BRPI0712395A2 - electrochemical process for the preparation of a compound containing a halogenated carbonyl group - Google Patents

Abstract

ELECTROCHEMICAL PROCESS FOR THE PREPARATION OF A COMPOUND CONTAINING A HALOGENATED CARBONILLA GROUP. The present invention relates to a process for the preparation of a compound containing a halogenated carbonyl group by electrochemically reacting the compound containing the corresponding carbonyl group with an HX hydrogen halide, an R1-X organic halide and / or a halide salt. Mn + -X? under substantially water-free conditions, where X is a chlorine, bromine or iodine atom, R1 is an alkyl or aryl group that can be linear or branched, optionally containing one or more hetero atoms such as oxygen, nitrogen, chloride, bromide, fluoride or iodide from which the halogen atom X can be electrochemically separated, M + is a cation of quaternary ammonium, alkaline earth metal, alkali metal or metal, and n is a positive integer from 1 to 5, depending on the valence of the metal cation M? +.

Description

Report of the Invention Patent for "ELECTROCHEMICAL PROCESS FOR PREPARING A COMPOUND CONTAINING A HALOGENED CARBONILE GROUP".

The present invention relates to a novel electrochemical process for the preparation of a compound containing a halogenated carbonyl group, such as a carboxylic acid. In one specific embodiment, it refers to the chlorination of acetic acid to manufacture monochlorochloric acid.

In industry, monocloroacetic acid is prepared by reacting acetic acid with chlorine. Such a process for preparing monochloroacetic acid is generally known and generally employs a reactor wherein a mixture of liquid acetic acid (HAc) is reacted with chlorine gas under anhydrous conditions. A large number of compounds can be used to create these anhydrous conditions. If acetic anhydride is used, it will be converted immediately with hydrochloric acid to acetyl chloride, which is the catalyst for this process. The process is generally carried out at a pressure of (1 to 6 bars and a temperature of 80 to 180 ° C. In the reactor, monochloric acid (MCA) and gaseous HCI are formed together with the by-products. of which dichloroacetic acid (DCA) and trichloroacetic acid (TCA) are examples.

After the MCA-containing reaction product mixture has passed into the reactor (s) and catalyst recovery section, DCA is present in a significant amount, typically from about 3 to .10%. The MCA / DCA-containing product mixture is then conducted one unit to reduce the amount of DCA in MCA. This can be done by physical separation, such as melt crystallization, or by chemical conversion, such as a reduction where DCA is reduced with hydrogen in the presence of a hydrogenation catalyst, for example, a catalyst based of metal. This catalyst not only reduces DCA, but also reduces MCA to some extent, which is naturally undesirable. Moreover, such a reduction unit and its operation are expensive, and this increases the production costs of the final MCA product. The low boiling components are then removed from the MCA by conventional vacuum distillation.

A process for the preparation of MCA by an electrochemical process has been described by A. Youtz et al., "Depolarization of the Chlorine Electrode by Organic Compounds" in J. Am. Chem. Soc., 1924, 46, 549. The process encompasses the reaction of 70% acetic acid in an aqueous solution with hydrochloric acid to obtain chloroacetic acid.

An electrochemical process for preparing a halogenated (derivative) carboxylic acid in an aqueous environment has the disadvantage that only a small amount of the desired (halogenated) carboxylic acid is formed. Furthermore, in an aqueous chloride environment the main product of electrolysis is often chlorine gas, which is undesirable as it represents an additional residual current and in addition to the fact that the combination of chlorine gas and Hydrogen gas can make the outlet gas mixture explosive.

An object of the invention is to present a process for the preparation of a compound containing a halogenated carbonyl group by using starting materials which are cheap and available on a large scale, while at the same time no further treatment is done. required for the co-produced compound (s). Another object of the present invention is to present a process which results in a compound containing a monohalogenated carbonyl group which has a lower content of a di-, tri- or polyhalogenated by-product with respect to the industrial process described above. Furthermore, an object of the invention is to provide a process that can be easily integrated into existing hardware used for the prior art industrial process described above, while not requiring intense physical conditions. Yet another object is to present a process for the production of a compound containing a carbonyl group that is selectively halogenated at the α-carbon atom (that is, the carbon atom adjacent to the carbonyl group). Yet another objective is to present a process that yields a higher product yield, for example when compared to the aqueous electrochemical process of Youtz et al., And which forms a byproduct of a good value.

