734-17-8Relevant articles and documents
Hammett analysis of photodecarbonylation in crystalline 1,3-diarylacetones
Resendiz, Marino J. E.,Garcia-Garibay, Miguel A.
, p. 371 - 374 (2007/10/03)
(Chemical Equation Presented) The relative quantum yields and chemical efficiencies of crystalline p,p′-disubstituted 1,3-diphenyl-2-propanones with 4-MeO, 4-Me, 4-F, 4-CF3, and 3,4-diMeO groups were determined by parallel irradiation of polycrystalline samples. Variations in quantum yields that span a factor of 4 are analyzed in terms of the effects of substituents on the stability of the benzylic radical. All solid-state reactions proceeded with 100% chemoselectivity and in >95% chemical yield.
Organomolybdenum and Organotungsten Reagents, V. - On the Additive, Reductive Carbonyl Dimerization (ARCD Reaction)
Kauffmann, Thomas,Jordan, Jan,Voss, Karl-Uwe,Wilde, Heinz-Wilhelm
, p. 2083 - 2092 (2007/10/02)
Reagents of the type R4(PrO)4(μ-PrO)2W2 (3; R = Me, Et, Pr, Bu, sBu, iBu, Hex, Me3SiCH2, Ph) prepared in situ by the action of organolithium or Grignard compounds on (PrO)4(μ-PrO)2W2Cl4 (2), react with aromatic aldehydes or ketones and with the α,β-unsaturated ketone benzylidene acetone in a novel reaction, called the ARCD reaction, to give products 4 of the type RR'R''C-CRR'R'' with mostly good yields.In the case of benzylidene acetone and furfural besides the ARCD products the rearranged products 27 and 29 are formed.With the reagent Ph4(PrO)4(μ-PrO)2W2 (3b) ARCD reactions are also possible in moderate yields with aliphatic aldehydes and ketones.The more closely investigated reagent Me4(PrO)4(μ-PrO)2W2 (3a; decomposition at about -45 deg C) tolerates the aromatic bound functional groups Cl, F, OH, OMe, and NMe2 in the substrates, but not the NO2 and CO2Et substituents.It reacts with PhCOX (X = OEt, Cl, OCOPh) via acetophenone to give PhCMe2-CMe2Ph. - For the ARCD reactions a radical mechanism (Scheme 7) is postulated. - Key Words: Tungsten complexes/ Carbonyl dimerization
Dicyanobenzene sensitized carbon-carbon bond cleavage in methoxybicumenes. Products and mechanistic studies
Maslak, Przemyslaw,Chapman Jr., William H.
, p. 2715 - 2724 (2007/10/02)
Radical cations of p-methoxy-p-X-bicumenes generated by ET to excited-state dicyanobenzene undergo rapid irreversible C-C bond scission giving cumyl cations and radicals. The photoefficiency of the process (Φ = 0.13 for X = MeO, Φ 0.005 for X = CN) and the fate of the radicals produced depends strongly on substitution.
HYDROGEN ABSTRACTION FROM THE ISOMERIC CYMENES
Sulpizio, A.,Mella, M.,Albini, A.
, p. 7545 - 7552 (2007/10/02)
The irradiation of cerium (IV) ammonium nitrate in the presence of ortho, meta and para cymene yields products from attack at the methyl group (the nitrates - these ones in 55 to 69percent isolated yield-, the nitro derivatives, and the aldehydes) as well as at the isopropyl group (the acetophenones, not obtained from the ortho isomer), with minimal ring nitration.The formation of bibenzyls on irradiation with t-butyl peroxide of the same substrates is also studied.The mechanisms of the reactions with the NO3 radical, a good electron acceptor, and with the alkoxy radical are contrasted and compared with photochemical hydrogen abstraction by n?* and, respectively, ??* excited states.
Photochemical Hydrogen Abstraction from Cymenes
Albini, A.,Sulpizio, A.
, p. 2147 - 2152 (2007/10/02)
The three isomeric cymenes are examined in photochemical reactions involving hydrogen transfer with 1,4-naphthalenedicarbonitrile (NDN), α,α,α-trifluoroacetophenone (TFA), and benzophenone (BP).Selectivity for attack at primary vs tertiary position (P/T) and quantum yield are determined.The reactions are rationalized as involving loose perpendicular complexes yielding a low P/T ratio in the products (with BP n? triplet), a face-to-face charge transfer complex yielding a high P/T (with TFA ??* triplet and also NDN singlet, but only as far as the benzylnaphthalenes 1 and 2 are concerned), and a tighter charge transfer complex yielding again a low P/T in the formation of dibenzomethanocyclooctenes 3, the main products from NDN.The energetic limit of such a directing effect of the conformation of the intermediate complex onto photochemical reactivity is evidenced by the different results obtained with o-cymene.
CYANOETHYLATION OF HYDROCARBONS, INITIATED BY AUTOOXIDATION
Galust'yan, G. G.
