25569-80-6Relevant articles and documents
Palladium-catalysed synthesis of nonsymmetrically disubstituted-1,1′- biphenyls from o-substituted aryl iodides through aryl coupling and delayed hydrogenolysis
Deledda, Sara,Motti, Elena,Catellani, Marta
, p. 741 - 747 (2005)
In the presence of Pd(OAc)2 and norbornene as catalysts, two molecules of an ortho-substituted aryl iodide undergo aryl-aryl coupling to a palladium-bonded biphenylyl intermediate, which is hydrogenolyzed by benzyl alcohol to give 2,3′-disubsti
Congener-specific dechlorination of dissolved PCBs by microscale and nanoscale zerovalent iron in a water/methanol solution
Lowry, Gregory V.,Johnson, Kathleen M.
, p. 5208 - 5216 (2008/01/27)
Polychlorinated biphenyl (PCB)-contaminated sediments remain a significant threat to humans and aquatic ecosystems. Dredging and disposal is costly, so viable in situ technologies to dechlorinate PCBs are needed. This study demonstrates that nanoscale zerovalent iron (ZVI) dechlorinates PCBs to lower-chlorinated products under ambient conditions, provides insight into structure-activity relationships between PCB isomers, and compares the reactivity of nanoscale ZVI to that of palladized microscale ZVI. Six PCB congeners were studied (22′, 34′, 234, 22′35′, 22′45′, and 33′44′) to compare the initial rate of dechlorination of each and to monitor the order in which chlorines are removed. Using 200 g/L of nanoscale ZVI in a 30% MeOH/water mixture, observed surface-area-normalized pseudo-first-order PCB dechlorination rate constants ranged from 1 × 10-6 to 5.5 × 10-4 L yr -1 m-2 depending on the PCB congener tested. Using 200 g/L of palladized (0.05 wt %) microscale ZVI, surface-area-normalized pseudo-first-order PCB dechlorination rate constants were significantly faster and ranged from 3.8 × 10-2 to 1.7 × 10-1 L yr-1 m-2, but these rates were not sustainable. For nanoscale ZVI, nonorthosubstituted congeners had faster initial dechlorination rates than orthosubstituted congeners in the same homologue group. Chlorines in the para and meta position were predominantly removed over chlorines in the ortho position, which suggests that more-toxic coplanar PCB congeners are not likely to form from less-toxic noncoplanar, orthosubstituted congeners. Complete dechlorination was not observed over the course of the experiments. PCB dechlorination is rapid enough that nanoscale ZVI may offer novel in situ remedial alternatives for PCB-contaminated sediments.
Vapour-phase Chemistry of Arenes. Part 13. Reactivity and Selectivity in the Gas-phase Reactions of Hydroxyl Radicals with Monosubstituted Benzenes at 563 K
Mulder, Peter,Louw, Robert
, p. 1167 - 1174 (2007/10/02)
The reactions of hydroxyl radicals with benzene derivates C6H5Z (Z = H, Me, F, Cl, Br, I, CF3, or CN) have been studied in a flow reactor at 563 K in nitrogen, using the thermolysis of ButOOH as a source of .OH.Under these conditions there are two product-forming pathways.The major one involves hydrogen abstraction to give aryl radicals ZC6H4. (II) as the first step; depending on Z, its displacement to form phenol may also occur.Relative rates for hydrogen abstraction were determined in competition experiments using side-chain hydrogen abstraction from added toluene as a reference.This resulted in the order (for Z =): 1,8(Me), 1.0(H), 0.47(F), 0.29(Cl), 0.34(CF3), 0.20(CN), consonant with the electrophilic nature of .OH.The site selectivity of hydrogen abstractions was determined by scavenging part of the aryl radicals (II) with iodine.A Hammett plot, using ? constants for meta and para positions, led to ρ -1.0.The features of hydrogen abstraction by .OH are discussed and compared with those for the analogous reaction of Cl.The formation of phenol was found to decrease in importance in the order F, Cl, Br, and I.This result is rationalized on a thermochemical kinetic basis.
Gas-phase thermolysis of tert-butyl hydroperoxide with benzene and chlorobenzene in the temperature range 200-300 deg C
Mulder, Peter,Louw, Robert
, p. 282 - 287 (2007/10/02)
Thermolysis of tert-butyl hydroperoxide (1) in nitrogen with an excess of benzene in the temperature range 200-300 deg C, leads to biphenyl (2) as the only observable benzene-derived product.With chlorobenzene, dichlorobiphenyls (4) are formed, together with chlorobiphenyl (5), ca. 12percent on 4, and phenol (20-25percent on 4); chlorophenols are not produced.The use of ca. equimolar quantities of iodine based on 1 results in formation of iodobenzene (3) and chloroiodobenzenes (7), respectively, at the expense of biaryl.In air, chlorobenzene and 1 produce chlorophenols (8), biaryl then being a minor product.Hydroxyl radicals produced from 1 abstract hydrogen from benzene to give phenyl radicals (Ph.) which, in notrogen, arylate benzene.From isomer distributions of 7 and of 4 it is inferred that hydrogen abstraction from chlorobenzene leads to chlorophenyl radicals, with a ratio o/m/p ca. 24/52/24.With chlorobenzene, ipso substitution, PhCl + .OH -> PhOH, also takes place.In the presence of oxygen or iodine, formation of biaryls involves irreversible addition of (chloro)phenyl radical, the intermediate adduct radicals reacting with oxygen or iodine.In nitrogen, however, the first step in arylation is reversible.Apart from undergoing O-O bond homolysis, 1 is attacked by .Me (formed from Me3CO.) and, to some extent, by aryl radicals.A large arene/1 intake ratio (>100), or the addition of either iodine or air suppresses - or even prevents - free-radical-induced decomposition of 1.
PALLADIUM(II)-CATALYZED OXIDATIVE COUPLING OF ARENES BY THALLIUM(III)
Yatsimirsky, Anatoly K.,Deiko, Sergei A.,Ryabov, Alexander D.
, p. 2381 - 2392 (2007/10/02)
Oxidation of benzenes with electron-donating and moderate electron-withdrawing substituents by thallium(III) trifluoroacetate in the presence of catalytic amounts of palladium(II) acetate affords biaryls in good yields.The GLC study of the isomer distribution has shown that 4,4'-biaryls are the major products.Thus, the 4,4'-biaryls can be easily isolated either by recrystallization or column chromatography.The competitive experiments and kinetic study using arenes and arylthallium derivatives as starting materials as well as quenching experiments have demonstrated the first step of the reaction to be fast thallation of arene to form arylthallium intermediate ArTl(OOCCF3)2.The latter undergoes the rate-determining transmetallation step reacting with monomeric complex Pd(OAc)2, which is formed upon depolymerization of trimer Pd3(OAc)6.Subsequent fast decomposition of arylpalladium species gives the final reaction products.The thallation of arene and substitution of TlIII for PdII in ArTl(OOCCF3)2 are characterized by the slopes of Hammet plots of -5.6 (?+) and -3.0 (?), respectively.
