CN110869537A

CN110869537A - Electrochemical process for preparing aryl alkyl or diaryl carbonates

Info

Publication number: CN110869537A
Application number: CN201880044918.2A
Authority: CN
Inventors: V.德留; S.艾登; D.考比奇; J.吕斯塔阿尔瓦雷斯; M.科佩尔; M.菲格雷多; J.海尔; N.迈恩
Original assignee: Covestro Deutschland AG
Current assignee: Covestro Deutschland AG
Priority date: 2017-07-03
Filing date: 2018-06-29
Publication date: 2020-03-06
Also published as: TW201920770A; WO2019007828A1; KR20200024871A; EP3649277A1

Abstract

The invention relates to a method for the electrochemical production of aryl alkyl carbonates or diaryl carbonates, characterized in that a compound (1) R of the formula₁-OH, wherein the radical R₁Represents an alkyl group, preferably a group selected from the following series: c₁‑C₆-alkyl, preferably methyl, or ethyl,Isopropyl or tert-butyl, or cycloalkyl, preferably cyclohexyl, with a compound of the formula (2) R₂-OH, wherein the radical R₂Preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, particularly preferably phenyl, by anodic reaction with CO on electrodes using gold as heterogeneous electrocatalyst, and to the use thereof for the preparation of polycarbonates.

Description

Electrochemical process for preparing aryl alkyl or diaryl carbonates

The present invention relates to an electrochemical process for the preparation of an arylalkyl or diaryl carbonate.

Arylalkyl carbonates and diaryl carbonates are important precursors in the preparation of polycarbonates and are therefore of great economic importance.

The preparation of aromatic Polycarbonates by the melt transesterification process is known and is described, for example, in "Schnell" Chemistry and Physics of Polycarbonates, Polymer Reviews, volume 9, Interscience publishers, New York, London, Sydney 1964, in D.C. Prevorsek, B.T. Debona and Y.Kersten, Corporation Research Center, Allied Chemical Corporation, Moristown, New Jersey 07960, "Synthesis of Polymer (ester) Polycarbonates" in Journal of Science, Polymer Chemistry Edition, volume 19, 75-90 (1980), also in D.Freego, U.G.G., P.R. ü, H.C. Chemistry, catalog Edition, volume 19, volume 83, cell electronics, cell Corporation, volume 83, cell Corporation, cell 718, cell electronics, cell Corporation, cell 19, cell 648, cell III, cell Corporation, cell III.

The preparation of diaryl carbonates for use in the melt transesterification process of aromatic Polycarbonates, for example by the interfacial process, is described in principle in the literature, see for example in Chemistry and Physics of Polycarbonates, Polymer Reviews, H.Schnell, volume 9, John Wiley and Sons, Inc. (1964), page 50/51. The preparation of diaryl carbonates is carried out here by reaction of phenol with carbonyl dihalides (for example phosgene), which are prepared starting from carbon monoxide.

The preparation of diaryl carbonates can likewise be carried out by oxidative carbonylation. Here, phenol reacts directly with carbon monoxide as a carbonylation reagent, as described, for example, in Journal of Molecular Catalysis a: chemical, 1999, 139, 109-. In this oxidative carbonylation of phenol, the choice of catalyst appears to be limited to palladium-based materials. No examples of phenol oxidative carbonylation reactions that can be successfully carried out without palladium-based catalysts have been found in the prior art.

The preparation of arylalkyl carbonates which can be carried out by oxidative carbonylation using palladium-based catalysts is also described in green. chem., 2013, 15, 1146-one 1149. In the first step, methyl formate is activated by means of an alkali metal methoxide and disproportionated in an equilibrium reaction to carbon monoxide and methanol. Subsequent carbonylation with phenol is carried out with a Pd (II) salt (e.g. PdBr)₂、Pd(OAc)₂) And Mn (acac)₃The formation of the homogeneous catalyst-cocatalyst system takes place at elevated pressure. The need to use a coupling catalyst system which is also present in homogeneous form and the need to use elevated pressures are great disadvantages for the chemical oxidative carbonylation for preparing arylalkyl carbonates.

Oxidative carbonylation for the preparation of diaryl carbonates and alkyl aryl carbonates has not been applied industrially to date.

