Polybasic conjugates

The definition of pH is pH = —log[H+] (which will be modified to include activity later). Ka is the equilibrium constant for the dissociation of an acid HA + H20 H30+ + A-. Kb is the base hydrolysis constant for the reaction B + H20 BH+ + OH. When either Ka or Kb is large, the acid or base is said to be strong otherwise, the acid or base is weak. Common strong acids and bases are listed in Table 6-2, which you should memorize. The most common weak acids are carboxylic acids (RC02H), and the most common weak bases are amines (R3N ). Carboxylate anions (RC02) are weak bases, and ammonium ions (R3NH+) are weak acids. Metal cations also are weak acids. For a conjugate acid-base pair in water, Ka- Kb = Kw. For polyprotic acids, we denote the successive acid dissociation constants as Kal, K, K, , or just Aj, K2, A"3, . For polybasic species, we denote successive hydrolysis constants Kbi, Kb2, A"h3, . For a diprotic system, the relations between successive acid and base equilibrium constants are Afa Kb2 — Kw and K.a Kbl = A w. For a triprotic system the relations are A al KM = ATW, K.d2 Kb2 = ATW, and Ka2 Kb, = Kw. 

Equation (1) represents the course of a reaction between a cation Mn+ and the conjugate acid of a ligand L, represented for simplicity as monobasic the same principles will apply pari passu to polybasic ligands. 

A solution of a weak acid and its salt (conjugate base) or a weak base and its conjugate acid acts as a buffer solution. The quantities of buffer components required to prepare buffers solutions of known pH can be calculated from the Henderson-Hasselbalch equation. The buffering capacity of a buffer solution is maximum at the pK of the weak acid component of the buffer. Universal buffers are mixtures of polybasic and monobasic acids that are effective over a wide range of pH. 

Soybean fatty acids are conjugated thermally or catalytically to yield dimer and tri-mer polybasic acids (Erhan et al., 2005). Hydrolyzed dimer acids improve color and oxidative stability. These are used in polyamide resins, paints, plastics, and coatings, bodying/curing/flexibilizing agents, corrosion inhibitors, antiwear agents, lubricants, fuel, and lubricant additives (Antonucci et al., 1984 Bhowmick Basu, 1988 Kale et al., 1991 Savastano, 2001 Watanabe et al., 1996). The annual dimer acid production is about 18,000 MT (20,000 t). 

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