DE1618078B1 - Process for the preparation of 3,5-cyclohexadiene-1-2-dicarboxylic acid or 2,5-cyclohexadiene-1,4-dicarboxylic acid - Google Patents

Description

It is known that by partial electrochemical hydrogenation of o-phthalic acid in dilute sulfuric acid as a catholyte at temperatures above 70 ⁰ C 3,5-cyclohexadiene: L, can produce 2-dicarboxylic acid. According to reports from the Deutsche Chemischen Gesellschaft, Vol. 39 (1906), pp. 2933 to 2942, and according to Zeitschrift für Elektrochemie, Vol. 35 (1929), pp. 769 to 779, the reaction on specially prepared, pure lead cathodes in 15 % sulfuric acid carried out. U.S. Patents 2,477,579 and 2,477,580 "describe the disadvantages of lead cathodes and therefore recommend the use of mercury cathodes and 5% sulfuric acid. In addition, U.S. Pat. No. 2,537,304 Devices -described, which are intended to help avoid occurrence of poisoning phenomena. When using lead cathodes, poisoning phenomena occur which are expressed in greatly reduced reactivity. In addition, brown, tarry by-products arise, which discolor the reaction product and make special cleaning processes necessary.

- - Even when using mercury, even if only after a longer reaction time, symptoms of intoxication noticeable at the cathode. It is therefore necessary to keep the mercury running out of the hydrogenation cell to remove, to clean and to supply the purified mercury to the hydrogenation cell again. Man must therefore work with a mercury cycle in which at least one cleaning stage is switched on.

ίο In this way, although the ability to reduce Cathode obtained, however, is a technically complex one

, Working method necessary in order to carry out the electrochemical process over a longer period of time to be able to. Also, as a result of the physiological Dangers when using mercury and especially when operating a mercury cycle observe special safety regulations.

As the following table shows, temperatures above 8O ⁰ G are necessary with the known processes,

ao to achieve a technically usable concentration of phthalic acid in the catholyte.

Solubility of o-phthalic acid (oPS) in 5% sulfuric acid 25th 35 45 T. ( ⁰ C)
""'55 ■ 65 - - 75 85 0.20 0.40- 0.86 1.28 1.78 2.76 4.95 Grams of oPS in 100 g of H ₂ SO ₄ , 5%

A Phthalsäurekonzentration .and _r so one. Depolarisätörkdnzeritratiöri -von Huf '4'15is jmaxirnär "^" 5% ι ¹¹ catholytes is for electrochemical reductions -35 nen quite low. As a result, especially at higher current densities, as are necessary in the interests of high throughput, high space-time yield and correspondingly small apparatus, undesirably high concentration polarizations occur at the cathode. As a result, the current yield and the energy yield (increasing decomposition voltage) are adversely affected, ie reduced. Measurements of the current-voltage curves showed that with decreasing phthalic acid concentration, e.g. B. from 25 to 5 percent by weight, the current-voltage curves against the base curve (absence of phthalic acid, hydrogen evolution) are shifted to more negative values. Likewise, the potential-time :; Curve with increasing "time and higher current density s'q negative."'"~~' ■ · —--—--'- —-----—--- j ^ -., - Another disadvantage of the poor solubility is

in that to achieve high space-time yields

and a high capacity of the hydrogenation cell, the handling of a large amount of liquid - and also Work-up little economical large apparatuses are required.

The high reaction temperatures required with regard to the stability of the 3,5-cyclohexadiene-l ^ -dicarboxylic acid formed are very disadvantageous for the processes mentioned. From the literature (including A. v. Baeyer, Lieb. Ann. D. Chem. Vol. 269 [1892], p. 190) it is known that rearrangements occur in the presence of acids or alkalis, especially at higher temperatures comes in. As a rearrangement product, v. B aeyer and also, inter alia, in U.S. Patents 2,477,579, 2,477,580 and 2,537,304, the 2,6-cyclohexadiene-1,2-dicarboxylic acid is given. According to more recent investigations (Journal of / the American Chemical Society, Vol. 87 [1965], p. 1925), however, the rearrangement product is 2 ₃ 5-cyclohexadiene-1,2-dicarboxylic acid. This finding could be confirmed by UV and nuclear magnetic resonance examinations. ;. :.

