Tetrapropylammonium Explained

Tetrapropylammonium (TPA) is a quaternary ammonium cation with the formula, also denoted (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.^[1]

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:

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^[2] and titanium-bearing TS-1 catalysts.^[3] After synthesis, TPA is removed by thermolysis.^[4]

The TPA salt tetrapropylammonium perruthenate (TPAP) is an effective and highly selective oxidiser, with numerous applications in organic synthesis.^{[5] [6]} Combined with a cooxidant, it serves as a catalyst for the oxidation of primary and secondary alcohols to aldehydes and ketones.

Notes and References

1. 10.1149/2.0671602jes . Electrochemical Stability of Quaternary Ammonium Cations: An Experimental and Computational Study . 2016 . Mousavi . Maral P. S. . Kashefolgheta . Sadra . Stein . Andreas . Bühlmann . Philippe . Journal of the Electrochemical Society . 163 . 2 . H74–H80 . 11858/00-001M-0000-0029-2301-3 . free .
2. 10.1039/C9CP05423E . Defining aluminum-zoning during synthesis of ZSM-5 zeolites . 2020 . Li . Teng . Krumeich . Frank . Chen . Ming . Ma . Zhiqiang . Van Bokhoven . Jeroen A. . Physical Chemistry Chemical Physics . 22 . 2 . 734–739 . 31832632 . 2020PCCP...22..734L . 20.500.11850/383611 . free .
3. 10.1021/acs.cgd.2c01291 . Tetrapropylammonium Hydroxide Treatment of Aged Dry Gel to Make Hierarchical TS-1 Zeolites for Catalysis . 2023 . Yang . Zhenyuan . Guan . Yanan . Xu . Lei . Zhou . Yangtao . Fan . Xiaolei . Jiao . Yilai . Crystal Growth & Design . 23 . 3 . 1775–1785 . 36879771 . 9983304 .
4. 10.1016/0021-9517(85)90224-6 . Influence of decomposition conditions of TPA-ZSM-5 on surface and catalytic properties of the resulting H a Na-ZSM-5 . 1985 . Choudhary . V. . Journal of Catalysis . 94 . 2 . 573–575 .
5. 10.1055/s-1994-25538 . Tetrapropylammonium Perruthenate, Pr₄N⁺RuO₄ ^-, TPAP: A Catalytic Oxidant for Organic Synthesis . 1994 . Ley . Steven V. . Norman . Joanne . Griffith . William P. . Marsden . Stephen P. . Synthesis . 1994 . 7 . 639–666 .
6. 10.1002/1521-3897(200009)342:7<728::AID-PRAC728>3.3.CO;2-I . Tetra-n-propyl Ammonium Perruthenate (TPAP) - an Efficient and Selective Reagent for Oxidation Reactions in Solution and on the Solid Phase . 2000 . Langer . Peter . Journal für Praktische Chemie . 342 . 7 . 728–730 .