The invention relates to a process for electrochemical preparation of metal alcoholates, particularly for preparing iron(II) ethanolate as a first step for the further synthesis of ferrocene.

A construction of an electrolytic cell for electrochemical preparation of iron(II) ethanolate was described by W. Eisenbach and H. Lehm uhl (Chem. Ing. Techn. 54. _/ 690 (1982) . In this embodiment, a part of the iron(II) ethanolate which is insoluble in ethanol precipitated in the form of an isolating layer on the cathode, and had to be removed mechanically. During continuous operation, the electrolytic cell contained rotating, disk-shaped cathodes made of stainless steel, whereby the surface of the cathode was kept free of iron(II) ethanolate with the aid of scrapers. Already due to this, the optimal size of a cell was limited. For a size in the range of, for instance, 3000 amperes, it was necessary to arrange several cells since the diameter of the cathodes could not be enlarged at pleasure, due to the increasing weight. The same was valid for the number of cathodes per cell, and also for the thickness of the anodes and the adapted form thereof.

The greatest disadvantage with this cell construction is the transfer of great current strength to the rotating cathode shaft. A transfer with mercury as a transfer medium which is very good operating in small scale, proves to be a problem with the greater cells. On the one hand, in this case the voltage drop is becoming apparent in a disturbing way which led, among other things, to a strong heating up of the mercury. However, it is more problematical that during maintenance and repair works on the shaft, the mercury chamber has to be discharged, which is not always possible without straining the environment.

Surprisingly, it has been found now that by using a fixed cathode instead of a rotating cathode, a precipitation of the formed iron(II) ethanolate is prevented due to transfer by pumping of the electrolyte at a high velocity. However, a separation of the formed iron(II) ethanolate outside of the cell can only be done, if a as low as possible flow rate is installed in the so-called settling vessel. Thus, the presently found method provides two recirculation streams, whereby the electrolyte is pumped over in the cell at a greater velocity, and it is pumped over behind the cell in the settling vessel at a lower velocity.

The electrolyte cell which is used according to this method is shown in figure 1. It consists, for instance, of a housing made of acrylic glass, a rectangular iron anode having a size of 200 x 200 mm and a thickness of 10 mm which is attached to the back wall of the cell with the power connection, and a cathode of the same size made of polished V2A metal sheet having a thickness of 2 mm, which is bent at the upper and lower part in order to get a better flow distribution, as can be seen from the figure.

The cathode can be readjusted according to the dissolution of the anode by an adjusting means, in such a way that it is possible to electrolyze with an almost constant electrode spacing.

The circulating electrolyte is fed via a distributing pipe to the lower end of the cell. A uniform flow of the electrolyte in the electrolyte gap is assured by a suitable formation of this distributing pipe, in such a way that iron(II) ethanolate can not be precipitated in any place between the electrodes and can lead to a constraint of the current conduction. The electrolyte (suspension) , together with the formed hydrogen, flows over the anode from the cell.

The new part of the flow diagram for the electrochemical preparation of iron(II) ethanolate is shown in figure 2. The

alcoholate suspension which is formed in cell (1) is pumped over at a high velocity by means of the circulating pump (8) via the buffer vessel (9) which serves for compensating the volume change in the cell either by temperature variations or by a decrease of the thickness of the anode during the electrolysis.

Clear electrolyte from the working up of the alcoholate suspension is metered to this cycle, in order do keep the alcoholate suspension constant, in such a way, that to the same extent suspension flows over from the buffer vessel (9) . This part of the suspension is separated and worked up in a known and technically practiced manner by precipitation in a settling vessel and centrifugating the thickened suspension. The thus obtained clear electrolyte is returned to the above cycle.

Example 1

An iron anode having a thickness of 10 mm and a size of 200 x 200 mm made of ARMCO-iron - weight: 3324.6 g - and a V2A anode, having a thickness of 2 mm and approximately the same size, are incorporated into the cell, described in figure 1, with a space of 2 mm. In the arrangement, schematically shown in figure 2, it was electrolyzed at a constant current strength of 30 amperes. The current strength was kept constant by electronic control (readjusting the voltage) since the electrode space could not be kept constant at 100%. The cathode was readjusted (300 ampere hours correspond to 1 mm decrease of the thickness of the anode) at a certain time interval - normally twice in 24 h - according to the quantity of electricity passed through. The voltage varied at this conditions between 6.0 volts at an electrode space of 2 mm and 9.5 volts at approximately 3.5 mm. The electrolyte flow through the cell was 455 1/h, 45 1/h thereof being inlet of clear electrolyte and outlet of suspension, respectively.

After a time of electrolysis of 63 hours, corresponding to a current passage of 2269.6 Ah or 84.687 Faraday, the electrolysis

- A - was finished, the cell was rinsed out, opened, and the electrodes dismounted. After this time, the anode had been dissolved uniformly to a degree of 70.6%. The weight loss was 2347.3 g or 42.031 mole, corresponding to a current efficiency Of 99.3%.

The weight of the cathode had been increased by 3.65 g. Provided that in this case, it refers to metallic iron, this weight increase corresponds to 0.155% iron which is dissolved at the anode.

The iron(II) ethanolate which is formed during the electrolysis flocculated in the settling vessel in the form of a green product, precipitated well and could be separated by means of a centrifugal decanter as a solid having an electrolyte moisture content of approximately 65%.

Example 2

The V2A cathode was replaced by a cathode made of normal plain and low carbon steel sheet in the same apparatus and the same electrolysis cell as in example 1.

It was electrolyzed during 51 hours at a temperature of approximately 30°C at a constant current strength of 50 amperes, whereby, as described in example 1, the cathode was readjusted from time to time, and the voltage adjusted to between 7.6 and 15.2 volts. The quantity of electricity flown through was 2510.7 Ah or 93.883 Faraday. The flow rates corresponded to the ones of example 1.

It had been shown in the experiments that among all possible experimental conditions, approximately 0.1-0.2% of the iron which is dissolved at the anode was precipitated again in the form of a metal, and which, thereby, could lead to defects. The current strength was decreased to approximately 20% after 24 hours, respectively, before the readjusting of the cathode, and

the iron which was deposited during this time was redissolved by pole reversal of the current direction, in order to prevent these side effects.

The anode had been dissolved uniformly to an degree of 77.8%. The weight loss was 2600.6 g or 46.565 moles. This corresponds to a current efficiency of 99.4%.

Example 3

The current strength was increased to 64 amperes (end of the capacity of the used rectifier) , corresponding to a current density of 16 A/dm ² , in the same apparatus and the same electrolysis cell as in example 1. The amount of clear electrolyte which also was cooled during the step of working-up of the alcoholate suspension was increased to 60 1/h, in order to prevent the heating-up of the electrolyte in the cell by the greater Joule heat.

During this experiment, the cathode was dismounted after 24 hours, respectively, and the amount of the precipitated iron was determined. Between 0.087 and 0.117% of the anodically dissolved iron were found.

The anode had been dissolved uniformly with a smooth surface to a degree of 87.50%. The weight loss was 2946.8 g = 52.766 mole. The current efficiency was - as in the other examples - almost quantitively. It was 98.8%.

Furthermore, the current density, and thereby the efficiency per time, can be markedly increased by providing means to remove the Joule heat by effective product condensers. The current density is determined by the capacity of the rectifier in this example.