It has now been found that 3,5-cyclohexadiene-1,2-dicarboxylic acid or 2,5 »cyclohexadiene-1,4-dicarboxylic acid can be obtained by electrochemical hydrogenation of o-phthalic acid or terephthalic acid in dilute aqueous sulfuric acid at temperatures up to to 8O ⁰ C, especially below 70 ⁰ C and at current densities of 1 to 40 A / dm ² customary using cathode advantageous than previously obtained when the catholyte miscible with water, liquid at room temperature, inert under the reaction conditions ether, carboxamides und / oder.Nitrile added as a solvent. ~. 'At that. Process according to the invention, the electrochemical partial hydrogenation of o-phthalic acid to S ^ -cyclohexadiene-l ^ -dicarboxylic acid with a -phthalic acid concentration-int-catholyte-up to 50%> on. the usual untreated cathodes, e.g. B. from lead, with a higher current efficiency and high yield of S. ^ CjcIöJtexaaien-tlji-dicarboxylic acid up to 99.2% of theory and with a «2, ^ - Gyelohexadien-1,2-dicarboxylic acid content <1 ^ carried out will.

It is known that the addition of organic solvents to the catholyte increases the solubility of an organic compound to be reduced; can be increased using either a conductive salt ■ in a virtually anhydrous system or alcohol in an acidic aqueous electrolyte. However, in the Zeitschrift für Elektrochemie, Vol. 35 (1929), pp. 771, 774 775, it is stated that the electrochemical ^: hydrogenation of phthalic acid with the addition of alcohol takes an unfavorable course, namely one occurs

faster poisoning of the lead cathode than · without the addition of alcohol a. The yield of> 3,5-cyclohexadiene-1,2-dicarboxylic acid also falls noticeably from; among other things, S ^ -cyclohexadiene-l ^ -dicarboxylic acid ester formed as a by-product. . :.

It was therefore surprising that when other organic solvents are used, not only the yield of S ^ -Cyclohexadiene-l ^ -dicarboxylic acid increases, but above all that there is no poisoning or fatigue of the cathodes. It's not even there required for the reduction the already proposed cathode materials, namely amalgamated Lead, cadmium, tin, thallium or bismuth or alloys of at least two of the metals Lead, mercury, silver, cadmium, tin, thallium and bismuth, which can also be amalgamated, or to use pure cadmium, tin or bismuth? because normal lead cathodes can be used with good success without pretreatment.

The cathode fatigue is measured by tracking the cathode potential at constant Current density as a function of time (potential-time curve). While the potential in pursuit the basic curve (without addition of phthalic acid, hydrogen evolution) remains constant, it becomes in the presence of 5% o-phthalic acid in aqueous sulfuric acid becomes more negative over time, and the faster the larger the Current density, and after a certain time it even intersects the base curve. Parallel to this are a increasing hydrogen development and a decrease in the current efficiency with regard to the formation of 3,5-cyelohexadiene-1,2-dicarboxylic acid tied together.

If, on the other hand, one measures the potential-time curve of a catholyte with 20% o-phthalic acid, 5% sulfuric acid, Surprisingly, water and one of the solvents used according to the invention are thus produced determines that the potential-time curve always remains more positive than the base curve. The potential difference is around 150 to 200 mV and even increases slightly over time. Hence in this case one is temporal increasing hydrogen evolution not given. This potential distance between the base curve and The current-voltage curve is sufficient to avoid the deposition of hydrogen in large quantities.

