Tetrapropylammonium

Tetrapropylammonium (TPA) is a quaternary ammonium cation with the formula [N(C3H7)4]+, also denoted [NPr4]+ (where Pr = propyl group). It is a precursor to several significant industrial and laboratory catalysts.

Properties
TPA is chemically similar to other quaternary ammonium cations with saturated alkyl groups. As such, it is highly electrochemically stable, degrading only in the presence of particularly strong bases and nucleophiles.

It is isoelectronic with 4,4-dipropylheptane and the tetrapropylboranuide anion.

Synthesis
Like other quaternary ammonium cations, TPA is prepared by the alkylation of the corresponding ammonia analogue, tripropylamine. Treatment of the amine with a primary propyl halide such as n-bromopropane yields the corresponding TPA halide salt in a Menshutkin reaction:


 * (C3H7)3N + C3H7Br -> (C3H7)4N+Br-

The halide salts are then converted to the more industrially valuable hydroxide by reaction with aqueous silver oxide, electrolysis, ion-exchange resin, or electrodialysis.

Applications
The tetrapropylammonium cation is used as a structure-directing agent in the production of synthetic zeolites, in particular ZSM-5 and titanium-bearing TS-1 catalysts. After synthesis, TPA is removed by thermolysis.

The TPA salt tetrapropylammonium perruthenate (TPAP) is an effective and highly selective oxidiser, with numerous applications in organic synthesis. Combined with a cooxidant, it serves as a catalyst for the oxidation of primary and secondary alcohols to aldehydes and ketones.