DOCSLIB.ORG

The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 5-2012 The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds Zhao Li Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Organic Chemistry Commons, and the Physical Chemistry Commons Recommended Citation Li, Zhao, "The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds" (2012). All Graduate Theses and Dissertations. 1407. https://digitalcommons.usu.edu/etd/1407 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. THE KINETICS AND MECHANISMS OF SOME FUNDAMENTAL ORGANIC REACTIONS OF NITRO COMPOUNDS by Zhao Li A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Chemistry Approved: _________________________ _________________________ Vernon D. Parker, Ph.D. Lance C. Seefeldt, Ph.D. Major Professor Committee Member _________________________ _________________________ Alvan C. Hengge, Ph.D. Roger A. Coulombe, Jr, Ph.D. Committee Member Committee Member _________________________ _________________________ Cheng-Wei Tom Chang, Ph.D. Mark R. McLellan, Ph.D. Committee Member Vice President for Research and Dean of the School of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2012 ii Copyright © Zhao Li 2012 All Rights Reserved iii ABSTRACT The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds by Zhao Li, Doctor of Philosophy Utah State University, 2012 Major Professor: Dr. Vernon D. Parker Department: Chemistry and Biochemistry The central topic of this dissertation is to seek the answer to the question: Is the single transition state model appropriate for (1) the proton transfer reactions of nitroalkanes and (2) the aromatic nucleophilic reactions of trinitroarenes? If not, what are the real mechanisms? This objective has been accomplished by careful kinetic and mechanistic studies which take advantage of modern digital acquisition of absorbance – time data, combined with extensive new data analysis of results from pseudo-first-order kinetic measurements. Several new analysis procedures for pseudo-first-order kinetics that are capable of distinguishing between single-step and multi-step mechanisms have been introduced and intensively confirmed during the application in the kinetic study of the target reactions. The procedures include (1) half-life dependence of apparent rate constant, (2) sequential linear pseudo-first-order correlation, (3) approximate instantaneous rate constant analysis, and (4) time-dependent apparent kinetic isotope effects. iv Various conventional and nonconventional pseudo-first-order kinetic analyses of the reactions of nitroalkanes in aqueous solutions revealed that the reactions are complex and involve kinetically significant intermediates. The spectral evidence for the formation of reactive intermediates was obtained by carrying out the kinetic experiments at the isosbestic points where changes in reactant and product absorbance cancel. The apparent deuterium kinetic isotope effects studies indicated that the deuterium kinetic isotope effects are not associated with the formation of the intermediates. The observations of anomalous Brønsted exponents previously found for this reaction series could be rationalized well with the complex mechanisms proposed in this work, which indicate that the nitroalkane anomaly does not exist, but arises from an interpretation based upon the incorrect assumption that the reactions follow a simple one-step mechanism. Simulations revealed that the generally accepted competitive mechanism was not appropriate to describe the Meisenheimer complex formation during the reaction of 2,4,6-trinitroanisole with methoxide ion in methanol. This conclusion is supported by the conventional pseudo-first-order kinetic analysis. A reversible consecutive mechanism that accounts for the kinetic behavior has been proposed, which involves an intermediate dianion complex that is formed reversibly from the initial 1,3-σ-complex, and then eliminates methoxide ion to form the 1,1-σ-complex product. (296 pages) v PUBLIC ABSTRACT The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds Zhao Li, Ph.D. Department of Chemistry and Biochemistry Utah State University, 2012 In chemistry, kinetics is the study of the rates of chemical reactions. A reaction mechanism describes in detail exactly what takes place at each stage of an overall chemical reaction from reactants to products. The work outlined in this dissertation was carried out in order to find out the true mechanisms of some fundamental organic reactions of nitro compounds by means of a series of novel kinetic techniques and analysis methods. The target reactions include (1) the proton transfer reactions of nitroalkanes