CN114272946B - Graphite-phase carbon nitride-loaded low-spin monatomic Fe heterogeneous catalyst, preparation method and catalysis method - Google Patents
Graphite-phase carbon nitride-loaded low-spin monatomic Fe heterogeneous catalyst, preparation method and catalysis method Download PDFInfo
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Abstract
The invention provides a graphite-phase carbon nitride-loaded low-spin monatomic Fe heterogeneous catalyst, a preparation method and a catalysis method. The carbon-nitrogen element ratio of the graphite phase carbon nitride carrier is C/N = 0.4-0.7, the Fe and four N atoms on the surface of the graphite phase carbon nitride carrier form an Fe-N four-coordination structure, and the bond length of the Fe-N is
The load capacity of the monoatomic Fe is 3-10 wt%, and the monoatomic Fe is firstly used for catalyzing the reaction of ethanol and benzimidazole to prepare 2- (1-hydroxyethyl) -benzimidazole. The heterogeneous catalyst consists of uniformly dispersed monatomic Fe and a graphite-phase carbon nitride carrier, and low-spin states with different ratios are obtained by controlling the conditions of the preparation process, so that the catalytic reaction yield is influenced.
Description
Technical Field
The invention relates to the technical field of ethanol catalytic conversion and related catalysis, in particular to a graphite-phase carbon nitride-loaded low-spin monatomic Fe heterogeneous catalyst, a preparation method and a catalysis method.
Background
Thiabendazole, also known as thiabendazole, is an important imidazole-based broad-spectrum fungicide, and can be synthesized by using 2- (1-hydroxyethyl) -benzimidazole as a raw material according to the reaction steps in the following scheme 1 (chemical reagent, 2016,38,1235-1238).
Wherein, 2- (1-hydroxyethyl) -benzimidazole is used as an important precursor of thiabendazole, the industrial and laboratory preparation method is shown in a route 2, o-phenylenediamine and lactic acid are used as reactants, high-concentration hydrochloric acid is used as a catalyst, 2- (1-hydroxyethyl) -benzimidazole hydrochloride is prepared through condensation reaction under the reflux condition, and then ammonia water is used for deprotonation to obtain 2- (1-hydroxyethyl) -benzimidazole (org. Chem. Front.,2019,6,205-208).
However, the disadvantage of this route is that concentrated hydrochloric acid is used as a catalyst, which is corrosive, and the reaction is carried out at high temperature, and the reflux temperature is above 80 ℃, which is liable to cause safety hazards.
Therefore, a catalyst and a catalytic reaction route for preparing 2- (1-hydroxyethyl) -benzimidazole, which have mild reaction processes and are environment-friendly, are sought, and a reaction which needs to be solved urgently is needed.
Disclosure of Invention
In order to solve the problems, the invention provides a graphite-phase carbon nitride supported low-spin monatomic Fe heterogeneous catalyst which is used for catalyzing the reaction of ethanol and benzimidazole to prepare 2- (1-hydroxyethyl) -benzimidazole for the first time. The heterogeneous catalyst consists of uniformly dispersed monoatomic Fe and a graphite-phase carbon nitride carrier, and low-spin states with different ratios are obtained by controlling the conditions of the preparation process, so that the catalytic reaction yield is influenced.
The technical scheme of the invention is as follows:
the invention provides a graphite-phase carbon nitride-loaded low-spin monatomic Fe heterogeneous catalyst, which consists of uniformly dispersed monatomic Fe and a graphite-phase carbon nitride carrier, wherein,
the carbon-nitrogen element ratio of the graphite-phase carbon nitride carrier is C/N = 0.4-0.7, and the Fe and four N atoms on the surface of the graphite-phase carbon nitride carrier formA Fe-N four-coordinate structure with a Fe-N bond length of
The load of the monoatomic Fe is 3wt% -10 wt%. />
Further, in the heterogeneous catalyst, the low-spin state of the monatomic Fe accounts for 20 to 90% of the total amount of the monatomic Fe.
Further, in the heterogeneous catalyst, the monatomic Fe in the low spin state accounts for 80% of the total monatomic Fe.
