Phosphonates
Phosphonates and phosphonic acids are organophosphorus compounds containing C−PO(OH)2 or C−PO(OR)2 groups (where R = alkyl, aryl). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly soluble in organic solvents, but soluble in water and common alcohols. Many commercially important compounds are phosphonates, including glyphosate, the herbicide "Roundup", and ethephon, a widely used plant growth regulator. Bisphosphonates are popular drugs for treatment of osteoporosis.
In biology and medicinal chemistry, phosphonate groups are used as stable bioisoteres for phosphate, such as in the antiviral nucleotide analogue, Tenofovir, one of the cornerstones of anti-HIV therapy.
Phosphonates feature tetrahedral phosphorus centers. They are structurally closely related to (and often prepared from) phosphorous acid.
Phosphonate salts are the result of deprotonation of phosphonic acids, which are diprotic acids:
Phosphonate esters are the result of condensation of phosphonic acids with alcohols.
Several methods exist for the preparation of phosphonic acids and their salts.
Most processes begin with phosphorous acid (aka phosphonic acid, H3PO3), exploiting its reactive P−H bond.
Phosphonic acid can be alkylated under Mannich conditions to give aminomethylated phosphonates, which are useful as complexants. One example is the industrial preparation of nitrilotris(methylenephosphonic acid):
Phosphonic acid also can be alkylated with acrylic acid derivatives to afford carboxyl functionalized phosphonic acids. This reaction is a variant of the Michael addition:
Phosphonic esters are prepared using the Michaelis–Arbuzov reaction. For example, methyl iodide catalyses the conversion of trimethylphosphite to the phosphonate ester dimethyl methylphosphonate:
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