KR20200024871A - Electrochemical Methods for Making Arylalkyl Carbonates or Diaryl Carbonates - Google Patents

Abstract

The invention relates to the formula (1) R ₁ -OH, wherein the radical R ₁ is an alkyl radical, preferably C ₁ to C ₆ alkyl, preferably methyl or ethyl, isopropyl or tert-butyl, or cycloalkyl, preferably Preferably a radical of the range from the cyclohexyl compound of the formula (2) R ₂ -OH where the radical R ₂ is an aryl radical, preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, Is an phenyl radical) and an anode is reacted with CO in an electrode having gold as a heterogeneous electrocatalyst, electrochemical preparation of arylalkyl carbonate or diaryl carbonate, and polycarbonate Its use relates to the manufacture of nates.

Description

Electrochemical Methods for Making Arylalkyl Carbonates or Diaryl Carbonates

The present invention relates to an electrochemical process for preparing aryl alkyl carbonates or diaryl carbonates.

Aryl alkyl carbonates and diaryl carbonates are important economics because they are important precursors in the production of polycarbonates.

The preparation of aromatic polycarbonates by melt transesterification processes is known and described, for example, in "Schnell", Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964, in D.C. Prevorsek, B.T. Debona and Y. Kersten, Corporate Research Center, Allied Chemical Corporation, Moristown, New Jersey 07960], "Synthesis of Poly (ester) carbonate Copolymers" in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 19, 75-90 (1980), in D. Freitag, U. Grigo, P. R. Mueller, H. Nouvertne, BAYER AG], "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, Vol. 11, Second Edition, 1988, pages 648-718 and finally Dres. U. Grigo, K. Kircher and P.R. Mueller "Polycarbonate" in Becker / Braun, Kunststoff-Handbuch, Volume 3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299.

The preparation of diaryl carbonates for use in melt transesterification processes for aromatic polycarbonates, for example by interfacial processes, is described in principle (see, for example, Chemistry and Physics of Polycarbonates, Polymer Reviews, H. Schnell, Vol. 9, John Wiley and Sons, Inc. (1964), p 50/51). The production of diaryl carbonates here is carried out by the reaction of phenol with carbonyl dihalide (eg phosgene) made from carbon monoxide.

The preparation of the diaryl carbonates can likewise be carried out by oxidative carbonylation. Phenol is reacted directly with carbon monoxide as a carbonylation reagent, for example as described in Journal of Molecular Catalysis A: Chemical, 1999, 139, 109-119. In this oxidative carbonylation reaction of phenol, the choice of catalyst appears to be limited to palladium-based materials only. There is no example in the prior art for oxidative carbonylation, a phenolic reaction that can be successfully performed without a palladium-based catalyst.

The preparation of aryl alkyl carbonates is also described in Green. Chem., 2013, 15, 1146-1149, by oxidative carbonylation using a palladium-based catalyst. In the first step methyl formate is activated by alkali metal methoxide and disproportionate to equilibrium reaction to obtain carbon monoxide and methanol. Subsequent carbonylation with phenol is carried out at elevated pressure on a homogeneous catalyst-procatalyst system consisting of Pd (II) salts (eg PdBr ₂ , Pd (OAc) ₂ ) and Mn (acac) ₃ . The need to use coupled catalyst systems, which are also present in homogeneous form, and the need to use elevated pressures, is a major disadvantage in chemical oxidative carbonylation for the production of aryl alkyl carbonates.

Oxidative carbonylation for the production of diaryl carbonates and alkyl aryl carbonates has never been used on an industrial scale.

For sustainable industrial chemistry, it would be advantageous to use carbon dioxide as an alternative feedstock for polymer production. In this way the fossil feedstock could be replaced and the greenhouse gas carbon dioxide could be recycled back to the resource cycle, also commonly known as the closure of the carbon cycle. In this way, the CO2 footprint can be reduced entirely, which will contribute to global climate protection goals. Carbon dioxide can be considered as a sustainable feedstock because it is available as waste in many chemical processes. Another advantage is that carbon dioxide is easy to handle as a non-combustible gas.

