Thallation of anisole and phenetole with an equimolar amount of thallic trifluoroacetate in trifluoroacetic acid yields predominantly the para-thallated derivatives using short reaction times, but ortho-thallated species using long reaction times. With an excess of thallic trifluoroacetate, dithallation occurs and 2,4-bis[bis(trifluoroacetato)thallio]- anisole and -phenetole have been isolated. Each gives the corresponding 1 -alkoxy-2,4-diiodobenzene as the sole organic product on treatment with aqueous sodium iodide. Complete dithallation of thiophen has been achieved on reaction with an excess of thallic trifluoroacetate in acetonitrile, as indicated by quantitative formation of 2,5-diiodothiophen on treatment of that thallation product with aqueous iodide ions. Use of an excess of thallic trifluoroacetate in refluxing trifluoroacetic acid causes partial dithallation of toluene, m-xylene, and benzene.