EP0219367A1 - Organic electrolysis cell with a consumable electrode - Google Patents

Abstract

The present invention relates to a cell for the organic electrosynthesis of organic or organometallic compounds, containing two electrodes (2) and (4) of which only one (4) is sacrificed by the electrochemical reaction of which it forms the seat. The sacrificial electrode (4) consists of at least one solid metal block and is applied under the influence of its own weight against the other electrode (2) from which it is separated by an electrical insulating material (5) which allows the passage of the electrolytic solution (6) and of which the shape and the dimensions enable the active substances of the two electrodes (2) and (4) to remain parallel. The active surface of the electrode (2) has a constant inclination relative to a direction D (9) forming an angle less than 45 degrees with the vertical on the one hand, and an inclination less than 45 degrees relative to the vertical on the other. Any straight line in direction D (9) passing through any point on the electrode (4) passes through the active surface of the electrode (2).

Description

The present invention relates to an electrolysis cell for electrosynthesis, in an organic medium, of organic or organometallic compounds, comprising two electrodes, one and only one of which is consumed during electrosynthesis by the electrochemical reaction of which it is the seat.

US Patents 3,573,178 and US 3,141,841 describe the synthesis of tetraethyl lead in an electrolysis cell comprising an anode constituted by lead beads separated from the cylindrical cathode by a porous insulating wall. Balls are added during electrolysis to replace those which are consumed. However, this device does not work well for very reducing metals such as magnesium, aluminum, zinc, titanium, which are covered with an insulating oxide layer which considerably increases the contact resistance between grains. Furthermore, the presentation in granules of these metals is sometimes expensive. In addition, metallic sludge and dust often form, which disrupts operation.

South African patent No. 6806413 describes the synthesis of tetraethyl lead in an electrolysis cell comprising a consumable anode in the form of a metallic strip which passes between two cathodes in the form of discs. This system has a number of drawbacks. The thickness of the anode must in particular be small so that the interelectrode space remains constant; the speed of advance of the anode must therefore be rapid, and, to avoid breaking the ribbon, the device requires a relatively complicated mechanical system.

Also known are several mechanical devices, often very complicated, allowing the distance between the electrodes to be controlled in order to keep it constant or allowing replacement of the used anodes. German patent 2107305 describes for example such a device.

Electrolysis cells comprising a consumable anode have already been described for the electrosynthesis of oxalic acid from carbon dioxide, on the one hand with aluminum in Chim. Ind. (Milan) 55. (1973) 156 and on the other hand with zinc in J. Appl. Electrochem. 11 (1981) 743, for the electrocarboxylation of ethylene (Tetrahedron Lett. 1973, 3025) and for that of thioethers (Patent of the Democratic Republic of Germany No. 203537).

These cells are without diaphragm and generally have a coaxial cylindrical symmetry. In some cases the central electrode acts as a consumable anode (metal bar for example); in others, it acts as a cathode (graphite for example). These laboratory cells do not lend themselves to industrial use, in particular continuously, because on the one hand they require frequent and inconvenient renewal of the anode and on the other hand the distance between the 2 electrodes varies over time.

The present invention aims to provide an electrolysis cell allowing simple continuous industrial use, having the advantages of the above-mentioned industrial cells, namely in particular maintaining a constant gap between the electrodes, without having the disadvantages.

• - l'électrode consommable est constituée d'au moins un bloc métallique massif et s'applique, sous l'effet de son propre poids, contre l'autre électrode dont elle est séparée par un matériau isolant électrique laissant passer la solution d'électrolyse et dont la forme et les dimensions permettent aux surfaces actives des deux électrodes de rester parallèles au cours de l'électrosynthèse,
• - la surface active de l'électrode non consommable présente en tous ses points d'une part une inclinaison constante par rapport à une direction D faisant un angle inférieur à 45 degrés avec la verticale et d'autre part une inclinaison inférieure à 45 degrés par rapport à la verticale.
• - toute droite de direction D passant par un point quelconque de l'électrode consommable traverse la surface active de l'électrode non consommable.

The electrolysis cell according to the invention, for electrosynthesis in an organic medium, of organic or organometallic compounds, comprising two electrodes, only one of which is consumed during electrosynthesis by the electrochemical reaction of which it is the seat, is characterized in that:

• - the consumable electrode consists of at least one solid metal block and is applied, under the effect of its own weight, against the other electrode from which it is separated by an electrical insulating material allowing the electrolysis solution to pass and whose shape and dimensions allow the active surfaces of the two electrodes to remain parallel during electrosynthesis,
• the active surface of the non-consumable electrode has at all points on the one hand a constant inclination relative to a direction D making an angle less than 45 degrees with the vertical and on the other hand an inclination less than 45 degrees by compared to the vertical.
• - any straight line of direction D passing through any point of the consumable electrode crosses the active surface of the non-consumable electrode.

The inclination, at a point of a surface, with respect to a direction D is conventionally considered as being the angle formed by the plane of tangency to the surface at this point and by the line having the direction D passing through this point .

A direction can be materialized by an infinity of parallel lines.

Preferably, the direction D with respect to which the surface of the non-consumable electrode has a constant inclination is the vertical direction. In this preferred case, for which the directions D and vertical are combined, the angle formed by these two directions is zero.

By any point of the consumable electrode is meant a point as well located on its surface as inside the (or) block, solid metal constituting this electrode.

The cell according to the invention has many advantages. First of all, it allows a constant and preferably small gap (less than 5 mm) to be maintained between the two electrodes during the entire duration of the electrolysis, which is very important in an organic conductive medium, in order to avoid excessive power consumption and overheating by Joule effect.

One of the two electrodes being progressively consumed during the electrochemical reaction, a means is necessary necessarily allowing the distance between the two electrodes to be kept constant, which is obtained in the context of this invention, thanks to the particular design and geometry of the cell. In addition, it is necessary to be able to easily replace the consumable electrode as soon as it is completely consumed, or better, for continuous processes, as it is consumed, without stopping and disturbing the electrolysis.

