CN115717250A - Electrochemical method for paired preparation of butanediol and vanillin - Google Patents

Abstract

The invention provides an electrochemical method for preparing butanediol and vanillin in pairs. The method comprises the following steps: 1) Mixing 2-bromoethanol, p-hydroxybenzaldehyde, ammonia electrolyte and alcohol solvent, and adding into an electrolytic bath; 2) Carrying out electrolytic reaction on the electrolyte in the electrolytic cell in the step 1), and obtaining butanediol and vanillin after the reaction is finished. The method can effectively reduce the reaction of the raw material p-hydroxybenzaldehyde at the cathode, and simultaneously produces the 1, 4-butanediol as a byproduct, has high current efficiency, and is suitable for wide industrial application.

Description

Electrochemical method for paired preparation of butanediol and vanillin

Technical Field

The invention relates to the technical field of vanillin preparation, in particular to an electrochemical method for preparing butanediol and vanillin in pairs.

Background

1, 4-butanediol (BDO for short) is an important chemical raw material, and the main downstream application of BDO comprises the following steps: THF, GBL, PBT, PU, PBS/PBAT. With the growing concern for plastic contamination and the implementation of new releases of "plastic prohibited", the downstream product applications of BDO will meet an explosion period, while also enabling BDO to meet new peaks of growing applications.

Until 2020, the 1, 4-butanediol capacity of China accounts for 66% of the global capacity, the yield is 220 ten thousand tons/year, wherein an alkyne-aldehyde method is mainly used, the preparation process is that acetylene gas is prepared from calcium carbide by a wet method, and formaldehyde is produced from methanol produced by self through oxidation; reacting formaldehyde and the purified acetylene gas in an ethynylation reactor to produce BYD (butynediol), rectifying the BYD, removing ions, feeding the BYD into a hydrogenation device to produce a BDO crude product, and rectifying the crude BDO to obtain a qualified BDO product.

Vanillin is an important and widely used spice, is a synthetic spice with the largest global yield, is also an indispensable raw material in the field of food additive industry, has elegant, strong and lasting aroma, and can be directly used in industries such as cosmetics, perfumed soaps, cigarettes, cakes, candies, barbecue food and the like. In addition, vanillin molecule contains aromatic ether, aldehyde group and phenol light group, which can generate many chemical reactions to synthesize many medicines, agricultural chemicals and daily chemicals.

At present, vanillin can be divided into methyl vanillin and ethyl vanillin, the synthesis method is basically the same, taking ethyl vanillin as an example, the current mainstream method is a glyoxylic acid method, namely, o-ethoxyphenol and glyoxylic acid are used as raw materials, the condensation reaction is carried out under the alkaline condition to generate 3-ethoxy-4-hydroxyphenylglycolic acid, then the oxidation is carried out under the high-temperature condition through a catalyst to generate 3-ethoxy-3-hydroxyphenylacetic acid, and finally the decarboxylation is carried out under the acidic condition to obtain the ethyl vanillin. The method has the defects of complex process, low reaction efficiency, high pollution, various raw materials, long process flow and the like. In addition, a method for synthesizing ethyl vanillin by taking p-hydroxybenzaldehyde as a raw material is also provided, wherein the p-hydroxybenzaldehyde is dissolved in a certain solvent to carry out substitution reaction with bromine to obtain 3-bromine-4-hydroxybenzaldehyde, and then sodium ethoxide is added to introduce ethoxy to generate the ethyl vanillin. The reaction conditions of the process are not severe, the reaction efficiency is higher, but a plurality of auxiliary reagents are required to be added in the reaction, the operation is complex, and the process is not suitable for large-scale industrial production.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides an electrochemical method for preparing butanediol and vanillin in pairs, which comprises the steps of electrolyzing 2-bromoethanol to generate butanediol by using alcohols as a solvent and amines as an electrolyte and electrolyzing p-hydroxybenzaldehyde to generate vanillin by using an anode.

