Dipyridinium

This complex, formerly called pyridine perchromate and now finding application as a powerful and selective oxidant, is violently explosive when dry [1], Use while moist on the day of preparation and destroy any surplus with dilute alkali [2], Preparation and use of the reagent have been detailed further [3], The analogous complexes with aniline, piperidine and quinoline may be similarly hazardous [4], The damage caused by a 1 g sample of the pyridine complex exploding during desiccation on a warm day was extensive. Desiccation of the aniline complex had to be at ice temperature to avoid violent explosion [4]. Pyridinium chlorochromate is commercially available as a safer alternative oxidant of alcohols to aldehydes [5], See Chromium trioxide Pyridine Dipyridinium dichromate See Other AMMINECHROMIUM PEROXOCOMPLEXES... 

Studies in cation-radical chemistry began with works by Weiss (1941) and Michaelis et al. (1941). However, intense investigations in this field started after instrumental methods emerged (ESR and optical spectroscopy in particular). Optical spectroscopy revealed a very intriguing case where direct sublimation of methylviologen (l,l -dimethyl-4,4 -dipyridinium) dichloride provokes the formation of methylviologen cation-radical monochloride. This phenomenon was established by Poizat et al. (1984), but remains unexplained. 

When mechanical vibration of bis(pyridinium) salts (see Scheme 5.5) was conducted with a stainless steel ball in a stainless steel blender at room temperature under strict anaerobic conditions, the powdery white snrface of the dicationic salts turned deep blue-purple (Kuzuya et al. 1993). Single-line ESR spectra were recorded in the resnlting powder. No ESR spectra were observed in any of the dipyridinium salts when mechanical vibration was conducted with a Teflon-made ball in a Teflon-made blender nnder otherwise identical conditions. When observed, the ESR signals were quickly quenched on exposnre to air and the starting dicationic salts were recovered. Each of the resulting powders was dissolved in air-free acetonitrile, and the ESR spectra of the solution were recorded after the material had been milled nnder anaerobic conditions. Analysis of the signal hyperflne structure confirmed the formation of the corresponding cation-radicals, which are depicted in Scheme 5.5. 

Dipyridinium dichromate, 3304 Disodium 4-nitrophenylphosphate, 2185 Dodecamethyltetraplatinum(lV) perchlorate, 3587 Ethanedial, 0723 Ethyl cyanoacetate, 1889... 

An interesting variant uses acyl- or aroyl-methylpyridinium salts with ammonia or an amine to produce dipyridiniumdihydropyridine salts (655). With aromatic aldehydes the dihydropyridines are produced directly or the intermediate (654) can be isolated and subsequently treated with perchloric acid (75LA849). With formaldehyde (giving dihydropyridines without a substituent in position 4), the 1,5-diketone can be isolated and cyclized by ammonia (75LA864). The dipyridinium salts (655) undergo some useful transformations they can be oxidized to pyridines (656), and these dipyridinium pyridine salts give... 

The photoinduced charge separation between N-alkyl-N -methyl-4,4 -dipyridinium dichloride (CnMV2+ Cn = dodecyl, tetradecyl, hexadecyl, and octadecyl) and Ru(bpy)j + was also strongly affected by the presence of CTAC micells 21 . Upon reduction by Ru(bpy)j +, the viologen aquires hydrophobic properties leading to solubilization into micells (Eq. (13)). The subsequent recombination reaction is retarded by the positive surface of the micell. This decreases the rate constant of the back electron transfer at least by 500. 

When mechanical vibration of dipyridinium dications (see Scheme 7-7) was conducted with a stainless steel ball in a stainless steel twin-shell blender at room temperature under... 

Di-2-propenyl phosphonite, see Diallyl phosphite, 2450 Dipropionyl peroxide, 2436 Dipropylaluminium hydride, 2547 f Dipropylamine, 2563a f Dipropyl ether, 2538 Dipropylmercury, 2532 Dipropyl peroxide, 2542 Dipropyl peroxydicarbonate, 3030 Dipropylzinc, 2546 Dipyridinesodium, 3274 Dipyridinium dichromate, 3298... 

Stoddart has extensively investigated the interaction of dibenzocrown ethers with the dipyridinium dications, diquat and paraquat [19]. Dibenzocrown ether... 

The reaction of both acyclic and cyclic ketones with 1,2-ethanedithiol leads to substituted 1,4-dithiins. It is considered that added l,l -(ethane-l,2-diyl)dipyridinium bistribromide (EDPBT) initially catalyses the formation a 1,3-dithiolane with which it then reacts, bringing about a ring expansion to the dithiin (Scheme 48) <9TL1007>. 

The reaction of (/ )-2,2 -di(bromoethyloxy)-l,r-binaphthyl with 4,4 -bipyridine gave bis-pyridinium complex, which with l,3-di(dibromomethyl)benzene afforded (9.4%) of the bis(dipyridinium) complex 32 <07OL5393>. 

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]. 

T - Dimethyl - 3,3 - [NN - hexamethylenebis(methyl-carbamoyloxy)]dipyridinium dibromide C22H32Br2N404 = 576.3 CAS—15876-67-2... 

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