Method for preparing alkyl iodide by utilizing light and electro-catalysis

Abstract

The invention discloses a method for preparing alkyl iodide by utilizing light and electrocatalysis, which comprises the following steps: (1) in a photoelectric reaction tank, using a selenium-doped cadmium sulfide photoelectrode coordinated with thiohydracrylic acid as a working electrode, installing the working electrode and a reference electrode in an anode chamber, installing a counter electrode in a cathode chamber, and adding an equal amount of organic solvent into each of the two chambers; and (2) adding a reaction substrate potassium iodide and tetraalkyl ammonium hexafluorophosphonate substituted by different alkyl chain lengths into the cathode chamber and / or the anode chamber, applying light intensity and / or bias voltage to the photoelectrochemical reaction tank, and reacting to obtain the alkyl iodide. According to the method, the total yield of 190% or above of the target product can be achieved, meanwhile, the reaction condition is mild, the reaction can be conducted at the normal temperature, the reaction efficiency is high, and no toxic substance is generated in the reaction process.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing alkyl iodide by photo and electrocatalysis. BACKGROUND

[0002] Alkyl halide is a valuable reagent in the fields of organic chemistry, molecular biology and biochemistry, which can be made into drugs to treat many fatal diseases such as cancer, HIV, diabetes and arthritis. Alkyl halide also plays an important role in the assembly of nanomaterials and nanotechnology. In recent years, alkyl iodide can directly prepare alkylated proteins, RNA related compounds, and even living cells, but the substance is not stable at room temperature or even at low temperature of 4℃, and it is easy to decompose quickly, resulting in the product becoming dark and containing impurities. Therefore, it is very necessary to quickly prepare fresh high-purity alkyl iodide in the fields of organic chemistry, medicinal chemistry, drug discovery and molecular biology.

[0003] There are many methods for synthesizing alkyl iodide in the prior art. The traditional method is to use the reaction of alcohol and phosphorus triiodide to generate, but this method generates toxic phosphoric acid; alkyl iodide can also be produced by hydrogen iodide acid cleavage of dialkyl ether, but the acquisition of alkyl ether is difficult, and the product yield can only be maintained at 60-80%; it also includes the reaction of alcohol with cesium iodide in the presence of p-toluenesulfonic acid, nucleophilic substitution of alkyl chloride with excess sodium iodide, rapid reaction of organic boron reagent with iodine in alkaline environment, and ionic liquid method. The above-mentioned synthesis of alkyl iodide has problems such as harsh reaction conditions, generation of toxic substances, low reaction yield and low reaction efficiency. SUMMARY

[0004] The purpose of the present application is to provide a method for preparing alkyl iodide by photo and electrocatalysis, which can achieve a total yield of target product of more than 190%, and the reaction conditions are mild, the reaction can be carried out at room temperature, the reaction efficiency is high, and no toxic substances are generated during the reaction.

[0005] Technical scheme: The method for preparing alkyl iodide by photo and electrocatalysis according to the present application comprises the following steps:

[0006] (1) In a photoelectric reaction cell, a selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid is used as a working electrode, a reference electrode is installed in an anode chamber, and a counter electrode is installed in a cathode chamber, and equal amounts of organic solvents are added to the two chambers;

[0007] (2) Add reaction substrates potassium iodide and tetraalkylammonium hexafluorophosphate to the cathode chamber and / or the anode chamber, apply light intensity and / or bias to the photoelectrochemical reaction cell, and after reaction, obtain alkyl iodide.

[0008] Based on the substrate SN 2 nucleophilic substitution reaction, product can be reached in the anode or cathode chamber can be more than 90wt% yield; potassium iodide and tetraalkylammonium ion reaction equation as follows:

[0009]

[0010] In step (1), the photoelectric reaction cell is H-type reaction cell; the reference electrode is Ag / AgCl electrode or saturated calomel electrode; the counter electrode is platinum electrode or graphite rod electrode; the organic solvent is acetonitrile or tetrahydrofuran.

