A method of electrochemically synthesizing isothiocyanates
By using carbon-supported noble metal and transition metal bimetallic alloy nanoparticle catalysts in a diaphragm-free electrolyzer, and optimizing the potential range and electrolysis solvent, the safety risks and selectivity issues in isothiocyanate synthesis were resolved, achieving efficient and sustainable electrochemical synthesis.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- LUDONG UNIVERSITY
- Filing Date
- 2025-09-26
- Publication Date
- 2026-05-19
AI Technical Summary
Existing methods for synthesizing isothiocyanate compounds have problems such as high safety risks, insufficient sustainability and limited scalability. Furthermore, electrochemical oxidation faces challenges in terms of high Faradaic efficiency and selectivity, especially in the difficulty of achieving CH activation and intermediate adsorption regulation.
In a membrane-free electrolytic cell, a bimetallic alloy nanoparticle catalyst formed by carbon-supported noble metals and transition metals is used. The catalyst reacts with a specific electrolytic solvent (such as 1,2-dichloroethane/hexafluoroisopropanol) in a potential range of 0.3 to 2.0 V. Combined with the design of a membrane-free electrolytic cell, the catalyst and reactants are fully contacted, thus optimizing the electrocatalytic performance.
It improves the synthesis efficiency and selectivity of isothiocyanates, reduces energy demand, enables the joint production of renewable energy and chemicals, and provides more efficient electrocatalytic performance.
Smart Images
Figure CN120866838B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for the electrochemical synthesis of isothiocyanates. Background Technology
[0002] Isothiocyanates, as multifunctional synthetic structural units, play a crucial role in constructing the organic framework of heterocyclic compounds such as thioureas, carbamates, thiazoles, and imidazoles. These compounds also demonstrate significant value in medicinal chemistry; the isothiocyanate group in their molecular structure constitutes the core pharmacophore of anticancer and antibacterial drugs, exerting therapeutic effects through mechanisms such as inducing cancer cell apoptosis, inhibiting tumor angiogenesis, and interfering with pathogen metabolic systems by releasing isothiocyanate gas or decomposition products (such as cyanide). Furthermore, based on their naturally pungent properties derived from cruciferous plants, isothiocyanates are also used as flavor additives in the food industry. Currently, traditional synthetic methods mainly involve the reaction of benzylamine with the highly toxic reagent phosgene, or reflux with potassium thiocyanate under strongly acidic conditions. However, these methods have significant drawbacks, including high safety risks, insufficient sustainability, and limited scalability. Despite the important applications of isothiocyanates, their most economical atom-economical synthetic route—the direct C(sp) synthesis of ethylbenzene derivatives—remains a challenge. 3 The )-H thiocyanate reaction still faces challenges in terms of synthesis technology.
[0003] Electrochemical oxidation offers an alternative strategy for synthesizing isothiocyanates (the technology itself has existed for some time, but its application to isothiocyanate synthesis is a first). This strategy not only reduces energy demand by replacing the oxygen evolution reaction (OER) with the electrooxidation of high-value small molecules, but also enables the co-production of renewable energy and chemicals, providing a dual-benefit approach to sustainable energy conversion. However, achieving high Faradaic efficiency and selectivity remains challenging, primarily due to difficulties in regulating CH activation and intermediate adsorption on the electrocatalyst. Summary of the Invention
[0004] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing an electrochemical method for synthesizing isothiocyanates.
[0005] The purpose of this invention is to provide a method for electrochemically synthesizing isothiocyanate. In this method, electrolyte, electrolytic solvent, and reaction substrate are added sequentially to an electrolytic cell without a diaphragm. Anode and cathode are inserted, and the mixture is stirred. The reaction is carried out under constant current and atmospheric pressure. After the reaction is completed, the electrolyte is subjected to organic extraction and then separated and purified to obtain isothiocyanate.
[0006] The potential range is 0.3~2.0 V; the electrolytic solvent is haloalkanes and / or haloalcohols; the reaction substrate is aromatic derivatives with ethyl groups and trimethyl isothiocyanate; and the temperature is controlled at 10~40 °C.
[0007] The cathode and anode are modified with a catalyst, which is a bimetallic alloy nanoparticle formed by carbon-supported noble metals and transition metal elements.
[0008] Furthermore, aromatic derivatives containing ethyl groups include one or more compounds with the following structures:
[0009] .
