Microlog p Application

Niflumic acid was studied both pH-metrically and spectroscopically using the shake-flask method [8]. The macroscopic log P was measured as 3.88 in 0.15 m NaCl. It was assumed that a negligible amount of zwitterion XH1 partitions into octanol. Because there is an equilibrium between the two micro-forms of the XH species in the aqueous phase (tautomeric ratio, Eq. (33), was measured spectroscopically to be 17.4), the macro-log P value differs from the micro-log p value according to Eq. (41): log pXHo = log PXH + log K, - log k° = 5.1. The value determined by shake-flask measurements was 4.8, indicating good agreement. The number is quite a bit higher than the macro log P.

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