[0011] In step (1), the formula of the mercapto propionic acid ligand selenium doped cadmium sulfide photoelectrode is CdS 1-x Se x -MPA; wherein 0X<1; prepared by the following method, the specific steps are as follows:

[0012] (1.1) the cleaned conductive glass is inclined to the inner wall of the reaction device;

[0013] (1.2) a mixed solution containing selenium salt and cadmium sulfide precursor is prepared; the mixed solution is poured into the reaction device of step (1.1), sealed and subjected to hydrothermal reaction at high temperature;

[0014] (1.3) after the reaction, the conductive glass with the grown conductive crystal is taken out, washed, dried and annealed on the side with the grown conductive crystal to obtain the selenium doped cadmium sulfide photoelectrode;

[0015] (1.4) the selenium doped cadmium sulfide photoelectrode is placed in a mixed solution containing methanol, chloroform (mixing of the two organic solvents generates reactive active groups which are conducive to the growth of mercapto propionic acid) and mercapto propionic acid, and the mixed solution is adjusted to strong alkaline by tetramethylammonium hydroxide, sealed, heated in the dark and subjected to coordination reaction;

[0016] (1.5) after the coordination reaction, the photoelectrode is washed, vacuum dried and the mercapto propionic acid ligand selenium doped cadmium sulfide photoelectrode is obtained.

[0017] The mercapto propionic acid ligand selenium doped cadmium sulfide photoelectrode can greatly improve the transmission efficiency of electric charge and the contact area of the electrode and the reaction substrate, thereby improving the reaction rate and the product yield.

[0018] In step (1.4), the volume ratio of methanol, chloroform and mercapto propionic acid is 1:1:0.1; the heating temperature is 55-60℃, and the reaction time is 6.5-7h; the pH of the mixed solution is adjusted to 11-13 by tetramethylammonium hydroxide.

[0019] In step (1.5), the solvent for rinsing the photoelectrode after the coordination reaction is one of dilute hydrochloric acid, acetone, ethanol or hydrofluoric acid, and the rinsing is excessive.

[0020] In step (2), the light intensity is 1-3 sun, and the bias is 1-1.5 V vs Ag / AgCl; after the addition of the reaction substrate, the concentration of potassium iodide in the reaction solution is 1-4 mM, preferably 2-4 mM, and further preferably 2 mM; and the concentration of tetraalkylammonium hexafluorophosphate is 0.5-4 mM, preferably 1-3 mM, and further preferably 3 mM.

[0021] In step (2), the reaction time is 8-10 h.

[0022] Advantages: Compared with the prior art, the present application has the following significant advantages: (1) The method of the present application generates alkyl iodide by means of light and electrocatalysis, which can avoid the generation of toxic products compared with the traditional synthesis process of alcohol and phosphorus triiodide. The method of the present application has low energy consumption, high conversion directionality and high product yield, and the total yield of alkyl iodide can reach more than 190% under the simultaneous action of light and bias; (2) The method of the present application uses a selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid, which can effectively improve the charge transfer efficiency and the contact area between the electrode and the substrate in the reaction process without a supporting electrolyte, thereby generating more target products in a shorter time, so that the present application has high yield and high reaction efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 EIS, LSV and transient current-time curves of the selenium-doped cadmium sulfide photoelectrode prepared in Example 1 and the cadmium sulfide photoelectrode; wherein the test conditions are as follows: the light source is an AM1.5 xenon lamp (light intensity is 100 mW / cm 2 ), the solvent is acetonitrile, the supporting electrolyte is 1M tetrabutylammonium hexafluorophosphate, and the bias for transient current-time test is 1V vs Ag / AgCl;

[0024] Figure 2 Stability comparison chart of the single cadmium sulfide photoelectrode and the selenium-doped cadmium sulfide photoelectrode prepared in Example 1;

[0025] Figure 3 (a) UV-Vis spectrum, (b) steady-state photoluminescence spectrum, and (c) time-resolved transient photoluminescence spectrum of the single cadmium sulfide, the selenium-doped cadmium sulfide prepared in Example 1, and the mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode prepared in Example 2;

[0026] Figure 4The butyl iodide yields after 1 hour under different test conditions for Examples 3 and 5-9 are shown. The test conditions from left to right in the figure are: light + bias, no light + no bias, no light, no bias, a selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid as cathode (Se-CdS-MPA as cathode), and reaction in a Pt cathode cell.

[0027] Figure 5 This is a sacrificial agent experiment for determining the free radical generation reaction of butyl iodide under the test conditions of Example 3. The specific experimental process is as follows: 4 mM of sacrificial agent is added to the reaction system before the reaction begins, and the product yield after 1 hour is measured compared with the change when no sacrificial agent is added; wherein IPA is isopropanol, CH3OH is methanol, DDQ is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, PBQ is p-benzoquinone, and DMPO is 5,5-dimethyl-1-pyrroline-N-oxide;

[0028] Figure 6 It is the signal peak of electron paramagnetic resonance test of hole-electron pairs;

[0029] Figure 7 This is a color development experiment of the butyl iodide reaction under the test conditions of Example 3. (a) is the color before the reaction starts, (b) is the color after the reaction ends, and (c) is the color after adding 1 mL of amylose solution after the reaction ends.

