Kryptofix

Kryptofix refers to a family of cryptand ligands used as phase-transfer catalysts in organic synthesis. Cryptands are three-dimensional, polyether ligands that tightly bind alkali metal cations. Kryptofix ligands, particularly Kryptofix 2.2.2, form strong complexes with cations such as potassium and sodium, effectively sequestering the cation and increasing the reactivity of the associated anion in nonpolar or weakly polar solvents.

By complexing the countercation, Kryptofix increases the nucleophilicity of the anion in organic solvent, enabling SN2 substitutions and other reactions that would be sluggish in the absence of a solubilizing cation. The resulting ion pairs can perform substitutions, metalations, and other transformations with improved rates and selectivity.

The best-known application is in PET radiochemistry, where Kryptofix 2.2.2 with potassium carbonate is used to prepare [18F]-fluoride for nucleophilic labeling, often in dry acetonitrile; it is also used as a general phase-transfer catalyst for fluoride and other nucleophiles in organic synthesis.

Kryptofix 2.2.2 is the most widely used member of the line, though other cryptands in the Kryptofix family exist with different cavity sizes to accommodate other cations. The Kryptofix line is a trademark of Merck KGaA. Cryptands, the broader class to which Kryptofix belongs, were originally developed by researchers such as Jean-Marie Lehn and have since found widespread use in coordination chemistry and catalysis.

Safety handling of Kryptofix reagents is important; they should be handled with appropriate PPE, in a fume hood, and disposed of according to institutional and regulatory guidelines.