The cell according to the invention allows very easy replacement of the consumable electrode, without stopping the electrolysis, by superposition of one (or more) another block on the solid metal block (s) constituting the consumable electrode, which is a considerable advantage when implementing continuous processes. In addition, the entire electrode is consumed, without falling or loss. The cell according to the invention also allows the use of massive consumable electrodes, therefore not very bulky for a given mass, and of various shapes. This fact is economically very interesting.

Another advantage is the fact that, given the geometry of the cell and in particular the inclination of the non-consumable electrode, the footprint on the ground is very small, which allows an economically significant gain in space.

In many cases the consumable electrode is the anode (anodic oxidation) as for the examples which follow but sometimes the consumable electrode is the cathode as is the case for the electrosynthesis of tetramethyl lead in acetonitrile medium from methyl bromide with lead cathode according to HE. Ulery JECS 116, 1201, 1969:

The consumable electrode consists of at least one solid metal block. Preferably, the metal is chosen from the group consisting of magnesium, aluminum, zinc and their alloys, namely any alloy containing at least one of the three aforementioned metals. Many other metals are also suitable, such as copper, nickel, and lead. The choice of metal depends inter alia on the compound which one wants to synthesize. In the case of electrosynthesis of organometallic derivatives, the consumable electrode is for example constituted by the corresponding metal or an alloy based on this metal.

In the case of electrosynthesis of carboxylic acids by reduction of organic halides in the presence of C0 _2, magnesium is preferred. For the electrosynthesis of alcohols by electrochemical reduction of organic halides in the presence of carboxylated derivatives as well as for the electrosynthesis of ketones and aldehydes by electrochemical reduction of organic halides in the presence of organic acid anhydrides, a metal chosen from the group formed by magnesium, zinc, aluminum and their alloys.

The solid metal blocks can be, for example, ingots whose cross section is square, or rectangular, or trapezoidal, or circular, or in any other form. They can optionally be machined before use so that their geometry is adapted to that of the non-consumable electrode. Preferably, but without this having an imperative character, such machining is carried out to facilitate the start of electrolysis.

According to a preferred variant, the consumable electrode consists of solid metal blocks stacked, each layer of the stack comprising only one block. According to another variant, at least one layer of the stack comprises several blocks arranged side by side.

The consumable electrode is applied under the effect of its own weight, by gravity, against the other non-consumable electrode. According to a preferred variant, the consumable electrode is applied against the other electrode under the sole effect of its own weight. According to another variant, the consumable electrode is applied against the other electrode under the effect, in addition to its own weight, of that of an inert charge resting on the consumable electrode. Preferably, the inert charge is electrically conductive and also serves to ensure the electrical supply of the consumable electrode.

According to another variant, the consumable electrode is applied against the other electrode under the effect, in addition to its own weight, of the force produced by a compressed spring between the upper part of the consumable electrode and a wall of the cell.

According to another preferred variant, the geometry of the non-consumable electrode is such that it alone maintains the consumable electrode, that is to say that no other wall of the cell performs this function. This is the case, for example, when the active surface of the non-consumable electrode is conical or dihedral. These two preferred variants are described later. (Figures 1 to 4).

The consumable electrode can also be maintained, according to another variant, both by the non-consumable electrode and by an inert wall of the cell. This is the case, for example, when the active surface of the non-consumable electrode is in the form of a flat surface forming a dihedral with an inert wall of the cell. This variant is also described later (Figure 5).

The non-consumable electrode is made of a conductive material. Without limitation, mention may be made of metals such as iron, aluminum and nickel, alloys such as stainless steel, metal oxides such as Pb0 ₂ and Nio ₂ , graphite. Preferably, it is made of a metal chosen from the group consisting of nickel and stainless steel.

Preferably, the distance between the active surfaces of the two electrodes is less than 5 mm. This distance is conventionally measured on a common perpendicular, between the two parallel surfaces.

The two electrodes are separated by an electrical insulating material allowing the electrolysis solution to pass and whose shape and dimensions allow the active surfaces of the 2 electrodes to remain parallel during electrosynthesis. Of course, this electrical insulating material must have sufficient mechanical strength to support the consumable electrode which rests on this material.

Preferably, the electrical insulating material is a plastic material in the form of a grid whose thickness is less than 5 mm and whose mesh consists of two networks of parallel wires, these two networks being superimposed, crossed, fixed one on the other at the contact points of the wires, the thickness of the wires of each network being the same. In general the two networks are fixed to each other by welding and the wires of the two networks have the same thickness.

As an indication, the distance between the wires of each network is between a few millimeters and a few centimeters.

The wires of each network may not be parallel their thickness may not be constant provided that after assembly of the networks, the mesh has a constant maximum thickness at several points, less than about 5 mm.

The cross section of the wires can be arbitrary, for example square, rectangular, circular, elliptical, trapezoidal.

The plastic material can be, for example, polypropylene, polyethylene or polytetrafluoroethylene.

Such plastic gratings have on the one hand a high vacuum rate, which allows easy circulation of the electrolysis solution between the two electrodes and on the other hand a relatively small contact surface with the electrodes, which avoids an excessive reduction in their active surface.

As other materials separating the two electrodes, it is possible to use, within the framework of the present invention, a fabric, a canvas or a porous material of constant thickness such as for example a ceramic or a felt.

The renewal of the electrolysis solution between the electrodes can, for example, be ensured by mechanical agitation or by forced circulation using a pump, for example.

During electrolysis, the active surface of the consumable electrode opposite the active surface of the other electrode becomes _s out. The consumable electrode therefore descends gradually, by gravity, under the simple effect of its own weight. Furthermore, the dissolution being stronger at the locations closest to the non-consumable electrode, the consumable electrode tends to conform as best as possible to the shape of the non-consumable electrode, which limits the risks of irregular dissolution.

