Process for the preparation of hexadiin(2,4)-diol-1,6.

0001Hexadiin (2,4) diol-1,6 can be prepared by ethynylation of diacetylene with formaldehyde. Because of the high risk potential of diacetylene (tendency to explosive decomposition), the use of this compound is only recommended in high dilution. An economically sensible production process can hardly be realized in this way.

0002Hexadiin (2,4) -diol-1,6 can also be produced from propargyl alcohol in a far less dangerous way by oxidative coupling according to Glaser. L. Brandsma describes in "Preparative Acetylenic Chemistry" Elsevier Publishing Company, Amsterdam, 1971, page 166, a corresponding method. The disadvantage of this process described there is that the hexadiol diol precipitates out of the reaction mixture because it is relatively poorly water-soluble. The processing of such a crystal slurry is known to be very complex.

0003The crystal slurry also contains salts from the catalyst for the oxidative coupling of propargyl alcohol. Since hexadiin (2,4) diol-1,6 is soluble in water, even if only slightly, water washing can only be used with product loss. Separation by distillation is also unsuitable since hexadiine (2,4) diol-1,6 is thermally labile and boils higher than water in vacuo.

0004The common route via ion exchangers is suitable in such a case if the salt content is not too high. However, when the exchanger is regenerated, saline eluates are to be expected, which not only result in a loss of product, but also an environmental impact. Desalination by reverse osmosis would not be an option here either: the resistance of the membrane and the permeate flow in organic media pose problems, and the saline retentate requires further processing.

0005This gave rise to the task of finding a process which makes it possible to produce hexadiene (2,4) diol-1,6 in an economical manner, the salts being removed in the workup.

0006This object is achieved according to the information in the claims.

0007Surprisingly, precipitation of the 1,6-hexadinediol formed can be avoided by adding butanol to the reaction mixture. A heterogeneous mixture of two phases is formed, with the 1,6-hexadiindiol dissolving almost completely in the butanol. After the reaction has ended and the stirrer has been switched off, the butanolic solution of the hexadinediol separates quickly and cleanly from the aqueous catalyst solution by phase separation.

0008N-, Iso- and tert-butanol are suitable as butanol. The ratio of catalyst phase to butanol phase is 5: 1 to 1: 5, preferably 3: 1 to 1: 2, in particular approximately 2: 1. A solution of 5 to 50% is preferably added to the aqueous catalyst solution with stirring. especially from 10 to 30% propargyl alcohol in butanol and optionally water (stream 2 in Fig. 1).

0009As a catalyst, copper salt complexes are generally used in aqueous solution, for example a Cu^I.Cl / NH₄Cl complex.

0010The reaction is generally carried out in a pressure vessel equipped with a stirrer, pressure-maintaining valve and thermometer (reactor R in Fig. 1), into which the aqueous catalyst solution which is prepared, for example, from about 2 to 8% copper (I) chloride, about 10, is added to 26% ammonium chloride and about 66 to 88% water. Catalyst solutions with a low salt concentration are unfavorable because they prolong the reaction time uneconomically or no longer catalyze the oxidative coupling.

0011The reaction mixture is brought to the reaction temperature of 5 to 80.degree. C., preferably 10 to 50.degree. C., and the glaser coupling is initiated by pressing on oxygen. The heat of reaction is removed by cooling. The pressure is adjusted to 0.1 to 5 bar gauge pressure, preferably 0.5 to 3 bar gauge pressure. Air can be used instead of pure oxygen. In this case, however, a continuous flow of waste gas from the reactor must be ensured to maintain the oxygen concentration.

0012The reaction is complete when the propargyl alcohol content has dropped to <0.5%.

0013The process can be carried out batchwise or continuously.

0014The reactor is then let down, the stirrer is switched off and the butanol phase which separates out is discharged. The catalyst solution remains in the reactor and can be used for further reactions.

0015The butanol phase still contains residual amounts of salts of approximately 0.1 to 2 percent by weight. The residual amounts of salts are removed according to the invention with the aid of electrodialysis, using butanol, a proprietary, product-free, organic solvent with a little water and propargyl alcohol, as the receiver solution, whereby the salts are separated from the reaction mixture and used with the receiver for the catalytic use of the reaction can be returned. This means that both the desalination and the recovery of the salts take place without polluting the environment.

0016The reaction mixture is led from the reactor R as stream 3 (FIG. 1) into the electrodialysis E, in which it is freed from the salts electrodialytically, for example in a membrane stack E. Commercial membranes can be used as the membrane, preferably with a chamber thickness of 0.3 to 3 mm and a membrane thickness of 0.1 to 0.3 mm.

0017The membranes generally consist of styrene-divinylbenzene with attached functional groups on fabrics made of polyvinyl chloride (in the case of a cation exchange membrane) or polypropylene (anion exchange membrane). The cation or anion exchange activity is e.g. B. accomplished by attached sulfonate or quaternary amino groups.

0018A voltage of 2 to 10 V is generally applied to each pair of chambers. The specific conductivity of the starting mixture is generally 400 to 1000 [µS / cm], and the current density is 1 to 50 [mA / cm²]. During electrodialysis, the specific conductivity and thus the current intensity decrease. Electrodialysis is generally carried out at low temperatures, preferably at 10 to 40 ° C., in particular at 20 to 30 ° C.

