ither the 4 or 5 ringposition; and wherein R is an aliphatic radical having from 1-5 carbon atoms and is selected from the group consisting of lower alkyls and fluoro-substituted lower alkyls.It is within the scope of the invention to use mixtures of the 4- and 5-iodo isomers of the invention esters, said mixture being represented by the general formulae ##STR2## wherein --CH.sub.3 and --COOR are