The present invention now provides a process for preparing a compound containing a halogenated carbonyl group by electrochemically reacting the corresponding carbonyl group containing compound with a hydrogen halide H-X1, an organic halide R1-X and / or a salt of halide Mn + -Xn "under substantially water-free conditions, wherein X is a chlorine, bromine or iodine atom, R 'is an alkyl or aryl group which may be straight or branched, optionally containing one or more heteroatoms such as oxygen, nitrogen, chloride, bromide, fluoride or iodide from which the halogen atom X can be electrochemically separated, Mn + is a quaternary ammonium, alkali metal, alkaline earth metal or metal cation, and η is an integer positive from 1 to 5, depending on the valence of the metal cation Mn +.

Substantially water-free conditions are defined as having less than 1 wt% of water in the reaction mixture, preferably less than 0.1 wt%, and more preferably about zero; more preferably, the conditions are completely anhydrous, which is achieved when the reaction mixture contains compounds that act as water decontaminants.

Surprisingly, halogen X can only be selected from the chlorine, bromine and iodine group since fluorination is not possible using the process of the present invention. In the prior art, see, for example, P. Sartori, N. Ignafev, "The current state of our knowledge about the mechanism of electrochemical fluorination in anhydrous hydrogen fluoride (Simons process)", Journal of Fluorine Chemistry 87 ( 1998), pages 157 to 162, a process for the fluorination of various organic compounds is described; however, these reactions are usually carried out in such a manner that they result in polyfluorination and do not lead to specific α-carbon fluorination.

When the process of the invention is used, no halogen gas (such as chlorine gas) is required, but preferably hydrogen halide, organic halides or halide salts, which are generally much more preferred, may be used. widely available and cheaper than the starting materials of this industrial process. The process of the present invention results in the compound containing the halogenated carbonyl group and hydrogen as reaction products. Any unreacted halide source can be easily recycled and the same applies to the compound containing the unreacted carbonyl group. The hydrogen byproduct that is formed can be readily isolated and can be used, for example, as a source of energy or a starting compound for other chemical processes, and thus represents a commercial value.

Surprisingly, it was found that only a very insignificant amount of the compound containing the dihalogenated and / or higher carbonyl group was formed; typically, when a carboxylic acid is halogenated, the amount of dihalogenated carboxylic acid has been found to be below 0.3 wt.% and the amount of trihalogenated or higher carboxylic acid, if actually formed is below the detection limit (ie 50 ppm). Since the reaction by-product is hydrogen gas (ie bubbles), the reaction mixture remains well-mixed and agitation is not necessary, which is also advantageous.

In the process of the invention, electrical current yields were obtained to produce 80% monohalogenated (derivative) carboxylic acid. Even higher current yields are expected to be obtained. On the other hand, electrochemical chlorination of acetic acid in an aqueous environment results in low current yields typically below 1%.

Current yield (also called current efficiency) is described in Bard-Stratman, Encyclopedia of Electrochemistry, Organic Electrochem., Vol. 8, chapter 2.3.1, page 31, to which reference is made. In a nutshell, current efficiency or current efficiency refers to the fraction of the cell's electrical current - or (integrated over time) the fraction of the transferred charge - that is used to form the product.

Surprisingly, it has been found that in the process of the invention compounds containing a dihalogenated and / or higher carbonyl group are also effectively converted to the compound containing a monohalogenated carbonyl group. Accordingly, in one embodiment, the starting material may be a mixture of compounds comprising at least compounds containing a dihalogenated and / or higher carbonyl group (R1-X) and a compound containing a nonhalogenated carbonyl group wherein The amount of the dihalogenated and / or higher carbonyl group-containing compound preferably is at most equal to the amount of the nonhalogenated carbonyl-group-containing compound. It has been found that the use of such a starting mixture further results in a reaction product comprising mainly the compound containing the monohalogenated carbonyl group, or, in other words, an extremely low amount of compound containing the dihalogenated carbonyl group and / or higher Hydrogen halide is prepared in situ as a result of the electrochemical reaction of the compound containing the dihalogenated and / or higher carbonyl group in the cathode under electrochemical conditions.