and (2) the aromatic nucleophilic reactions of trinitroarenes, both of which are undeniably among the most elementary and significant processes in organic chemistry and biochemistry. Rigorous kinetic investigations have found that both reactions actually take place by multi-step mechanisms involving kinetically significant intermediates. This result challenges the long-held assumption that the reactions follow a simple one-step mechanism. Although the assumption of the one-step mechanism can be applied to evaluate the magnitude of the rate of the overall reaction, it fails to provide a detailed vi description of chemical reactions, especially those behaving abnormally. This is obvious in the conundrum found in the description of the proton transfer reactions of nitroalkanes which is commonly known as the nitroalkane anomaly. However, adopting the multi-step mechanisms proposed in this dissertation should end this chapter of organic chemistry. Reaction mechanism is a primary topic for organic chemical studies that provides a framework for appropriate application in the chemical and pharmaceutical industry, and in agricultural applications. An essential objective of this work is to point out that more attention should be paid to the importance of reaction mechanism in the field of organic chemistry. A broad impact of this work on academic studies may be achieved via promoting a revision of the mechanisms believed to be established over the past seventy years. It will have a broad effect in other branches of chemistry as well as in biochemistry. This work is a sub-project of the three-year $665,000 international cooperative project of “Is the single transition state model appropriate for the fundamental reactions of organic chemistry?” initiated by Professor Vernon D. Parker at USU, collaborating with Professors Jin-Pei Cheng and Xiao-Qing Zhu in China’s Nankai University. This international project, supported by both NSF (National Science Foundation) and NSFC (National Natural Science Foundation of China), has been fostering cooperation and good will between the scientific communities of the United States and China. Contact: [email protected] vii ACKNOWLEDGMENTS The primary acknowledgment goes to my advisor, Dr. Vernon D. Parker, for his consistent guidance, support, and help during my time at Utah State University. His breadth and depth of knowledge in physical organic chemistry was a constant source of support to encourage my independent and original thought, and to provide me a model of what a successful scientist should be. I am honored that I could have an opportunity to study in his group. What I have learned from him is invaluable for me and my future career development. I would also like to express my appreciation to the other professors in my supervisory committee, Dr. Alvan C. Hengge, Dr. Cheng-Wei Tom Chang, Dr. Lance C. Seefeldt, and Dr. Roger A. Coulombe, Jr, for their support, guidance, and helpful suggestions. I am grateful for their experience in their respective fields. I especially thank Dr. Jin-Pei Cheng, our collaborator and my former advisor at Nankai University, for providing me the opportunity to join the USU-Nankai International Cooperative Graduate Program, as well as for his extensive help and encouragement over the past five years. I am also grateful to the other collaborator at Nankai University, Prof. Xiao-Qing Zhu, for his efforts in the funding application and helpful suggestions in my research. Great thanks to Dr. Donald Bethell, professor at the University of Liverpool, for his help in the study of isosbestic point. I wish to express my appreciation to my colleagues, Dr. Weifang Hao for her numerous helps throughout my educational experience at USU; Xiaosong Xue for his viii cooperation in calculations; Chad Jacobs for helping with the kinetic study of SNAr reactions; Dr. Rui Cao, Xiaozhen Han, and Russell Scow for their helpful discussion and friendship. I am profoundly grateful to the Parker couple (Vernon and Monica) and the Zhang couple (Tao and Weifang). Their friendship and considerate help made me feel part of a large family. Deep gratitude also belongs to my parents, Lanlin Li and Xueping Wang, for their constant strength, love, and faith in me. I also owe many thanks to all my friends and relatives, whose names are not mentioned here. Your love and support mean a lot to me. Last but not least, I would express my appreciation
Load more

Recommended publications
  • Chemistry Grade Level 10 Units 1-15
