KR930003755B1 - Process for preparing tetra alkyl 1,2,3,4-butane tetra carboxylate - Google Patents

Abstract

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Description

Method for preparing tetraalkyl 1,2,3,4-butanetetracarboxylate

1 is a bar graph illustrating the yield of tetramethyl butanetetracarboxylate and other products obtained using electrolysis in methanol containing various electrolytes.

2 is a bar graph illustrating the yield of tetramethyl butanetetracarboxylate and other products obtained by electrolysis in methanol by applying various cathode electrodes.

3 is a graph of TMBTC hydrolysis rate constant versus acid concentration.

4 is a graph showing TMBTC hydrolysis versus time at different temperatures.

5 is a graph showing TMBTC hydrolysis vs. time for different TMBTC / H ₂ SO ₄ mole ratios.

6 is a flowchart of an experimental procedure for manufacturing BTCA.

The present invention relates to a method for preparing 1,2,3,4-butanetetracarboxylic acid, and more particularly, electrohydrodimerization of dialkyl maleate in alkanol to obtain tetraalkyl butanetetracarboxylate, The present invention relates to a method for preparing 1,2,3,4-tetracarboxylic acid by hydrolysis thereof, and the method includes oxidatively purifying and removing impurities causing color development in butanetetracarboxylic acid.

The 1,2,3,4-butanetetracarboxylic acid compound has been found by the US Department of Agriculture as an effective prepressive agent for polyester-cotton blend fabrics and has been found to be used in large quantities for this purpose. Accordingly, effective methods for preparing this compound would be very useful. Such a manufacturing method must produce a product having a property of acceptable color, since it is a very important factor to be suitable as a preservative.

After oxidizing the gas containing ozone and then oxidatively decomposing tetraphthalic acid or anhydride, which was oxidized to gas containing molecular oxygen, the mixture was heated with a peroxide (for example, H ₂ O ₂ ) at 100 ° C., 1.2, A method for preparing 3,4-butanetetracarboxylic acid has been reported. ; Reference. Japanese Patent 55/49336 [80/493363], April 9, 1980 Chem. Abstracts, 93 (13), 132082h; Japanese Patent 54/151906 [79/151906], November 29, 1979, Chem. Abstracts, 92 (23), 197937g. In another report, 1,2,3,4-butanetetracarboxylic acid without HNO ₃ is obtained by oxidizing delta-4-tetra hydrophthalic anhydride to HNO ₃ and stirring at 90 ° C. for 1 hour (after oxidation). This is obtained by heating for 30 minutes in 140 ° C. ethylene glycol. The polycarboxylic acid obtained by oxidizing C _5-1ν cycloalkene with HNO ₃ was purified by oxidation treatment. See German Publication DE3016225 Al, October 29, 1981, Chem. Abstracts, 96 (3), 19672z.

The present invention encompasses different pathways for butanetetracarboxylic acids, including the hydrolysis of tetraalkyl butanetetracarboxylates, wherein tetraalkyl butanetetracarboxylates are used for the electrolytic hydrodimerization of dialkyl malate in alkanols. Is obtained.

Electrolytic reductive coupling of various activated olefins has been observed and reported in the past. Most of these operations involve aqueous systems in divided cells, sometimes together with electrolyte salts with negative discharge potentials, such as quaternary ammonium salts. In addition to reducing coupling, other reactions such as simple reduction or polymerization also occur frequently. The various parameters of this reaction and the use of different electrolytes are described in organic electrochemistry (1983, Marcel Dekker, N.Y., N.Y.) compiled by Manuel M. Bayer and Henning Lund. In this reference page 669, an undivided cell shows that (1) the olefin and the product are largely not oxidized at the anode electrode and (2) the oxygen released from the anode wood electrode in the aqueous system has an unwanted side reaction. It is explained that it is selected under the condition that it does not occur. This reference also refers to the effect of alkali metal cations, for example on pages 669 and 672, which increase the rate of redundancy of diethyl maleate and of radicals of anions.

Electrolytic hydrogen duplication of diethyl maleate has been reported by Bayer and Petrovic. (J.Electrochem. Soc., 114 (10), 1024-1025 (1967)): Here, the water of dimethylformamide in a separate cell is catalysed with sodium ions in the same state. It was pointed out that more hydrodimerization occurs in the presence of tetraethylammonium ions. The electrolysis was carried out for three (3) hours and showed a conversion of about 50% and produced a certain amount of hydrogen dimer and other products.

Methanol has been used as a solvent in the reduction reaction mechanism studies (see Dimitra Sazou et al, "Electrochemical Reduction of Maleic and Fumaric Acids and There Dimethyl Esters in Methanol at a Mercury Electrode," Coll. Czech, Chem. Comm. , 52, 2132-2141 (1957)). A cyclic voltammogram of acid was given in a methanol solution containing several feed electrolytes using a hanging mecury drop electrode and a reduction mechanism. This has been discussed. The reduction of the double bond of the corresponding dimethyl ester is described as occurring in one step. The described process uses very dilute acids, for example 0.0025 or 0.005 moles per liter.

The present invention includes an effective method for converting dialkyl malate to tetraalkyl butanetetracarboxylate in high yield and conversion by electrolytic hydrogen duplication in alkanols, which converts tetraalkyl butanetantetracarboxylate to butanetetra It is combined with an effective method for hydrolysis to carboxylic acid. This electrolytic hydrogen duplication provides tetraalkyl butanetetracarboxylates in alkanol solutions and is a suitable form for separation-purification by crystallization, which contributes to the purity of the resulting butanetetra carboxylic acid. Some aspects of the invention relate to the acid production reaction while others relate to the electrolysis reaction.

The present invention utilizes high purity, very low or negligible levels of chromophores from tetraalkyl butanetetracarboxylate (TABTC) using effective conditions and processes to provide acceptable yields of products in high yield, high purity and color testing. And a process for preparing the excipient 1,2,3,4-butanetetracarboxylic acid (BTCA). In a particular aspect, the present invention utilizes a relatively high concentration of TABTC and acid catalyst compared to water to convert tetraalkyl butanetetracarboxylate to butanetetracarboxylic acid in order to achieve a good reaction rate and a short reaction time, that is, within 6 hours. It involves decomposing and adding water to replace the distilled while distilling alkanol and water during hydrolysis to proceed with the reaction.

The invention also includes crystallizing tetraalkyl butanetetracarboxylates from alkanols prior to the hydrolysis step to remove byproducts from the tetracarboxylates, especially in the case of tetramethyl butanetetracarboxylate (TMBTC), High recoveries are obtained by crystallization from methanol at temperatures below 0 ° C., for example around −10 ° C. and by adding optional water upon separation.

The present invention further comprises treating butanetetracarboxylic acid with an oxidant to effect oxidation of the chromophore. To be very effective at this point, it is oxidized to aqueous hydrogen peroxide (aq. Hydrogen peroxide) at elevated temperatures up to 55 ° C and destroys excess peroxide at higher temperatures.

The present invention may also use an aqueous washing method prior to the hydrolysis step in which tetraalkyl butanetetracarboxylate is extracted at a temperature above its melting point with an aqueous solution such as water to remove other water soluble impurities, including salts and coloring substances. .

The present invention can also utilize the crystallization process as a convenient and effective method for cooling the butanetetracarboxylic acid product in aqueous solution, generally by cooling to room temperature sufficient for crystallization. Butanetetracarboxylic acid that is not separated includes the remaining acid catalyst and can be reused by filtration until the hydrolysis step.

The present invention provides a process for preparing butanetetracarboxylate from tetraalkylbutanetetracarboxylate with a high yield and recovery rate of, for example, about 83%, using a series of relatively simple reactions and industrial equipment. to provide.