As described in Green Chemistry, 2003, 5, 497-507, carbon dioxide is already used as feedstock for the production of aryl alkyl carbonates and diaryl carbonates on an industrial scale. A major disadvantage here is that the synthesis described in this patent document requires a number of synthetic steps:

The process proceeds from ethylene oxide prepared from ethylene. Subsequently, the reaction of ethylene oxide with carbon dioxide gives ethylene carbonate which is then transesterified with methanol to give dimethyl carbonate. This is followed by further transesterification with phenol to yield aryl alkyl carbonates. This is then disproportionated to the last reaction to give the diaryl carbonate.

Since carbon dioxide is a reaction-inert molecule, it is difficult to use carbon dioxide as a feedstock. Therefore, energy supply is required to convert carbon dioxide into good chemicals. In order to produce a product with a low carbon dioxide footprint, the generation of supply energy should also be associated with the lowest possible carbon dioxide emissions. For this purpose, for example, a current obtained from a renewable energy source is suitable.

Despite the advantageous use of carbon dioxide as feedstock, the process described above has several disadvantages. For example, numerous synthesis steps are required, which complicates the method. In addition, ethylene oxide is used, the use of which requires special safety measures with increasing complexity. Due to the low equilibrium constant of the transesterification reaction to obtain dimethyl carbonate, a very excess methanol is required (Catal Surv Asia, 2010, 14, 146-163). There is also a need for a continuous multistage distillation column. Individual steps of transesterification with phenols to obtain aryl alkyl carbonates also require the use of a plurality of catalysts such as, for example, Pb (OPh) ₂ and Bu ₂ SnO and have a high energy consumption and reactive distillation column (Catal. Surv. Asia, 2010, 14, 146-163). In addition, the reactive distillation apparatus used in the prior art contains a large amount of heterogeneous and homogeneous catalysts.

Electrochemical methods for the preparation of diaryl carbonates are described in J. Chem. Phys. Chem. C, 2012, 116, 10607-10616. This again relates to an electrochemical modification of the oxidative carbonylation reaction of aryl alcohol using a palladium-based material as catalyst. The electrocatalytic reaction is carried out on a palladium catalyst consisting of nanoparticles, and the researchers note that only nanoparticles in the <2 nm range have sufficient catalytic activity. If the nanoparticles are> 6 nm, the electrocatalyst is inert. In view of this apparent limitation on catalyst size, the same group is described in subsequent studies in ACS Catal., 2013, 3, 389-392, Res. Chem. Intermed., 2015, 41, 9497-9508 and Catal. Sci. Technol., 2016, 6, 6002-6010, further reduced the size of the palladium-based electrocatalyst by using only homogeneous palladium complexes. The use of homogeneous catalysts is well known to be disadvantageous because they hinder product separation.

WO 2011/024327 A1 also describes the preparation of diaryl carbonates by homogeneous catalysis with palladium. This application focuses on constructing the reaction as efficiently as possible, and only using gold electrodes as discharge or reoxidation electrodes to convert the catalyst inert Pd ⁰ back to a homogeneously dissolved catalytically active Pd ²⁺ . It is described. The actual catalyst here is a homogeneous Pd ²⁺ as described above.

In contrast, JP H673582 describes heterogeneous electrocatalysis on palladium electrodes, but produces only dialkyl carbonates. As shown by Comparative Example 6, the formation of diaryl carbonate or aryl alkyl carbonate was not detected when using this electrode.

Likewise, US 2003/070910 A1 also describes only the preparation of dialkyl carbonates.

WO 2014/046796 A2 describes in particular the preparation of (phosgene) COCl ₂ as a starting material for carbonyl by electrochemical conversion of CO ₂ to CO and the hydrogen halide or halide salt to halogen. Since this involves first forming a phosgene and then converting it to a carbonate, it is not an in situ preparation of CO from CO ₂ in the preparation of diaryl or aryl alkyl carbonates.

It is an object of the present invention that heterogeneous catalysts with less catalytic steps than in the prior art and which have catalytic activity not based on palladium and not limited to a particle size range of <2 nm can be used as the electrocatalyst, It is to provide an electrochemical method for the preparation of aryl alkyl carbonates or diaryl carbonates in which the current can be used as an energy source.

