18543-92-5Relevant academic research and scientific papers
Aromatic Iodination: Evidence of Reaction Intermediate and of the ?-Complex Character of the Transition State
Galli, Carlo
, p. 3238 - 3245 (1991)
The reactivity of the four different procedures of aromatic iodination is compared under the same experimental conditions, and their selectivity toward two substrates in competition, i. e., mesitylene (1,3,5-trimethylbenzene, MES) and durene (1,2,4,5-tetramethylbenzene, DUR), is evaluated.Two of these procedures, namely, S2O82-/I2 and Ce(IV)/I2, present strong oxidizing capacity.Since the same MES/DUR relative reactivity is obtained from the four procedures, it becomes possible to state that a common reactive intermediate, most likely the I+ ion, is generated.The use of the MES/DUR mechanistic probe allows one to describe the reactivity picture of the iodination reaction as one of electrophilic substitution at the aromatic nucleous, with a transition state properly represented in terms of a ?-complex.The radical cation of durene also forms when the iodination is carried out by means of oxidizing agents, but it is solely responsible for the formation of side-chain substitution products and is not involved in the nuclear substitution process.
Oxidation of alkylarenes by nitrate catalyzed by polyoxophosphomolybdates: Synthetic applications and mechanistic insights
Khenkin, Alexander M.,Neumann, Ronny
, p. 6356 - 6362 (2007/10/03)
Alkylarenes were catalytically and selectively oxidized to the corresponding benzylic acetates and carbonyl products by nitrate salts in acetic acid in the presence of Keggin type molybdenum-based heteropolyacids, H3+xPVxMo12-xO40 (x = 0-2). H 5PV2Mo10O40 was especially effective. For methylarenes there was no over-oxidation to the carboxylic acid contrary to what was observed for nitric acid as oxidant. The conversion to the aldehyde/ketone could be increased by the addition of water to the reaction mixture. As evidenced by IR and 15N NMR spectroscopy, initially the nitrate salt reacted with H5PV2Mo10O 40 to yield a NVO2+[H 4PV2Mo10O40] intermediate. In an electron-transfer reaction, the proposed NVO2 +[H4PV2Mo10O40] complex reacts with the alkylarene substrate to yield a radical-cation-based donor-acceptor intermediate, NIVO2[H4PV 2Mo10O40]-ArCH2R+.. Concurrent proton transfer yields an alkylarene radical, ArCHR., and NO2. Alternatively, it is possible that the NVO 2+[H4PV2Mo10O 40] complex abstracts a hydrogen atom from alkylarene substrate to directly yield ArCHR. and NO2. The electron transfer-proton transfer and hydrogen abstraction scenarios are supported by the correlation of the reaction rate with the ionization potential and the bond dissociation energy at the benzylic positions of the alkylarene, respectively, the high kinetic isotope effect determined for substrates deuterated at the benzylic position, and the reaction order in the catalyst. Product selectivity in the oxidation of phenylcyclopropane tends to support the electron transfer-proton transfer pathway. The ArCHR. and NO2 radical species undergo heterocoupling to yield a benzylic nitrite, which undergoes hydrolysis or acetolysis and subsequent reactions to yield benzylic acetates and corresponding aldehydes or ketones as final products.
The Liquid-phase Oxidation of the Methylbenzenes by the Cobalt-Copper-Bromide System
Okada, Toshihiko,Kamiya, Yoshio
, p. 2724 - 2727 (2007/10/02)
The liquid-phase oxidation of the methylbenzenes catalyzed by a catalyst system composed of cobalt(II) and copper(II) acetates and sodium bromide was carried out in the acetic acid at 150 deg C.The corresponding benzyl acetates and benzaldehydes were obtained in high selectivities in most cases.A nuclear-brominated product, i.e., 3-bromo-4-methoxytoluene was also obtained in the oxidation of p-methoxytoluene, wich has two different reaction sites, i.e., o-positions to the electron-donating methoxyl substituent and the benzyl position.However, the substitution of the bromide ion for the acetate ion in the catalyst system gave satisfactory selectivities for the side-chain oxidation products.In the p-xylene oxidation, α,α'-diacetoxy-p-xylene and p-(acetoxymethyl)benzoic acid were also obtained, as well as p-methylbenzyl acetate, though their amounts were small.The oxidation of polymethylbenzenes was also carried out.
