Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 201238, 7 pages http://dx.doi.org/10.1155/2013/201238 Research Article Determination of the Ionization Constants of Some Benzoyl Thiourea Derivatives in Dioxane-Water Mixture Gun Binzet, 1 Bülent Zeybek, 2 Esma Kılıç, 3 Nevzat Külcü, 4 and Hakan Arslan 4 1 Department of Chemistry, Faculty of Education, Mersin University, 33343-Mersin, Turkey 2 Department of Chemistry, Faculty of Arts and Sciences, Dumlupnar University, 43000-Kütahya, Turkey 3 Department of Chemistry, Faculty of Sciences, Ankara University, 06100-Ankara, Turkey 4 Department of Chemistry, Faculty of Arts and Science, Mersin University, 33343-Mersin, Turkey Correspondence should be addressed to Hakan Arslan; hakan.arslan.acad@gmail.com Received 26 June 2012; Accepted 29 August 2012 Academic Editor: Jose�na Pons Copyright © 2013 Gun Binzet et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e stoichiometric ionization constants of N,N-dialkyl- � -(4-substituted benzoyl) thiourea (Substitutes: H, Cl, and Br; alkyl groups: ethyl, n-propyl, n-butyl, and phenyl) derivatives have been determined potentiometrically in dioxane-water (v:v, 50:50) mixture at ionic strength of 0.1 M and 25.0 ± 0.1 ∘ C. e ionization constants were calculated with the BEST computer program and the formation curves using the data obtained from the potentiometric titrations. e effects of substituents and alkyl groups on the ionization constants of the benzoyl thiourea derivatives have been investigated. A comparison of the basicities of ethyl, n-propyl, and n-butyl thiourea derivatives (−C 2 H 5 <−C 3 H 7 <−C 4 H 9 ) shows that the n-butyl group is a more powerful electron-releasing group than the other groups in 50% dioxane-50% water mixture (v:v). So, the acidity of benzoyl thiourea derivative compounds decreases, while the length of alkyl chain increases. e orders of p  values for all thiourea derivatives are as expected in the light of steric, resonance and inductive effects of substituents. Furthermore, when the basicities of halogen derivatives of the same substitution pattern are compared, orders obtained (4-Br <4-Cl <4-H) can be explained by considering the total electronic substituent effect (electron-withdrawing and electron-donating effects) except the 4-Br_Ph derivative. 1. Introduction iourea derivatives and their transition metal complexes have been known since the beginning of the 20th century. e syntheses of the thiourea derivatives are easily with good yields [1]. iourea and its derivatives represent a well- known important group of organic compounds due to the diverse application in �elds such as medicine, agriculture, coordination, and analytical chemistry [2]. e benzoyl thiourea derivatives have a wide range of biological activities including antiviral [3], antibacterial [4–6], antifungal [7], antitubercular [8, 9], herbicidal [10], insecticidal [11], and pharmacological properties [12] and acting as chelating agents [13, 14]. Although the synthesis, characterization, and applica- tions of many benzoyl thiourea derivatives were reported in the literature [15–25]; to the best of our knowledge, there is no report on the determination of ionization constants of substitute benzoyl thiourea derivatives. On the continuation of our research on the determination of ionization constants of some industrial useful organic compounds in this study, we report the stoichiometric ionization constants of some sub- stituted benzoyl thioureas in dioxane : water mixture (v : v, 50 : 50). Various techniques can be used to determine ioniza- tion constants, such as potentiometry, conductometry, and spectrophotometry [26]. For more bene�t, in this research, we select the potentiometric titration technique. Since the solubility of these compounds in water is too low, dioxane- water mixtures were used as medium in the experiments. e stoichiometric ionization constants have been measured by the potentiometric titration, and calculations were per- formed by the BEST computer soware [27, 28]. In addition, in this research, the effects of substituents and alkyl groups on the ionization constants of the benzoyl thiourea derivatives have been discussed.