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Wisbey, Cedric Harry (1961) The hydration of some phenyl acetylene derivatives by aqueous sulphuric acid. Doctoral thesis, Sir John Cass College.
The following compounds have been prepared:
- phenyl propiolic acid
- p-tolyl propiolic acid
- p-nitro-phenyl propiolic acid
- phenylacetylene
- p-tolylacetylene
- p-nitro-phenylacetylene
- o-nitro-phenylacetylene
The kinetics of the hydration of the propiolic acid derivatives have been studied in aqueous sulphuric acid. The kinetics of the hydration of the phenylacetylene derivatives have been similarly studied with 13% methanol by weight present to effect solubility. The concentration of reactant present was 10-2M or less, and the reaction was conducted at temperatures (mainly) between 25°C and 45°C, with a few experiments at 0°C. The sulphuric acid concentration was varied between 35% (for p-tolylacetylene) and 100% (for p-nitro-phenyl propiolic acid).
The kinetics were followed by spectrophotometry on samples withdrawn from the reaction mixture. All the above compounds have absorption spectra in the wavelength range 2300-3000 Angstrom spectra of the products of hydration tend to overlap those of the The reactants; but it is possible in each case to select a wavelength where the difference in extinction coefficients between reactant and product is sufficient to follow the progress of the reaction. This is however not possible in the case of m-nitro-phenylacetylene.
The rate of reaction has been found to be proportional to the Hammett acidity function Ho, inasmuch as this is known or could be estimated, though slightly anomalous results were obtained in the vicinity of 100% sulphuric acid.
A experiments were carried out in a stature of sulphuric acid and glacial acetic acid, and one on aqueous perchloric acid.
So variation on the Arrhenius energy of activation with sulphuric acid concentration was observed, and the differences in energy of activation between the different compounds studied are in general insufficient to account for the differences in reaction rates.
Several possible mechanisms are discussed.
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