• - La figure 1 représente une vue de face d'un premier mode de réalisation d'une cellule d'électrolyse selon l'invention,
• - La figure 2 représente, en coupe droite selon la ligne II-II, la cellule représentée figure 1,
• - La figure 3 représente une vue de face d'un second mode de réalisation d'une cellule d'électrolyse selon l'invention,
• - La figure 4 représente, en coupe droite selon IV-IV, la cellule représentée figure 3.
• - La figure 5 représente une coupe en section droite d'un troisième mode de réalisation d'une cellule d'électrolyse selon l'invention,
• - La figure 6 représente une vue en perspective d'une matière plastique en forme de grillage utilisable comme matériau isolant électrique entre les deux électrodes, et
• - La figure 7 représente un schéma synoptique d'une installation complète d'électrolyse.

The following description of three particular embodiments of the invention illustrates the invention, without limiting it.

• FIG. 1 represents a front view of a first embodiment of an electrolysis cell according to the invention,
• FIG. 2 represents, in cross section along line II-II, the cell represented in FIG. 1,
• FIG. 3 represents a front view of a second embodiment of an electrolysis cell according to the invention,
• - Figure 4 shows, in cross section along IV-IV, the cell shown in Figure 3.
• FIG. 5 represents a cross-section in cross section of a third embodiment of an electrolysis cell according to the invention,
• FIG. 6 represents a perspective view of a plastic material in the form of a grid usable as an electrical insulating material between the two electrodes, and
• - Figure 7 shows a block diagram of a complete electrolysis installation.

The electrolysis cell shown in FIGS. 1 and 2 comprises a tank, one of the walls of which is constituted by cathode 2, which is not consumable. The active surface of the non-consumable electrode 2 consists of two rectangular surfaces, of the same dimensions, arranged in the form of a dihedron whose edge 3, horizontal, constitutes the lowest part of the tank.

This active surface has at all points a constant inclination of 17 degrees relative to direction 9, which is the vertical direction and which can for example be materialized by the vertical of the section plane along _I I-II passing through the edge 3.

The other walls of the tank are on the one hand vertical walls passing through the edges of the cathode 2 other than the aforementioned edge 3 and on the other hand a horizontal wall 10 closing the tank at its upper part. All these walls, other than those constituting the cathode 2, are made of an electrical insulating material or internally covered with an electrical insulator 1, for example a paint or any other electrically insulating coating.

The anode 4 consists of a stack of solid metal ingots of trapezoidal section. Each layer of the stack comprises only one ingot. The dimensions (length and width) of the ingots are slightly smaller than those of the tank.

Any straight line of direction 9 passing through any point of the consumable anode 4 crosses the active surface of the non-consumable cathode 2.

The anode 4 is applied under the sole effect of its own weight against the cathode 2 which, alone, ensures the maintenance of the anode 4.

The anode 4 and the cathode 2 are separated by a plastic material 5 in the form of a grid. Figure 6 shows a perspective view. The mesh consists of two networks of parallel wires A † B ₁ C ₁ ... N ₁ on the one hand and A ₂ B ₂ C ₂ ... N ₂ on the other. The wires of these two networks are cylindrical, with a diameter of 1 mm. The distance between the wires is 1 cm.

The two networks are superimposed, crossed at right angles and welded to the contact points of the wires.

The electrolysis solution 6 circulates from bottom to top in the cell read the. Pipes 8 allow the arrival and the exit of this solution 16, in the direction of the arrows 7.

The electrodes 2 and 4 are supplied with electric current by a DC voltage source, not shown in FIGS. 1 and 2.

When the cell is rotated around the edge 3 by an alpha angle, the direction 9 becomes a direction D making an alpha angle with the vertical direction the active surface of the non-consumable electrode 2 always has all its points a constant inclination of 17 degrees relative to this direction D and any straight line of direction D passing through any point of the consumable anode 4 crosses the active surface of the non-consumable cathode 2. First of all alpha must be less than 45 degrees in the context of the present invention. Moreover, with respect to the vertical, the inclination of the active surface of the electrode 2 is (17 + alpha) to one of _the rectangular surfaces and areas 117 - alpha) to each other, is 117 + or - alpha!. In the context of the present invention, this inclination 1 ₁ 7 + or - alpha relative to the vertical must be less than 45 degrees, that is to say for this particular embodiment, that alpha must be less than 28 degrees. Otherwise, there may be significant anomalies in the operation of the cell, in particular in the movement of the consumable electrode.

The electrolysis cell shown in Figures 3 and 4 comprises a tank whose bottom wall is formed by the cathode 12, which is not consumable. The active surface of the non-consumable electrode 12 is conical, the tip of the cone being directed downwards. This active surface has at all points a constant inclination of 15 degrees relative to the direction 19 which is that of the axis of the cone. For the cell shown in Figures 3 and 4 this axis is vertical.

The upper wall 21 of the tank is cylindrical and extends the cone so that the cylinder and the cone have the same axis, the diameter of the cylinder being the same as that of the base circle of the cone.

A horizontal circular wall 20, of diameter equal to that of the cylinder, closes the tank at its upper part.

The walls 20 and 21 are made of an electrical insulating material or internally covered with an electrical insulator 11, for example a paint or any other electrically insulating coating.

The anode 14 consists of a stack of cylindrical solid metal ingots whose diameter is slightly less than that of the cylindrical wall 21 of the tank. It is applied under the sole effect of its own weight against the cathode 12 which, alone, ensures the maintenance of the anode 14.

Any straight line 19 passing through any point of the consumable anode 14 crosses the active surface of the non-consumable cathode 12.

The anode 14 and the cathode 12 are separated by a plastic material 15 in the form of a grid such as that shown in FIG. 6 and previously described.

The electrolysis solution 16 circulates from bottom to top in the cell. Pipes 18 allow the arrival and the exit of this solution 16, in the direction of the arrows 17.

The inlet pipe extends the tip of the cathode 12 along the axis of the cell. The electrodes 12 and 14 are supplied with electric current by a DC voltage source, not shown in FIGS. 3 and 4.

