Hemiortho esters and hydrotrioxides as the primary products in the low-temperature ozonation of cyclic acetals: an experimental and theoretical investigation

Tell Tuttle, Janez Cerkovnik, Božo Plesničar, Dieter Cremer

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Low-temperature ozonation (-78°C) of 1,3-dioxolanes 1a-1f and 1,3-dioxanes 1g and h in acetone-d6, methyl acetate, and fert-butyl methyl ether produced both the corresponding hemiortho esters (2a-h, ROH) and acetal hydrotrioxides (3a-h, ROOOH) in molar ratios ROH/ROOOH ranging from 0.5 to 23. Both types of intermediates were fully characterized by 1H, 13C, and 17O NMR spectroscopy. DFT calculations suggest that ozone abstracts a hydride ion from 1 to form an ion pair, R+ -OOOH, which subsequently collapses to either the corresponding hemiortho ester (ROH) or the acetal hydrotrioxide (ROOOH). Hemiortho esters decomposed quantitatively into the corresponding hydroxy esters. Experi-mentally obtained activation parameters for the decomposition of 2a (Ea = 13.5 ± 1.0 kcal/mol, log A = 8.3 ± 1.0) are in accord with a highly oriented transition state involving, according to B3LYP calculations (ΔH a(298) = 13.2 kcal/mol), two molecules of water as a bifunctional catalyst. This mechanism is also supported by the magnitude of the solvent isotope effect for the decomposition of 2e, i.e., kH2O/kD 2O = 4.6 ± 1.2. Besides the hydroxy esters and oxygen ( 3O2/1O2), dihydrogen trioxide (HOOOH) was formed in the decomposition of most of the acetal hydrotrioxides (ROOOH) investigated. The activation parameters for the decomposition of the hydrotrioxides 3a-e in various solvents were Ea = 20 ± 2 kcal/mol, log A = 13.5 ± 1.5. Several mechanistic possibilities for the decomposition of ROOOH were tested by experiment and theory. The formation of the hydroxy esters and oxygen could be explained by the intramolecular transfer of the proton to form the hydroxy ester. The assistance of water in the decomposition of ROOOH to form the hydroxy esters, either directly or via hemiortho esters, was also investigated. According to DFT calculations, the formation of a hydroxy ester via hemiortho ester is energetically more favorable (ΔHa(298) = 14.5 kcal/mol), again due to the catalytic effect of two water molecules. HOOOH generation requires the involvement of water in the decomposition of ROOOH where the direct formation out of ROOOH is energetically preferred. The energy for a reaction between two molecules of water and singlet oxygen (Δ1O2) is too high to occur in solution.

LanguageEnglish
Pages16093-16104
Number of pages12
JournalJournal of the American Chemical Society
Volume126
Issue number49
Early online date17 Nov 2004
DOIs
Publication statusPublished - 15 Dec 2004

Fingerprint

Acetals
Ozonization
Esters
Temperature
Decomposition
Water
Discrete Fourier transforms
Molecules
Oxygen
Dioxanes
Chemical activation
Ions
Methyl Ethers
Singlet Oxygen
Ozone
Acetone
Hydrides
Isotopes
Nuclear magnetic resonance spectroscopy
Protons

