The reaction volumes for the protonation of 4-isopropyltropolone (Hipt)(ΔVH°: Hipt+H+ ⇌ H2ipt+) ) and for the reaction of the Fe(III) ion with Hipt(ΔVFeL°: Fe3+ + Hipt ⇌ Fe(ipt)2+ + H+) have been determined spectrophotometrically in acidic aqueous media under pressure up to 250 MPa. The obtained values are: ΔVH° (cm3 mol-1) =+2.8±0.1, ΔVFeL° (cm3 mol-1)=7.8±0.1. The activation volume for the dissociation of Fe(ipt)2+ was calculated to be -16.5±0.9 cm3 mol-1 by using ΔVFeL° and the reported activation volume for the formation of Fe(ipt)2+. The negative volume of activation for the dissociation reaction confirms associative activation for the reaction of the Fe3+ ion.
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