Isomerization of Azo Compounds. Cleavage Recombination Mechanism of Azosulfides

Abstract

(Z)-4-Nitrophenyl tert-butylsulfide [(Z)-4-NO2−1], upon formation of its radical anion, isomerizes to the (E)-isomer at a very fast rate of 6.3 × 106 s-1, about 103 times faster than azobenzene, while the 4-fluoro tert-butylsulfide (4-F−1) cleaves without isomerization. The particular behavior of 4-NO2−1 is related to the occurrence of a cleavage recombination mechanism, different from the usual inversion rotation mechanism. The existence of a reversible cleavage for the radical anion of 4-NO2−1 bears consequences on the mechanism of SRN1 reactions of azosulfides; the attack of the nucleophile would take place on the intermediate diazenyl radical and not on the ensuing aryl radical as previously proposed.

Smart Electrospun Nanofibers for Controlled Drug Release: Recent Advances and New Perspectives

“…Below 315 nm, the ultra-violet (UV) light is not suitable for therapeutic purposes since the high-energy photons start to damage DNA directly [123]. Light-responsive drug-loaded electrospun nanofibers (L-RDLEF) have attracted much attention because of their fast response [124] and avoidance of chemical stimulants and byproducts [125]. For safety considerations, L-RDLEF should be able to respond to light with a wavelength longer than 315 nm, and if possible, L-RDLEF should be restorable to its original state by other stimuli.…”

Aryldiazenyl Radicals from Arylazo Sulfones: Visible Light‐Driven Diazenylation of Enol Silyl Ethers

“…These elusive radicals are claimed to be electrophilic species due to the negatively polarized N=N group . and in rare instances their reaction with negatively charged nucleophiles to give either an aromatic substitution (with malononitrile anion to form II ) or an azaderivative (e. g. by reaction with a thiolate to form III , Scheme b) was reported . Indeed, the reaction rate of the coupling between the 4‐nitroaryldiazenyl radical with thiolate anion was reported to be very high (8.9×10 8 M −1 s −1 ) .…”

“…and in rare instances their reaction with negatively charged nucleophiles to give either an aromatic substitution (with malononitrile anion to form II ) or an azaderivative (e. g. by reaction with a thiolate to form III , Scheme b) was reported . Indeed, the reaction rate of the coupling between the 4‐nitroaryldiazenyl radical with thiolate anion was reported to be very high (8.9×10 8 M −1 s −1 ) . In the last years we embarked in the study of the photoreactivity of arylazo sulfones IV (Scheme c) and we found that, upon irradiation under visible light, these compounds generate an aryl radical V via homolytic cleavage of the N−S bond and nitrogen loss of the so‐obtained aryldiazenyl radical ( I ) .…”

Polymer pattern formation on SiO2 surfaces using surface monolayer initiated polymerization

“…Both types of compounds may undergo cis-trans photoisomerization, although this is not always readily observable. 27 Mixed aliphatic-aromatic compounds more closely resemble the pure aliphatic series in their photochemical behavior. 28 Figure 3 shows the UV-vis spectra of the initiators synthesized in this work along with the conventional radical initiator AIBN.…”