The present invention also provides a process for the preparation of the aforementioned heterogeneous catalyst, which process, in one particular embodiment of the invention, comprises the steps of:
step A1: respectively preparing a dicyandiamide solution and a Fe (III) salt solution, wherein the concentration of the dicyandiamide solution is 0.4-0.8 mol/L, the concentration of the Fe (III) salt solution is 0.03-0.06 mol/L, slowly pouring an iron salt solution into the dicyandiamide solution at normal temperature to obtain a deep red Fe (III) -dicyandiamide complex solution, pouring the complex solution into an evaporation vessel, and evaporating water to dryness to obtain a khaki Fe (III) -dicyandiamide complex flaky solid;
step B1: grinding the Fe (III) -dicyandiamide complex flaky solid into fine powder, putting the fine powder into a tubular furnace, heating the fine powder to 450-650 ℃ at the heating rate of 5-15 ℃/min, carrying out heat treatment for 2-3 h in the atmosphere of inert gas, then naturally cooling, uniformly grinding the obtained product, and dispersing the product in dilute HNO 3 In the solution, under the condition of magnetic stirring, keeping the obtained suspension at the temperature of 40-60 ℃ for 4-6 h, filtering, washing the filtrate to be neutral, and carrying out vacuum drying in a vacuum drying oven at the temperature of 40-60 ℃ for 4-8 h to obtain the Fe-N-GCN-SAs-LS-in-situ carbonization method, which means that the in-situ carbonization method is used for preparing the graphite-phase carbon nitride loaded monatomic Fe.
Wherein, GCN: graphite-phase carbon nitride, SAs: monoatomic, LS: a low spin state.
Further, in step A1, the Fe (III) salt is Fe (NO) 3 ) 3 ·9H 2 O。
Further, in step A1, the water is evaporated to dryness at a temperature of 90 ℃.
Further, in step B1, the inert atmosphere may be selected from the group consisting of a thermal treatment atmosphere selected from N 2 /He/Ar。
Further, in step B1, the dilute HNO 3 The concentration of the solution is 1.5-2.5 mol/L.
Further, in the step B1, the frequency of the magnetic stirring is 300 to 500rpm.
Further, in step B1, the washing is performed with deionized water and 95% ethanol.
Further, in the step B1, the temperature of the tube furnace is raised to 550-600 ℃.
The temperature of the graphite phase carbon nitride is stable at 450 to 650 c, preferably, is most stable at 550 to 600 c. At the temperature, the Fe (III) dicyandiamide compound is carbonized into graphite-phase carbon nitride in situ, and the combination mode and the low-spin state of Fe and graphite-phase carbon nitride are influenced by the difference of the temperature. When in-situ carbonization is carried out at 550-600 ℃, the proportion of the low-spin monatomic Fe in the total number of the monatomic Fe atoms is higher.
In another embodiment of the present invention, the method comprises the steps of:
step A2: weighing dicyandiamide (M =84.08 g/mol), heating to 450-650 ℃ in a tube furnace at a heating rate of 5-15 ℃/min, and heating to N 2 After heat treatment for 2-3 h under the atmosphere, naturally cooling to obtain yellow solid which is graphite phase carbon nitride GCN;
and step B2: adding GCN yellow solid into a round bottom rotary evaporation bottle, dissolving ferric salt in absolute ethyl alcohol, pouring into the rotary evaporation bottle, carrying out reduced pressure rotary evaporation at 40-60 ℃ for 20-40 min to obtain dry yellow solid, placing the yellow solid in a tubular furnace, heating to 450-650 ℃ at a heating rate of 5-15 ℃/min, carrying out heat treatment under an inert gas atmosphere for 2-3 h, naturally cooling, uniformly grinding the obtained product, and dispersing in dilute HNO 3 In the solution, under the condition of magnetic stirring, keeping the obtained suspension liquid at the temperature of 40-60 ℃ for 4-6 h, filtering, washing until the filtrate is neutral, and carrying out vacuum drying in a vacuum drying oven at the temperature of 40-60 ℃ for 4-8 h to obtain the Fe-N-GCN-SAs-LS-impregnation methodMeaning that the graphite phase carbon nitride is prepared by an impregnation method and loaded with single-atom Fe.
Wherein, the GCN: graphite-phase carbon nitride, SAs: monoatomic, LS: a low spin state.
Further, in step B2, the Fe (III) salt is FeCl 3 ·9H 2 O。
Further, in the step B2, the concentration of Fe (III) in the absolute ethyl alcohol is 0.1-0.3 mol/L.
Further, in the step B2, the temperature of the tube furnace is raised to 550-600 ℃.
Further, in step B2, the inert atmosphere may be selected from the group consisting of a thermal treatment atmosphere selected from N 2 /He/Ar。
Further, in step B2, the diluted HNO 3 The concentration of the solution is 1.5-2.5 mol/L.
Further, in the step B2, the frequency of the magnetic stirring is 300 to 500rpm.