According to the invention, 2-bromoethanol is electrolyzed by a cathode to generate butanediol and bromine, wherein bromide ions continuously participate in the anode reaction, so that bromide ions do not need to be additionally introduced into the anode reaction, and the problems of reduced reaction selectivity and serious raw material loss caused by the side reaction that p-hydroxybenzaldehyde is electrolytically reduced and dimerized at the cathode to generate 1, 2-bis- (hydroxyphenyl) -ethylene glycol can be effectively solved.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the invention provides an electrochemical process for the paired preparation of butanediol and vanillin, said process being carried out in a diaphragm-free electrolytic cell, comprising the steps of:

1) Mixing 2-bromoethanol, p-hydroxybenzaldehyde, ammonia electrolyte and alcohol solvent, and adding into an electrolytic bath;

2) And (2) carrying out an electrolytic reaction on the electrolyte in the electrolytic cell in the step 1), carrying out an electrolytic reaction on 2-bromoethanol on a cathode to generate butanediol and bromine, and carrying out an electrolytic reaction on p-hydroxybenzaldehyde on a cathode to generate vanillin by bromine generated by the electrolytic reaction of the cathode.

In step 1) of the present invention, the amount of the 2-bromoethanol is 30 to 70 mol%, preferably 40 to 50 mol%, of the p-hydroxybenzaldehyde.

In step 1) of the invention, the ammonia electrolyte is selected from any one or a combination of at least two of ammonia water, ammonium bromide, ammonium carbonate and triethylamine, preferably ammonia water and/or ammonium carbonate, wherein the concentration of the ammonia water is 28-30wt%;

preferably, the ammonia-based electrolyte is added in an amount of 5 to 20% by mole, such as 5%, 10%, 15%, 20%, preferably 5 to 10% by mole based on the molar amount of p-hydroxybenzaldehyde.

In the step 1), the alcohol solvent is methanol and/or ethanol;

the vanillin comprises methyl vanillin and ethyl vanillin, the selection of the solvent is determined according to the type of the synthesized vanillin, if the methyl vanillin is synthesized, methanol is selected as the solvent, and if the ethyl vanillin is synthesized, ethanol is selected as the solvent;

preferably, the amount of the alcohol solvent is 2 to 5 times, such as 2 times, 3 times, 4 times, 5 times, preferably 2.5 to 3.5 times of the mass of the parahydroxybenzaldehyde.

In step 2) of the invention, the electrolysis temperature is-10-10 ℃, such as-10 ℃, 5 ℃, 0 ℃, 5 ℃, 10 ℃, preferably-5-5 ℃; the electrolysis time is 5-20h, such as 5h, 10h, 15h, 20h, preferably 10-15h.

The inventionIn the step 2), the electrolytic reaction is carried out, wherein the voltage range of the electrolytic cell is 4-8V, such as 4V, 5V, 6V, 7V, 8V, preferably 5-6V; the electrolytic current density is 1200-2500A/m ² E.g. 1200A/m ² 、1500A/m ² 、1800A/m ² 、2000A/m ² 、2500A/m ² Preferably 1500 to 2000A/m ² 。

In the step 2), after the electrolysis reaction is finished, the obtained reaction system contains a mixture of 1, 4-butanediol and vanillin;

preferably, after the electrolysis reaction is finished, the post-treatment processes such as desolventizing, filtering for desalting, rectifying and the like are also included, for conventional operation in the field, for example, in some examples, the reaction liquid obtained from the electrolysis reaction is preferably sequentially passed through a desolventizing tower, a filtering device, a light component removing tower, a butanediol removing tower, a vanillin removing tower and a heavy component removing tower, so as to respectively obtain 1, 4-butanediol and vanillin products.

In the process of the invention, the electrolytic cell comprises an anode and a cathode;

preferably, the anode is selected from a platinum electrode, a platinum titanium electrode, a graphite electrode or a DSA electrode, preferably a Ti-based PbO electrode ₂ 、IrO ₂ 、RuO ₂ Or a tin antimony oxide electrode;

preferably, the cathode is a copper electrode;

the material of the electrolytic cell is PP, PTFE and titanium, preferably titanium.

The invention does not limit the shape and arrangement of the electrodes in the electrolytic cell, and all the shapes and cathode and anode arrangements that can realize the electrolysis function are covered in the method of the invention.

In the research of the electrolytic synthesis of vanillin, the invention discovers that the proper amount of 2-bromoethanol is introduced into the system simultaneously, so that the self-polymerization reaction of the p-hydroxybenzaldehyde at the cathode can be inhibited. Meanwhile, the inventor also unexpectedly finds that in the electrolytic reaction, bromide ions generated after the cathode electrolytic reaction of the 2-bromoethanol can participate in the anode reaction, so that bromine does not need to be added into the reaction system.

