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Reaction progress kinetic analysis

Reaction progress kinetic analysis is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Reaction progress kinetic analysis rather than just read about it. In short: In chemistry, reaction progress kinetic analysis (RPKA) is a subset of a broad range of kinetic techniques utilized to determine the rate laws of chemical reactions and to aid in elucidation of reaction mechanisms. While the concepts guiding reaction progress kinetic analysis are not new, the process was formalized by Professor Donna Blackmond (currently at Scripps Research Institute) in the late 1990s and has since…

Reaction progress kinetic analysis — main illustration
Reaction progress kinetic analysis — illustration

Key takeaways

  • Reaction progress kinetic analysis belongs to chemistry; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Reaction progress kinetic analysis to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Reaction progress kinetic analysis from memory before moving on to harder problems.

Reference excerpt

In chemistry, reaction progress kinetic analysis (RPKA) is a subset of a broad range of kinetic techniques utilized to determine the rate laws of chemical reactions and to aid in elucidation of reaction mechanisms. While the concepts guiding reaction progress kinetic analysis are not new, the process was formalized by Professor Donna Blackmond (currently at Scripps Research Institute) in the late 1990s and has since seen increasingly widespread use. Unlike more common pseudo-first-order analysis, in which an overwhelming excess of one or more reagents is used relative to a species of interest, RPKA probes reactions at synthetically relevant conditions (i.e. with concentrations and reagent ratios resembling those used in the reaction when not exploring the rate law.) Generally, this analysis involves a system in which the concentrations of multiple reactants are changing measurably over the course of the reaction. As the mechanism can vary depending on the relative and absolute concentrations of the species involved, this approach obtains results that are much more representative of reaction behavior under commonly utilized conditions than do traditional tactics. Furthermore, information obtained by observation of the reaction over time may provide insight regarding unexpected behavior such as induction periods, catalyst deactivation, or changes in mechanism.

Monitoring reaction progress Reaction progress kinetic analysis relies on the ability to accurately monitor the reaction conversion over time. This goal may be accomplished by a range of techniques, the most common of which are described below. While these techniques are sometimes categorized as differential (monitoring reaction rate over time) or integral (monitoring the amount of substrate and/or product over time), simple mathematical manipulation (differentiation or integration) allows interconversion of the data obtained by either of the two. Regardless of the technique implemented, it is generally advantageous to confirm the validity in the system of interest by monitoring with an additional independent method.

Reaction progress NMR NMR spectroscopy is often the method of choice for monitoring reaction progress, where substrate consumption and/or product formation may be observed over time from the change of peak integration relative to a non-reactive standard. From the concentration data, the rate of reaction over time may be obtained by taking the derivative of a polynomial fit to the experimental curve. Reaction progress NMR may be classified as an integral technique as the primary data collected are proportional to concentration vs. time. While this technique is extremely convenient for clearly defined systems with distinctive, isolated product and/or reactant peaks, it has the drawback of requiring a homogeneous system amenable to reaction in an NMR tube. While NMR observation may allow for the identification of a reaction intermediates, the presence of any given species over the course of the reaction does not necessarily implicate it in a productive process. Reaction progress NMR may, however, often be run at variable temperature, allowing the rate of reaction to be adjusted to a level convenient for observation. Examples of utilization of reaction progress NMR abound, with notable examples including investigation of Buchwald–Hartwig amination (One might note that considerable debate surrounded the best approach to mechanistic development of the Buchwald-Hartwig amination as indicated by a number of contradictory and competing reports published over a short period of time. See the designated article and references therein.)

In situ FT-IR In situ infrared spectroscopy may be used to monitor the course of a reaction, provided a reagent or product shows distinctive absorbance in the IR spectral region. The rate of reactant consumption and/or product formation may be abstracted from the change of absorbance over time (by application of Beers' Law). Even when reactant and product spectra display some degree of overlap, modern instrumentation software is generally able to accurately deconvolute the relative contributions provided there is a dramatic change in the absolute absorbance of the peak of interest over time. In situ IR may be classified as an integral technique as the primary data collected are proportional to concentration vs. time. From these data, the starting material or product concentration over time may be obtained by simply taking the integral of a polynomial fit to the experimental curve. With increases in the availability of spectrometers with in situ monitoring capabilities, FT-IR has seen increasing use in recent years. Examples of note include mechanistic analysis of the amido-thiourea catalyzed asymmetric Strecker synthesis of unnatural amino acids and of the Lewis base catalyzed halolactonization and cycloetherification.

