Methylphosphonic acid
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| ImageFile = methylphosphonic_acid.svg
| ImageSize =
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|Section1={{Chembox Identifiers
| CASNo = 993-13-5
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 329W4YM10Z
| EINECS = 213-607-2
| PubChem = 13818
| ChemSpiderID = 13220
| SMILES = CP(=O)(O)O
| InChI = 1/CH5O3P/c1-5(2,3)4/h1H3,(H2,2,3,4)
| InChIKey = YACKEPLHDIMKIO-UHFFFAOYAB
| StdInChI = 1S/CH5O3P/c1-5(2,3)4/h1H3,(H2,2,3,4)
| StdInChIKey = YACKEPLHDIMKIO-UHFFFAOYSA-N
| RTECS =
| MeSHName = C032627
| ChEBI = 45129
| KEGG = C20396}}
|Section2={{Chembox Properties
| Formula = CH5O3P
| MolarMass = 96.02
| Appearance = White Solid
| Density =
| MeltingPtC = 105 to 107
| BoilingPt =
| Solubility = }}
|Section3={{Chembox Hazards
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Methylphosphonic acid is an organophosphorus compound with the chemical formula CH3P(O)(OH)2. The phosphorus center is tetrahedral and is bonded to a methyl group, two OH groups and an oxygen. Methylphosphonic acid is a white, non-volatile solid that is poorly soluble in organic solvent but soluble in water and common alcohols.{{cite web|title=methylphosphonic acid - Compound Summary|url=https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=13818|publisher=NCBI|accessdate=12 December 2013}}
Preparation
Methylphosphonic acid can be prepared from triethylphosphite by first using a Michaelis-Arbuzov reaction to generate the phosphorus(V) centre:{{cite journal|last1=Katritzky|first1=Alan R.|authorlink1=Alan R. Katritzky|last2=Pilarski|first2=Boguslaw|last3=Johnson|first3=Jack W.|pages=209–213|year=1989|doi=10.1080/00304949009458197|title=A One-Pot Procedure For the Preparation of Phosphonic Acids From Alkyl Halides|journal=The New Journal for Organic Synthesis|volume=22|issue=2}}
:CH3Cl + P(OC2H5)3 → CH3PO(OC2H5)2 + C2H5Cl
The resulting dialkylphosphonate is then treated with chlorotrimethylsilane before hydrolysis of the siloxyphosphonate to generate the desired product.
:CH3PO(OC2H5)2 + 2 Me3SiCl → CH3PO(OSiMe3)2 + 2 C2H5Cl
:CH3PO(OSiMe3)2 + 2H2O → CH3PO(OH)2 + 2 HOSiMe3
The reaction pathway proceeds via the siloxyphosphonate intermediate due to the difficulty in directly hydrolysing dialkylphosphonates. Katritzky and co-workers published a one-pot synthesis of methylphosphonic acid in 1989.