In the preparation of methylphosphonic acid, triethyl phosphite is first subjected to the Michel-Albuzov reaction to generate a pentavalent phosphorus center:
CH3Cl + P(OC2H5)3 → CH3PO(OC2H5)2 + C2H5Cl
The resulting dialkylphosphonate reacts with trimethylchlorosilane, and then the siloxophosphonate is hydrolyzed to produce the desired product.
CH3PO(OC2H5)2 + 2 Me3SiCl → CH3PO(OSiMe3)2 + 2 C2H5Cl
CH3PO(OSiMe3)2 + 2H2O → CH3PO(OH)2 + 2 HOSiMe3
ChEBI: Methylphosphonic acid is a one-carbon compound that is phosphonic acid in which the hydrogen attached to the phosphorus is substituted by a methyl group. It is a one-carbon compound and a member of phosphonic acids. It is functionally related to a phosphonic acid. It is a conjugate acid of a methylphosphonate(1-).
Methylphosphonic acid [993-13-5] M 96.0, m 104-106o, 105-107o, 108o, pK 1 2.12, pK 2 7.29. If it tests for Cl-, then add H2O and evaporate to dryness, repeat several times till free from Cl-. The residue solidifies to a wax-like solid. Alternatively, dissolve the acid in the minimum volume of H2O, add charcoal, warm, filter and evaporate to dryness in a vacuum over P2O5. [Kosolapoff J Am Chem Soc 75 3379 1953.] The di-Na salt is prepared from 24g of acid in 50mL of dry EtOH, and a solution of 23g Na dissolved in 400mL EtOH is added. A white precipitate is formed, but the mixture is refluxed for 30minutes to complete the reaction. Filter off the solid and recrystallise it from 50% EtOH. Dry the crystals in a vacuum desiccator. [Thompson J Chem Soc 3292 1952, Beilstein 4 IV 3498.]