    COPPELL ISD SUBJECT YEAR AT A GLANCE ​ ​ ​ ​​ ​ ​​ ​ ​ ​ ​ ​ ​ GRADE HEMISTRY UNITS C LEVEL 1-15 10 Program Transfer Goals ​ ​ ​ ​ ● Ask questions, recognize and define problems, and propose solutions. ​ ​​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ● Safely and ethically collect, analyze, and evaluate appropriate data. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ● Utilize, create, and analyze models to understand the world. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ● Make valid claims and informed decisions based on scientific evidence. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ● Effectively communicate scientific reasoning to a target audience. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PACING 1st 9 Weeks 2nd 9 Weeks 3rd 9 Weeks 4th 9 Weeks ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit Unit Unit Unit Unit Unit Unit Unit Unit ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 7 8 9 10 11 12 13 14 15 1.5 wks 2 wks 1.5 wks 2 wks 3 wks 5.5 wks ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 1.5 2 2.5 2 wks 2 2 2 wks 1.5 1.5 ​ ​ ​ ​ wks wks wks wks wks wks wks Assurances for a Guaranteed and Viable Curriculum ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Adherence to this scope and sequence affords every member of the learning community clarity on the knowledge and skills ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ on which each learner should demonstrate proficiency. In order to deliver a guaranteed and viable curriculum, our team ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ commits to and ensures the following understandings: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shared Accountability: Responding
    [Show full text]
  • The Practice of Chemistry Education (Paper)
    CHEMISTRY EDUCATION: THE PRACTICE OF CHEMISTRY EDUCATION RESEARCH AND PRACTICE (PAPER) 2004, Vol. 5, No. 1, pp. 69-87 Concept teaching and learning/ History and philosophy of science (HPS) Juan QUÍLEZ IES José Ballester, Departamento de Física y Química, Valencia (Spain) A HISTORICAL APPROACH TO THE DEVELOPMENT OF CHEMICAL EQUILIBRIUM THROUGH THE EVOLUTION OF THE AFFINITY CONCEPT: SOME EDUCATIONAL SUGGESTIONS Received 20 September 2003; revised 11 February 2004; in final form/accepted 20 February 2004 ABSTRACT: Three basic ideas should be considered when teaching and learning chemical equilibrium: incomplete reaction, reversibility and dynamics. In this study, we concentrate on how these three ideas have eventually defined the chemical equilibrium concept. To this end, we analyse the contexts of scientific inquiry that have allowed the growth of chemical equilibrium from the first ideas of chemical affinity. At the beginning of the 18th century, chemists began the construction of different affinity tables, based on the concept of elective affinities. Berthollet reworked this idea, considering that the amount of the substances involved in a reaction was a key factor accounting for the chemical forces. Guldberg and Waage attempted to measure those forces, formulating the first affinity mathematical equations. Finally, the first ideas providing a molecular interpretation of the macroscopic properties of equilibrium reactions were presented. The historical approach of the first key ideas may serve as a basis for an appropriate sequencing of
    [Show full text]
  • Chapter 12 Lecture Notes
    Chemical Kinetics “The study of speeds of reactions and the nanoscale pathways or rearrangements by which atoms and molecules are transformed to products” Chapter 13: Chemical Kinetics: Rates of Reactions © 2008 Brooks/Cole 1 © 2008 Brooks/Cole 2 Reaction Rate Reaction Rate Combustion of Fe(s) powder: © 2008 Brooks/Cole 3 © 2008 Brooks/Cole 4 Reaction Rate Reaction Rate + Change in [reactant] or [product] per unit time. Average rate of the Cv reaction can be calculated: Time, t [Cv+] Average rate + Cresol violet (Cv ; a dye) decomposes in NaOH(aq): (s) (mol / L) (mol L-1 s-1) 0.0 5.000 x 10-5 13.2 x 10-7 10.0 3.680 x 10-5 9.70 x 10-7 20.0 2.710 x 10-5 7.20 x 10-7 30.0 1.990 x 10-5 5.30 x 10-7 40.0 1.460 x 10-5 3.82 x 10-7 + - 50.0 1.078 x 10-5 Cv (aq) + OH (aq) → CvOH(aq) 2.85 x 10-7 60.0 0.793 x 10-5 -7 + + -5 1.82 x 10 change in concentration of Cv Δ [Cv ] 80.0 0.429 x 10 rate = = 0.99 x 10-7 elapsed time Δt 100.0 0.232 x 10-5 © 2008 Brooks/Cole 5 © 2008 Brooks/Cole 6 1 Reaction Rates and Stoichiometry Reaction Rates and Stoichiometry Cv+(aq) + OH-(aq) → CvOH(aq) For any general reaction: a A + b B c C + d D Stoichiometry: The overall rate of reaction is: Loss of 1 Cv+ → Gain of 1 CvOH Rate of Cv+ loss = Rate of CvOH gain 1 Δ[A] 1 Δ[B] 1 Δ[C] 1 Δ[D] Rate = − = − = + = + Another example: a Δt b Δt c Δt d Δt 2 N2O5(g) 4 NO2(g) + O2(g) Reactants decrease with time.
