Journal of Chemical Thermodynamics, volume 73, pages 140-147

Thermochemistry of 2,2,5,7,8-pentamethylchroman-6-ol (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox)

Carlos Bernardes ^{1, 2}

Ricardo G Simões ³

Hermínio P. Diogo ⁴

M. F. M. Piedade ³

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Centro de Química e Bioquímica e Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal |

Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal |

Centro de Química e Bioquímica e Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal. |

⁴

Centro de Quı́mica Estrutural, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal |

Publication type: Journal Article

Publication date: 2014-06-01

Elsevier

Journal: Journal of Chemical Thermodynamics

Quartile SCImago

Quartile WOS

Impact factor: 2.6

ISSN: 00219614, 10963626

DOI: 10.1016/j.jct.2013.11.032

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Physical and Theoretical Chemistry

Atomic and Molecular Physics, and Optics

General Materials Science

Abstract

2,2,5,7,8-Pentamethylchroman-6-ol (PMC, CAS number 950-99-2) and 6-hydroxy-2,5,7,8-tetramethyl chroman-2-carboxylic acid (trolox, CAS number 53188-07-1) are perhaps the two most widely used model compounds for α-tocoferol, the main active antioxidant form of vitamin E. Because the antioxidant activity of α-tocoferol, and of phenol derivatives (ArOH) in general (such as PMC and trolox), is intimately related to the breaking of the ArO H bond, considerable efforts have been made to investigate how the energetics of that bond is linked to the structure and energetics of both the ArO radical and the ArOH parent compound, which are reflected by the corresponding enthalpies of formation. In this work the standard molar enthalpies of formation of crystalline PMC (triclinic, space group P 1 ¯ phase) and trolox (monoclinic, space group P 2 1 / c phase), at T = 298.15 K, were obtained as Δ f H m o ( PMC,cr ) = −(513.7 ± 3.4) kJ · mol −1 and Δ f H m o ( trolox, cr I ) = −(892.5 ± 4.1) kJ · mol −1 by combustion calorimetry. The results of drop-sublimation Calvet microcalorimetry experiments and vapor pressure vs. temperature measurements by the Knudsen effusion method, combined with C p ,m o ( cr ) and C p ,m o ( g ) data obtained by differential scanning calorimetry and calculated at the B3LYP/6-31+G(d, p) level of theory, respectively, led to Δ sub H m o ( PMC ) = (107.4 ± 0.8) kJ · mol −1 and Δ sub H m o ( trolox ) = (136.9 ± 2.5) kJ · mol −1 at T = 298.15 K. From the obtained Δ sub H m o ( cr ) and Δ sub H m o values it was possible to derive Δ sub H m o ( PMC, g ) = −(406.3 ± 3.5) kJ · mol −1 and Δ sub H m o = −(755.6 ± 4.8) kJ · mol −1 at T = 298.15 K. These results led to the conclusion that, in terms of the homodesmotic stabilization enthalpy criteria the replacement of a CH 3 group in PMC by a COOH group in trolox approximately conforms to group additivity with no significant contribution from the possible presence of a weak intramolecular hydrogen bond in trolox.

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Bernardes C. et al. Thermochemistry of 2,2,5,7,8-pentamethylchroman-6-ol (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox) // Journal of Chemical Thermodynamics. 2014. Vol. 73. pp. 140-147.

GOST all authors (up to 50) Copy

Bernardes C., Simões R. G., Diogo H. P., Piedade M. F. M. Thermochemistry of 2,2,5,7,8-pentamethylchroman-6-ol (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox) // Journal of Chemical Thermodynamics. 2014. Vol. 73. pp. 140-147.

RIS |

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RIS Copy

TY - JOUR

DO - 10.1016/j.jct.2013.11.032

UR - https://doi.org/10.1016/j.jct.2013.11.032

TI - Thermochemistry of 2,2,5,7,8-pentamethylchroman-6-ol (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox)

T2 - Journal of Chemical Thermodynamics

AU - Bernardes, Carlos

AU - Simões, Ricardo G

AU - Diogo, Hermínio P.

AU - Piedade, M. F. M.

PY - 2014

DA - 2014/06/01

PB - Elsevier

SP - 140-147

VL - 73

SN - 0021-9614

SN - 1096-3626

ER -

BibTex

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BibTex Copy

@article{2014_Bernardes,

author = {Carlos Bernardes and Ricardo G Simões and Hermínio P. Diogo and M. F. M. Piedade},

title = {Thermochemistry of 2,2,5,7,8-pentamethylchroman-6-ol (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox)},

journal = {Journal of Chemical Thermodynamics},

year = {2014},

volume = {73},

publisher = {Elsevier},

month = {jun},

url = {https://doi.org/10.1016/j.jct.2013.11.032},

pages = {140--147},

doi = {10.1016/j.jct.2013.11.032}

}

Found error?

Publisher

Elsevier

Journal

Journal of Chemical Thermodynamics

Quartile SCImago

Quartile WOS

Impact factor

2.6

ISSN

00219614 (Print)
10963626 (Electronic)