DE1568094A1 - Process for the preparation of cyclohexadiene dicarboxylic acids - Google Patents

Description

BADISCHE ASIHXS "& SODA-FABRIK AG 1568094

our time OZ 24 158 Rä / Kn Iiudwigshafen am

Process for the preparation of cyclohexadiene dicarboxylic acids

It is known that one can produce by partial electrochemical hydrogenation of o-phthalic acid in dilute sulfuric acid as a catholyte at temperatures above 60 ⁰ C Cyclohexadiendicarbonsäure. According to 'reports of the German Chemical Society, Volume 39 (1906), pages 2933 to 294-2' and according to 'Zeitschrift für Elektrochemie, Volume 35 (1929), pages 769 to 779 * the reaction on specially prepared, purest lead cathodes in 15% sulfuric acid carried out »In the USA patents 2,477,579 and 2,477,580 the caustic parts of the lead cathodes are described, and the use of mercury cathodes and 5% sulfuric acid is therefore recommended 304 described devices which are intended to help avoid symptoms of poisoning * When using BleikatMoäexi, symptoms of poisoning occur that are manifested in a greatly reduced ability to react. In addition, brown, tea-like © by-products arise, which discolor the reaction product and make special cleaning processes necessary. Even if you use mercury, you will suffer symptoms of poisoning, albeit only after a longer reaction time

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Cathode noticeable * 'It is therefore necessary to remove the mercury continuously removed from the hydrogenation cell, cleaned and the purified mercury fed back to the electrolytic cell. So you have to work with a mercury cycle in which at least one cleaning stage is switched on. To this Although the cathode's ability to reduce is maintained, a technically complex procedure is necessary, among other things to be able to carry out the electrochemical process over a longer period of time. They are also due to the physiological Dangers when using mercury and especially when operating a mercury circuit, special safety regulations to be observed.

It has now been found that cyclohexadiene dicarboxylic acids can be obtained by electrochemical hydrogenation of corresponding phthalic acids in dilute aqueous sulfuric acid at temperatures above 7O ⁰ O and with current densities of 1 to 40 A / dm, optionally using lead or mercury cathodes, without the lead or The usual difficulties with mercury cathodes are encountered when the cathode is amalgamated lead, cadmium, tin, thallium or bismuth, or alloys, which can also be amalgamated, from at least 2 of the metals lead, mercury, silver, cadmium, tin, thallium and bismuth or pure cadmium, tin or bismuth are used.

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When using cathodes according to the invention no symptoms of poisoning even when the process is carried out continuously observed. In the course of time, the cathode potential becomes negative, which results in a makes little hydrogen development noticeable, but causes this hydrogen evolution a better convection and thus a favorable change in the concentration of the phthalic acid to be hydrogenated or the hydrogenation product directly at the Cathode »The advantages of the new process are obvious ϊ compared to processes in which lead cathodes are used no malfunctions occur, compared to processes in which mercury cathodes are used, a much simpler mode of operation is possible.

If amalgamated cathodes are used, they are that is, lead coated with lead-mercury alloy, cadmium coated with cadmium-mercury alloy, with tin-mercury alloy coated tin, with thallium-mercury alloy coated thallium, or bismuth coated with a bismuth-mercury alloy. Unless binary, ternary or higher Alloys are used, it is lead-mercury, Lead-silver, lead-cadmium, lead-tin, lead-bismuth, lead-thallium, mercury-silver, mercury-cadmium, Mercury-tin, mercury-bismuth, mercury-thallium, cadmium-tin, cadmium-bismuth, cadmium-thallium, tin-bismuth,

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Tin-thallium, bismuth-thallium alloys or lead-mercury-silver, Lead-mercury-cadmium, lead-mercury-tin, lead-mercury-bismuth, lead-mercury-thallium, lead-silver-cadmium, Lead-silver-tin, lead-silver-bismuth, 31ei-silver-thallium, Lead-cadmium-tin, lead-cadmium-wiamut, Lead-cadmium-thallium, lead-tin-bismuth, lead-tin-thallium, Lead-thallium-bismuth, mercury-silver-cadmium, mercury-silver-tin, Mercury-silver-bismuth, mercury-silver-thallium, mercury-cadmium-tin, mercury-thallium-bismuth, Mercury-Cadmium-Bismuth-, Mercury-Cadmium-Thalllum-, Mercury-pine-bismuth, mercury-tin-thallium, silver-cadmium-tin, Silver-cadmium-bismuth, silver-cadmium-thallium, Silver-tin-bismuth, silver-tin-thallium, silver-thallium-bismuth, Cadmium-tin-bismuth, cadmium-tin-thallium, cadmium-thallium-bismuth, Tin-thallium-bismuth alloys or equivalent higher e.g. quaternary alloys of this type such as lead-mercury-silver-tin, lead-mercury-silver-thallium, Lead-thallium-oadmium-tin etc., all of which are amalgamated can.

The proportions of the individual metals can be in a wide range, the limits being due to the mechanical Machinability of the resulting alloy are given. In the case of cadmium, tin or bismuth, pure, i.e. 100 $ metals be used. If mercury is used as an amalgam or in leather

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alloy is used, the content should be chosen so that the mercury alloy or the amalgamated metal is retained as a solid phase at the reaction temperature. In the case of lead-mercury, there are limits between 30; 70 to 99.5 i 0.5 or 0.1 -2g mercury / dm ² lead surface for amalgamation, or for thallium-mercury, for example, those from 50 s 50 to 99.9 s 0.1, for lead-mercury such silver of 30: 69.5: 0.5 to 99.5: 0.5 t 0 to 30 ϊ 0.5: 69.5 parts by weight. The situation is similar for other mercury-containing cathodes. For example, it is preferred the use of cadmium, cadmium tin ζ - 100 ί 0 to 50: 50, lead ί mercury = 50: 50 to 90 ι 10, lead, mercury ι ι silver = 50 '.: 30: 20 to 90 ι 9p. ι 0.5, lead: bismuth = 30 ι 70 to 80 ϊ 20, lead: tin = 20 ι 80 to 80 s 20, lead ι cadmium = 0.5 ί 99.5 to 80 ι 20, cadmium ί bismuth = 100 : 0 to 20 s 80, all cathodes with and without amalgamation and amalgamated lead.

