Preparation of phosphonic acid derivatives
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United States of America Patent
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Apr 10, 2001
Grant Date -
N/A
app pub date -
Sep 5, 2000
filing date -
Jan 10, 1998
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Abstract
A method for the preparation of alkene phosphonic acids and salts thereof, such as VDPA (vinylidene diphosphonic acid) is disclosed. The products can be produced in a stable, substantially pure form and in high yield. The method includes the azeotropic removal of water from salts of .alpha.-hydroxy-alkane diphosphonic acid dimer or corresponding acids thereof, and the pyrolysis of the dehydrated reactant at a temperature of from 170.degree. C. to 300.degree. C. There may be included a step to convert anhydrides which have been formed during the pyrolysis. The method may include the use of heat transfer agents and/or bases, and may be carried out at elevated or reduced pressure.
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