Stopped-flow studies of carbon dioxide hydration and bicarbonate dehydration in H/sub 2/O and D/sub 2/O. Acid-base and metal ion catalysis

Journal Article · Wed Sep 28 00:00:00 EDT 1977 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00462a012· OSTI ID:7278520

Pocker, Y; Bjorkquist, D W

The approach to equilibrium between carbon dioxide and bicarbonate has been followed by zero-order kinetics both from direction of CO/sub 2/ hydration and HCO/sub 3//sup -/ dehydration. The rates are monitored at 25.0/sup 0/C using stopped-flow indicator technique in H/sub 2/O as well as D/sub 2/O. The hydration of CO/sub 2/ is subject to catalysis by H/sub 2/O (k/sub 0/ = 2.9 x 10/sup -2/ s/sup -1/) and OH/sup -/ (k/sub OH/sup -// = 6.0 x 10/sup 3/ M/sup -1/ s/sup -1/). The value of 0.63 for the ratio k/sub OH/sup -///k/sub OD/sup -// is consistent with a mechanism utilizing a direct nucleophilic attack of OH/sup -/ on CO/sub 2/. In reverse direction HCO/sub 3//sup -/ dehydration is catalyzed predominantly by H/sub 3/O/sup +/ (k/sub H/sub 3/O/sup +// 4.1 x 10/sup 4/ M/sup -1/ s/sup -1/) and to a much lesser degree by H/sub 2/O (k/sub 0/ = 2 x 10/sup -4/ s/sup -1/). The value of 0.56 for ratio k/sub H/sub 3/O/sup +///kD/sub 3/O/sup +// indicates that HCO/sub 3//sup -/ may be protonated either in a preequilibrium step or in a rate-determining dehydration step. Both the hydration of CO/sub 2/ and the dehydration of bicarbonate are subject to general catalysis. For CO/sub 2/, dibasic phosphate, a zinc imidazole complex, and a copper imidazole complex all enhanced the rate of hydration with respective rate coefficients of 3 x 10/sup -1/, 6.0, and 2.5 M/sup -1/ s/sup -1/. For bicarbonate, monobasic phosphate catalyzed the rate of dehydration (k/sub H/sub 2/PO/sub 4//sup -// = 1 x 10/sup -1/ M/sup -1/ s/sup -1/). Additionally in going from an ionic strength of 0.1 to 1.0 there was a negligible salt effect for the water-catalyzed hydration of CO/sub 2/. However, the rate constant for the hydronium ion catalyzed dehydration of HCO/sub 3//sup -/ was reduced from 4.1 x 10/sup 4/ M/sup -1/ s/sup -1/ to 2.3 x 10/sup 4/ M/sup -1/ s/sup -1/ for the same change in ionic strength. Finally the rate of CO/sub 2/ uptake by the complex Co(NH/sub 3/)/sub 5/OH/sub 2//sup 3 +/ was followed spectrophotometrically both in H/sub 2/O and D/sub 2/O to determine the solvent isotope effect for a reaction known to involve a nucleophilic attack of a Co(III)-hydroxo complex on CO/sub 2/.

• Research Organization: Univ. of Washington, Seattle
• OSTI ID: 7278520
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 99:20
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
DEUTERIUM
ISOTOPE EFFECTS
ACID CARBONATES
CARBON DIOXIDE
CATALYSIS
CHEMICAL REACTION KINETICS
DEHYDRATION
EQUILIBRIUM
HEAVY WATER
HYDRATION
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPES
KINETICS
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
OXIDES
OXYGEN COMPOUNDS
REACTION KINETICS
SOLVATION
STABLE ISOTOPES
WATER
400302* - Organic Chemistry- Isotope Effects- (-1987)