Purification Methods
This fireproofing agent, and ingredient for making polymers, is obtained as a syrup on hydrolyzing vinylphosphonyl dichloride with cold H2O and solidifies on prolonged drying over P2O5/KOH. When distilled at 235-240o/0.0006mm, it gives the anhydride (d 1.304, n 1.5874) [Kabachnik & Medvedi Izvest Akad Nauk SSSR, Ser Khim 868 1953, Chem Abstr 54 10834 1960]. It is best kept as the sodium salt (m 350o) which precipitates when a solution of EtOH containing NaOEt (from 2g of Na) is added to vinylphosphonic acid (3.2g), and is recrystallised from EtOH (5.1g, quantitative). The p-anisidinium salt forms mauve prisms m 250o (from EtOH/Et2O). The dimethyl ester, M 136.1, d4 1.1405, nD 1.4330, has b 72.5o/10mm and 197-202o/760mm. [Kabachnik et al. J Gen Chem USSR (Engl Trans) 33 375 1963, Beilstein 4 IV 3568.]
