Electrolysis electrosynthesis

Electrosynthesis — Synthesis performed with the help of -> electrolysis. Electrosynthesis is performed both on laboratory as well as on an industrial scale, and both organic and inorganic compounds are synthesized. In most cases, electrosynthesis affords divided cells, i.e., separation of the -> anolyte and -> catholyte by a -> diaphragm to prevent reactions between the products of the reaction proceeding at the -> anode with those formed at the -> cathode. 

Electrolysis of carboxylate ions, which results in decarboxylation and combination of the resulting radicals, is called the Kolbe reaction or the Kolbe electrosynthesis. 

Marken F, Compton RG, Davies SG et al (1997) Electrolysis in the presence of ultrasound cell geometries for the application of rates of mass transfer in electrosynthesis. J Chem Soc (Perkin Trans) 2(10) 2055-2059... 

Details of many synthetic processes are never reported and, hence, as noticed by Pletcher and Walsh [10], any contribution of electrosynthesis remains speculative. Crucial factors are generally the availability and costs of the starting materials, the material yield, a simple product isolation, the stability of the electrolysis medium and acceptable current densities. 

Slightly more sophisticated preparative electrolysis setups can be obtained from The Electrosynthesis Co., Inc, 72 Ward Road, Lancaster, NY 14086-9779. 

The direct electrosynthesis of S—N bonds from disulfides and amines has been shown to occur through a reaction of the amine with the oxidized disulfide being a strong electrophile. In contrast to the results, the cross-coupling of phthahmide (16) with disulfide does not proceed in a direct electrolysis. However, the electrosynthesis of sulfenimides (17) can be achieved by a [Br]" "-mediated cross-coupling reaction of imides with disulfides (Scheme 7). The electrolysis of a mixture of (16) and dicyclohexyl disulfide in an MeCN-NaBr-(Pt) system affords... 

The direct electrosynthesis of sulfen-imines (19) from a-aminoalkanoates (18) and diaryl disulfides proceeds in a CH2CI2-H20-MgBr2-(Pt) system in 70 96% yields (Scheme 8) [50]. Electrolysis of sulfenami-des (20) is considered to be the intermediates in the direct conversion of (18)— (19). 

Electrosynthesis of ammonia has been achieved using a W(dppe)2 complex. Controlled potential electrolysis of trans-[W(NNH2) (dppe)2TsO]+ (382) (Scheme 138) in a THF-Bu4BF4-(Hg) system generates free NH3 and N2H4 along with... 

The Barhier-type reaction of aldehydes and ketones with allyl halides (485) in the presence of Sml2, leading to homoallyl alcohols (486), has received recent interest as a one-step alternative to the Grignard reaction. However, the reactions require the use of stoichiometric amounts of the reducing Sm(III) species. Recently, the electroreductive Barhier-type allylation of carbonyl compounds in an SmH-mediated reaction has been developed [569]. The electrolysis of (485) is carried out in a DMF-SmCl3-(Mg/Ni) system in an undivided cell to give the adduct (486) in 50 85% yields (Scheme 168) [569]. Electrosynthesis of y-butyrolactones has been achieved by the reductive coupling of ethyl 3-chloropropionate with carbonyl compounds in the presence of a catalytic amount of SmCfi [570]. 

The formation of crystalline fulleride salts at the electrode occurs when less polar solvents and bulky cations are used for the electrosynthesis. The first fulleride salt was synthesized by Wudl by bulk electrolysis of in o-dichlorobenzene with tetraphenylphosphonium chloride as supporting electrolyte [39, 80]. This black microcrystalline material with the composition (Ph4P )3(Cgg )(Cr)2 exhibits an ESR line with a g-value of 1.9991 and a line width of 45 G at room temperature. Single crystals of the slightly different salts (Ph4P )2(Cgg )(Cr) and (Ph4P )2(C50 )(Br ) could be obtained by electrocrystallization and their crystal structure was determined [82, 83]. Magnetic measurements showed the presence of unpaired spins. 

Furthermore, the presence of pyridine in electrosynthesis reaction mixtures can disturb some couphng reactions, its nucleophilic properties being in some cases a drawback when electrophilic species are added to an electrolysis mixture. 

Therefore, the solvent used for successful electrosynthesis of PcCu should be inert in relation to PA and, on the other hand, should have electroconductivity. The compounds used as promoters [41] could theoretically serve as such solvents. Tetramethylurea (TMU) and l-methyl-2-pyrolidinone were chosen by the authors of Ref. 32 among other promoters used in the work [41]. The first one has a nature close to that of the principal precursor (urea), and thus should not influence the reaction course negatively. The TMU has sufficient conductivity to permit electrolysis in its medium, and reasonable viscosity. The boiling point of 174-178 C is ideal for such research, since conventional syntheses of Pc from urea and PA are carried out at similar temperatures. The results of TMU use as a solvent are presented in Table 5.7. The results seem promising, and this solvent is recommended to study Pc formation in its medium in further research work. In the case of l-methyl-2-pyro-lidinone, no phthalocyanine formation was observed. No phthalocyanine was observed also in the following systems (1) urea, PA, TBA, TMU (without copper) (2) urea, PA, TBA, TMU, Sb, or Mg (anodes (3) TMU, urea (or without urea), phthalimide, TBA (in all cases with or without electrolysis). 

It is possible to improve the existing techniques of synthesis of PcCu and other metal phthalocyanines from phthalimide or urea and PA, applying electrosynthesis. These processes have many peculiarities. The solvent nature greatly affects the course of the majority of reactions of coordination compound formation [119,120]. The solvent used for PcCu preparation must be inert in order not to influence the desirable reaction course, and simultaneously must have electroconductivity to carry out electrolysis. It is recommended to use the derivatives of urea as such solvents and promoters at the same time. The use of a standard electrochemical procedure [9-14,20,121-124a] could be useful for the PcCu industry, since a typical industrial... 

When planning an electrosynthesis one should however always keep in mind that competing nonelectrolytic reactions can be decelerated and thus successfully suppressed by low temperature electrolysis. 

Gattrell M, MacDougall B. The electrochemistry of chlorophenols and its implications for waste water treatment. Abstract of the 10th International Forum on Electrolysis in the Chemical Industry. Clear Water Beach, FL The Electrosynthesis Co., 1996... 

Electrolysis offers an alternative route for organic synthesis via the formation of anion and cation radical intermediates. However, traditional electrolytic methods suffer from a number of limitations such as heterogeneity of the electric field, thermal loss due to heating and obligatory use of supporting electrolytes. These factors either hamper electrosynthetic efficiency or make the separation process cumbersome. The combination of electrosynthesis and microreaction technology effectively overcomes these difficulties. 

Since boron-doped diamond electrodes are commercially available, most of these suppliers offer a wide variety of electrolysis cells. Modular electrochemical cells equipped with BDD electrodes have been reported in detail [122]. However, most of these cells were designed for waste water treatment and were not suitable for electrosynthesis in organic media. Electrolysis cells for synthetic purposes designed for a small volume made of organic-compatible materials are required. Additionally, any contact of the support with the organic electrolyte has to be strictly eliminated in order to avoid the corrosion. Most BDD electrodes are on a silicon support which causes eventual loss of the BDD electrode by the brittle nature of crystalline silicon. Consequently, the material used for sealing has to be inert but soft enough to avoid friction of the silicon support. The available BDD... 

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