Ionische und radikalische Dediazonierungen von Aryldiazoniumsalzen: Ein Beispiel für wellenlängenabhängige Photoreaktionen

Abstract

Die Photolyse von p‐substituierten Benzoldiazonium‐tetrafluoroboraten in Methanol bzw. Äthanol/Acetonitril liefert bei Einstrahlung in die Absorptionsmaxima der Diazoniumsalze (313 nm) höhere Mengen an ionisch entstandenen Dediazonierungsprodukten (ArOR und ArF), als nach der für Elektronenübertragungen gültigen Beziehung ΔG*=E 1/2Ox(Donor) − E 1/2Red (ArN 2+) − Ehv erwartet wird. Bei Wellenlängen > 330 nm oder in Gegenwart des auch bei 313 nm absorbierenden Donors Pyren werden dagegen überwiegend Reduktionsprodukte (die entsprechenden aromatischen Kohlenwasserstoffe) gebildet. Die Verhältnisse werden an Hand der von Salem u.a. entwickelten Symmetrievorstellungen erörtert. Es ergibt sich, daß die photochemische Dediazonierung von Aryldiazoniumsalzen wahrscheinlich aus dem schwingungsangeregten Grundzustand heraus erfolgt und demzufolge in einigen Fällen ähnliche Produktverhältnisse liefert wie die Thermolyse.

Experimental and Theoretical Studying of Photoconductivity of Polymeric Layers With Dyes

“…This phenomenon is characteristic for the twoquantum processes and confirms earlier obtained the results [5,6]. Note that when irradiated the sample through the filter UFS-1 rezazuryne concentration C=10 3 mol/l , it has been found the following relationship:…”

“…This phenomenon is characteristic for the two-quantum processes and confirms earlier obtained the results [5,6]. Note that Представлены результаты экспериментального и теоретического изучения фотопроводимости полимерных слоев с красителями.…”

“…To present time there are carried out numerous experimental and theoretical works data showing that the excitation relaxation processes in polymeric materials with different impurities do not prevent leakage of important science and practice processes in the highly excited states such as generation of carriers, photochemical and radiationchemical processes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Studying photo-conductivity of the polyacene linear crystals (anthracene, tetracene, pentatsen) showed that its high quantum efficiency is observed only under irradiation of the highly excited molecules when there is possible a birth of holes and free electrons.…”

Radical reactions of arenediazonium ions: An easy entry into the chemistry of the aryl radical

“…270 To further check the intermediacy of the aryl radical, even in the cuprous-induced reactions of diaryliodonium salts, an experiment has been attempted, making use of a competing mixture of Br" and Cl" in the presence of a cuprous salt and of a cupric salt271 (eq 85). A ^Cu(I) Ph2I+ + Br" + Cl" + Cu(II)--Phi + PhBr + PhCI (85) mixture of phenyl halides is obtained, from which a kBl/ka ratio of 3.2 is reckoned for the relative efficiency of transfer of bromide and chloride as ligands. A similar ratio (i.e., 2.9) is obtained when a stannous salt is employed as the reductant.…”

Dediazoniation of Arenediazonium Ions in Homogeneous Solution. Part XII. Solvent effects in competitive heterolytic and homolytic dediazoniations

“…We did not discuss dediazoniations in the presence of good electron-transfer reagents such as transition metal ions (footnote 5) nor did we discuss photolytic dediazoniations. However, Becker et al [40] recently discovered that some substituted benzenediazonium salts underwent predominant heterolytic decomposition in methanol or ethanovacetonitrile if irradiated at 313 nm, the absorption maximum of the diazonium ion, but when light of wavelengths longer than 330 nm was used, mainly homolytic products were formed. They assumed that heterolytic photochemical dediazoniations start from the vibrational excited ground state and that excitation of a charge transfer state between electron donors and arenediazonium salts gives rise to electron transfer and therefore to homolytic dediazoniation.…”