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EP0245707A1 - Process for manufacturing of cyclic hemiacetals - Google Patents

Process for manufacturing of cyclic hemiacetals Download PDF

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EP0245707A1
EP0245707A1 EP87106233A EP87106233A EP0245707A1 EP 0245707 A1 EP0245707 A1 EP 0245707A1 EP 87106233 A EP87106233 A EP 87106233A EP 87106233 A EP87106233 A EP 87106233A EP 0245707 A1 EP0245707 A1 EP 0245707A1
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thf
electrolyte
cyclic
current densities
electrolysis
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EP0245707B1 (en
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Fritz Prof. Dr. Beck
Bernd Dr. Wermeckes
Harry Dr. Schulz
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BASF SE
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    • 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

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  • This invention relates to a process for the preparation of ⁇ -hydroxyaldehydes or their cyclic hemiacetals by anodic oxidation of cyclic ethers.
  • ⁇ -Hydroxyaldehydes are valuable intermediate products as ⁇ , ⁇ -bifunctional compounds.
  • these compounds tend to form cyclic semiacetals, namely ⁇ -hydroxy-tetrahydrofuran (THF- OH) or ⁇ -hydroxy-tetrahydropyrans.
  • THF-OH ⁇ -hydroxy-tetrahydrofuran
  • ⁇ -hydroxyaldehydes are easily accessible through aldol condensation, ⁇ -hydroxyaldehydes are less easy to produce.
  • THF-OH is obtained by chemical oxidation of tetrahydrofuran (THF) with aryldiazonium salts:
  • ⁇ -hydroxyaldehydes (I) or their cyclic hemiacetals (II) of the formulas in which A is a saturated hydrocarbon radical with 2 to 16 carbon atoms, which may contain the bridge member -O-, can be produced with high selectivities by using cyclic ethers of the formula in which A has the abovementioned meaning, anodized in aqueous solution at current densities of over 30 mAcm ⁇ 2.
  • the starting materials of formula III are e.g. THF, tetrahydropyran or 1,4-dioxane.
  • the cyclic ethers of the formula III are used in the form of their aqueous solutions in the electrolysis.
  • the electrolyte solutions preferably contain acids with anodically stable anions, in particular sulfuric acid or phosphoric acid.
  • cosolvents for example methanol or acetonitrile, are added in concentrations of 10 to 80% by weight.
  • the starting material can be emulsified in the electrolyte.
  • electrolytes 0.1 to 5, in particular 0.5 to 2, molar aqueous solutions of the acids mentioned are used as electrolytes.
  • the electrolytes can also contain buffer substances in order to adjust the pH of the electrolyte to values from 0 to 6.
  • conductive salts known per se such as sodium sulfate.
  • the content of the cyclic starting materials in the electrolyte is about 1 to 6 mol / dm3.
  • cathode material such as steel, stainless steel, graphite, graphite-filled plastic or copper, is used as the cathode in electrolysis.
  • the platinum metals or their oxides are particularly suitable as anode material. Smooth platinum, e.g. as a sheet metal or as a composite electrode.
  • graphite and glass-carbon are also useful anode materials.
  • the conversion of the cyclic ether is advantageously kept in the range from 10 to 80%, preferably 20 to 60%. But you can also electrolyze with higher sales, because e.g. Have the THF and THF-OH separated slightly by distillation. Electrolysis is e.g. at temperatures from 0 to 50 ° C, preferably at 30 to 40 ° C.
  • Electrolysis is carried out at current densities of over 30 mAcm ⁇ 2, e.g. in a range from over 30 to 1000, preferably 100 to 300 mAcm ⁇ 2.
  • the current densities refer to the true surface, so in the case of smooth platinum they are practically identical to the current density based on the geometric surface. In view of the high platinum costs, the fact that the current yields increase with increasing current densities is a welcome effect.
  • Electrolysis is preferably carried out in divided cells or in quasi-divided cells, as described in Chem. Ber. 118, 3771-3779 (1985), are carried out in order to avoid a reduction in the aldehyde function. However, you can also work in undivided cells if you use cathodes with a low hydrogen overvoltage.
  • the process according to the invention gives, for example, THF-OH from THF with high selectivity. This advantageous result could not be expected, since succinic acid is obtained in the known electrolytic oxidation of THF, as described, for example, in GB-PS 590 310 and in which current densities of 10 mAcm ⁇ 2 are used.
  • a cylindrical glass vessel of 400 ml with an internal thermometer and a reflux condenser with a cooling jacket and flat ground cover served as the electrolytic cell.
  • the electrolyte was stirred magnetically.
  • the unreacted THF was also analyzed by HPLC, but with a methanol / water mixture 1/4 V / V as eluent (2 ml min ⁇ 1). 108 mmol of unreacted THF was recovered, i.e. So 92 mmol THF were implemented. The material yields were 88% (THF-OH) and 1.7% (BL).
  • the crude product was distilled in vacuo (1.5 torr). For stabilization, a little 85% phosphoric acid or cation exchange membrane pieces in the H+ form were added to the crude product. The boiling point was 24 to 30 ° C (2 mm Hg).
  • the platinum loss found on the anode after the experiment was 0.26 mg, corresponding to a specific amount of 0.04 mg / Ah.
  • the average cell voltage was 7.0 V. After 27 minutes, corresponding to a theoretical current conversion of 60%, the experiment was stopped.
  • the direct determination of the products in the electrolysis discharge resulted in: THF-OH: 3.5% SA; BL in traces; BS in traces.
  • THF-OH was formed selectively, but only with a low current efficiency due to the small oxygen overvoltage of the electrode.