In two document, that is, L.N. Nekrasov et al., "Effect the small amounts of tetramethyl- and tetraethylammonium ions on electrolyte kinertics of certain organic compounds in solutions of tetrabutylammonium salts", Elektrokhimiya, Vol. 24, ns. 4, pages 560 to 563, 1988, and A. Inesi, L. Rampazzo, "Electrochemical reduction of halogen containing compounds at a mercury cathode: chloroacetic, dichloroacetic acids and corresponding ethylesters in dimethylformamide", Electroanalytical Chemistry and Interfacial Electrochemistry, 44 (1973) ), pages 25 to 35, it is indicated that trichloroacetic acid may be reduced to dichloroacetic acid by employing an electrochemical process, but it is not indicated or suggested that this compound can be used as a halogen source (ie is, as compound R1-X defined) for the halogenation of a carbonyl group-containing compound for the preparation of the monohalogenated carbonyl group-containing compound. Thus, in one embodiment the invention features a process wherein the organic halide R1-X is a compound containing the dihalogenated and / or higher carbonyl group, or, in other words, a process for preparing a compound containing a halogenated carbonyl group by electrochemically reacting the corresponding carbonyl group-containing compound with a dihalogenated and / or higher carbonyl group-containing compound, optionally one H-X1 hydrogen halide another R1-X organic halide and / or a halide salt Mn + -Xn "under substantially water-free conditions, wherein X is a chlorine, bromine or iodine atom, R1 is an alkyl or aryl group which may be straight or branched, optionally containing one or more. more heteroatoms such as oxygen, nitrogen, chloride, bromide, fluoride or iodide, of which halogen atom X may be electrochemically separated, Mn + is a quaternary ammonium, alkali metal, alkaline earth metal cation o or metal, and η is a positive integer from 1 to 5, depending on the valence of the metal cation Mn +.

The process of the invention may also be used as a second step in a conventional process for preparing a compound containing a monohalogenated carbonyl group by chemically reacting a compound containing a carbonyl group and a halogen source. In addition, the process of the invention may be used to treat the mother liquor that results when, for example, monohalogenated (derivative) carboxylic acid is separated from a reaction mixture comprising both carboxylic acids both dihalogenated and / or higher (derivatives), and such mother liquor then comprises a mixture of the remaining monohalogenated (derivative) carboxylic acid and a relatively high amount of dihalogenated and / or higher carboxylic acids (or derivatives thereof). vados).

Separation methods include the usual separation methods available to a person skilled in the art, such as distillation, extraction and crystallization, of which crystallization is most preferred.

In this regard, the invention provides a process for preparing a halogenated carbonyl group-containing compound by first chemically reacting the carbonyl group-containing compound with chlorine, bromine or iodine molecules and then electrochemically treating it. the reaction mixture according to the electrochemical process indicated above, and the invention provides a process wherein the starting mixture is the mother liquor obtained when the compound containing a monohalogenated carbonyl group is separated from a reaction mixture. which contains a compound containing a monohalogenated carbonyl group and a compound containing the dihalogenated and / or higher carbonyl group.

In the process with a mixture of a compound containing a carbonyl group and the corresponding dihalogenated and / or higher carbonyl group containing compound, the net reaction is that the compound containing a dihalogenated and / or higher carbonyl group containing the compound containing the corresponding carbonyl group to obtain the compound containing a monohalogenated carbonyl group.

The embodiment comprising a conventional process followed by an electrochemical process according to the invention has the overriding advantage that the conventional process products (i.e. hydrogen halide and a mixture of the carbonyl group-containing compound, the compound containing a monohalogenated carbonyl group, and the compound containing the dihalogenated and / or higher carbonyl group) are the starting materials of the electrochemical step. Therefore, processing the product stream from the conventional process is not necessary; instead, the conventional process product stream can be used directly as the starting material stream in the electrochemical step.

Suitably higher halogenated means that up to 10, and preferably 3 to 6, chlorine, bromine and / or iodine groups are present in the carbonyl group-containing compound.

The invention also features an apparatus for performing the above processes. In this regard, an apparatus comprising a chemical reactor (a) connected to an electrochemical reactor (B) via an output (5) and optionally outputs (2), (3) and (4) is provided. wherein the reactor (B) is connected to a physical separation unit (C) through an output (9). The apparatus is illustrated in figure 1.

