Analytical Sciences

Reevaluation of Donor Number Using Titration Calorimetry

Misaki KATAYAMA,* Mitsushi SHINODA,** Kazuhiko OZUTSUMI,* Shigenobu FUNAHASHI,** and Yasuhiro INADA*

*Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
**Laboratory of Analytical Chemistry, Department of Chemistry, Faculty of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan

Many empirical parameters have been suggested to measure solvent effects in chemical reactions. Gutmann’s donor number has been a successful parameter to quantify the electron-donating property of the solvent molecule; it is defined as the enthalpy change of the addition reaction of solvent molecule to SbCl₅ in 1,2-dichloroethane. Calorimetric measurements can be applied to determine the quantity. Because the existence of water is critical for reactions in organic solvents, we have analyzed the enthalpy change using the titration calorimetry while considering the complexation with water. The determined donor numbers of formamide, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and 1,1,3,3-tetramethylurea (TMU) are 22.4, 26.5, 30.0, and 40.4, respectively. The values of DMF and DMSO are in perfect agreement with those of Gutmann. A reliable value for TMU is obtained for the first time on the basis of the enthalpy change for the addition reaction.

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