[0030] Figure 8 This is a graph showing the yield changes over time in the anode chamber and cathode chamber in the synthesis of butyl iodide in Example 3 and Examples 16 to 31. DETAILED DESCRIPTION

[0031] Example 1

[0032] A method for preparing a selenium-doped cadmium sulfide photoelectrode comprises the following steps:

[0033] (1) After the surface of the FTO conductive glass is cleaned with acetone, isopropyl alcohol, and deionized water, it is placed obliquely on the inner wall of the polytetrafluoroethylene liner of the hydrothermal kettle;

[0034] (2) Weigh 0.0005 mol of thiourea, 0.0005 mol of cadmium nitrate tetrahydrate, and 0.0003 mol of cysteine ​​(the molar ratio of thiourea: cadmium nitrate tetrahydrate: cysteine ​​is 1:1:0.6), and dissolve them in 10 mL of a mixed solvent; in the mixed solvent, the mixed volume of ethanol and deionized water is 1:3; add 0.000025 mol (i.e., 5 wt%) of sodium selenite to the solution, stir for 1 hour, and then pour the mixed solution into the inner tank of a hydrothermal kettle; react at 180°C in a forced air drying oven for 24 hours, remove the FTO after the reaction, and then use ethanol and deionized water to wash the electrode sheet in sequence;

[0035] (3) After the electrode sheet is dried in a vacuum drying oven, it is placed in a tube furnace with the side with the conductive crystal grown facing upward, and annealed at 400°C for 1 hour in a nitrogen atmosphere to obtain a selenium-doped cadmium sulfide photoelectrode.

[0036] Compared with a single CdS electrode, Se-doped CdS has a lower impedance (e.g. Figure 1 (a) shows that the photocurrent density of the Se-doped CdS photoelectrode increases more rapidly at a bias voltage greater than 0.2 V vs Ag / AgCl (e.g. Figure 1 (b) shows that the photocurrent density also increases from 160 μA / cm2 of single CdS to 160 μA / cm3 of single CdS at a bias voltage of 1 V vs Ag / AgCl. 2 Increased to 300μA / cm for selenium-doped cadmium sulfide 2 The photocurrent density increases by nearly one-fold. Figure 1 (c) Compared with the single cadmium sulfide photoelectrode, the stability of selenium-doped cadmium sulfide has also been greatly improved, as shown in Figure 2 As shown. At 100mW / cm 2 Under the light intensity of , the photocurrent of cadmium sulfide photoelectrode and selenium-doped cadmium sulfide photoelectrode increased due to the self-decomposition. 1-n Se 0<n<0.25 ), which makes the photocurrent increase greater than that of cadmium sulfide photoelectrode. The photocurrent reaches its peak around 350-400s and then slowly decays. As the semiconductor continues to decompose and peel, when the photocurrent is lower than 50μA / cm 2 When the photocurrent of the cadmium sulfide photoelectrode decays to 50 μA / cm 2 When the photocurrent of selenium-doped cadmium sulfide photoelectrode is still greater than 100μA / cm 2 Therefore, the photoelectrode can still continue to be used for photoelectrocatalytic conversion. Compared with the single cadmium sulfide photoelectrode, the stability of the selenium-doped cadmium sulfide photoelectrode is significantly improved.

[0037] Example 2

[0038] A method for preparing a mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode, comprising the following steps:

[0039] (1) 5 mL of methanol, 5 mL of chloroform and 0.5 mL of mercaptopropionic acid are mixed to obtain a mixed solution, and tetramethylammonium hydroxide is added to adjust the pH of the mixed solution to 11. The selenium-doped cadmium sulfide photoelectrode prepared in Example 1 is placed in the mixed solution with pH = 11, sealed from light, heated to 55°C, and allowed to coordinate for 7 h;

[0040] (2) After the coordination reaction, the photoelectrode is washed with excess acetone and vacuum dried to obtain a mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode.

