Reaction Response Research Articles

Pictet–Spengler-Based Multicomponent Domino Reactions to Construct Polyheterocycles

The Pictet–Spengler reaction is one of the important methodological arsenals in synthetic and medicinal chemistry, acting as an amenable tool for preparing tetrahydroisoquinoline, tetrahydro-β-carbolines, polycyclic skeletons, and value-added products. More than 100 years after its initial discovery, the Pictet–Spengler reaction's response has not withdrawn from the stage, but it has once again become the focus of attention with new features. The review summarizes recent advances in Pictet–Spengler-based multicomponent reactions from 2007 to 2022, including three-component and four-component Pictet–Spengler cyclization reactions in the presence of metal catalysts, organocatalysts, biological enzyme catalysts, and so on. These Pictet–Spengler-based multicomponent protocols provide an atom-/step economic approach for the synthesis of a library of new chemical entities.

Comparative analysis on sorption enhanced steam reforming and conventional steam reforming of hydroxyacetone for hydrogen production: Thermodynamic modeling

The chemical thermodynamics of sorption enhanced steam reforming (SESR) of hydroxyacetone for hydrogen production were investigated and contrasted with hydroxyacetone steam reforming (SR) by means of Gibbs free energy minimization principle and response reactions (RERs) method. Hydrogen is mainly derived methane steam reforming reaction from and water gas shift reaction. The former reaction contributes more than the latter one to hydrogen production below 550 °C and at higher temperature the latter one tends to dominate. The maximum hydrogen concentration is 70% in SR, which is far below hydrogen purities required by fuel cells. In SESR, hydrogen purities are over 99% in 525–550 °C with a WHMR greater than 8 and a CHMR of 6. The optimum temperature for SESR is approximately 125 °C lower than that for SR. In comparison with SR, SESR has the advantage of almost complete inhibition of coke formation in 200–1200 °C for WHMR ≥ 3.

Unique Stoichiometric Representation for Computational Thermochemistry

Evaluation of the enthalpy of formation of species via quantum chemical methods, as well as the evaluation of their performance, is mainly based on single reaction schemes, i.e., reaction schemes that involve a minimal number of reference species where minimal means that, if a reference species is omitted, there is no way to write a balanced reaction scheme involving the remaining species. When the number of reference species exceeds the minimal number, the main problem of computational thermochemistry is inevitably becoming an optimization problem. In this communication we present an exact and unique solution of the optimization problem in computational thermochemistry along with a stoichiometric interpretation of the solution. Namely, we prove that the optimization problem may be identically solved by enumerating a finite and unique set of reactions referred to as group additivity (GA) response reactions (RERs).

An Exact Stoichiometric Representation of the Resonance Energy

The energetic measure of aromaticity usually referred to as resonance energy (RE) is shown to possess a remarkable stoichiometric interpretation. Namely, the RE may be uniquely partitioned into a linear sum of contributions associated with group additivity (GA) response reactions (RERs). This new result is a powerful tool for critical analyses of various energetic approaches to RE. In particular, the single reaction scheme approach that is routinely used to evaluate RE is shown to be a particular case of the general GA method.

Sustainable hydrogen production for fuel cells by steam reforming of ethylene glycol: A consideration of reaction thermodynamics

The use of renewable biomass, such as ethylene glycol (EG), for hydrogen production offers a more sustainable system compared to natural gas and petroleum reforming. For the first time, the reaction thermodynamics of steam reforming and sorption enhanced steam reforming of EG have been investigated. Gibbs free energy minimization method was used to study the effect of pressure (1–5 atm), temperature (500–1100 K) and water to EG ratio (WER 0–8) on the production of hydrogen and the formation of associated by-products (CH 4, CO 2, CO, C). The results suggest that hydrogen production is optimum when steam reforming occurs at atmospheric pressure, 925 K and with a WER of 8. Moreover, working at high temperature (>900 K) and with a WER above 6 inhibits almost entirely the production of methane and carbon. The main source of hydrogen in the system is found to be steam reforming of methane and water gas shift reaction by the analysis of the response reactions (RERs). Hydrogen production is governed by the former reaction at low temperatures while the latter one comes into prominence as temperature increases. By coupling with in situ CO 2 capture using CaO, the formation of CO 2 and CO can be avoided and high purity of hydrogen (>99%) can be achieved.

Stress-Induced Hyperthermia in Translational Stress Research

The stress-induced hyperthermia (SIH) response is the transient change in body temperature in response to acute stress. This body temperature response is part of the autonomic stress response which also results in tachycardia and an increased blood pressure. So far, a SIH response has been found in a variety of species (including rodents, baboons, turtles, pigs, impalas and chimpanzees), and there are indications that stress exposure alters body temperature in humans. This review aims to assess the translational potential and the different aspects of the body temperature reaction in response to stress. If stress-induced temperature changes are consistent across species, the SIH paradigm may be employed in preclinical and clinical setups and provide a tool to examine the pharmacological, genetic and mechanistic background of stress at both the preclinical and the clinical level.

