585-32-0Relevant articles and documents
Cerium-Catalyzed C-H Functionalizations of Alkanes Utilizing Alcohols as Hydrogen Atom Transfer Agents
An, Qing,Chen, Yuegang,Liu, Weimin,Pan, Hui,Wang, Xin,Wang, Ziyu,Zhang, Kaining,Zuo, Zhiwei
, p. 6216 - 6226 (2020/04/27)
Modern photoredox catalysis has traditionally relied upon metal-to-ligand charge-transfer (MLCT) excitation of metal polypyridyl complexes for the utilization of light energy for the activation of organic substrates. Here, we demonstrate the catalytic application of ligand-to-metal charge-transfer (LMCT) excitation of cerium alkoxide complexes for the facile activation of alkanes utilizing abundant and inexpensive cerium trichloride as the catalyst. As demonstrated by cerium-catalyzed C-H amination and the alkylation of hydrocarbons, this reaction manifold has enabled the facile use of abundant alcohols as practical and selective hydrogen atom transfer (HAT) agents via the direct access of energetically challenging alkoxy radicals. Furthermore, the LMCT excitation event has been investigated through a series of spectroscopic experiments, revealing a rapid bond homolysis process and an effective production of alkoxy radicals, collectively ruling out the LMCT/homolysis event as the rate-determining step of this C-H functionalization.
Acid Is Key to the Radical-Trapping Antioxidant Activity of Nitroxides
Haidasz, Evan A.,Meng, Derek,Amorati, Riccardo,Baschieri, Andrea,Ingold, Keith U.,Valgimigli, Luca,Pratt, Derek A.
, p. 5290 - 5298 (2016/05/19)
Persistent dialkylnitroxides (e.g., 2,2,6,6-tetramethylpiperidin-1-oxyl, TEMPO) play a central role in the activity of hindered amine light stabilizers (HALS)-additives that inhibit the (photo)oxidative degradation of consumer and industrial products. The accepted mechanism of HALS comprises a catalytic cycle involving the rapid combination of a nitroxide with an alkyl radical to yield an alkoxyamine that subsequently reacts with a peroxyl radical to eventually re-form the nitroxide. Herein, we offer evidence in favor of an alternative reaction mechanism involving the acid-catalyzed reaction of a nitroxide with a peroxyl radical to yield an oxoammonium ion followed by electron transfer from an alkyl radical to the oxoammonium ion to re-form the nitroxide. In preliminary work, we showed that TEMPO reacts with peroxyl radicals at diffusion-controlled rates in the presence of acids. Now, we show that TEMPO can be regenerated from its oxoammonium ion by reaction with alkyl radicals. We have determined that this reaction, which has been proposed to be a key step in TEMPO-catalyzed synthetic transformations, occurs with k ～ 1-3 × 1010 M-1 s-1, thereby enabling it to compete with O2 for alkyl radicals. The addition of weak acids facilitates this reaction, whereas the addition of strong acids slows it by enabling back electron transfer. The chemistry is shown to occur in hydrocarbon autoxidations at elevated temperatures without added acid due to the in situ formation of carboxylic acids, accounting for the long-known catalytic radical-trapping antioxidant activity of TEMPO that prompted the development of HALS.
Self-propagated Lossen rearrangement induced by a catalytic amount of activating agents under mild conditions
Hoshino, Yujiro,Shimbo, Yuki,Ohtsuka, Naoya,Honda, Kiyoshi
supporting information, p. 710 - 712 (2015/01/30)
A mild self-propagated Lossen rearrangement induced by a catalytic amount of activating agents in medium to high polar organic solvents has been developed. The rearrangement of aromatic and aliphatic hydroxamic acids in the presence of a catalytic amount (0.01 equiv) of acetic anhydride and an equimolar amount of base such as well-dried potassium carbonate afforded the corresponding amines in high yields. This alternative to traditional Lossen rearrangement provides a simple and mild method for the synthesis of amines from free hydroxamic acids.
