Discovering and Evaluating the Reducing Abilities of Polar Alkanes and Related Family Members as Organic Reductants Using Thermodynamics

Abstract

In this work, the pK a values of 69 polar alkanes (YH 2 ) in acetonitrile were computed using the method developed by Luo and Zhang in 2020, and representative 69 thermodynamic network cards on 22 elementary steps of YH 2 and related polar alkenes (Y) releasing or accepting H 2 were naturally established. Potential electron reductants (YH − ), hydride reductants (YH − ), antioxidants (YH 2 and YH − ), and hydrogen molecule reductants (YH 2 ) are unexpectedly discovered according to thermodynamic network cards. It is also found that there are great differences between YH 2 and common hydrogen molecule reductants (XH 2 ), such as Hantzsch ester (HEH 2 ), benzothiazoline (BTH 2 ), and dihydro-phenanthridine (PH 2 ), releasing two hydrogen ions to unsaturated compounds. During the hydrogenation process, XH 2 release hydrides first, then the oxidation state XH + release protons. However, in the case of YH 2 , YH 2 release protons first, then YH − release hydrides. It is the differences on acidic properties of YH 2 and XH 2 that result in the behavioral and thermodynamic differences on YH 2 and XH 2 releasing two hydrogen ions (H − −H + ). The redox mechanisms and behaviors of Y, YH − , and YH 2 as electron, hydrogen atom, hydride, and hydrogen molecule donors or acceptors in the chemical reaction are reasonably investigated and discussed in this paper using thermodynamics.

Thermodynamics regulated organic hydride/acid pairs as novel organic hydrogen reductants

“…The thermodynamic ability of an XH releasing a hydride (XH → X + + H − ) is defined as the relevant Gibbs free energy change, Δ G H − D (XH). 8 Δ G H − D (XH) values could be derived from the mole enthalpy changes of the XHs releasing hydrides, Δ H H − D (XH), from our previous works using eqn (1),Δ G H − D (XH) = Δ H H − D (XH) − 4.9 kcal mol −1 .…”

Thermodynamics of the elementary steps of organic hydride chemistry determined in acetonitrile and their applications

“…In 2022, Shen revealed and evaluated the reducing abilities of polar alkanes anions and related family members as organic reductants using thermodynamics. 120 With in-depth study, we believe that more applications will be further expanded by synthetic chemists. Certainly, the thermodynamic data from the database not only can help us discover and evaluate novel and potential organic reductants but guide the identification and design of the reduction mechanism based on thermodynamics.…”

“…The reliability was proven by previous reports in the literature. 1,120 It is indisputable that the experimentally determined enthalpy changes values are the foundational data to study the intrinsic relationship between thermodynamics and kinetics. According to the kinetic equation, a new characteristic physical parameter is defined for the chemical reactants, which is called the thermo-kinetic parameter of the reactants, i.e., thermo-kinetic parameters ΔG ‡ °(XH 2 ) and ΔG ‡ °(YH + ).…”

“…98 The constructed TAPs of HEH 2 and Y in this review provide a thermodynamic explanation and energy profiles for the hydrogenation mechanism. 120…”

“…The reliability was proven by previous reports in the literature. 1,120 It is indisputable that the experimentally determined enthalpy changes values are the foundational data to study the intrinsic relationship between thermodynamics and kinetics.…”