    [Show full text]
  • Chapter 9. Atomic Transport Properties
    NEA/NSC/R(2015)5 Chapter 9. Atomic transport properties M. Freyss CEA, DEN, DEC, Centre de Cadarache, France Abstract As presented in the first chapter of this book, atomic transport properties govern a large panel of nuclear fuel properties, from its microstructure after fabrication to its behaviour under irradiation: grain growth, oxidation, fission product release, gas bubble nucleation. The modelling of the atomic transport properties is therefore the key to understanding and predicting the material behaviour under irradiation or in storage conditions. In particular, it is noteworthy that many modelling techniques within the so-called multi-scale modelling scheme of materials make use of atomic transport data as input parameters: activation energies of diffusion, diffusion coefficients, diffusion mechanisms, all of which are then required to be known accurately. Modelling approaches that are readily used or which could be used to determine atomic transport properties of nuclear materials are reviewed here. They comprise, on the one hand, static atomistic calculations, in which the migration mechanism is fixed and the corresponding migration energy barrier is calculated, and, on the other hand, molecular dynamics calculations and kinetic Monte-Carlo simulations, for which the time evolution of the system is explicitly calculated. Introduction In nuclear materials, atomic transport properties can be a combination of radiation effects (atom collisions) and thermal effects (lattice vibrations), this latter being possibly enhanced by vacancies created by radiation damage in the crystal lattice (radiation enhanced-diffusion). Thermal diffusion usually occurs at high temperature (typically above 1 000 K in nuclear ceramics), which makes the transport processes difficult to model at lower temperatures because of the low probability to see the diffusion event occur in a reasonable simulation time.
    [Show full text]
  • Opportunities for Catalysis in the 21St Century
    Opportunities for Catalysis in The 21st Century A Report from the Basic Energy Sciences Advisory Committee BASIC ENERGY SCIENCES ADVISORY COMMITTEE SUBPANEL WORKSHOP REPORT Opportunities for Catalysis in the 21st Century May 14-16, 2002 Workshop Chair Professor J. M. White University of Texas Writing Group Chair Professor John Bercaw California Institute of Technology This page is intentionally left blank. Contents Executive Summary........................................................................................... v A Grand Challenge....................................................................................................... v The Present Opportunity .............................................................................................. v The Importance of Catalysis Science to DOE.............................................................. vi A Recommendation for Increased Federal Investment in Catalysis Research............. vi I. Introduction................................................................................................ 1 A. Background, Structure, and Organization of the Workshop .................................. 1 B. Recent Advances in Experimental and Theoretical Methods ................................ 1 C. The Grand Challenge ............................................................................................. 2 D. Enabling Approaches for Progress in Catalysis ..................................................... 3 E. Consensus Observations and Recommendations..................................................
    [Show full text]
  • Solvent Effects on Structure and Reaction Mechanism: a Theoretical Study of [2 + 2] Polar Cycloaddition Between Ketene and Imine
    J. Phys. Chem. B 1998, 102, 7877-7881 7877 Solvent Effects on Structure and Reaction Mechanism: A Theoretical Study of [2 + 2] Polar Cycloaddition between Ketene and Imine Thanh N. Truong Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112 ReceiVed: March 25, 1998; In Final Form: July 17, 1998 The effects of aqueous solvent on structures and mechanism of the [2 + 2] cycloaddition between ketene and imine were investigated by using correlated MP2 and MP4 levels of ab initio molecular orbital theory in conjunction with the dielectric continuum Generalized Conductor-like Screening Model (GCOSMO) for solvation. We found that reactions in the gas phase and in aqueous solution have very different topology on the free energy surfaces but have similar characteristic motion along the reaction coordinate. First, it involves formation of a planar trans-conformation zwitterionic complex, then a rotation of the two moieties to form the cycloaddition product. Aqueous solvent significantly stabilizes the zwitterionic complex, consequently changing the topology of the free energy surface from a gas-phase single barrier (one-step) process to a double barrier (two-step) one with a stable intermediate. Electrostatic solvent-solute interaction was found to be the dominant factor in lowering the activation energy by 4.5 kcal/mol. The present calculated results are consistent with previous experimental data. Introduction Lim and Jorgensen have also carried out free energy perturbation (FEP) theory simulations with accurate force field that includes + [2 2] cycloaddition reactions are useful synthetic routes to solute polarization effects and found even much larger solvent - formation of four-membered rings.
