Functional Applications of Alkylphosphine Derivatives
·
Anti-corrosion Agents:
Ionic liquids containing the very hydrophobic
trihexyl(tetradecyl)phosphonium cation in combination with
metal-coordinating phosphinate or phosphate anions are excellent
anti-corrosion agent for magnesium alloys such as AZ31. (Anti-Corrosion Agents
references)
·
Bio-transformations:
The use of enzymes and living cells in bio-reactors are
currently in commercial use. One drawback which limits
production rates and capacities is the toxicity of substrates
and/or products to the organisms. The use of biphasic reactor
systems where one phase acts as the substrate reservoir
alleviates the toxicity issue. Certain phosphonium-based ionic
liquids such as CYPHOS® IL 103 and 109 perform very
well in these applications. They have been demonstrated to be
compatible with enzymes and living cells for the bio-degradation
of waste aqueous phenol.
Read more.
Additionally, CYPHOS IL 109 can be used is a biphasic reactor
system in the dioxygenase-catalysed conversion of toluene to
2,3-dihydroxytoluene with minimal inhibitory effect on the
organism – E. coli.
Read more. CYPHOS IL 104 has been successfully
employed for the enzymatic hydrolysis of penicillin G to
6-aminopenicillanic acid.
Read more.
·
Clay Modification:
Long chain alkylphosphonium salts are very effective in
exfoliating Montmorillonite clays to render them compatible with
various monomers. Because of the high thermal stability of
phosphonium salts such exfoliated clays can be employed in high
temperature polymer applications such as modified nylon polymers
or vulcanizing rubber.
Read more.
(Clays Exfoliated with Phosphonium Salts
references).
·
Electrolytes:
The wide electrochemical window of ionic liquids makes them well
suited as electrolytes for various devices such as batteries,
capacitors and solar cells.
·
Lubricants:
The use of ionic liquids as lubricants is a relatively recent
application of these novel compounds as functional fluids. In
addition to their tribological properties and compatibility with
base oils, phosphonium-based ionic liquids have the highest
thermal stability. The phosphonium cation also lacks acidic
protons which results in low wear. CYPHOS IL 105 which has a
relatively low viscosity and high viscosity index is one of the
more effective lubricants.
(Phosphonium Ionic Liquids as Lubricants
references)
·
Metal Extraction:
CYPHOS IL 101 (trihexyl(tetradecyl)phosphonium chloride) either
in a diluents or immobilized on a solid support can be used to
extract various metals such as Pd, Pt, Hg, Au, Bi, Zn and a
variety of actinides and rare earths. In addition, CYPHOS IL 101
is an effective extractant to remove iron from iron/nickel
solutions. (Phosphonium Ionic as Metal Extractants
references)
·
Metal Surface Treatment:
As a result of the polar nature of the weak phosphinic and
phosphonic acids, they coordinate with various metal surfaces.
Thus phosphinic and phosphonic acids can perform as coupling
agents. In addition, CYPHOS SM 194
(2,4,4-trimethylpentylphosphonic acid), when applied as a thin
film on metal dies, is a very effective mold release agent.
·
Nano-Particle Synthesis:
Since their inception in the early 90’s, the preferred solvent
to for the synthesis of cadmium sulfide, selenide and telluride
nano particles (quantum dots) has been trioctylphosphine.
Cytec‘s CYTOP®
380 is the only industrial scale source of this
solvent. To enhance their properties and to prevent
agglomerization, the quantum dots are typically coated with a
layer of a tertiary alkylphosphine oxide, phosphinic acid or
phosphonic acid. Tri octylphosphine oxide as well as
tetradecylphosphonic acid have historically been used for this
purpose and more recently bis 2,4,4-trimethylpentylphosphinic
acid. Cytec is the main industrial supplier of trioctylphosphine
oxide (CYANEX®
921) as well as for bis 2,4,4-trimethylpentyl
phosphinic acid (CYANEX 272). Lately, phosphonium-based ionic
liquids have also been used as a solvent to prepare
nano-particles.(Nano Particle Synthesis
references)
·
Phase Transfer Catalysis:
The traditional application of tetra alkylphosphonium salts has
been for phase transfer catalysis (PTC). While ammonium
quaternary salts are more commonly used as PTCs, the much
enhanced thermal stability of phosphonium salts lends them to be
much more valuable for high temperature applications.
Conversely, any PTC application that has slow kinetics at low or
moderate temperatures may have enhanced rates when run at higher
temperatures. (Phase Transfer
Catalysts references)
·
Plasticizers:
The higher molecular weight alkylphosphonium salts such as
CYPHOS IL 101, 103, 201, 202, 203 and 204 are very effective as
plasticizers for such polymers as PVC. In addition, these
products are leach and migration resistant. (Plasticizer
references)
·
Reaction Solvents:
The other major application for ionic liquids is as novel
reaction solvents. In many reactions which perform well in “normal”
molecular solvents (i.e., where yields are high and with easy work up),
there is no need to convert to a more expensive “ionic liquid”
solvent. However, there are many reaction classes in which the
use of a phosphonium ionic liquid will dramatically increase
yields, reduce the reaction time, and provide an easier
work up. Reactions that especially benefit from the use of a phosphonium ionic liquid are the Heck and Suzuki reactions. With
the appropriate process engineering designs, the ionic liquid
and the expensive palladium catalyst can be recycled many times
with negligible effect on the reaction kinetics and yields. (Heck
/ Suzuki references)
Other significant reactions which can be carried out in
phosphonium ionic liquids are: hydroformylation (Hydroformylation
references), hydroamination (Hydroamination
references), Michael addition, Henry reaction,
oxidations, reductions, Diels-Alder, esterification, nitration, radical polymerization, bio-transformation reactions (with
living cells or enzymes), and even Grignard reactions. (additional
references)
The
thermal stability and low vapor pressure of ionic liquids
provide an easy method of recovering volatile products and/or
starting materials.
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