, p. 811 - 815 (2007/10/02)
Oxygen was used as an initiator of the free-radical cyanoethylation of alkylbenzenes (toluene, o-, m-, and p-xylenes, mesitylene, ethylbenzene, p-cymene) and tetralin (0.25-0.66 liter of oxygen to 1 liter of the hydrocarbon) The reactions were carried out in an autoclave at 150-350 deg C with a carbon-acrylonitrile ratio of 100:1.The initiation evidently results mainly from homolytic dissociation of the hydroperoxide formed during the autooxidation of the hydrocarbons.The effectiveness of oxygen for the initiation of the cyanoethylation of hydrocarbons depends on the oxidizability of the hydrocarbons.
Extent of Charge Transfer in the Photoreduction of Phenyl Ketones by Alkylbenzenes
Wagner, Peter J.,Truman, Royal J.,Puchalski, Alan E.,Wake, Ronald
, p. 7727 - 7738 (2007/10/02)
Rate constants for triplet-state reaction of various ring-substituted benzophenones (BPs), acetophenones (APs), and α,α,α-trifluoroacetophenones (TFAs) with toluene and p-xylene have been determined by a combination of flash kinetics, steady-state quenching, and quantum yield measurements.The relative amounts of primary and tertiary radicals formed by reaction of the same ketons with p-cymene have also been measured.For all three types of ketones, rate constants correlate well with triplet ketone reduction potentials.The magnitude of the kinetic isotope effects observed with toluene-d8 and p-xylene-d10 diminishes as the ketones become easier to reduce.All of the ketone triplets react with alkylbenzenes primarily by a charge-transfer mechanism, with the rate-determining step changing from complexation to hydrogen transfer as the ketones become harder to reduce.The least reactive AP triplets probably react significantly via simple hydrogen atom abstraction as well.Those ketones with n,?* lowest triplets (all BPs and some APs) react with p-cymene to give primary/tertiary radical ratios that vary no more than a factor of 2 from the 0.40 value displayed by tert-butoxy radicals; those with ?,?* lowest triplets (TFAs and some APs) give ratios that favor primary radicals and that vary by an order of magnitude with the triplet ketone reduction potential.The variation in cymene product ratios reflect different orientations for attack on cymene by n,?* and ?,?* triplets and differing degrees of partial electron transfer within the exciplexes, which are not tight radical ion pairs.The variation seen for ?,?* triplets represents a stereoelectronic effect within face-to-face exciples, as evidenced by the excerptional behavior of p-diacylbenzenes, which give the highest ratio of tertiary radicals from cymene.There is no set intrinsic ratio of reactivity for ?,?* triplets vs. n,?* triplets in these CT reactions.The two types of triplets show similar reactivity for the more easily reduced triplets, with the harder to reduce ?,?* triplets being only one-tenth as reactive as n,?* triplets of comparable triplet reduction potential.When the extent of electron transfer in the exciplex is small, hydogen transfer is rate determining and ?,?* reactivity drops.A study of two radical reactions which generate benzyl and α-hydroxy-α-methylbenzyl radicals indicates that radical disproportionation cannot explain the low quantum yields (0.10) of most ketone-toluene photoreductions, which apparently involve substantial radiation less decay by the exciplex intermediates.
Pressure Effects on Azocumene Decomposition Rates, Efficiencies of Radical Production, and Semibenzene Dimers
Neuman, Robert C.,Amrich, Michael J.
, p. 4629 - 4636 (2007/10/02)
Rates of thermal decomposition of azocumene (1a) and p,p'-dimethylazocumene (1b) in cumene or chlorobenzene are decreased by pressure with decomposition activation volumes of +5 cm3/mol (1a,cumene), +4.3 cm3/mol (1a,chlorobenzene) and +4.6 cm3/mol (1b,cumene).Efficiencies (f) of radical production, with di-tert-butyl nitroxide (DBNO) or thiophenol as scavengers, decrease with pressure; however, the pressure dependence of f with DBNO is anomalous.This is explained by the formation of semibenzene dimers as cage products, which subsequently decompose to give cumyl radicals.The corresponding α-ortho semibenzene dimers of cumyl radicals are formed from both 1a and 1b.The α-para semibenzene dimer from decomposition of 1a in chlorobenzene appears to rearrange to give p-cumylcumene.No such rearrangements appears to occur from the α-ortho dimers nor is it likely that any α-para dimer is formed from 1b decomposition.An apparent activation volume for thermal decomposition of the α-ortho semibenzene dimer in cyclohexane at 20 deg C is ca. +6 cm3/mol.Pressure favors disproportionation over coupling for geminate cumyl radicals.
ELECTRON-TRANSFER PROCESSES. NEW SYNTHESIS OF γ-LACTONES BY PEROXYDISULFATE OXIDATION OF ISOPROPYLBENZENES AND ALIPHATIC CARBOXYLIC ACIDS
Giordano, Claudio,Belli, Aldo,Citterio, Attilio,Minisci, Francesco
, p. 3559 - 3562 (2007/10/02)
A new synthesis of γ-lactones by peroxydisulfate oxidation of isopropylbenzenes is described.Evidence concerning the free-radical mechanism is reported; the intermediate formation of alkyl and benzyl radicals is evidenced by trapping them with quinoxaline.The role of the iron catalyst is discussed.