[0041] By performing ultraviolet-visible light tests on single cadmium sulfide photoelectrodes, selenium-doped cadmium sulfide photoelectrodes, and mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrodes, as shown in Figure 3 (a), it is proved that the mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode has the strongest light absorption capacity, and thus may exhibit the highest photo / photoelectrocatalytic reaction activity in actual catalytic conversion processes. Further steady-state photoluminescence and time-resolved transient photoluminescence tests on the three electrodes, as shown in Figure 3 (b) and (c), show that within 650 nm, the signal intensity of the selenium-doped cadmium sulfide photoelectrode is lower than that of the single cadmium sulfide photoelectrode, indicating that the recombination degree of photoinduced carriers caused by light with a wavelength less than 650 nm is lower for the selenium-doped cadmium sulfide photoelectrode, and the utilization rate of the carriers is higher; but the recombination degree of photoinduced carriers of single cadmium sulfide is lower in the wavelength band of visible light greater than 650 nm. The carrier lifetime of the selenium-doped cadmium sulfide photoelectrode is 15.66 ns, slightly higher than that of the single cadmium sulfide photoelectrode of 14.34 ns, proving that overall, the selenium-doped cadmium sulfide is more stable in maintaining catalytic activity than the single cadmium sulfide. However, after being coordinated with mercaptopropionic acid, the recombination degree of photoinduced carriers of the selenium-doped cadmium sulfide photoelectrode is lower in the entire visible light wavelength band than that of the single cadmium sulfide and the selenium-doped cadmium sulfide, indicating that mercaptopropionic acid can effectively transfer photoinduced charges to the substrate with high efficiency while avoiding the loss of charge recombination; and the carrier lifetime of the photoelectrode is 22.23 ns, significantly higher than that of the single cadmium sulfide and the selenium-doped cadmium sulfide photoelectrodes. In summary, the mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode has the highest light absorption capacity, the lowest recombination degree of photoinduced carriers, and the longest lifetime of photoinduced carriers.

[0042] Example 3

[0043] A method for preparing butyl iodine by using photo and electrocatalysis, comprising the following steps:

[0044] (1) The selenium-doped cadmium sulfide photoelectrode prepared in Example 2 was used as the working electrode, and silver / silver chloride was used as the reference electrode. The working electrode and the reference electrode were installed in the anode chamber of an H-type reaction cell. A platinum electrode was used as the counter electrode and was installed in the cathode chamber. Ten milliliters of acetonitrile was added to each of the two chambers.

[0045] (2) The anode chamber was added with 2 mM of the reaction substrate potassium iodide and 1 mM of tetrabutylammonium hexafluorophosphate. The reaction was carried out under a light intensity of 100 mW / cm2and a bias of 1 V vs. Ag / AgCl. 2

[0046] (3) After 1 h of reaction, the product butyl iodide was obtained.

[0047] Example 4

[0048] Example 4 was completely identical to the method for preparing butyl iodide in Example 3, except that in step (1), the working electrode was a selenium-doped cadmium sulfide photoelectrode, and the reaction time in step (3) was 2 h.

[0049] Table 1

[0050]

[0051] As shown in Table 1, the yield of butyl iodide after 2 h of reaction was 11.88 wt% when the selenium-doped cadmium sulfide photoelectrode was used as the working electrode, and the yield of butyl iodide after 1 h of reaction was 28.20 wt% when the selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid was used as the working electrode. The results showed that the selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid used as the working electrode could obtain a higher yield of butyl iodide in a shorter time, which embodied the higher catalytic activity of the electrode. The previous analysis also proved that mercaptopropionic acid could more effectively transfer the photo-generated charges from the electrode to the substrate, and the diffusion of mercaptopropionic acid itself could also improve the contact area between the electrode and the substrate, thereby promoting a higher reaction efficiency and product yield.

[0052] Example 5

[0053] Example 5 was completely identical to the method for preparing butyl iodide in Example 3, except that in step (2), the reaction was not provided with light and bias, and the substrate was allowed to naturally mix and react.

[0054] Example 6

[0055] Example 6 was completely identical to the method for preparing butyl iodide in Example 3, except that in step (2), the reaction was not provided with light, but only relied on the bias.

[0056] Example 7

[0057] ​The method for preparing butyl iodide in Example 7 is exactly the same as that in Example 3, with the only difference being that in step (2), the reaction is not biased and is carried out only by light.

[0058] Example 8

[0059] The method for preparing butyl iodide in Example 8 is exactly the same as that in Example 3, with the only difference being that in step (1), a Pt sheet electrode is used as the anode (working electrode), and a selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid is used as the cathode (counter electrode).

[0060] Example 9

[0061] The method for preparing butyl iodide in Example 9 is exactly the same as that in Example 3, with the only difference being that in step (2), the reaction substrates potassium iodide and 1 mM tetrabutylammonium hexafluorophosphonate at a concentration of 2 mM are added to the cathode chamber, but the working electrode is still the selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid, and the light and bias are still applied to the anode chamber.

