Process for the preparation 6-chloro-2,4,8,10-tetra-butyldibenzo[d,f][1,3,2]dioxaphoshepin

A process for the preparation of a compound of formula I ##STR4## wherein n has a value of 0 or 1;

• when n is 0, Q is a direct bond,
• when n is 1, Q is --CR.sup.1 R.sup.2 wherein each R.sup.1 and R.sup.2 independently represents hydrogen, straight chain alkyl of 1 to 18 carbon atoms, branched chain alkyl of 1 to 12 carbon atoms, phenyl, tolyl or anisyl;
• each Y.sup.1, Y.sup.2, Z.sup.2 and Z.sup.3 independently represents hydrogen, a straight or branched chain alkyl of 1 to 18 carbon atoms, bicycloalkyl of 7 to 10 carbon atoms, phenyl, benzyl, 1-phenylethyl, cyclohexyl, 1-methylcyclohexyl, cyano, halogen, nitro, trifluoromethyl, hydroxy, amino, alkanoyl of 2 to 18 carbon atoms, alkoxy of 1 to 18 carbon atoms or E.sup.1 E.sup.2 E.sup.3 Si where E.sup.1, E.sup.2 and E.sup.3 are independently hydrogen, alkyl of 1 to 4 carbon atoms or phenyl;
• which process comprises
• reacting a bisphenol of formula II ##STR5## with phosphorus trichloride in an organic solvent containing 1-methyl-2-pyrrolidinone, where the molar ratio of bisphenol to phosphorus trichloride is from 1:1 to 1:10, and the amount of 1-methyl-2-pyrrolidinone catalyst is from 1 to 20 mol percent, based on the bisphenol,
• maintaining the temperature of the solution from room temperature to about 150.degree. C., while passing a stream of nitrogen through the solution till the evolution of hydrogen chloride essentially stops, and
• isolating the phosphorochloridite product.