These basic measurements in the two catholyte systems have shown that the Poisoning of the cathodes known from literature, which results in a shift in the cathode potential in negative direction expresses in the presence of the organic solvents used according to the invention does not occur even with a high concentration of phthalic acid. -. .

All these advantages - high phthalic acid concentration at temperatures below 70 ^° C, no poisoning and fatigue of the cathodes, no rearrangement to 2,5-cyclohexadiene-1,2-dicarboxylic acid, no use of conductive salts, high 3,5-cyclohexadiene-1, 2-dicarboxylic acid and current efficiency, high. Space-time yield, easy processing of small amounts of liquid - the new procedure is far superior to the already known processes in aqueous sulfuric acid. .

The table below shows the good solubility of o-phthalic acid in some of the compounds according to the invention solvents used:

Organic solvent system .. (LM): 6.5% H ₂ SO ₄ , 68.7% organic solvent, 24.8% H ₂ O dioxane, g oPS / 100 g LM.
THF, g oPS / 100 g LM ..
DMF, g oPS / 100 g LM.

(THF = tetrahydrofuran,
DMF = dimethylformamide,
oPS = o-phthalic acid.)

T ¹ ^
¹ > C. 35 20th 25th 18.2 16.2 17.6 29.3 26.1 27.9 54.6 47.1 49.2

According to the invention, a mixture of ethers, carboxamides and / or nitriles which are liquid at room temperature and which _; miscible with water, are advantageously completely miscible under the reaction conditions, e.g. B. dioxane, tetrahydrofuran, glycol monomethyl ether, dimethylformamide or acer tonitrile, used with water and sulfuric acid. The content of water and sulfuric acid in the catholyte is kept in such a way that good conductivity is ensured. The sulfuric acid content is generally 0.5 to 10 percent by weight, in particular 2 to 7 percent by weight, based on the total system of water, sulfuric acid, aromatic carboxylic acid and organic solvent. Conductivity measurements have shown that with a content of 3 to 5 percent by weight sulfuric acid in these catholytes, the maximum conductivity is already set. The water content of the catholyte is generally between 5 and 50 percent by weight, in particular between 10 and 30 percent by weight. The process can be carried out with the aromatic carboxylic acid content corresponding to the maximum solubility. However, it is advantageous to keep the concentration below saturation in order to avoid crystallization in metering pumps or supply lines. The concentration of aromatic carboxylic acids is expediently between 15 and 40 percent by weight, depending on the reaction temperature and solvent. The content of organic solvent should be as high as possible in the interests of high phthalic acid solubility. On the other hand, care must be taken that the conductivity of the catholyte is not reduced. The concentration is usually between 20 and 80 percent by weight, in particular between 40 and 70 percent by weight. A mixture of the organic solvents can also be used.

The process can be used for the partial electrochemical hydrogenation of o-phthalic acid and terephthalic acid use. Instead of o-phthalic acid, phthalic anhydride can also be used, the hydrolyzed when dissolving in the catholyte.

Dilute aqueous sulfuric acid is usually used as the anolyte, the concentration of which is preferably increased 1 to 30 percent by weight is set. It is favorable to the concentration of sulfuric acid in the anolyte to choose something higher than that of the catholyte. Usually it is 3 to 20 percent by weight "

The current densities are 1 to 40 A / dm ² , preferably 3 to ^{25 A / dm a} . One of the main advantages of the new process is the possibility of maintaining lower reaction temperatures than in the previously known processes. The optimum reaction temperature to be considered is that at which the highest possible benzene carboxylic acid concentration is guaranteed and no rearrangement reaction occurs. In principle, the reaction can also occur in the case of deeper

1 β18 078

5 6

Temperatures are carried out, ζ. B. with heat The hydrogenation can; but also in other electrical

Discharge through cooling brine or, in the case of higher temperature devices, without a diaphragm, among other things

doors, e.g. B. up to the boiling point of the pair of electrodes used with vibrating, as in the luxem-

organic solvent, with provided that burg below 80. ⁰ C Patent 51,508 described or boil,?. BL tetrahydrofuran. When executing the 5 hooves of stationary, of the reaction mixture

If the temperature is below 80 ⁹ C, the relocation of the electrode pairs through which the flow is flowing can be carried out

formed S ^ -Cyclohexadiene-l ^ -dicarboxylic acid to the end.