[0010] Furthermore, the electrolytic solvent is 1,2-dichloroethane and / or hexafluoroisopropanol.
[0011] Furthermore, the electrolyte is tetrabutylammonium hexafluorophosphate.
[0012] Furthermore, the precious metal is one of Pt, Pd, and Ru.
[0013] Furthermore, the transition metal is one of Fe and Cu.
[0014] Furthermore, in the bimetallic alloy nanoparticles, the molar ratio of noble metal to transition metal is 30-90:10-75.
[0015] Furthermore, the catalyst is dispersed in an ethanol solution of Nafion, coated onto nickel foam as the anode, and coated onto a Pt / C electrode as the cathode.
[0016] Furthermore, the specific preparation process of the catalyst is as follows:
[0017] Bimetallic alloy nanoparticles formed by noble metal and transition metal elements were obtained by stirring and reacting noble metal salts and transition metal salts as metal precursors in a reducing environment.
[0018] Bimetallic alloy nanoparticles were mixed and dispersed with a commercial carbon support in a solvent, then sonicated, centrifuged to collect the product, and washed and dried.
[0019] Furthermore, the noble metal salt and transition metal salt are acetylacetone metal.
[0020] Based on Nørskov's d-band model, the electrocatalytic activity of the ethylbenzene oxidation reaction (EOR) can be adjusted by modifying the adsorption energy of the reaction intermediates. Optimization, which fundamentally depends on the suborbital electron occupancy of noble metal catalysts, is crucial. Palladium (Pd), with its tunable d-band center (εd), is a promising candidate for EOR due to its intrinsic ability to balance adsorption-desorption kinetics. However, single-metal palladium exhibits excessive adsorption of intermediates due to its complete occupancy of d suborbitals, leading to severe charge polarization and slow reaction kinetics. This confined electron origin lies in the half-filled antibonded state of Pd (εd). The limited electron transfer during the EOR process is due to the work function difference between Pd and M, which restricts efficient electron transfer. To address this issue, alloying Pd with a second metal (M) introduces a cooperative electronic effect: the work function difference between Pd and M induces intermetallic charge transfer (M→Pd or Pd→M). This charge redistribution modulates the d-band centers of surface Pd atoms, optimizing antibonding. Orbital layout. For example, alloying Pd with electron-donating metals (Cu, Ni) increases the electron density of the Pd d orbitals, bringing εd closer to the Fermi level (Ef). This enhances the adsorption strength of oxygen-containing intermediates while avoiding catalyst poisoning—a delicate balance achieved through suborbital hybridization between the Pd d and Ms / p orbitals.
[0021] The electrolytic cell used in this invention must be a diaphragm-less electrolytic cell; other types of electrolytic cells cannot efficiently synthesize the product. The potential range is 0.3~2.0 V; other potential ranges, such as -1 V or no current, will not allow the reaction to produce isothiocyanate compounds. The electrolyte is a mixture of 1,2-dichloroethane / hexafluoroisopropanol; other polar solvents, such as acetonitrile and ethanol, cannot efficiently catalyze the product formation. The temperature is controlled between 10~40 °C; other temperature ranges will not result in a reaction. The bimetallic alloy nanoparticles must be one of PtCu, PdCu, RuCu, PtFe, PdFe, or RuFe; other catalysts, such as commonly used commercial Pt and Pd, cannot efficiently catalyze the formation of isothiocyanate products.
[0022] The reasons why a diaphragm-less electrolyzer must be used are as follows:
[0023] The core reason lies in the fact that the structural characteristics of this type of electrolyzer meet the reaction mechanism requirements for the efficient synthesis of isothiocyanates, while the separating effect of a diaphragm-type electrolyzer significantly hinders the reaction process. The synthesis reaction of isothiocyanates depends on the efficient collision and transformation of active intermediates generated at the anode and cathode during electrolysis in the electrolyte. In a diaphragm-free electrolyzer, the anode and cathode regions are directly connected, and the electrolyte can flow freely, allowing the anodic oxidation products and cathodic reduction products (or active species in the electrolyte) to come into rapid contact in the mixture, shortening the reaction path. This invention uses a 1,2-dichloroethane / hexafluoroisopropanol mixture as the electrolyte. The polarity and ion conduction characteristics of this system can only achieve optimal results in a diaphragm-free environment. If a diaphragm is present, the retention of solvent or ions by the diaphragm may disrupt the compositional homogeneity of the electrolyte, leading to a decrease in ion conduction efficiency, a deviation of the potential range from the optimal reaction range, and consequently affecting the catalyst activity and reaction rate.
