Mechanistic Insights into Substituent Effects on Reactivity of 2‐(Methoxymethyl)benzene‐1,4‐diamine

In the series of benzene‐1,4‐diamines (p‐phenylenediamines) investigated, 2‐(methoxymethyl)benzene‐1,4‐diamine (2‐methoxymethyl‐p‐phenylenediamine) is the most slowly oxidized, with removal of the first electron being rate determining. This electron‐withdrawing methoxymethyl group also drove a faster coupling step with 3‐aminophenol (m‐aminophenol) than for the analogs with electron‐donating groups. However, the series parent, benzene‐1,4‐diamine, exhibited the fastest coupling step. Since both N(1) and N(4) of the primary intermediates react with m‐aminophenol, it seems that steric hindrance by the 2‐substituents slows the overall rate. When 3‐amino‐2,6‐dimethylphenol is the coupler, the kinetics are biphasic. Nonproductive adducts are formed reversibly with all the primary intermediates by ipso attack at C(6). For 2‐(methoxymethyl)benzene‐1,4‐diamine, formation of this nonproductive adduct is favored more than for the other compounds in the series, in what seems to be a kinetically rather than thermodynamically controlled process. This slows the overall rate of color formation.