The object is according to the invention an aryl alkyl carbonate or diaryl carbonate, characterized in that the compound of formula (1) is reacted with CO in an electrode having gold as an electrocatalyst together with the compound of formula (2). Achieved by the electrochemical preparation of carbonates:

(1) R ₁ -OH

The radical R ₁ here represents a radical from the group of an alkyl radical, preferably C ₁ -to C ₆ -alkyl, preferably methyl or ethyl, isopropyl or tert-butyl, or cycloalkyl, preferably cyclohexyl ,

(2) R ₂ -OH

The radical R ₂ here represents an aryl radical, preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, particularly preferably a phenyl radical. The electrocatalyst is heterogeneous and preferably free of palladium.

A particular advantage of the process according to the invention is that it is not so complicated that aryl alkyl carbonates or diaryl carbonates, in particular methyl phenyl carbonate (MPC) or diphenyl carbonate (DPC) It is possible to produce electrochemicals. The gold-based heterogeneous electrocatalysts used are also simply reusable over a wide range of particle sizes because the complex separation process of catalytically active metal complexes can be omitted. The absence of size constraints in the <2 nm range for the electrocatalyst results in greater degrees of freedom in the design of the electrode. Larger particle sizes of electrocatalysts can also increase their long term stability.

The process according to the invention uses the compounds of the formulas (1) and (2). Preferred starting compounds of formula (1) are those selected from the group:

Particularly preferably one selected from the group:

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

Particularly preferably one selected from the group:

및

와 일산화탄소의 반응의 예를 사용하여 도식적으로 예시된다:The reaction scheme for the process according to the invention for the electrochemical preparation of aryl alkyl carbonates or diaryl carbonates is

And

Schematically illustrated using examples of the reaction of with carbon monoxide:

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

By electrochemical anode activation, the resulting dimethyl carbonate can be obtained by transesterification with phenol to methyl phenyl carbonate:

Methyl phenyl carbonate can be transesterified in an additional step to obtain diphenyl carbonate:

The sequence of electrochemical reactions carried out here has not been described in this way to date and has been demonstrated by in-situ spectroscopic analysis.

Reaction sequences including the following have been demonstrated with reference to spectroscopic analysis:

1. formation of dialkyl carbonates by electrochemical anode reaction of alkyl alcohols with CO,

2. Provision of aryl alkyl carbonates by electrochemically activated transesterification of the resulting dialkyl carbonates,

3. Provision of diaryl carbonates by further electrochemically activated transesterification of the resulting aryl alkyl carbonates.

This involved first charging dimethyl carbonate into the electrolyte and monitoring the reaction resulting from the addition of phenol under electrochemical activation.

This potentiostatic experiment was performed at room temperature with a three electrode setup. The counter electrode was a platinum wire and a commercially available Ag / AgCl electrode was used as reference. The working electrode gold sheet disk was first polished with an aluminum suspension and treated with MilliQ water (18.4 MΩ) for 5 minutes in an ultrasonic bath. Electrode potential was controlled with an E-DAQ ER466 electrostatic potential. After the electrolyte solution was purged with Ar for 10 minutes until there was no oxygen, the electrolyte solution was saturated with CO and maintained through additional CO supply during the experiment.

Characterization by in situ FTIR at a potential of 0-1 V versus Ag / AgCl for an electrolyte consisting of 0.1 mol / L LiClO ₄ , 0.1 mol / L dimethyl carbonate and 0.1 mol / L phenol in acetonitrile The spectrum shown in Figure 1 was obtained through.

From the spectrum it is apparent that a characteristic band for diphenyl carbonate is formed from an electrode potential of ˜0.7 V versus Ag / AgCl. This indicates that diphenyl carbonate is formed from the precursor dimethyl carbonate in effect and that the formation is effected through electrochemical activation.

In a first advantageous embodiment of the invention, the cathode reaction is for example the reduction of carbon dioxide to carbon monoxide:

^{_{CO 2 + 2 e - + H}} 2 O → CO + 2 OH -

The OH ^- ions formed here are neutralized with protons from the anode reaction to form water:

^{2 OH - + 2 H + →} 2 H 2 O

The use of carbon dioxide in the cathode reduction reaction to provide carbon monoxide has the advantage that the greenhouse gas carbon dioxide can thus be recycled back to the resource cycle, also known as the closure of the carbon cycle. Carbon dioxide is available as waste in many chemical processes and can therefore be used as a sustainable feedstock. Another advantage is that carbon dioxide is easy to handle as a non-combustible gas. The feature of the process according to the advantageous embodiments described above is thus particularly sustainable. It is preferable that in-situ generation of carbon dioxide is concerned. In particular, the CO thus obtained is preferably reacted directly with the anode reaction with a gold electrocatalyst in the process according to the invention for the electrochemical preparation of aryl alkyl carbonates or diaryl carbonates.

