Electronic spectroscopy was used to study the kinetics of the reaction between Co(II)TnPc(2-) and SOCl2 in 1,2-dichlorobenzene. SOCl2 reacts rapidly with Co(II)TnPc(2-) to yield the two-electron-oxidized species Cl2CoIII. TnPc(1-) and a (SOCl2)Co(II)TnPc(2-) adduct; estimates of the rate constants for formation of these species are derived from stopped-flow data. The adduct further reacts with another molecule of SOCl2 (k(4) - 1.51 +/- 0.50 M(-1) s(-1) at 22.2 degrees C, Delta H double dagger = 13.5 +/- 1.1 kcal/mol, Delta S double dagger = -11.9 +/- 3.3 cal/(mol deg) to yield Cl(2)Co(III)TnPc(1-). In the presence of HCl, oxidation to form only Cl(2)Co(III)TnPc proceeds very slowly. Implications for Li/SOCl2 batteries are discussed.