The electrochemical method disclosed by the invention is used for synthesizing 1, 4-butanediol and vanillin in pairs, and the principle of the electrochemical method is analyzed in that 2-bromoethanol and p-hydroxybenzaldehyde are used as raw materials, in the electrolytic process, on one hand, the 2-bromoethanol reacts on the surface of a cathode to generate 1, 4-butanediol and bromide ions, the generated bromide ions are oxidized on an anode to form a bromine simple substance, the bromine simple substance is used as a reactant of a halogenated reaction to continuously react with the p-hydroxybenzaldehyde, methanol or ethanol to generate the methyl vanillin or the ethyl vanillin, wherein the bromide ions can be recycled, and meanwhile, the added ammonia electrolyte can ensure that a system is in an alkaline environment, so that the volatilization of the bromine simple substance and the generation of a byproduct HBr in the reaction process are avoided.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that:

the method has the advantages of high total product yield, small equipment investment, low operation risk and mild reaction conditions, and meanwhile, the 1, 4-butanediol is byproduct, the current efficiency is high, and the method is suitable for wide industrial application.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be merely illustrative of the invention and not limiting of its scope.

The main raw material sources used in the examples and comparative examples of the present invention are as follows:

graphite material, hebei black strong carbon new materials Co., ltd;

2-bromoethanol, aladdin reagent, inc., purity 95%;

p-hydroxybenzaldehyde, aladdin reagent, inc., purity > 98%;

methanol, aladdin reagent, inc., purity > 99.9%;

ammonia, alatin reagent limited, purity 30%;

trimethylamine, allantin reagent, inc., with a purity of not less than 98%;

ammonium carbonate, aladdin reagent, inc., purity > 99%;

copper electrodes, shanghai xianren instruments ltd, C2620;

a platinum titanium electrode, siam Tai gold, inc., with a plating thickness of 1 μm;

ti radical IrO ₂ An anode, jiangsu Yianteng special electrode Co., ltd., an iridium titanium mesh 50 x 100;

ti-based PbO ₂ Anode, jiangsu Yianteng special electrode Co., ltd., lead-titanium mesh 50X 100;

ti-based RuO ₂ Anode, jiangsu Yianite Special electrodes Inc., 50X 100 ruthenium-titanium mesh;

other starting materials or reagents are commercially available, unless otherwise specified.

Diaphragm-free electrolytic cell: a box-type diaphragm-free small-scale test electrolytic cell made of titanium is manufactured by Jiangyin-sky original electrochemical equipment Limited.

The main test methods used in the inventive examples and comparative examples are as follows:

vanillin analysis method:

high performance liquid chromatography, chromatograph: daidan U3000; a chromatographic column: diamonsil C18 (4.6 mm. Times.200 mm); mobile phase: methanol/0.1% phosphoric acid water (35/65); flow rate: 1.0mL/min; a detector: an RI 2000 type differential refraction detector; detection wavelength: 233nm; sample injection volume: 10 mu L of the solution; the quantitative method comprises the following steps: external standard curve method.

1, 4-butanediol analysis method:

the invention uses a gas chromatography area correction normalization method, and the instrument types are as follows: shimadzu GC2010; a chromatographic column: DB-5 (30X 0.32X 0.25); column temperature: temperature programming (50 ℃ for 4min, then 5 ℃/min heating rate to 100 ℃, then 25 ℃/min heating rate to 300 ℃, and 5min holding); sample inlet temperature: 230 ℃; FID temperature: 300 ℃; n is a radical of hydrogen ₂ Flow rate: 1mL/min; h ₂ Flow rate: 40mL/min; shock insulator purging (N) ₂ ) Flow rate: 3mL/min; carrier gas (N) ₂ ) Flow rate: 1mL/min; split-flow sample introduction, split-flow ratio: 50; sample introduction amount: 0.1. Mu.L.

The hydrogen spectra of vanillin and 1, 4-butanediol in the following examples were characterized using a nuclear magnetic resonance apparatus (Brucker ARX-400).