When the axis of the cell is rotated by an alpha angle around the tip of the cone, the active surface of the non-consumable electrode 12 always has at all points a constant inclination of 15 degrees relative to the direction D represented by the axis of the cell and any straight line of direction D passing through any point of the consumable anode 14 crosses the active surface of the cathode 12 which is not consumable. First of all alpha must be less than 45 degrees in the context of the present invention. Furthermore, relative to the vertical, the inclination of the active surface of the non-consumable electrode 12 is between (15 + alpha) and 115 - alpha ,.

In the context of the present invention, the inclination relative to the vertical must be less than 45 degrees, that is to say for this particular embodiment, that alpha must be less than 30 degrees. Otherwise, there may be significant anomalies in the functioning of the cell.

The electrolysis cell shown in FIG. 5 comprises a cell, one of the walls of which is constituted by the cathode 32, which is not consumable. The active surface of the cathode 32 is a rectangular surface, one of the sides 33 of which is horizontal and constitutes the lowest part of the tank. This active surface has at all points a constant inclination of 20 degrees relative to the direction 39 which is the vertical direction which can for example be materialized by the vertical of the cutting plane passing through the side 33.

The other walls of the tank are on the one hand vertical walls passing through the 4 sides of the rectangular cathode 32 and on the other hand a horizontal wall 40 closing the tank at its upper part. All these walls, other than that constituting the cathode 32 are made of an electrically insulating material or internally covered with an electrical insulator 31, for example a paint or any other electrically insulating coating.

Anode 34 consists of a stack of metal ingots massive rectangular section. Each layer of the stack comprises only one ingot.

The dimensions (length and width) of the ingots are slightly smaller than those of the tank.

The anode 34 is applied under the sole effect of its own weight against the cathode 32 and against the wall 42 of the tank which passes through the side 33 and which forms a dihedral with the cathode 32.

Any straight line 39 passing through any point of the consumable anode 34 crosses the active surface of the non-consumable cathode 32.

The anode 34 and the cathode 32 are separated by a plastic material 35 in the form of a grid such as that shown in FIG. 6 and previously described.

The electrolysis solution 36 circulates from bottom to top in the cell. Pipes 38 allow the arrival and exit of this solution 36, in the direction of the arrows 37.

The electrodes 32 and 34 are supplied with electric current by a DC voltage source, not shown in FIG. 5.

When the cell is rotated by an alpha angle around the side 33 constituting the lowest part of the tank, the direction 39 becomes a direction D making an alpha angle with the vertical direction 39.

The active surface of the cathode 32 always has of course at all points a constant inclination of 20 degrees relative to this direction D.

• 1) D fait un angle inférieur à 45 degrés avec la verticale donc alpha est inférieur à 45 degrés.
• 2) La surface active de la cathode 32 présente une inclinaison inférieure à 45 degrés par rapport à la verticale.

In the context of the present invention:

• 1) D makes an angle less than 45 degrees with the vertical so alpha is less than 45 degrees.
• 2) The active surface of the cathode 32 has an inclination less than 45 degrees relative to the vertical.

to meet all of these two conditions, the cell can be rotated either by an alpha angle less than 25 degrees clockwise while looking at Figure 5, or by an alpha angle less than 45 degrees in reverse.

The upper walls 10, 20 and 40 of the electrolysis cells according to the invention are removable or have a removable part so as to allow the introduction of solid metal blocks.

A complete installation allowing the continuous electrolysis of a solution is schematically represented in FIG. 7. It consists of a closed circuit comprising a reactor 51 with double jacket allowing the loading and the recovery of the products, an electrolysis cell 52 and a pump 53 allowing the circulation of the electrolysis solution in the circuit. The lower part of the reactor 51 is connected to the lower part (inlet) of the cell 52 and the outlet of the cell 52 is connected to the upper part of the reactor 51.

The jacketed reactor 51 is cooled by a circulation of water, symbolized by the arrows 54.

The direction of circulation of the electrolysis solution previously defined is symbolized by the arrows 55.

The cell 52 shown diagrammatically in FIG. 7 is that shown in FIGS. 1 and 2.

The present invention also relates to the use of the new electrolysis cells described above, provided with an anode consumable in a metal chosen from the group formed by magnesium, zinc, aluminum and their alloys for electrosynthesis. in an organic solvent medium of organic compounds chosen from the group consisting of carboxylic acids, alcohols, ketones and aldehydes by electrochemical reduction of organic halides.

According to a first variant, an electrolysis cell is used provided with an anode consumable in a metal chosen from the group formed by magnesium and its alloys for the electrosynthesis of carboxylic acids by electrochemical reduction of organic halides in the presence of carbon dioxide.

It has been found that, completely unexpectedly, very high yields are obtained with little or no by-products, while the implementation is very simple and does not require one or more catalysts. This particular use applies to the electrosynthesis of a very large number of carboxylic acids, both aliphatic and aromatic. As the aliphatic chain, mention may, for example, be made of alkyl or cycloalkyl chains, substituted or not, unsaturated or not, containing from 1 to 21 carbon atoms.

As aromatic chains, mention may, for example, be made of substituted or unsubstituted phenyl, thiophene, furan and pyridine rings. The carboxyl group can as well be linked to an aliphatic carbon as to a carbon of an aromatic ring. The use of a magnesium anode provides the best results. In particular, tests have been carried out with an anode either of aluminum or of zinc, all other conditions identical elsewhere. The yields are then lower than those obtained with the magnesium anode. The organic solvents used are the low-protic solvents usually used in organic electrochemistry, such as hexamethylphosphorotriamide (HMPT) tetrahydrofuran (THF), N-methylpyrolidone (NMP), dimethylformamide (DMF).

The organic solvent conventionally contains an indifferent electrolyte such as tetrabutylammonium tetrafluoroborate (BF4NB _U4 ) or lithium perchlorate.

