Quinonediimine hydrogenation

According to a general rule, not only dihydric phenols, but also those diamines of the p-series which still contain one hydrogen atom attached to each nitrogen, are dehydrogenated to quinone or quinonediimine with great ease. Hence in the oxidation solution emeraldine is also immediately converted into the doubly quinonoid chain... 

Leucoemeraldine is the formal hydrogenation product of emeraldine. As shown in reaction 12, each tetramer unit contains one reducible quinonediimine moiety. 

There are two related hydrogenation reactions for which there are requisite enthalpy of formation data p-benzoquinone to hydroquinone and p-xylylene to p-xylene. For the former reaction, the enthalpies of hydrogenation are —179 kJmol-1 (s) and —142 kJ moL1 (g). For the latter62, the gas-phase hydrogenation enthalpy is ca —192 kJmol-1. An interpolated gas-phase hydrogenation enthalpy for p-quinonediimine is ca — 167 kJ mol-1. Based on the benzoquinone/hydroquinone example, the solid-phase value presumably would be more negative. The enthalpy of formation of solid emeraldine thus would be at least 534 kJmol-1. 

Irradiation (X > 300 nm) of solutions of the Schiff bases N-benzylidenebenzyl-amine and N-benzylideneaniline in propan-2-ol in the presence of either platinised titanium(IV) oxide or platinised CdS induces transfer hydrogenation to give the corresponding secondary amines, dibenzylamine and N-benzylaniline respectively. Donor-acceptor compounds of the type N,N -dicyanobenzo[b]-naphtho[2,3-e][l, 4]dithiin-6,11 -quinonediimine, N,N -dicyanobenzo[b]naphtho... 

---