[0024] The advantages of diaphragm-free electrolyzers are:
[0025] (1) The diaphragmless electrolyzer achieves free mass transfer of substances in the electrolyte by eliminating physical separation;
[0026] (2) Highly efficient ion conduction;
[0027] (3) Sufficient contact between the catalyst and the reactants.
[0028] These three characteristics, along with the potential range, electrolyte system, and alloy catalyst defined in this invention, form a synergistic effect, which is a necessary condition for the efficient synthesis of isothiocyanate compounds. Diaphragm-type electrolyzers, due to their ability to hinder mass transfer and disrupt system homogeneity, cannot meet the above reaction requirements and therefore cannot replace the function of diaphragm-free electrolyzers.
[0029] The reasons why Pt / Pd / Ru-based catalysts must be used are as follows:
[0030] Pt / Pd / Ru-based catalysts exhibit good activity and stability in electrocatalytic reactions, and their suitable d-band center positions allow for the regulation of adsorption between the catalyst and substrate molecules through alloying and other methods. This method utilizes transition metals such as Fe / Cu to form alloys with Pt / Pd / Ru, enhancing the adsorption strength with ethylbenzene and effectively activating the CH group at the benzyl group of ethylbenzene, thus enabling the efficient production of isothiocyanate products.
[0031] If other Pt / Pd / Ru catalysts are used, such as commercial Pd / C, the adsorption between Pd atoms and substrate molecules is too weak to activate the substrate, and ultimately the reaction cannot occur efficiently.
[0032] The reactive site is either 1 or 2 in the lower molecule.
[0033]
[0034] The advantages of Pt / Pd / Ru-based catalysts are:
[0035] (1) The bonding ability between Pt / Pd / Ru atoms in the alloy and substrate molecules is enhanced, and they have shorter electron transfer paths, which can greatly improve the electron transfer efficiency of the catalyst.
[0036] (2) The d-band center of Pt / Pd / Ru atoms in the alloy moves upward, which can directly activate benzyl hydrogen. Its special electronic structure helps to modulate the adsorption of the substrate and improve catalytic efficiency and selectivity.
[0037] (3) The introduction of transition metals Fe and Cu into Pt / Pd / Ru atoms reduces the amount of noble metals used, enabling the catalyst to achieve better catalytic effect with lower Pd loading.
[0038] In summary, this invention utilizes a membraneless electrolyzer, with electrodes modified by carbon-supported nanoparticle catalysts, and limits the reaction substrate, reaction temperature, potential range, and solvent type to effectively promote substrate adsorption, improve electrocatalytic performance, and increase the efficiency of isothiocyanate production, making the preparation process more convenient and efficient. Attached Figure Description
[0039] Figure 1 Catalyst A (Pd) obtained in Example 1 78 Cu 22 Transmission electron microscopy image and elemental distribution map of bimetallic alloy nanoparticles;
[0040] Figure 2 To change the feed amount of catalyst A (Pd) 51 Cu 49 Transmission electron micrograph and elemental distribution of ).
[0041] Figure 3 To change the feed amount of catalyst A (Pd) 31 Cu 69 Transmission electron micrograph and elemental distribution of ).
[0042] Figure 4 The chromatogram and NMR spectrum of product 1 in the electrolytic cell are shown.
[0043] Figure 5 The electrochemical test results are for the catalysts prepared in Example 1 and Comparative Example 1. Detailed Implementation
[0044] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.
[0045] Catalyst Synthesis
[0046] Example 1
[0047] The noble metal precursor was weighed and added to oleylamine, followed by the addition of a certain amount of reducing agent and surfactant (the reducing agent was glucose and benzoic acid, and the surfactant was CTAB). An appropriate amount of transition metal precursor was then added and ultrasonically homogenized. The mixture was heated to 180 °C and reacted for 5 hours. After the reaction, the mixture was centrifuged, washed, and dried to obtain bimetallic alloy nanoparticles.