The present invention is also useful in terms of selectivity and yield, and conditions that can be applied and useful processes for the production of tetraalkylbutanetetracarboxylates by the effective electrolytic hydrogen duplexing of substantial concentrations of dialkylmaleates in media containing alkanols. It includes. The invention further includes carrying out such hydrogen duplication in a non-separated cell using a metal salt such as an alkali metal salt as the feed electrolyte. Alkanols, which are generally used in anhydrous form, can serve as proton donors that affect the addition of hydrogen ions during the reaction. The use of alcohol rather than water as the electrolyte medium can prevent the hydrolysis of maleate ester groups and avoid the acidification of the medium that can result from such hydrolysis. Surprisingly, tetraalkyl butanetetracarboxylates can be obtained in very high yields in the alkanol medium of unisolated cells and the yield in electrolysis with sodium or other alkali metal salts is obtained in electrolysis with tetraalkylammonium salts. It turns out that it can surpass. The presence of alkanols prevents the hydrolysis of dialkyl maleates even in the presence of basic salts, since solvolysis of the alkyl groups replaces them with alkyl groups. The alkyl acid malate therefore does not form well and the medium does not become strongly acidic. Therefore, high yields of hydrogen dimers can be obtained at high conversion rates rather than an increase in the amount of reaction product (dialkyl succinate) resulting from acidification of the medium due to the nature of the electrolytic hydrogen duplication of dialkyl maleates in aqueous media. . During electrolysis in an aqueous medium, the pH changes from alkali to acidic conditions and the pH usually decreases to 4.

Such acidic pH conditions do not increase when no water is present in the alkanol medium and no noticeable increase in succinate product is observed. It is noted that this procedure is free of monoalkyl maleates in the electrolysis medium. Since this process can be effectively performed in a non-separable cell, it can be said that it is a great advantage to avoid the electrical resistance, the cost of the membrane, and other disadvantages generated in the separate cell. In general, the present invention involves the use of an electrolysis solution containing a very high concentration of maleate reactant and the use of a large amount of current during electrolysis to obtain a large amount of tetraalkyl butanetetracarboxylate product in a suitable reaction time.

According to the present invention there is provided a process for preparing 1,2,3,4-butanetetracarboxylic acid. This process is carried out by hydrolyzing the tetraalkyl butanetetracarboxylate produced to obtain butanetetracarboxylic acid by hydrolysis of the resulting tetraalkyl butanetetracarboxylate in order to obtain butanetetracarboxylic acid in the acid medium with electrolysis hydrogen duplication in alkanol. Obtaining the butanetetracarboxylic acid converts the dialkyl maleate to tetraalkyl butanetetracarboxylate in high yield and conversion. Purification of the resulting butanetetracarboxylic acid results in a product having a low amount of color contaminants and a sufficiently high purity to be suitable for use as a flame retardant in polyester-cotton mixed tissues.

[Electrolysis Hydrogen Duplexing]

The electrolytic hydrogenation step of the present invention may generally be done with dialkyl maleates, but in practice maleates of lower alkyl groups such as those of 1-6 carbons are most suitable. Dimethyl maleate (DMM) is the preferred reactant and is used in the examples herein but diethyl maleate, dipropyl maleate, dihexyl maleate and the like can also be used. Increasing the size of alkyl, whether in the ester or in the alkanol solvent, tends to increase the electrical resistance, thereby making the use of power less effective. In addition, the use of large molecular weight alkanols that tend to be solid at room temperature is inappropriate. Tetraalkylbutanetetracarboxylate is used to convert to butanetetracarboxylic acid as described above. Tetramethylester, the simplest ester, is well suited for this purpose and there is usually no reason to choose another tetraalkylester as an intermediate to obtain the same product.

The reaction occurring during the electrolysis of the inventive method can be extracted as follows.

Methoxymethanol, a hemiacetal of formaldehyde, is also a similar product. However, the presence of formaldehyde is confirmed, which may be due to the dissociation of methoxymethanol. Another intermediate is the acid (ten thousand and one if used) from the + CH ₂ OH and CH ₂ OH · and protons and acetate in the reaction of enoic wood pole (anode). Alkoxides such as CH ₃ O can also result from reactions at the cathode.

CH ₂ OH as a likly intermediate in the epoxide can be added to maleate double bonds and can produce other byproducts, resulting in a significant loss of selectivity to the desired hydrogen dimer when a non-separated cell is used. Can give However, these undesirable side reactions do not occur to a significant extent because very good results are obtained in non-isolated cells. In non-isolated cells, the protons generated at the anodes move freely and react with the methoxide generated by hydrogen duplication at the cathode, thereby preventing the reaction and polymerization of the methoxide.

Fortunately, this electrolysis is not only very effective when simple alkali metal salts are used as the feed electrolyte, but the results of using these salts are actually much better than those obtained with some commonly used expensive electrolytes. Was found. In addition to these preferred alkali metal salts, the process may use other feed electrolytes known in the art.

Feed electrolytes are used to provide ions that carry current during the electrolysis process. Generally, electrolytes can be used that dissociate into ions in the electrolysis medium to carry current and do not excessively interfere with the desired reaction or excessively drive competition. Most electrolytes can be considered salts because they obtain cations from bases and anions from acids. However, it is also possible to use a base as an electrolyte, which is sometimes suitable for lowering acidity. Dialkyl maleates undergo reduction at less negative potential than many suitable cations, so competitive discharge of cations is generally not a concern. Alkaline earth metal compounds and quaternary ammonium compounds having very low discharge negative charges, as well as alkali metal compounds such as sodium, potassium, lithium compounds can also be used. In general, acid anions will act as anions of the electrolyte, but will generally be selected because they have acceptable solubility in the alkanol system and minimize interference, competition and electrode degradation. Such anions include carboxyl anions, halide ions, and aromatic sulfonic acid anions.

In the present invention, fortunately it has been found that very simple salts such as sodium acetate have a very good function as an electrolyte in the electrohydrogen duplication of alkylmaleates. It has conventionally been thought that quaternary ammonium salts generally give better results than alkali metal salts. However, it has been found in the present invention that alkali metal salts can give better results in the electrohydrogenation of dimethyl maleate, especially in selectivity to the desired product. Such useful electrolytes include sodium, potassium and lithium acetate, propionate and succinate, sodium toluene sulfonate, tetrabutylammonium, P-toluene sulfonate, tetra butylammonium hydroxide, tetrabutylammonium acetate, tetrabutylammonium chloride There is. Similar salts may also be used with sulfate, phosphate and tetrafluoroborate anions, but these salts may also cause degradation of the enowood pole when suitable graphite is used as the enowood pole. Some halide salts, for example sodium halides, are very suitable for use because they have very limited solubility in methanol. In the case of calcium chloride, since chlorine is theoretically bound to calcium relatively tightly, it acts as an acid catalyst to form a dialkyl2-methoxysuccinate (commonly called methoxydialkyl succinate) to select the desired hydrogen dimer. Falls. Solubility of calcium acetate is poor, but calcium nitrate has good properties in this respect.

The present electrolysis process can be carried out under a wide range of electrolysis conditions, including a wide range of current intensities and current densities used in the electrodes. The process be operated at a very low current density of less than 100 and 200mA per 1cm ² below per 1cm ² 5mA. Preferred current densities range from about 15 to 50 mA per cm ² in operation, for example 25 mA per cm ² for long electrode lifetimes and good product selectivity at relatively low cell voltages. To maximize the use of the battery, it is advantageous to work at high current densities, but there must be a balance between heat generation and resistance and high voltage cells which affect the price.

The present electrolysis can be carried out in a wide range of concentrations of from about 5% up to about 50% by weight, based on the weight of the dialkyl maleate reactant, with good selectivity resulting in the desired range of dimers. Generally at least 15% to 35% to 40% is the most suitable concentration and in particular cases the concentration of the product is lower due to yields and conversions of up to 100%, but this range is very suitable. This process is suitable for producing large quantities of kilograms or larger units of product. The use of relatively high concentrations of reactants reduces the amount of material to be treated. However, the electrical resistance of the solution increases with the concentration of the reactants. Moreover, solubility problems only occur at some high concentrations. During electrolysis, although not always, all components are preferably used in a homogeneous phase.

