/sup 18/O-isotope effect in /sup 13/C nuclear magnetic resonance spectroscopy. 4. Oxygen exchange of (1-/sup 13/C, /sup 18/O/sub 2/)acetic acid in dilute acid

Journal Article · Wed Jul 29 04:00:00 EDT 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00405a017· OSTI ID:6231891

Risley, J M; Van Etten, R L

The /sup 18/O-iosotope shift in /sup 13/C NMR spectroscopy is shown to provide a widely applicable technique for studying the kinetics of oxygen exchange reactions in a nearly continuous assay mode. Here, the technique is used to study the acid-catalyzed medium carboxyl(oxygen)-water exchange reaction of (1-/sup 13/C, /sup 18/O/sub 2/)acetic acid at 32/sup 0/C. The /sup 18/O-isotope-induced shift fo the /sup 13/C NMR signal of the /sup 13/C-enriched carboxyl carbon in acetic acid permits a facile and direct measurement of the relative concentrations of the three (oxygen) isotopic species of acetic acid. The pseudo-first-order rate constant is evaluated as a function of pH and added salt for the salts sodium chloride and sodium perchlorate. The pH profile is typical of those observed for related acid-catalyzed oxygen exchange reactions of the carboxyl group. In the dilute-acid region the rate is approximately first order in hydrogen ion. The present results definitively establish the salt effect on the exchange reaction, resolving a conflict between earlier reports. The rate of the exchange reaction is decreased by increasing concentrations of the two salts. The magnitude of the rate decrease depends on he nature as well as the concentration of the salt. Possible interpretations of the results are discussed.

• Research Organization: Purdue Univ., West Lafayette, IN
• OSTI ID: 6231891
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 103:15; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ACETIC ACID
ALKALI METAL COMPOUNDS
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
CHLORIDES
CHLORINE COMPOUNDS
DATA
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HALIDES
HALOGEN COMPOUNDS
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MONOCARBOXYLIC ACIDS
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PERCHLORATES
PH VALUE
RESONANCE
SODIUM CHLORIDES
SODIUM COMPOUNDS
SODIUM PERCHLORATES
SPECTRA
STABLE ISOTOPES