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  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
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  • Metallurgy (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

Verfahren zur Herstellung von ω-Hydroxyaldehyden (I) oder deren zyklischer Halbacetale (II) der Formeln

Figure imga0001
in denen A einen gesättigten Kohlenwasserstoffrest mit 2 bis 16 C-Ato­men, der das Brückenglied -O- enthalten kann, bedeutet, bei dem man zyklische Ether der Formel
Figure imga0002
 in der A die obengenannte Bedeutung hat, in wäßriger Lösung bei Strom­dichten von über 30 mAcm⁻² anodisch oxidiert. Process for the preparation of ω-hydroxyaldehydes (I) or their cyclic hemiacetals (II) of the formulas
Figure imga0001
 in which A is a saturated hydrocarbon radical with 2 to 16 carbon atoms, which may contain the bridge member -O-, in which cyclic ethers of the formula
Figure imga0002
 in which A has the abovementioned meaning, anodized in aqueous solution at current densities of over 30 mAcm⁻².

Description

Diese Erfindung betrifft ein Verfahren zur Herstellung von ω-Hydroxy­aldehyden oder deren zyklischer Halbacetale durch anodische Oxidation zyklischer Ether.This invention relates to a process for the preparation of ω-hydroxyaldehydes or their cyclic hemiacetals by anodic oxidation of cyclic ethers.

ω-Hydroxyaldehyde stellen als α,ω-bifunktionelle Verbindungen wertvolle Zwischenprodukte dar. Im Falle des ω-Hydroxy-butanals bzw. ω-Hydroxy-­pentanals tendieren diese Verbindungen stark zur Ausbildung der zykli­schen Semiacetale, nämlich des α-Hydroxy-tetrahydrofurans (THF-OH) bzw. α-Hydroxy-tetrahydropyrans. Während z.B. β-Hydroxyaldehyde durch Aldol­kondensation leicht zugänglich sind, lassen sich die ω-Hydroxyaldehyde weniger einfach herstellen. So wird z.B. THF-OH durch chemische Oxidation von Tetrahydrofuran (THF) mit Aryldiazoniumsalzen erhalten:

Figure imgb0001
ω-Hydroxyaldehydes are valuable intermediate products as α, ω-bifunctional compounds. In the case of ω-hydroxybutanal or ω-hydroxypentanal, these compounds tend to form cyclic semiacetals, namely α-hydroxy-tetrahydrofuran (THF- OH) or α-hydroxy-tetrahydropyrans. For example, while β-hydroxyaldehydes are easily accessible through aldol condensation, ω-hydroxyaldehydes are less easy to produce. For example, THF-OH is obtained by chemical oxidation of tetrahydrofuran (THF) with aryldiazonium salts:
Figure imgb0001

Die Ausbeuten sind aber bei diesem in Angew. Chem. 70, 211 (1958) be­schriebenen Verfahren gering. Die eigene Nacharbeitung zeigte, daß wenig THF-OH neben viel Butyrolacton (BL) und daneben auch Bernsteinsäure (BS) entsteht. THF-OH läßt sich auch durch Hydratation von 2,3-Dihydrofuran herstellen (Bull. Soc. Chim. France, Memoires Presentés à la Société Chimique 1950, S. 668):

Figure imgb0002
The yields in this are in Angew. Chem. 70 , 211 (1958) described methods low. Our own rework showed that little THF-OH was produced in addition to a lot of butyrolactone (BL) and also succinic acid (BS). THF-OH can also be produced by hydration of 2,3-dihydrofuran (Bull. Soc. Chim. France, Memoires Presentés à la Société Chimique 1950, p. 668):
Figure imgb0002

Nach eigenen Arbeiten gelingt die letzte Stufe mit 60 % Ausbeute.According to our own work, the last stage succeeds with a 60% yield.