For sustainable industrial chemistry, it would be advantageous to use carbon dioxide as an alternative feedstock for polymer production. In this way, fossil raw materials can be replaced and the greenhouse gas carbon dioxide can be returned to the material cycle, which is also generally referred to as the closing of the carbon cycle. This can add up to a reduction in carbon dioxide footprint, which will contribute to world-wide climate protection goals. Carbon dioxide is provided as a waste product in many chemical processes and can therefore be considered a sustainable feedstock. It is also advantageous that carbon dioxide is easy to handle as a non-flammable gas.

Carbon dioxide has been used commercially as a starting material for the preparation of arylalkyl and diaryl carbonates as described in Green Chemistry, 2003, 5, 497-reservoir 507. One great disadvantage here is that the synthesis described therein requires a number of synthesis steps:

it starts from ethylene oxide prepared from ethylene. Ethylene carbonate is then obtained by reaction of ethylene oxide with carbon dioxide, which is then exchanged with methanol ester to dimethyl carbonate. And then further transesterified with phenol to an arylalkyl carbonate. And then disproportionated to diaryl carbonate in a final reaction.

The use of carbon dioxide as a feedstock is a challenge because carbon dioxide is a reactive inert molecule. Therefore, an energy supply is required to convert carbon dioxide to high value chemicals. In order to produce a product with a low carbon dioxide footprint, the generation of supplied energy should in turn be associated with as little carbon dioxide emissions as possible. Suitable for this purpose are, for example, electric currents obtained from renewable energy sources.

Although carbon dioxide is advantageously used as a feedstock, the above-described processes have a number of disadvantages. For example, many synthetic steps are required, thus making the process complicated. Furthermore, ethylene oxide is used, the use of which requires special safety measures with increased complexity/expenditure. Since the equilibrium constant of the transesterification reaction to dimethyl carbonate is small, a large excess of methanol is required (Catal Surv Asia, 2010, 14, 146-163). In addition, the method can be used for producing a composite materialContinuous multi-stage distillation columns are required. The individual steps of transesterification with phenol to give arylalkyl carbonates are also carried out in reactive distillation columns which have a high energy requirement and require the use of catalysts, for example Pb (OPh)₂And Bu₂SnO (Catal Surv Asia, 2010, 14, 146-. Furthermore, the reactive distillation apparatus used in the prior art has a large number of heterogeneous catalysts and simultaneously homogeneous catalysts.

An electrochemical process for the preparation of diaryl carbonates is described in j. phys. chem. C, 2012, 116, 10607-. It relates to an electrochemical variant of the oxidative carbonylation of aryl alcohols, in which palladium-based materials are in turn used as catalysts. The electrocatalytic reaction was carried out on a palladium catalyst consisting of nanoparticles, wherein the authors indicated that only nanoparticles in the <2 nm range were sufficiently catalytically active. If the nanoparticles are > 6 nm, the electrocatalyst is inactive. In view of this apparent limitation in catalyst size, this same workgroup further reduced the size of palladium-based electrocatalysts in subsequent work by using only homogeneous palladium complexes as well, as described in ACS cal, 2013, 3, 389-. It is well known that the use of homogeneous catalysts is disadvantageous, since the separation of the products thereby becomes difficult.

The preparation of diaryl carbonates by homogeneous catalysis with palladium is also described in WO 2011/024327A 1. The application focuses on tailoring the reaction as efficiently as possible, and only the use of gold electrodes as discharge-or reoxidation electrodes, which are non-catalytically active Pd, is described here⁰And converted into catalytically active, homogeneously dissolved Pd²⁺. As mentioned above, the actual catalyst here is homogeneous Pd²⁺。

In contrast, JP H673582 describes heterogeneous electrocatalysis on palladium electrodes, but in which only dialkyl carbonates are prepared. As shown in comparative example 6, the formation of diaryl carbonate and arylalkyl carbonate could not be detected using this electrode.

Likewise, US 2003/070910 a1 also describes only the preparation of dialkyl carbonates.

WO 2014/046796A 2 describes, inter alia, (phosgene) COCl as starting product for carbonylation products (Carbonyl)₂Preparation of (2) by reacting CO₂Electrochemical conversion to CO and electrochemical conversion of hydrogen halide or halogen salt to halogen. The use of CO for the preparation of diaryl or arylalkyl carbonates is not mentioned₂CO is prepared in situ because phosgene is first formed and then converted to carbonate.

The object of the present invention is to provide an electrochemical process for preparing arylalkyl carbonates or diaryl carbonates, in which an electrical current can be used as an energy source, in which fewer reaction steps are to be produced than in the prior art, and in which non-palladium-based heterogeneous catalysts can also be used as electrocatalysts, and the catalytic activity of which is not limited to a particle size range of <2 nm.

