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

• This invention relates to a new electrochemical process for the production of phthalaldehyde acetals.
• Phthalaldehyde acetals can be e.g. by reacting phthalaldehydes with o-esters (J. Chem. Soc. Perkin II, 1975, 1656).
• the phthalaldehydes required as starting materials are e.g. according to the sommelet process from bis (chloromethyl) benzenes and hexamethylenetetramine. This e.g. in J. Chem. Soc.
• the process described in 1950, 2141 to 2145 provides only moderate yields and is not very environmentally friendly.
• a process for the preparation of phthalaldehyde acetals is known from DE-OS 31 08 790, in which ⁇ , ⁇ , ⁇ , ⁇ '-tetrahalo-xylenes are reacted with alkali metal alcoholates.
• a disadvantage of this synthesis is the poor accessibility of the tetrahalogen xylenes, which arise in the halogenation of xylenes only in poor selectivities in a mixture with xylenes of different degrees of halogenation.
• phthalaldehyde acetals of the general formula I in which R is an alkyl radical having 1 to 4 carbon atoms can advantageously be prepared by alkoxymethylbenzenes of the general formula electrochemically oxidized in the presence of an alkanol of the formula ROH, where R has the meaning given above. It is particularly surprising that the oxidation state of the dialdehydes can be selectively achieved by the process of the invention.
• Alkoxyme t hylbenzole of the formula may be mentioned are called II: 1,2-, 1,3- or 1,4-bis (methoxymethyl) benzene, 1,2-, 1,3- or l, 4-bis ( ethoximethyl) benzene, 1,2-, 1,3- or 1,4-bis (propoximethyl) benzene, 1,2-, 1,3- or 1,4-bis (isopropoximethyl) benzene and 1,2-, 1,3- or 1,4-bis (tert-butox-methyl) benzene.
• Alcohols of the formula ROH are, for example, methanol, ethanol, propanol and butanol. Hee / GS
• the electrochemical oxidation according to the invention can be carried out in technically customary electrolysis cells. Undivided flow cells are particularly suitable.
• a solution of the bis- (alkoxymethyl) benzene of the formula II in the alkanol is expediently used as the electrolyte, which solution may contain an auxiliary electrolyte to improve the conductivity.
• Suitable auxiliary electrolytes are, for example, bases such as alkali alcoholates, neutral salts such as fluorides, tetrafluoroborates, sulfonates and sulfates and acids such as alkyl sulfonic acids, alkanesulfonic acids and sulfuric acid.
• Neutral auxiliary electrolytes such as KF and KSO 3 C 6 H 5 or acidic auxiliary electrolytes such as H 2 SO 4 , CH 3 SO 3 H or C 6 H 5 SO 3 H are preferably used.
• Precious metals metal oxides such as Ru0 2 and Pb0 2 or graphite are used as anodes in the electrolysis according to the invention.
• the preferred anode material is graphite.
• suitable cathode materials are steel, iron, nickel, lead or graphite.
• the current densities are 0.1 to 20 A / dm, current densities between 2 and 8 A / dm are preferred.
• the temperatures are expediently at least 5 ° C. below the boiling point of the alkanol used, provided the electrolysis is carried out without pressure. For example, electrolysis is carried out at -5 to 55 ° C, preferably 10 to 50 ° C.
• the electrolysis is carried out with 4 to 12 F / mol of bis (alkoxymethyl) benzene. It is preferably electrolyzed with 7 to 10 F / mol of bis (alkoxymethyl) benzene, so that the bis (alkoxymethyl) benzene is largely reacted.
• the electrolysis can be carried out batchwise or continuously.
• the electrolysis discharges are preferably worked up by distillation. Unreacted alkanol can be returned to the electrolysis without purification. Electrode inactivations or electrode corrosion are not observed even when the electrolyte is reused many times.
• the phthalaldehyde acetals obtainable by the process of the invention are intermediates e.g. for the production of dyes and optical brighteners and also for the synthesis of special polymers.
• the electrolyte was pumped through the cell at a flow rate of 200 l / h via a heat exchanger. After the electrolysis had ended, the electrolysis discharge was neutralized with sodium methylate. Then methanol was distilled off at normal pressure and 65 to 75 ° C. and the precipitated salt was separated off at 60 to 70 ° C. using a pressure filter. The residue was pure distilled at 100 to 120 ° C and 3 mbar. This gave 3.5 g of 1,4-bis (methoxymethyl) benzene and 222.2 g of terephthalaldialdehyde tetramethyl acetal.
• the electrolyte was pumped through the cell at a flow rate of 200 l / h via a heat exchanger.
• the electrolysis discharge was like described in Example 1, but worked up without the addition of sodium methylate. Working up gave 0.4 g of 1,4-bis (methoxymethyl) benzene and 158.2 g of terephthalaldehyde tetramethyl acetal. From this, a conversion of 1,4-bis (methoxymethyl) benzene of 99.7%, a yield of terephthalaldehyde tetramethyl acetal of 80.1% and a selectivity for terephthalaldehyde tetramethyl acetal of 80.4% are calculated.
• the recovered methanol and potassium benzene sulfonate could be used again for electrolysis.
• the electrolyte was pumped through the cell at a flow rate of 200 l / h via a heat exchanger.
• methanol was distilled off from the electrolysis discharge at atmospheric pressure and 65 to 80.degree.
• the precipitated potassium benzene sulfonate was separated off using a pressure filter and the filtrate was fractionally distilled at 100 to 120 ° C. and 5 mbar. This gave 3.8 g of 1,2-bis (methoxymethyl) benzene and 230.3 g of o-phthalaldehyde tetramethyl acetal.

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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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Citations (3)

• 1984
  • 1984-06-14 DE DE19843421976 patent/DE3421976A1/de not_active Withdrawn
• 1985
  • 1985-06-07 EP EP85107063A patent/EP0164705B1/fr not_active Expired
  • 1985-06-07 DE DE8585107063T patent/DE3560532D1/de not_active Expired
  • 1985-06-14 JP JP60128382A patent/JPH0647746B2/ja not_active Expired - Lifetime

Patent Citations (3)

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