Further, in step B2, the washing is performed with deionized water and 95% ethanol.
The invention also provides a catalytic method for preparing 2- (1-hydroxyethyl) -benzimidazole by using the heterogeneous catalyst, which is shown in the following reaction scheme 3, ethanol and benzimidazole are used as reaction raw materials, organic peroxide is used as mediation, and monatomic Fe with a low spin state is used as a catalytic active center to prepare the 2- (1-hydroxyethyl) -benzimidazole, wherein the monatomic Fe catalyst with the low spin state is the heterogeneous catalyst of graphite-phase carbon nitride supported low spin monatomic Fe.
Further, the catalytic process comprises the steps of:
adding benzimidazole (M =118.14 g/mol) into a reaction vessel, adding absolute ethyl alcohol to fully dissolve the benzimidazole, adding 1.5 to 2.5 times of equivalent of trifluoroacetic acid calculated based on molar amount of benzimidazole, adding a solution containing 4 times of equivalent of trifluoroacetic acid calculated based on molar amount of benzimidazole10mol% of Fe, pumping out air in the system and introducing N 2 Protection at N 2 Under the protection of gas, injecting tert-butyl hydroperoxide (TBHP) with 4-8 times of equivalent weight calculated by molar weight of benzimidazole, reacting at 20-40 ℃ for 6-18 h under magnetic stirring;
and after the reaction is finished, filtering and separating the heterogeneous catalyst, carrying out rotary evaporation on the obtained filtrate at the temperature of 40-60 ℃ to obtain a small amount of brown liquid, adding alkali to remove acid, adjusting the pH to be = 9-10 to deprotonate the reaction product, and purifying to obtain the target product 2- (1-hydroxyethyl) -benzimidazole.
Further, the reaction vessel is a Schlenk bottle, and is a glass instrument with a piston branch pipe, which is designed for conveniently vacuumizing and filling inert gas.
Further, the frequency of the magnetic stirring is 300 to 500rpm.
Further, the alkali is ammonia water.
Further, the purification is column purification by adding a small amount of methanol.
The invention has the following beneficial effects:
1. the heterogeneous catalyst consists of a single-atom Fe and graphite-phase carbon nitride carrier, the carbon nitrogen element content of the carrier and the spin state of the single-atom Fe can be regulated, wherein the prepared single-atom Fe catalyst with the low spin state of about 80 percent is used for catalyzing the reaction of ethanol and benzimidazole to obtain the yield of 2- (1-hydroxyethyl) -benzimidazole of 87 percent, and the reaction for preparing the 2- (1-hydroxyethyl) -benzimidazole by the reaction of the ethanol and the benzimidazole is reported for the first time, which is the innovation of the invention.
2. The present invention adopts two reaction paths to prepare heterogeneous catalyst. The steps A1 and B1 adopt a one-step preparation scheme of in-situ carbonization of Fe and a carrier. The steps A2 and B2 adopt the sequence of firstly preparing GCN and then loading monatomic Fe on a GCN carrier. Two different preparation paths influence the combination mode of Fe and the carrier, and further influence the low-spin state and the occupation ratio of Fe. The higher the low spin state ratio, the more active centers and the higher the catalytic activity.
3. The heterogeneous catalyst is stable in the reaction process and can be recycled for 5 times or more.
4. The catalytic reaction condition is mild, the reaction can be carried out at normal temperature (25 ℃), and compared with the existing industrial condensation method (100 ℃) of o-phenylenediamine and lactic acid catalyzed by hydrochloric acid, the reaction process is safer and environment-friendly.
Drawings
FIG. 1 is a FT-IR diagram of a Fe-N-GCN-SAs-LS series catalyst synthesized in examples 1 to 3 of the present invention; wherein the abscissa is the wavenumber, unit: cm -1 (ii) a The ordinate represents transmittance.
FIG. 2 HAADF-STEM (HAADF-STEM: high angle annular dark field-scanning transmission electron microscope) of the Fe-N-GCN-SAs-LS series catalysts synthesized in examples 1 to 3 of the present invention.
FIG. 3 EXAFS fitting results (EXAFS: extended X-ray absorption fine structure) for the Fe-N-GCN-SAs-LS series catalysts synthesized in examples 1-3 of the present invention.
FIG. 4 is a schematic structural diagram of the Fe-N-GCN-SAs-LS-80 catalyst synthesized in example 1 of the present invention.
FIG. 5 Mossbauer spectra of Fe-N-GCN-SAs-LS series catalysts synthesized in inventive examples 1-3; wherein the abscissa is doppler velocity, unit: cm of -1 (ii) a The ordinate is the gamma ray count rate.