According to the invention, this object is achieved by a process for the electrochemical preparation of arylalkyl carbonates or diaryl carbonates, characterized in that a compound of the formula

（1）R₁-OH,

Wherein the radical R₁Represents an alkyl group, preferably a group selected from: c₁-C₆-alkyl, preferably methyl, or ethyl, isopropyl or tert-butyl, or cycloalkyl, preferably cyclohexyl,

with a compound of the formula

（2）R₂-OH,

Wherein the radical R₂Represents aryl, preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, particularly preferably phenyl,

an anodic reaction with CO was carried out on an electrode using gold as an electrocatalyst. Here, the electrocatalyst is heterogeneous, preferably free of palladium.

A particular advantage of the process according to the invention is that it enables the electrochemical preparation of aryl alkyl or diaryl carbonates, in particular Methyl Phenyl Carbonate (MPC) or diphenyl carbonate (DPC), with low complexity/expenditure and a small number of reaction steps. The gold-based heterogeneous electrocatalysts used can be reused in a wide particle size range in themselves simply, since complicated separation processes of the catalytically active metal complexes can be omitted. By discarding the size limitation of the <2 nm range of the electrocatalyst, a greater degree of freedom is created in the electrode design. Likewise, its long-term stability can be improved by a larger electrocatalyst particle size.

The process according to the invention makes use of compounds of the formulae (1) and (2). Preferred starting compounds of formula (1) are those selected from the group consisting of:

the following are particularly preferred:

particularly preferred starting compounds of formula (2) are those selected from the group consisting of:

the following are particularly preferred:

the reaction equation of the process according to the invention for the electrochemical preparation of arylalkyl carbonates or diaryl carbonates is used, for example, in

And

the reaction scheme with carbon monoxide shows:

the formation of the arylalkyl carbonate or diaryl carbonate results from a series of coupled reaction steps. In a first step, dimethyl carbonate is formed from the methanol anode used:

by electrochemical anodic activation, the dimethyl carbonate formed can be exchanged with phenol to methylphenyl carbonate:

in a further step, methyl phenyl carbonate may be transesterified to diphenyl carbonate:

the sequence of electrochemical reactions carried out here has not been described so far and can be confirmed by in situ spectroscopic analysis.

The reaction sequence comprising the following steps was confirmed by means of spectroscopic analysis:

1. dialkyl carbonate is formed by electrochemical anodic reaction of alkyl alcohol with CO,

2. electrochemically activating transesterification of the formed dialkyl carbonate to aryl alkyl carbonate,

3. the formed arylalkyl carbonate is further electrochemically activated transesterified to diaryl carbonate.

Here, dimethyl carbonate was previously added to the electrolyte and the reaction caused by the addition of phenol under electrochemical activation was monitored.

The potentiostatic experiments were carried out at room temperature in a 3-electrode apparatus. A platinum wire served as the counter electrode and a commercially available Ag/AgCl electrode was used as reference. The working electrode, gold plate-disc (Scheibe), was first polished with an aluminum suspension and treated with miq water (18.4M Ω) and in an ultrasonic bath for 5 minutes. The electrode potential was controlled with the ER466 potentiostat of E-DAQ. Prior to the experiment, the electrolyte solution was purged with Ar for 10 minutes until oxygen free, then saturated with CO and maintained by further supply of CO during the experiment.

For a catalyst consisting of 0.1 mol/L LiClO₄An electrolyte consisting of 0.1 mol/L dimethyl carbonate and 0.1 mol/L phenol in acetonitrile, characterized by in situ FTIR at a potential of 0-1V versus Ag/AgCl, giving the spectra shown in FIG. 1.

As can be seen from the spectrum of FIG. 1, a characteristic band of diphenyl carbonate is formed from an electrode potential of 0.7V vs. Ag/AgCl. This indicates that diphenyl carbonate is indeed formed from the precursor dimethyl carbonate and that this formation is carried out by electrochemical activation.

