4,4 -Bipyridinium salt

K. Adachi, Y. Ohira, G. Tomizawa, S. Ishihara, S. Oishi, Electrophilic fluorination with N,N -difluoro-2,2 -bipyridinium salt and elemental fluorine, J. Fluorine Chem. 120 (2003) 173-183. 

There has been considerable interest in diquaternary salts of 2,2 -bipyr-idine. Simple 1,1-dialkyl-2,2 -bipyridinium salts are obtained by reaction of 2,2 -bipyridine with excess of an alkyl halide or dialkyl sulfate and related processes, - " and dialkyl diquaternary salts of substituted 2,2 -bipyridines are obtained likewise. " Bridged diquaternary salts are formed by reaction of 2,2 -bipyridines with 1,2-dibromoethane. Thus the parent compound alfords 6,7-dihydrodipyrido-[l,2-a 2, T-c]pyrazinediium... 

Dutta and co-workers focused on the completely intrazeolitic Ru(bpy)3 + and bipyridinium ion systems [141]. Three N,N -dialkyl-2,2 -bipyridinium ions and methylviologen (4,4 -bipyridinium ion) with reduction potentials varying from —0.37 to —0.65 V (vs. NHE) were studied. For the 2,2 -bipyridinium salts (members... 

The corresponding 2,2 -bipyridinium salt occurs predominantly in the anti conformation, but the cis conformation can be enforced by a connection of the nitrogen atoms via an ethylene bridge (diquat). Only the latter compound gives stable radicals upon reduction (Scheme 7.2.20) 378 nm e = 30,000) (Sum-... 

Vagias, C., Tsitsimpikou, C., Rapti, T, and Roussis, V. (2000) 1,1 -Dimethyl-[2,2 ]-bipyridinium salt from the bivalve Callista chione. Nat. Prod. Lett., 14, 425-428. 

Organic Molecules It can be seen from our earlier discussion that the presence of a transition metal ion is not always required for an electrochromic effect. Indeed, many organic molecules can yield colored products as a result of reversible reduction or oxidation. 4,4 -Bipyridinium salts are the best known example of such compounds. These compounds can be prepared, stored, and purchased in colorless dicationic form (bipm +). One electron reduction of the dication leads to the intensely colored radical cation (bipm+ ). Such radical cations exist in equilibrium with their dimers (bipm ). In the case of methyl viologen, the radical cation is blue and the dimer is red. By varying the substient group in the molecule, different colors can be obtained. 

The basic structure of the 4,4 -bipyridinium-salts 7qx is also included in the iso-rr-electronic bipyrylium and bithiopyrylium salts 75ox and 16ox - The more positive potentials are already expressed in the synthetic route which leads initially to 75red and... 

Bipyridine resembles nicotine in its pharmacological properties but is not as active. The 3,4 -bipyridine derivative 113 known as amrinone and its relatives are of interest as cardiotonic agents. 4,4 -Bipyridine has been tested as an insecticide, but it is not of practical value.It is used in the study of the electrochemistry of cytochrome c and acts as a polymerization catalyst or hardening agent for various resins. l-Hexyl-4,4 -bipyridinium salts are especially effective as electron carriers in photochemical hydrogen producing systems. l,l -Dimethyl-4,4 -bipyridinium (92 R = R = CHj) and l,l -dibenzyl-4,4 -bipyridinium... 

Some bipyridinium salts are remarkable herbicides. They rapidly desiccate all green plant tissue with which they come into contact, and they are inactivated by adsorption on to clay minerals in the soil. This potent herbicidal activity is found only in quaternary salts, e.g. diquat (254) and paraquat (255), with redox potentials for the first reduction step between -300 and -500 mV (equations 158 and 159) (B-80MI20504). The first reduction step, which is involved in herbicidal activity, involves a completely reversible, pH independent, one-electron transfer to yield the resonance stabilized radicals (256) and (257). The second reduction step, (256 -> 258) and (257 -> 259), is pH dependent and the p-quinoid species formed are good reducing agents that may readily be oxidized to diquatemary salts. 

In the late 1980s, Stoddart and coworkers reported complexes between bisphenyl-ene crown ethers 24 (electron-rich, donors) and iV V -bipyridinium salts (electron-... 

The low redox potential of Af,AT-dialkyl-4,4 -bipyridinium salts (viologens) has prompted their incorporation into various polymeric systems. Addition polymerizable viologens have been prepared, for example, by reaction of monoalkylated bipyridyl with vinylbenzyl chloride (Scheme 30). Aqueous free radical polymerization and copolymerization of... 

