Boron Hydrides. III. Hydrolysis of Sodium Borohydride in Aqueous Solution
The hydrolysis of sodium borohydride in aqueous buffer solutions at 25 deg s catalyzed by general acids. The Bronsted constant is nearly 0.9. Salt effects and solvent isotope effects were measured. A mechanism involving a ratedetermining proton transfer from a general acid onto the borohydride ion is consistent with the data of numerous investigators. One reactive intermediate was trapped by hydrolyzing sodium borohydride in aqueous trimethylamine. Trimethylamine borane was produced in 1.45 t 0.09% yield while the remainder of the borohydride gave hydrogen gas. Hydrolysis of sodium borodeuteride occurs faster than the hydrolysis of sodium borohydride. The primary inverse isotope effect, k/sub H//k/sub D/, is 0.70 plus or minus 0.02 at 25 deg . The isotope effect for the boron-hydrogen bond was calculated. Several likely models of the activated complex give values of k/sub H// k/sub D/ from 0.60 to 0.95. A simplified model predicts 0.65 if the amount of primary bond breaking is proportional to the amount of secondary bond stiffening. The possible role of steric effects on secondary hydrogen isotope effects was estimated on a static model. The results show that both normal and inverse secondary isotope effects can be explained in this manner.
- Research Organization:
- Purdue Univ., Lafayette, Ind.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-16-013041
- OSTI ID:
- 4800265
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 6 Vol. 84; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
ACIDITY
ACTIVATION
AMINES
BINDING ENERGY
BORON
BORON HYDRIDES
BROENSTED THEORY
BUFFERS
CATALYSIS
COMPLEXES
DEUTERIUM COMPOUNDS
GASES
HYDROGEN
HYDROLYSIS
ISOTOPE EFFECTS
MEASURED VALUES
METHYL RADICALS
PROTONS
SODIUM BORIDES
SOLUTIONS
TEMPERATURE
THERMODYNAMICS
WATER