Three meso-tetra(o-substituted phenyl)porphins have been prepared by the Rothemund reaction, and a by-product has been isolated from one reaction mixture. The mechanism of the Rothemund reaction is discussed.

[18]Annulene 1,4:7,10:13,16-trisulphide has been synthesized. It has been found to be a stable non-planar non-aromatic system in which the three thiophen rings are linked by three essentially olefinic vinylene groups.

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Pyrolyscs of toluene, ethylbenzene, propylbenzene, and b u tylbeuzene have given the compounds listed in thc Table . The yields of higher p l ycyclic hydrocarbons varied with the nature of the aliphatic side chain, arid mechanisms of formation based on scission of molecules to radical intermediates and re-synthesis are proposcd. The highest yields of the carcinogenic hydrocarbons 3,4-benzopyrene and 3,4-benzofluoranthene were obtained from butylbenzene.

The linear heterocyclic compounds pyrazine, quinoxaline, phenazine, 2 : 3-benzophenazine, etc., have been compared with their carbocyclic analogues, and Dutt's claim (J., 1926, 1179) to have prepared 5 : 7 : 12 : 14tetra-azapentacene (VII) and 5 : 7 : 9 : 14 : 16 : 18-hexa-azaheptacene (VIII) is disputed. A dihydro-derivative of (VII) has been prepared by a number of methods, and has been given the structure (IX). On reductive acetylation it gave 5 : 7 : 12 : 14-tetra-acetyl-5 : 7 : 12 : 14-tetrahydro-5 : 7 : 12 : 14-tetraazapentacene (XI). Mild oxidation failed to give the aromatic structure (VII), and more vigorous oxidation gave 5 : 7 : 12 : 14-tetra-azapentacene-6 : 13-quinone (XII), which was converted into 6 : 13-diacetoxy-5 : 7 : 12 : 14tetra-acetyl-5 : 7 : 12 : 14-tetrahydro-5 : 7 : 12 : 14-tetra-azapentacene (XIII) on reductive acetylation. The quinonoid dihydro-compound (IX) seems to be more stable than the aromatic structure (VII).IT is well known that in the series of linear benz-homologues of benzene, namely, benzene, naphthalene, anthracene, naphthacene, pentacene, etc., there is a very pronounced increase in the " reactivity " of the meso-positions as the number of rings increases. This is also correlated with the increased stability of the meso-dihydro-derivatives, with an increasing shift in the positions of the absorption bands towards the red, and with an increasing depth of the colours of the compounds themselves (Clar, '' Aromatische Kohlenwasserstoffe," Springer-Verlag, * Part 111, preceding paper.

A number of azoxy-derivatives have been isomerised to o-hydroxyazoderivatives by exposure to sunlight, the oxygen atom migrating from nitrogen to the further nucleus. An intramolecular mechanism is therefore proposed.The supposed red " isomers " of the azoxynaphthalenes are mixtures. CUMMING and STEEL (J., 1923, 123, 2464) reported that exposure of yellow 1 : 1'-azoxynaphthalene to sunlight or ultra-violet light rapidly converted it into a red form. A similar change was claimed for 2 : 2'-azoxynaphthalene (Cumming and Ferrier, J., 1924, 125, 1108). In each case the two forms had identical or almost identical melting points, and it was suggested that they were structural isomers. On the other hand, many azoxycompounds (including 1 : 1'-azoxynaphthalene) are known to be converted into o-hydroxyazo-compounds by prolonged exposure to light (Cumming and Ferrier,