FIG. 6 shows NMR spectra of 2- (1-hydroxyethyl) -benzimidazole 1 H-NMR (left) and NMR carbon spectra 13 C-NMR (right).
Detailed Description
The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.
Example 1
A graphite-phase carbon nitride-supported low-spin monatomic Fe heterogeneous catalyst composed of a homogeneously dispersed monatomic Fe and a graphite-phase carbon nitride support, wherein,
the carbon-nitrogen element ratio of the graphite phase carbon nitride carrier is C/N =0.5, the Fe and four N atoms on the surface of the graphite phase carbon nitride carrier form an Fe-N four-coordination structure, and the bond length of the Fe-N is
The loading amount of the monatomic Fe was 8.0wt%, and the monatomic Fe in the low spin state accounted for 80% of the total amount of the monatomic Fe.
The preparation process comprises the following steps:
step A1: 24.0g dicyandiamide (M =84.08 g/mol) was weighed out and dissolved in 400mL deionized water, and 9.0g Fe (NO) was weighed out 3 ) 3 ·9H 2 Dissolving O (M =404.0 g/mol) in 100mL of deionized water, slowly pouring a ferric nitrate solution into a dicyandiamide solution at 25 ℃ to obtain a deep red Fe (III) -dicyandiamide complex solution, pouring the complex solution into an evaporation dish, and evaporating water to dryness at 70 ℃ to obtain a khaki Fe-dicyandiamide complex flaky solid;
step B1: grinding the Fe (III) -dicyandiamide complex flaky solid into fine powder, putting the fine powder into a tube furnace, heating to 580 ℃ at the heating rate of 10 ℃/min, and N 2 Naturally cooling after 2h of heat treatment in the atmosphere, uniformly grinding the obtained product, and dispersing the product in 2mol/L dilute HNO 3 In the solution, under the magnetic stirring of 400rpm, keeping the obtained suspension at 50 ℃ for 6h, filtering, washing with deionized water and 95% ethanol until the filtrate is neutral, and carrying out vacuum drying in a vacuum drying oven at 40 ℃ for 12h to obtain the Fe-N-GCN-SAs-LS-80-in-situ carbonization method, which means that the graphite phase carbon nitride prepared by the in-situ carbonization method is loaded with monoatomic Fe, and the monoatomic Fe in a low-spin state accounts for about 80% of the total amount of the monoatomic Fe.
The catalytic method comprises the following steps:
the heterogeneous catalyst obtained in example 1 was used to catalyze the reaction of benzimidazole with ethanol to prepare 2- (1-hydroxyethyl) -benzimidazole. 1.0mmol of benzimidazole (M =118.14 g/mol) was charged in a Schlenk flask, 4mL of absolute ethanol was added to dissolve it sufficiently, 2 times equivalent of trifluoroacetic acid based on benzimidazole, 35mg of Fe-N-GCN-SAs-LS-80 catalyst (5 mol% Fe in total based on the molar amount of benzimidazole) was added, air in the system was evacuated, and N was introduced thereinto 2 Protection at N 2 Under the protection of gas, injecting 5 times of equivalent of tert-butyl hydroperoxide (TBHP) based on benzimidazole, reacting at 25 ℃ for 12h under the magnetic stirring of 400 rpm;
after the reaction is finished, filtering and separating the heterogeneous catalyst, carrying out rotary evaporation on the obtained filtrate at 40 ℃ to obtain a small amount of brown liquid, adding ammonia water to remove acid, adjusting the pH to be = 9-10 to deprotonate the reaction product, adding a small amount of methanol, and purifying by a column to obtain the target product 2- (1-hydroxyethyl) -benzimidazole with the yield of 87%.
Example 2
A graphite-phase carbon nitride-supported low-spin monatomic Fe heterogeneous catalyst composed of a homogeneously dispersed monatomic Fe and a graphite-phase carbon nitride carrier, wherein,
the carbon-nitrogen element ratio of the graphite-phase carbon nitride carrier is C/N =0.6, the Fe and four N atoms on the surface of the graphite-phase carbon nitride carrier form an Fe-N four-coordination structure, and the bond length of the Fe-N is
The loading amount of the monatomic Fe is 4.0wt%, and the monatomic Fe in the low spin state accounts for 40% of the total amount of the monatomic Fe.