In der EP-B-129 802 wird eine Rh-komplex-katalysierte Hydroformylierung von Allylalkohol beschrieben

    CH₂ = CH - CH₂OH + H₂ + CO → CHO - (CH₂)₃ - OH,

bei der neben dem gewünschten Produkt (79 % Selektivität) mehrere Neben­produkte erhalten werden.EP-B-129 802 describes a Rh complex-catalyzed hydroformylation of allyl alcohol

CH₂ = CH - CH₂OH + H₂ + CO → CHO - (CH₂) ₃ - OH,

in which several by-products are obtained in addition to the desired product (79% selectivity).

Es wurde nun überraschend gefunden, daß man ω-Hydroxyaldehyde (I) oder deren zyklische Halbacetale (II) der Formeln

Figure imgb0003
in denen A einen gesättigten Kohlenwasserstoffrest mit 2 bis 16 C-Ato­men, der das Brückenglied -O- enthalten kann, bedeutet, mit hohen Selek­tivitäten dadurch herstellen kann, daß man zyklische Ether der Formel
Figure imgb0004
 in der A die obengenannte Bedeutung hat, in wäßriger Lösung bei Strom­dichten von über 30 mAcm⁻² anodisch oxidiert.It has now surprisingly been found that ω-hydroxyaldehydes (I) or their cyclic hemiacetals (II) of the formulas
Figure imgb0003
 in which A is a saturated hydrocarbon radical with 2 to 16 carbon atoms, which may contain the bridge member -O-, can be produced with high selectivities by using cyclic ethers of the formula
Figure imgb0004
 in which A has the abovementioned meaning, anodized in aqueous solution at current densities of over 30 mAcm⁻².

Im Falle des Tetrahydrofurans (THF) ist der elektrochemische Prozeß wie folgt zu formulieren:

Figure imgb0005
In the case of tetrahydrofuran (THF), the electrochemical process should be formulated as follows:
Figure imgb0005

Als Ausgangsstoffe der Formel III kommen z.B. THF, Tetrahydropyran oder 1,4-Dioxan in Betracht.The starting materials of formula III are e.g. THF, tetrahydropyran or 1,4-dioxane.

Die cyclischen Ether der Formel III werden in Form ihrer wäßrigen Lösun­gen in die Elektrolyse eingesetzt. Die Elektrolytlösungen enthalten vor­zugsweise Säuren mit anodisch stabilen Anionen, insbesondere Schwefel­säure oder Phosphorsäure. Im Falle der zyklischen Ether mit höherer Koh­lenstoffzahl werden Colösungsmittel, z.B. Methanol oder Acetonitril, in Konzentrationen von 10 bis 80 Gew.% zugesetzt. Zusätzlich oder unabhängig davon kann das Edukt im Elektrolyt emulgiert sein.The cyclic ethers of the formula III are used in the form of their aqueous solutions in the electrolysis. The electrolyte solutions preferably contain acids with anodically stable anions, in particular sulfuric acid or phosphoric acid. In the case of cyclic ethers with a higher carbon number, cosolvents, for example methanol or acetonitrile, are added in concentrations of 10 to 80% by weight. In addition or independently of this, the starting material can be emulsified in the electrolyte.

Zweckmäßigerweise verwendet man als Elektrolyte 0,1 bis 5, insbesondere 0,5 bis 2 molare wäßrige Lösungen der genannten Säuren. Anstelle der Säuren können die Elektrolyte aber auch Puffersubstanzen enthalten, um den pH des Elektrolyten auf Werte von 0 bis 6 einzustellen. Außerdem kann man auch an sich bekannte Leitsalze, wie Natriumsulfat zusetzen. Der Gehalt der zyklischen Ausgangsstoffe im Elektrolyten beträgt etwa 1 bis 6 Mol/dm³.Advantageously, 0.1 to 5, in particular 0.5 to 2, molar aqueous solutions of the acids mentioned are used as electrolytes. Instead of the acids, the electrolytes can also contain buffer substances in order to adjust the pH of the electrolyte to values from 0 to 6. In addition, it is also possible to add conductive salts known per se, such as sodium sulfate. The content of the cyclic starting materials in the electrolyte is about 1 to 6 mol / dm³.