Reactions for the cathode formation of carbon monoxide are in principle, for example, as described in Bull, Chem. Soc. Jpn, 1987, 60, 2517-2522.

This includes, for example, saturating a solution of TEAP (tetraethylammonium perchlorate) (0.1 mol / L) in acetonitrile with CO ₂ . After 30 minutes the system is hermetically sealed and the saturated electrolyte is circulated at a rate of 1 mL / min. CO ₂ is the cathode of a -2.6 V electrode potential (vs. Ag / AgCl / (0.01 mol / L LiCl + 0.1 mol / L TEAP / CH ₃ CN)-reference electrode) at a copper, indium, silver, palladium or gold electrode React. A charge of 100 C flows.

In a further advantageous embodiment of the invention, the anode electrochemical reaction is 0.1-5000 mA / cm ² , preferably 0.1-500 mA / cm ² , particularly preferably 0.1-100 mA / cm ² , very particularly preferably Is carried out at a current density in the range of 0.2-50 mA / cm ² . This means that it is also possible to implement on a large industrial scale.

In a further advantageous embodiment of the invention, the solvent used is methanol as the alcohol of formula (1), or an alcohol of formula (1) and other solvents, in particular acetonitrile, propylene carbonate, dimethylformamide, dimethyl sulfoxide Seed, 1,2-dimethoxyethane, dichloromethane or a mixture with a solvent selected from N-methyl-2-pyrrolidone. The upstream cathode reaction is carried out in particular in acetonitrile as solvent, but other aprotic solvents such as propylene carbonate, dimethylformamide, dimethyl sulfoxide, 1,2-dimethoxyethane, or N-methyl-2-pyrroli It may be done in money or in water. By selecting a suitable solvent from the above choices, the reaction can be run very selectively.

In a further embodiment of the process according to the invention, lithium chloride, lithium bromide, lithium perchlorate, sodium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, sodium phenoxide, lithium phenoxide, tetrabutylammonium chloride, Preferably lithium perchlorate or imidazolium-, ammonium-, phosphonium- or pyridinium-based ionic liquids, preferably 1-ethyl-3-methylimidazolium tetrafluoroborate, can be used as the conductive salt. . It is particularly preferred that the ionic liquid comprises imidazolium, ammonium, phosphonium or pyridinium as the cation.

In a further advantageous embodiment, the anode electrochemical reaction can be carried out at a temperature in the range of 10 ° C. to 250 ° C., in particular in the range of 20 ° C. to 100 ° C., particularly preferably in the range of room temperature.

In a further advantageous embodiment of the invention, the reaction can be carried out at standard pressure or at elevated pressure, in particular at overpressure of up to 1 bar. In particular, higher local concentrations and thus better productivity can be achieved at the electrode when operated at elevated pressure. Gas diffusion electrodes can preferably be used to carry out novel processes for the preparation of alkyl aryl carbonates and diaryl carbonates. In particular, the reaction for the cathode formation of carbon monoxide can be carried out at the gas diffusion electrode. The use of gas diffusion electrodes is also advantageous for the anode reaction to form aryl alkyl carbonates or diaryl carbonates.

In an advantageous embodiment of the invention, the anode reaction is carried out using a gas diffusion electrode, wherein the gas diffusion electrode comprises at least one sheet-like electrically conductive carrier and gas diffusion layer, and an electrocatalyst applied on the carrier,

기체 wherein the gas diffusion layer contains a mixture of electrocatalyst and hydrophobic polymer,

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

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

An advantage of gas diffusion electrodes is that the carbon monoxide generated for in-situ reactions in gases, for example cathodes, can be reacted directly at the electrodes. This results in a locally increased concentration of gaseous reactants at the electrode and achieves higher current densities than conventional electrodes, which is related to industrial utility.

Also in the cathode reduction of carbon dioxide to carbon monoxide, a gas diffusion electrode can be used as the cathode.