    [Show full text]
  • Andrea Deoudes, Kinetics: a Clock Reaction
    A Kinetics Experiment The Rate of a Chemical Reaction: A Clock Reaction Andrea Deoudes February 2, 2010 Introduction: The rates of chemical reactions and the ability to control those rates are crucial aspects of life. Chemical kinetics is the study of the rates at which chemical reactions occur, the factors that affect the speed of reactions, and the mechanisms by which reactions proceed. The reaction rate depends on the reactants, the concentrations of the reactants, the temperature at which the reaction takes place, and any catalysts or inhibitors that affect the reaction. If a chemical reaction has a fast rate, a large portion of the molecules react to form products in a given time period. If a chemical reaction has a slow rate, a small portion of molecules react to form products in a given time period. This experiment studied the kinetics of a reaction between an iodide ion (I-1) and a -2 -1 -2 -2 peroxydisulfate ion (S2O8 ) in the first reaction: 2I + S2O8 I2 + 2SO4 . This is a relatively slow reaction. The reaction rate is dependent on the concentrations of the reactants, following -1 m -2 n the rate law: Rate = k[I ] [S2O8 ] . In order to study the kinetics of this reaction, or any reaction, there must be an experimental way to measure the concentration of at least one of the reactants or products as a function of time. -2 -2 -1 This was done in this experiment using a second reaction, 2S2O3 + I2 S4O6 + 2I , which occurred simultaneously with the reaction under investigation. Adding starch to the mixture -2 allowed the S2O3 of the second reaction to act as a built in “clock;” the mixture turned blue -2 -2 when all of the S2O3 had been consumed.
    [Show full text]
  • A Brief Introduction to the History of Chemical Kinetics
    Chapter 1 A Brief Introduction to the History of Chemical Kinetics Petr Ptáček, Tomáš Opravil and František Šoukal Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.78704 Abstract This chapter begins with a general overview of the content of this work, which explains the structure and mutual relation between discussed topics. The following text provides brief historical background to chemical kinetics, lays the foundation of transition state theory (TST), and reaction thermodynamics from the early Wilhelmy quantitative study of acid-catalyzed conversion of sucrose, through the deduction of mathematical models to explain the rates of chemical reactions, to the transition state theory (absolute rate theory) developed by Eyring, Evans, and Polanyi. The concept of chemical kinetics and equilib- rium is then introduced and described in the historical context. Keywords: kinetics, chemical equilibrium, rate constant, activation energy, frequency factor, Arrhenius equation, Van’t Hoff-Le Châtelier’s principle, collision theory, transition state theory 1. Introduction Modern chemical (reaction) kinetics is a science describing and explaining the chemical reac- tion as we understand it in the present day [1]. It can be defined as the study of rate of chemical process or transformations of reactants into the products, which occurs according to the certain mechanism, i.e., the reaction mechanism [2]. The rate of chemical reaction is expressed as the change in concentration of some species in time [3]. It can also be pointed that chemical reactions are also the subject of study of many other chemical and physicochemical disciplines, such as analytical chemistry, chemical thermodynamics, technology, and so on [2].
    [Show full text]
  • Reaction Mechanism
    Reaction Mechanism A detailed sequence of steps for a reaction Reasonable mechanism: 1. Elementary steps sum to the overall reaction 2. Elementary steps are physically reasonable 3. Mechanism is consistent with rate law and other experimental observations (generally found from rate limiting (slow) step(s) A mechanism can be supported but never proven NO2 + CO NO + CO2 2 Observed rate = k [NO2] Deduce a possible and reasonable mechanism NO2 + NO2 NO3 + NO slow NO3 + CO NO2 + CO2 fast Overall, NO2 + CO NO + CO2 Is the rate law for this sequence consistent with observation? Yes Does this prove that this must be what is actually happening? No! NO2 + CO NO + CO2 2 Observed rate = k [NO2] Deduce a possible and reasonable mechanism NO2 + NO2 NO3 + NO slow NO3 + CO NO2 + CO2 fast Overall, NO2 + CO NO + CO2 Is the rate law for this sequence consistent with observation? Yes Does this prove that this must be what is actually happening? No! Note the NO3 intermediate product! Arrhenius Equation Temperature dependence of k kAe E/RTa A = pre-exponential factor Ea= activation energy Now let’s look at the NO2 + CO reaction pathway* (1D). Just what IS a reaction coordinate? NO2 + CO NO + CO2 High barrier TS for step 1 Reactants: Lower barrier TS for step 2 NO2 +NO2 +CO Products Products Bottleneck NO +CO2 NO +CO2 Potential Energy Step 1 Step 2 Reaction Coordinate NO2 + CO NO + CO2 NO22 NO NO 3 NO NO CO NO CO 222In this two-step reaction, there are two barriers, one for each elementary step. The well between the two transition states holds a reactive intermediate.
