Sodium hydride functions as an extremely strong, non-nucleophilic base in anhydrous biochemical synthesis, particularly for selective deprotonation of alcohols, amides, and active methylene compounds in protecting group chemistry and polyketide analog preparation.
Chemical Properties
Sodium hydride (NaH, MW 24.00 g/mol) appears as a silvery-to-whitish powder (density 0.92–1.40 g/cm³) with a face-centered cubic NaCl-type structure (a = 4.98 Å), where each Na⁺ ion octahedrally coordinates six H⁻ anions (Na–H distance 2.48 Å, ionic radii H⁻ 146 pm). It is insoluble in organic solvents but highly reactive; it violently hydrolyzes with water (NaH + H2O → NaOH + H2 ↑, ΔH = -123 kJ/mol) evolving hydrogen gas and decomposes above 300°C to Na and H₂.
Biochemical Applications
In organic synthesis, 1–2 eq. of 60% NaH/DMF slurries are employed for clean O-silylation of carbohydrates (forming alkoxides quantitatively without over-deprotonation) or N-protection of amino sugars as Na-amides. In peptide chemistry, it is used for active ester formation from Fmoc-amino acids, deprotonating carboxylates while avoiding racemization. Nucleotide laboratories generate 2'-O- or 3'-O-anions for regioselective alkylation in 2'-5A analog synthesis. In lipid chemistry, NaH is applied to dry DMF extracts prior to diazomethane methylation to scavenge residual water.
