Hydrogen phthalate ion

For the weak acid, hydrogen phthalate ion HA", in aqueous solution, the dissociation constant may be written as... 

The rate of formation of sulphoxides from sulphides and iodine in aqueous solution has been found to be relatively slow. It may be, however, accelerated by certain nucleophiles, such as phthalate ion S hydrogen phosphate ion and E(-cyclodextrin phosphate ion . The selective oxidation of JV-acetylmethionine and N-acetylmethionine methyl ester to the corresponding S-oxides was achieved using iodine in the presence of dicarboxylate ions. 

The P in KHP refers to phthalate. The phthalate ion is a benzene ring with two carboxyl groups on adjacent carbons. See Figure 5.8. Potassium hydrogen phthalate (KHP) is useful as a primary standard because it possesses all the qualities sought in a primary standard. See Section 4.5.2. 

The major conclusion which was reached from the work of Jarret and Saunders was that intramolecularly hydrogen-bonded protons generally give values of (p below the value for a similar proton which is not involved in an intramolecular hydrogen bond. For example, a value of (p of 0.77 was obtained for the hydrogen-bonded site in the maleate ion [12] compared to 0.94 for acetic acid. The value for the phthalate ion [10] was higher, (p = 0.95. The value of (p = 0.95 was obtained for the salicylate ion [22] in comparison to the result for phenol, tp = 1.13. 

The effect is easily achieved in the ion chromatography system where the preferred buffer solution (potassium hydrogen phthalate (5xlO 3M at pH 4.6) has a strong ultraviolet response with tanax at 280nm. At this... 

Calculate the hydronium ion concentration of a buffer that is 0.0500 M in potassium hydrogen phthalate (KHP) and 0.150 M in potassium phthalate (K2P). 

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