Electroorganic processes

Attempts to emulate the few large-scale electroorganic processes, eg, production of tetraalkyUead and adiponittile, have often led to fmstration. 

Product Recovery. Comparison of the electrochemical cell to a chemical reactor shows the electrochemical cell to have two general features that impact product recovery. CeU product is usuaUy Uquid, can be aqueous, and is likely to contain electrolyte. In addition, there is a second product from the counter electrode, even if this is only a gas. Electrolyte conservation and purity are usual requirements. Because product separation from the starting material may be difficult, use of reaction to completion is desirable ceUs would be mn batch or plug flow. The water balance over the whole flow sheet needs to be considered, especiaUy for divided ceUs where membranes transport a number of moles of water per Earaday. At the inception of a proposed electroorganic process, the product recovery and refining should be included in the evaluation to determine tme viabUity. Thus early ceU work needs to be carried out with the preferred electrolyte/solvent and conversion. The economic aspects of product recovery strategies have been discussed (89). Some process flow sheets are also available (61). 

Economic Aspects. Several pubUcations probe the various areas of electroorganic process cost. CeUs (90), overaU process costs (41,91—93), economic optimization (94,95), and a comparison between the chemical and electrochemical methods (91,96) are aU discussed. 

Table 5. Some Electroorganic Processes Operated on a Pilot-Plant or Commercial Scale...

Maltol. Otsuka Chemical Co. in Japan has operated several electroorganic processes on a small commercial scale. It has used plate and frame and aimular cells at currents in the range of 4500—6000 A (133). The process for the synthesis of maltol [118-71 -8], a food additive and flavor enhancer, starts from furfural [98-01-1] (see Food additives Flavors and spices). The electrochemical step is the oxidation of a-methylfurfural to give a cycHc acetal. The remaining reaction sequence is acid-catalyzed ring expansion, epoxidation with hydrogen peroxide, and then acid-catalyzed rearrangement to yield maltol, ie ... 

Electroorganic synthesis will be covered in section 4.5.4. It is appropriate, however, to make a reference here to the role of u/s in electroorganic processes. Atobe et al. (2000) have reported the effect of u/s in the reduction of acrylonitrile and mixtures of acrylonitrile and methyl acrylate. The selectivity for adiponitrile in the reduction of acrylonitrile was significantly increased under u/s irradiation with a power intensity over the u/s cavitation threshold ( 600 cm ). This favourable influence of u/s can be attributed to the improved mass transfer of acrylonitrile to the electrode interface by the cavitational high-speed jet-stream. 

Asami R, Atobe M, Fuchigami T (2006) Ultrasonic effects on electroorganic processes. Part 27. Electroreduction of acrylonitrile at suspended lead particle-electrode. Ultrason Sonochem 13 19-23, and the series... 

Danly [70, 71] has presented three criteria on which commercialization of electroorganic process depends ... 

Danly D In Emerging opportunities for electroorganic processes, Marcel Dekker, New York, p 229 through (40)... 

The use of Zn powder in a multiphase system is a way to solve many of the difficulties involved in the operation of electroorganic processes under a low maximum current density [513-516]. A three-phase system, water/organic, substrate/metal powder can be used for the reduction of halides and nitro compounds under a high... 

Danly D (1984) in Emerging Opportunities for Electroorganic Processes, Marcel Dekker, New York p 229 ff... 

Currently, adiponitrile is the only organic chemical produced in large quantity (108 kg/yr) by an electrochemical route. Other smaller-scale products include gluconic acid, piperidine, and p-aminophenol. Electroorganic syntheses in supercritical organic electrolytes have been demonstrated in bench-scale reactors. Production of dimethyl carbonate from the mixture-critical region was performed. There are at least a dozen electroorganic processes that are... 

The direct electrochemical methoxylation of furan derivatives represents another technically relevant alkoxylation process. Anodic treatment of furan (14) in an undivided cell provides 2,5-dimethoxy-2,5-dihydrofuran (15). This particular product represents a twofold protected 1,4-dialdehyde and is commonly used as a C4 building block for the synthesis of N-heterocycles in life and material science. The industrial electroorganic processes employ graphite electrodes and sodium bromide which acts both as supporting electrolyte and mediator [60]. The same electrolysis of 14 can be carried out on BDD electrodes, but no mediator is required The conversion is performed with 8% furan in MeOH, 3% Bu4N+BF4, at 15 °C and 10 A/dm2. When 1.5 F/mol were applied, 15 is obtained in 75% yield with more or less quantitative current efficiency. Treatment with 2.3 F/mol is rendered by 84% chemical yield for 15 and a current efficiency of 84% [61, 62]. In contrast to the mediated process, furan is anodically oxidized in the initial step and subsequently methanol enters the scene (Scheme 7). 

This cell is very convenient for many electroorganic processes and is probably the most successful system in respect of the numbers of realized industrial processes. 

In electroorganic processes, the typical workup procedure is accomplished in three steps ... 

Figure 20. Factors important for successful electroorganic processes.

Fig. 5.4. Thermography of an electroorganic process in acetonitrile under microwave irradiation.

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