The preparation process comprises the following steps:
step A1: the same as example 1;
step B1: grinding the Fe (III) -dicyandiamide compound flake solid into fine powder, putting the fine powder into a tube furnace, heating to 480 ℃ at the heating rate of 10 ℃/min, and heating N 2 Naturally cooling after 2h of heat treatment in the atmosphere, uniformly grinding the obtained product, and dispersing the product in 2mol/L dilute HNO 3 In the solution, under the magnetic stirring of 400rpm, keeping the obtained suspension at 50 ℃ for 6h, filtering, washing with deionized water and 95% ethanol until the filtrate is neutral, and carrying out vacuum drying in a vacuum drying oven at 40 ℃ for 12h to obtain the Fe-N-GCN-SAs-LS-40-in-situ carbonization method, which means that the graphite phase carbon nitride prepared by the in-situ carbonization method is loaded with monoatomic Fe, and the monoatomic Fe in a low-spin state accounts for about 40% of the total amount of the monoatomic Fe.
The catalytic method comprises the following steps:
the heterogeneous catalyst obtained in example 2 was used to catalyze the reaction of benzimidazole with ethanol to prepare 2- (1-hydroxyethyl) -benzimidazole. 1.0mmol of benzimidazole (M =118.14 g/mol), 4mL of absolute ethanol was added to dissolve the mixture sufficiently, 2 equivalents of trifluoroacetic acid based on benzimidazole was added,70mg of Fe-N-GCN-SAs-LS-40 catalyst (containing 5mol% of Fe calculated based on the molar amount of benzimidazole), air in the system was purged and N was introduced 2 Protection at N 2 Under the protection of gas, 5 times equivalent of t-butyl hydroperoxide (TBHP) based on benzimidazole was injected and the reaction was carried out at 25 ℃ for 12 hours under magnetic stirring at 400 rpm. After the reaction is finished, filtering and separating the heterogeneous catalyst, carrying out rotary evaporation on the obtained filtrate at 40 ℃ to obtain a small amount of brown liquid, adding ammonia water to remove acid, adjusting the pH to be = 9-10 to deprotonate the reaction product, adding a small amount of methanol, and purifying by a column to obtain the target product 2- (1-hydroxyethyl) -benzimidazole with the yield of 67%.
Example 3
A graphite-phase carbon nitride-supported low-spin monatomic Fe heterogeneous catalyst composed of a homogeneously dispersed monatomic Fe and a graphite-phase carbon nitride carrier, wherein,
the carbon-nitrogen element ratio of the graphite-phase carbon nitride carrier is C/N =0.6, the Fe and four N atoms on the surface of the graphite-phase carbon nitride carrier form an Fe-N four-coordination structure, and the bond length of the Fe-N is
The loading amount of the monatomic Fe was 6.0wt%, and the monatomic Fe in the low spin state accounted for 25% of the total amount of the monatomic Fe.
The preparation process comprises the following steps:
step A2: weighing 24.0g dicyandiamide (M =84.08 g/mol) in a tube furnace to raise the temperature to 550 ℃ at a heating rate of 10 ℃/min, N 2 After heat treatment for 2h under the atmosphere, naturally cooling to obtain a yellow solid which is graphite phase carbon nitride GCN;
and step B2: 2.0g of yellow solid was added to a round bottom rotary evaporator flask and 0.96g of FeCl was weighed 3 ·6H 2 Dissolving O (M =270.3 g/mol) in 20mL of absolute ethanol, pouring into the rotary evaporation bottle in the step A, carrying out reduced pressure rotary evaporation at 40 ℃ for 30min to obtain a dry yellow solid, placing the yellow solid in a tube furnace, heating to 550 ℃ at a heating rate of 10 ℃/min, and placing the yellow solid in a tube furnace 2 Naturally cooling after heat treatment for 2h under the atmosphere, uniformly grinding the obtained product, and dispersing the product in 2mol/L dilute HNO 3 In solution, under magnetic stirring at 400rpmAnd keeping the obtained suspension at 50 ℃ for 6h, filtering, washing with deionized water and 95% ethanol until the filtrate is neutral, and performing vacuum drying in a vacuum drying oven at 40 ℃ for 12h to obtain the Fe-N-GCN-SAs-LS-25-impregnation method, which means that the graphite phase carbon nitride prepared by the impregnation method is loaded with the monatomic Fe, and the monatomic Fe in the low-spin state accounts for about 25% of the total monatomic Fe.
