Synthesis of Phosphites - Typical Routes and Problems

Substitution reactions of various trivalent phosphorus compounds with alcohols are common for the construction of the P-O bond in phosphites. Aryl 

An alternative but hkewise less frequently used strategy is the substitution reaction of phosphorous triamides (phosphortriamidites) with alcohols (Route III, amide method ) [58, 63, 64]. Mixed strategies are also possible under the condition that the substitution reactions can be performed stepwise [65]. Since all these reactions constitute equilibriums, the shift in favor of the phosphites has to be managed by additives and/or by the formation of particularly stable, for example, cyclic, products. The nucleophilic strength of alcohols can be enhanced by conversion into the corresponding metal alkoxides [66]. 

All three reactions are slightly exothermic. In general, a small excess of phenol is used. While the liberated HCl of the first two reactions evaporates under 

Occasionally, at the end of the condensation protocol, the excess PCI3 has been removed by co-distillation with benzene [73]. Residues of unreacted alcohol can be separated from the product via a column using an inert gas as desorbing agent [74]. 

Phosphites of lower molecular weight [triphenylphosphite, tris(nonylphenyl) phosphite] can be purified by distillation under vacuum. The yields are excellent. A serious problem during the production in the metric ton scale is caused by foam formation, which can be overcome by a special design of the distillation apparatus [69] or by performing the reaction in a solvent [75]. 

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