Als Kathoden verwendet man bei Elektrolysen übliches Kathodenmaterial, wie Stahl, Edelstahl, Graphit, graphitgefüllter Kunststoff oder Kupfer. Als Anodenmaterial sind die Platinmetalle oder deren Oxide besonders gut geeignet. Bevorzugt sind glattes Platin, z.B. als Blech- oder als Ver­bundelektrode. Im Prinzip sind auch Graphit und Glas-Kohlenstoff brauch­bare Anodenmaterialien.Common cathode material, such as steel, stainless steel, graphite, graphite-filled plastic or copper, is used as the cathode in electrolysis. The platinum metals or their oxides are particularly suitable as anode material. Smooth platinum, e.g. as a sheet metal or as a composite electrode. In principle, graphite and glass-carbon are also useful anode materials.

Den Umsatz des zyklischen Ethers hält man bei diskontinuierlichen Elek­trolysen zweckmäßigerweise im Bereich von 10 bis 80 %, vorzugsweise 20 bis 60 %. Man kann aber auch mit höheren Umsätzen elektrolysieren, da sich z.B. THF und THF-OH leicht destillativ trennen lassen. Die Elektro­lyse wird z.B. bei Temperaturen von 0 bis 50°C, vorzugsweise bei 30 bis 40°C durchgeführt.In discontinuous electrolysis, the conversion of the cyclic ether is advantageously kept in the range from 10 to 80%, preferably 20 to 60%. But you can also electrolyze with higher sales, because e.g. Have the THF and THF-OH separated slightly by distillation. Electrolysis is e.g. at temperatures from 0 to 50 ° C, preferably at 30 to 40 ° C.

Man elektrolysiert bei Stromdichten von über 30 mAcm⁻², z.B. in einem Bereich von über 30 bis 1000, vorzugsweise 100 bis 300 mAcm⁻². Die Strom­dichten beziehen sich auf die wahre Oberfläche, sind also im Falle des glatten Platins praktisch identisch mit der Stromdichte, bezogen auf die geometrische Oberfläche. Daß die Stromausbeuten mit zunehmenden Strom­dichten ansteigen ist in Anbetracht der hohen Platinkosten ein willkomme­ner Effekt.Electrolysis is carried out at current densities of over 30 mAcm⁻², e.g. in a range from over 30 to 1000, preferably 100 to 300 mAcm⁻². The current densities refer to the true surface, so in the case of smooth platinum they are practically identical to the current density based on the geometric surface. In view of the high platinum costs, the fact that the current yields increase with increasing current densities is a welcome effect.

Der Elektrolyt wird durch Zwangskonvektion bewegt, z.B. durch Rühren, Umpumpen oder Vibrieren. Da aber an der Anode auch immer etwas Sauerstoff entsteht, ist eine sehr effektive Konvektion schon allein aus diesem Grunde gegeben. Die Elektrolyse wird bevorzugt in geteilten Zellen oder in quasigeteilten Zellen, wie sie in Chem. Ber. 118, 3771-3779 (1985) beschrieben werden, durchgeführt, um eine Reduktion der Aldehydfunktion zu vermeiden. Man kann aber auch in ungeteilten Zellen arbeiten, wenn man Kathoden mit kleiner Wasserstoffüberspannung einsetzt.The electrolyte is moved by forced convection, e.g. by stirring, pumping over or vibrating. However, since there is always some oxygen at the anode, convection is very effective for this reason alone. Electrolysis is preferably carried out in divided cells or in quasi-divided cells, as described in Chem. Ber. 118, 3771-3779 (1985), are carried out in order to avoid a reduction in the aldehyde function. However, you can also work in undivided cells if you use cathodes with a low hydrogen overvoltage.

Nach dem erfindungsgemäßen Verfahren erhält man z.B. THF-OH aus THF mit hoher Selektivität. Dieses vorteilhafte Ergebnis konnte nicht erwartet werden, da man bei der bekannten elektrolytischen Oxidation von THF, wie sie z.B. in der GB-PS 590 310 beschrieben wird und bei der man mit Strom­dichten von 10 mAcm⁻² arbeitet, Bernsteinsäure erhält.The process according to the invention gives, for example, THF-OH from THF with high selectivity. This advantageous result could not be expected, since succinic acid is obtained in the known electrolytic oxidation of THF, as described, for example, in GB-PS 590 310 and in which current densities of 10 mAcm⁻² are used.