Keywords

  • low-temperature ozonation
  • decomposition
  • intramolecular transfer

Cite this

@article{1a843913639f470b8bdf27852fffc2f8,
title = "Hemiortho esters and hydrotrioxides as the primary products in the low-temperature ozonation of cyclic acetals: an experimental and theoretical investigation",
abstract = "Low-temperature ozonation (-78°C) of 1,3-dioxolanes 1a-1f and 1,3-dioxanes 1g and h in acetone-d6, methyl acetate, and fert-butyl methyl ether produced both the corresponding hemiortho esters (2a-h, ROH) and acetal hydrotrioxides (3a-h, ROOOH) in molar ratios ROH/ROOOH ranging from 0.5 to 23. Both types of intermediates were fully characterized by 1H, 13C, and 17O NMR spectroscopy. DFT calculations suggest that ozone abstracts a hydride ion from 1 to form an ion pair, R+ -OOOH, which subsequently collapses to either the corresponding hemiortho ester (ROH) or the acetal hydrotrioxide (ROOOH). Hemiortho esters decomposed quantitatively into the corresponding hydroxy esters. Experi-mentally obtained activation parameters for the decomposition of 2a (Ea = 13.5 ± 1.0 kcal/mol, log A = 8.3 ± 1.0) are in accord with a highly oriented transition state involving, according to B3LYP calculations (ΔH a(298) = 13.2 kcal/mol), two molecules of water as a bifunctional catalyst. This mechanism is also supported by the magnitude of the solvent isotope effect for the decomposition of 2e, i.e., kH2O/kD 2O = 4.6 ± 1.2. Besides the hydroxy esters and oxygen ( 3O2/1O2), dihydrogen trioxide (HOOOH) was formed in the decomposition of most of the acetal hydrotrioxides (ROOOH) investigated. The activation parameters for the decomposition of the hydrotrioxides 3a-e in various solvents were Ea = 20 ± 2 kcal/mol, log A = 13.5 ± 1.5. Several mechanistic possibilities for the decomposition of ROOOH were tested by experiment and theory. The formation of the hydroxy esters and oxygen could be explained by the intramolecular transfer of the proton to form the hydroxy ester. The assistance of water in the decomposition of ROOOH to form the hydroxy esters, either directly or via hemiortho esters, was also investigated. According to DFT calculations, the formation of a hydroxy ester via hemiortho ester is energetically more favorable (ΔHa(298) = 14.5 kcal/mol), again due to the catalytic effect of two water molecules. HOOOH generation requires the involvement of water in the decomposition of ROOOH where the direct formation out of ROOOH is energetically preferred. The energy for a reaction between two molecules of water and singlet oxygen (Δ1O2) is too high to occur in solution.",
keywords = "low-temperature ozonation, decomposition, intramolecular transfer",
author = "Tell Tuttle and Janez Cerkovnik and Božo Plesničar and Dieter Cremer",
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Hemiortho esters and hydrotrioxides as the primary products in the low-temperature ozonation of cyclic acetals : an experimental and theoretical investigation. / Tuttle, Tell; Cerkovnik, Janez; Plesničar, Božo; Cremer, Dieter.

In: Journal of the American Chemical Society , Vol. 126, No. 49, 15.12.2004, p. 16093-16104.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Hemiortho esters and hydrotrioxides as the primary products in the low-temperature ozonation of cyclic acetals