The catalytic method comprises the following steps:
the heterogeneous catalyst obtained in example 3 was used to catalyze the reaction of benzimidazole with ethanol to prepare 2- (1-hydroxyethyl) -benzimidazole. 1.0mmol of benzimidazole (M =118.14 g/mol), 4mL of absolute ethanol was added to dissolve the benzimidazole sufficiently, 2 equivalents of trifluoroacetic acid based on the benzimidazole, 47mg of Fe-N-GCN-SAs-LS-25 catalyst (5 mol of Fe calculated based on the molar amount of benzimidazole) was added, air in the system was evacuated, and N was introduced 2 Protection at N 2 Under a gas blanket, 5 times equivalent of t-butyl hydroperoxide (TBHP) based on benzimidazole was injected and the reaction was carried out at 25 ℃ for 12 hours under magnetic stirring at 400 rpm. And after the reaction is finished, filtering and separating the catalyst, carrying out rotary evaporation on the obtained filtrate at 40 ℃ to obtain a small amount of brown liquid, adding ammonia water to remove acid, adjusting the pH to be = 9-10 to deprotonate a reaction product, adding a small amount of methanol, and purifying by a column to obtain the target product 2- (1-hydroxyethyl) -benzimidazole with the yield of 38%.
As shown in FIG. 1, FIG. 1 is a FT-IR chart of a graphite-phase carbon nitride supported monatomic Fe catalyst synthesized in examples 1 to 3 of the present invention and an Fe-unsupported sample, in which 1556cm is 1556cm -1 Corresponding to the stretching vibration of carbon-nitrogen double bonds of the graphite phase carbon nitride triazine structure, 893cm -1 And 810cm -1 The band corresponds to out-of-plane bending vibration of the triazine structure of graphite phase carbon nitride, and this characterization demonstrates that the synthesized support structure is graphite phase carbon nitride.
As shown in FIG. 2, FIG. 2 is a HAADF-STEM diagram of the graphite-phase carbon nitride-supported monatomic Fe catalysts synthesized in examples 1 to 3 of the present invention, and the bright spots in the diagram represent Fe dispersed on an atomic level on a composite oxide support, and it is apparent that Fe in the catalysts prepared in examples 1 to 3 is uniformly dispersed in a monatomic state.
As shown in fig. 3, fig. 3 is the bookThe results of the fitting of the EXAFS of the graphite-phase carbon nitride-supported monatomic Fe catalysts synthesized in inventive examples 1 to 3 were obtained by fitting calculation from the raw data of the EXAFS, and it was understood from the fitting results that the monatomic Fe was formed because Fe and the carrier formed Fe — N coordination. Taking Fe-N-GCN-SAs-LS-80 as an example, the Fe-N bond has a bond length of
Fe and four nitrogen atoms on the surface of the carrier form an Fe-N four-coordination structure, and the schematic diagram of the structure is shown in FIG. 4, wherein black is an iron atom, yellow is a carbon atom, and blue is a nitrogen atom.
As shown in fig. 5, fig. 5 is a mossbauer spectrum of Fe-N-GCN-SAs-LS series catalysts synthesized in embodiments 1 to 3 of the present invention, in which the position indicated by an arrow is an Fe center having a low spin state, and the Fe centers having a low spin state are about 80%,40% and 25% in all Fe species in three samples, respectively, and can be calculated by mossbauer spectrum fitting. As known from the theory of crystal field, the formation of the Fe center in the low spin state is due to the formation of the internal orbital Fe-N four-coordination structure which is filled with t 2g (d xy ,d xz ,d yz ) Electron orbitals of low-energy triplet degenerated states and vacate e g (d x2-y2 ,d z2 ) High energy dual degenerate state electron orbitals. e.g. of the type g The orbit is easy to accept lone pair electrons due to higher energy, so that the activation of tert-butyl hydroperoxide and ethanol molecules is promoted simultaneously, and the reaction for preparing 2- (1-hydroxyethyl) -benzimidazole by ethanol and benzimidazole is promoted according to reaction conditions.
As shown in fig. 6, the obtained 2- (1-hydroxyethyl) -benzimidazole was a white solid with the nuclear magnetic data:
1 H NMR(600MHz,DMSO-d 6 ):δ12.24(s,1H),7.49(d,J＝8.4Hz,2H),7.13(dd,J＝5.4,2.4Hz, 2H),5.78(d,J＝4.8Hz,1H),4.97-4.93(m,1H),1.52(d,J＝6.6Hz,3H).
13 C NMR(150MHz,DMSO-d 6 ):δ158.53,143.04,134.12,121.44,120.92,118.37,111.21,63.66, 22.95.
the performance data in examples 1-3 demonstrate that the graphite phase carbon nitride supported 80% low spin state monatomic Fe catalyst Fe-N-GCN-SAs-LS-80 described in example 1 is the best choice.