Systematic generation of thermochemical cycles for water splitting

Based on the observation that a thermochemical cycle is tantamount to a reaction route (RR) we employ the well-developed concepts of response reactions (RERs) and direct reaction routes (RRs) to develop an algorithm for a systematic enumeration of thermodynamically feasible thermochemical cycles for water splitting. The input is a set of chemical species along with their thermodynamic characteristics. A unique set of reactions is next generated from a list of species using the formalism of RERs. These are further screened and reduced to a subset of thermodynamically favorable RERs. Alternatively, the reactions may be selected from a separately build database of chemical reactions. The reactions are next assembled into direct RRs (thermochemical cycles), i.e., linear combinations of reactions that produce the desired overall reaction (OR), i.e., 2H 2O = 2H 2 + O 2. Only the direct RRs that satisfy the thermodynamic feasibility condition are further retained. The proposed algorithm is a new powerful tool for automatic generation and screening of thermodynamically feasible thermochemical cycles.

Buffer capacity in multiple chemical reaction systems involving solid phases

The buffer capacity of a chemical species in a multiple chemical reaction system is discussed in terms of a special class of stoichiometrically unique reactions referred to as response reactions (RERs). More specifically, it is shown that the buffer capacity may be partitioned into a sum of contributions associated with RERs. This finding provides a deeper understanding of the factors that determine the buffer capacity. In particular, the main contributions to the buffer capacity come from the RERs involving the most abundant species. Concomitantly, the RERs approach provides a simple stoichiometric algorithm for the derivation and analysis of the buffer capacity that may be easily implemented into a computer software.Key words: buffer capacity, response reaction, heterogeneous system, stoichiometric coefficient.

Thermodynamic Stability of Chemical Species in Multiple Reaction Systems

A general thermodynamic and stoichiometric method, recently developed by us to study subtle forms of stability/instability relations among chemical species, such as resonance and strain energies (Fishtik, I.; Datta, R. J. Phys. Chem. A 2004, 108, 5727-5739), is extended to stability relations in multiple chemical reaction systems. Namely, a new definition as well as a new algorithm of evaluation of the stabilities of chemical species, referred to as the overall stabilities, is proposed. It is further shown that the overall stabilities may be partitioned into a sum of contributions associated with a complete set of stoichiometrically unique response reactions (RERs). This finding reveals that the conventional stability analysis is stoichiometrically and thermodynamically inconsistent in that it involves only a part of RERs.

A General Thermodynamic and Stoichiometric Theory of Stability of Chemical Species

A new approach to the evaluation of stability of chemical species is proposed. The main idea is to allow the species to conceptually interact via a special type of chemical reaction so that an equilibrium state is achieved. Additionally, the energies of the species are allowed to vary from their initial (standard) to their equilibrium values so that the energy change of any conceivable reaction at equilibrium is equal to zero. The equilibrium energies of the species are further evaluated using an optimization procedure similar to that of the least-squares method. A species is considered unstable if the difference between its initial and equilibrium energy is positive (the species releases energy). On the contrary, if the difference between the initial and the equilibrium energy of a species is negative, the species is stable (the species absorbs energy). This type of stability of species is referred to as the overall stability. Employing the response reactions (RERs) formalism, one shows further that the overall stabilities of the species may be partitioned into different types of contributions. In particular, it is shown that the conventional definition of stability of the species is just an appropriately normalized part of the overall stability.

A NEW APPROACH FOR THE CLASSIFICATION AND ENUMERATION OF UNIQUE REACTION ROUTES AND UNIQUE OVERALL REACTIONS IN MULTIPLE CHEMICAL REACTION SYSTEMS

The methodology of response reactions (RERs) introduced earlier from thermodynamic and kinetic considerations is used in this work to develop a new algorithm for the classification and enumeration of unique/direct reaction routes (RRs) and overall reactions (ORs). According to the RERs approach, a unique set of both RRs and ORs may be generated starting from any conceivable set of linearly independent RRs and ORs. In particular, the direct ORs may be most conveniently enumerated starting from the formula matrix of the terminal species (reactants and products), i.e., without any relation to the elementary reactions comprising the detailed mechanism. Depending on the type of ORs produced by the RRs one can distinguish between two distinct types of direct RRs. Namely, one option is to define a direct RR by specifying the intermediate species that need to be eliminated. This type of RR is referred to as Milner RRs. The other option is to require the direct RRs to produce RERs, thus resulting in RRs referred to as Happel-Sellers RRs.

A Stoichiometric Approach to Quantitative Structure—Property Relationships (QSPR).