Beispiel 1example 1

Als Elektrolysezelle diente ein mit einem Innenthermometer und einem Rückflußkühler versehenes zylindrisches Glasgefäß von 400 ml Inhalt mit Kühlmantel und Planschliffdeckel. Die Anode, ein Blech aus glattem Platin, 50 × 50 × 0,1 mm, d.h. A = 50 cm² (beidseitig), war in der Mitte zwischen zwei Drahtkathoden (1,5 mm ⌀, V2A) angeordnet. Die Abstände zwischen Blechanode und Drahtkathode betrugen je 1,5 cm. Der Elektrolyt wurde magnetisch gerührt.A cylindrical glass vessel of 400 ml with an internal thermometer and a reflux condenser with a cooling jacket and flat ground cover served as the electrolytic cell. The anode, a sheet of smooth platinum, 50 × 50 × 0.1 mm, i.e. A = 50 cm² (on both sides), was arranged in the middle between two wire cathodes (1.5 mm ⌀, V2A). The distances between sheet metal anode and wire cathode were 1.5 cm each. The electrolyte was stirred magnetically.

In die Zelle wurden 200 ml eines wäßrigen Elektrolyten eingefüllt, der 1 M an THF und 1 M an H₂SO₄ war. Die Elektrolyse wurde bei einem Strom von 10,0 A, entsprechend einer Anodenstromdichte von 200 mAcm⁻² durchge­führt. Die Elektrolyttemperatur wurde durch Wasserkühlung auf 35°C gehal­ten. Die Zellspannung betrug 6,5 V. Die Elektrolysegase verließen die Zelle durch einen solegekühlten Rückflußkühler. Ausgetragene THF-Anteile wurden durch Nachfüllen von frischem THF ergänzt (konstantes Elektrolyt­volumen). Nach 38,6 Minuten, entsprechend 6,43 Ah bzw. einem theoreti­schen Stromumsatz (2 F/Mol THF) von 60 %, wurde die Elektrolyse unter­brochen. Nach Abkühlen auf 20°C wurde eine Probe (1 ml) des Elektrolyten nach Verdünnen 1:5 mit dem Laufmittel (wäßrige H₂SO₄ vom pH 1,7) via HPLC analysiert.In the cell, 200 ml of an aqueous electrolyte were filled, which was 1 M in THF and 1 M in H₂SO₄. The electrolysis was carried out at a current of 10.0 A, corresponding to an anode current density of 200 mAcm⁻². The electrolyte temperature was kept at 35 ° C by water cooling. The cell voltage was 6.5 V. The electrolysis gases left the cell through a brine-cooled reflux condenser. Discharged THF fractions were supplemented by replenishing fresh THF (constant electrolyte volume). After 38.6 minutes, corresponding to 6.43 Ah or a theoretical current conversion (2 F / mol THF) of 60%, the electrolysis was interrupted. After cooling to 20 ° C, a sample (1 ml) of the electrolyte was diluted 1: 5 with the eluent (aqueous H₂SO₄ pH 1.7) analyzed by HPLC.

Die Auswertung des HPLC-Diagramms, die aus Tabelle 1 ersichtlich ist, läßt erkennen, daß THF-OH als dominierendes Produkt neben etwas Butyro­lacton (BL) und dessen Hydrolyseprodukt, ω-Hydroxybuttersäure, entstanden ist. Die beiden ersten Peaks sind unbekannter Herkunft.

Figure imgb0006
The evaluation of the HPLC diagram, which can be seen from Table 1, shows that THF-OH as the dominant product alongside some butyrolactone (BL) and its hydrolysis product, ω-hydroxybutyric acid, was formed. The first two peaks are of unknown origin.
Figure imgb0006

Mit der o.a. Strommenge (6,43 Ah) wären bei 100 % Stromausbeute 120 mMol THF-OH entstanden. Die gefundenen 80,8 mMol entsprechen also einer Strom­ausbeute von 67,3 %. Weiter wären theoretisch 60 mMol BL bei 100 % Strom­ ausbeute entstanden. Die gefundene Menge (1,6 mMol) entspricht also 2,7 % Stromausbeute.With the above-mentioned amount of electricity (6.43 Ah), 120 mmole of THF-OH would have resulted with a 100% current yield. The 80.8 mmol found thus correspond to a current yield of 67.3%. Theoretically, further would be 60 mmol BL at 100% electricity yield arose. The amount found (1.6 mmol) thus corresponds to a current yield of 2.7%.

Das nichtumgesetzte THF wurde ebenfalls via HPLC, aber mit einem Metha­nol/Wassergemisch 1/4 V/V als Laufmittel (2 ml min⁻¹) analysiert. Es wur­den 108 mMol nichtumgesetztes THF wiedergefunden, d.h. also 92 mMol THF wurden umgesetzt. Die Materialausbeuten betrugen also 88 % (THF-OH) bzw. 1,7 % (BL).The unreacted THF was also analyzed by HPLC, but with a methanol / water mixture 1/4 V / V as eluent (2 ml min⁻¹). 108 mmol of unreacted THF was recovered, i.e. So 92 mmol THF were implemented. The material yields were 88% (THF-OH) and 1.7% (BL).