Speaking 2,5-Cyclohexadiencarbonsäure largely One advantage of this way of working is that it is relatively small

avoid. The most favorable temperature range is cell voltage of 5 to 7 V with current densities of 20

therefore between 20 and 80 ° C, in particular between 10 and 25 A / dm ² , even in systems that contain only 1% sulfur

25 and 70 ° C. contains acid. Especially, favorable results will be

As a result of the reaction temperatures below 80 ° C in the FaU of the vibrating electrode pairs at kiemek can be obtained as diaphragms instead of the usual frequencies (10; to 20 Hz). Ceramic material ion exchangers used as cathodes are suitable here galvanically leaded? ,, thin amalgam membranes, as they are e.g. B. for the Adipinsäuredinitril- 15 mated brass or iron networks, as anode Pt or production from Belgian patent 679 514 bes Ti-Netzej which are covered with a thin PbO ₂ layer, which are drawn at temperatures. The insulating intermediate layer is not resistant above 80 ° C. Your advantage: B. off. Glass fiber fleece with a thickness of 0.15 mm. once ¹ in a lower electrical resistance The reaction product is isolated from the clay diaphragms; Furthermore, the diffusion is ao by distilling off the ^; organic solvent, or permeation of organic substances to a crystallization, filtration or drying. Depreciated at a minimum. In the interest of a possible discoloration of the reaction solution, a balanced pH balance in the electrode spaces after the cell can be preceded by a vessel with activated carbon for decolourisation, preferably cation exchange membranes in the distillation exercise. Use $, 5-Cyclo-H + form. - - 25 hexadiene-1,2-dicarboxylic acid is a very reactive

In the new process, known electrocapable substance that one can work up the reac-

den, are used. tibnsgemisches, ie. the cutting and drying,

The anode used is usually lead or, advantageously, at the lowest possible temperatures

Platinum metals. However, lead dioxide and short dwell times can also be used for this purpose, so that discoloration

Graphite, silicon carbide, magnetite or others against chemical and secondary reactions, e.g. B. rearrangements,

Anodic dissolution, permanent or at least white to be avoided. The process can also be carried out continuously

walking resistant materials; use, of course, by adding distillate and filtrate, ie

The cathodes can be circulated from the usual cathode - the catholyte freed from the solids

material exist. It is precisely an advantage of becoming. .

driving that no specially prepared cathodes 35 -. , .... ..., .- _ut,, _. . "

or certain alloys must be used. Working method for the following examples.

So may. B. normal lead without amalgamation or As a hydrogenation cell is used in the continuous other surface treatment (e.g. after J. Taf'-el ·, look for (Examples 1 to 3); a double-jacket pipe from reports · of the Deutsche Chemischen-Gesellschaft, Glas , which is cooled with water in order to dissipate heat as a cathode with good success 40. The cathode made of lead (about and without symptoms of poisoning and fatigue 99.99% i, ig ). is designed as a. cylinder and: lies on the. But it can also be used in an inner wall of the glass tube ^. It: surrounds the cathodes described earlier in the cylinder, namely shaped & clay diaphragm, the anode and cathode amalgamated lead, cadmium. , Tin, thaffium or the room. The anode consists of. A. Lead-bismuth or alloys of at least two of the water-cooling tubes. = Lead, mercury, silver, cadmium, tin, thal - As. Anolyte: 5. P / ₀ ige. Aqueous sulfur rockic acid, verlium and bismuth, which is also amalgamated. The catholyte contains about 20: weight percent can, or pure cadmium, tin or bismuth, one-o-phthalic acid. something 55 percent by weight organic should be set. Solvent, about .20 percent by weight water and

The new process is usually used in electrolysis 5% concentrated sulfuric acid.

