Phosphite-Lithium Chloride System

The polycondensation reaction of p-ABA has been carried out in various solvents capable of solvating LiCl, and results are compiled in Table 9, which reveals that carboxamide solvents such as NMP or N,N-dimethylacetamide are effective whereas no polyamides are obtained in DMF, DMSO or in ethers such as diglyme. It is assumed that solvents may affect the formation and the reactivity of 8 and/or 9 as described as follows (11 and 12)  

Various polyamides have been prepared in quantitative yield by carrying out the polycondensation reaction with triphenyl phosphite in NMP containing 4 wt-% LiCl (Table 10). The combination of adipic acid and diamines, especially 4,4 -diaminodi-phenyl ether, yields polymers of high viscosity, whereas the use of aromatic dicar-boxylic acids affords polyamides of lower viscosities, probably because of slow ami-nolysis of 12. 

The polycondensation reaction is more profitably utilized in the preparation of polyhydrazides and poly(amide-hydrazides) with high molecular weights 19 which are difficult to be produced by the phosphorylation reaction with triphenyl phosphite and pyridine20. The results of the polycondensation reaction of p-aminoben-zoylhydrazide(p-ABH) with dicarboxylic acids in the presence of triphenyl phosphite and LiCl are listed in Table 11. 

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The highly functionalized imidazole 3 can be polymerized by active phosphite ester methods [4] to afford the A-B polyamide. The monomer is dissolved in a mixed solvent system of N-methylp3n rolidinone and pyridine containing dissolved lithium chloride. Upon addition of triphenyl phosphite, the reaction immediately takes on a yellow color. During the course of the polymerization, the color increases in intensity until the pol5rmerization mixture appears black. The products are isolated as fine yellow powders by precipitation in methanol followed by a methanol wash. 

This type of reaction was first applied to the preparation of polyamides, as discussed above, for which it is somewhat more effective in forming high molecular weight polymers, but it has now been used for the synthesis of a wide variety of aromatic polyesters, either by the self-condensation of hydroxyacids or by the co-condensation of dicarboxylic acids and difunctional phenols.A fairly wide variety of phosphorous compounds can be used as reducing or dehydrating agents in these reactions, in addition to phosphines, including phosphites, chlorophosphates, phosphates, polyphosphates and phosphazenes. In most cases, lithium chloride is added and the reaction is run in either pyridine or an amide solvent system. The reaction has also been found to be catalyzed by tertiary amine salts. 

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