An unusual analogy between the quantitative structure-property relationships (QSPR), stoichiometry, chemical thermodynamics, and kinetics is presented. Namely, the conventional ordinary least-squares (OLS) QSPR analysis is modified so as to explicitly minimize the residuals of the species subject to a set of linear relations among the residuals. The ways the linear relations among the residuals are visualized and defined totally resemble the formalism of chemical stoichiometry and, therefore, were called isostructural reactions. It is further proved that the residuals may be uniquely partitioned into a sum of contributions associated with a set of isostructural reactions that have the same properties as the response reactions (RERs) previously deduced by us from chemical thermodynamics and kinetics. This finding is shown to be a useful tool for a deeper understanding of the QSPR. In particular, the isostructural RERs approach may be effectively used to detect the outliers.

Group Additivity vs Ab Initio

An extension of the concept of response reactions (RERs) is presented that allows the generation of thermochemical data from group additivity (GA) and ab initio methods using precisely the same stoichiometric and mathematical procedures. This goal is achieved by (i) reformulating the ordinary least squares (OLS) analysis in terms of GA reactions, (ii) realizing that the modified OLS analysis is equally applied to both GA and ab initio methods, and (iii) proving that the errors (residuals) may be uniquely partitioned into a sum of contributions associated with GA RERs. These new findings provide a remarkable interpretation and direct comparison of the accuracies and capabilities of the GA and ab initio methods.

A stoichiometric approach to quantitative structure-property relationships (QSPR).

An unusual analogy between the quantitative structure-property relationships (QSPR), stoichiometry, chemical thermodynamics, and kinetics is presented. Namely, the conventional ordinary least-squares (OLS) QSPR analysis is modified so as to explicitly minimize the residuals of the species subject to a set of linear relations among the residuals. The ways the linear relations among the residuals are visualized and defined totally resemble the formalism of chemical stoichiometry and, therefore, were called isostructural reactions. It is further proved that the residuals may be uniquely partitioned into a sum of contributions associated with a set of isostructural reactions that have the same properties as the response reactions (RERs) previously deduced by us from chemical thermodynamics and kinetics. This finding is shown to be a useful tool for a deeper understanding of the QSPR. In particular, the isostructural RERs approach may be effectively used to detect the outliers.

Response Reactions: A Mathematical Well-Defined Way to Obtain Accurate Thermochemistry from ab Initio Calculations

The concept of stoichiometrically unique reactions referred to as response reactions (RERs), earlier deduced by us in applications of chemical thermodynamics and kinetics, is extended to isodesmic reactions. Namely, it is shown that the additional stoichiometric constraints according to which the number and type of chemical bonds in a multiple chemical reaction system are conserved may be formally appended to the conventional RERs formalism. As a result, one can define and generate a stoichiometrically unique class of isodesmic RERs. Along with the conventional RERs, the newly defined isodesmic RERs are shown to be effective in converting the total enthalpies of the species obtained from ab initio calculations into accurate values of the standard enthalpies of formations for large species.

A thermodynamic approach to the systematic elucidation of unique reaction routes in catalytic reactions

The directness (uniqueness) of both reaction routes (mechanisms) and overall reactions is deduced from chemical thermodynamics. Namely, starting from general thermodynamic relations, the basic kinetic equation is shown to be identically transformed so as to be decomposable into a sum of contributions originating from a finite and unique set of reactions called response reactions (RERs). For a general chemical reaction system involving terminal species (reactants and products) and intermediates, the basic kinetic equation may be further partitioned into contributions coming from RERs involving only terminal species and those RERs involving at least one intermediate. When the intermediate are assumed to obey the quasi-steady state approximation, the contributions coming from the RERs involving at least one intermediate vanish. As a result, the basic kinetic equation may be presented as a sum of contributions coming from RERs involving only terminal species, i.e., overall RERs. This approach is shown to provide an adequate physicochemical basis of mechanisms and overall reactions as well as an effective algorithm of their enumeration.

A thermodynamic analysis of hydrogen production by steam reforming of ethanol via response reactions

The thermodynamics of ethanol steam reforming is considered in terms of response reactions (RERs). These have the property of being independent of the usually arbitrary initial choice of a set of independent reactions, and follow in a natural way from the fundamental equations of chemical thermodynamics. A simple algorithm is proposed for deriving a unique set of RERs, which can be used to rationalize the effect of process variables on steam reforming of ethanol to produce hydrogen. Further, from sensitivity analysis, the dominant reactions in the system can be identified and used in subsequent thermodynamic and kinetic analysis. These are usually arrived at through guess work. At or above 700–800 K, and high water/ethanol ratios the desired reaction of ethanol steam reforming can be made predominant and the effect of undesirable side reactions can be minimized.

Novel Formulation of the Gibbs–Energy Change in Terms of Stoichiometrically Unique Response Reactions

Abstract The equation for the change of Gibbs energy in complex chemical systems is reformulated in terms of the newly conceived response reactions (RERs). The present formulation has the remarkable property of being unique: the composition of the species unequivocally determines the response reactions and via them the change of the Gibbs energy of the system. Furthermore, it enables one to reinterpret and rationalize some basic concepts of chemical thermodynamics, as coupling between reactions, sensitivity coefficients, etc.