Hypochlorous acid (HOCl) is a highly toxic molecule that reacts with essential biomolecules, resulting in oxidative damage. A chemist helped out his molecular biologist and biochemist colleagues explore the expanse of hypochlorous acid reactivity by working on NaOCl treatment (in vitro) of bulkier (heterocyclic and aromatic) amines that are environmentally or biologically relevant. The N-chlorination of all amine functional groups reached completion. The following mechanism has been proposed to generalize the reactions (R represents the bulky groups):
H2O + OCl− ⇌ HOCl + OH− Fast, equilibrium constant, K1
HOCl + NHR2 → H2O + NR2Cl Slow, rate constant k2
OCl− + NHR2 → OH− + NR2Cl Overall reaction in basic solution
The first step is in equilibrium and the second step is rate-determining. Calculate the value of the rate constant k2 for the second step. Note that the Ka for HOCl is 3.5×10−8 and assume that the overall rate constant k in Rate = k[OCl−][NHR2] / [OH−] is 20 s−1.