Although the concentration of the feed electrolyte can vary very widely, it is not necessary to exceed the very dilute concentration for conductivity. Higher concentrations increase conductivity, but salts are generally less soluble in methanol, so using salts in excess of solubility does not help. The amount of salt may be any minimum amount at which electrical conduction can occur, but is generally used in the range of 0.5 to 2 or 3 wt%, rarely 5 wt% for special purposes. Minimizing costs requires keeping salt concentrations low because the cost of supplying or reusing salt increases with the amount of salt. It is preferable to use relatively inexpensive salts (eg sodium acetate) that can be consumed rather than reused.

Because concentrations change during the electrolysis process, the concentration range of the maleate reactant here refers to the initial concentration usually acting in a batch reaction or batch reactions. The selectivity to the desired product is still large when there is a high conversion, and in order to avoid unnecessary steps in the treatment and cost issues of isolating unreacted malate, electrolysis reactions generally occur when 75% or 80% or more of malate is reacted. It will be a high conversion rate. It is preferable to perform at a 95% maleate conversion rate. Higher conversions are possible but it is known that large electrolysis may occur if electrolysis continues with little or no amount of maleate reactant present.

It is known that there is a competitive chemical side reaction in which methoxydimethylsuccinate is produced. In general, the amount of this reaction depends on the time the maleate reactant is exposed to the reaction system components. Therefore, it is preferable that the electrolysis reaction is performed at a relatively low initial malate concentration and continuous electrolysis in which malate is added as the reaction proceeds. The final reaction can then be obtained at high conversions prior to separating the product. Another way to minimize the contact time of maleates is to use large electrolysis cells, especially for the electrode surface area, relative to the amount of material in the reaction system and the amount of maleate reactants. Another method is to use a constant stirred tank reactor that performs continuous feeding and discharging to keep the concentration of the DMM low enough to reduce the chemical driving force of this side reaction. .

The control of the electrolysis reaction time can be expressed by the electric current supply. The conversion of a certain amount of maleate reactant requires a number of corresponding amper-hours for the current and the time required to accumulate the number of ampere-hours needed for electrolysis is dependent on the size, number and current of the electrolysis cell. Can be changed by As described above, although reactions within 15 hours are effective, less by-products are generated at reaction times of less than 10 hours. If the same current is used, amper-hours will be collected at twice the speed as described above with a total of 16 cells as described above. Of course, 16 cells use higher voltages for the same current. Batteries to obtain large amounts of product are expected to use at least 5 amps, or 10 or more amps. Regarding the number and amperes of cells used, the procedure is preferably performed in an amount of 50 g or less of dimethyl maleate of 25 g or less per cell-amperage so as not to exceed 100 g of dimethyl maleate per cell-amperage. We will use the maleate and current of (battery-amperes), which means the number of batteries × amps and is equal to the amperes-hours per hour.

This electrolysis can be affected by a reductive coupling reaction that is different from the common electrode used for electrohydrogen duplexing. Various metal and graphite electrodes are suitable. In general, preferred electrodes are those having a higher hydrogen overvoltage than those of copper. However, electrodes with low overvoltage can also be used. Materials that can be used as the cathode are graphite, graphite felt, mercury, copper amalgam, gold, copper, cadmium, tin and aluminum, of which graphite, graphite felt and lead are more suitable. Mercury can be an effective cathode electrode but is unsuitable for general flow cell configurations because it is in a liquid state. It has been found that graphite electrodes give the best results, whether flat or felt. Surprisingly, it is an advantage of this process that very good results can be obtained with graphite electrodes. Graphite is much cheaper than many other cell materials, such as platinum or even lead or cadmium cells, and does not add heavy metals to the solution through corrosion and is also suitable for anodes as well as cathodes.

The present electrolysis can be carried out using alkanols, such as methanol, as a substance which acts only as a carrier for maleate esters and electrolyte salts. Generally industrial methanol without water is well suited for this purpose. Some water obtained in contact with air will generally not have much effect on the results. For example, about 2000 ppm of water in solution has little effect. However, as the amount of water increases, even a small percentage of water can lead to a decrease in selectivity, so this should be avoided and in the presence of water above 5 wt% is very inadequate. If desired, aprotic solvents such as dimethyl formamide, special cosolvents such as dimethylsulfoxide or acetonitrile may be used with the alkanols. Although the use of cosolvents is generally undesirable, there are some special cases where solubility or other factors require cosolvents.

At the end of the electrolysis, the tetraalkyl butanetetracarboxylate product is present in the solution in the electrolysis medium at a concentration of, for example, about 25 wt%. The tetraalkylbutanetetracarboxylate product may be isolated by crystallization from solution and then by filtration. In the case of tetramethyl butanetetracarboxylate (TMBTC) the crystallization is influenced by cooling conditions, for example below 0 ° C, generally from 0 ° C to -10 ° C. The separation process removes the product from the electrolysis medium and also separates the product from unreacted maleate reactants, succinates and by-product alkoxysuccinates. The butanetetracarboxylate tetraester product is then hydrolyzed and purified to yield a butanetetracarboxylic acid suitable for the preservative.

[Hydrolysis of Tetraalkyl Butanetetracarboxylate]

The hydrolysis step of the process of converting tetraalkyl butanetetracarboxylate to butanetetracarboxylic acid includes several hydrolysis steps to obtain a product that has the desired purity and low level of color contaminants to form an acid and a desired purity. It includes.

The implementation method includes the following steps.

1. Filter the TMBTC methanol solution to remove particulates

2. Crystallize TMBTC from solution and separate by filtration or centrifugation

3. Extract TMBTC with water to remove salt

4. Hydrolyze TMBTC to generate BTCA

5. Oxidize BTCA solution to remove color contaminants

6. Crystallize BTCA in aqueous solution and separate by filtration or centrifugation

7. Wash BTCA crystal with water to remove remaining acid

Or 7A. Neutralize sodium hydroxide partially or completely with the same base to remove residual acid and isolate BTCA crystals by filtration or centrifugation

Sometimes it is desirable to provide BTCA in the form of an aqueous solution for use rather than separating and washing with BTCA as in steps 6 and 7 above. Since the remaining acid has a very large effect on color development, removal of such acid is relatively important for a purpose, but in some cases this effect can be canceled or left by subsequent treatment. In the practice, tetramethyl butanetetracarboxylate can be used as a sample of tetraalkylbutanetetracarboxylate which can be used under similar conditions, that is, generally under the conditions using a corresponding alkanol as a solvent. Since TMBTC is very suitable as an intermediate for producing the desired BTCA, it will generally not be necessary to use other tetraalkyl butanetetracarboxylates to produce BTCA. However, tetraethyl butanetetracarboxylate and ethyl alcohol can be used under similar conditions to produce similar results.

Hydrolysis reaction included in the present invention is as follows.

The reaction involves the reaction of water with tetramethyl esters in which the amount of reaction or equilibrium concentration of the reaction depends on the concentration of the reactants comprising water. The reaction proceeds to the right, where the conversion of tetramethyl butanetetracarboxylate increases with increasing water concentration. Often, the hydrolysis reaction uses a large amount of water, for example about 10 wt% of the hydrolysis solution for esterification. This reaction is also generally affected by a slightly dilute acid catalyst concentration, for example 1-5 wt% acid. In the case of tetramethyl butanetetracarboxylate, it has been found that the reaction rate is very low at low ester and acid concentrations. This slow rate will require batch reaction times of 20-24 hours. In the present invention, it was found that high concentrations of TMBTC and acid catalyst allow relatively short batch reaction time (about 4-5 hours) and excellent reaction rate. In this reaction, BTCA is present at 20 wt% or more, i.e. 25 to 35% or more of the hydrolysis reaction mixture. Acids such as sulfuric acid are used in amounts of at least 5 wt% of the reaction mixture and at least 10 wt% of the water present in the hydrolysis mixture. In the case of a total hydrolysis mixture, it is advantageous to have at least 1 g equivalent of acid per kg of hydrolysis mixture. To increase the effect of the acid it is advantageous to limit the amount of water present. However, water is a reactant of hydrolysis and must be met for this purpose.