Comparative example 1
2- (1-hydroxyethyl) -benzimidazole was prepared by catalyzing benzimidazole with ethanol using iron tetraphenylporphyrin chloride (M =704.02 g/mol). 1.0mmol of benzimidazole (M =118.14 g/mol), 4mL of absolute ethanol was added to dissolve the benzimidazole sufficiently, 2 equivalents of trifluoroacetic acid and 35mg of tetraphenylporphyrin Fe (containing 5mol% Fe in total) were added to the solution, air in the system was evacuated, and N was introduced into the solution 2 Protection at N 2 Under the protection of gas, 5 times equivalent of tert-butyl hydroperoxide (TBHP) based on benzimidazole was injected, and the reaction was carried out at 25 ℃ for 12 hours under shaking table. After the reaction is finished, a small amount of red liquid is obtained by rotary evaporation, ammonia water is added to remove acid, the pH = 9-10 is adjusted to remove the proton of the reaction product, a small amount of methanol is added, and the target product 2- (1-hydroxyethyl) -benzimidazole is obtained by column purification with the yield of 54%.
From the reaction results of the examples and comparative example 1, it can be seen that the heterogeneous monatomic Fe catalyst Fe-N-GCN-SAs-LS-80 described in example 1 has better performance in catalyzing the preparation of 2- (1-hydroxyethyl) -benzimidazole from benzimidazole and ethanol than the homogeneous complex iron tetraphenylporphyrin chloride.
Comparative example 2
2- (1-hydroxyethyl) -benzimidazole was prepared by catalyzing benzimidazole with ethanol using copper tetraphenylporphyrin (M =676.27 g/mol). 1.0mmol of benzimidazole (M =118.14 g/mol), 4mL of absolute ethanol was added to the flask to dissolve it sufficiently, 2 equivalents of trifluoroacetic acid based on the benzimidazole and 35mg of tetraphenylporphyrin Fe (containing 5mol% Fe in total) were added thereto, air in the system was evacuated, and N was introduced thereinto 2 Protection at N 2 Under the protection of gas, 5 times equivalent of tert-butyl hydroperoxide (TBHP) based on benzimidazole was injected, and the reaction was carried out at 25 ℃ for 12 hours with shaking table. After the reaction is finished, performing rotary evaporation to obtain a small amount of red liquid, adding ammonia water to remove acid, adjusting the pH = 9-10 to deprotonate a reaction product, adding a small amount of methanol, and purifying by a column to obtain a target product 2- (1-hydroxy-1-carboxylic acid)Ethyl) -benzimidazole in 5% yield.
From the reaction results of the examples, the comparative example 1 and the comparative example 2, it can be known that the performance of the Fe catalyst in catalyzing the preparation of 2- (1-hydroxyethyl) -benzimidazole by benzimidazole and ethanol is far stronger than that of the Cu catalyst.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, but any modifications or equivalent variations made according to the technical spirit of the present invention are within the scope of the present invention as claimed.
Claims (8)
1. A catalytic method for preparing 2- (1-hydroxyethyl) -benzimidazole by using graphite-phase carbon nitride supported low-spin monatomic Fe is characterized in that the method is carried out by using heterogeneous catalyst of graphite-phase carbon nitride supported low-spin monatomic Fe, and is shown in the following reaction scheme 3, ethanol and benzimidazole are used as reaction raw materials, organic peroxide is used as mediation, monatomic Fe with low spin state is used as a catalytic activity center, and the 2- (1-hydroxyethyl) -benzimidazole is prepared, wherein the heterogeneous catalyst of graphite-phase carbon nitride supported low-spin monatomic Fe consists of uniformly dispersed monatomic Fe and graphite-phase carbon nitride carriers,
the carbon-nitrogen element ratio of the graphite phase carbon nitride carrier is C/N = 0.4-0.7, the Fe and four N atoms on the surface of the graphite phase carbon nitride carrier form an Fe-N four-coordination structure, and the bond length of the Fe-N is
The load capacity of the monatomic Fe is 3wt% -10 wt%, the monatomic Fe in the low-spin state accounts for 20-90% of the total amount of the monatomic Fe,
2. the catalytic process according to claim 1, wherein in the heterogeneous catalyst, the monatomic Fe in the low spin state accounts for 80% of the total monatomic Fe.