According to a first advantageous embodiment of the invention, the reduction of carbon dioxide to carbon monoxide, for example, serves as a cathodic reaction:

CO₂+ 2 e^-+ H₂O →CO + 2OH^-

OH formed here^-The ions are neutralized by protons from the anode reaction into water: 2 OH^-+ 2 H⁺→2 H₂O

The advantage of using carbon dioxide in the cathodic reduction reaction to provide carbon monoxide is that the greenhouse gas carbon dioxide can thus be returned back into the material cycle, which is also commonly referred to as the closing of the carbon cycle. Carbon dioxide is provided as a waste product in many chemical processes and can therefore be used as a sustainable feedstock. It is also advantageous that carbon dioxide is easy to handle as a non-flammable gas. The method according to the advantageous embodiment described above is therefore characterized by particular sustainability. This preferably involves the in situ generation of carbon dioxide. In particular, the CO thus obtained is preferably reacted directly on the electrocatalyst gold in the anode reaction in the process according to the invention for the electrochemical preparation of arylalkyl carbonates or diaryl carbonates.

The reaction for the cathodic formation of carbon monoxide can in principle be carried out in a manner analogous to that described, for example, in Bull, chem. Soc. Jpn,1987, 60, 2517-2522.

Here, for example, a solution of TEAP (tetraethylammonium perchlorate) (0.1 mol/L) in acetonitrile is reacted with CO₂And (4) saturation. After 30 minutes, the system was hermetically sealed and saturated electrolyte was circulated at a rate of 1 mL/min. CO 2₂At an electrode potential of-2.6V on a copper-, indium-, silver-, palladium-or gold electrode (vs Ag/AgCl/(0.01 mol/L LiCl +0.1 mol/L TEAP/CH)₃CN) electrode as reference) was performed. Where 100C of charge flows.

According to another advantageous embodiment of the invention, the anodic electrochemical reaction is between 0.1 and 5000 mA/cm²Preferably 0.1 to 500 mA/cm²Particularly preferably 0.1 to 100 mA/cm²And very particularly preferably from 0.2 to 50 mA/cm²At a current density of (3). This can also be achieved on a large industrial scale.

According to another advantageous embodiment of the invention, methanol as alcohol of formula (1) or a mixture of the alcohol of formula (1) with other solvents, in particular solvents selected from acetonitrile, propylene carbonate, dimethylformamide, dimethyl sulfoxide, 1, 2-dimethoxyethane, dichloromethane or N-methyl-2-pyrrolidone, is used as solvent. The upstream cathodic reaction is carried out in particular in acetonitrile as solvent, but may also be carried out in other aprotic solvents such as propylene carbonate, dimethylformamide, dimethyl sulfoxide, 1, 2-dimethoxyethane or N-methyl-2-pyrrolidone, or in water. By selecting a suitable solvent from the above choices, it can be performed very selectively.

As conductive salts, according to a further embodiment of the process according to the invention, lithium chloride, lithium bromide, lithium perchlorate, sodium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, sodium phenate, lithium phenate, tetrabutylammonium chloride, preferably lithium perchlorate, or ionic liquids based on imidazolium, ammonium, phosphonium or pyridinium, preferably 1-ethyl-3-methylimidazolium tetrafluoroborate, can be used. Particularly preferably, the ionic liquid comprises imidazolium, ammonium, phosphonium or pyridinium as cation.

According to another advantageous embodiment, the anodic electrochemical reaction can be carried out at a temperature of 10 to 250 ℃, in particular 20 to 100 ℃, particularly preferably room temperature.

According to another advantageous embodiment of the invention, the reaction can be carried out at normal or elevated pressure, in particular at an overpressure of at most 1 bar. In particular, when operating at high pressures, higher local concentrations at the electrodes can be achieved, resulting in better production rates. To carry out the novel process for preparing alkyl aryl carbonates and diaryl carbonates, gas diffusion electrodes can preferably be used. In particular, the reaction for the cathode to form carbon monoxide may be carried out on a gas diffusion electrode. The use of a gas diffusion electrode is also advantageous for the anodic reaction for forming aryl alkyl or diaryl carbonates.

According to one advantageous embodiment of the invention, a gas diffusion electrode is used for the anode reaction, wherein the gas diffusion electrode comprises at least one planar electrically conductive support and a gas diffusion layer applied to the support and an electrocatalyst applied to the support,

-wherein the gas diffusion layer comprises a mixture of electrocatalyst and hydrophobic polymer

-wherein the electrocatalyst is present in the form of gold powder and/or in the form of gold particles supported on a carbon support, wherein the carbon support is selected from the group consisting of activated carbon, carbon black, graphite, graphene or carbon nanotubes, in particular carbon black, and

-wherein the hydrophobic polymer is a fluorine substituted polymer, particularly preferably Polytetrafluoroethylene (PTFE).

