H2N  CN HN•C:NH HN•C•NH2 HN•C•N Various thiopurins have been obtained by E .

Fischer (Ber., 1898, 31, p . 431), principally by acting with potassium sulphydrate on chlorinated purin compounds . 2.6.8-Trithiopurin is obtained from the corresponding trichlorpurin and potassium sulphydrate . It forms a light yellow mass which carbonizes on heating . It is almost insoluble in water and alcohol; but readily dissolves in dilute solutions of the caustic alkalis and of ammonia . Much work has been done by J . Tafel (Ber., 1900, seq.) on the electrolytic reduction of the members of the purin group . The substance to be reduced is dissolved in a 50–75% solution of sulphuric acid and placed in a porous cell containing a lead cathode, the whole being then placed in a 2o–6o% solution of sulphuric acid in the anode cell . It is found that xanthine and its homologues take up four atoms of hydrogen per molecule and give rise to the so-called desoxy-compounds, which are stronger bases than the original substances . Uric acid takes up six hydrogen atoms per molecule and gives purone, C5HEN402, and it is apparently the oxygen atom attached to the carbon atom number 6 which is replaced by hydrogen, since when purone is heated with baryta, two molecules of carbon dioxide are liberated for one of purone . Consequently purone must contain two urea residues, which necessitates the presence of the> CO groups in positions 2 and 8 .

(F . G . P .