The yields obtained in the carboxylate formed are high, very often greater than 99%. The yields of isolated carboxylic acid vary from 70 to 90% of the yield of carboxylate formed.

According to a second variant, use is made of an electrolysis cell provided with an anode consumable from a metal chosen from the group formed by magnesium, zinc, aluminum and their alloys for the electrosynthesis of alcohols, by electrochemical reduction of organic halides having an atom or a functional group stabilizing carbanions attached to the carbon carrying halogen, in the presence carbonyl derivatives.

The latter can be aldehydes as well as ketones; the yields are high and the implementation relatively simple.

The organic halides have at least one atom or a functional group stabilizing carbanions, attached to the carbon carrying the halogen, that is to say located in the alpha position relative to the halogen.

The atoms and functional groups which stabilize carbanions are well known to those skilled in the art. Mention may be made, for example, of halogens, ester, ketone, allyl, benzene, alkoxy or nitrile groups.

• - un groupement benzylique, substitué ou non substitué
  
  Ar représentant un groupement aromatique)
• - un groupement allylique, substitué ou non substitué
  
• - un groupement alpha monohalogéné
  
  alpha dihalogéné
  
  ou alpha trihalogéné (CX₃)
• - un groupement alpha ester
  
• - un groupement alpha cétonique
  

Preferably, the organic halides which can be used in the context of the present invention correspond to the general formula _RX in which X represents a halogen atom and R represents:

• - a benzyl group, substituted or unsubstituted
  
  Ar representing an aromatic group)
• - an allylic group, substituted or unsubstituted
  
• - a monohalogenated alpha group
  
  alpha dihalogenated
  
  or trihalogenated alpha (CX ₃ )
• - an alpha ester group
  
• - an alpha ketone group
  

By way of illustration and without limitation, mention may be made, for example, of benzyl chloride, benzyl bromide, allyl chloride, 3-chloro 2 methyl propene, 3-chloro 1 butene, 1-chloro 1-methyl ethyl acetate, carbon tetrachloride, dichlorophenylmethane, 1-phenyl 3-chloro propene and 1-methyl 3-chloropropene.

dans laquelle R₁ et R₂, identiques ou différents, représentent :

• - un atome d'hydrogène,
• - une chaîne aliphatique ou cycloaliphatique, substituée ou non substituée, saturée ou non saturée,
• - un groupement aryle, substitué ou non substitué,

ou bien encore, R₁ et R₂, conjointement avec l'atome de carbone auxquels il sont attachés, forment un cycle, saturé ou non saturé, substitué ou non substitué, comportant éventuellement un ou plusieurs hétéroatomes comme l'azote, l'oxygène, le phosphore ou le soufre. A titre illustratif et non limitatif, on peut citer par exemple l'acétone, la cyclohexanone, la méthyléthylcétone, l'acé- taldehyde, la benzophénone et la dichlorobenzophénone.According to a particular embodiment, the carbonyl derivatives correspond to the general formula

in which R ₁ and R ₂ , identical or different, represent:

• - a hydrogen atom,
• - an aliphatic or cycloaliphatic chain, substituted or unsubstituted, saturated or unsaturated,
• - an aryl group, substituted or unsubstituted,

or alternatively, R ₁ and R ₂ , together with the carbon atom to which they are attached, form a ring, saturated or unsaturated, substituted or unsubstituted, optionally comprising one or more heteroatoms such as nitrogen, oxygen , phosphorus or sulfur. By way of illustration and without limitation, mention may, for example, be made of acetone, cyclohexanone, methyl ethyl ketone, acetaldehyde, benzophenone and dichlorobenzophenone.

dans laquelle R, R₁ et R₂ ont la signification précitée.
De façon particulièrement préférée, lorsque les dérivés carbonylés sont des cétones, c'est-à-dire lorsque R₁ et R₂ sont différents de l'hydrogène, on obtient des alcools tertiaires.According to a preferred variant, the alcohols obtained according to the process which is the subject of the present invention correspond to the general formula

in which R, R ₁ and R ₂ have the abovementioned meaning.
Particularly preferably, when the carbonyl derivatives are ketones, that is to say when R ₁ and R ₂ are different from hydrogen, tertiary alcohols are obtained.

In general, to carry out the present invention, it is quite obvious to the skilled person that the carbonyl derivative must be more difficult to reduce than the organic halide and none of the substituents carried by R ₁ and R ₂ must be more electrophilic. than the carbonyl group itself.

The organic solvents and the indifferent electrolytes used are the same as those mentioned above for the synthesis of carboxylic acids. Preferably, DMF is used as solvent and the electrolysis is carried out at a temperature of between -20 ° C. and + 30 ° C.

According to a third variant, an electrolysis cell is used provided with an anode consumable in a metal chosen from the group formed by magnesium, zinc, aluminum and their alloys for the electrosynthesis of ketones and aldehydes by electrochemical reduction of organic halides in the presence of organic acid anhydrides. The implementation is simple and the mass and faradaic yields high.

• - une chaîne aliphatique ou cycloaliphatique, substituée ou non substituée, saturée ou non saturée,
• - un groupement aryle, substitué ou non substitué,
• - un hétérocycle aromatique, substitué ou non substitué, comme par exemple le cycle thiophène, furanne ou pyridine.

According to a particular embodiment, the organic halides correspond to the general formula R ₃ X in which _X represents a halogen chosen from the group consisting of chlorine, bromine and iodine and R ₃ represents:

• - an aliphatic or cycloaliphatic chain, substituted or unsubstituted, saturated or unsaturated,
• - an aryl group, substituted or unsubstituted,
• - an aromatic heterocycle, substituted or unsubstituted, such as for example the thiophene, furan or pyridine ring.

Preferably, R ₃ represents an aliphatic chain substituted by at least one aromatic group, for example in benzyl chloride, benzyl bromide, 1-phenyl 1-chloro ethane and 1-phenyl 1-chloro propane.

