New polyamidation through the activation of amino groups with phenyl dichlorophosphite in pyridine

Polyamidation with phenyl dichlorophosphite (PDCP) as a new condensing agent was studied. A model reaction of benzoic acid and aniline with PDCP through a change in their addition order revealed that PDCP reacted with aniline more favorably than it did with the acid, and it could activate about 2 mol of aniline to produce benzanilide in a nearly quantitative yield. A preferential reaction with aniline occurred even in the presence of the acid. The reaction was applied to the polyamidation of dicarboxylic acids and diamines or of p ‐aminobenzoic acid (PABA) with 0.6 equiv of PDCP with respect to the amino groups in pyridine/ N ‐methyl‐2‐pyrrolidone in the presence of LiCl. Polyterephthalamides and polyisophthalamides with moderate inherent viscosity values were produced. The polycondensation of PABA was significantly promoted by the slow addition of PDCP over a period of 20–40 min and the presence of LiCl, producing poly( p ‐benzamide) with inherent viscosity values of about 2.4. Unsubstituted PDCP and PDCPs with an electron‐donating methoxy substituent afforded better results.