Pyridines cathodic

Anode(Al) 1 C1CI3 (pyridine), Bu4NBr, CO, pyridine Cathode... 

Selectivity of propylene oxide from propylene has been reported as high as 97% (222). Use of a gas cathode where oxygen is the gas, reduces required voltage and eliminates the formation of hydrogen (223). Addition of carbonate and bicarbonate salts to the electrolyte enhances ceU performance and product selectivity (224). Reference 225 shows that use of alternating current results in reduced current efficiencies, especiaHy as the frequency is increased. Electrochemical epoxidation of propylene is also accompHshed by using anolyte-containing silver—pyridine complexes (226) or thallium acetate complexes (227,228). 

According to U.S. Patent 2,966,493, the 2,3-bis-(3-pyridyl)-2,3-butanedlol used as the starting material may be prepared as follows. A solution of 1,430 g of 3-acetyl-pyridine in 7,042 ml of a 1 N aqueous solution of potassium hydroxide is placed into a cathode chamber containing a mercury cathode with a surface of 353 cm and is separated from an anode chamber by an Alundum membrane. As anode a platinum wire is used and the anolyte consists of a 1 N solution of aqueous potassium hydroxide which Is replenished from time to time. 

Supporting electrolyte. Prepare a supporting electrolyte composed of l.OOM pyridine and 0.50M chloride ion, adjusted to a pH of 7.0 0.2 for use with a silver anode, or LOOM pyridine, 0.30M chloride ion and 0.20M hydrazinium sulphate, adjusted to a pH of 7.0 0.2, for use with a platinum cathode. A small background current is obtained with the latter. 

A further difficulty arises during preparative electrolyses in aprotic solvents because of the bulk pH change which commonly occurs. Thus cathodic reductions often require proton abstraction from the solvent in order to yield stable products, while many anodic oxidations, mcluding those of aromatic and aliphatic hydrocarbons, give rise to a quantitative yield of proton and the consequent changes in the pH. of the electrolysis media would be expected to lead to a variation in the products with the duration of the electrolysis. Unfortunately, the pH can be a very difficult parameter to control in aprotic solvents and most work reported in the literature has been carried out in unbuffered conditions. In the case of oxidations, organic bases, e.g. pyridine, have... 

The water concentration in the paint and in the paint film has been determined using a Mitsubishi moisture meter. The anode cell was filled with Karl-Flscher reagent and the cathode cell with a mixture of pyridine, formamlde and Karl-Flscher reagent (70/30/6Z (v/v)). Paint samples were injected directly into the cathode solution. 

Lithium iodide is the electrolyte in a number of specialist batteries, especially in implanted cardiac pacemakers. In this battery the anode is made of lithium metal. A conducting polymer of iodine and poly-2-vinyl pyridine (P2VP) is employed as cathode because iodine itself is not a good enough electronic conductor (Fig. 2.3a). The cell is fabricated by placing the Li anode in contact with the polyvinyl pyridine-iodine polymer. The lithium, being a reactive metal, immediately combines with the iodine in the polymer to form a thin layer of lithium iodide, Lil, which acts as the electrolyte ... 

Ion-exchange reactions were used for the accumulation of europium(III) [158] and iron(III) [159] ions on the surface of GCE coated with Nafion , and chromium(VI) ions on the surface of GCE covered by a pyridine-functionalized sol-gel film [160], which were combined with the stripping SWV Furthermore, a cathodic stripping SWV was used for the determination of sulfide [161,162], thiols [163-166], selenium(lV) [167-170], halides [171-173] and arsenic [174] accumulated on the snrface of mercury electrode. 

Another example concerns the initial electronic reduction of a-nitrostilbene (Todres et al. 1982, 1985, Todres and Tsvetkova 1987, Kraiya et al. 2004). The reduction develops according to direction a in Scheme 2.9 if the mercury cathode as well as cyclooctatetraene dianion are electron sources and according to direction b if the same stilbene enters the charge-transfer complexes with bis(pyridine)-tungsten tetra(carbonyl) or uranocene. For direction b, the charge-transfer bands in the electronic spectra are fixed. So the mentioned data reveal a great difference in electrochemical and chemical reduction processes a and b as they are marked in Scheme 2.9. 

Electrolytic reduction using a lead cathode in 20% sulfuric acid converted pyridine a-carboxaldehyde to a mixture of 41% of a-picoline, 25% of a-pipecoline and 11% of 2-methyl-1,2,3,6-tetrahydropyridine [443]. 

Reaction of 1,2 -dicarboxylic acids has been used for the formation of a number of strained alkenes and also applied to the Diels-Alder addition products from maleic anhydride (Table 9.5). Both cis- and tr s-diacids take part in the process. Aqueous pyridine containing, triethylamine as a strong base, is considered the best solvent and higher yields are obtained at temperatures of around 80 "C [130]. Use of a divided cell avoids a possibility of electrocatalytic hydrogenation of the product at the cathode. The addition of /a/-butylhydroquinone as a radical scavenger prevents polymerization of the product [127], An alternative chemical decarboxylation process is available which uses lead tetraacetate [131] but problems can arise because of reaction between the alkene and lead tetraacetate. 

