Acid‐base Properties of Terbutaline in Terms of Protonation Macro‐ and Microconstants

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Abstract

The acid/base chemistry of terbutaline was characterized at the molecular level in terms of protonation macroconstants and microconstants. The macroconstants were measured by potentiometry and calculated by standard evaluation methods. The stepwise macroconstant values were log K1 = 11·01, log K2 = 9·89, and log K3 = 8·57 at 250°C and 0·2 m ionic strength. The microconstants were deduced using the relationships between macro‐ and microconstants and an appropriate data set of model compounds (resorcinol and phenylephrine). The molecule of terbutaline contains three ionizable functional groups. In the unprotonated form of the molecule, the two identical phenolate groups are slightly more basic than the secondary amino group, whereas the amino basicity significantly exceeds that of the phenolate site, when the other phenol is protonated. This is due to the large phenolate‐phenolate intramolecular interaction. The phenolate‐phenolate and the phenolate‐amino interactivity parameters were found to be −1·21 and −0·41 log E units, respectively. 1995 Royal Pharmaceutical Society of Great Britain

Original languageEnglish
Pages (from-to)431-435
Number of pages5
JournalJournal of Pharmacy and Pharmacology
Volume47
Issue number5
DOIs
Publication statusPublished - May 1995

ASJC Scopus subject areas

  • Pharmacology
  • Pharmaceutical Science

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