In situ UV-vis Analogously to the in situ IR experiments described above, in situ UV-visible absorbance spectroscopy may be used to monitor the course of a reaction, provided a reagent or product shows distinctive absorbance in the UV spectral region. The rate of reactant consumption and/or product formation may be abstracted from the change of absorbance over time (by application of Beer's Law), again leading to classification as an integral technique. Due to the spectral region utilized, UV-vis techniques are more commonly utilized on inorganic or organometallic systems than on purely organic reactions, and examples include exploration of the samarium Barbier reaction.

Reaction calorimetry Calorimetry may be used to monitor the course of a reaction, since the instantaneous heat flux of the reaction, which is directly related to the enthalpy change for the reaction, is monitored. Reaction calorimetry may be classified as a differential technique since the primary data collected are proportional to rate vs. time. From these data, the starting material or product concentration over time may be obtained by simply taking the integral of a polynomial fit to the experimental curve. While reaction calorimetry is less frequently employed than a number of other techniques, it has found use as an effective tool for catalyst screening. Reaction calorimetry has also been applied as an efficient method for mechanistic study of individual reactions including the prolinate-catalyzed α-amination of aldehydes and the palladium catalyzed Buchwald-Hartwig amination reaction.

… excerpt ends here. Continue reading the full article.

Illustrations

Reaction progress kinetic analysis: a) The simplest case of steady state kinetics involves one substrate reversibly forming an intermediate complex (to which the steady-state approximation is applied) with the catalyst, followed by irreversible product formation. b) In a more complex example, two substrates bind the catalyst to sequentially form two intermediates (and the steady-state approximation is applied to both) followed by irreversible product formation. Note that because I2 is kinetically invisible, this is the same as for the case where I1 goes directly to free product and catalyst. For both (a) and (b), i) describes the catalytic cycle with relevant rate constants and concentrations, ii) displays the concentration of product and reactant over the course of the reaction, iii) describes the rate of the reaction as substrate is consumed from right to left, and iv) shows that the catalyst resting state is entirely the free catalyst while the concentrations of the intermediates remain small and approximately unchanging as substrate is consumed from right to left.
a) The simplest case of steady state kinetics involves one substrate reversibly forming an intermediate complex (to which the steady-state approximation is applied) with the catalyst, followed by irreversible product formation. b) In a more complex example, two substrates bind the catalyst to sequentially form two intermediates (and the steady-state approximation is applied to both) followed by irreversible product formation. Note that because I2 is kinetically invisible, this is the same as for the case where I1 goes directly to free product and catalyst. For both (a) and (b), i) describes the catalytic cycle with relevant rate constants and concentrations, ii) displays the concentration of product and reactant over the course of the reaction, iii) describes the rate of the reaction as substrate is consumed from right to left, and iv) shows that the catalyst resting state is entirely the free catalyst while the concentrations of the intermediates remain small and approximately unchanging as substrate is consumed from right to left.
Reaction progress kinetic analysis: a) The simplest case of pre-equilibrium kinetics involves one substrate rapidly and reversibly forming an intermediate complex with the catalyst, followed by irreversible product formation. b) In a more complex example, two substrates sequentially bind the catalyst rapidly and reversibly followed by irreversible product formation. For both (a) and (b), i) describes the catalytic cycle with relevant rate constants and concentrations, ii) displays the concentration of product and reactant over the course of the reaction, iii) describes the rate of the reaction as substrate is consumed from right to left, and iv) shows that the catalyst resting state is an equilibrium distribution of free catalyst and intermediates where the distribution is shifted increasingly toward free catalyst as substrate is consumed from right to left.
a) The simplest case of pre-equilibrium kinetics involves one substrate rapidly and reversibly forming an intermediate complex with the catalyst, followed by irreversible product formation. b) In a more complex example, two substrates sequentially bind the catalyst rapidly and reversibly followed by irreversible product formation. For both (a) and (b), i) describes the catalytic cycle with relevant rate constants and concentrations, ii) displays the concentration of product and reactant over the course of the reaction, iii) describes the rate of the reaction as substrate is consumed from right to left, and iv) shows that the catalyst resting state is an equilibrium distribution of free catalyst and intermediates where the distribution is shifted increasingly toward free catalyst as substrate is consumed from right to left.