I. 4-methoxyacetophenone (30 //moles) was added as an internal standard. The reaction was stopped after 2 hours by partitioning the mixture between methylene chloride and saturated sodium bicarbonate solution. The aqueous layer was twice extracted with methylene chloride and the extracts combined. The products were analyzed by GC after acetylation with excess 1 1 acetic anhydride/pyridine for 24 hours at room temperature. The oxidations of anisyl alcohol, in the presence of veratryl alcohol or 1,4-dimethoxybenzene, were performed as indicated in Table III and IV in 6 ml of phosphate buffer (pH 3.0). Other conditions were the same as for the oxidation of veratryl alcohol described above. TDCSPPFeCl remaining after the reaction was estimated from its Soret band absorption before and after the reaction. For the decolorization of Poly B-411 (IV) by TDCSPPFeCl and mCPBA, 25 //moles of mCPBA were added to 25 ml 0.05% Poly B-411 containing 0.01 //moles TDCSPPFeCl, 25 //moles of manganese sulfate and 1.5 mmoles of lactic acid buffered at pH 4.5. The decolorization of Poly B-411 was followed by the decrease in absorption at 596 nm. For the electrochemical decolorization of Poly B-411 in the presence of veratryl alcohol, a two-compartment cell was used. A glassy carbon plate was used as the anode, a platinum plate as the auxiliary electrode, and a silver wire as the reference electrode. The potential was controlled at 0.900 V. Poly B-411 (50 ml, 0.005%) in pH 3 buffer was added to the anode compartment and pH 3 buffer was added to the cathode compartment to the same level. The decolorization of Poly B-411 was followed by the change in absorbance at 596 nm and the simultaneous oxidation of veratryl alcohol was followed at 310 nm. The same electrochemical apparatus was used for the decolorization of Poly B-411 adsorbed onto filter paper. Tetrabutylammonium perchlorate (TBAP) was used as supporting electrolyte when methylene chloride was the solvent. 

When these CCH conditions were applied to o-iodonitrobenzene (1), cr iodoaniline (2) together with iodoaniline (4) and nitrobenzene (1) were obtained in the yields indicated in Scheme 1 (88% mass balance), which corresponds to a 62% selectivity for the formation of o iodoaniline (3). Under the same conditions, the ECH of o-iodonitrobenzene (2) gave aniline (90% yield) as the sole product. There was complete hydrogenolysis of the C-I bond (no selecti vity). Thus, in basic medium (pH 12.5), CCH method is much more selective than ECH. However, in weakly acidic medium (pH 3, pyridine.HCl buffer), it has been reported that ECH at a RCu cathode in methanol-water 95 5 (v/v) gave o-iodoaniline in a 97% yield (1, 3). 

Miller and his co-workers60) reported surprisingly high optical yields, close to 50 %, in the reduction of 2-acetylpyridine in the presence of strychnine. They also prepared chemically modified electrodes with optically active amino acids and attempted asymmetric induction in both reduction and oxidation61 . The best optical yield, only 14.5 %, seemed to be obtained in the reduction of 4-acetyl-pyridine on a graphite cathode modified with (S)-phenylalanine methyl ester. 

Lithium cannot be obtained by the electrolysis of aq. soln. of its salts, but L. Kahlenberg obtained it by the electrolysis of soln. of the chloride 14 in pyridine, acetone, or in various alcohols. Silvery white lithium was obtained from a cone, soln. of lithium chloride in pyridine at the room temp, using a graphite plate as anode, and an iron plate as cathode with 0 2 to 0 3 amp. per 100 sq. cm. of cathode surface, and a potential difference of 14 volts. 

Pentafluoropyridine (292) is reduced440 in dry DMF at a mercury cathode to perfluoro-4,4 -bipyridyl (293) in the presence of hydroquinone as proton donor, 2,3,5,6-tetrafluoropyridine (294) is obtained [Eq. (150)]. Pentachloro-pyridine gives on reduction in dry DMF very little bipyridyl derivative, but tetrachloropyridine and bis(tetrachloropyridyl) mercury. 

Electrochemical reduction of pyridines to piperidines can be achieved using various methods. Piperidines can be obtained in high yield by the electrochemical reduction of pyridine on a lead cathode in the presence of carbon dioxide and Pd — Ni or Cu — Ni catalysts (89KFZ1120). In the absence of catalyst, 4,4 -bipyridine was produced as the major product. 

Since bromo(pyridine)cobaloxime(III) was not commerically available and its synthesis was not convenient36, we utilized chloro(pyridine)bis(dimethylglyoximato)-cobalt(III) (Equation 3) (also known as chloro(pyridine)cobaloxime (III)) instead. It has four cathodic waves in polarography when observed in acetonitrile. Its half wave potentials are located at -0.65, -1.45, -2.42, and -2.92 volts vs the Ag/AgNC>3 electrode, corresponding to the reduction of the cobalt from +3 to +2, +1, and 0, and the reduction of the ligand, respectively. 

Polymerization by an electron supplied at the cathode in electrolysis was first suggested by Yang, McEwer and Kleinberg (18). They employed anhydrous pyridine, magnesium electrodes, sodium iodide and styrene monomer. Two samples of polystyrene of molecular weight 1800 and 1600 were formed the former was made in the usual manner and did not contain nitrogen, and the latter was obtained when styrene was... 

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