The Esterification of Trifluoroacetic Acid: A Variable Temperature NMR Kinetics Study

Gallaher, T. N.; Gaul, David A.; Schreiner, Serge

doi:10.1021/ed073p465

Cited by 13 publications

(10 citation statements)

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“…In some cases, even more active trifluoroacetylating reagents, such as trifluoroacetyl triflate (TFAT) were employed for the formation of trifluoroacetates from certain alcohols. TFA was reported to form esters with alcohols, but under harsh reaction conditions (neat TFA with alcohol, or refluxing in the presence of a strong acid, such as concd H 2 SO 4 ). Nonetheless, we conducted the reaction by mixing TFA with ethanol (10:1) in chloroform- d and monitoring the progress by 1 H NMR.…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Pathways in CF₃COOH-Mediated Deacetalization Reactions

Li¹,

Liu²,

Wu³

et al. 2010

J. Org. Chem.

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It has been widely accepted that both the protection of carbonyls and the deprotection of acetals and ketals involve the participation of a water molecule: formation of acetals and ketals is a dehydration process, whereas the deprotection is often referred to as hydrolysis, which, as implied by its name, always requires the presence of water. Herein, we report experimental evidence and mechanistic investigations that provide an alternative view to this process. We have demonstrated that water is not required to convert acetals and ketals to the corresponding carbonyls. The (1)H NMR experimental results revealed that the TFA-mediated transformation of acetal to aldehyde occurs via a hemiacetal TFA ester intermediate, which differentiates itself from the classic acid-catalyzed hydrolysis, where the hemiacetal is the putative intermediate responsible for the formation of the aldehyde. More interestingly, alcohols are not the final byproducts as they are in the classical hydrolysis, rather, the two alcohol molecules are converted to two TFA esters under the reaction conditions. On the basis of the NMR evidence, we have proposed that the two TFA esters are formed in two separate steps via a different mechanism along the reaction pathway. Formation of the TFA esters renders the reaction irreversible. To the best of our knowledge, the cascade reaction pathway presented by the TFA-mediated conversion of acetals and ketals to carbonyls has never been previously postulated.

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Section: Resultsmentioning

confidence: 99%

Mechanistic Pathways in CF₃COOH-Mediated Deacetalization Reactions

Li¹,

Liu²,

Wu³

et al. 2010

J. Org. Chem.

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Section: Introductionmentioning

confidence: 99%

“…The use of HMQC, COSY, TOCSY, NOE, or NOESY NMR experiments has become commonplace, especially due to improvements in the ease of data acquisition and data processing. In addition, several experiments have been shown to use the variable temperature function on the NMR spectrometer to utilize changes in temperature to explore reaction kinetics, 6 ligand substitution, 7 hydrogen bonding thermodynamics, 8 spin crossover effects, 9 and molecular conformation. 10 In chemistry, it is common to encounter circumstances where a dynamic process exists: conformation changes, host− guest complex formation, intramolecular tautomerism, reversible synthetic reactions, and more.…”

Section: ■ Introductionmentioning

confidence: 99%

Variable Temperature NMR Experiment Studying Restricted Bond Rotation

et al. 2020

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Nuclear magnetic resonance (NMR) spectroscopy has become a cornerstone tool for studying a variety of molecular features in advanced chemistry laboratories. In this experiment, students prepare a pyrrole-β-amide via a one-pot, three-step synthesis and use NMR spectroscopy to confirm its molecular structure. In addition, variable temperature (VT) 1H NMR spectroscopy is used to study the dynamic amide bond, a functional group with restricted rotation about the C–N bond. The VT NMR data allow the students to determine the coalescence temperature associated with the slow equilibrium at room temperature and the corresponding energy barrier (ΔG ⧧) for the restricted rotation about the C–N bond.

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“…Consequently, a laboratory experiment to include enzyme kinetics was designed to expand on the classical experiments routinely implemented in the undergraduate curriculum. This flexible and robust package of exercises employs 1 H NMR spectroscopy to measure the kinetics of the enzymatic hydrolysis of sucrose to its initial products (Scheme 1), the reaction used to generate the liquid center of cordial creams in the confectionary industry. This reaction, commonly known as the inversion of sucrose, is catalyzed by β-fructofuranosidase (invertase, sucrase), producing initially α-glucose and β-fructose.…”

mentioning

confidence: 99%

Exploring the Hydrolysis of Sucrose by Invertase Using Nuclear Magnetic Resonance Spectroscopy: A Flexible Package of Kinetic Experiments

et al. 2014

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Nuclear magnetic resonance spectroscopy (NMR) is a viable alternative to current methods to introduce enzymatic reactions and monitor kinetics in the undergraduate curriculum. Using NMR to observe the invertase-catalyzed conversion of sucrose to fructose and glucose, one can gather information about the order of the reaction, as well as the maximum rate (v max) and the Michaelis constant (K M). Kinetic parameters determined in this NMR study are comparable to the results obtained through polarimetry, the method often used to study this reaction at the undergraduate level. The breadth of information that NMR provides can give students a better understanding of the changes in reactant and product concentration over time, giving a visual connection to the rate law they derive.

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The Esterification of Trifluoroacetic Acid: A Variable Temperature NMR Kinetics Study

Cited by 13 publications

References 0 publications

Mechanistic Pathways in CF₃COOH-Mediated Deacetalization Reactions

Mechanistic Pathways in CF₃COOH-Mediated Deacetalization Reactions

Variable Temperature NMR Experiment Studying Restricted Bond Rotation

Exploring the Hydrolysis of Sucrose by Invertase Using Nuclear Magnetic Resonance Spectroscopy: A Flexible Package of Kinetic Experiments

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The Esterification of Trifluoroacetic Acid: A Variable Temperature NMR Kinetics Study

Cited by 13 publications

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Mechanistic Pathways in CF3COOH-Mediated Deacetalization Reactions

Mechanistic Pathways in CF3COOH-Mediated Deacetalization Reactions

Variable Temperature NMR Experiment Studying Restricted Bond Rotation

Exploring the Hydrolysis of Sucrose by Invertase Using Nuclear Magnetic Resonance Spectroscopy: A Flexible Package of Kinetic Experiments

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Product

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Mechanistic Pathways in CF₃COOH-Mediated Deacetalization Reactions

Mechanistic Pathways in CF₃COOH-Mediated Deacetalization Reactions