Phosphine,
also called Hydrogen Phosphide, PH3, is a colourless,
poisonous, spontaneously flammable gas, with a disagreeable, garlic-like odour;
melting point -133.5 C, boiling point -87.4 C. Phosphine is manufactured by the
hydrolysis of metal phosphides, by the electrolysis of phosphorus in the
presence of hydrogen, or by the phosphorus-steam reaction. Phosphine has the
structure of ammonia (NH3) but with phosphorus
in place of nitrogen. It is slightly soluble in cold water and soluble in
alcohol. Phosphine is less soluble in water than ammonia. Phosphine is used in
the synthesis of organophosphines and phosphonium derivatives and as a dopant in
the manufacture of semiconductors. Aluminium or magnesium phosphide are used
as formulations prepared for fumigation in pest control, and zinc phosphide
is used as a rodenticide. Phophene is a starting material
for the preparation of
pesticides and flame retardants. Organophosphines are used as solvents for the extraction
and separation processes, flame retardants, and in formulating fumigants and
electronics applications of semiconductor manufacturing. Tertiary
alkylphosphines act as chemical intermediate and catalyst in the production of
industrial acids, alcohols, flavors & fragrances, and pharmaceuticals.
Phosphonium describes a univalent radical, PH4.
Quaternary phosphonium salts, obtained from tertiary
alkylphosphines with the treatment with alkyl or aromatic halides, are replacing
phase transfer catalysts and biocides functions for quaternary ammonium salts due
to more effective performance and higher thermal stability. Phosphonium salts
are used as epoxy curing agents. A variety
of phosphine transition metal complexes including chiral complexes are
synthesized as the very reactive and versatile homogeneous catalysts and
stereospecific as well. |
'Phase transfer
catalysis (PTC)' methodology is a powerful tool improving process efficiency,
product selectivity and providing mild reaction conditions in organic chemical
reactions. In many chemical reaction situations, there are different species
(immiscible liquids or solid and liquid) which don't react each other due to
separation by an interface. Small quantity of ‘phase-transfer catalyst’,
involves a substrate (soluble in the organic layer) and an anionic reagent or a
nucleophile (dissolved in the aqueous layer), extracts one of the reactants,
most commonly an anion, across the interface into the other phase where reaction
can take place with the substrate and reaction can proceed. The quaternary
ammonium salts can carry the nucleophile from the aqueous to organic phase and
are used as the most commonly used as phase-transfer catalyst’. The phosphonium
derivatives favoring higher thermal stability property are also used. Crown
ethers and polyethylenglycol compounds are also widely used in this
application. |