Zur Aufarbeitung des Elektrolyseaustrages wurde in einem kontinuierlichen Extraktor (Perforator) 12,5 h mit Ether extrahiert. Der Etherextrakt (ca. 200 ml) wurde mit 15 ml gesättigter wäßriger K₂CO₃-Lösung gerührt, mit wasserfreiem Na₂SO₄ getrocknet und im Wasserstrahlvakuum im Rotationsver­dampfer eingedampft. Es verblieben 6,3 g Rohprodukt. 822 mg des Rohpro­duktes wurden in 1 M H₂SO₄ zu 10 ml aufgefüllt; 1 ml hiervon wurde mit 5 ml Eluent (ca. 0,01 M H₂SO₄ vom pH 1,7) verdünnt und der HPLC-Analyse unterworfen. Dabei ergab sich eine Konzentration an THF-OH von 0,84 M. Dies entspricht einer molaren Menge von 64,4 mMol THF-OH, entsprechend einer Stromausbeute von 54 % für das extrahierte Produkt.To work up the electrolysis discharge, extraction was carried out with ether in a continuous extractor (perforator) for 12.5 h. The ether extract (about 200 ml) was stirred with 15 ml of saturated aqueous K₂CO₃ solution, dried with anhydrous Na₂SO₄ and evaporated in a water jet vacuum in a rotary evaporator. 6.3 g of crude product remained. 822 mg of the crude product were made up to 10 ml in 1 M H₂SO₄; 1 ml of this was diluted with 5 ml of eluent (approx. 0.01 M H₂SO₄ of pH 1.7) and subjected to the HPLC analysis. This resulted in a concentration of THF-OH of 0.84 M. This corresponds to a molar amount of 64.4 mmol THF-OH, corresponding to a current efficiency of 54% for the extracted product.

Das Rohprodukt wurde im Vakuum (1,5 Torr) destilliert. Zur Stabilisierung wurde dem Rohprodukt wenig 85 %ige Phosphorsäure bzw. Kationenaus­tauschermembranstückchen in der H⁺-Form zugesetzt. Der Siedepunkt betrug 24 bis 30°C (2 mm Hg).The crude product was distilled in vacuo (1.5 torr). For stabilization, a little 85% phosphoric acid or cation exchange membrane pieces in the H⁺ form were added to the crude product. The boiling point was 24 to 30 ° C (2 mm Hg).

Die gaschromatographische Untersuchung des in Ether aufgenommenen Rohpro­duktes (Kapillarsäule, 10 m, polare stationäre Phase, 100°C, He, 25 ml/­min) ergab 5 Peaks (Retentionszeiten in Minuten):

  • 1) 0,69    +++
  • 2) 0,90    +  (BL)
  • 3) 3,01    ++
  • 4) 3,23    (+)
  • 5) 3,56    ++
Gas chromatographic examination of the crude product taken up in ether (capillary column, 10 m, polar stationary phase, 100 ° C., He, 25 ml / min) revealed 5 peaks (retention times in minutes):
  • 1) 0.69 +++
  • 2) 0.90 + (BL)
  • 3) 3.01 ++
  • 4) 3.23 (+)
  • 5) 3.56 ++

Die vier unbekannten Peaks sind wahrscheinlich Oligoacetalen, die auf der Säule entstehen, zuzuordnen. In Gegenwart von Säurespuren in der ethe­rischen Lösung nimmt der 1. Peak auf Kosten der anderen (3,4,5) signifi­kant zu.The four unknown peaks are likely to be assigned to oligoacetals that are formed on the column. In the presence of traces of acid in the ethereal solution, the 1st peak increases significantly at the expense of the others (3,4,5).

Auch bei GC-MS-Kopplung wurden entsprechende Produkte identifiziert mit den Massen (88)n mit n = 1 bis 5. Ein weiterer Teil des Rohprodukts wurde mit einem ca. 5fachen molaren Überschuß von 2,4-Dinitrophenylhydrazin in 2N HCl umgesetzt. Das gelbe 2,4-Dinitrophenylhydrazon entstand mit einer Materialausbeute von 90 %, bezogen auf den THF-OH-Gehalt und hatte einen Schmelzpunkt von 117,6°C.Corresponding products were also identified with GC-MS coupling with the masses (88) n with n = 1 to 5. Another part of the crude product was reacted with an approx. 5-fold molar excess of 2,4-dinitrophenylhydrazine in 2N HCl. The yellow 2,4-dinitrophenylhydrazone was formed with a material yield of 90%, based on the THF-OH content, and had a melting point of 117.6 ° C.

