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
  • C25B3/23—Oxidation

Definitions

• the acetals I serve - especially in the form of the corresponding benzaldehydes - as fragrances or as intermediates for medicines or fragrances. Some of them are known or can be produced by known processes.
• Compounds I can also be prepared from dialkyl-substituted benzenes by electrooxidation.
• DE-A 3 322 399 the oxidation of p-xylene to p-methylbenzaldehyde dimethyl acetal proceeds with a selectivity of 79%.
• an alkyl substituent is branched, such as in p-cymene (p-isopropyltoluene)
• the selectivity of the reaction to compounds I drops drastically due to oxidation of the isopropyl group (ES 2 009 174).
• ES 2 009 174 According to J. Chem. Res. (S), 228-9 (1986), the electrooxidation of o-xylene also leads to a number of by-products.
• the object of the invention was to make acetals I from benzyl ethers II more selective and thus more economically accessible.
• the method according to the invention can be illustrated as follows:
• the starting compounds II are known and can be obtained by known methods, for example from the appropriately substituted benzyl chlorides.
• alkyl, cycloalkyl and aryl groups can carry substituents, C1-C2-alkyl radicals or halogen being preferred.
• the electrochemical oxidations can be carried out in divided, preferably undivided, flow cells.
• the electrolyte is composed of the starting compound II, an alcohol R1-OH and an auxiliary electrolyte.
• the electrolyte may contain a solvent which is inert under the electrolysis conditions, such as acetonitrile; however, the electrolysis is preferably carried out without such a solvent.
• the electrolyte preferably contains 1-49%, preferably 5-30% by weight of the benzyl ether II, 50-98.9%, preferably 70-95% by weight of the alkanol R1-OH and 0.1-5%, preferably 0.2-3% by weight of the auxiliary electrolyte
• Weakly basic or neutral or acidic salts are particularly suitable as auxiliary electrolytes. Examples are fluorides, tetrafluoroborates, sulfonates, sulfates, phosphates and phosphonates of alkali metals such as potassium fluoride and sodium phenyl sulfonate.
• Ammonium salts such as tetramethylammonium methyl sulfate and acidic compounds such as sulfuric acid, alkyl and aryl sulfonic acids such as methyl or benzenesulfonic acid are also suitable.
• the electrolysis is carried out in the acidic, neutral or weakly basic range. This range is indicated by the pH of the electrolyte.
• the pH of the electrolyte is determined in such a way that equal volumes of electrolyte and water are mixed and the pH of the resulting solution is measured using known methods. The measured pH should be less than 10, but a neutral or acidic solution is preferred.
• Precious metals such as platinum or oxides such as chromium and ruthenium oxide and mixed oxides such as Ti / RuO x are suitable as anode materials.
• the preferred material is graphite.
• the electrolysis can be carried out batchwise or continuously, it being possible, if desired, for unreacted starting material to be returned to the reaction.
• the current density for the process according to the invention can be chosen within wide limits from 0.1 to 25 A / dm2, preferably 1-10 A / dm2.
• the oxidations are carried out at temperatures from 0 to 120 ° C., preferably 20-80 ° C. There may be reduced pressure or normal pressure. In the presence of low-boiling components, it is also possible to work under increased pressure up to 10 bar, preferably up to 3 bar.
• the amounts of charge are generally 1.5 to 6 F / mol II, preferably 2 to 4 F / mol II.
• the reaction solution is worked up in a known manner, preferably by distillation.
• the process according to the invention allows the benzaldehyde acetals I to be prepared selectively, the product generally only having to be separated off from incompletely reacted starting material.
• the oxidation of the side group R3R4CH- is not observed or only to a minimal extent in the process according to the invention.
• the acetals I can be hydrolyzed to the corresponding benzaldehydes in a manner known per se. Some of these themselves serve as fragrances, for example o-tolylaldehyde and p-tolylaldehyde, or they are valuable intermediates. Cuminaldehyde, for example, is a precursor for the production of (4-isopropylcyclohexyl) methanol (mayol).

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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)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Cited By (4)

Citations (10)

• 1992
  • 1992-01-22 DE DE4201544A patent/DE4201544A1/de not_active Withdrawn
  • 1992-12-24 EP EP92121990A patent/EP0554564A1/fr not_active Withdrawn

Patent Citations (10)

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