4-chloro-2-methylphenol (142.5 g) was dissolved in a mixture of hexane (200 cm3) and toluene (400 cm3) and sodium hydride (30.0 g of 80% suspension in mineral oil) was added. After stirring for 3 hrs, this suspension was added during 2 hr to a stirred solution of thiophosphoryl chloride (84.5 g) in hexane (100 cm3). The mixture was stirred for a further 18 hrs at ambient temperature, then diluted with ether (1000 cm3), filtered, and concentrated by distillation of solvents under reduced pressure yielding crude bis (4-chloro-2-methylphenyl) chlorothiophosphate, a brown oil (192 g). 31PNMR, singlet, 57 ppm). Some of this compound was converted to the thiophosphoramide by reaction with ammonia as described in Example 9 (31PNMR, singlet 62.7 ppm) sodium hydride (2.07 g, 80% suspension) was added to a stirred solution of the thiophosphoramide (10.4 g) and the chlorothiophosphate (11.4 g) in dry tetrahydrofuran (50 cm3). Stirring at ambient temperature was continued for 18 hrs. The solvent was distilled under reduced pressure and the residue was taken up in hexane and the suspension was filtered. Purification by extraction into 5% aqueous methanol and back extraction as described in Example 15, gave tetrakis (4-chloro-2-methylphenyl) thioimidodiphosphate (9.4 g), (31P NMR, singlet, 49.3 ppm) a brown oil of 81% purity as estimated by titration (MW711). The product of Formula I in which R1 =R2 =R3 =R4 =4-chloro-2-methylphenoxy was examined as an extractant by Tests 2 and 3 with the results listed in Tables 2 and 3 respectively, which show that it is a stronger extractant for zinc than the substituted phenoxy derivatives of Examples 9, 14 and 15 and that it has has good selectively over iron.
