Lipophilicity Study of Salicylic and Acetylsalicylic Acids Using Both Experimental and Calculations Methods

In this work the lipophilicity of salicylic acid (SA) and acetylsalicylic acid (ASA) by means of both experimental and calculations methods were determined. The chromatographic parameters of lipophilicity (RMW) of the studied compounds were determined using RP-TLC method on different chromatographic plates with methanol–water mixture as the mobile phases (at various pH of water). Chromatographic conditions such as RP18W plates and methanol–water (pHwater = 2.56) as the mobile phase are suitable for the estimation of lipophilicity of examined salicylic and acetylsalicylic acids. Experimental n-octanol-water partition coefficients (logPexp) determined by traditional shake-flask method were equal to 2.35 and 1.14 for salicylic and acetylsalicylic acids, respectively. The results of lipophilicity measurements obtained by both analytical methods were compared with the theoretical values of partition coefficients estimated by use of well-known software products and also with those that were calculated by a newly developed method based on numerical values of the topological indexes (M, oB, 1B, W, and IB). Comparison of these results indicates that our new method of calculation of partition coefficients, the theoretical n-octanol-water partition coefficients, and also chromatographic lipophilicities are powerful tools in the determination of logP values of salicylic and acetylsalicylic acids.