Phosphonic acid,[9-chloro-3-(2-chloroethoxy)-6-(2-chloroethyl)-1,4-dimethyl-2,5,7-trioxa-3,6-diphosphanon-1-yl]-,8-chloro-2,5-bis(2-chloroethoxy)-1,4-dimethyl-3,6-dioxa-2,5-diphosphaoct-1-yl-2-chloroethylester,P,P',P'',P'''-tetraoxide