Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/25—Reduction

Definitions

• the present invention relates to an electro-reduction process of nitro derivatives.
• the yield does not exceed 80%; the side reactions are numerous leading to the formation of light amines and of heavy residue which must be separated from the desired amino alcohol, by several successive rectifications which result in a significant investment and consumption of energy; in addition, one cannot avoid the formation of N-CH3 derivative which is then difficult to separate from the desired amino derivative.
• Reaction (1) takes place at an electronegative potential close to -0.8 volts. It can therefore be implemented on a large number of materials with low hydrogen overvoltage such as stainless steel, copper, nickel.
• the reaction (2) on the contrary requires a potential close to or greater than -1.5 volts; it can only be carried out on materials with a high oxygen sustension in order to favor the reduction of the -NHOH group, with respect to that of the proton.
• the choice of material is then limited to four or five metals such as mercury, lead, zinc, cadmium, tin or carbon-based materials such as graphite and glassy carbon.
• the cathode consists of a support metal and an active element which, depending on the potential of the surface of the support metal, will either be in solution in the form of a cation, or reduced to a metal constituting a metallic deposit on the support metal.
• support metal is quite wide; it will be done among the elements for which the equilibrium potential M n + + ne ⁇ ⁇ Mo (3) is clearly less electro-negative than the potential of reaction (1) thus guaranteeing the inalterability of the support metal; in addition the support metal will be endowed with a high electrical conductivity; copper and nickel are particularly well suited.
• the active element will be chosen from among the elements for which the equilibrium potential of the reaction (3) is between the potentials reactions (1) and (2); in addition, when the active element is in the Mo state, the metal surface thus produced must be such that the hydrogen overvoltage there is as high as possible so that the reaction (2) is favored therein. proton reduction screw; finally, the active element, in the state (M n + ) must be soluble in the catholyte.
• Zinc and cadmium are elements well suited to this use.
• Zinc will preferably be chosen because of the low toxicity of the Zn++ cation.
• the method of electrochemical reduction of alphatic nitro derivatives is implemented with reactivation of the cathode.
• the active element has the property of changing state according to the potential of the support metal, and of being either in the form of a cation in solution in the catholyte or in the form of a metallic deposit on the support metal so that these transformations are obtained simultaneously with the successive reactions of reduction of the nitro derivative, they involve with each operation, a complete renewal of the electro-active surface with high hydrogen overvoltage.
• the electro-deposition of the active element on the support metal takes place under good conditions when the quantity of metal cation present in an operation is between 1 and 10 millimoles per dm2 of cathode, preferably 2 to 6 millimoles.
• a cell with two separate compartments is used.
• a copper cathode is immersed in an aqueous sulfuric solution of nitroalcohol in which a small quantity of soluble salts of zinc (Zn++), cadmium (Cd++) has been added; an electric current is established and maintained between the two electrodes such that the reduction reactions of the group -NO2 take place at a sufficient speed; the copper cathode then takes a potential which rises gradually with the evolution of the organic electro-reduction in -NHOH then -NH2 to a more electronegative value than the potential of equilibrium (3); the cation is then reduced and becomes a metallic deposit, constituting on the copper a surface with a high hydrogen overvoltage on which the reduction of the proton will be inhibited in favor of the transformation into amine of the hydroxyl amine group.
• the temperature of the catholyte can be between 10 and 100 ° C, preferably between 20 and 60 ° C.
• the density of the optimal cathode current is not very related to the transformation implemented; it will be chosen to obtain the maximum productivity of the device, taking into account the maximum current density, tolerable without deterioration by the membrane and the unit energy consumption, which largely depends on the geometric structure of the cell .
