Determination of stability constants from optical rotatory dispersion measurements. Camphor–phenol system in carbon tetrachloride
✍ Scribed by Jürg Meier; Takeru Higuchi
- Publisher
- John Wiley and Sons
- Year
- 1965
- Tongue
- English
- Weight
- 323 KB
- Volume
- 54
- Category
- Article
- ISSN
- 0022-3549
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✦ Synopsis
A spectropolarimetric method of determining stability constants of complexes formed through hydrogen bonding has been develo ed and applied to the camphorphenol system. A variation of the Rossotti an$ Rossotti method modified to account for formation of complex species containing two molecules of phenol is shown to yield a stability constant in carbon tetrachloride of 12.2 L./mole at 25'.
LTHOUGH it is generally recognized that such Adiverse factors as solubility behaviors of nonelectrolytes in nonaqueous solvents, thermodynamic properties of organic solutes in organic solvents, rate of elution of sample components from GLC columns, melting points of organic solids, formation of molecular compounds and adducts, specific activities of drugs, etc., are usually strongly influenced by tendencies of polar centers in molecules to attract each other, relatively little quantitative information appears to be available in the literature. The present communication is concerned with preliminary results of an essentially little used but promising approach to this problem. Although stability constants of bonds formed between acidic hydrogen compounds and hydrogen accepting species can be determined by a number of different techniques including NMR, I.R., solubility studies, extraction studies, etc. (l), the feasibility of utilizing polarimetric methods seems not to have been thoroughly tested.
Discussion
Theoretically, measurement of optical rotatory power appears to permit determination of physical constants with precision rarely possible with conventional commercial sensing instruments aside from gravimetric balances. Ultraviolet spectrophotometers, for example, can with only great care detect concentration differences of 3 ~0 . 1 % . Corresponding infrared instruments are probably no better than &l%. NMR suffers from lack of both sensitivity and precision. Presently available commercial spectropolarimeters, on the other hand, appear to permit measurements of a few tenths of a millidegree in samples having rotations of several degrees corresponding to usable sensitivity approaching a few parts in 100,000.
For the computation of stability constants, a ~