Tripotassium Phosphate: From Buffers to Organic Synthesis

Introduction

Tripotassium phosphate (potassium phosphate tribasic, K₃PO₄) is a strong inorganic base (pK_a = 12.32 for the conjugate acid). It is non-toxic, very inexpensive, and available from many chemical supply companies. This chemical is used as a food additive or to form stable phosphate buffer solutions in water. However, it is soluble in organic solvents (both in polar and nonpolar), and thus has been used as an alternative non-nucleophilic base in several reactions.

The choice of base in an organic reaction depends on various factors. In several cases, a super strong base like n-BuLi is not needed for the deprotonation and chemists rely on weaker organic amines or inorganic salts. Organic amines (e.g., triethylamine, pyridine) are usually foul smelling liquids soluble in most solvents, but can cause problems with nucleophilic attack or coordination to metals. Inorganic salts used in organic synthesis include K₂CO₃ and Cs₂CO₃, although the former is only soluble in polar solvents and the latter is very expensive and can be moisture-sensitive. K₃PO₄ is slightly hygroscopic, but its melting point is 1380 ˚C so it can be easily heated to remove water without decomposition.

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