Heinz G. O. Becker

Relais-synthesen von heterocyclen—II : Neue synthesen von 3-amino- und 3-hydrazino-pyridazinen

Zusammenfassung Das 4-Aminotriazol enthalt formal die Struktureinheiten des Formamidins, Formamidrazons bzw. Formhydrazidins. Durch Verknupfung des 4-Amino-1,2,4-triazols mit dem Ringsystem des Pyridazins (Kondensation mit β-Diketonen), Quaternierung des erhaltenen s-Triazolo-[4.3b]-pyridazins und anschliessende alkalische Hydrolyse gelingt es, den Triazolring selektiv aufzuspalten. Aus den Alkyl-oder Benzylquaternierungsprodukten erhalt man die entsprechenden 3-(β-Formyl-β-alkyl-hydrazino)-bzw. 3-(β-Formyl-β-benzyl-hydrazino)-pyridazine. Wenn mit α-Halogentketonen, α-Chloracetonitril oder α-Chloressigsaureester quaterniert wurde, fuhrte die nachfolgend alkalische Hydrolyse nicht nut zur Spaltung des Triazolrings sondern auch zu einer N—N-Bindungsspaltung und ergibt die entsprechenden 3-Aminopyridazine. Es wird bewiesen, dass die Quaternierung der verwendeten s-Triazolo-[4.3b]-pyridazine am N-2-Atom erfolgt und die Reaktionsprodukte die formulierte Struktur besitzen. Es wird eine Anzahl von Derivaten des Pyridazins durch diese neue Methode hergestellt.

Photoinduced electron transfer between aromatic hydrocarbons and arene diazonium salts in micellar solutions

Abstract In micellar sodium dodecylsulfate (SDS) solution ground-state charge-transfer complexes between aromatic hydrocarbons and diazonium salts can be detected by UV absorption. The hydrocarbon fluorescence quenching occurs by both static and dynamic mechanisms and can be described by an established kinetic scheme.

Evidence for the marcus inverted region of back-electron-transfer in solution by means of chemically induced dynamic nuclear polarization

In order to detect the Marcus inverted region in electron-transfer reactions in solution it is more appropriate to follow not the forward but the back reaction. This can be done by means of chemically induced dynamic nuclear polarization, measuring the polarization of re-formed educts. The 13C-CIDNP enhancement factors V(13C) of re-formed arene diazonium salts in the photochemical electron transfer from singlet-excited rubrene to a series of para-susbstituted benene diazonium tetrafluoroborates in chloroform have been determined. On plotting V(13C) against the standard free reaction enthalpies of the back-electron-transfer, bell-shaped behaviour of the Marcus type is obtained. Taking the reorganizational energy (λ= 0.81eV) from the maximum of this curve the Franck–Condon factors FFC= exp (–ΔG‡/RT) were calculated according to the Marcus quadratic equation, which, on plotting against V(13C), give a linear correlation. The Franck–Condon factors (0, 2,…,1) show that the back-electron-transfer proceeds with nearly the theoretical maximum value k0.

CIDNP Effects of Sensitized Photochemical Dediazoniation of Arene Diazonium Salts Manipulating CIDNP Intensities by the Experimental Conditions

13C and 15N photo-CIDNP effects were determined for the reversible electron transfer from pyrene to arene diazonium salts on excitation of the charge transfer band at 360 nm. The diazonium salts being the products of back electron transfer (“cage products”) show enhanced absorption for 13 C(1) and the 15N-enriched diazonium group, whereas the escape products, ArH or 15N2, respectively, yield emission signals. It was shown that the intensities of the CIDNP effects depend on the rates of intersystem crossing kisc within the geminate radical pair, i.e. on the magnetic nucleus used as a probe of the CIDNP effect. Using 1H, 13C or 15N the time domain of observation can be manipulated in the ranges of 90-100 ns, 15-20 ns and 3-5 ns, respectively. Furthermore, the CIDNP intensities depend on the proper balance of the rate of electron back transfer, k-e, and the rate kp of formation of the escape product. Since k-e increases with increasing energy of the geminate radical pair, this balance and therefore the CIDNP intensities vary according to the substituent present and the electron donor used