Isomer distribution data are reported for the addition of tritium atoms, generated by photolysis of thiophenol-/, to monosubstituted benzenes at 40°. These data are combined with literature values of the total rate constant for the addition of H atoms to substituted benzenes, and relative rate constants are calculated for the rate of addition to the ortho, meta, and para positions (so called partial rate factors). A Hammett correlation of the meta and para partial rate factors gives a p of -0.24 ± 0.09; a correlation of meta data only gives a p of -0.28 ± 0.12. These p values are compared with values derived from studies of H atoms generated by aqueous radiolysis. A compilation is given of Hammett p values for the abstraction of hydrogen from the benzylic position of toluenes by various free radicals and the addition of radicals.to monosubstituted benzenes. Unexpectedly, the p values for the two reactions are quite similar for the five of the six radicals for which both p values are known; it is suggested that this similarity may be general. The use of the Hammett equation to correlate radical reactions is discussed.The hydrogen atom adds to aromatic compounds to form a cyclohexadienyl radical.3-7 Kinetic data for this reaction (eq 1) have been published from a X ortho, meta, and para isomers number of laboratories using aqueous solutions of the aromatic compounds and high energy radiolysis of water to generate the H atoms. The techniques used in these studies give the total rate constant for eq 1 and do not distinguish the partial rate constants k0, km, and kp for addition to the carbons ortho, meta, or para to the X substituent. Despite the fact that the fraction of the hydrogen atoms which add to each of the three isomeric positions in the aromatic compounds was not determined, the data for eq 1 have been correlated using the Hammett equation. Since it was not possible to decide whether am or values should be used with the data available, Anbar, Meyerstein, and Neta8 and Neta and Schuler9 correlated the values of ktotal with both meta and para values. Using this method, they obtain Hammett correlations with p values of -0.7 and -0.4,(1) This research was supported in part by National Institutes of Health Grant 11908 and National Science Foundation Grant GP 3820.(2) This publication is part VI in the series, "Reactions of the Hydrogen Atom in Solution." Previous publications in this series: (a) part I, W.

A mixture of acetic and sulfuric acids converts haematoporphyrin into a complex mixture of porphyrins of which the main product has been characterized as the diacetate (1g). Other compounds identified in the reaction mixture were the known vinylporphyrins (1b-d), (1h) and (li) and the isomeric monoacetoxyethyl(monohydroxyethyl)porphyrins (11) and (1m). Analysis of the reaction mixture was complicated by the presence of 1'-ethoxyethyl derivatives (1e) or (1f), (1j) and (1k)which presumably arose by solvolysis of the corresponding acetate with ethanol present in the chloroform used for the chromatographic separation.

Several polyhydroxy- and polyacetoxy-porphyrins have been prepared and their properties studied as part of an investigation to find suitable porphyrins for use in the detection and/or treatment of malignant tumours. Low solubility in aqueous media has so far prevented a clear assessment of their biological properties.

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Ausgehend vom Pyrrol (Ia) wird über die Stufen (Ib), (IIa)‐(IId) das 5‐Acetoxy‐methylderivat (III) dargestellt, das in das Porphyrin (IVa) [nachfolgende Hydrolyse →(IVb)] übergeführt wird.