The kinetics and mechanism of the reaction of p-nitrocumyl bromide with nitrite ions in dimethyl sulfoxide. Evidence for a non-chain reaction giving a high nitro/nitrite ratio in the product
The reaction of p-nitrocumyl bromide (RBr) with sodium nitrite in [2H6]dimethyl sulfoxide gives none of the conventional evidence for an SRN1 chain reaction but the initial values of the [RNO2]/[RONO] ratio (2.5–5) are far higher than would be expected for the attack of a nitrite ion on the carbocation R+ and increase with the concentration of nitrite ions. The high values of [RNO2]/[RONO] are considered to derive from a mechanism in which a nitrite ion attacks a π-complex derived from the carbocation R+ and a second nitrite ion. This interpretation is supported by a kinetic term that is second order with respect to nitrite ions. An attempt to provide evidence for alternative radical pair intermediates from 15N CIDNP effects was unsuccessful.