In general, R ₃ can carry non-electro-reducible functions or more difficult to reduce than the R ₃ -X bond, under the experimental conditions of electrosynthesis. Such non-electroreducible functions are, for example, the cyano, ether, sulfide or ester functions.

dans laquelle, R₄ représente :

• - un atome d'hydrogène,
• - une chaîne aliphatique ou cycloaliphatique, substituée ou non substituée, saturée ou non saturée,
• - un groupement aryle, substitué ou non substitué,ou
• - un hétérocycle aromatique, substitué ou non substitué, comme par exemple le cycle furanne, thiophène ou pyridine, et R₅ représente :
• - une chaîne aliphatique ou cycloaliphatique, substituée ou non substituée, saturée ou non saturée,
• - un groupement aryle substitué ou non substitué,
• - un hétérocycle aromatique, substitué ou non substitué, comme par exemple le cycle furanne, thiophène ou pyridine,ou
• - un groupement OR₆ dans lequel R₆ représente :
  • ^* une chaîne aliphatique ou cycloaliphatique, substituée ou non substituée, saturée ou non saturée,
  • ^* un groupement aryle, substitué ou non substitué,
  • ^* un hétérocycle aromatique, substitué ou non substitué, comme par exemple le cycle furanne, thiophène ou pyridine,

ou bien encore R₄ et R₅ forment au moins un cycle, substitué ou non substitué, comme c'est le cas par exemple pour l'anhydride phtalique ou l'anhydride succinique.According to another particular embodiment, the anhydrides of organic acids correspond to the general formula

in which, R ₄ represents:

• - a hydrogen atom,
• - an aliphatic or cycloaliphatic chain, substituted or unsubstituted, saturated or unsaturated,
• - an aryl group, substituted or unsubstituted, or
• - an aromatic heterocycle, substituted or unsubstituted, such as for example the furan, thiophene or pyridine ring, and R ₅ represents:
• - an aliphatic or cycloaliphatic chain, substituted or unsubstituted, saturated or unsaturated,
• - a substituted or unsubstituted aryl group,
• - an aromatic heterocycle, substituted or unsubstituted, such as for example the furan, thiophene or pyridine ring, or
• - an OR ₆ group in which R ₆ represents:
  • ^* an aliphatic or cycloaliphatic chain, substituted or unsubstituted, saturated or unsaturated,
  • ^* an aryl group, substituted or unsubstituted,
  • ^* an aromatic heterocycle, substituted or unsubstituted, such as for example the furan, thiophene or pyridine ring,

or alternatively R ₄ and R ₅ form at least one ring, substituted or unsubstituted, as is the case for example for phthalic anhydride or succinic anhydride.

When R ₅ represents an OR ₆ group, the corresponding anhydrides are then mixed anhydrides of carboxylic acids and carbonic acid. In the other cases, they are anhydrous carboxylic acids.

lorsque les halogénures organiques répondent à la formule générale :

When R ₄ represents a hydrogen atom, aldehydes are obtained. In this case, when the organic halides correspond to the general formula R ₃ X previously defined, the aldehydes obtained correspond to the general formula R ₃ CHO. In the other cases, when R ₄ does not represent a hydrogen atom, ketones are obtained. These ketones correspond to the general formula

when the organic halides correspond to the general formula:

In general, R ₄ and R ₅ can carry non-electro-reducible functions, or more difficult to reduce than the R ₃ -X bond, under the experimental conditions of electrosynthesis, and none of the functions carried by R ₃ or R ₄ does must be more electrophilic than the anhydride function itself.

Preferably, _R4 and _R5 represent a linear or branched alkyl chain.

Also preferably, R ₄ and R ₅ are identical.

In a particularly preferred manner, R ₄ and R ₅ are identical and represent an alkyl chain, linear or branched, as is the case for example for acetic anhydride.

The organic solvents and the indifferent electrolytes used are the same as those mentioned above for the synthesis of carboxylic acids. Preferably, DMF is used as solvent.

As a general rule, when using an electrolysis cell according to the invention for electrosynthesis, in organic medium, of organic or organometallic compounds and in particular for the electrosynthesis of the abovementioned organic derivatives, the direction _D is to preferably the vertical direction.

The following examples illustrate the invention without limiting it.

EXAMPLE 1 Synthesis of Phenylacetic Acid

An electrolysis cell such as that shown in FIGS. 1 and 2 is used. The cathode, made of stainless steel, has an active surface of 20 dm ² . The other walls of the tank are also made of stainless steel but are internally covered with an electrically insulating paint.

The anode 4 consists of a stack of massive magnesium ingots. These ingots have the following dimensions: length: 360 mm, upper width: 130 mm, lower width laughing: 120 mm, height: 50 mm.

The plastic material 5 in the form of a mesh is polypropylene. This mesh is just placed on the active surface of the cathode 2, the shape of which it follows, before the introduction of the anode 4. The complete installation is such as that shown diagrammatically in FIG. 7.

For the first electrolysis, the three lower ingots are machined so as to best match the dihedral shape of the cathode. The other ingots are then stacked thereon to the top of the cell.

After having mixed in the reactor 3 kg of benzyl chloride (23.7 mol), 300 g of tetrabutylammonium fluoroborate and 27 1 of anhydrous NMP and imposed in the installation a carbon dioxide pressure of 4 bar, the solution thus obtained in the installation and in particular in the electrolysis cell.

We operate at a constant intensity of 60 A for 24 hours. During electrolysis, the voltage quickly stabilizes at around 12 volts, which proves the proper functioning of the cell, namely in particular that the active surfaces of the two electrodes remain well parallel with a constant deviation. At the end of the electrolysis, the phenylcetic acid formed is isolated, and identified according to the usual methods well known to those skilled in the art.

By double weighing of the anode, a weight loss of 590 g was measured.

The acid formed was isolated after extraction with ether and then evaporation. Phenylacitic acid was identified by its melting point (76 ° C) and by its NMR and IR spectra. The yield obtained in isolated product is 90% relative to the initial benzyl chloride.