In the practice, a preferred limited amount of water is initially used, and when water is used in the reaction or removed by distillation, it is added to generally maintain the initial amount of water. During the hydrolysis, methanol was removed by distillation to remove the product and proceed with the reaction and water was distilled along with methanol. During hydrolysis, a relatively large amount of water is used. For example, when the amount of water initially added was 260 parts, the total amount of water added was 1454 parts and the amount of water distilled and removed during the reaction was 1438 parts.

The present invention is limited to about 50% or about 50% to about 75% of the amount of water in the hydrolysis mixture, wherein a large amount of additional water is removed during the hydrolysis process, at least 3 to 4 times greater than the original amount of water. A process that is added to replace water. This controlled water is used in conjunction with relatively high acid concentrations, such as 10 wt% or more of the water present. For the total reaction mixture, a minimum of 0.6 g equivalent acid per kg of reaction mixture is preferred, preferably about 1 g equivalent acid more preferably 1.5 g equivalent acid.

The invention is illustrated by the following examples. More detailed embodiments of the present invention are provided in several hydrolysis processes involving the hydrolysis of tetramethyl butanetetracarboxylate as detailed in Examples 8-13 and the process is summarized in Table 5. The data of Examples 10-13 were also used in the graphs illustrating the effect of temperature and concentration on the rate of hydrolysis as shown in FIGS. 3 to 5 and more details are as follows.

[Electrolysis Hydrogen Duplexing]

Example 1

Electrolysis was carried out in a jacketed resin pot using water as the medium and the presence of 22% dimethyl maleate based on the weight of the electrolysis medium as the second phase. The cathode pole was lead and the anode pole was platinum. A mixture of tetrabutylammonium nitrate and tetrabutyl ammonium hydroxide was used as electrolyte and electrolysis was carried out at a current density of 30 milliamps per square centimeter of the cathode surface. Electrolysis began at basic pH, but became more acidic due to the hydrolysis catalyzed by a base where dimethyl maleate became monomethyl maleate. The pH quickly approached about 4. The analysis showed 22 parts by weight of dimethyl succinate, a simple reduction product of 47 parts by weight of tetramethyl butanetetracarboxylate to starting maleate. This corresponds only to the selectivity of 2.1 parts by weight of hydrogen dimer to 1 part by weight of succinate material. It is clear that acidic conditions cause a large loss of simple reduction reactions and that even the use of basic electrolytes did not prevent the development of acidic conditions. Analysis of the electrolysis medium also shows the presence of unreacted dimethyl maleate in the ratio of 41 to 47 parts by weight and 22 parts by weight of the hydrogen dimer and succinate. Therefore, this reaction has only had relatively low conversion. Similar results were obtained by different reactions with aqueous media using graphite or lead cathode electrodes, platinum anode materials and non-isolated resin pot cells at various current densities of 30-70 mA / cm ² . The electrolytes used include tetrabutylammonium nitrate, tetraethyl ammonium P-toluene sulfonate, tetra butylammonium hydroxide and tetrabutyl ammonium sulfate. The ratio of hydrogen dimer to succinate varied from 2.1, reported above, to 0.43, the high value obtained when excess tetrabutylammonium hydroxide is present to maintain high pH.

Example 2

Electrolysis was carried out using non-isolated resin pott cells as described in Example 1 but with methanol as the medium. Various electrolysis results of the quaternary ammonium electrolyte in various conditions and electrodes are shown in Table 1. In the table, various values for dimethyl maleite (DMM) dimethyl succinate (DMS) and tetramethyl butanetetra carboxylate (TMBTC) were reported as analyte figures that can be compared to provide a ratio of the materials recorded. The ratio of TMBTC to DMS ranged from 2.55 in runs 1 to 0.89 in runs 3 and the results were better than with water as solvent. Runs 5 and 6 used 90% methanol and 33% methanol, respectively, and the result was worse than that obtained with undiluted methanol.

TABLE 1

x 90% methanol in water

xx 33% methanol in water

Abbreviations in Table 1 and in the specification will be named and used as follows.

DMM is dimethyl maleate; DMS is dimethyl succinate; MeODMS is methoxydimethyl succinate; TMBTC is tetramethylbutane tetracarboxylate; TBAFB is tetrabutylammonium tetrafluoroborate; TBAH is tetrabutylammonium hydroxide; TEAT is tetraethylammonium-P-toluenesulfonate; P1 is DMM wt% payload in solution; CD is the current density of mA / cm ² .

Example 3

The non-isolated resin potted cell in Example 1 was used with methanol as the medium and with a low concentration of metal salt as the electrolyte and the results are reported in Table 2.

TABLE 2

Good selectivity was obtained by using alkali metal salts in sodium acetate and methanol, as seen from the ratio of hydrogen dimer to succinate (88/12) 7.17 in Example 1, and high conversion was achieved by dimethyl maleate in the resulting solution. Obtained as shown by low or zero values for.

Example 4

Electrolysis was carried out in a small flow cell of parallel plates designed to have a gap between the electrodes of about 1 mm and a cathode of 19 cm ² .

The outflow through the cell was about 1 L / min. The cell was connected to a jacketed reservoir cooled by tap water (at about 15 ° C.). Electrolysis was carried out with dimethyl maleate and about 1% by weight of selected metal salts and the results are reported in Table 3.

While there is a significant variation between these and other results in the cell, the ratio of dimer to high succinate of 3.5 was obtained using alkali metals in methanol.

Example 5

Electrolysis of dimethyl maleate was carried out in methanol using various electrolytes. The electrolysis cell was a 150 ml jacketed resin pot equipped with a 25 cm ² graphite plate electrode (5 cm x 5 cm x 0.5 cm) and a magnetic stirrer on the surface of the cathode electrode facing the anode. The cell was cooled with tap water (15-20 ° C.). Power was usually supplied at a constant power at 1 amp. The main battery was charged with 75 g of methanol and 25 g of dimethyl maleate 1 to 2 g of an auxiliary electrolyte. Electrolysis was started and continued until nearly all of the dimethyl maleate was consumed as quantified by gas chromatography. Selectivity to the three main products (as a percentage of the three products) was measured by gas chromatography and can be seen in the bar graph of FIG. It will be noted that high TMBTC selectivity is obtained with alkali metal acetates, in particular lithium and sodium acetate. The results described are generally based on comparable processes. Other results may be obtained under different conditions, while the illustrated results show that high selectivity can be obtained, which shows that it can be obtained under standard conditions, in particular with sodium acetate, in other processes. Despite the very low selectivity with CaCl ₂ , halide anions could be used. Higher levels of methoxydimethyl succinate indicate that methoxylation of catalysis, competing with CaCl ₂ and LiCl, has occurred.

Example 6

The electrolysis used various cathodes as in Example 5, and sodium acetate was used as the electrolyte. The selectivity obtained for the three main products is shown in the bar graph of FIG.

Example 7

High flow cells were used to prepare tetramethyl butanetetra carboxylate by electrolysis with sodium acetate as electrolyte. The cell had eight cells but was later modified into 16 cells by Electro Syn Cell (Svenska Utrekling Saketbologet, Swedish National Development Company).

The cell has a plastic film between a 500 cm ² graphite plate with a spacing of about 1 mm and a pole that aids in flow dispersion. The cells were connected by centrifugal pumps, 18.93 liter (5 gallon) reservoirs and polyvinyl chloride pipes in stainless steel heat exchangers. The system contained about 8 kg of dimethyl maleate, 15 kg of methanol and 200 g of sodium acetate. The solution was circulated through the cell at about 75.7 L (20.2 gallons) / minute. The cell was operated at 12.5 amps (65-90 volts) for about 7.5 hours (16 cells).

Typical analyzes of the resulting solution were 25% tetramethyl butanetetracarboxylate, 5% dimethylsuccinate, 5% methoxydimethyl succinate, 5% dimethylmaleate and the remainder methanol.