Die Elementaranalyse ergab:

Figure imgb0007
The elementary analysis showed:
Figure imgb0007

Ein anderer Teil, nämlich 1,0 g des Rohprodukts, wurde in t-Butanol ge­löst und mit einer konzentrierten, wäßrigen NH₂OH·HCl-Lösung umgesetzt. Nach Abdestillieren des Lösungsmittels und Extraktion mit Ether sowie Strippen des Ethers verblieb THF-OH als farbloses Öl (0,61 g) mit einem Berechnungsindex von n

Figure imgb0008
,1,5 °C = 1,4608. Das NMR-Spektrum des Produkts ergab die folgenden Werte:

Gefunden: δ = 1,9 ppm (m, 4H); δ = 3,9 ppm (m, 3H); 5,1 und 5,4 ppm (m, zusammen 1H).
Figure imgb0009
 Another part, namely 1.0 g of the crude product, was dissolved in t-butanol and reacted with a concentrated, aqueous NH₂OH · HCl solution. After distilling off the solvent and extracting with ether and stripping the ether, THF-OH remained as a colorless oil (0.61 g) with a calculation index of n
Figure imgb0008
, 1.5 ° C = 1.4608. The NMR spectrum of the product gave the following values:

Found: δ = 1.9 ppm (m, 4H); δ = 3.9 ppm (m, 3H); 5.1 and 5.4 ppm (m, together 1H).
Figure imgb0009

Der Platinverlust, der an der Anode nach dem Versuch festgestellt wurde, betrug 0,26 mg, entsprechend einer spezifischen Menge von 0,04 mg/Ah.The platinum loss found on the anode after the experiment was 0.26 mg, corresponding to a specific amount of 0.04 mg / Ah.

Beispiel 2Example 2

In der Zelle nach Beispiel 1 wurden 200 ml eines wäßrigen Elektrolyten, der 4 M an THF und 1 M an H₂SO₄ war, bei 75 mA cm⁻², entsprechend 3,75 A, und 35°C an glattem Platin umgesetzt. Die Zellspannung betrug im Mittel 4,7 V. Nach 6 Stunden und 54 Minuten, entsprechend einem theoretischen Stromumsatz von 60 %, wurde der Elektrolyseversuch abgebrochen. Die direkte Bestimmung der Produkte im Elektrolyseaustrag ergab:
THF-OH: 66,4 % SA, MA = 85 %; BL: 13,7 % SA, MA = 6 %, BS in Spuren. Der ganz schwach gelblich gefärbte Elektrolyt wurde wie in Beispiel 1 aufge­arbeitet. Es wurden 17,6 g Rohprodukt erhalten. Der spezifische Platin­verlust betrug wiederum nur 0,04 mg/Ah. (Mit SA ist die Stromausbeute und mit MA die Materialausbeute gemeint.)In the cell of Example 1, 200 ml of an aqueous electrolyte, which was 4 M in THF and 1 M in H₂SO₄, at 75 mA cm⁻², corresponding to 3.75 A, and 35 ° C on smooth platinum. The cell voltage averaged 4.7 V. After 6 hours and 54 minutes, corresponding to a theoretical power conversion of 60%, the electrolysis attempt was stopped. The direct determination of the products in the electrolysis discharge resulted in:
THF-OH: 66.4% SA, MA = 85%; BL: 13.7% SA, MA = 6%, BS in traces. The very slightly yellowish colored electrolyte was worked up as in Example 1. 17.6 g of crude product were obtained. The specific platinum loss was again only 0.04 mg / Ah. (SA means the current yield and MA the material yield.)

Beispiel 3Example 3

In der Zelle nach Beispiel 1 wurden 200 ml des in Beispiel 1 genannten Elektrolyten an einer zylindrischen (h = 7 cm, ⌀ = 5 cm) Titan-Streck­metall-Anode, 8 Maschen/cm², die mit RuO₂ (4 g Ru/m², RuO₂:TiO₂ = 1:1) aktiviert worden war, unter folgenden Bedingungen elektrolysiert:

Strom 17,9 A (Anodenfläche = 228 cm², beidseitig), Stromdichte 75 mA cm⁻², Gegenelektrode: Axiale V2A-Drahtelektrode, 1,5 mm ⌀, Tempe­ratur 35°C.In the cell according to Example 1, 200 ml of the electrolyte mentioned in Example 1 were placed on a cylindrical (h = 7 cm, ⌀ = 5 cm) titanium expanded metal anode, 8 meshes / cm², which was coated with RuO₂ (4 g Ru / m², RuO₂: TiO₂ = 1: 1) had been activated, electrolyzed under the following conditions:

Current 17.9 A (anode area = 228 cm², both sides), current density 75 mA cm⁻², counter electrode: Axial V2A wire electrode, 1.5 mm ⌀, temperature 35 ° C.