• nitro derivatives in particular to nitro-alcohols represented by the formula: wherein R1 and R2 together or separately are hydrogen, a hydroxyalkyl radical, such as hydroxymethyl, or a linear or branched alkyl radical, in particular, methyl, ethyl, propyl or containing a number of carbon atoms greater than three.
• a cell comprising three parallelepipedic compartments separated by two partitions composed of a cation-exchange membrane of the sulfonic type sold under the brand "Ionac 3470" (Company Ionac), consisting of a polypropylene support and cation-exchange sites, the cathode is placed in the central compartment and two anodes made of ruthenium titanium plate in the external anode compartments.
• Ionac 3470 Company Ionac
• the anolyte is a 20% sulfuric acid solution. We operate at constant intensity corresponding to a cathode current density of 10 A / dm2 (amperes per square decimeter). The load of material to be reduced is 150 millimoles of nitro derivative.
• the anolyte is stationary, while the catholyte is recycled, for the duration of the test, on an external circuit consisting of a peristaltic pump and a glass exchanger allowing thermal conditioning of the catholyte.
• the temperature of the catholyte is maintained between 20 and 30 ° C during the first stage in which it receives an effective quantity of electricity of 4 M / mole; then it is raised to 60 ° C.
• the progress of the reaction is monitored by potentiometric analysis of the catholyte which measures the contents of H+, R-NHOH, R-NH2; a semi-quantitative metric pH assay allows the presence or disappearance or nitro derivative to be ascertained.
• the cathode is a copper plate: its useful surface is 80 cm2; the interpolar voltage varies between 3 and 5 volts.
• the cathode is a copper plate cadmium-plated by conventional electroplating methods.
• test 2 a new copper plate is used and, in solution in the catholyte, at the start of the operation, 1 g of Cd++ is added in the form of cadmium sulphate previously dissolved: at the end of the operation , we see that the copper plate is covered with a gray deposit of metallic cadmium but quite irregular and not very adherent.
• test 3 the procedure is as in test 2, replacing the cadmium sulfate with zinc sulfate, and thus 580 mg of Zn++ is introduced; at the end of the operation, the copper plate is covered with a zinc deposit of more regular appearance, and more adherent than that of cadmium.
• the electrolyte is stopped periodically and the cathode is examined; at the first examination, carried out when the current used is around 3 F / mole, the cathode has found the characteristic red color of copper over almost its entire surface; after 4 F / mole, it resumed a uniform gray appearance characteristic of a cadmium deposit.
• the total cathode surface is 4 dm2; it consists of two copper plates 1 mm thick, slid into each of the cathode compartments; the anodes are made of platinum titanium.
• the anolyte is an 18% aqueous sulfuric solution.
• the nitroalcohol used is nitro-2-methyl-2-propanediol 1-3.
• Test 6 was carried out after test 5 without adding Zn++, the concentration given in the table resulting from an a posteriori assay by pickling and chemical analysis at the end of test 6; the same for test 7 compared to test 8.
• Av (RF> 95%) is the progress of the reaction expressed in the same unit, which was reached before the overall faradaic yield fell below 95%.
• nitropropane formylation product which mainly contains nitro-2-butanol-1 but also nitropropane and nitro-2-ethyl 2 propanediol 1-3.
• the results below are given relative to an average molecular weight of nitro derivative deduced from the following standard analysis: Nitrobutanol 86% Nitroethylpropanediol 11% Nitropropane 1% H2O 1.5%
• the energy consumption is 14.5 kwh.kg.
• the advancement rate, reached before the current yield falls below 95%, is 4.8 F / mole.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
• Nitrogen Condensed Heterocyclic Rings (AREA)

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• 1987
  • 1987-04-16 FR FR8705428A patent/FR2614044B1/fr not_active Expired - Fee Related
• 1988
  • 1988-03-29 EP EP88400751A patent/EP0287419B1/de not_active Expired - Lifetime
  • 1988-03-29 ES ES88400751T patent/ES2021847B3/es not_active Expired - Lifetime
  • 1988-03-29 DE DE8888400751T patent/DE3862795D1/de not_active Expired - Lifetime
  • 1988-03-29 AT AT88400751T patent/ATE63576T1/de active
  • 1988-04-11 US US07/180,053 patent/US4830717A/en not_active Expired - Fee Related
  • 1988-04-15 CA CA000564313A patent/CA1309968C/fr not_active Expired - Lifetime
  • 1988-04-15 JP JP63091881A patent/JPS63277781A/ja active Pending
• 1991
  • 1991-05-16 GR GR90401235T patent/GR3001948T3/el unknown

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