Isoelectronic reagents. II. Standard formation enthalpies of phenyl and pfluorophenyl iodine dichlorides

The formation heats ΔH^o_fPhICl₂(c) = 21.7 kJ mol^?1 and ΔH^o_fpFC₆H₄ICl₂(c) = ?173.0 kJ mol^?1 were determined by reaction of iodides with excess chlorine in methyl cyanide. These heats are used to show:(i) that thermal or photo-decompositions of aryl iodine dichlorides are kinetically controlled,(ii) the greater halogenating ability of aryl iodine dichlorides than Ph₃ACl₂ (A = P, As, Sb) compounds, and(iii) the weakening of halogenating ability with phenylation.