In more detail, the cell was modified to operate in a bipolar fashion with an end plate attached to the power supply. The above mentioned amounts of dimethyl maleate, methanol and sodium acetate were put into the reservoir as indicated by DMM, MeOH and NaOAc (recorded in Table 4 below). The circulation pump is activated and 75.7-79.5 The sample was uniformed by circulation at a flow rate of (20-21 gallons) / min. Samples were typically taken at 0 hours with low charge DMM because they were diluted by the remainder of the previous run. The electrolysis was performed at 25 mA / cm ² until the power supply was activated and the power was cut off at the recorded time. Samples were taken and the assay results were reported in% of the reaction mixture with the number of g of DMM reacted and the selectivity to the product measured therefrom. The results of three different runs are reported in Table 4. High product selectivity of 83% was obtained in the third run and, as with other runs in methanol, was accompanied by a high conversion of dimethyl maleate of at least 95% based on the amount of maleate reacted and the maleate in the product sample analysis. Comparison of Examples 1 and 8 with electrolysis of 8 cells and Examples 2 and 3 with electrolysis of 16 cells showed that increasing the cell reduced the reaction time and also the amount of methoxymethyl succinate product. It shows that the selectivity for the desired hydrogen dimer is increased. In general, the production of by-products produced for chemical reactions is not only by limiting the maximum amount, or by lowering the reaction temperature, but also by operating throughput with a high electrolysis cell compared to other methods of shortening the capacity or reaction time of the reservoir. Can be reduced.

TABLE 4

Hydrolysis of Tetraalkyl Butanetetracarboxylate

Example 8

To one flask was added 43.8 g (0.151 mol) of tetramethyl 1,2,3,4-butanetetracarboxylate, 589.3 g of deionized water and 0.79 g (6.8 mol) of phosphoric acid. The flask was fixed with a stirrer and distillation head. The flask was heated to distill the water and methanol mixture. After conversion the amount of methanol collected was analyzed. Further 408.9 g of water was added at 2.75 h. An additional 2.37 g of 85% phosphoric acid was added at 4.2 hours. At 7 o'clock 389.7 g of water were added. The reaction capacity was heated again at reflux overnight. Distillation continued later. An additional 254.8 g of water was added at 50.3 h. Distillation finished at 54 o'clock. Accumulated methanol analysis showed 86% conversion of the ester to the free carboxylic acid. The pot reaction temperature was 100 ° C. except for the first 20 minutes.

The procedure described above has been carried out over several days since it has to be reacted for a long time due to the low reactivity of tetramethyl-1,2,3,4-butanetetracarboxylate. Essentially, the reaction consisted of 6.9 wt% tetramethyl-1,2,3,4-butanetetracarboxylate, 0.5% phosphoric acid and 92.6% water. Methanol was continuously distilled from water and methanol reactant. Water was added to replace the distilled one. The reaction temperature was 100 ° C. Under these conditions the conversion of ester to free acid was 90% for 54 hours. This process is summarized in Table 5 as Example 8.

Example 9

Benzenesulic acid was used as a hydrolysis catalyst. One 28.5 g of TMBTC, 502.2 g of deionized water and 1.1 g initial amount, and 3.3 g after 2.2 g of time after 1.1 hours were added to the four neck flask of 6.6 g of benzenesulfonic acid. Methanol was removed with it being formed. Water was added at 432.6 g and 403.0 g at 1.05 and 2.25 hours, respectively. Three distillation cuts were collected. They were 316.6 g at 1 h, 450.9 g at 2.2 h and 520.6 g at 3.6 h. At this point the reaction was stopped. The cut analysis showed a 60% response after 3.6 hours.

Example 10

Sulfuric acid was used as a hydrolysis catalyst. In a 500 ml four-necked flask fixed with a distillation head, a condenser and an addition funnel, 68.4 g (0.235 mol) of tetramethyl 1,2,3,4-butanetetracarboxylate and 129.5 g of water were added. This mixture was heated at 100 ° C. 20.6 g of concentrated sulfuric acid (95.5%, 0.201 mol) was added. In almost every run the pot temperature was 103 ° C. Methanol and some water formed by this reaction continued to strip from the reaction. Water was added continuously to maintain a certain amount of reactant. The reaction was complete 99.8% after 5 hours.

Example 11

The hydrolysis reaction of Example 10 was repeated except that less sulfuric acid catalyst was used. The reaction was 68.7 g (0.236 mole) tetraester and 142.8 g water. This mixture was heated at 100 ° C. and then 6.73 g of concentrated sulfuric acid (95.5%, 0.065 mol) was added. This procedure was carried out in the same manner as in the above example using 20.6 g of acid. A conversion of 97.0% was obtained after 8.5 hours at 101 ° C. The example using 20.6 g obtained a conversion of 97% after 3.1 hours. In this example the conversion was only about 94% after 6.5 hours.

Example 12

The conditions of Example 10 were repeated except that the temperature of the reaction volume was maintained at a control pressure of 58.7 pKa at 54.0 KPa (405 Torr) at 80 ° C. To the instrument described in the previous example was added 68.4 g (0.236 mole) of tetramethyl 1,2,3,4-butanetetracarboxylate and 129.4 g of water. It was heated to 78 ° C. and then 20.4 g of concentrated sulfuric acid (95.5%, 0.199 mol) was added. The reaction pressure was adjusted to maintain a reaction temperature of 80 ° C. The reaction was 94% complete after 9.4 hours. The same experiment, with the exception of the reaction temperature of 103 ° C., achieved 94% conversion after 2.7 hours.

Example 13

Hydrolysis was carried out in accordance with the procedure of Example 1 except that 10.3 g of 95.5% (0.100 mole) sulfuric acid was used. A reaction time of 5 hours yielded a conversion of 94.7%.

TABLE 5

* Phosphoric acid as catalyst

** Benzenesulfonic Acid as Catalyst

As used in typical hydrolysis reactions in the tables of Examples 8 and 9, large amounts of water and low acid concentrations were used and very slow reactions occurred. In Example 10 a small amount of water and a high concentration of acid were used which provided about 1.83 g equivalent acid per kg of reaction mixture and the reaction proceeded very fast. The acid concentration in Example 11 was still quite strong but much slower than in Example 10. From the reaction rates of 10, 11 and 13, the constant rate of reaction was plotted against sulfuric acid concentration as described in FIG. It can be seen that the reaction rate increases linearly with increasing acid concentration. The prediction from this result is expressed by the following equation.

K = 0.580638 g (equivalent H ₂ SO ₄ /kg+0.045685)

Using a high concentration of acid yields a good reaction rate, such as at least 1 g equivalent of H ₂ SO ₄ per kg of reaction mixture, and is sufficient to complete the batch reaction within about 6 hours with a reaction rate constant of at least 0.6 hours. There is an advantage in obtaining the reaction rate. It is more preferable to use an acid concentration of 1.5 g acid equivalent or more per kg of the reaction mixture.

In FIG. 4 hydrolysis at two different temperatures (Examples 10 and 12 above) was plotted against the reaction time by the equivalent of unhydrolyzed ester per kg of reaction mixture. The result of the semi-log paper is the reaction at 103 ° C. (Example 10), which is somewhat completed in 4 hours or more, and the reaction at 80 ° C., which is not completed after 10 hours because the time required to complete the reaction is very long (Example In both cases, a constant decrease is shown. These results indicate that the use of diagrams is very important for relatively high reactions, such as near or above 100 ° C or above 95 ° C, in order to have good reaction rates. Hydrolysis at temperatures and pressures of 100 ° C. or higher is preferred.

In FIG. 5, the hydrolysis results of Examples 10, 11 and 13 showed reactions using different molar ratios in which the TMBTC ratios for H ₂ SO ₄ were 1.17 (Example 10), 3.61 (Example 11) and 2.3 (Example 13). Plot on semi-log paper for. The reaction with the TMBTC / H ₂ SO ₄ ratio of 1.17 was originally completed within 5 hours, while the TMBTC / H of 3.61, which indicated that it took more than 9 hours to reach the 97% conversion line (star line below 0.1 line). Other reactions with a tendency to ₂ SO ₄ reactions were slower. These results indicate that it is useful to use a relatively low TMBTC / H ₂ SO ₄ molar ratio not exceeding about 2.