An advantage of a gas diffusion electrode is that gases, such as carbon monoxide generated in situ at the cathode for the reaction, can be reacted directly at the electrode. The concentration of the gaseous reactants on the electrode is thereby locally increased and a higher current density can be achieved compared to conventional electrodes, which is of great relevance for industrial applications.

For the cathodic reduction of carbon dioxide to carbon monoxide, a gas diffusion electrode may be used as the cathode.

Gas diffusion electrodes are electrodes in which the three states of matter-solid, liquid and gaseous-are in contact with each other and a solid, electron-conducting catalyst catalyzes the electrochemical reaction between the liquid and gaseous phases.

According to the present invention, the electrocatalyst may be present in the form of gold particles supported on a carbon support. The carbon support itself may comprise activated carbon, carbon black such as Ketjenblack EC-300j or EC 600 JD, graphite, graphene or carbon nanotubes, in particular Ketjenblack.

Preferred is an embodiment of the gas diffusion electrode, characterized in that the gold particles have a median particle diameter (d measured by means of laser diffraction) of 1 to 100 μm, preferably 2 to 90 μm₅₀) The median particle diameter of the gold particles present and/or supported on carbon is from 2 nm to 100 μm, preferably from 2 nm to 1 μm.

It is furthermore preferred that the proportion of the electrocatalyst in powder form is from 80 to 97% by weight, preferably from 90 to 95% by weight, based on the total weight of electrocatalyst and hydrophobic polymer, or the proportion of the electrocatalyst in particle form on the carbon support is from 40 to 60% by weight, based on the total weight of electrocatalyst and hydrophobic polymer.

It can furthermore be provided that the electrocatalyst in powder form and the hydrophobic polymer are applied to a support and compacted and form a gas diffusion layer.

It is further preferred that the gas diffusion electrode based on gold powder as electrocatalyst has a mass of 5 mg/cm²To 300mg/cm²Preferably 10 mg/cm²To 250 mg/cm²And/or the gas diffusion electrode based on gold particles supported on carbon has a total loading of the catalytically active component of 0.5 mg/cm²To 20 mg/cm²Preferably 1mg/cm²To 5 mg/cm²The total loading of the catalytically active component (b).

According to a further advantageous embodiment of the invention, the support of the gas diffusion electrode may comprise nickel, gold or silver or a combination of nickel and gold or silver. Furthermore, the support can be formed as a net, a woven fabric, a knitted fabric, a weft-knitted fabric, a nonwoven fabric, a drawn metal net or a foam, preferably a woven fabric, particularly preferably a net.

The gas diffusion electrode can be produced according to DE 10.148.599a1 by applying the catalyst powder mixture directly to the support.

In a particularly preferred embodiment, the preparation of the powder mixture is carried out by mixing the catalyst powder with the binder and optionally further components.

The mixing is preferably carried out in a mixing device having a rapidly rotating mixing element, for example a fly cutter. For mixing the components of the powder mixture, the mixing elements are preferably rotated at a speed of 10 to 30m/s or at a number of revolutions of 4000 to 8000 revolutions per minute. After mixing, the powder mixture is preferably sieved. The sieving is preferably performed with a sieving device equipped with a sieve mesh or the like having a mesh size of 0.04 to 2 mm.

Energy is introduced into the powder mixture by mixing in a mixing device with rotating mixing elements, whereby the powder mixture is intensively heated. In case the powder is excessively heated, deterioration of the electrode performance is monitored, and therefore the temperature during the mixing process is preferably 35 to 80 ℃. This may be done by cooling during mixing, for example by adding a coolant such as liquid nitrogen or other inert endothermic substance. Another possibility of temperature control can be carried out by interrupting the mixing to cool the powder mixture or by selecting a suitable mixing kit or changing the filling amount in the mixer.

The application of the powder mixture to the electrically conductive support is carried out, for example, by spreading. The spreading of the powder mixture on the carrier can be carried out, for example, by means of a sieve. Particularly advantageously, a frame-like template is placed on the support, wherein the template is preferably selected such that it just surrounds the support. Alternatively, the template may be chosen to be smaller than the area of the support. In this case, the uncoated edge of the support remains the electroless chemically active coating after the powder mixture is dusted on and pressed with the support. The thickness of the template may be selected depending on the amount of powder mixture to be applied on the carrier. The template is filled with the powder mixture. The excess powder can be removed by means of a scraper. The template is then removed.

