When hemin, bile pigments, and a large number of dipyrrylmethanes and dipyrrylmethenes are treated with H2O2, followed by NaOH-Na2S2O4, red colored substances are formed with a characteristic absorption band at wave length 525 m[mu]. This is called the pentdyopent reaction, and the name pentdyopent is suggested for the red colored substances. The pentdyopents may be formed from the so called propentdyopents. Propentdyopent VI, 4,3[image]-dimethyl 3,4[image]-diethyl-5, 5''-dioxy-dipyrryl-methanol, is formed from etiohemin I, by treating a CHCl3 soln. of the latter compound at [long dash]10[degree] with MeONa, followed by H2O2. The propentdyopent forms white crystals, decomposing at 155[degree], absorption band at 523 m[mu]. Propentdyopent X, 4,4''-dimethyl-3,3''-diethyl-5,5''-dioxy-dipyrryl-methanol can be formed from 4,4''-dimethyl-3,3''-diethyl-5,5''-dicarboxy-pyrromethane, by dissolving the latter in 20% NaOH soln., adding H2O2, and allowing the mixture to stand in the ice box for some wks. The crystals decompose at 209[degree], the absorption band being at 521 mu. Propentdyopent X may also be prepared from 4,4''-dimethyl-3,3''-diethyl-5,5''-dibrom-pyrromethene, by refluxing the methene with a mixture of anhydrous KOAc in HOAc, followed by treatment with NaOH soln. Pentdyopent may be prepared from either propentdyopent VI or X. A conc. soln. of the propentdyopent in 10% NaOH is prepared, which is reduced with Na2S2O4, or ascorbic acid, or hydrogenated with a Pt catalyst. From these solns. red, prismatic crystals separate which are unstable in the air, have a yellow luster in indicent light and show typical dichroism. The crystals dissolve in pyridine, alc. and H2O with gradual loss of color. Pentdyopent may be a dioxypyrromethene. Cu and Zn salts of propentdyopents may also be prepared. Propentdyopents are found in the urine and gallstones of man and animals. These propentdyopents are formed from urobilin and bili-rubin, perhaps in the kidneys.