Lead or platinum metals are usually used as the anode.

You can also use lead dioxide, graphite, silicon carbide or others resistant or at least to anodic dissolution

use largely "resistant materials.

The electrolysis is carried out in conventional electrolysis cells, in which the anode and cathode compartments are separated by a diaphragm, e.g. made of porous clay. Cathodes and anodes are common Forms formed, e.g. one can use a double toll pipe

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use that can be heated or cooled, in which the cathode as Cylinder lies on the inner wall of the tubular cell or represents the inner wall of the tube and surrounds the likewise cylindrical diaphragm. The anode consists e.g. of a water-cooled lead pipe. However, trough cells with plate-shaped electrodes and suitable cooling elements can just as well be used use.

The process can be used in the same way for the partial hydrogenation of o-phthalic acid, which can also be used in the form of phthalic anhydride, of isophthalic acid or of terephthalic acid. The phthalic acid is dispersed in a concentration of 2 to 8, preferably 3 to 6, in dilute aqueous sulfuric acid which generally contains more than 2, but not more than 50% by weight, preferably 3 to 20% by weight, of sulfuric acid. At temperatures above 70 ⁰ C, a sufficiently large amount of the respective phthalic acid goes into solution, that the partial hydrogenation proceeds smoothly. It is advisable to use the maximum solubility of phthalic acid at the respective reaction temperature and the given sulfuric acid content. The values can easily be determined by simple experiments, for example, at 85 ^° C. in 100 g of 5% sulfuric acid, 4 »95 g of o-phthalic acid dissolve. In general, it is not necessary to use temperatures above 100 ⁰ C "Preferably, the method is in the temperature range of 80 to 98 ⁰ C performed.

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As an anolyte, one also uses dilute sulfuric acid in two masses - approximately in the same concentration as in catholyte use. But you can also maintain a slightly higher concentration.

The electrolysis is carried out with current densities of 1-40 A / dm, in particular 3 to 20 A / dm (cathode current). In a preferred, continuous procedure, the catholyte is fed to the cathode compartment of the electrolytic cell with a metering pump, the phthalic acid-sulfuric acid mixture being allowed to flow through the electrolytic cell from bottom to top. The resulting hydrogen provides additional convection. The reaction mixture is cooled to Yerweilzeiten of, for example 0.1 to 5 hrs in the electrolytic cell, preferably to below 15 ⁰ C. The dihydrophthalic formed then crystallizes. It is separated off in the usual way, and the mother liquor can be fed back to the electrolysis cell after adding phthalic acid.

The dihydrophthalic acids produced are extremely pure after simply washing them with water. Since the dihydrophthalic acids are very reactive because of their double bonds, it is advisable to carry out ^{the work-up at relatively low temperatures, preferably below 20 ° C.}

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example 1

A double-jacket tube made of glass is used as the hydrogenation cell. with a cylindrical amalgamated lead cathode, a cylindrical clay diaphragm and a water-cooled one Lead pipe is provided as an anode. The catholyte is fed under the cell with the aid of a metering pump and removed from above.

Height of the tubular cell 57 cm, diameter of the tubular cell 6.5 cm

Cathode area 10 dm ²

ρ anode area 3.1 dm

Cathode compartment 1 liter

Reaction temperature ^{85 0 C}

Current density 10 Λ / dm ²

Electricity sales 150 ^c / o

Catholyte 5 # H ₉ SO. + 4.5

* * o-phthalic acid

Anolyte 5 # H ₂ SO.

j / h '206.5 g o-phthalic acid)

Catholyte throughput 4 »6 kg / h

o-phthalic acid conversion 100 #

^ 3,5-dihydrophthalic acid yield 88 $> the theory space-time yield 0.184 kg dihydrophthalic acid /

1 reaction room and hour

Current efficiency 58.75 i °

In continuous operation over 8 days there was no change in the result found as a result of poisoning the cathode. ^ 2,6-dihydro- ^ Phthalic acid could not be detected in the reaction product * Tar-like impurities did not occur.

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Examples 2-5

With cathodes of a different composition, the following results were obtained under the same conditions as in Example 1: i

example

cathode

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st

2 Pb: Hg = 75; 25 amalgamated

3 Pb: Hg = 75 ι 25 not amalgamated

4 Pb ί Hg; Ag ss 80: 19: 1 not amalgic.

5 Gd: Sn = 90: 10 not amalgamated

, 5-EHPS yield Ström fo d.iDheorie yield $>

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Claims (1)

Claim Process for the production of cyclohexadienecarboxylic acids by electrochemical hydrogenation of the corresponding phthalic acids in dilute aqueous sulfuric acid at temperatures above 7O ⁰ O and with current densities of 1 to 40 A / dm, optionally using lead or mercury cathodes, characterized in that amalgamated lead is used as the cathode , Cadmium, tin, thallium or bismuth or alloys of at least 2 of the metals lead, mercury, silver, cadmium, tin, thallium and bismuth, which can also be amalgamated, or pure cadmium, tin or bismuth is used. BADISCHE ANILIN- & SODA-FABRIK AG 009819/1888