To then carry out other electrolysis, it is possible, before or during the electrolysis, to add a few ingots to the remaining stack in order to compensate for those having been consumed during the first electrolysis. For these other electrolyses, the optimal operating conditions are met from the start of the electrolysis since the anode is then already in the optimal position relative to the cathode.

Example 2. Synthesis of dimethylbenzylcarbinol

An electrolytic cell such as that shown in FIGS. 1 and 2 is used. The nickel cathode 2 has an active surface of 1 dm ² . The other walls of the tank are made of stainless steel and are internally covered with an electrically insulating paint 1. The anode 4 consists of a stack of cubic blocks (50 mm in dimension) made of aluminum.

The plastic material 5 and the installation are the same as those of Example 1. For the first electrolysis, the lower aluminum block was machined so that its cross section is trapezoidal and can thus, when the wedge horizontally at the top of the cathode, have from the start of electrolysis, a larger active surface. The other cubes are not machined and are stacked on the first to the top of the cell. After having mixed 200 g of benzyl chloride (1.58 mol), 20 g of tetrabutylammonium iodide, 280 g of DMF and 1500 g of acetone in the reactor, the solution thus obtained is circulated in the installation.

For the first electrolysis, we first operate at a constant intensity of 1A. As soon as the lower aluminum block reaches the bottom of the cell, a constant intensity of 2.5 A is maintained. The electrolysis voltage then remains stable, at around 15 V, which proves the proper functioning of the cell. The electrolysis is stopped after 42 h.

After stopping the electrolysis, the dimethylbenzylcarbinol formed is isolated, and identified according to the usual methods, well known to those skilled in the art. The alcohol formed was isolated after hydrolysis of the solution using an aqueous chloride solution of ammonium and extraction with ether. After evaporation of the ether, the crude alcohol was purified by distillation. The pure alcohol thus isolated (purity verified by CPG) is identified by its NMR and IR spectra. The yield of distilled dimethylbenzylcarbinol thus obtained is 56% (purity greater than 95%).

To then carry out other electrolyses, the intensity of the current is fixed at the start at 2.5 A since the optimal operating conditions are then already met, the anode being in the optimal position relative to the cathode.

Example 3. Synthesis of dimethylbenzylcarbinol

The same test is carried out as that of Example 2 but without machining the lower block of the anode. The same result is obtained but the operating equilibrium takes longer to reach.

Example 4. Synthesis of dimethylbenzylcarbinol

An electrolysis cell such as that shown in FIGS. 3 and 4 is used. The cathode 12, made of stainless steel, is a cone with a height of 100 mm and a base diameter of 53 mm. The other walls of the tank are made of stainless steel and are internally covered with an inert electrical insulating coating 11. The anode 14 consists of a stack of cylindrical aluminum blocks with a diameter of 50 mm and a height of 100 mm.

The plastic material 15 and the installation are the same as those of Example 1. For the first electrolysis, the lower aluminum block was machined so that it is approximately in the form of a cone. 100 mm high and 50 mm base diameter, which is easily achieved from a cylindrical block with these dimensions.

After positioning the plastic material 15 in the form of a grid on the active surface of the cathode, the block is introduced. machined which follows the shape of the cathode, then stacked on this lower block several other blocks to the top of the cell.

The operation is then carried out under the same conditions as for example 2. The electrolysis voltage stabilizes very quickly, due to the machining of the first block. The yield of distilled dimethylbenzylcarbinol obtained is 60% (purity greater than 95%).

Example 5. Synthesis of dimethylbenzylcarbinol

The same test is carried out as that of Example 4 but without machining the lower block before the first electrolysis. The same result is obtained but the operating equilibrium is much longer to reach.

Example 6. Synthesis of dimethylbenzylcarbinol

The same test is carried out as that of Example 3, with the only difference that the anode 4 consists of a stack of blocks of length 50 mm, height 50 mm and width 25 mm, each layer of the stack. consisting of 2 blocks placed side by side. Pure dimethylbenzylcarbinol is obtained with a yield of 53%.

Example 7. Synthesis of dimethylbenzylcarbinol

An electrolysis cell such as that shown in FIG. 5 is used. The nickel cathode 32 has an active surface of 0.5 dm ² . The other walls of the tank are made of stainless steel and are internally covered with an electrically insulating paint 31.

The anode 34 consists of a stack of aluminum blocks of length 50 mm, height 50 mm and width 30 mm.

The plastic 35 and the installation are the same as those of Example 1. For the first electrolysis, the ₂ lower blocks so that their geometry is combined with that of the dihedral lower part of the cell. We then stack on these 2 blocks, other blocks not machined to the top of the cell. The operation is then carried out under the same conditions as those of Example 2.

Pure dimethylbenzylcarbinol is obtained with a yield of 51 _% .

To then carry out other electrolysis, it suffices to add a few blocks at the top of the cell since the optimal operating conditions are already met, the anode being in the optimal position relative to the cathode.

Examples 8 to 23. Synthesis of Various Other Organic Acids

The following examples were carried out under the same general conditions as those of Example 1. The halogenated derivatives listed in Table I were used in place of benzyl chloride. Table I also specifies the solvent used and the results obtained. The acids obtained were identified by IR and NMR spectrometries as well as by their melting point for some of them.

The yields of isolated acid are expressed in% relative to the starting organic halide.

Examples 23 to 32. synthesis of various other alcohols

The following examples were carried out under the same general conditions as those of Example 2.

Table II specifies for each example the halogenated derivative and the starting carbonylated derivative, the nature of the solvent of the electrolyte and of the electrodes, the temperature at which the electrolysis is carried out, the molar ratio between the two starting materials, the Faraday number per mole of organic halide, the yield of isolated pure alcohol expressed in% relative to the starting organic halide. The alcohols obtained were identified by spectrometry IR and NMR sorting.