Die Zellspannung betrug im Mittel 7,0 V. Nach 27 Minuten, entsprechend einem theoretischen Stromumsatz von 60 %, wurde der Versuch abgebrochen. Die direkte Bestimmung der Produkte im Elektrolyseaustrag ergab:
THF-OH: 3,5 % SA; BL in Spuren; BS in Spuren. Auch hier entstand THF-OH selektiv, aber nur mit geringer Stromausbeute infolge der kleinen Sauer­stoffüberspannung der Elektrode.The average cell voltage was 7.0 V. After 27 minutes, corresponding to a theoretical current conversion of 60%, the experiment was stopped. The direct determination of the products in the electrolysis discharge resulted in:
THF-OH: 3.5% SA; BL in traces; BS in traces. Here too, THF-OH was formed selectively, but only with a low current efficiency due to the small oxygen overvoltage of the electrode.

Claims (9)

1. Verfahren zur Herstellung von ω-Hydroxyaldehyden (I) oder deren zyklischer Halbacetale (II) der Formeln
Figure imgb0010
 in denen A einen gesättigten Kohlenwasserstoffrest mit 2 bis 16 C-­Atomen, der das Brückenglied -O- enthalten kann, bedeutet, dadurch gekennzeichnet, daß man zyklische Ether der Formel
Figure imgb0011
 in der A die obengenannte Bedeutung hat, in wäßriger Lösung bei Stromdichten von über 30 mAcm⁻² anodisch oxidiert.1. Process for the preparation of ω-hydroxy aldehydes (I) or their cyclic hemiacetals (II) of the formulas
Figure imgb0010
 in which A is a saturated hydrocarbon radical with 2 to 16 carbon atoms, which may contain the bridge member -O-, characterized in that cyclic ethers of the formula
Figure imgb0011
 in which A has the abovementioned meaning, anodized in aqueous solution at current densities of over 30 mAcm⁻². 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man als Elek­trolyt eine saure wäßrige Lösung des Ausgangsstoffes verwendet.2. The method according to claim 1, characterized in that an acidic aqueous solution of the starting material is used as the electrolyte. 3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man einen Elektrolyten verwendet, der Schwefelsäure oder Phosphorsäure enthält.3. The method according to claim 1, characterized in that one uses an electrolyte which contains sulfuric acid or phosphoric acid. 4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man bei Strom­dichten von über 30 bis 1000 mA cm⁻² elektrolysiert.4. The method according to claim 1, characterized in that electrolysed at current densities of over 30 to 1000 mA cm⁻². 5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man bei Strom­dichten von 100 bis 300 mA cm⁻² elektrolysiert.5. The method according to claim 1, characterized in that electrolysed at current densities of 100 to 300 mA cm⁻². 6. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man als Anodenmaterial ein Metall oder Oxid der Platingruppe verwendet.6. The method according to claim 1, characterized in that a metal or oxide of the platinum group is used as the anode material. 7. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man den theo­retischen Stromumsatz auf 60 % begrenzt.7. The method according to claim 1, characterized in that one limits the theoretical power conversion to 60%. 8. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man als zyklischen Ether der Formel III Tetrahydrofuran, Tetrahydropyran oder 1,4-Dioxan oxidiert.8. The method according to claim 1, characterized in that is oxidized as the cyclic ether of the formula III tetrahydrofuran, tetrahydropyran or 1,4-dioxane. 9. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man die Elektrolyse bei 0 bis 50°C durchführt.9. The method according to claim 1, characterized in that one carries out the electrolysis at 0 to 50 ° C.
EP87106233A 1986-05-07 1987-04-29 Process for manufacturing of cyclic hemiacetals Expired - Lifetime EP0245707B1 (en)

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CHEMICAL ABSTRACTS, Band 82, 1975, Seite 388, Zusammenfassung Nr. 97398q, Columbus, Ohio, US; M. SUGAWARA et al.: "Electrolytic oxidation of tetrahydrofuran in aqueous solutions" *
ELECTROCHIMICA, Band 30, Nr. 6, 1985, Seiten 767-772, GB; G. HORANYI et al.: "Electrocatalytic oxidation of tetrahydrofuran at a platinized platinum electrode in aqueous acidic medium" *

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