Vanillin selectivity = vanillin molar yield/p-hydroxybenzaldehyde molar consumption 100%

1, 4-butanediol selectivity =1, 4-butanediol molar yield 2/2-bromoethanol molar consumption 100%

Current efficiency = (vanillin mole production +1, 4-butanediol mole production x 2) × 96500/(electrolysis current x electrolysis time) × 100%

Example 1

An electrochemical process for the pair-wise preparation of 1, 4-butanediol and methyl vanillin comprising the steps of:

1) 50g (0.41 mol) of p-hydroxybenzaldehyde, 100g of methanol, 20.5g (0.164 mol) of 2-bromoethanol and 7.17g (0.061 mol) of 30wt% ammonia water are uniformly mixed and transferred to a diaphragm-free electrolytic cell, wherein the using amount of the methanol is 2 times of the mass of the p-hydroxybenzaldehyde, the adding amount of the ammonia water is 15 percent of the molar amount of the p-hydroxybenzaldehyde, and the adding amount of the 2-bromoethanol is 40 percent of the molar amount of the p-hydroxybenzaldehyde.

2) The anode of the electrolytic cell adopts a graphite electrode, and the cathode adopts a nickel cathode. The temperature in the electrolytic cell is reduced to-10 ℃ and then the electrolytic reaction is started, and the current density of the electrolytic cell is 1200A/m ² The electrolytic potential is 5V, and the reaction is finished after 20 hours of electrolytic reaction.

And (3) sequentially passing the reaction liquid obtained by the electrolysis reaction through a desolventizing tower, a filtering device, a light component removing tower, a butanediol removing tower, a vanillin removing tower and a heavy component removing tower to respectively obtain 1, 4-butanediol and methyl vanillin.

The data of the 1, 4-butanediol nuclear magnetic hydrogen spectrum are as follows:

1H NMR(600MHz,CDCl ₃ )：δ3.65(2H)，3.50(4H)，1.53(4H)。

the data of the nuclear magnetic hydrogen spectrum of the methyl vanillin are as follows:

1H NMR(600MHz,CDCl ₃ )：δ9.61(1H)，7.38(1H)，7.27(1H)，7.23(1H)，5.35(1H)，3.83(3H)。

in this example, the conversion rate of p-hydroxybenzaldehyde as a raw material was 98.2%, the conversion rate of 2-bromoethanol as a raw material was 86.1%, the selectivity of synthesized methyl vanillin was 93.3%, the selectivity of 1, 2-bis- (hydroxyphenyl) -ethylene glycol as a byproduct was 3.2%, the selectivity of 1, 4-butanediol as a byproduct was 65.7%, and the current efficiency was 159.3%.

Example 2

An electrochemical process for the pair-wise preparation of 1, 4-butanediol and ethyl vanillin comprising the steps of:

1) 50g (0.41 mol) of p-hydroxybenzaldehyde, 125g of ethanol, 15.37g (0.123 mol) of 2-bromoethanol and 2g (0.02 mol) of ammonium bromide are uniformly mixed and transferred to a diaphragm-free electrolytic cell, wherein the dosage of the ethanol is 2.5 times of the mass of the p-hydroxybenzaldehyde, the addition amount of the ammonium bromide is 5mol percent of the mol of the p-hydroxybenzaldehyde, and the addition amount of the 2-bromoethanol is 30 mol percent of the mol of the p-hydroxybenzaldehyde.

2) The anode of the electrolytic cell adopts a platinum-titanium electrode, and the cathode adopts a copper cathode. The temperature in the electrolytic cell is reduced to-5 ℃ and then the electrolytic reaction is started, and the current density of the electrolytic cell is 2500A/m ² And the electrolytic potential is 8V, and the reaction is finished after 5 hours of electrolytic reaction.

And (3) sequentially passing the reaction liquid obtained by the electrolysis reaction through a desolventizing tower, a filtering device, a light component removing tower, a butanediol removing tower, a vanillin removing tower and a heavy component removing tower to respectively obtain 1, 4-butanediol and ethyl vanillin.

The nuclear magnetic hydrogen spectrum data of the ethyl vanillin are as follows:

1H NMR(600MHz,CDCl ₃ )：δ9.61(1H)，7.38(1H)，7.27(1H)，7.23(1H)，5.35(1H)，4.09(2H)，1.32(3H)。

in this example, the conversion rate of p-hydroxybenzaldehyde as a raw material was 97.5%, the conversion rate of 2-bromoethanol as a raw material was 84.3%, the selectivity of synthesized ethyl vanillin was 94.2%, the selectivity of by-produced 1, 2-bis- (hydroxyphenyl) -ethylene glycol was 2.9%, the selectivity of by-produced 1, 4-butanediol was 68.4%, and the current efficiency was 157.5%.