Reaction progress kinetic analysis: a) The simplest case of saturation kinetics extends from the pre-equilibrium situation in which rapid substrate complexation with a catalyst is followed by slow formation of the product. b) The straight portion of the graph for substrate concentration over time is indicative of a zero-order dependence on substrate for most of the reaction, but the curve at low [A] is indicative of a change to (in this case) a first-order dependence on [A]. c) Saturation of the catalyst is apparent at high concentrations of substrate (where the rate has no dependence on [A], but as substrate is consumed, the reaction rate drops with a first-order dependence on [A] to pass through the origin. d) The catalyst resting state also changes, where it exists almost entirely as the substrate-bound complex, Cat–A, at high [A] but increasingly as the free catalyst, Cat, as [A] decreases over the course of the reaction.
a) The simplest case of saturation kinetics extends from the pre-equilibrium situation in which rapid substrate complexation with a catalyst is followed by slow formation of the product. b) The straight portion of the graph for substrate concentration over time is indicative of a zero-order dependence on substrate for most of the reaction, but the curve at low [A] is indicative of a change to (in this case) a first-order dependence on [A]. c) Saturation of the catalyst is apparent at high concentrations of substrate (where the rate has no dependence on [A], but as substrate is consumed, the reaction rate drops with a first-order dependence on [A] to pass through the origin. d) The catalyst resting state also changes, where it exists almost entirely as the substrate-bound complex, Cat–A, at high [A] but increasingly as the free catalyst, Cat, as [A] decreases over the course of the reaction.
Reaction progress kinetic analysis: The rate of product formation in the cyanosilylation of ketone, A, shows a slight non-linear dependence on catalyst loading at high catalyst concentrations. a) This observation, among others, is accounted for by the reversible formation of inactive catalyst complexes. b) Similar behavior at multiple conversion points is consistent with one dominant mechanism operating over the entire course of the reaction.[18]
The rate of product formation in the cyanosilylation of ketone, A, shows a slight non-linear dependence on catalyst loading at high catalyst concentrations. a) This observation, among others, is accounted for by the reversible formation of inactive catalyst complexes. b) Similar behavior at multiple conversion points is consistent with one dominant mechanism operating over the entire course of the reaction.[18]
Reaction progress kinetic analysis: a) According to the proposed mechanism for the palladium-catalyzed amination of aryl halides, an induction period will be present as the active catalyst is generated from an inactive pre-catalyst (where L = BINAP). b) This induction period may be observed at early conversion points, before the catalyzed reaction reaches its maximum rate. In same-excess experiments, this will manifest itself in the non-overlying portions of curves designed to intercept the original reaction at intermediate conversion points. Here, a same-excess (e = 0.60 M) of [ArX] relative to [HNR2] and [MOR] is utilized for each of the curves.
a) According to the proposed mechanism for the palladium-catalyzed amination of aryl halides, an induction period will be present as the active catalyst is generated from an inactive pre-catalyst (where L = BINAP). b) This induction period may be observed at early conversion points, before the catalyzed reaction reaches its maximum rate. In same-excess experiments, this will manifest itself in the non-overlying portions of curves designed to intercept the original reaction at intermediate conversion points. Here, a same-excess (e = 0.60 M) of [ArX] relative to [HNR2] and [MOR] is utilized for each of the curves.

Worked examples

Example 1 — a first encounter with Reaction progress kinetic analysis

Start with the simplest possible case. Write down what Reaction progress kinetic analysis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Reaction progress kinetic analysis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Reaction progress kinetic analysis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Reaction progress kinetic analysis

In research
Reaction progress kinetic analysis appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Reaction progress kinetic analysis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Reaction progress kinetic analysis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical kinetics, so understanding it makes those chapters shorter.
In everyday life
Look for Reaction progress kinetic analysis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Reaction progress kinetic analysis in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Reaction progress kinetic analysis means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Reaction progress kinetic analysis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Reaction progress kinetic analysis in simple terms?

In chemistry, reaction progress kinetic analysis (RPKA) is a subset of a broad range of kinetic techniques utilized to determine the rate laws of chemical reactions and to aid in elucidation of reaction mechanisms. While the concepts guiding reaction progress kinetic analysis are not new, the proce…

Why does Reaction progress kinetic analysis matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Reaction progress kinetic analysis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Reaction progress kinetic analysis.

Tags

  • Chemical kinetics

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