DE4200444A1 - Stannous chloride recovery by electrolytic redn. of stannic chloride - in aq. acid in cell with cation exchange membrane, used in hydrazine cpds. prodn. - Google Patents

Abstract

Electrolytic redn. of SnCl4 to SnCl2 in aq. HCl soln. is carried out in the cathode compartment of an electrolysis cell with a cation exchange membrane separator, whilst the anode compartment is supplied with aq. HCl. Redn. is carried out in such a way that the SnCl2 soln. still contains 0.1-4.5 (wt.)% Sn4+, depending on the current density used. USE/ADVANTAGE - The process is useful for recovering SnCl2 solns. from solns. used for reducing organic diazonium salt solns. to mono-substd. hydrazines. High yields are obtd. without using an asbestos diaphragm and the solns. are pure enough for re-use without further treatment

Description

Monosubstituted hydrazines can be prepared by reducing organic diazonium salt solutions (Houben-Weyl, Methods of Organic Chemistry Vol. 10/2 p. 197 ff). A proven method is the reduction with SnCl ₂ in a strongly hydrochloric acid solution, whereby SnCl ₄ is obtained. The disposal of this SnCl ₄ solution has hitherto consisted of precipitation as tin (IV) hydroxide, annealing of the residue and reduction with carbon to metallic tin, which was converted back to SnCl ₂ with hydrochloric acid.

This method has serious disadvantages: considerable amounts of Na trium hydroxide needed; Difficulties arise in the filtration of the tin (IV) hy droxids on; it is a significant energy expenditure for drying and thermal Reduction required. US 15 97 653 describes Sn- (IV) -containing solution to reduce electrolytically. This process uses an electrolytic cell used with a diaphragm made of asbestos or a material containing asbestos consists. It is known that asbestos in use and in the treatment of healthy damage caused. In addition, tin (IV) solution was observed conditions, provided that they come from the processes described at the outset, when initiated in the anode compartment, as described in US 15 97 653, is very malodorous Lead reaction products from the remaining organic compounds.

The present invention now relates to a process for the production of SnCl ₂ solutions from SnCl ₄ solutions using a cation exchange membrane which separates an electrolytic cell into an anode and a cathode space, the SnCl ₄ solution being passed only through the cathode space . In order to prevent the reduction down to the metallic tin, a residual amount of SnCl ₄ must remain in solution, which is withdrawn from the cathode compartment. Hydrochloric acid is introduced into the anode compartment of the cell. Gaseous chlorine is deposited on the anode, while the protons diffuse through the membrane into the cathode compartment. The electrodes consist of graphitized carbon, as used in technical hydrochloric acid electrolysis (Ullmannn's Encyclopedia of Industrial Chemistry, Vol. A 6 (1984) p. 459 and Winacker-Küchler, Chemical Technology 2I (1982) 442 ).

The following reaction equations apply:

• a) in the anode compartment 2 HCl-2e → Cl ₂ +2 H⊕
• b) in the cathode compartment SnCl ₄ +2 H⊕ + 2e → SnCl ₂ +2 HCl.

The electrolysis takes place in particular at a current density of 0.5 to 5 kA / m ² , preferably at 2 to 3 kA / m ² , cell voltages being set as a function of the total resistance of the cell; in the experiments described below, they are between 2.3 and 4.4 volts.

The remaining amount of Sn ⁴⁺ , which remains in the catholyte (solution in the cathode compartment) in order to prevent the reduction to metallic tin, is 0.1 to 4.5% by weight, depending on the current density, if from 10 to 11% by weight .-% Sn ⁴⁺ solutions is assumed, the remaining amount of Sn ⁴⁺ may be lower at lower current densities than at higher current densities.

The hydrochloric acid in the anode compartment is preferably about 20% by weight, since then maximum conductivity is given.

The advantages of the process according to the invention are that, without using asbestos, an SnCl ₂ solution is obtained in high yield, which, owing to its purity, can be reintroduced into the reduction process without further workup. Another advantage is that, unlike the process according to US Pat. No. 1,597,653, residual amounts of Sn (II), such as remain in the reduction of organic diazo compounds, are not oxidized at the anode with additional expenditure of energy before the reduction in the cathode compartment he follows. The use of an ion exchange membrane, selective for cations, leads to higher current yields and avoids the transfer of chlorine into the cathode chamber, as is done by the process of US 15 97 653. In the method according to the invention, the formation of explosive nitrogen-halogen compounds which can arise in the anode compartment is avoided.

Fig. 1 shows an apparatus for performing the method according to the invention.

• 1) is a storage vessel for aqueous hydrochloric acid, which reaches the anode compartment ( 4 ) in the manner indicated and is guided in a circle via the intermediate vessel ( 7 ), which is provided with a heating device ( 9 ) and a cooler ( 11 ). Chlorine gas is removed via line ( 13 ), and any hydrogen that is formed is removed via line ( 14 ). Both products can still be used. ( 15 ) denotes the membrane, ( 16 ) the cathode and ( 17 ) the anode of the electrolytic cell.
• 2) is a storage vessel for an aqueous, hydrochloric acid solution of SnCl ₄ , which still contains small amounts of SnCl ₂ and possibly small amounts of organic products. In the manner indicated, this solution enters the cathode compartment ( 3 ) of the electrolytic cell ( 5 ). After passing through the intermediate vessel ( 6 ), which is provided with a heating device ( 8 ) and a cooler ( 10 ), the electrolyzed solution can again be guided into the cathode compartment ( 3 ) or into the storage vessel ( 12 ) for receiving the solution SnCl ₂ , which still contains small amounts of SnCl ₄ and, if appropriate, small amounts of organic products.

The claimed method is described in more detail below:

An aqueous, strongly hydrochloric acid solution with contents between 5-25% by weight SnCl ₄ , preferably 5-15% by weight and a residual content of 1-15% by weight SnCl ₂ , preferably 1-5% by weight , was separated after separation of the organic hydrazine compound with residual contents of these compounds into the cathode compartment of the cell according to FIG. 1. Cation exchange membranes, such as are used in processes for chlorine extraction and are described by D. Bergner, Chem. Ing. Techn. 54 (1982), 562, are suitable as membranes. Membranes made of polyperfluoroethylene and containing sulfonic acid groups are particularly suitable. Such membranes are known from hydrochloric acid electrolysis. The graphite electrodes used in the hydrochloric acid electrolysis are used as electrodes.

example 1

A hydrochloric acid aqueous solution with 10% by weight of Sn ⁴⁺ , approx. 2% by weight of Sn ²⁺ and 0.5-1% by weight of organic constituents is electrolyzed in the apparatus according to FIG. 1. The distance between the electrodes (80 cm ² ) is 20 mm. Nafion 430 (DuPont) was installed symmetrically as the membrane. Table 1 shows the test conditions and test results:

Claims (3)

1. Process for the electrolytic reduction of SnCl ₄ to SnCl ₂ in hydrochloric acid, aqueous solution by means of an electrolytic cell, characterized in that the hydrochloric acid, aqueous SnCl ₄ solution is passed through the cathode compartment, that at the same time aqueous hydrochloric acid is passed through the anode compartment and that The cathode and anode compartments are separated from one another by a cation exchange membrane. 2. The method according to claim 1, characterized in that the electrolytic reduction is carried out at current densities of 0.5 to 5 kA / m ² . 3. The method according to claim 1, characterized in that the electrolytic reduction is carried out so that the SnCl ₂ solution obtained still has contents of 0.1 to 4.5 wt .-% Sn ⁴⁺ depending on the current density used.