In a three-necked round-bottomed flask equipped with a mechanical stirrer, a reflux condenser and a dropping funnel, the first P-O component (PIII-OH) is added under nitrogen protection. This P-O component (see column 5 of Table 1) may be selected from H3PO3, monoalkyl phosphite or mixtures thereof and may additionally comprise dialkyl phosphite. Subsequently, the first P-O component is heated to the temperature specified in column 11 of Table 1 (T° step a) for step a). Next, the second P-O component (see column 6 of Table 1) is added while maintaining the appropriate temperature. The mixture was allowed to react for the time indicated in column 13 of Table 1 (reaction time step a), followed by step b). The alcohol R1-OH (see column 3 of Table 1) is then added dropwise while maintaining the temperature specified in column 12 of Table 1 (T° step b). After the mixture was reacted for the time indicated in column 14 of Table 1 (reaction time b), it was cooled to room temperature and analyzed by 31P NMR.
