, Baridua 9th Mile, Ri-Bhoi, Meghalaya, 793101¸ India
Keywords:
Nucleophilicity, Pyridine-N-Oxides, Nitrophenylbenzoate esters, Picrate, Reaction kinetics, Nucleophiles.
Abstract:
Aims: Understanding nucleophilicity of poor nucleophiles like pyridine-N-oxides.
Background: Nucleophilicity plays a vital role in substitution reactions. It helps to determine the
possibility and extent of the substitution reactions. The study of the nucleophilicity of poor nucleophiles
is challenging, and it has limited substrate scope. Understanding the strength of nucleophilicity
of such poor nucleophiles in a quantitative way is important.
Objective: Understanding the strength of nucleophilicity of such poor nucleophiles in a quantitative
way. Selection of appropriate electrophile for the reactions with the poor nucleophilespyridine-
N-oxides. Development of suitable methodology for kinetic studies of the reaction.
Methods: UV-Vis spectroscopic methods for monitoring the reactions.
Results: The kinetic studies revealed that the second-order rate constants of the nucleophilic reactions
are 1.67× 102 L mol-1 min-1, 29.8 L mol-1 min-1, 2.51 L mol-1 min-1, where the nucleophiles
are p-methylpyridine-N-oxide, pyridine-N-oxide, and p-nitropyridine-N-oxide, respectively. The
UV-Vis spectroscopic analysis revealed the nucleophilicity of p-methylpyridine-N-oxide > pyridine-
N-oxide > p-nitropyridine-N-oxide.
Conclusion: This comparative study suggests that the strength of nucleophilicity of the pmethylpyridine-
N-oxide is 5.6 times and 66.53 times more than that of pyridine-N-oxide and pnitropyridine-
N-oxide, respectively, whereas the strength of nucleophilicity of the pyridine-Noxide
is 11.87 times more than that of p-nitropyridine-N-oxide.