Example 33 Synthesis of Benzyl Methyl Ketone (Phenyl Acetone)

An electrolysis cell such as that shown in FIGS. 1 and 2 is used. The cathode 2, made of nickel, has a surface of 1- dm2. The other walls of the tank are made of stainless steel and are internally covered with an electrically insulating paint.

Anode 4 consists of a stack of cubic blocks (50 mm side) made of magnesium. The plastic material 5 and the installation are the same as those of Example 1.

For the first electrolysis, the lower magnesium block was machined so that its cross section was trapezoidal. The other cubes are not machined and are stacked on the first to the top of the cell.

After having mixed in the reactor 100 g of benzyl chloride (0.79 mol), 700 g of acetic anhydride (1.86 mol), 1100 g of DMF and 20 g of tetrabutylammonium fluoroborate, the solution is circulated in this way obtained in the installation.

The electrolysis intensity is 2A and the temperature 25 ° C. After 23 h of electrolysis (2.2 Faraday per mole of benzyl chloride), the DMF is evaporated and the residue is hydrolyzed with hot diluted _HC l. The be: is isolated: .zylmethylketone by extraction with ether with a yield of 39%. The pure benzylmethylketone thus isolated was identified by its IR and NMR spectra and its purity was checked by GC (> 95%).

Example 34 Synthesis of 4-tert-butylphenylacetone

The procedure is as in Example 33, replacing the benzyl chloride with 4 tert-butylphenylchloromethane.

The pure 4 tert-butylphenylacetone thus isolated (yield 73%) was identified by its IR and NMR spectra and its purity was checked. trusted by CPG (> 95%).

Example 35 Synthesis of 3,4 Dimethoxyphenylacetone

The procedure is as in Example 33, replacing the benzyl chloride with 3,4 dimethoxyphenylchloromethane.

The ₃ , 3 dimethoxyphenylacetone pure thus isolated (yield 25 _% ) was identified by its IR and NMR spectrums and its purity was checked by GC (> 95%).

Claims (15)

1. Electrolysis cell for electrosynthesis in organic medium of organic or organometallic compounds, comprising two electrodes (2-12) and (4-14) of which only one (4-14) is consumed during the electrosynthesis by the electrochemical reaction of which it is the seat, characterized in that: - the consumable electrode (4-14) consists of at least one solid metal block and is applied under the effect of its own weight against the other electrode (2-12) from which it is separated by an insulating material electric (5-15) letting through the electrolysis solution (6-16) and whose shape and dimensions allow the active surfaces of the two electrodes (2-12) and (4-14) to remain parallel during i electrosynthesis; - the active surface of the non-consumable electrode (2-12) has on the one hand a constant inclination with respect to a direction D (9-19) making an angle less than 45 degrees with the vertical and on the other hand a tilt less than 45 degrees from the vertical; - any straight line D (9-19) passing through any point of the consumable electrode (4.14) crosses the active surface of the consumable electrode (2-12). 2. Electrolysis cell according to claim 1 characterized in that the direction D (9-19) is the vertical direction. 3. Electrolysis cell according to any one of claims ₁ and 2 characterized in that the consumable electrode (4-14) consists of solid metal blocks stacked, each layer of the stack comprising only one block . 4. Electrolysis cell according to any one of the preceding claims, characterized in that the active surface of the non-consumable electrode (2-12) consists of two rectangular surfaces of the same dimensions, arranged in the form of a dihedron. 5. Electrolysis cell according to any one of claims 1 to 3 characterized in that the active surface of the non-consumable electrode (2-12) is conical. 6. Electrolysis cell according to any one of the preceding claims, characterized in that the non-consumable electrode (2-12) is made of a metal chosen from the group consisting of nickel and stainless steel. 7. Electrolysis cell according to any one of the preceding claims, characterized in that the distance between the active surfaces of the two electrodes (2-12) and (4-14) is less than 5 mm. 8. Electrolysis cell according to any one of the preceding claims, characterized in that the consumable electrode (4-14) is applied against the other electrode (2-12) under the effect, in addition to its own weight , that of an inert charge, based on the consumable electrode (4-14). 9. An electrolysis cell according to claim 8 characterized in that the inert charge is electrically conductive and serves to ensure the electrical supply of the consumable electrode (4-14). 10. Electrolysis cell according to any one of claims 1 to 7 characterized in that the consumable electrode (4-14) is applied against the other electrode (2-12) under the sole effect of its own weight . ₁₁ . Electrolysis cell according to any one of the preceding claims, characterized in that the electrical insulating material (5-15) is a plastic material in the form of a grid, the thickness of which is less than 5 mm and the mesh of which consists of two networks of parallel wires, these two networks being superimposed, crossed, fixed one on the other at the contact points of the wires, the thickness of the wires of each network being the same. 12. Use of an electrolysis cell provided with an anode consumable in a metal chosen from the group formed by magnesium, zinc, aluminum and their alloys according to any one of the preceding claims for electrosynthesis by organic solvent medium of organic compounds chosen from the group consisting of carboxylic acids, alcohols, ketones and aldehydes, by electrochemical reduction of organic halides. 13. Use, according to claim 12, of an electrolysis cell provided with an anode consumable in a metal chosen from the group formed by magnesium and its alloys for the electrosynthesis of carboxylic acids by electrochemical reduction of halides organic in the presence of carbon dioxide. 14. Use, according to claim 12, of an electrolysis cell provided with an anode consumable in a metal chosen from the group formed by magnesium, aluminum, zinc and their alloys for the electrosynthesis of alcohols by electrochemical reduction of organic halides having an atom or a functional group stabilizing carbanions attached to the carbon carrying the halogen, in the presence of carbonyl derivatives. - 15. Use, according to claim 12, of an electrolysis cell provided with an anode consumable in a metal chosen from the group formed by magnesium, aluminum, zinc and their al bonding for the electrosynthesis of ketones or aldehydes by electrochemical reduction of organic halides in the presence of organic acid anhydrides.

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