The Ammonolysis of Esters in Liquid Ammonia.

Joseph M. Griffin, John Atherton, Michael Page

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The rates of ammonolysis of alkyl benzoate and phenylacetate esters in liquid ammonia increase with the acidity of the leaving group alcohol and show relatively large Brønsted βlg values of −1.18 and −1.34, respectively, when plotted against the aqueous pKa of the alcohol. The Brønsted βlg obtained using the pKa of the leaving group alcohol in liquid ammonia is significantly reduced to ~ −0.7, which indicates that the rate-limiting step involves a reaction of the tetrahedral intermediate with little C–OR bond fission in the transition state. The solvolysis reaction is subject to significant catalysis by ammonium ion, which, surprisingly, generates a similar Brønsted βlg indicating little interaction between the ammonium ion and the leaving group. It is concluded that the rate-limiting step for the ammonium-ion-catalysed solvolysis of alkyl esters in liquid ammonia is the diffusion-controlled protonation of the zwitterionic tetrahedral intermediate T+- to give T+, which is rapidly deprotonated to give T0 which is compatible with the rate-limiting step for the uncatalysed reaction being the formation of the neutral T0 by a ‘proton switch’.
Original languageEnglish
Pages (from-to)1032-1037
Number of pages6
JournalJournal of Physical Organic Chemistry
Volume26
Issue number12
DOIs
Publication statusPublished - 2013

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ammonolysis
liquid ammonia
Ammonium Compounds
Ammonia
esters
Esters
Alcohols
Ions
solvolysis
alcohols
Liquids
Protonation
Benzoates
Acidity
ions
Catalysis
Protons
Switches
acidity
catalysis

Cite this

Griffin, Joseph M. ; Atherton, John ; Page, Michael. / The Ammonolysis of Esters in Liquid Ammonia. In: Journal of Physical Organic Chemistry. 2013 ; Vol. 26, No. 12. pp. 1032-1037.
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title = "The Ammonolysis of Esters in Liquid Ammonia.",
abstract = "The rates of ammonolysis of alkyl benzoate and phenylacetate esters in liquid ammonia increase with the acidity of the leaving group alcohol and show relatively large Br{\o}nsted βlg values of −1.18 and −1.34, respectively, when plotted against the aqueous pKa of the alcohol. The Br{\o}nsted βlg obtained using the pKa of the leaving group alcohol in liquid ammonia is significantly reduced to ~ −0.7, which indicates that the rate-limiting step involves a reaction of the tetrahedral intermediate with little C–OR bond fission in the transition state. The solvolysis reaction is subject to significant catalysis by ammonium ion, which, surprisingly, generates a similar Br{\o}nsted βlg indicating little interaction between the ammonium ion and the leaving group. It is concluded that the rate-limiting step for the ammonium-ion-catalysed solvolysis of alkyl esters in liquid ammonia is the diffusion-controlled protonation of the zwitterionic tetrahedral intermediate T+- to give T+, which is rapidly deprotonated to give T0 which is compatible with the rate-limiting step for the uncatalysed reaction being the formation of the neutral T0 by a ‘proton switch’.",
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Griffin, JM, Atherton, J & Page, M 2013, 'The Ammonolysis of Esters in Liquid Ammonia.', Journal of Physical Organic Chemistry, vol. 26, no. 12, pp. 1032-1037. https://doi.org/10.1002/poc.3148

The Ammonolysis of Esters in Liquid Ammonia. / Griffin, Joseph M.; Atherton, John; Page, Michael.

In: Journal of Physical Organic Chemistry, Vol. 26, No. 12, 2013, p. 1032-1037.

Research output: Contribution to journalArticle

TY - JOUR

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AU - Atherton, John

AU - Page, Michael

PY - 2013

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N2 - The rates of ammonolysis of alkyl benzoate and phenylacetate esters in liquid ammonia increase with the acidity of the leaving group alcohol and show relatively large Brønsted βlg values of −1.18 and −1.34, respectively, when plotted against the aqueous pKa of the alcohol. The Brønsted βlg obtained using the pKa of the leaving group alcohol in liquid ammonia is significantly reduced to ~ −0.7, which indicates that the rate-limiting step involves a reaction of the tetrahedral intermediate with little C–OR bond fission in the transition state. The solvolysis reaction is subject to significant catalysis by ammonium ion, which, surprisingly, generates a similar Brønsted βlg indicating little interaction between the ammonium ion and the leaving group. It is concluded that the rate-limiting step for the ammonium-ion-catalysed solvolysis of alkyl esters in liquid ammonia is the diffusion-controlled protonation of the zwitterionic tetrahedral intermediate T+- to give T+, which is rapidly deprotonated to give T0 which is compatible with the rate-limiting step for the uncatalysed reaction being the formation of the neutral T0 by a ‘proton switch’.

AB - The rates of ammonolysis of alkyl benzoate and phenylacetate esters in liquid ammonia increase with the acidity of the leaving group alcohol and show relatively large Brønsted βlg values of −1.18 and −1.34, respectively, when plotted against the aqueous pKa of the alcohol. The Brønsted βlg obtained using the pKa of the leaving group alcohol in liquid ammonia is significantly reduced to ~ −0.7, which indicates that the rate-limiting step involves a reaction of the tetrahedral intermediate with little C–OR bond fission in the transition state. The solvolysis reaction is subject to significant catalysis by ammonium ion, which, surprisingly, generates a similar Brønsted βlg indicating little interaction between the ammonium ion and the leaving group. It is concluded that the rate-limiting step for the ammonium-ion-catalysed solvolysis of alkyl esters in liquid ammonia is the diffusion-controlled protonation of the zwitterionic tetrahedral intermediate T+- to give T+, which is rapidly deprotonated to give T0 which is compatible with the rate-limiting step for the uncatalysed reaction being the formation of the neutral T0 by a ‘proton switch’.

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