[0048] Bimetallic alloy nanoparticles dispersed in 10 mL of cyclohexane were mixed with a commercial carbon support (Vulcan XC-72) (10 mg), dispersed in 20 mL of cyclohexane, and then sonicated for 2 hours. The product was collected by centrifugation and washed twice with cyclohexane / ethanol (5 / 1 v / v). Finally, the product was collected by centrifugation, washed twice with cyclohexane / ethanol (5 / 1 v / v), and dried under ambient conditions to obtain catalysts A / B / C / D / E / F for further use.
[0049] Among them, the noble metal precursor and the transition metal precursor are Pt(acac)2, Pd(acac)2, Ru(acac)3, Fe(acac)3, and Cu(acac)2, respectively.
[0050] By adjusting the types and molar ratios of noble metal precursors and transition metal precursors, bimetallic alloy nanoparticle catalysts with the compositions shown in Table 1 were prepared.
[0051] Table 1 Catalysts in Example 1
[0052]
[0053] Comparative Example 1
[0054] Weigh 1.0 g of a single noble metal precursor or transition metal precursor and add it to 50 mL of oleylamine. Then add a certain amount of reducing agent and surfactant, heat to 180 °C and react for 5 hours. After the reaction, centrifuge, wash and dry to obtain single metal nanoparticles.
[0055] Single-metal nanoparticles dispersed in 10 mL of cyclohexane were mixed with a commercial carbon support (Vulcan XC-72) (10 mg), dispersed in 20 mL of cyclohexane, and then sonicated for 2 hours. The product was collected by centrifugation and washed twice with cyclohexane / ethanol (5 / 1 v / v). Finally, the product was collected by centrifugation, washed twice with cyclohexane / ethanol (5 / 1 v / v), and dried under ambient conditions to obtain catalyst G / H / I / J / K for further use.
[0056] Table 2 Catalysts in Comparative Example 1
[0057]
[0058] Figure 1 The images show transmission electron microscopy (TEM) images and elemental distribution diagrams of the bimetallic alloy nanoparticles of catalyst A obtained in Example 1. It can be seen that the metal precursor forms a nano-alloy material through a reducing agent and a structure directing agent.
[0059] Figure 2 These are catalyst A (Pd) after changing the feed amount. 51 Cu 49 The transmission electron microscopy (TEM) images and elemental distributions show that the constituent elements of the material did not change after reacting with different amounts of metal precursors.
[0060] Figure 3 These are catalyst A (Pd) after changing the feed amount. 31 Cu 69 The transmission electron microscopy (TEM) images show that the constituent elements Pd and Cu of the material remained unchanged after reacting with different metal precursors. This indicates that the method used in this invention, utilizing palladium acetylacetone and copper acetylacetone as metal precursors, can yield nano-alloy catalysts with different proportions.
[0061] Example 2
[0062] Weigh out 5.3 mL of ethylbenzene and 9.6 mL of trimethylsilyl isothiocyanate, add them to a mixed solution of 36 mL of 1,2-dichloroethane and 12 mL of hexafluoroisopropanol, and add 100 mg of tetrabutylammonium hexafluorophosphate. Both the anode and cathode of the electrolytic cell use catalyst A (Pd). 51 Cu 49 The catalyst was modified by dispersing it in an ethanol solution of Nafion, coating it onto nickel foam as the anode, and coating it onto a Pt / C electrode as the cathode.
[0063] The constant current method was selected for testing, with a potential range of 0.3~2.0 V. After the reaction was completed by stirring in the electrolytic cell, the product was obtained by rotary evaporation, washing and purification to obtain product 1.
[0064] The reaction process is as follows:
[0065]
[0066] Figure 4The chromatogram and NMR spectrum of product 1 in the electrolyzer show that a signal of 1-phenylethyl isothiocyanate appears at the 6.5 min position. The characteristic peak of this product was also detected in the NMR spectrum. This further demonstrates that the method provided by this invention can efficiently prepare isothiocyanates.
[0067] Figure 5 The electrochemical test results of the catalysts prepared in Example 1 and Comparative Example 1 show that Pd 51 Cu 49 The catalyst exhibits a lower potential and a higher current density, demonstrating that the supported alloy catalyst can effectively promote substrate adsorption and improve the electrocatalytic efficiency of isothiocyanate production.
[0068] Comparative Example 2
[0069] Compared to Example 2, no electricity was applied, and the reaction was stirred.
[0070] Comparative Example 3
[0071] Compared to Example 2, the potential was selected at 2.5 V.