[0062] like Figure 4 As shown, the reaction of potassium iodide and tetrabutylammonium hexafluorophosphonate proceeds spontaneously without external stimulation, but the reaction rate is limited, resulting in only 8.01 wt% of butyl iodide produced within 1 hour. Compared to Example 5, Examples 6-7 significantly increased the yield of butyl iodide by applying only light or only bias voltage.

[0063] Figure 5 The sacrificial agent experiment showed that methanol (hole sacrificial agent), isopropyl alcohol (hydroxyl radical sacrificial agent), p-benzoquinone (peroxide radical sacrificial agent), and DMPO (multiple free radical scavengers) had no inhibitory effect on the yield of butyl iodide. Only after the addition of DDQ (electron sacrificial agent), the yield of butyl iodide rapidly decreased to 1.46wt%, indicating that the reaction system is not a free radical mechanism, but is only related to the transmission of electrons.

[0064] Figure 6The electron paramagnetic resonance triplet signal peak of the hole-electron pair also confirms this. In contrast, the addition of methanol (37.04 wt%) or p-benzoquinone (40.08 wt%) increases the yield of butyl iodide, indicating that the photoexcitation of the photoelectrode inhibits the generation of the oxidizing active species, such as the hole and superoxide radical, in the system. The application of a bias voltage alone can to some extent avoid the generation of photo-generated holes and other oxidizing species in the photoelectrode; single light irradiation will make the reaction become a pure photocatalysis, and photo-generated holes and electrons will be generated simultaneously in the anode chamber, and potassium iodide itself is an excellent hole sacrificial agent, and the remaining electron pair reaction in the system has obvious promotion effect, therefore, the butyl iodide obtained under the single variable test condition will be more than that obtained under the simultaneous application of light and bias voltage (62.15 wt%). It is worth noting that since the system is electron-dominated, the mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode can also be used as a cathode (28.75 wt%) and the reaction can also be carried out in the cathode chamber where the Pt sheet is located (49.08 wt%), and the product yield is higher than that under the simultaneous application of light and bias voltage, which proves the inhibitory effect of the photo-generated hole and other oxidizing active species on the reaction.

[0065] Example 10

[0066] Example 10 is exactly the same as the method for preparing butyl iodide in Example 3, the only difference being that in step (2), the concentration of tetrabutylammonium hexafluorophosphate is 0.5 mM.

[0067] Example 11

[0068] Example 11 is exactly the same as the method for preparing butyl iodide in Example 3, the only difference being that in step (2), the concentration of tetrabutylammonium hexafluorophosphate is 2 mM.

[0069] Example 12

[0070] Example 12 is exactly the same as the method for preparing butyl iodide in Example 3, the only difference being that in step (2), the concentration of tetrabutylammonium hexafluorophosphate is 3 mM.

[0071] Example 13

[0072] Example 13 is exactly the same as the method for preparing butyl iodide in Example 3, the only difference being that in step (2), the concentration of tetrabutylammonium hexafluorophosphate is 4 mM.

[0073] Example 14

[0074] Example 14 is exactly the same as the method for preparing butyl iodide in Example 3, the only difference being that in step (2), the concentration of potassium iodide is 1 mM.

[0075] Example 15

[0076] Example 15 is exactly the same as Example 3 in preparing butyl iodide, the only difference is that in step (2), the concentration of potassium iodide is 4 mM.

[0077] The butyl iodide yield obtained from the reaction with different concentrations of potassium iodide and tetrabutylammonium hexafluorophosphate is shown in Table 2.

[0078] Table 2

[0079]

[0080]

[0081] Note: a: The butyl iodide yield of Example 32 is the sum of the butyl iodide yield of the anode and cathode chambers.

