Kinetic Studies of Hantzsch Ester and Dihydrogen Donors Releasing Two Hydrogen Atoms in Acetonitrile

Abstract

In this work, kinetic studies on HEH 2 , 2-benzylmalononitrile, 2-benzyl-1 H -indene-1,3(2 H )-dione, 5-benzyl-2,2-dimethyl-1,3-dioxane-4,6-dione, 5-benzyl-1,3-dimethylpyrimidine-2,4,6(1 H ,3 H ,5 H )-trione, 2-(9 H -fluoren-9-yl)malononitrile, ethyl 2-cyano-2-(9 H -fluoren-9-yl)acetate, diethyl 2-(9 H -fluoren-9-yl)malonate, and the derivatives (28 XH 2 ) releasing two hydrogen atoms were carried out. The thermokinetic parameters Δ G ⧧ ° of 28 dihydrogen donors (XH 2 ) and the corresponding hydrogen atom acceptors (XH • ) in acetonitrile at 298 K were determined. The abilities of releasing two hydrogen atoms for these organic dihydrogen donors were researched using their thermokinetic parameters Δ G ⧧ °(XH 2 ), which can be used not only to compare the H-donating ability of different XH 2 qualitatively and quantitatively but also to predict the rates of HAT reactions. Predictions of rate constants for 12 HAT reactions using thermokinetic parameters were determined, and the reliabilities of the predicted results were also examined.

Quantitative evaluation of the actual hydrogen atom donating activities of O–H bonds in phenols: structure–activity relationship

“…In previous works, 8,[20][21][22][23][24] four physical parameters of H-donor XH, bond dissociation free energy DG o (XH), kinetic intrinsic resistance energy DG s XH/X , thermo-kinetic parameter DG so (XH) and DG so (X), have been used to evaluate the H-donating and Habstraction activities of XH and the corresponding radical X in thermodynamics, kinetics and actual HAT reactions, respectively. DG o (XH) is the thermodynamic factor and usually used to assess the potential H-donating capacity of XH and Habstraction capacity of X. DG s XH/X is the activation free energy of the self-exchange HAT reaction for XH (XH + X / X + XH).…”

Quantitative Evaluation of the Hydrogen‐Donating Abilities ofAmines and Amides in Acetonitrile

“…Here the H‐donating thermo‐kinetic parameters Δ G ≠ °(XH) of XH are discussed, as they represent the actual activities of the amines and amides to donate the hydrogen atom in chemical reaction during certain reaction time. According to the physical meaning of Δ G ≠ °(XH) discussed in previous articles, [19–24] the greater positive value of Δ G ≠ °(XH) is, the weaker H‐donating ability of XH is. In order to obtain information on the role of structural effects on the thermo‐kinetic parameters of amines and amides, visual comparison of Δ G ≠ °(XH) in acetonitrile at 298 K are shown in Scheme 2.…”

“…In this study, information on the antioxidant abilities of amines and amides were provided by a new parameter, thermo‐kinetic parameter Δ G ≠ °(XH), which was proposed in our previous work [19] and can be used to characterize the hydrogen‐donating ability in a certain HAT reaction during a certain reaction time [20–24] . The thermo‐kinetic parameter Δ G ≠ °(XH) is consisted of 1/2Δ G o (XH) and 1/2Δ G ≠ XH/X (equation 2).…”

Thermodynamic and Kinetic Studies of the Activities of Aldehydic C−H Bonds toward Their H‐Atom Transfer Reactions

“…The thermo-kinetic parameter ΔG ¼ 6 °(XH) was proposed by a new kinetic model (eq 2) in the previous works, [15,16] which was defined as one half of the sum of the ΔG o (XH) and the ΔG ¼ 6 XH/X (eq 3), usually used not only to describe the actual H-donating ability of XH in a HAT reaction during a certain reaction time, but also to predict the rate of HAT reaction (eq 1) by kinetic equation 2. [17][18][19][20][21][22] DG 6 ¼ XH=Y ¼ DG 6 ¼� ðXHÞ þ DG 6 ¼� ðYÞ (2)…”

“…It's the kinetic resistance of the HAT reaction as the thermodynamic driving force is zero, which means the kinetic intrinsic resistance barrier of XH in HAT reaction. The thermo‐kinetic parameter Δ G ≠ °(XH) was proposed by a new kinetic model (eq 2) in the previous works, [15,16] which was defined as one half of the sum of the Δ G o (XH) and the Δ G ≠ XH/X (eq 3), usually used not only to describe the actual H‐donating ability of XH in a HAT reaction during a certain reaction time, but also to predict the rate of HAT reaction (eq 1) by kinetic equation 2 [17–22] 23 $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr \Delta G{^{{\ne} }}{_{{\rm XH}/{\rm Y}}}=\Delta G{^{{\ne} }}{^\circ}({\rm XH})+\Delta G{^{{\ne} }}{^\circ}({\rm Y})\hfill\cr}}$$$ $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr \Delta G{^{{\ne} }}{^\circ}({\rm XH})\equiv 1/2[\Delta G{^{{\ne} }}{_{{\rm XH}/{\rm X}}}+\Delta G{^{{\rm o}}}({\rm XH})]\hfill\cr}}$$$ …”