[0072] Comparative Example 4
[0073] Compared to Example 2, the temperature was selected at 60 °C.
[0074] Comparative Example 5
[0075] The solvent used in Example 2 was acetonitrile.
[0076] After chromatographic characterization, the target product was not detected in comparative examples 2, 3, 4 and 5, indicating that the reaction cannot be carried out effectively under conditions other than those of this invention.
[0077] Example 3
[0078] Compared to Example 2, the reaction substrate was replaced with p-methoxyethylbenzene instead of ethylbenzene, and NMR analysis showed that the product contained ethyl 1-(4-methoxyphenyl)isothiocyanate.
[0079] Example 4
[0080] Compared to Example 2, the reaction substrate was replaced with 1-ethylnaphthalene, and NMR analysis showed that the product contained 1-(1-naphthyl)ethyl thioisocyanate.
[0081] Examples 3 and 4 demonstrate that isothiocyanate products can be generated when the reaction substrate is an aromatic derivative containing an ethyl group.
[0082] Examples 5-9
[0083] Compared to Example 2, the catalyst was replaced with B (Pd). 47 Fe53 ) / C(Pt 48 Cu 52 ) / D(Pt 75 Fe 25 ) / E(Ru 85 Cu 15 ) / F(Ru 78 Fe 22 ).
[0084] Comparative Examples 6-10
[0085] Compared to Example 2, the catalyst was replaced with G / H / I / J / K.
[0086] Table 3 Electrosynthesis results of catalysts A / B / C / D / E / F
[0087]
[0088] Table 4 Electrosynthesis Results of Catalysts G / H / I / J / K
[0089]
[0090] The results of Examples 5-9 and Comparative Examples 6-10 show that when the catalyst is a bimetallic alloy formed by Pt / Pd / Ru noble metal and Fe / Cu transition metal element, it has good catalytic performance; while when the catalyst is a single metal, the catalytic performance is poor.
[0091] For any points not covered above, existing technologies shall apply.
[0092] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for the electrochemical synthesis of isothiocyanates, characterized in that, Electrolyte, electrolyte, and reaction substrate were added sequentially to a membraneless electrolytic cell. Anode and cathode were inserted, and the mixture was stirred. The reaction was carried out under constant current and atmospheric pressure. After the reaction was completed, the electrolyte was subjected to organic extraction and then separated and purified to obtain isothiocyanate. The potential range is 0.3~2.0 V; the electrolytic solvent is haloalkanes and / or haloalcohols; the reaction substrate is aromatic derivatives with ethyl groups and trimethyl isothiocyanate; and the temperature is controlled at 10~40 °C. The cathode and anode are modified with a catalyst, which is a bimetallic alloy nanoparticle formed by carbon-supported noble metals and transition metal elements. Aromatic derivatives containing ethyl groups are selected from one or more compounds with the following structures: ； The precious metal is one of Pt, Pd, and Ru; The transition metal is one of Fe and Cu.
2. The method for electrochemical synthesis of isothiocyanate as described in claim 1, characterized in that, The electrolytic solvent is 1,2-dichloroethane and / or hexafluoroisopropanol.
3. A method for electrochemical synthesis of isothiocyanate as described in claim 1 or 2, characterized in that, The electrolyte is tetrabutylammonium hexafluorophosphate.
4. The method for electrochemical synthesis of isothiocyanate as described in claim 1, characterized in that, In bimetallic alloy nanoparticles, the molar ratio of noble metal to transition metal is 30-90:10-75.
5. The method for electrochemical synthesis of isothiocyanate as described in claim 1, characterized in that, The catalyst was dispersed in an ethanol solution of Nafion, coated onto nickel foam as the anode, and coated onto a Pt / C electrode as the cathode.
6. The method for electrochemical synthesis of isothiocyanate as described in claim 1, characterized in that, The specific preparation process of the catalyst is as follows: Bimetallic alloy nanoparticles formed by noble metal and transition metal elements were obtained by stirring and reacting noble metal salts and transition metal salts as metal precursors in a reducing environment. Bimetallic alloy nanoparticles were mixed and dispersed with a commercial carbon support in a solvent, then sonicated, centrifuged to collect the product, and washed and dried.
7. The method for electrochemical synthesis of isothiocyanate as described in claim 6, characterized in that, The noble metal salt and transition metal salt are acetylacetone metal.