[0082] In Table 2, when the concentration of tetrabutylammonium hexafluorophosphate is constant at 1 mM, and the concentration of potassium iodide is 1 mM, 2 mM, and 4 mM, the butyl iodide yield is 21.15 wt%, 28.20 wt%, and 30.00 wt%, respectively. As the concentration of iodide ion increases, the reaction rate also increases, indicating that the substitution reaction is related to the concentration of the nucleophile. When the concentration of potassium iodide is constant at 2 mM, and the concentration of tetrabutylammonium hexafluorophosphate is 0.5 mM, 1 mM, 2 mM, 3 mM, and 4 mM, the butyl iodide yield is 8.88 wt%, 28.20 wt%, 56.95 wt%, 60.72 wt%, and 63.32 wt%, respectively. As the concentration of the amine group increases, the reaction rate also increases significantly, indicating that the substitution reaction is also related to the concentration of the leaving group. Therefore, it is proved that the reaction of butyl iodide formation follows the SN2 nucleophilic substitution mechanism. The electron transfer of iodide ion to the lone pair of electrons on the amine group causes the formation of butyl iodide and trimethylamine. Although iodide ion can transfer electrons to the tetrabutylamine group, the bias applied to the reaction system or the photo-generated electrons can also attack the tetrabutylamine group of tetrabutylammonium hexafluorophosphate, causing a large amount of tetrabutylammonium phosphate to be consumed. Therefore, in order to ensure that the amine group and iodide ion are sufficient, the substrate concentration in Example 12 is used as a reference for the subsequent reaction. N 2 nucleophilic substitution mechanism. The electron transfer of iodide ion to the lone pair of electrons on the amine group causes the formation of butyl iodide and trimethylamine. Although iodide ion can transfer electrons to the tetrabutylamine group, the bias applied to the reaction system or the photo-generated electrons can also attack the tetrabutylamine group of tetrabutylammonium hexafluorophosphate, causing a large amount of tetrabutylammonium phosphate to be consumed. Therefore, in order to ensure that the amine group and iodide ion are sufficient, the substrate concentration in Example 12 is used as a reference for the subsequent reaction.

[0083] Example 16

[0084] Example 16 is exactly the same as Example 12 in preparing butyl iodide, the only difference is that in step (3), the reaction time is 2 h.

[0085] Example 17

[0086] Example 17 is exactly the same as Example 12 in preparing butyl iodide, the only difference is that in step (3), the reaction time is 3 h.

[0087] Example 18

[0088] The method for preparing butyl iodide in Example 18 is exactly the same as that in Example 12, with the only difference being that in step (3), the reaction time is 4 h.

[0089] Example 19

[0090] The method for preparing butyl iodide in Example 19 is exactly the same as that in Example 12, with the only difference being that in step (3), the reaction time is 6 h.

[0091] Examples 20 to 23

[0092] The methods for preparing butyl iodide in Examples 20 to 23 are exactly the same as those in Example 12, with the only difference being that in step (3), the reaction times are 8 h, 10 h, 12 h, and 14 h, respectively.

[0093] like Figure 8 As shown, in the anode chamber, as the reaction time increases, the yield of butyl iodide first increases and then decreases. The yield of butyl iodide reaches the highest at 83.66wt% when the reaction is 10h. Since the nucleophilicity of the amino group and the iodide ion to the alkyl group is similar, there is a balance between butyl iodide and tetrabutylamine. In addition, due to the attack of oxidizing species such as photogenerated holes and photogenerated electrons and bias electrons on tetrabutylamine, it is difficult for all iodide ions to combine with the alkyl group to generate butyl iodide. It is worth noting that in the anode chamber, as the reaction time increases, the solution of the system will gradually turn yellow ( Figure 7 The yellowing may be due to the formation of iodine trifluoride, elemental iodine, or cadmium iodide. Iodine trifluoride is very unstable and easily decomposes spontaneously into colorless iodine pentafluoride, which is inconsistent with the experimental phenomenon. When 1 mL of amylose solution was added to the reaction system, it did not turn blue, indicating that elemental iodine was not formed in the system. This indirectly proves that cadmium iodide soluble in acetonitrile was generated during the reaction, and the combined action of cadmium iodide and the photoelectrode improved the stability of the system.

[0094] Example 24

[0095] The method for preparing butyl iodide in Example 24 is exactly the same as that in Example 12, with the only difference being that in steps (1) and (3), the substrate is added to the cathode chamber and the reaction time is 2 h.

[0096] Example 25

[0097] The method for preparing butyl iodide in Example 25 is exactly the same as that in Example 24, with the only difference being that in step (3), the reaction time is 3 h.

[0098] Example 26

[0099] The method for preparing butyl iodide in Example 26 is exactly the same as that in Example 24, with the only difference being that in step (3), the reaction time is 4 h.

[0100] Examples 27 to 31

[0101] The methods for preparing butyl iodide in Examples 27 to 31 are exactly the same as those in Example 24, with the only difference being that in step (3), the reaction times are 6 h, 8 h, 10 h, 12 h and 14 h, respectively.

[0102] Since the reaction is driven by electrons, the yield of butyl iodide in the cathode chamber changes with time. Figure 8 As shown in the figure, the cathode compartment generates no additional iodide or oxidizing species, except for the transfer of photogenerated and biased electrons. Therefore, the concentration of various groups in the cathode compartment is higher than that in the anode compartment, resulting in a faster reaction rate and a higher yield of butyl iodide. The maximum yield of butyl iodide, 92.23 wt%, was reached after 8 hours of reaction.