T2 - Journal of the American Chemical Society

AU - Tuttle, Tell

AU - Cerkovnik, Janez

AU - Plesničar, Božo

AU - Cremer, Dieter

PY - 2004/12/15

Y1 - 2004/12/15

N2 - Low-temperature ozonation (-78°C) of 1,3-dioxolanes 1a-1f and 1,3-dioxanes 1g and h in acetone-d6, methyl acetate, and fert-butyl methyl ether produced both the corresponding hemiortho esters (2a-h, ROH) and acetal hydrotrioxides (3a-h, ROOOH) in molar ratios ROH/ROOOH ranging from 0.5 to 23. Both types of intermediates were fully characterized by 1H, 13C, and 17O NMR spectroscopy. DFT calculations suggest that ozone abstracts a hydride ion from 1 to form an ion pair, R+ -OOOH, which subsequently collapses to either the corresponding hemiortho ester (ROH) or the acetal hydrotrioxide (ROOOH). Hemiortho esters decomposed quantitatively into the corresponding hydroxy esters. Experi-mentally obtained activation parameters for the decomposition of 2a (Ea = 13.5 ± 1.0 kcal/mol, log A = 8.3 ± 1.0) are in accord with a highly oriented transition state involving, according to B3LYP calculations (ΔH a(298) = 13.2 kcal/mol), two molecules of water as a bifunctional catalyst. This mechanism is also supported by the magnitude of the solvent isotope effect for the decomposition of 2e, i.e., kH2O/kD 2O = 4.6 ± 1.2. Besides the hydroxy esters and oxygen ( 3O2/1O2), dihydrogen trioxide (HOOOH) was formed in the decomposition of most of the acetal hydrotrioxides (ROOOH) investigated. The activation parameters for the decomposition of the hydrotrioxides 3a-e in various solvents were Ea = 20 ± 2 kcal/mol, log A = 13.5 ± 1.5. Several mechanistic possibilities for the decomposition of ROOOH were tested by experiment and theory. The formation of the hydroxy esters and oxygen could be explained by the intramolecular transfer of the proton to form the hydroxy ester. The assistance of water in the decomposition of ROOOH to form the hydroxy esters, either directly or via hemiortho esters, was also investigated. According to DFT calculations, the formation of a hydroxy ester via hemiortho ester is energetically more favorable (ΔHa(298) = 14.5 kcal/mol), again due to the catalytic effect of two water molecules. HOOOH generation requires the involvement of water in the decomposition of ROOOH where the direct formation out of ROOOH is energetically preferred. The energy for a reaction between two molecules of water and singlet oxygen (Δ1O2) is too high to occur in solution.

AB - Low-temperature ozonation (-78°C) of 1,3-dioxolanes 1a-1f and 1,3-dioxanes 1g and h in acetone-d6, methyl acetate, and fert-butyl methyl ether produced both the corresponding hemiortho esters (2a-h, ROH) and acetal hydrotrioxides (3a-h, ROOOH) in molar ratios ROH/ROOOH ranging from 0.5 to 23. Both types of intermediates were fully characterized by 1H, 13C, and 17O NMR spectroscopy. DFT calculations suggest that ozone abstracts a hydride ion from 1 to form an ion pair, R+ -OOOH, which subsequently collapses to either the corresponding hemiortho ester (ROH) or the acetal hydrotrioxide (ROOOH). Hemiortho esters decomposed quantitatively into the corresponding hydroxy esters. Experi-mentally obtained activation parameters for the decomposition of 2a (Ea = 13.5 ± 1.0 kcal/mol, log A = 8.3 ± 1.0) are in accord with a highly oriented transition state involving, according to B3LYP calculations (ΔH a(298) = 13.2 kcal/mol), two molecules of water as a bifunctional catalyst. This mechanism is also supported by the magnitude of the solvent isotope effect for the decomposition of 2e, i.e., kH2O/kD 2O = 4.6 ± 1.2. Besides the hydroxy esters and oxygen ( 3O2/1O2), dihydrogen trioxide (HOOOH) was formed in the decomposition of most of the acetal hydrotrioxides (ROOOH) investigated. The activation parameters for the decomposition of the hydrotrioxides 3a-e in various solvents were Ea = 20 ± 2 kcal/mol, log A = 13.5 ± 1.5. Several mechanistic possibilities for the decomposition of ROOOH were tested by experiment and theory. The formation of the hydroxy esters and oxygen could be explained by the intramolecular transfer of the proton to form the hydroxy ester. The assistance of water in the decomposition of ROOOH to form the hydroxy esters, either directly or via hemiortho esters, was also investigated. According to DFT calculations, the formation of a hydroxy ester via hemiortho ester is energetically more favorable (ΔHa(298) = 14.5 kcal/mol), again due to the catalytic effect of two water molecules. HOOOH generation requires the involvement of water in the decomposition of ROOOH where the direct formation out of ROOOH is energetically preferred. The energy for a reaction between two molecules of water and singlet oxygen (Δ1O2) is too high to occur in solution.

KW - low-temperature ozonation

KW - decomposition

KW - intramolecular transfer

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