Moderate reaction rates and short reaction times have the advantage of enabling adequate production rates with the equipment used. It is conceivable that batch runs of 8 hours or less, such as 6 hours or less, are usually very useful to meet the experimental schedule. As the reactants, the hydrolysis reaction mixture with TMBTC contains water and methanol, so by removing methanol and some water later in the reaction, 103 ° C is the best that can be obtained during most reactions, even if the temperature is not 111 ° C or much higher. Temperature. Further temperatures can be obtained using pressure or by adjusting the composition. The amount of methanol in the reaction mixture can be maintained at around 100 ° C. if methanol is to be accumulated before being removed by distillation, thus affecting the reaction temperature. It is therefore desirable to provide sufficient heat to distill methanol from the reaction mixture at a suitable rate. Since methanol is a product in the equilibrium reaction, it tends to delay the reaction, which is an additional reason for removing methanol. Upon distillation, water is removed at a relatively high rate and replaced with additional water to provide the water needed for the reaction. The overall water supplied during the hydrolysis process is generally at least four times the average amount present during the hydrolysis process.

BTCA samples generally contain some chromophores. These materials are the source of the color that gives the BTCA color, ie yellow, or the color that appears when BCTA is heated. For testing, the sample was heated in a vacuum oven for at least 24 hours to give color to the sample. The chromophore can be neutralized or almost eliminated by treatment of peroxides. This process involves adding a small amount of hydrogen peroxide to the BTCA hydrolysis solution and stirring it at 50 ° C. for a short time, for example 30 minutes, to allow for a sufficiently high temperature, for example to allow the reaction to take place sufficiently. The mixture was then refluxed by heating to 106 ° C. to decompose excess peroxides and peracids. The reaction may take a long time in the absence of metal contaminants or other substances that will promote degradation, but could be completed in approximately 30 minutes.

Example 14

In this example, the peroxide treatment following the hydrolysis of TMBTC has been described. A 500 ml four-necked flask was charged with a mixture of 86.2 g (0.297 moles) of TMBTC and 26.0 g (0.265 moles) of concentrated sulfuric acid (95.5%) in 163.3 g of mole. The mixture was mechanically stirred and heated to the extent that hydrolysis of the tetraester occurred. The mixture of methanol and water was continuously distilled out of the flask. Water was added to keep the mass constant. After 7.5 hours the hydrolysis reaction was complete. 161.6 g of a bright yellow hydrolysis solution containing BTCA was recovered. 100.0 g of aliquot hydrolysis solution was placed back into a 500 ml flask. 1.02 g of 30% hydrogen peroxide (H ₂ O ₂ ) was added thereto. The solution was slowly heated to reflux at 110 ° C. This solution was immediately tested for the presence of peroxides with iodine-starch test paper. This solution showed a negative test after 9.75 hours of reflux. In this process the heating for reflux was heated very slowly to give enough time for the reaction to occur in the range of 50-60 ° C.

[Characteristics of Butanetetracarboxylic Acid]

Example 15

Several different BCTA samples were evaluated for color according to the following test. Parameters and results are listed in Table 6.

Color levels of BTCA samples were evaluated by spectrophotometry. Some samples were heated to 89 ° C. in solid state before testing. Color determination was done in a 10% sample solution in aqueous KOH Na-ion water. UN / Visible Spectrum (200 nm to 800 nm) was obtained for each sample with an HP8451A diode array spectrophotometer. Absorbance measurements were recorded at a single wavelength of 400 nm in the visible range. Color is the sum of several wavelengths, while absorbance at 400 nm provides a secondary measurement of each solution. BTCA alone does not absorb light at 400 nm.

TABLE 6

Absorbance at 400 nm of BTCA Aqueous Solution

In Table 6, BTCA from this method is provided as base line and designated as Factor 1. Other rates were calculated from the ratio of absorbance of the sample compared to baseline BTCA. The results according to the pilot plant BTCA show that it is improved by recrystallization, peroxide treatment or neutralization of residual sulfuric acid. Other results on laboratory BTCA show that it is improved by peroxide treatment. The benefits of extracting TMBTC with water have been shown. This result also indicates that higher purity of color can be obtained than that obtained from a commercial sample, which is a sample after neutralizing sulfuric acid showing only 40% of the heat absorbed commercial sample absorbance. The commercial sample of # 1 (Aldrich Chemical, Inc.) is extracted with the product obtained by oxidative decomposition of tetrahydrophthal anhydride. The results clearly indicate the benefits of peroxide treatment. However, in addition to the above results, some of the above water and other samples according to the present method will have an effect that is excessive as other preservatives because of the excessive effect as a preservative. The pilot plant BTCA generally had more impurities than those represented by the pilot plant BTCA. Filtration of TMBTC precursors is poorly separated and should be better filtered and separated.

The laboratory BTCA was made on an experimental scale by a process comprising the same steps of making the experimental pilot plant described above, but as shown in Table 6 some modifications were given and no acid neutralization step was used.

The pilot plant BTCA contained residual H ₂ SO ₄ as expected in the aqueous solution by filtration. Titration with NaOH solution neutralized the amount of H ₂ SO ₄ . A commercial BTCA sample (Aldrich Chemical) in a 12% solution was determined to have a pH of 1.68 at 25 ° C., 1.76 at 24 ° C., and 1.85 at 22 ° C. A titration of 12 wt% pilot plant wet cake solution contained 4.06 wt% sulfuric acid. 785.6 g of pilot plant BTCA samples were slurried in a flask with 202 g of deionized water. The calculated 31.88 g of sulfuric acid required 26 g of NaOH for neutralization. 51.4 g of 50% NaOH solution was slowly stirred at 80 ° C. and added to the slurry to add stoichiometrically equivalent amounts of sodium hydroxide. The slurry was cooled to 35 ° C. and filtered to give 436.3 g of BTCA crystals. The pH of the caustic treated 12% solution of BTCA crystals was 1.80 at 24 ° C. This material is referred to as "after neutralization" in Table 6, "complete BTCA" in Table 7, and "Monsanto BTCA" in Table 8. Slurries are more suitable for neutralization solutions to avoid loss of high yields due to BTCA solubility. Commercially, it would be desirable to reuse the filtrate in subsequent batch neutralization processes to reduce BTCA losses.

Example 16

Another method is to evaluate the color development of BTCA by heating. At this time, 10 g of BTCA was dissolved in 93 g of ethylene glycol and refluxed at 198 ° C. for 24 hours. Then the absorbance at 400 nm was measured. The results are shown in Tables 7 and 8. Ethylene glycol was used as the baseline and was assigned a rate of 1.

TABLE 7

Heat discoloration test

Effects of different stages

Table 7 shows the progress of the various steps. Omitted steps indicate that the sample is dark in color both before and after heating.

TABLE 8

Heat discoloration test

BCTA in ethylene glycol

1.heat at 198 ℃ for 24 hours

2. Processing in the lab after purchase

In Table 8, the Monsanto BTCA produced by the present invention, with or without peroxide treatment, was compared with a commercial sample. Monsanto BTCA # 6, which had been treated with peroxides, was superior to that of commercial samples and was superior to the Monsanto samples without peroxide treatment. Commercial BTCA # 2 is a source unknown commercial sample. The literature on peroxide treated Aldrich BTCA refers to the treatments carried out and described in Table 8 rather than to say that commercially useful materials have been treated with peroxides.

Example 17

6 is a reaction flow diagram illustrating the various unit processes and flow streams involved in preparing butanetetra carboxylic acid from tetramethyl butanetetra carboxylate according to an exemplary embodiment of the present invention.

The method is particularly useful for preparing carboxylic acids from tetramethyl butanetetracarboxylic acid salts obtained as products in electrohydrogenation, as described herein. Tetramethylbutanetetra carboxylate (TMBTC) obtained from the electrohydrogenation reaction may be provided as a methanol solution containing 24-25% by weight of TMBTC.

6, the TMBTC solution in the feed storage tank 101 is pumped as stream 1 through the filter 201 and the polishing filter 204, and injected into the crystallizer 202 as stream 2. The TMBTC solution supplied comprises a small amount of black particles, possibly graphite obtained from electrode corrosion in an EHD cell. Particles can cause the formation of a rag layer during the extraction step that is part of the process of the present invention, where the separation of oil and water phase in the extraction step is significantly improved by removing the particles in advance. In the absence of particles substantially, separation does not require much time, and therefore it is advantageous to filter when particles are present. Of course, filtration would not be very useful if the particles were not present, such as in the case of TMBTC being produced using metal electrodes or by methods other than EHD.