Gas diffusion electrodes are electrodes in which three phases of material-solid, liquid and gas-are in contact with each other and a solid electron-conductive catalyst catalyzes the electrochemical reaction between the liquid phase and the gas phase.

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

The gold particles have a median particle diameter (d ₅₀ measured by laser diffraction) in the range of 1 to 100 μm, preferably in the range of 2 to 90 μm, and / or the median particle diameter of the gold particles supported on carbon Preferred embodiments of the gas diffusion electrode are characterized in that they range from 2 nm to 100 μm, preferably from 2 nm to 1 μm.

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

It may also be provided that the hydrophobic polymer and the electrocatalyst in powder form are applied over the carrier and compressed to form a gas diffusion layer.

A gas diffusion electrode based on gold powder as an electrocatalyst has a total loading of catalytically active component in the range of 5 mg / cm ² to 300 mg / cm ² , preferably 10 mg / cm ² to 250 mg / cm ² , and / or carbon The gas diffusion electrode based on the supported gold particles further has a total loading of catalytically active components in the range of 0.5 mg / cm ² to 20 mg / cm ² , preferably 1 mg / cm ² to 5 mg / cm ² . desirable.

In a further advantageous embodiment of the invention, the carrier of the gas diffusion electrode may contain nickel, gold or silver, or a combination of nickel and gold or silver. The carrier may also be in the form of a mesh, a woven fabric, a loop-forming knit fabric, a loop-soft knit fabric, a nonwoven web fabric, an expanded metal or a foam, preferably a woven fabric, particularly preferably a mesh.

The preparation of the gas diffusion electrode can be carried out according to DE 10.148.599A1 by applying the catalyst powder mixture directly onto the carrier.

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

Preferably the mixing is carried out in a mixing device having a rapidly rotating mixing element, for example a beater blade. In order to mix the components of the powder mixture, the mixing element is preferably rotated at a speed of 10 to 30 m / s or at a rotational speed of 4000 to 8000 rpm. After mixing the powder mixture is preferably sieved. The sieving is preferably carried out with a sieving device equipped with a mesh or the like having a mesh perforation size of 0.04 to 2 mm.

Mixing in a mixing device with a rotary mixing member introduces energy into the powder mixture such that the powder mixture undergoes significant heating. If the powder is heated excessively, deterioration of the electrode performance is observed so that the temperature during the mixing process is between 35 ° C and 80 ° C. This can be effected by cooling during mixing, for example by the addition of a cooling medium such as liquid nitrogen or other inert heat-absorbing material. Additional means for temperature control may be to stop mixing to cool the powder mixture, or by selecting a suitable mixer or by changing the filling level in the mixer.

The application of the powder mixture on the electrically conductive carrier can be carried out, for example, by sparging. Spraying the powder mixture onto the carrier can for example be achieved through a sieve. Particularly advantageously a frame-shaped template is placed on the carrier and the template is preferably chosen to only encompass the carrier. Alternatively, the template may also be chosen to be smaller than the area of the carrier. In this case, the uncoated edge of the carrier remains free of the electrochemically active coating after sparging of the powder mixture and compaction with the carrier. The thickness of the template may be selected depending on the amount of powder mixture applied on the carrier. The template is filled with a powder mixture. Excess powder can be removed using a skimmer. The template is then removed.

In a particularly preferred embodiment, the powder mixture is compressed with the carrier in the next step. Compression can be carried out in particular with a roller. Preferably a pair of rollers is used. However, it is also possible to use one roller on an essentially flat surface, in which case the roller or surface is moved. Compression can also be performed by a compression piston. The force during compression is in particular 0.01 to 7 kN / cm.

A further aspect relates to the use of aryl alkyl carbonates or diaryl carbonates obtained from the process according to the invention, preferably by melt transesterification processes, for the production of polycarbonates.

The transesterification reaction can be described, for example, in the following formula:

The above advantages of the process according to the invention also apply similarly to the proposed use of aryl alkyl carbonates or diaryl carbonates in the production of polycarbonates, preferably by melt transesterification processes. .

The invention is more particularly illustrated by the following examples, which do not constitute any limitation of the invention.

