A SPECTROSCOPIC STUDY OF ETHANOL-IODINE COMPLEX

The spectroscopic properties of the charge-transfer band and the thermodynamic properties for the formation of the electron donor-acceptor complex between ethanol and iodine have been measured in solution in n-heptane and in methylene chloride. The measured absorbance of the complex in the ultraviolet region has been analyzed by the Liptay-Scott procedure to give Kf and ∊ic; measurements at different temperatures give ΔHf° and ΔSf°. In this analysis there was a slight trend with wavelength; consideration of possible causes suggests that the most likely reason may be that the molar absorptivity of uncomplexed iodine changes as ethanol is added to the I2 solution in n-heptane. The Liptay-Scott procedure is modified slightly to take this possibility into consideration and remoee the trend in data, but the resulting values of Kf and ∊o are not changed drastically. The formation constant of the ethanol-I2 complex in n-heptane is about twice as large as that found for the same complex in methylene chloride solution, but the stability (as measured by ΔHf) is about the same in both solutions. The complex is found to be more stable (ΔHf = –4.5 kcal/mol in n-heptane) than had been previously reported. The maximum of the charge-transfer absorption is observed at 233 mμ (or about 0.3 eV to higher energies than previously reported), and the intensity is greater by about a factor of 2 than that previously reported. Reasons for these discrepancies are presented. © 1969, American Chemical Society. All rights reserved.