Dechlorination of PCBs by electrochemical reduction with aromatic radical anion as mediator

Chemosphere ◽  
2005 ◽  
Vol 58 (7) ◽  
pp. 897-904 ◽  
Author(s):  
Atsushi Matsunaga ◽  
Akio Yasuhara
Keyword(s):  
Electrochemical Reduction ◽  
Radical Anion ◽  
Aromatic Radical

Chemical and electrochemical reduction of pyrazino[2,3-g]quinoxalines and of their benzo and dibenzo derivatives; the structure of fluorindine and the formation of tetraanion

1987 ◽  
Vol 65 (7) ◽  
pp. 1619-1623 ◽  
Author(s):  
Joseph Armand ◽  
Line Boulares ◽  
Christian Bellec ◽  
Jean Pinson
Keyword(s):  
Electrochemical Reduction ◽  
Catalytic Hydrogenation ◽  
Radical Anion ◽  
Reversible Systems ◽  
Restricted Class ◽  
Dihydro Derivative ◽  
Successive Formation

The structure of fluorindine is established by nmr as the 5,14-dihydroquinoxalino[2,3-b]phenazine. The catalytic hydrogenation of 2,3-di(p-methoxyphenyl)pyrazino[2,3-b]phenazine 2a leads to the 6,11-dihydro derivative 4a. The electrochemical reduction in an hydroorganic medium furnishes 4a and then the 1,4,6,11-tetrahydro derivative 8a. In dry DMSO the voltammogram shows four monoelectronic reversible systems corresponding to the successive formation of a radical anion, dianion, radical trianion, and tetraanion. Thus 2a appears as a new example of the very restricted class of compounds leading to tetraanions upon electrochemical reduction. The catalytic hydrogenation of 2,7-diphenylpyrazino[2,3-g]quinoxaline 1a or the reaction of LiAlH4 with 1,2,7,8-tetramethylpyrazino[2,3-g]quinoxaline 1b leads to 1,2,3,4-tetrahydro compounds. The electrochemical reduction of 1a and 1b in hydroorganic medium leads successively to 1,4-dihydro and then to 1,4,6,9-tetrahydro compounds which undergo a further rearrangement. In dry DMSO 1a and 1b behave differently from 2a: one only observes two reversible monoelectronic systems.

scholarly journals (2,3-Bis(methylen)bicycIo[2.2.2]octan)zirconocen: Synthese, Struktur und elektrochemische Reduktion/(2,3-Bis(methylene)bicyclo[2.2.2]octane)zirconocene: Synthesis, Structure, and Electrochemical Reduction

1985 ◽  
Vol 40 (2) ◽  
pp. 150-157 ◽  
Author(s):  
Gerhard Erker ◽  
Klaus Engel ◽  
Carl Krüger ◽  
Yi-Hung Tsay ◽  
Edmond Samuel ◽  
...  
Keyword(s):  
Electrochemical Reduction ◽  
Structure Determination ◽  
Radical Anion ◽  
Nmr Spectra ◽  
Activation Barrier ◽  
Intramolecular Rearrangement ◽  
Dynamic Nmr ◽  
Space Group ◽  
X Ray

Photolysis of diphenylzirconocene and 2,3-bis(methylene)bicyclo[2.2.2]octane in toluene at -25 °C yields biphenyl and (2,3-bis(methylene)bicyclo[2.2.2]octane)zirconocene (lg) (67.5% isolated yield).1g exhibits dynamic NMR spectra indicating rapid alternation of diene faces coordinated to zirconium (ring-flip mechanism). This degenerate intramolecular rearrangement is characterized by an extremely low activation barrier (⊿G≠-131°C = 7.1 ± 0.3 kcal/mol). 1g crystallizes in space group P1̄with a = 7.215(1) Å, b = 9.654(1) Å, c = 11.831(1) Å, α = 94.97(1)°, β = 91.81(1)°, and γ = 103.22(1)°. The X-ray structure determination reveals a pronounced metal alkyl character of the (diene)ZrCp2 moiety. Accordingly, 1g is easily reduced electrochemically to give a Zr(III) radical anion (7) observed by esr (g = 1.990; a(H) = 2.976 G; a(Zr) = 18.36 G).

Fragmentation Rates of Aromatic Radical Anions and the π*— σ* Orbital Crossing Point

1984 ◽  
Vol 39 (1) ◽  
pp. 49-54 ◽  
Author(s):  
H. O. Villar ◽  
E. A. Castro ◽  
R. A. Rossi
Keyword(s):  
Carbon Atom ◽  
Molecular Orbital ◽  
Qualitative Agreement ◽  
Radical Anion ◽  
Reaction Coordinate ◽  
Radical Anions ◽  
Aromatic Radical ◽  
Orbital Crossing ◽  
Crossing Point

The reaction coordinate of the fragmentation of aromatic radical anions with nucleofugal groups was studied by the INDO and MNDO techniques. The reaction coordinate turned out as the stretching between the nucleofugal group bonded to the carbon atom of the aryl moiety. It was found that to fragment a π* radical anion, the odd electron has to be transferred to the σ* molecular orbital of the aryl-nucleofugal bond by an orbital crossing, which is reached by the lengthening of this bond. There is a qualitative agreement between the length of the bond to reach the orbital crossing point and the experimental fragmentation rates of the aromatic radical anions. Finally, some considerations about the σ-π coupling are made, since it is defining the possibility of a transfer from the π* to the σ* molecular orbital.

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