763025-01-0Relevant articles and documents
After 118 years, the isolation of two common radical anion reductants as simple, stable solids
Scott, Thomas A.,Ooro, Betty A.,Collins, David J.,Shatruk, Michael,Yakovenko, Andrey,Dunbar, Kim R.,Zhou, Hong-Cai
, p. 65 - 67 (2009)
Two common radical anion reductants, potassium benzophenone ketyl (K(Ph2CO)) and potassium naphthalenide (K2(C 10H8)2(THF)), have been isolated and characterized for the first time in solvent-free for
Isolation of a stable pyridine radical anion
Schr?der, Jan,Himmel, Daniel,Kratzert, Daniel,Radtke, Valentin,Richert, Sabine,Weber, Stefan,B?ttcher, Tobias
supporting information, p. 1322 - 1325 (2019/01/30)
Reduction of 2,6-bis(diazaboryl)pyridine with KC8 gives a room-temperature-stable yellow colored solution containing the corresponding radical anion. The radical was characterized by single crystal XRD, EPR spectroscopy, UV-vis absorption spectroscopy and electrochemically, supported by theoretical calculations. The negative charge and spin density are mainly distributed over the atoms of the pyridine ring, making this the first isolated pyridine radical anion as its potassium salt.
Electron Transfer Reactions: KO tBu (but not NaO tBu) Photoreduces Benzophenone under Activation by Visible Light
Nocera, Giuseppe,Young, Allan,Palumbo, Fabrizio,Emery, Katie J.,Coulthard, Graeme,McGuire, Thomas,Tuttle, Tell,Murphy, John A.
supporting information, p. 9751 - 9757 (2018/07/21)
Long-standing controversial reports of electron transfer from KOtBu to benzophenone have been investigated and resolved. The mismatch in the oxidation potential of KOtBu (+0.10 V vs SCE in DMF) and the first reduction potential of benzophenone (of many values cited in the literature, the least negative value is -1.31 V vs SCE in DMF), preclude direct electron transfer. Experimental and computational results now establish that a complex is formed between the two reagents, with the potassium ion providing the linkage, which markedly shifts the absorption spectrum to provide a tail in the visible light region. Photoactivation at room temperature by irradiation at defined wavelength (365 or 400 nm), or even by winter daylight, leads to the development of the blue color of the potassium salt of benzophenone ketyl, whereas no reaction is observed when the reaction mixture is maintained in darkness. So, no electron transfer occurs in the ground state. However, when photoexcited, electron transfer occurs within a complex formed from benzophenone and KOtBu. TDDFT studies match experimental findings and also define the electronic transition within the complex as n → π, originating on the butoxide oxygen. Computation and experiment also align in showing that this reaction is selective for KOtBu; no such effect occurs with NaOtBu, providing the first case where such alkali metal ion selectivity is rationalized in detail. Chemical evidence is provided for the photoactivated electron transfer from KOtBu to benzophenone: tert-butoxyl radicals are formed and undergo fragmentation to form (acetone and) methyl radicals, some of which are trapped by benzophenone. Likewise, when KOC(Et)3 is used in place of KOtBu, then ethylation of benzophenone is seen. Further evidence of electron transfer was seen when the reaction was conducted in benzene, in the presence of p-iodotoluene; this triggered BHAS coupling to form 4-methylbiphenyl in 74% yield.
Stoichiometry and mechanism of protonation of alkali metal salts of benzophenone radical anions by weak proton donors and its relevance to the base-catalyzed decomposition of benzopinacol
Screttas, C. G.,Ioannou, G. I.,Georgiou, D. G.
, p. 78 - 86 (2007/10/02)
The stoichiometry of the protonation of lithium and potassium salts of benzophenone radical anions and of the lithium salt of the fluorenone radical anion by methanol has been measured and found to be *->/ = 2 : 1.This result, which was obtained by the method of magnetic titration, implies that paramagnetism decays by the reaction between a ketyl anion and a ketyl radical (i.e., a protonation ketyl anion).The reactivities of alkali metal salts of fluorenone radical anions in relation to methanol exhibit a pronounced dependence on the nature of the counterion.No kinetic deuterium isotope effect has been found for the protonation of the lithium salt of the benzophenone radical anion in tetrahydrofuran (THF) by tert-pentyl alcohol.The lithium salt of the benzophenone radical anion in N,N,N',N-tetramethylethylenediamone (TMEDA) bhaves markedly differently.Namely, its protonation by methanol exhibits 1 : 1 stoichiometry and it reacts considerably more slowly with sec-butyl alcohol, k(THF)/k(TMEDA) = 2.5.Benzopinacol undergoes decomposition by an alkoxide base to diphenyl ketyl, which decays into an equimolar mixture of benzophenone and benzohydrol.The reaction follows second-order kinetics and the specific rate constants exhibit an inverse relationship with respect to the initial concentration of the alkoxide.With a very strong base benzopinacol decomposes into two diphenyl ketyl anions.On the basis of this information as well as on studies of products, relevant mechanisms are proposed for the protonation of ketyl anions and for the decomposition of aromatic pinacols in basic media. - Key words: benzophenone, radical anion; benzopinacol; protonation, stoichiometry, mechanism.