We have examined the photosensitized reduction of a series of + 4,4 -bipyridinium salts, CnV2+, (2), (where n=l-16) with Ru(bpy)l as sensitizer and (NHi jEDTA as electron donor in a water-in-toluene microemulsion media. Under steady state illumination the quantum yield of CjjVt" formation strongly depends on the alkyl chain length of the electron acceptor (Figure 4). It improves as the hydro-... 

A redox reaction of trichloromethylarenes with pyridines results in N-(a-chloroarylmethyl)substituted pyridinium chlorides, which on hydrolysis give aromatic aldehydes and 4-chloropyridines or l,4 -bipyridinium salts <95TL(36)5075>. 

Fig. 30a, b. Photosynthetic assemblies for C02 fixation to methane a) A photosystem composed of Ru(bpz)2+ as photosensitizer and electron carrier, b) A photosystem composed of Ru(bpy)2 + as photosensitizer and different bipyridinium salts, 23-26, as electron acceptors... 

It was found, that also Ru and Os colloids can act as catalysts for the photoreduction of carbon dioxide to methane [94, 95]. [Ru(bpy)3]2+ plays a role of a photosensitizer, triethanolamine (TEOA) works as an electron donor, while bipyridinium electron relays (R2+) mediate the electron transfer process. The production of hydrogen, methane, and small amounts of ethylene may be observed in such a system (Figure 21.1). Excited [Ru(bpy)3]2+ is oxidized by bipyridinium salts, whereas formed [Ru(bpy)3]3+ is reduced back to [Ru(bpy)3]2+ by TEOA. The reduced bipyridinium salt R + reduces hydrogen and C02 in the presence of metal colloids. Recombination of surface-bound H atoms competes with a multi-electron C02 reduction. More selective reduction of C02 to CH4, ethylene, and ethane was obtained using ruthenium(II)-trisbipyrazine, [Ru(bpz)3]2+/TEOA/Ru colloid system. The elimination of hydrogen evolution is thought to be caused by a kinetic barrier towards H2 evolution in the presence of [Ru(bpz)3]2+ and noble metal catalysts [96]. 

Conifer needles also contain volatile products which are mainly composed of mono- and sesquiterpenoids. The volatile turpentine constituents are used in the production of flavors and perfumes and in various technical and pharmaceutical products. The turpentine and rosin production of trees can be increased considerably by injecting suspensions of pitch canker fungus or chemicals such as "paraquat" (1,r-dimethyl-4,4 -bipyridinium salt) which has been found to be very effective. 

These exceptional characteristics have been used later in several interesting applications. An elastic polymer film containing the same MV2 + salts as part of the main chain was found to be photochromic and results indicate that data can be written optically X > 365 nm) and erased thermally [212]. The photo-chromism was also observed in monolayer assemblies (Langmuir-Bloodgett films) made of mixtures of N,N hexadecyl-4,4 -bipyridinium salts of TFPB-and arachidic acid [213, 214, 215]. 

Bifurcated hydrogen bonds between dipyridinium cations and coordinated dithiooxalates have been used to assemble tapes [130] with similar geometry to those in which coordinated halides act as acceptors [15]. Replacement of dipyridinium with 4-carboxypiperidinium gave a structure in which the anions are linked by carboxylic acid dimer assembled dications. Similar bifurcated hydrogen bonds were observed in the structures of bipyridinium salts of anilic acids [131]. 

Hunig and co-workers have investigated the polarography of 4,4 -bipyrylium, bithiopyrylium, and bipyridinium salts in CHjCN (73LA1036). The process involves two reversible one-electron processes, involving the dication 13, the radical cation 55, and the neutral compound 14, as indicated by Eq. (1). 

The thiophene-bridged 4,4 -bipyridinium salts 149 and 150 can be prepared by alkylation of bis-bipyridinium cations <1999T4709>. The order of alkylation is crucial. Whereas in the thiophene derivative the xylene core is introduced in the last step, it is not possible to obtain the benzothiophene derivative in the same way due to the less stable bis-cation. Therefore, the benzothiophene unit is introduced in the last ring-closing step. 

Reetz, M. T., Hoger, S. and Harms, K. (1994). Proton-transfer-dependent reversible phase changes in the 4,4 -bipyridinium salt of squaric acid. Angew. Chem., Int. Ed. Engl, 2,2, 181-3. [214,218]... 

Aromatic hydrocarbons are called 7r bases because of their rather low ionization potentials. On the other hand, aromatic compounds containing a nitrogen atom possess lower MO energy than the parent hydrocarbons, and they show less electron-donating character or electron-accepting character. The mode of action of the herbicide paraquat 300 (1,1 -dimethyl-4,4 -bipyridinium salt) is thought to be connected with its reversible reduction-oxidation reactivity. The compounds with a lower level of activity possess higher reduction potentials, and their one-electron transfer is not quite quantitatively reversed. 

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