to the molecule number of the aromatic compound reacted each other hereinafter the ratio is referred to as iodine substrate aromatic compound ratio for simplicity was 59 4 mmoles 119 mmoles 0 5 also as an indicator of the reaction selectivity for the monoiodination and the diiodination the ratio of 4 iodobiphenyl 4 4 39 diiodibiohenyl hereinafter the ratio is referred to as mono compound di compound ratio for simplicity was used the results are shown in table 1 below also the relation of the iodine substrate ratio and the mono compound di compound ratio is shown in fig1 by following the same procedure as example 1 except that the amounts of biphenyl glacial acetic acid and distilled water were changed as shown in table 1 below the products were obtained and the purity of each product was determined the results are shown in table 1 also the relation of iodine substrate ratio and mono compound di compound ratio is shown in fig1 table 1______________________________________ solventbiphenyl acetic a a mono biphenyl i sub acid water water c di csample g ratio ml ml ratio ratio______________________________________1 18 32 0 5 50 50 1 66 52 10 0 0 917 80 80 1 23 43 11 45 0 8 25 25 1 26 34 13 09 0 7 40 40 1 38 05 13 09 0 7 25 25 1 33 06 18 32 0 5 70 17 5 4 38 37 18 32 0 5 25 25 1 74 98 30 54 0 3 25 25 1 128 79 18 32 0 5 90 10 9 30 5c 1 9 0 1 015.