Example 3

An electrochemical process for the paired preparation of 1, 4-butanediol and methyl vanillin comprising the steps of:

1) 50g (0.41 mol) of p-hydroxybenzaldehyde, 175g of methanol, 35.9g (0.287 mol) of 2-bromoethanol and 3.93g (0.041 mol) of ammonium carbonate are uniformly mixed and transferred into a diaphragm-free electrolytic tank, wherein the dosage of the methanol is 3.5 times of the mass of the p-hydroxybenzaldehyde as the raw material, the addition amount of the ammonium carbonate is 10 percent of the molar amount of the p-hydroxybenzaldehyde, and the addition amount of the 2-bromoethanol is 70 percent of the molar amount of the p-hydroxybenzaldehyde.

2) The anode of the electrolytic cell adopts a platinum electrode, and the cathode adopts a nickel cathode. The temperature in the electrolytic cell is reduced to 5 ℃ and then the electrolytic reaction is started, and the current density of the electrolytic cell is 1500A/m ² And the electrolytic potential is 4V, and the reaction is finished after the electrolytic reaction is carried out for 10 hours.

And (3) sequentially passing the reaction liquid obtained by the electrolysis reaction through a desolventizing tower, a filtering device, a light component removing tower, a butanediol removing tower, a vanillin removing tower and a heavy component removing tower to respectively obtain 1, 4-butanediol and methyl vanillin.

In this example, the conversion rate of p-hydroxybenzaldehyde as a raw material was 96.1%, the conversion rate of 2-bromoethanol as a raw material was 85.2%, the selectivity of synthesized methyl vanillin was 91.6%, the selectivity of 1, 2-bis- (hydroxyphenyl) -ethylene glycol as a byproduct was 4.3%, the selectivity of 1, 4-butanediol as a byproduct was 68.9%, and the current efficiency was 152.3%.

Example 4

An electrochemical process for the pair-wise preparation of 1, 4-butanediol and methyl vanillin comprising the steps of:

1) 50g (0.41 mol) of p-hydroxybenzaldehyde, 250g of methanol, 25.6g (0.205 mol) of 2-bromoethanol and 8.28g (0.082 mol) of triethylamine are uniformly mixed and transferred to a diaphragm-free electrolytic cell, wherein the dosage of the methanol is 5 times of the mass of the p-hydroxybenzaldehyde, the addition amount of the triethylamine is 20 percent of the molar amount of the p-hydroxybenzaldehyde, and the addition amount of the 2-bromoethanol is 50 percent of the molar amount of the p-hydroxybenzaldehyde.

2) The anode of the electrolytic bath adopts Ti-based PbO ₂ The electrode and the cathode adopt a nickel cathode. The temperature in the electrolytic bath is reduced to 10 ℃, the electrolytic reaction is started, and the current density of the electrolytic cell is 2000A/m ² The electrolytic potential was 6V, and the reaction was completed after 15 hours of electrolytic reaction.

And (3) sequentially passing the reaction liquid obtained by the electrolysis reaction through a desolventizing tower, a filtering device, a light component removing tower, a butanediol removing tower, a vanillin removing tower and a heavy component removing tower to respectively obtain 1, 4-butanediol and methyl vanillin.

In this example, the conversion rate of p-hydroxybenzaldehyde as a raw material was 95.5%, the conversion rate of 2-bromoethanol as a raw material was 87.2%, the selectivity of synthesized methyl vanillin was 93.8%, the selectivity of 1, 2-bis- (hydroxyphenyl) -ethylene glycol as a byproduct was 2.9%, the selectivity of 1, 4-butanediol as a byproduct was 67.9%, and the current efficiency was 158.6%.

Example 5

An electrochemical process for the pair-wise preparation of 1, 4-butanediol and methyl vanillin comprising the steps of:

1) 50g (0.41 mol) of p-hydroxybenzaldehyde, 125g of methanol, 35.9g (0.287 mol) of 2-bromoethanol and 7.68g (0.062 mol) of 28% ammonia water are uniformly mixed and transferred to a diaphragm-free electrolytic cell, wherein the using amount of the methanol is 2.5 times of the mass of the p-hydroxybenzaldehyde, the adding amount of the 28wt% ammonia water is 15% of the molar amount of the p-hydroxybenzaldehyde, and the adding amount of the 2-bromoethanol is 70% of the molar amount of the p-hydroxybenzaldehyde.