In a next step, in a particularly preferred embodiment, the powder mixture is pressed with a carrier. The pressing can be carried out in particular by means of rollers. Preferably a pair of rollers is used. It is also possible to use a roller on a substantially flat base plate, wherein the roller or the base plate is moved. Further, pressing may be performed by a punch. The force during pressing is in particular 0.01 to 7 kN/cm.

Another aspect relates to the use of the arylalkyl carbonates or diaryl carbonates obtained by the process according to the invention, preferably by the melt transesterification process, for the preparation of polycarbonates.

The transesterification reaction can be described, for example, by the following equation:

the above-mentioned advantages of the process according to the invention apply analogously also to the use of the proposed arylalkyl carbonates or diaryl carbonates in the preparation of polycarbonates, preferably by the melt transesterification process.

The invention is illustrated in more detail below by means of examples, which, however, do not constitute any limitation of the invention.

Examples

The analytical method used was:

gas Chromatograph (GC)

Gas Chromatography (GC) was performed with the aid of Agilent Technologies' gas chromatograph 7890A and autosampler 7639. The interaction of the sample with the stationary phase was measured in a quartz capillary column DB-1701 (length: 30 m; inner diameter: 0.25 mm; thickness of the film covalently bonded to the stationary phase: 0.25 μm; pre-column: 5m, carrier gas: hydrogen; injector temperature: 150 ℃ C.; detector temperature: 310 ℃ C.; procedure: method "hart": 50 ℃ start temperature was held for 1 minute, heating rate: 15 ℃/minute, 260 ℃ end temperature was held for 8 minutes) of Agilent Technologies, USA.

IR spectroscopy

To characterize the products and intermediates, an in situ Fourier Transform Infrared (FTIR) spectrometer with the aid of a Bruker Vertex 80V IR spectrophotometer was also used. Using a catalyst consisting of CaF₂A prism formed with an angle of 60 deg., wherein the spectrum consists of 8 cm^-1And the average composition of 100 interferograms of p-polarized light.

The spectrum is obtained by means of pressing an electrode at a controlled potential against a prism window. In the absence of FaradayThe spectrum recorded at the potential of the range serves as a reference. The electrode potential is then varied and the sample spectrum is obtained after subtracting the reference spectrum. According to the equation

Wherein R and R₀Is the reflectance of the sample spectrum and the reference spectrum, the final spectrum being presented as absorbance a. In these differential spectra, the negative band (the downward pointing band) shows the consumption of the substance that is still present in the reference spectrum. The positive band (upward pointing band) shows the formation of new species that were not present at the time the reference spectrum was recorded. All spectrochemical experiments were performed with Ag/Ag at room temperature⁺z was performed as a reference electrode and a platinum wire as a counter electrode.

Example 1

Preparation of diphenyl carbonate on gold electrode

The potentiostatic experiments were carried out at room temperature in a 3-electrode apparatus. A platinum wire served as the counter electrode and a commercially available Ag/AgCl electrode was used as reference. The working electrode, gold plate-disc (Scheibe), was first polished with an aluminum suspension, treated with MiliQ water (18.4M Ω) and in an ultrasonic bath for 5 minutes. The electrode potential was controlled with the ER466 potentiostat of E-DAQ. The resulting current density was 0.2 mA/cm². Before the experiment, the electrolyte solution consisting of 0.1 mol/L methanol and 0.1 mol/L phenol was purged with Ar for 10 minutes until oxygen free, then saturated with CO and maintained by a further supply of CO during the experiment.

Characterization by in situ FTIR at a potential of 0-1V gave the spectra shown in FIG. 2 (FTIR spectra were obtained during scanning in a mixture consisting of 0.1 mol/L MeOH and 0.1 mol/L PhOH under a CO atmosphere in the positive potential direction of the Au disk electrode).

At a small potential of 0.3V (FIG. 2) (fourth line from the bottom relative to Ag/AgCl reference measurement), already at 1780 cm^-1And 1757 cm^-1Form aA positive band, which can be assigned to diphenyl carbonate and dimethyl carbonate, respectively. If the potential is now further increased, the band grows further.

Example 2

Preparation of carbon monoxide gas diffusion electrode by using gold as electrocatalyst

The gas diffusion electrode was prepared by a dry process in which 93% by weight of Ferro's gold powder SPF 1775, 7% by weight of dynoon TF2053 PTFE were mixed in Ika mill a11 basic. Subsequently, the powder mixture was pressed onto a nickel support web with a roller press at a force of 0.5 kN/cm. For a size of 24 cm²7.7g of the powder mixture was required.