The reaction temperature in the cell is between

and cathode compartment separated by a diaphragm 30. and * 50? C held. Current densities between 3: and

are. So can. z. For example, the 25 A / dm ² shown in more detail in the examples prove to be special in the apparatus

Written tubular cell made of glass, also made of; metal: or cheap-. -.- ■ .-. ■

Made of plastic, the cathode is the same * 55 The catholyte is supplied with a metering pump, the · cell

early can form the inner wall of the cell. Also fed in from below and removed from above. In one

Instead of tubular cells, trough rotary evaporators can also be used: under reduced

or - box-shaped - cells can be used. At · die- pressure the organic? Solvent and) that, water

sen the cathodes and anodes are plate-shaped · and gently * removed% where the: formed; DihydrophthaB

arranged parallel to each other. In this arrangement 60 acid fails. The solid product is separated from the

the separation · of cathodes · * and anodes »remaining aqueous! Sulfuric acid. · And leads distillate

Space is particularly favorable due to the use of ion exchange exchangers and filtrafc, again, of electrochemical reduction

burn or synthetic tissue, but also through the too. The solid product is washed with water and

common diaphragm materials are made and dried,

the. The heat dissipation can be built in; of 65 example ·!

Cooling elements or pumping · the catholyte or;.

Anolytes or - particularly advantageous by forming As a hydrogenation cell "is:. The ·; described above

the electrodes are provided as waste elements; water-cooled vertical standing: double jacket pipe

Claims (1)