[0103] Example 32

[0104] The method for preparing butyl iodide in Example 32 is exactly the same as that in Example 21, with the only difference being that in steps (1) and (3), 2 mM potassium iodide and 3 mM tetrabutylammonium hexafluorophosphonate are added simultaneously to the anode and cathode chambers.

[0105] Although the reaction rates within the anodic and cathodic chambers differed slightly, considering the slower reaction rate in the anodic chamber and the fact that the cathode chamber showed little change after 10 hours compared to 8 hours, a 10-hour reaction time was used to maximize the production of butyl iodide in both chambers. As shown in Table 2, after 10 hours of reaction, the total yield of butyl iodide reached 175.93 wt%, which is comparable to the sum of the butyl iodide yields from the corresponding reaction times in each chamber.

[0106] The method of the present invention uses a selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid as a working electrode, a silver-silver chloride electrode as a reference electrode, a platinum sheet as a counter electrode, acetonitrile as a solvent, potassium iodide and tetrabutylammonium hexafluorophosphonate as reaction substrates to construct a photoelectrocatalytic system. Butyl iodide can be generated in the next step under light irradiation or bias catalysis. Through free radical quenching experiments and experiments on regulating the concentrations of potassium iodide and tetrabutylammonium hexafluorophosphonate, it is proved that potassium iodide and tetrabutylammonium hexafluorophosphonate react with each other through S N 2. The mechanism of nucleophilic substitution to generate butyl iodide. This reaction can occur in both the cathode and anode chambers. Under the simultaneous action of light and bias, the total yield of butyl iodide can reach 175.93wt%.

[0107] Example 33

[0108] The method for preparing butyl iodide in Example 33 is exactly the same as that in Example 32, with the only difference being that in step (2), the reaction substrate is tetrapropylammonium hexafluorophosphonate.

[0109] Example 34

[0110] Example 34 is prepared in the same way as Example 32, except that in step (2), the reaction substrate is tetrahexylammonium hexafluorophosphonate.

[0111] The extension experiment by changing the alkyl chain length of the alkylammonium ion proves that iodine ions can react with ammonium ions of different alkyl chain lengths to generate corresponding alkyl iodides, as shown in Table 3. When n = 3, the total yield of propyl iodide reaches 151.66wt%; when n = 6, the total yield of hexyl iodide reaches 190.6wt%. The results show that the longer the alkyl chain length, the more complete the reaction. When n = 6, the substrate in the cathode chamber is almost completely converted into hexyl iodide, and the product yield in the anode chamber is slightly lower than that in the cathode chamber, which is related to the accumulation of a large amount of oxidizing active species in the anode chamber.

[0112] Table 3

[0113]

[0114] Example 35

[0115] Example 35 is prepared in the same way as Example 2, except that in step (1), the coordination time is 2h, and a mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode is obtained.

[0116] The mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode prepared in Example 35 is applied to prepare butyl iodide. Specifically, the mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode prepared in Example 35 is used as a working electrode, and silver / silver chloride is used as a reference electrode. The working electrode and the reference electrode are installed in the anode chamber of an H-type reaction cell. A platinum electrode is used as a counter electrode and is installed in the cathode chamber. 10mL of acetonitrile is added to each of the two chambers. A reaction substrate potassium iodide with a concentration of 2mM and tetrabutylammonium hexafluorophosphonate with a concentration of 1mM are added to the anode chamber. The reaction is carried out under a light intensity of 100mW / cm 2

[0117] Example 36

[0118] Example 36 is prepared in the same way as Example 2, except that in step (1), the coordination time is 12h, and a mercaptopropionic acid-coordinated selenium-doped cadmium sulfide photoelectrode is obtained.

[0119] ​The selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid prepared in Example 36 was applied to prepare butyl iodine. Specifically, the selenium-doped cadmium sulfide photoelectrode prepared in Example 35 was used as a working electrode, and silver / silver chloride was used as a reference electrode. The working electrode and the reference electrode were installed in the anode chamber of an H-type reaction cell. A platinum electrode was used as a counter electrode and was installed in the cathode chamber. Ten milliliters of acetonitrile was added to each of the two chambers. A 2 mM reaction substrate, potassium iodide, and 1 mM tetrabutylammonium hexafluorophosphate were added to the anode chamber. The reaction was carried out under a light intensity of 100 mW / cm2and a bias of 1 V vs. Ag / AgCl. After 1 h of reaction, butyl iodine was obtained as a product. 2 The selenium-doped cadmium sulfide photoelectrode prepared in Example 36 was applied to prepare butyl iodine. Specifically, the selenium-doped cadmium sulfide photoelectrode prepared in Example 35 was used as a working electrode, and silver / silver chloride was used as a reference electrode. The working electrode and the reference electrode were installed in the anode chamber of an H-type reaction cell. A platinum electrode was used as a counter electrode and was installed in the cathode chamber. Ten milliliters of acetonitrile was added to each of the two chambers. A 2 mM reaction substrate, potassium iodide, and 1 mM tetrabutylammonium hexafluorophosphate were added to the anode chamber. The reaction was carried out under a light intensity of 100 mW / cm2and a bias of 1 V vs. Ag / AgCl. After 1 h of reaction, butyl iodine was obtained as a product.

