Protic - Polar Aprotic Solvents

Polar Aprotic Solvents

Polar aprotic solvents are solvents that will dissolve many salts, but lack an acidic hydrogen. These solvents generally have intermediate dielectric constants and polarity. Although discouraging use of the term "polar aprotic", IUPAC describes such solvents as having both high dielectric constants and high dipole moments, an example being acetonitrile. Other solvents meeting IUPAC's criteria include DMF, HMPA, and DMSO.

Common characteristics of aprotic solvents:

  • solvents that can accept hydrogen bonds
  • solvents do not have an acidic hydrogen centers (acetone and esters fail this criterion)
  • solvents dissolve organic salts such as tetraethylammonium iodide

Polar aprotic solvents are often essential for reactions that involve strong bases, such as reactions involving Grignard reagents or n-butyllithium. These reagents react with protic solvents:

C4H9Li + HOCH3 → C4H + LiOCH3

An example of a dipolar aprotic solvent is methylpyrrolidone.

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