Example 3

Preparation of methyl phenyl carbonate on gas diffusion electrode with sodium phenolate conducting salt

In a 2-electrode apparatus, a filter-press cell (model: Micro Flowcell, volume: 0.001 m) from commercially available Electrocell Co²) In (1) was performed. As the counter electrode, iridium-MMO (iridium-mixed metal oxide electrode, commercially available in Electrocell) was used. The working electrode was a gas diffusion electrode prepared according to example 2, consisting of a mixture of gold powder and PTFE, which was rolled onto a support material made of nickel. The electrolysis was carried out at 1.2V for 1 hour (current density about 1 mA/cm)²). During this time, 40 mL of electrolyte was pumped at a rate of 2 mL/min. For the electrolyte, 1.06g LiClO was added₄(0.1 mol/L), 139 mg NaOPh (12 mmol/L) and 7.06g PhOH (0.75 mol/L) were dissolved in 100 mL MeOH.

Characterization by Agilent Technologies GC7809A gave the following results:

sample content of methyl phenyl carbonate = 0.96 μmol, corresponding to a yield of 0.51%.

Example 4

Preparation of methyl phenyl carbonate on gas diffusion electrodes

In a 2-electrode apparatus, a filter-press cell (model: Micro Flowcell, volume: 0.001 m) from commercially available Electrocell Co²) In (1) was performed. As the counter electrode, Ir-MMO (iridium-mixed metal oxide electrode, commercially available in Electrocell) was used. The working electrode is a gas diffusion electrode consisting of a mixture of gold powder and PTFE, which is rolled onto a support material made of nickel. The electrolysis was carried out at 1.2V for 1 hour (current density about 1 mA/cm)²). During this time, 40 mL of electrolyte was pumped at a rate of 2 mL/min. For the electrolyte, 1.06g LiClO was added₄(0.1 mol/L) and 7.06g PhOH (0.75 mol/L) were dissolved in 100 mL MeOH.

Characterization by Agilent Technologies GC7809A gave the following results:

sample content of methyl phenyl carbonate = 5.38 μmol, corresponding to a yield of 2.88%.

Comparative example 5

Preparation of palladium-based carbon monoxide-gas diffusion electrodes

The gas diffusion electrode was prepared by a dry process in which 93% by weight of Ferro palladium powder M8039, 7% by weight of dynoon TF2053 PTFE were mixed in Ika mill a11 basic. Subsequently, the powder mixture was pressed onto a nickel support web with a roller press under a force of 0.29 kN/cm. For a size of 32 cm²4.3g of the powder mixture was required.

Comparative example 6

Preparation of dimethyl carbonate on palladium-based carbon monoxide-gas diffusion electrodes

In a 2-electrode apparatus, a filter-press cell (model: Micro Flowcell, volume: 0.001 m) from commercially available Electrocell Co²) In (1) was performed. The gas diffusion electrode prepared according to comparative example 5 was anodically connected, and an iridium-MMO electrode (iridium-mixed metal oxide electrode, commercially available in Electrocell) was used as a counter electrode. At 0.2 mA/cm²The electrolysis was carried out for one hour at the current density of (1). Stream of COSpeed 0.5L/h, electrolyte (30 mL) at 2 mL min^-1The flow rate of (c) pump cycles. For the electrolyte, PhOH (14.11g, 0.15 mol, 0.75 mol L)^-1) And LiCl (114.5 mg, 2.7mmol, 0.014 mol L)^-1) Is dissolved in CH₃CN (200 mL).

By means of GC-HS analysis, neither DPC nor methyl phenyl carbonate was found. In this case, the following analysis was performed:

the experiments were performed on the following instruments of Agilent Technologies: GC7890A with column (HP-5: stationary phase: 5% phenylmethylpolysiloxane, length: 30 m.times.320. mu.m.times.0.25. mu.m, carrier gas: helium) and Headspace (HS) sampling system 7697. In each case, 3 mL of sample in a 20 mL vial was placed in an HS sampler and tempered in an oven at 80 ℃ for 15 minutes and to a pressure of 15 psi. Subsequently, 1 mL of the vapor phase was applied to the column in 10:1 split via transfer line (200 ℃). FID (flame ionization detector run at 300 ℃ and 40 mL/min hydrogen flow rate. column procedure: initial temperature 90 ℃ and hold for 2 minutes, then 50 ℃/minute temperature increase, until 250 ℃ again to 250 ℃ final temperature for 2 minutes.