[0120] The length of the coordination time directly determines the growth of mercaptopropionic acid on the photoelectrode, as shown in Table 4. When the coordination time is 2 h, the short time cannot guarantee the growth of a large amount of mercaptopropionic acid, and the charge transfer effect is poor. The promotion effect on the production of butyl iodine is not obvious, and the yield is only 14.86 wt%. However, a long coordination time can cause the solubilization effect of the ligand to increase, which rapidly reduces the stability of the photoelectrode. The photoelectrode is peeled off from the FTO in the early stage of the reaction, which rapidly disappears the catalytic effect, and the yield of butyl iodine is only 10.66 wt%.

[0121] Table 4

[0122]

Claims

1. A method for preparing alkyl iodides using photocatalysis and electrocatalysis, characterized in that: The steps include: (1) In a photoelectric reaction cell, a selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid is used as a working electrode, and a reference electrode is installed in the anode chamber, and a counter electrode is installed in the cathode chamber. Equal amounts of organic solvent are added to each chamber; (2) adding reaction substrates potassium iodide and tetraalkylammonium hexafluorophosphonate to the cathode chamber and / or the anode chamber, applying light intensity and / or bias voltage to the photoelectrochemical reaction cell, and obtaining alkyl iodide after reaction.

2. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 1, wherein: In step (1), the photoelectric reaction cell is an H-type reaction cell; the reference electrode is an Ag / AgCl electrode or a saturated calomel electrode; the counter electrode is a platinum electrode or a graphite rod electrode; and the organic solvent is acetonitrile.

3. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 1, wherein: In step (1), the chemical formula of the selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid is CdS 1-x Se x -MPA; wherein, 0<X<1.

4. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 3, wherein: The mercaptopropionic acid coordinated selenium-doped cadmium sulfide photoelectrode is prepared by the following method, and the specific steps are as follows: (1.1) Place the cleaned conductive glass against the inner wall of the reaction device; (1.2) preparing a mixed solution containing a selenium salt and a cadmium sulfide precursor; pouring the mixed solution into the reaction device of step (1.1), sealing it, and performing a hydrothermal reaction at a high temperature; (1.3) After the reaction, the conductive glass on which the conductive crystal has been grown is removed, cleaned and dried, and the side on which the conductive crystal has been grown is annealed to obtain a selenium-doped cadmium sulfide photoelectrode; (1.4) Place the selenium-doped cadmium sulfide photoelectrode in a mixture of methanol, chloroform, and mercaptopropionic acid. Adjust the mixture to a strong base with tetramethylammonium hydroxide. Seal the mixture in the dark and heat to carry out the coordination reaction. (1.5) The photoelectrode after the coordination reaction is rinsed and vacuum-dried to obtain a selenium-doped cadmium sulfide photoelectrode coordinated with mercaptopropionic acid.

5. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 4, wherein: In step (1.4), the mixed volume of methanol, chloroform and mercaptopropionic acid is 1:1:0.

1.

6. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 4, wherein: In step (1.4), the heating temperature is 55-60° C., and the reaction time is 6.5-7 h.

7. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 4, wherein: In step (1.4), the pH of the mixed solution is adjusted to 11-13 with tetramethylammonium hydroxide.

8. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 1, wherein: In step (2), the light intensity is 1 to 3 suns, and the bias voltage is 1 to 1.5 V vs Ag / AgCl.

9. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 1, wherein: In step (2), after the reaction substrate is added, the concentration of potassium iodide in the reaction solution is 1-4 mM, and the concentration of tetraalkylammonium hexafluorophosphonate is 0.5-4 mM.

10. The method for preparing alkyl iodides using photocatalysis and electrocatalysis according to claim 9, wherein: In tetraalkylammonium hexafluorophosphonate, the length of the alkyl carbon chain is C3 to C6.

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