In the first filter, 201, filtration is used to remove particles, for example, by using diatomaceous earth to feed storage tank 101 and using them to remove the particles, which are stirred to maintain the suspension. This is to provide a sufficient amount of diatomaceous earth so that a layer of about 1.27 cm is formed on the filter cloth in filter 201. The filtrate obtained from 201 is pumped back into filter 201 until a clean and clear filtrate is observed, after which it is pumped into a polishing filter 204 equal to 6 microns or finer filter paper and later pumped into crystallizer 202. The filtered solution contains 25wl% of TMBTC. TMBTC is crystallized from the solution by cooling to 10 ° C and stirring.

Crystallization can occur at temperatures below 0 ° C, but the recovery increases considerably as the temperature drops from 0 ° C to -10 ° C. There may be some improvement at temperatures below -10 ° C, but this is offset by cooling costs and time required to achieve cooling as available chillers. Usually a temperature of -10 ° C is preferred, but a temperature of -15 ° C or -20 ° C or lower may be used. At -10 ° C, about 88% of TMBTC crystallizes out of solution. TMBTC recovery is increased by adding water to the methanol solution containing TMBTC. When water is added to the amount of solution about three times, that is, to about 75% of water, the TMBTC recovery is improved to about 98% at -10 ° C. However, if 75% water is added, it may be more convenient to use a smaller amount of water, that is, 25% water, since a large volume must be used in the crystallizer vessel, and the recovery is somewhat reduced to 93%. .

The crystallization device 202 is maintained under nitrogen as a preventive measure due to the heating property of methanol. The crystal and liquid mixture from the crystallizer is sent to filter 301 by stream 3, where the crystals are separated from the liquid. The crystals are melted by heating to about 75 ° C. or higher and the melt is sent to extractor 401 as stream 4. In the extractor, from tank 403, deionized water as stream 6 is mixed with the melt and separated into water and oil phase to remove salts and other solution components.

The temperature is maintained at about 70-76 ° C. to prevent solid formation in the extractor. TMBTC melts within a temperature range of about 55-60 ° C., but the meso (MESO) -isomer has a melting point of 76 ° C. This temperature is preferred to prevent solid formation. The extraction is usually done by using the same amount of TMBTC and water, ie, by adding 171 parts of TMBTC and 175 parts of water while heating to 75 ° C., starting shaking and continuing for about 30 minutes. When shaking stops, phase separation begins. Agglomerated particles are separated in a few minutes at 75 ° C. but some particles are present, and a small rag layer is formed between the lower oil TMBTC layer and the upper water layer. Typical separations are 17.9 parts of a small piece of bed, 141.9 parts of an oil layer at the bottom and 184.6 parts of an upper water layer. The bottom oil layer is sent to the TMBTC oil hold tank 404 by stream 7. A small layer of stream 8 is stored in tank 405, where the scrap is slowly separated and the oil can be recovered as stream 28, sent back to the extractor, or slowly separated, and periodically hydrolyzed 501, while water is treated in stream 13. In the extractor 401 the water layer contains about 1% TMBTC and is collected from stream 9 for dispersion. From 404 the oil layer is sent back to the extractor by stream 11 and the extraction is repeated using 147 parts of deionized water. About 136.8 parts of the TMBTC oil layer from 404 are sent to hydrolysis unit 501 by streams 10 and 11. The hydrolyzer is a double-jacketed glass-lined vessel equipped with a stirrer and a cooler, which is also attached to a device for heating the ampoule. Hydrolysis proceeds with about two times the amount of TMBTC and water and a high concentration of inorganic acid catalyst. Methanol is also distilled from the reaction mixture to proceed with the reaction. To 136.8 parts of TMBTC, 127 parts of water are added via stream 15 and stirred. Add 38.1 parts of sulfuric acid from two sources: BTCA crystallization filtrate tank 702 and sulfuric acid reservoir 502. To provide the acid, the hydrolyzer is charged as a solution of 203 parts from tank 702 via strip 24 and 1.1 parts of fresh sulfuric acid from sulfuric acid reservoir 502 via stream 15. In addition to sulfuric acid, the filtrate provides a BTCA heel from BTCA crystallization and separation, and using this heel provides almost stoichiometric recovery of BTCA. The BTCA filtrate contains 17% BCTA by weight at room temperature. Hydrolysis is completed by reaction for about 4.5 hours stripping methanol at the same time, or by heating the flux until equilibrium is reached and then methanol strips. In the latter process, about 76% of the hydrolysis takes place within one hour, which is continued by distillation of methanol and water over a three hour period while adding a certain amount of water to replace the distillate. Appropriate addition rates maintain pot temperature at 103.5 ° C. However, at the beginning of distillation, the pot temperature is lowered by high concentrations of methanol and water is added at 5.57 parts / minute until the temperature reaches 103.5 ° C. After 3 hours of distillation, the addition of water is stopped and distillation is continued until the pot temperature reaches 111 ° C. The distillate of the hydrolyzer at 503 can be treated as water and small concentrations of methanol. In hydrolysis unit 501

Hydrolyzed masses contain several colors or objects that produce colors. They are significantly reduced by a simple oxidation process. Oxidants that can oxidize color and objects that produce color and do not leave possible color contaminants are suitable for use. Hydrogen peroxide is very good for this use.

The reaction with hydrogen peroxide proceeds in hydrolyzer 501 after the hydrolyzed solution is cooled to a temperature between 45 ° C and 55 ° C. To the hydrolyzed solution present at about 308 parts by weight, 2.5 parts by weight of 30% hydrogen peroxide in water is added via stream 18 from container 505. The solution is stirred at 45-55 ° C. for about 30 minutes. The temperature is then raised and the solution refluxed for 30 minutes or, if necessary, to decompose excess peroxides or peracids present. The absence of peroxides and peracids is determined by testing with acidified starch-iodine paper.

Hydrolyzed and oxidized 301.7 parts by weight of reactant from hydrolyzer 501 is pumped through stream 17 into BTCA crystallization system 601 as hot liquid. The crystallizer is a tank made of glass lined with chillers and agitators. The liquid as top water is cooled to about 22 ° C. and the product crystallizes.

When crystallization is complete, 310.7 parts by weight of crystallization material is transferred to filter 701 as strip 20. Since the aqueous sulfuric acid solution is corrosive, the filter must be corrosion resistant. Suitable filter media are 3-6 micron screens or filter paper. The mass in the crystallizer is divided into 105 parts by weight of BTCA crystals and 202 parts by weight of the filtrate. The filtrate is sent to tank 702 as stream 22 and sent back to the hydrolyzer as stream 24 for recycling as catalyst and heel.

In the crystal washing step, 24.7 parts by weight of deionized water is added to the filter by stream 21 and slurried again with BTCA. 30 parts by weight of the finally obtained filtrate is preferably sent directly to filter tank 702, or discarded as stream 29. BTCA crystals are either dried by hot air or packaged for shipment in accordance with the reported water analysis. In repeated production runs, the filtrate from BTCA is circulated back to the next batch filtration, so it can be expected that BTCA recovery is almost quantitative. The filtrate contains 16.5% of BTCA. Problems with impurities can develop if corrosion occurs or by-products occur in the filtrate. If the quality of the BTCA is affected, the problem can be minimized by removing the portion of the filtrate after each batch treatment. If consideration of filtrate quality requires the treatment of most filtrates, it is desirable to use a lower temperature than the ambient temperature for BTCA crystallization to increase the percentage of BTCA crystallized. Another alternative is to leave BTCA in solution and supply it for use in solution form. As described herein above, the BTCA produced by the present method comprises a significant amount of residual acid catalyst. In this process (not illustrated in the process diagram of FIG. 6), the BTCA product is treated as a base to remove the acid by neutralization. In order to completely neutralize the acid, it is preferable to provide sufficient base such as NaOH, but partial neutralization may also be advantageous, and bases which are stoichiometric or slightly less than the acid may be used. Excess base may be used, but this tends to make salts with BTCA and causes some loss due to water solubility. In order to avoid unnecessary mass loss of BTCA yield due to solubility, it may be desirable to make a slurry of BTCA using only a small amount of water in the neutralization reaction, where the caustic solution is slowly stirred. The BTCA is then filtered from the slurry into crystalline form.