Claims

1. A process for the electrochemical preparation of an arylalkyl or diaryl carbonate, characterized in that a compound of the formula

（1）R₁-OH,

Wherein the radical R₁Represents an alkyl group, preferably a group selected from the following series: c₁-C₆-alkyl, preferably methyl, or ethyl, isopropyl or tert-butyl, or cycloalkyl, preferably cyclohexyl,

with a compound of the formula

（2）R₂-OH,

an anodic reaction with CO was carried out on an electrode using gold as a heterogeneous electrocatalyst.

2. The process as claimed in claim 1, wherein the CO is reacted upstream from the CO on the cathode₂Is electrochemically generated.

3. The method according to claim 1 or 2, characterized in that the anodic electrochemical reaction is between 0.1 and 5000 mA/cm²Preferably 0.1 to 500 mA/cm²Particularly preferably 0.1 to 100 mA/cm²And very particularly preferably from 0.2 to 50 mA/cm²At a current density of (3).

4. Process according to any one of claims 1 to 3, characterized in that a mixture of the alcohol of formula (1) with a further solvent is used, in particular a solvent selected from acetonitrile, propylene carbonate, dimethylformamide, dimethyl sulfoxide, 1, 2-dimethoxyethane, dichloromethane or N-methyl-2-pyrrolidone.

5. The method according to any one of claims 1 to 4, characterized in that lithium chloride, lithium bromide, lithium perchlorate, sodium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, sodium phenoxide, lithium phenoxide, tetrabutylammonium chloride, preferably lithium perchlorate, or an imidazolium-, ammonium-, phosphonium-or pyridinium-based ionic liquid, preferably 1-ethyl-3-methyl-imidazolium-tetrafluoroborate, is used as electrochemically conductive salt.

6. The method according to any one of claims 1 to 5, characterized in that the anodic electrochemical reaction is carried out at a temperature of 10 to 250 ℃, in particular 20 to 100 ℃, particularly preferably room temperature.

7. Process according to any one of claims 1 to 6, characterized in that the reaction is carried out at normal or elevated pressure, in particular at an overpressure of at most 1 bar.

8. The method according to any one of claims 1 to 7, characterized in that a gas diffusion electrode is used for the anode reaction, wherein the gas diffusion electrode comprises at least one planar electrically conductive support and a gas diffusion layer applied thereon and an electrocatalyst applied thereon,

-wherein the electrocatalyst is present in the form of gold powder or in the form of gold particles supported on a carbon support, wherein the carbon support comprises activated carbon, carbon black, graphite, graphene or carbon nanotubes, in particular carbon black, and

9. The process according to claim 8, characterized in that the proportion of electrocatalyst in powder form is from 80 to 97% by weight, preferably from 90 to 95% by weight, based on the total weight of electrocatalyst and hydrophobic polymer, or the proportion of electrocatalyst in particle form on carbon support is from 40 to 60% by weight, based on the total weight of electrocatalyst and hydrophobic polymer.

10. The method according to claim 8 or 9, characterized in that the gold powder has a median particle diameter of 1 to 100 μ ι η, preferably 2 to 90 μ ι η, or the median particle diameter of the particles supported on carbon is 2 nm to 100 μ ι η, preferably 2 nm to 1 μ ι η.

11. Method according to any of claims 8 to 10, characterized in that the electrocatalyst and the hydrophobic polymer are applied in powder form on an electrically conductive support and compacted and formed into a gas diffusion layer.

12. The method according to any one of claims 8 to 11, characterized in that the gas diffusion electrode based on gold powder as electrocatalyst has 5 mg/cm²To 300mg/cm²Preferably 10 mg/cm²To 250 mg/cm²Has a total loading of the catalytically active component, or a gas diffusion electrode based on gold particles supported on carbon, of 0.5 mg/cm²To 20 mg/cm²Preferably 1mg/cm²To 5 mg/cm²The total loading of the catalytically active component (b).

13. A method according to any one of claims 8 to 12, characterized in that the electrically conductive carrier of the gas diffusion electrode comprises nickel, gold, or silver or a combination of nickel and gold or silver.

14. Method according to any of claims 8 to 13, characterized in that the electrically conductive carrier is formed as a mesh, a fabric, a knitted fabric, a weft-knitted fabric, a nonwoven, a drawn metal mesh or a foam, preferably a fabric.