0019The electrode stack consists of alternating anion and cation exchange membranes, which are placed between two electrodes. The electrodes can be rinsed with acid, alkali or a salt solution. Two membranes form a chamber. Two adjacent chambers, which are fed by transducer or dispenser solutions, form a functional cell as a pair of chambers. The stack is combined in two groups of membrane chambers to be connected in parallel, which are separated by the sensor or can be loaded into the dispenser solution as indicated in the examples. If the streams are circulated, continuous desalination takes place. However, if sufficient membrane chambers and stacks are provided (ie sufficient process route), desalination can also be carried out in one pass.

0020A mixture of propargyl alcohol, butanol and water reaches stream 1 in electrodialysis stack E, where it is loaded with the salts copper (I) chloride and ammonium chloride. The current thus corresponds to the sensor current. The salt-containing stream 2 corresponds to the required reaction mixture and is fed into the reactor R, where the conversion to hexadiin (2,4) diol-1,6 takes place. The reaction mixture is fed as stream 3 back into the electrodialysis stack (donor stream), in which the desalination takes place. Streams 2 and 3 form a salt cycle.

0021From electrodialysis, the hexadiine (2,4) diol-1,6 (stream 4 in Fig. 1) is worked up or further processed, for example hydrogenation to hexanediol-1,6. In a downstream column, 1,6-hexanediol and butanol can be separated. The butanol serves as a receiver stream for the salts in electrodialysis and then passes as stream 1 via the electrodialysis to the reactor for the conversion of propargyl alcohol. The electrodialytic desalination can be carried out continuously, semi-continuously or batchwise, preferably one works continuously, in special cases the batchwise mode of operation can also be advantageous.

0022The examples explain further details of the method according to the invention.

Example 1.1

0023A solution of 92.5 g of copper (I) chloride and 300 g of ammonium chloride in 1000 g of water is placed in a 2 l glass autoclave equipped with a stirrer, thermometer and pressure-maintaining valve. A solution of 140.3 g of propargyl alcohol in 500 g of butanol is added to this catalyst mixture. The reaction mixture is heated to 30 ° C. with stirring (700 rpm) and blown nitrogen-free by introducing oxygen. Then a reaction pressure p_e of 0.5 bar (overpressure). The heat of reaction is removed by water cooling. The reaction is complete after 100 min (propargyl alcohol content <0.1). The reactor is depressurized, the stirrer is switched off and the butanol phase (700 g) is suctioned off. The conversion of propargyl alcohol to hexadiindiol is almost quantitative. For desalination, the butanol phase is put into electrodialysis.

Example 1.2

(Fig. 1 to 4, tab. 1 to 3)

0024The electrodialysis stack contains alternating cations - (K) and anion exchange membranes (A), with a cation or anion exchange membrane next to the anode (a) or cathode (k). The electrodes are washed with 1 percent by weight H₂SO₄ (1) or 0.5 percent by weight NaOH (2) (see Fig. 2). The stack contains 6 membrane chambers for the receiver solution (3) and 5 chambers for the reaction mixture (4). The conductivity of the reaction mixture is monitored over time using cell Q (see Fig. 4). The compositions of the solutions and the technical data are summarized in Tables 1 and 3. After 5 hours 45 minutes, 93% of the salts (calculated on a chlorine basis) were transferred with an average electricity yield of 80%. After a further 4 hours 50 minutes, the desalination corresponds to 97% (Tab. 2).<tables id="tabl0001" num="0001"><img file="EP0297239A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0297239A2_D0002.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0297239A2_D0003.tif" /></tables>

Example 2.1

0025The procedure is as in Example 1.1, but air is used as the oxygen supplier instead of pure oxygen. A continuous exhaust gas flow of 20 l / h is therefore used. The reaction time is 685 min. The implementation is almost quantitative.

Example 2.2

(Fig. 3 and 4, Tab. 1, 4 and 5)

0026In this example, the transfer of H⁺ or OH⁻ ions from the ano- or catholyte chambers after electrolysis of water is avoided. A 1% by weight ammonium chloride solution is placed in both electrode circuits (1 and 2). There is only a shift of the NH₄⁺ Cu⁺ and Cl⁻ ions. (The disadvantage that the Cu⁺ ion is lost in the catholyte can be minimized with a large number of cell groups between the electrodes). The stack consists of 5 chambers for the transducer or the starting mixture. After 6 hours 50 minutes, 75% of the salts (chlorine base) were transferred with an average yield of 62%. After a further 15 hours 46 minutes, the desalination corresponds to 96% (Tab. 4).

Example 3

(Fig. 6 and 7, Tab. 1, 6 and 7)

0027The reaction proceeded as in Example 2.1, but a different electrodialysis stack was chosen, namely with an inch thickness of 0.4 mm and a membrane area of ​​220 cm². The membrane arrangement was also chosen so that the Cu⁺ ions are obtained in the two circuits (Fig. 4). The electrode rinsing solutions came from the same source, ie the two circuits had the same reservoir. Initially, only half of the available transducer solution, namely 4 136 g, was used. After about 200 minutes, the system was cleaned and the diluate (8,403 g) was further desalted using the remaining fresh half of the receiver solution. A very low salt concentration in the diluate was achieved in a shorter time.<tables id="tabl0004" num="0004"><img file="EP0297239A2_D0004.tif" /></tables><tables id="tabl0005" num="0005"><img file="EP0297239A2_D0005.tif" /></tables><tables id="tabl0006" num="0006"><img file="EP0297239A2_D0006.tif" /></tables><tables id="tabl0007" num="0007"><img file="EP0297239A2_D0007.tif" /></tables>