Although solubility considerations may be somewhat inconvenient, bases can generally be used for neutralization. However, alkali metal hydroxides, in particular sodium hydroxide and potassium, are convenient and readily available. Other known methods of removing acid contaminants can be used, which include ion exchange resins. In water, given the relatively high solubility of BTCA, the filtrate is saved in order to return to the subsequent neutralization batch and to use cooling to ambient temperature or as low as possible for separation. It is preferable. In some uses for BTCA, the use must be done in a controlled pH environment or otherwise include neutralization of residual acids, so neutralization is not necessary as part of the BTCA preparation process.

Table 9 is a mass balance table describing the reflected parts by weight of various components in the stream of the reaction flow chart of FIG. 6 when the inventive method is carried out in accordance with the above description and the feed materials as shown in the reaction flow chart and table. . In this table, DMM stands for dimethyl maleate, DMS stands for dimethyl succinate, and MeO-DMS stands for methoxy dimethyl succinate.

TABLE 9

For the hydrolysis step of the process of the present invention, a strong acid is a highly dissociated acid in the aqueous medium. Inorganic acids such as sulfur phase and phosphoric acid, and eutectic acids such as benzenesulfonic acid and P-toluene sulfonic acid may be used. Hydrochloric acid may also be used, but there are disadvantages due to volatility, loss of volatility, corrosiveness of the equipment, and the like. The use of sulfuric acid is chosen because of its good use, low efficiency, low cost and good utility.

Example 18

The test is conducted to determine the effect of temperature on the degree of recovery of tetramethyl butanetetra carboxylate from methanol and the solubility of the compound in methanol at a temperature within the range of interest. The starting concentration is about 25% of the TMBTC compound. The results are reported in Table 10.

TABLE 10

Example 19

The methanol solution containing TMBTC and various impurities was separated by crystallization and filtration to obtain 33% of crystals and 67% of filtrates. The distribution of various components between crystals and filtrates was determined at 10 ° C and the results are reported in Table 11. done.

TABLE 11

At lower temperatures from the results in Table 10, the TMBTC recovery significantly increased, producing the best results at the lowest temperature shown -11 ° C. The results in Table 10 show that crystallization is an effective method for separating TMBTC from various impurities as well as from methanol solvents.

Example 20

The effect of water on the recovery of TMBTC from methanol solution was tested using a TMBTC concentration of about 25% and a crystallization temperature of -10 ° C.

The results are reported in Table 12.

TABLE 12

Percent of water is based on total solution, ie 75% water means a solution with 75% water content. It can be seen that the recovery rate increases with increasing water content. Of course, the added water uses space in the crystallizer, thereby reducing the loading capacity of the TMBTC. The use of water in the crystallization medium can enhance the separation from dimethyl succinate, but this depends significantly on the percentage of water used.

Table 13 shows the change in TMBTC composition according to% water content.

TABLE 13

Filtration of TMBTC solutions has been found to be very useful for their effects in subsequent extraction processes, especially when the solutions are obtained by EHD reaction. Filtration is used to filter out insoluble impurities from the TMBTC solution. In special cases, the unfiltered EHD solution occupies about 3/1 of the volume of the extractor with a ray layer that prevents separation. With the filtered EHD solution, the fragment layer accounts for only about 5%. The starting TMBTC solution used here, obtained by the EHD reaction of dimethyl maleate, is characterized by the presence of small amounts of special reactants, by-products and other impurities. Among these substances are included dimethyl maleate, dimethyl succinate and methoxy dimethyl succinate. These substances are very effectively separated by the crystallization and filtration steps, most of which remain in methanol and are transferred to the filtrate, while TMBTC is filtered off as crystals.

As used in this process, water extraction is useful for removing electrolyte salts and some color matter. Some methanol is also removed, but this is not significant because methanol is produced and removed downstream in the hydrolysis step. The TMBTC solution, obtained from the EHD reaction, has a yellow color. This may be from organic chromosome objects or from corrosion of connections such as titanium connections on EHD electrodes.

Water extraction removes most of the color from titanium and partially removes it from organic contaminants. The second extraction seems to remove color beyond that removed by the first extraction. However, the number of extractions used depends not only on the time and efficiency of the extraction process but also on the degree of contaminants. In addition, extraction can be applied as appropriate in connection with subsequent oxidation treatments that can sufficiently remove color or color-forming material.

Extraction also removes salts such as sodium acetate. Water extraction is very appropriately performed as the ester to be purified because tetramethyl butanetetra carboxylate has very limited water solubility. In comparison, butanetetracarboxylic acid, a downstream hydrolysis product, has a very good degree of water solubility and thus does not aid in effective extraction. As used herein, the term "extraction" means washing TMBTC with water to extract and separate impurities therefrom, while TMBTC itself does not dissolve in the water system. For extraction, a method of effectively mixing the TMBTC with a water system and then separation (method) can be used. Rather than the batch system illustrated here, a counter-current-system can be used for systems in which streams are mixed and separated. There are several possible approaches and roots for the preparation of butanetetra carboxylic acids that do not include tetraalkyl butanetetra carboxylates. As a theoretical consideration, since tetraalkyl butanetetra carboxylate contains four electron recovery groups on adjacent carbon atoms, it is considered difficult to hydrolyze. However, using the process according to the invention, it is possible to hydrolyze all four ester groups in almost quantitative yield within a reasonable reaction time to substantially completely hydrolyze tetraalkyl butanetetra carboxylate 100%, It can also be seen that starting with tetraalkyl butanetetracarboxylate in a preliminary reaction mixture such as an EHD electrolysis solution, the overall process can be carried out according to various purification methods, with an acceptable purity and overall yield of 80 It turns out that butane tetra carboxylic acid which is -85% can be obtained.

Claims (11)

A liquid electrolysis medium containing alkanol and alkanol soluble alkali metal carboxylate feed electrolytes corresponding to alkyl groups of dialkyl maleate and dialkyl maleate at a concentration of at least 15% by weight is electrolyzed in a non-separated electrolysis cell to Tetraalkyl 1,2,3,4-butanetetracarboxylate is prepared by carrying out reductive coupling of alkyl malate to produce tetraalkyl 1,2,3,4-butanetetracarboxylate. Manufacturing method. The method of claim 1, wherein the dialkyl maleate is dimethyl maleate, the alkanol is methanol and the tetraalkyl 1,2,3,4-butanetetracarboxylate is tetramethyl 1,2,3,4-butanetetracarboxylate Manufacturing method characterized in that. The process according to claim 1, wherein the electrolysis is achieved with high conversion and little saponification of the dialkyl maleate reactant. The process of claim 1, wherein the electrolysis is at a rate sufficient to maintain the amount of dialkyl-2-methoxysuccinate produced in the chemical competition reaction to be 5% or less of the reacted dialkyl maleate. Manufacturing method. 2. The process of claim 1 wherein the alkanol soluble alkali metal carboxylate feed electrolyte is sodium acetate. The process according to claim 2, wherein the tetraalkyl 1,2,3,4-butanetetra carboxylate is separated from the electrolysis medium by cooling and crystallization. The process according to claim 2, wherein the electrolysis is continued until at least 95% of dimethyl maleate is reacted. 8. The method of claim 7, wherein the non-isolated electrolysis cell is a flow cell having a graphite electrode used at a current density of at least 15 mA / cm ² . The method of claim 8, wherein the current density is in the range of 15-100 mA / cm ² . The method of claim 1 wherein the kilogram amount of tetraalkyl 1,2,3,4-butanetetracarboxylate is prepared within 10 hours. 2. A process according to claim 1 wherein the liquid electrolysis medium contains little water.