Example

Analysis method used:

Gas Chromatography (GC)

Gas chromatography analysis (GC) was performed using a 7890A gas chromatograph from Agilent technologies and a 7639 autosampler. Interaction of the stationary phase and the sample was performed using a DB-1701 quartz capillary column (length: 30 m; inner diameter: 0.25 mm; film thickness of covalently bound stationary phase: 0.25 μm; preliminary column: 5 m, carrier from Agilent Technologies, USA). Gas: hydrogen; injector temperature: 150 ° C; detector temperature: 310 ° C; program: "hard" Method: 1 minute start temperature 50 ° C, heating rate: 15 ° C / min, 8 minutes final temperature 260 ° C do.

IR spectroscopy

In-situ using Bruker Vertex 80 V IR spectrophotometer for characterization of products and intermediates Fourier-transform infrared (FTIR) spectroscopy was also used. A prism made of CaF ₂ with an angle of 60 ° was used and the spectrum consisted of p-polarized light and a resolution of 8 cm ⁻¹ with an average of 100 interferograms.

(여기서 R 및 R₀은 샘플 스펙트럼/기준 스펙트럼의 반사도를 나타냄)에 따른 흡광도 A로서 제시된다. 이들 시차 스펙트럼에서, 음의 밴드 (아래쪽을 향하는 밴드)는 기준 스펙트럼에서 여전히 존재하는 종들의 소비를 제시한다. 양의 밴드 (위쪽을 향하는 밴드)는 기준 스펙트럼의 기록 동안에는 존재하지 않는 새로운 종들의 형성을 제시한다. 모든 분광화학적 실험은 Ag/Ag⁺ 기준 전극 및 백금 와이어 상대 전극으로 실온에서 수행하였다.Spectra were obtained from the setup where the electrode was pressed against the prism window under controlled potential. The reference was the spectrum recorded at the potential where the Faraday process was not performed. Subsequently the electrode potential was changed and the sample spectrum was obtained after subtraction of the reference spectrum. The final spectrum is expressed by

It is shown as absorbance A according to where R and R ₀ represent the reflectance of the sample spectrum / reference spectrum. In these parallax spectra, the negative band (downward facing band) shows the consumption of species still present in the reference spectrum. Positive bands (upward bands) suggest the formation of new species that do not exist during recording of the reference spectrum. All spectrochemical experiments were performed at room temperature with Ag / Ag ⁺ reference electrode and platinum wire counter electrode.

Example 1

Preparation of Diphenyl Carbonate on Gold Electrode

This potentiostatic experiment was performed at room temperature with a three electrode setup. The counter electrode was a platinum wire and a commercially available Ag / AgCl electrode was used as reference. The working electrode gold sheet disk was first ground with an aluminum suspension and treated with milliQ water (18.4 MΩ) for 5 minutes in an ultrasonic bath. Electrode potential was controlled by the E-DAQ ER466 electrostatic potential. This resulted in a current density of 0.2 mA / cm ² . 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 there was no oxygen, and then the electrolyte solution was saturated with CO and additional CO supply was supplied during the experiment. Maintained.

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

Even at small potentials of 0.3 V (measured against Ag / AgCl reference, fourth line from the bottom) (Figure 2), 1780 cm ^-1 and 1757 cm ^-1 (diphenyl carbonate and dimethyl carbonate, respectively) Positive bands). As the potential increases, the band grows further.

Example 2

Preparation of Carbon Monoxide Gas Diffusion Electrodes with Gold as Electrocatalyst

A gas diffusion electrode was prepared by a dry method of mixing 93% by weight of Ferro SPF 1775 gold powder and 7% by weight of DYNEON TF2053 PTFE in an Ika Muehle A11 basic mill. Subsequently, the powder mixture was compressed onto a nickel carrier mesh using a roller press with a force of 0.5 kN / cm. In the case of an electrode of size 24 cm ² 7.7 g of the powder mixture were required.

