The Determination of 1-OctanolMTater Partition Ratios: An Organic Chemistry Laboratory Experiment The 1-oetanollwater partitim awlfirient is of importance in envinmmental fate studies because it is used in predicting physical and biological phenomena such as soil adsorption, hiological uptake, lipophilic storage, and bioeoncentration.' T h e EPA uses it to help assess environmental fate as well as health and environmental effects of chemical suhstances.2 Therefore, suhstitutim of I-actanol for the ordinary solvents in the extraction experiment commonly done in the beginning organic chemistry laboratory makes it more interesting t o many students, 1-Oetanol compares favorably in tonicity and flammability with dichlommethane, ether, etc., and is not excessively expensive. T h e term parlition coefficient, P, means t h a t the data have been corrected for ionization, dimerization, etc. The term partition ratio refers to the uncorrected distribution, K = C,,,,.,;, laverlCwater T h e I-octanollwater partition ratios for a variety of carhoxylic acids can be determined by a procedure similar t o Moore and Dalrymple's method for the determination of a distribution coefficient for henmic acid heween dichlommethane and water.' In this a d a p t a t i d the quantity of acid originally present and the quantity left in the water layer after extraction are determined by titration with standard sodium hydroxide solution, and the quantity of acid extracted is calculated by difference. Commercial 1-octanol can he used without purification or saturation with water. Values ohtained for the log of the partition ratio by this simple procedure agree reasonably well with those reported for partition coefficients. For example, for propionic acid log K was found to he 0.27 as compared tu 0.M for log P:'and for hexanoic acid log K was found to be 1.92 as compared t o 1.88 and 1.92 for log
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A number of a,mmon acids have suitable ionization amstants and water solubilities. T h e acids are supplied to the students as approximately 0.02 M aqueous solutions. As neither the identity of theaeid nor the exact concentration is known to the student, the values ut'K ahtained can be graded. After the experiment has been completed, each student is provided with a tabulatim of the structures of the acids together with their average K values as determined by the class so that he or she can see the relationship between structure and partition ratio.
'See, for example, Neely. W. R., Branson, D. R., and Blau, G. E., Enuir. Sci.Teehnnl., 8, 1113 (1974). Fpderol Register. 45,77350 (1980). "Leo, A., Hansch, C., and Elkins, D., Chem R e " , 71,525 (1971). Moore, J. A.. Dalrymple, D.L., and Rodig, 0. R., "Experimental Methods in Organic Chemistry," Jrd ed., Saunders College Publishing, New York, 1982, p. 49. Q copy of the procedure furnished to students plus instructor's m t e s will be sent on request. Please enclose a stamped, self-addressed legal envelope.
Jean 6. Umland University of Houston Downtown College Houston. TX 77002
Volume 60
Number I2
D e c e m b e r 1983
1081