2) The anode of the electrolytic cell adopts Ti-based IrO ₂ The electrode and the cathode adopt a nickel cathode. The temperature in the electrolytic bath is reduced to-5 ℃, the electrolytic reaction is started, and the current density of the electrolytic cell is 1500A/m ² The electrolytic potential was 6V, and the reaction was completed after 20 hours of electrolytic reaction.

And (3) sequentially passing the reaction liquid obtained by the electrolysis reaction through a desolventizing tower, a filtering device, a light component removing tower, a butanediol removing tower, a vanillin removing tower and a heavy component removing tower to respectively obtain 1, 4-butanediol and methyl vanillin.

In this example, the conversion rate of p-hydroxybenzaldehyde as a raw material was 96.1%, the conversion rate of 2-bromoethanol as a raw material was 86.2%, the selectivity of synthesized methyl vanillin was 95.3%, the selectivity of 1, 2-bis- (hydroxyphenyl) -ethylene glycol as a byproduct was 2.2%, the selectivity of 1, 4-butanediol as a byproduct was 70.1%, and the current efficiency was 162.6%.

Example 6

An electrochemical process for the pair-wise preparation of 1, 4-butanediol and methyl vanillin comprising the steps of:

1) 50g (0.41 mol) of p-hydroxybenzaldehyde, 175g of methanol, 25.6g (0.205 mol) of 2-bromoethanol and 2.56g (0.021 mol) of 28% ammonia water are uniformly mixed and transferred to a diaphragm-free electrolytic cell, wherein the using amount of the methanol is 3.5 times of the mass of the p-hydroxybenzaldehyde, the adding amount of the 28wt% ammonia water is 5% of the molar amount of the p-hydroxybenzaldehyde, and the adding amount of the 2-bromoethanol is 50% of the molar amount of the p-hydroxybenzaldehyde.

2) The anode of the electrolytic cell adopts Ti-based RuO ₂ The electrode and the cathode adopt a nickel cathode. The temperature in the electrolytic cell is reduced to 5 ℃ and then the electrolytic reaction is started, and the current density of the electrolytic cell is 2000A/m ² And the electrolytic potential is 5V, and the reaction is finished after the electrolytic reaction is carried out for 10 hours.

And (3) sequentially passing the reaction liquid obtained by the electrolysis reaction through a desolventizing tower, a filtering device, a light component removing tower, a butanediol removing tower, a vanillin removing tower and a heavy component removing tower to respectively obtain 1, 4-butanediol and methyl vanillin.

In this example, the conversion rate of p-hydroxybenzaldehyde as a raw material was 94.3%, the conversion rate of 2-bromoethanol as a raw material was 82.8%, the selectivity of synthesized methyl vanillin was 93.4%, the selectivity of 1, 2-bis- (hydroxyphenyl) -ethylene glycol as a byproduct was 3.0%, the selectivity of 1, 4-butanediol as a byproduct was 69.6%, and the current efficiency was 158.7%.

Comparative example 1

The process referred to in example 1 differs only in that: and (2) replacing 2-bromoethanol with 2-chloroethanol in the step (1), and obtaining 1, 4-butanediol and methyl vanillin without changing other operations.

The conversion rate of p-hydroxybenzaldehyde as a raw material is 82.1 percent, the conversion rate of 2-chloroethanol as a raw material is 83.9 percent, the selectivity of synthesized methyl vanillin is 53.9 percent, the selectivity of 1, 2-bis- (hydroxyphenyl) -glycol as a byproduct is 28.6 percent, the selectivity of 1, 4-butanediol as a byproduct is 50.6 percent, and the current efficiency is 98.9 percent.

Comparative example 2

The process referred to in example 1 differs only in that: and (2) adding no 2-bromoethanol in the step (1), and keeping other operations unchanged to obtain the methyl vanillin.

The conversion rate of p-hydroxybenzaldehyde as a raw material is 52.1 percent, the selectivity of the synthesized methyl vanillin is 44.8 percent, the selectivity of the byproduct 1, 2-bis- (hydroxyphenyl) -glycol is 35.9 percent, and the current efficiency is 20.1 percent.

