Statistical thermodynamics unveils how ions influence an aqueous Diels-Alder reaction

TY - JOUR

T1 - Statistical thermodynamics unveils how ions influence an aqueous Diels-Alder reaction

AU - Reid, Joshua Elias Samuel James

AU - Aquino, Pedro H. G.

AU - Walker, Adam J.

AU - Karadakov, Peter Borislavov

AU - Shimizu, Seishi

N1 - © 2019 Wiley-VCH. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2019/6/4

Y1 - 2019/6/4

N2 - The kinetics of Diels-Alder (DA) reactions in water has been known to be altered by salts for a long time. Yet the question how salts influence the reaction rate, either as rate-enhancing or rate-reducing additives, has so far remained unresolved. Conflicting hypotheses involve (i) indirect salt contributions through the modulation of internal pressure and (ii) making (or breaking) of the so-called “water-structure” by salts that strengthen (or weaken) the hydrophobic effect. In contrast to the qualitative nature of these hypotheses, here we answer this question quantitatively through a combination of transition state theory and fluctuation adsorption-solvation theory (FAST) using the DA reaction between anthracene-9-carbinol and N-ethylmaleimide as an example. We show that rate enhancement is driven by the salting out of the hydrophobic reactant, while rate-enhancing salts exhibit stronger affinity to the transition state.

AB - The kinetics of Diels-Alder (DA) reactions in water has been known to be altered by salts for a long time. Yet the question how salts influence the reaction rate, either as rate-enhancing or rate-reducing additives, has so far remained unresolved. Conflicting hypotheses involve (i) indirect salt contributions through the modulation of internal pressure and (ii) making (or breaking) of the so-called “water-structure” by salts that strengthen (or weaken) the hydrophobic effect. In contrast to the qualitative nature of these hypotheses, here we answer this question quantitatively through a combination of transition state theory and fluctuation adsorption-solvation theory (FAST) using the DA reaction between anthracene-9-carbinol and N-ethylmaleimide as an example. We show that rate enhancement is driven by the salting out of the hydrophobic reactant, while rate-enhancing salts exhibit stronger affinity to the transition state.

KW - Diels-Alder reaction

KW - Kirkwood-Buff theory

KW - salts

KW - statistical thermodynamics

KW - water

UR - http://www.scopus.com/inward/record.url?scp=85064735486&partnerID=8YFLogxK

U2 - 10.1002/cphc.201900024R1

DO - 10.1002/cphc.201900024R1

M3 - Article

SN - 1439-4235

VL - 20

SP - 1538

EP - 1544

JO - ChemPhysChem

JF - ChemPhysChem

IS - 11

ER -