3. A catalytic process according to claim 1 or 2, comprising the steps of:
adding benzimidazole to a reaction vessel, adding absolute ethyl alcohol to sufficiently dissolve the benzimidazole, adding 1.5 to 2.5 times equivalent of trifluoroacetic acid calculated based on molar amount of benzimidazole, adding the heterogeneous catalyst containing 4 to 10mol% of Fe calculated based on molar amount of benzimidazole, evacuating air in the system, and introducing N 2 Protection at N 2 Under the protection of gas, injecting tert-butyl hydroperoxide with 4-8 times of equivalent weight calculated by molar weight of benzimidazole, reacting at 20-40 ℃ for 6-18 h under magnetic stirring;
and after the reaction is finished, filtering and separating the heterogeneous catalyst, carrying out rotary evaporation on the obtained filtrate at the temperature of 40-60 ℃ to obtain a small amount of brown liquid, adding alkali to remove acid, adjusting the pH to be = 9-10 to deprotonate a reaction product, and purifying to obtain the target product 2- (1-hydroxyethyl) -benzimidazole.
4. A catalytic process according to claim 1 or 2, characterized in that the heterogeneous catalyst is prepared by a process comprising the steps of:
step A1: respectively preparing a dicyandiamide solution and a Fe (III) salt solution, wherein the concentration of the dicyandiamide solution is 0.4-0.8 mol/L, the concentration of the Fe (III) salt solution is 0.03-0.06 mol/L, slowly pouring an iron salt solution into the dicyandiamide solution at normal temperature to obtain a deep red Fe (III) -dicyandiamide complex solution, pouring the complex solution into an evaporation vessel, and evaporating water to dryness to obtain a khaki Fe (III) -dicyandiamide complex flaky solid;
step B1: grinding the Fe (III) -dicyandiamide complex flaky solid into fine powder, putting the fine powder into a tubular furnace, heating the fine powder to 450-650 ℃ at the heating rate of 5-15 ℃/min, carrying out heat treatment for 2-3 h in the atmosphere of inert gas, then naturally cooling, uniformly grinding the obtained product, and dispersing the product in dilute HNO 3 In the solution, under the condition of magnetic stirring, the obtained suspension is kept for 4-6 h at the temperature of 40-60 ℃, filtered, the washing filtrate is neutral, and the temperature is 40-60 DEG CVacuum drying for 4-8 h in a vacuum drying oven to obtain Fe-N-GCN-SAs-LS-in-situ carbonization method, meaning that the in-situ carbonization method is used for preparing graphite phase carbon nitride loaded with single-atom Fe,
wherein, GCN: graphite-phase carbon nitride, SAs: monoatomic, LS: a low spin state.
5. The catalytic process according to claim 4, wherein in step A1, the Fe (III) salt is Fe (NO) 3 ) 3 ·9H 2 O。
6. The catalytic process according to claim 5, wherein in step B1, the dilute HNO 3 The concentration of the solution is 1.5-2.5 mol/L.
7. The catalytic process according to claim 6, wherein in step B1, the tube furnace is heated to 550 to 600 ℃.
8. The catalytic process according to claim 1 or 2, characterized in that it comprises the following steps:
step A2: weighing dicyandiamide in a tube furnace, heating to 450-650 ℃ at the heating rate of 5-15 ℃/min, and heating to N 2 Carrying out heat treatment for 2-3 h in the atmosphere, and then naturally cooling to obtain a yellow solid which is graphite-phase carbon nitride GCN;
and step B2: adding GCN yellow solid into a round bottom rotary evaporation bottle, dissolving ferric salt in absolute ethyl alcohol, pouring into the rotary evaporation bottle, carrying out reduced pressure rotary evaporation at 40-60 ℃ for 20-40 min to obtain dry yellow solid, placing the yellow solid in a tubular furnace, heating to 450-650 ℃ at a heating rate of 5-15 ℃/min, carrying out heat treatment under an inert gas atmosphere for 2-3 h, naturally cooling, uniformly grinding the obtained product, and dispersing in dilute HNO 3 In the solution, under the condition of magnetic stirring, keeping the obtained suspension liquid at the temperature of 40-60 ℃ for 4-6 h, filtering, washing until the filtrate is neutral, carrying out vacuum drying in a vacuum drying oven at the temperature of 40-60 ℃ for 4-8 h to obtain an Fe-N-GCN-SAs-LS-impregnation method, meaning that the impregnation method is used for preparing graphite-phase carbon nitride loaded monoatomic Fe,
wherein, GCN: graphite-phase carbon nitride, SAs: monoatomic, LS: a low spin state.
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