Comparative example 3

The process of example 1 is referred to with the only difference that: in the step (1), 2-bromoethanol is replaced by 1-bromopropanol, and other operations are not changed, so that 1, 6-hexanediol and methyl vanillin are obtained.

The conversion rate of p-hydroxybenzaldehyde as a raw material is 52.9%, the conversion rate of 1-bromopropanol as a raw material is 64.3%, the selectivity of synthesized methyl vanillin is 48.9%, the selectivity of a byproduct 1, 2-bis- (hydroxyphenyl) -ethylene glycol is 33.9%, the selectivity of a byproduct 1, 6-hexanediol is 41.7%, and the current efficiency is 56.6%.

Comparative example 4

The process of example 1 is referred to with the only difference that: in the step (1), the solvent methanol is replaced by propanol, other operations are not changed, the conversion rate of p-hydroxybenzaldehyde is 89.4%, the conversion rate of raw material 2-bromoethanol is 84.5%, the selectivity of 1, 4-butanediol methylindol is not detected to be 66.9%, and the current efficiency is 87.6%.

Claims (10)

1. Electrochemical process for the paired preparation of butanediol and vanillin, characterized in that it is carried out in a diaphragm-free electrolytic cell comprising the following steps:

1) Mixing 2-bromoethanol, p-hydroxybenzaldehyde, ammonia electrolyte and alcohol solvent, and adding into an electrolytic bath;

2) And (2) carrying out an electrolytic reaction on the electrolyte in the electrolytic cell in the step 1), carrying out an electrolytic reaction on 2-bromoethanol on a cathode to generate butanediol and bromine, and participating in an electrolytic reaction of p-hydroxybenzaldehyde on an anode to generate vanillin by the bromine generated by the cathode electrolytic reaction.

2. The electrochemical process according to claim 1, wherein the 2-bromoethanol is used in an amount of 30 to 70%, preferably 40 to 50%, based on the molar amount of p-hydroxybenzaldehyde in step 1).

3. The electrochemical method according to claim 1 or 2, wherein in step 1), the ammonia electrolyte is selected from any one or a combination of at least two of ammonia water, ammonium bromide, ammonium carbonate and triethylamine, preferably ammonia water and/or ammonium carbonate, wherein the ammonia water concentration is 28-30wt%.

4. The electrochemical process according to any one of claims 1 to 3, wherein the ammonia-based electrolyte is added in an amount of 5 to 20% by mole, preferably 5 to 10% by mole, based on the molar amount of p-hydroxybenzaldehyde in step 1).

5. The electrochemical process according to any of claims 1 to 4, wherein in step 1), the alcoholic solvent is methanol and/or ethanol.

6. The electrochemical method according to claim 5, wherein in step 1), the solvent is selected according to the type of vanillin synthesized, and methanol is selected as the solvent for synthesizing methyl vanillin, and ethanol is selected as the solvent for synthesizing ethyl vanillin.

7. The electrochemical process according to any one of claims 1 to 6, wherein the amount of the alcoholic solvent used in step 1) is 2 to 5 times, preferably 2.5 to 3.5 times, the mass of p-hydroxybenzaldehyde.

8. The electrochemical process according to any of claims 1 to 7, characterized in that in step 2), the electrolysis reaction is carried out at an electrolysis temperature of-10 to 10 ℃, preferably-5 to 5 ℃; the electrolysis time is 5-20h, preferably 10-15h.

9. The electrochemical process according to any of claims 1 to 8, characterized in that in step 2), the electrolysis reaction is carried out with an electrolysis cell voltage interval of 4 to 8V, preferably 5 to 6V; the electrolytic current density is 1200-2500A/m ² Preferably 1500 to 2000A/m ² 。

10. The electrochemical process of any one of claims 1 to 9, wherein the electrolytic cell comprises an anode and a cathode;

preferably, the anode is selected from a platinum electrode, a platinum titanium electrode, a graphite electrode or a DSA electrode, and the DSA electrode is preferably Ti-based PbO ₂ 、IrO ₂ 、RuO ₂ Or a tin antimony oxide electrode;

preferably, the cathode is a copper electrode;

the material of the electrolytic cell is PP, PTFE and titanium, preferably titanium.