Kolloidchemie und Photochemie

Ohne Zusammenfassung     

Pteridine. Teil LXXX. Synthese,Reaktionen und Photochemie von Pteridinthionen

Synthesis, Reactions, and Photochemistry of Pteridinethiones The pteridine-6(5H)-thione 1 and various pteridine-7(8H)-thiones ( 13, 22, 26 ) have been synthesized, and their photochemical reactivity has been investigated under aerobic conditions. The formation of different photooxidation products is pH-dependent. In acidic to neutral media, disulfides ( 2, 15, 23, 29 ) are formed, whereas neutral to alkaline solutions favour the formation of pteridinesulfinic ( 3, 17 ) and -sulfonic acids ( 6, 16, 24, 30 ). Prolonged irradiation of the disulfides 2 and 15 led to the intensively yellow fluorescing bis(thio)dilumazines 19 and 20 , respectively.     

Photochemie heterocyclischer enone—I : Photolyse und thermolyse von nalidixinsäure

The photolysis of nalidixic acid 1 in alkaline oxygen free solution was studied in the range up to 40000 cm^?1. The decarboxylation product 2, carbondioxide 3, ethylamine 4, and a new diketone 5 were isolated and identified—Thermolysis of nalidixic acid 1 was studied in the melt and in paraffin oil solution in the absence of oxygen. Besides the decarboxylation product 2, a dimer was isolated from this reaction. A structure for the dimer is proposed on the basis of masspectral and ¹H NMR-studies. A reaction scheme for the photolysis and thermolysis of 1 is proposed.     

Zur Photochemie von 1H- und 2H-Indazolen in saurer Lösung

On the Photochemistry of 1H- and 2H-Indazoles in Acidic Solution It is shown that 1H- and 2H-indazoles (cf. Scheme 2) on protonation (0, 1N H₂SO₄ in water or alcoholic solution) give analogous indazolium ions (see Fig. 1 and 2) which on irradiation undergo heterolytic cleavage of the N (1), N (2) bond whereby aromatic nitrenium ions in the singlet ground state are formed (cf. Scheme 13). If the para position of these nitrenium ions is not occupied by a substituent (e.g. a methyl group) they are readily trapped by nucleophiles present (e.g. water, alcohols, chloride ions) to yield the corresponding 5-substituted 2-amino-benzaldehydes or acetophenones (cf. Schemes 4–10). Photolysis of indazole ( 4 ) and 3-methyl-indazole ( 5 ) in 0,75N H₂SO₄ in alcoholic solutions gives in addition minor amounts of the corresponding 3-substituted 2-amino-benzaldehydes and acetophenones, respectively (cf. Schemes 6 and 8 and Table 2). Phenylnitrenium ions carrying a methyl group in the para position give in aqueous sulfuric acid mainly the reduction products, i.e. 2-amino-5-methyl-benzaldehydes (cf. Schemes 11 and 12 and Table 3). In methanolic sulfuric acid, in addition to the reduction products, 6-methoxy substituted benzaldehydes are found (cf. Schemes 11 and 12 and Table 3) which are presumably formed by an addition-elimination mechanism (cf. Scheme 18). It is assumed that precursors of the reduction products are the corresponding nitrenium ions in the triplet ground state. Singlet-triplet conversion of the nitrenium ions may become efficient when addition of nucleophiles to the singlet nitrenium ions is reversible (cf. Scheme 22) thus, enhancing the probability of conversion or when conjugation in the singlet nitrenium ions is disturbed by steric effects (cf. Scheme 20) thus, destabilizing the singlet state relative to the triplet state.     

Untersuchung der Photochemie von Polyenen mit Hilfe von mikroprozessor-gesteuerter HPLC

Ohne Zusammenfassung

---

Photochemical examination of polyenes by microprocessor controlled HPLC

---

Wir danken Frau Prof. Breyer-Pfaff für die Moglichkeit, im Institut für Toxikologie Densitogramme aufnehmen zu konnen, und der Deutschen Forschungsgemeinschaft für personelle und finanzielle Unterstiitzung.