    [Show full text]
  • Dehydrogenation by Heterogeneous Catalysts
    Dehydrogenation by Heterogeneous Catalysts Daniel E. Resasco School of Chemical Engineering and Materials Science University of Oklahoma Encyclopedia of Catalysis January, 2000 1. INTRODUCTION Catalytic dehydrogenation of alkanes is an endothermic reaction, which occurs with an increase in the number of moles and can be represented by the expression Alkane ! Olefin + Hydrogen This reaction cannot be carried out thermally because it is highly unfavorable compared to the cracking of the hydrocarbon, since the C-C bond strength (about 246 kJ/mol) is much lower than that of the C-H bond (about 363 kJ/mol). However, in the presence of a suitable catalyst, dehydrogenation can be carried out with minimal C-C bond rupture. The strong C-H bond is a closed-shell σ orbital that can be activated by oxide or metal catalysts. Oxides can activate the C-H bond via hydrogen abstraction because they can form O-H bonds, which can have strengths comparable to that of the C- H bond. By contrast, metals cannot accomplish the hydrogen abstraction because the M- H bonds are much weaker than the C-H bond. However, the sum of the M-H and M-C bond strengths can exceed the C-H bond strength, making the process thermodynamically possible. In this case, the reaction is thought to proceed via a three centered transition state, which can be described as a metal atom inserting into the C-H bond. The C-H bond bridges across the metal atom until it breaks, followed by the formation of the corresponding M-H and M-C bonds.1 Therefore, dehydrogenation of alkanes can be carried out on oxides as well as on metal catalysts.
    [Show full text]
  • Sustainable Catalysis
    Green Process Synth 2016; 5: 231–232 Book review Sustainable catalysis DOI 10.1515/gps-2016-0016 Sustainable catalysis provides an excellent in-depth over- view of the applications of non-endangered elements in Michael North (Ed.) all aspects of catalysis from heterogeneous to homogene- Sustainable catalysis: with non-endangered metals ous, from catalyst supports to ligands. The Royal Society of Chemistry, 2015 Four volumes of the book series are divided into RSC Green Chemistry series nos. 38–41 two sub-topics devoted to (i) metal-based catalysts and Part 1 (ii) catalysts without metals or other endangered ele- Print ISBN: 978-1-78262-638-1 ments. Each sub-topic comprises of two books due to the PDF eISBN: 978-1-78262-211-6 detailed analysis of catalytic applications described. All Part 2 chapters are written by the world-leading researchers in Print ISBN: 978-1-78262-639-8 the area; however, covering far beyond the scope of their PDF eISBN: 978-1-78262-642-8 immediate research interests, which makes the book par- ticularly valuable for a wide range of readers. Sustainable catalysis: without metals or other Sustainable catalysis: with non-endangered metals endangered elements begins with a very brief chapter which describes the Part 1 concept of elemental sustainability, overviewing the Print ISBN: 978-1-78262-640-4 abundance of the critical elements and perspectives on PDF eISBN: 978-1-78262-209-3 sustainable catalysts. The chapters follow the groups of EPUB eISBN: 978-1-78262-752-4 the periodic table from left to right, from alkaline metals to Part 2 lead spanning 22 chapters.
    [Show full text]
  • Part I Principles of Enzyme Catalysis
    j1 Part I Principles of Enzyme Catalysis Enzyme Catalysis in Organic Synthesis, Third Edition. Edited by Karlheinz Drauz, Harald Groger,€ and Oliver May. Ó 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA. j3 1 Introduction – Principles and Historical Landmarks of Enzyme Catalysis in Organic Synthesis Harald Gr€oger and Yasuhisa Asano 1.1 General Remarks Enzyme catalysis in organic synthesis – behind this term stands a technology that today is widely recognized as a first choice opportunity in the preparation of a wide range of chemical compounds. Notably, this is true not only for academic syntheses but also for industrial-scale applications [1]. For numerous molecules the synthetic routes based on enzyme catalysis have turned out to be competitive (and often superior!) compared with classic chemicalaswellaschemocatalyticsynthetic approaches. Thus, enzymatic catalysis is increasingly recognized by organic chemists in both academia and industry as an attractive synthetic tool besides the traditional organic disciplines such as classic synthesis, metal catalysis, and organocatalysis [2]. By means of enzymes a broad range of transformations relevant in organic chemistry can be catalyzed, including, for example, redox reactions, carbon–carbon bond forming reactions, and hydrolytic reactions. Nonetheless, for a long time enzyme catalysis was not realized as a first choice option in organic synthesis. Organic chemists did not use enzymes as catalysts for their envisioned syntheses because of observed (or assumed) disadvantages such as narrow substrate range, limited stability of enzymes under organic reaction conditions, low efficiency when using wild-type strains, and diluted substrate and product solutions, thus leading to non-satisfactory volumetric productivities.
    [Show full text]