Example 3

Preparation of Methyl Phenyl Carbonate at Gas Diffusion Electrode with Sodium Phenoxide Conductive Salts

Experiments were performed in a filter press cell (Model: Micro Flow Cell, Volume: 0.001 m ² ) commercially available from Electrocell in a two-electrode setup. The counter electrode used was iridium MMO (iridium mixed metal oxide electrode commercially available from ElectroCell). The working electrode is a gas diffusion electrode made of a mixture of PTFE and gold powder rolled onto a carrier material made of nickel and made according to Example 2. Electrolysis was performed for 1 hour at 1.2 V (current density about 1 mA / cm ² ). During this time 40 mL of electrolyte was recycled at a rate of 2 mL / min. In the case of an electrolyte, 1.06 g of LiClO ₄ (0.1 mol / L), 139 mg of NaOPh (12 mmol / L) and 7.06 g of PhOH (0.75 mol / L) are dissolved in 100 mL of MeOH.

Characterization by the Agilent Technologies GC 7809A instrument revealed the following:

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

Example 4

Preparation of Methyl Phenyl Carbonate at Gas Diffusion Electrode

Experiments were performed in a filter press cell (model: micro flow cell, volume: 0.001 m ² ) commercially available from the electrocell in a two-electrode setup. The counter electrode used was Ir MMO (iridium mixed metal oxide electrode commercially available from ElectroCell). The working electrode is a gas diffusion electrode consisting of a mixture of PTFE and gold powder rolled onto a carrier material made of nickel. Electrolysis was performed for 1 hour at 1.2 V (current density about 1 mA / cm ² ). During this time 40 mL of electrolyte was recycled at a rate of 2 mL / min. In the case of an electrolyte, 1.06 g of LiClO ₄ (0.1 mol / L) and 7.06 g of PhOH (0.75 mol / L) are dissolved in 100 mL of MeOH.

Characterization by the Agilent Technologies GC 7809A instrument revealed the following:

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

Comparative Example 5

Fabrication of Palladium-Based Carbon Monoxide Gas Diffusion Electrode

A gas diffusion electrode was prepared by a dry method in which 93% by weight of Ferro M8039 palladium powder and 7% by weight of DYNEON TF2053 PTFE were mixed in an Ica Muel A11 basic mill. Subsequently, the powder mixture was compressed onto a nickel carrier mesh using a roller press with a force of 0.29 kN / cm. For an electrode of size 32 cm ² 4.3 g of the powder mixture was required.

Comparative Example 6

Preparation of Dimethyl Carbonate at Palladium-Based Carbon Monoxide Gas Diffusion Electrode

Experiments were performed in a filter press cell (model: micro flow cell, volume: 0.001 m ² ) commercially available from the electrocell in a two-electrode setup. The gas diffusion electrode prepared according to Comparative Example 5 was connected in an anode manner and the counter electrode used was an iridium MMO electrode (iridium mixed metal oxide electrode commercially available from Electrocell). Electrolysis was performed for 1 hour at a current density of 0.2 mA / cm ² . The flow rate of CO was 0.5 L / h and the electrolyte (30 mL) was recycled to a flow rate of 2 mL / min. In the case of the electrolyte, PhOH (14.11 g, 0.15 mol, 0.75 mol / L) and LiCl (114.5 mg, 2.7 mmol, 0.014 mol / L) are dissolved in CH ₃ CN (200 mL).

GC-HS analysis showed neither DPC nor methyl phenyl carbonate. In this case the following analysis was performed:

Experiments were performed using a GC7890A instrument with a headspace (HS) 7697 sampling system from Agilent Technologies and an HP-5 column (fixed phase: 5% phenylmethylpolysiloxane, length: 30 mx 320 μm × 0.25 μm, carrier gas: helium) Was performed. In each case 3 mL of sample in a 20 mL vial was placed in an HS sampler, which was heated in an oven at 80 ° C. for 15 minutes and pressurized to 15 psi. Subsequently 1 mL of gas phase was applied to the column via a transfer line (200 ° C.) with a split of 10: 1. FID (flame ionization detector) was operated at a hydrogen flow rate of 40 mL / min and 300 ° C. Column Program: The starting temperature was 90 ° C. and after holding for 2 minutes the temperature was increased to 250 ° C. at 50 ° C./min. The final temperature of 250 ° C. was maintained again for 2 minutes.