(7 8 made of glass used. The storage vessel for the Katho B ei s t> i e 1 4 lyt and the supply pipes are slightly heated. Height of the tubular cell ... ~. \ ..... 57 cm ^To implement a trough-shaped hydrogenation apparatus Diameter of the tubular cell ... 6.5 cm, made of polypropylene like a filter press. Cathode area 10 dm ² 5 turns, which is composed of two units. Of the Anode area · ■ 3 1 dm ^{a first} ^ ^oc ^ consists of seven connected in series Cathode compartment 11 electrodes (five bipolar electrodes, six cathodes Reaction temperature "'.'. '.}'. V. '.'. '. 48 ° C and six anodes), the second of three in series ctmm ^ i ^ fo KA / j _m s switched electrodes (one bipolar electrode, two Electricity turnover .........: J. 120% * ° cathodes and two anodes). [For the circuit cf. Anolvt 5% H SO "Ullmann's Encyclopedia of Technical Chemistry", Catholyte y. '.'. Y. '.'. '.'. '.'. '.'. '.'. '.'. '.'. '. 55% dioxane, 20%? ^{d 6} ' ^S / ^{464 bi} t ⁴ ^ l ⁰ ? entire apparatus consists Water 5 ° / accordingly from eight cathodes and eight anodes. Catho- HSO '2O ⁰ / the and anode compartments are o-phthalic acid ^{15 mem} b ^{ranei1 on} the basis of sulfonated polystyrene, Catholyte throughput 1 93 kg / h as it is under the trade name Permaplex® C 20 o-Phthalic acid ^{conversion 100% is known s} . ⁱⁿ ? O ^ form) separated The cathode yield of 3,5-cyclohexadiene ^rauD «« Pf connected to one another by glass tubes. 1,2-dicarboxylic acid 99.2% of theory? ^he catholyte is continuously Space-time yield 0.387 kg of 3,5-cy- ^ao denraume pumped through (in each case catholyte tab- clohexadiene-partial ^catholyte influx), namely first through the 1 2-dicarboxylic acid ^{first uru} * ^ansc hh ' ^e ^ ^{en <} i through the second cell unit. re / ^ ^e lReaktions- electrodes are cooled by water. room and hour electrode area 170 cm ² (14.2-12 cm) Current efficiency 82.6% ^a5 membrane area 170 cm ² Content of 2,5-cyclohexadiene- distance cathode - membrane 0.2 cm 1,2-dicarboxylic acid <0.5% distance anode - membrane ... 1 cm Total cathode space 272 cm ³ Example2 30 Current density of the first cell unit .. 10 A / dm ² Current density of the second cell unit 5 A / dm ² In a manner analogous to that in Example 1, the o-phthalic reaction temperature is 35.degree acid using dimethylformamide as tt ^no } ^y \ J ₁ Jf ^ ² ^ j organic solvent component hydrogenated: catholyte 52% tetrahydro- iuran, Io / pn ^ u, Reaction ^{temperature 40 0} C ä0 5% H ₂ SO ₄ , 25% Current density 20 A / dm ² o-phthalic acid Electricity conversion 130% catholyte flow 1.34 kg / h Anolyte 5 ° / _o strength H ₂ SO ₄ o-Phthalsäureumsatz 100% Catholyte 52% dimethyl- S ^ -Cyclohexadiene-l ^ -dicarbon- formamid, 18% ⁴ acid yield 98.8% of theory Water, 5% space-time yield 1.26 kg 3,5-Cy- H ₂ SO ₄ , 25% clohexadiene o-phthalic acid 1,2-dicarboxylic acid Catholyte throughput 1.97 kg / h _re / l cathode o-Phthalic acid ^{conversion 100% 45} room and hour S ^ -Cyclohexadiene dicarboxylic acid content of 2,5-cyclohexadiene Yield 98.5% of theory 1,2-dicarboxylic acid <0.5% Space-time yield 0.469 kg of 3,5-cyclohexadiene example 5
1,2-dicarboxylic ^s ° According to the procedure described in Example 1 re / l reaction is terephthalic acid using Dimethylraum hour formamide selectively hydrogenated as solvent: Current efficiency 75.7% _,, ^. _{A 4} .. "_ 2,5-Cyclohexadiene content - reaction temperature 44 ° C 1 ? rlirarhnnqänrp <rb 5 "/ 5 ⁵ current density 10 A / dm ² 1,2-dicarboxylic acid <0.5 / ₀ ^^ lOo / jge H ₂ SO ₄ Catholyte 81% dimethylform For example 3 amide, 7% ter- τ. λγ j Ai-i-ii 1-t.T) phthalic acid, 10% ' When using acetonitrile under the same _{conditions, 6o} HO 2 ° / HSO conditions as in example the following results yield of ^ S-cyclohexadiene- * '* * ^achieved: 1,4-dicarboxylic acid 91% o-Phthalic acid conversion 94% of theory Current yield 65% S.S-Cyclohexadiene-l ^ -dicarbon- ".., acid yield 98.6% 6 ₅ Claims: Current efficiency 73.3% 1 process for the production of 3,5-cyclo- Content of 2,5-cyclohexadiene-hexadiene-1,2-dicarboxylic acid or 2,5-cyclohexadiene 1,2-dicarboxylic acid <1% diene-1,4-dicarboxylic acid by electrochemical hy- Dration of o-phthalic acid or terephthalic acid in dilute aqueous sulfuric acid at temperatures up to 80 ⁰ C, in particular below 70 ⁰ C, and at current densities of 1 to 40 A / dm ² using conventional cathodes, characterized in that the catholyte with Water-miscible ethers, carboxamides and / or nitriles which are inert under the reaction conditions and liquid at room temperature are added as solvents.
2. The method according to claim 1, characterized shows that an o-phthalic acid or terephthalic acid concentration 5 to 50 percent by weight is used in the catholyte. 3. The method according to claim 1 to 3, characterized in that that ion exchange membranes or plastic fabric are used as a diaphragm between the anode and cathode compartment. 4. The method according to claim 1 to 3, characterized in that that the catholyte freed from the solids during work-up as distillate and filate is led in a circle.