Claims (14)

Electrochemical preparation of aryl alkyl carbonates or diaryl carbonates, characterized in that the compound of formula (1) is reacted with CO in an electrode with gold as a heterogeneous electrocatalyst together with the compound of formula (2) Way:
(1) R ₁ -OH
The radical R ₁ here represents a radical from the group of an alkyl radical, preferably C ₁ -to C ₆ -alkyl, preferably methyl or ethyl, isopropyl or tert-butyl, or cycloalkyl, preferably cyclohexyl ,
(2) R ₂ -OH
The radical R ₂ here represents an aryl radical, preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, particularly preferably a phenyl radical. The method of claim 1 wherein the CO is generated electrochemically from CO ₂ at the cathode in an upstream reaction. The anode electrochemical reaction according to claim 1 or 2, wherein the anode electrochemical reaction is 0.1-5000 mA / cm ² , preferably 0.1-500 mA / cm ² , particularly preferably 0.1-100 mA / cm ² , very particularly preferably Is carried out at a current density in the range of 0.2-50 mA / cm ² . The process of claim 1, wherein the alcohol of formula (1) and other solvents, in particular acetonitrile, propylene carbonate, dimethylformamide, dimethyl sulfoxide, 1,2-dimethoxyethane, And a mixture with a solvent selected from dichloromethane or N-methyl-2-pyrrolidone is used. The lithium chloride, lithium bromide, lithium perchlorate, sodium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, sodium phenoxide, lithium phenoxide, tetrabutylammonium according to any one of claims 1 to 4. Chloride, preferably lithium perchlorate or imidazolium-, ammonium-, phosphonium- or pyridinium-based ionic liquids, preferably 1-ethyl-3-methylimidazolium tetrafluoroborate is an electrochemically conductive salt Used as a method. 6. The anode electrochemical reaction according to claim 1, wherein the anode electrochemical reaction is carried out at a temperature in the range of 10 ° C. to 250 ° C., in particular in the range of 20 ° C. to 100 ° C., particularly preferably in the range of room temperature. How to. The process according to claim 1, wherein the reaction is carried out at standard pressure or at elevated pressure, in particular at excess pressure of up to 1 bar. 8. The anode reaction according to claim 1, wherein the anode reaction is carried out using a gas diffusion electrode, wherein the gas diffusion electrode comprises at least one sheet-like electrically conductive carrier and gas diffusion layer, and an electrocatalyst applied on the carrier. Include,
Wherein the gas diffusion layer contains a mixture of electrocatalyst and hydrophobic polymer,
Wherein the electrocatalyst is in the form of a gold powder or in the form of gold particles supported on a carbon support, wherein the carbon support contains activated carbon, carbon black, graphite, graphene or carbon nanotubes, in particular carbon black,
Wherein the hydrophobic polymer is a fluorine-substituted polymer, particularly preferably polytetrafluoroethylene (PTFE)
Characterized by the above. The method of claim 8, wherein 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 the electrocatalyst and the hydrophobic polymer, or the particles on the carbon support. Wherein the proportion of the electrocatalyst in the form is 40% to 60% by weight based on the total weight of the electrocatalyst and the hydrophobic polymer. 10. The method according to claim 8 or 9, wherein the gold powder has a median particle diameter in the range of 1 to 100 μm, preferably in the range of 2 to 90 μm, or the median particle diameter of the particles supported on carbon is 2 a process in the range from nm to 100 μm, preferably in the range from 2 nm to 1 μm. The method of claim 8, wherein the hydrophobic polymer and the electrocatalyst in powder form are applied over the electrically conductive carrier and compressed to form a gas diffusion layer. The gas diffusion electrode based on gold powder as electrocatalyst according to claim 8, wherein the gas diffusion electrode is 5 mg / cm ² to 300 mg / cm ² , preferably 10 mg / cm ² to 250 mg / cm ^2. A gas diffusion electrode having a total loading of the catalytically active component in the range, or based on carbon-supported gold particles, is 0.5 mg / cm ² to 20 mg / cm ² , preferably 1 mg / cm ² to 5 mg / cm Characterized by having a total loading of the catalytically active component in the ^two ranges. The method according to any one of claims 8 to 12, wherein the electrically conductive carrier of the gas diffusion electrode contains nickel, gold or silver, or a combination of nickel and gold or silver. The electrically conductive carrier according to claim 8, wherein the electrically conductive carrier is a mesh, a woven fabric, a loop-forming knit fabric, a loop-soft knit fabric, a nonwoven web fabric, an expanded metal or a foam, preferably a woven fabric. In a form.

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