Figure 1 um relates to an apparatus for preparing halogenated carbonyl derivative according to the invention using a chemical reactor (A), an electrochemical reactor (B) and a physical separation unit (C).

The chemical reactor (A) may be a reaction vessel (eg heated and / or cooled and / or insulated) of a suitable material (eg glass coated steel). Preferably, the chemical reactor contains internal media such as mechanical stirrers, heat exchange tubes, inlet tubing (eg for raw materials and recycling streams), and / or contains sensors (such as temperature sensors). temperature, pressure sensors, liquid level sensors). Optionally, the chemical reactor (A) may be equipped with a UV irradiating medium to convert the halogen gas into a halogen atom, such as a UV lamp.

Referring to Figure 1 in more detail, a halide, a carbonyl group containing compound, optionally a catalyst, and an electrolyte are optionally placed in the chemical reactor (A) via inlets (1), (2), (3) and (4) respectively two or more of which may be combined into one input to react with an intermediate which is inserted into the electrochemical reactor (B) through the outlet (5). The gaseous components formed in the chemical reactor (A) and separated may optionally be partially or totally introduced into the electrochemical reactor (B) via outlet (6), in which case the outlet (6) may be combined. - nothing with output (5) as one output. Optionally, more or even all of the carbonyl group-containing compound, catalyst and electrolyte may be fed into the electrochemical reactor (B) via inputs (2), (3) and (4) respectively. or more of which can be combined as a single entry. In one embodiment, the electrochemical reactor (B) may be equipped with an additional input stream (7) containing a halide (gas or liquid).

The electrochemical reactor (B) is an apparatus containing at least one anode and at least one cathode of any suitable material as described above, and is preferably a vessel where the anode (s) and the ) Cathode (s) are placed in an appropriate geometry (such as parallel plates or concentric cylinders, stuffed or fluidized bed cells). In a more preferred embodiment, the electrochemical reactor contains one or more cell separators, such as diaphragms or membranes. In another preferred embodiment, the electrochemical reactor (B) is a reactor that contains parallel electrodes in a vessel with or without internal or external fluid recirculation. The anode and cathode are connected to a direct current power supply that supplies the electrical current to the electrodes. The electrodes can be connected to the power supply in a monopolar or bipolar arrangement. In a preferred embodiment, the electrochemical reactor (B) simultaneously produces monohalogenated compounds by halogenating the raw materials at the anode and dehalogenating higher dihalogenated compounds at the cathode. In some embodiments, hydrogen gas in the electrochemical reactor is produced in the cathode that is separated from the reactor through the outlet (8).

The substantially reduced dihalogenated and / or higher product of the electrochemical reactor (B) is passed to the physical separation unit (C) through the outlet (9). Hydrogen halide and other compounds formed in the chemical reactor (A) and / or the electrochemical reactor (B) are separated from the product via outlet (11), and optionally returned to the chemical reactor (A) and / or the reactor. electrochemical (B) through the outlet (10). In addition, the electrolyte may be fed into the chemical reactor (A) and / or the electrochemical reactor (B) through the inlet (4), and the electrolyte may be separated from the reaction products and reagents in the reactor unit. physical separation (C) and optionally be returned to reactors AeB via output (10).

The physical separation unit (C) is an apparatus which may comprise one or more distillation columns, extraction columns, absorption columns, or a combination thereof suitable for separating the electrochemical product from the reactor entering unit C through the outlet (9) in a halogenated product stream containing mainly mono- and dihalogenated carbonyl derivative exiting the apparatus of the invention via outlet (11).

In another embodiment, the apparatus comprises an additional separation unit (D) for separating the monohalogen compounds from the corresponding higher dihalogenated compounds. The apparatus is illustrated in figure 2.

Figure 2 is an apparatus for preparing halogenated carbonyl derivative according to the invention using a chemical reactor (A), an electrochemical reactor (B), a physical separation unit (C) and a separation unit for separating monohalogenated compounds from the corresponding dihalogenated (D) compounds and further activator.

Referring to Figure 2 in more detail, in the apparatus of this embodiment the chemical reactor product (A) is fed into a physical separation unit (C) through outlet (5) as described above to separate the electrolyte and other components or products formed in chemical reactor A of the mixture of mono-, dihalogenated and / or higher carbonyl products carried to separation unit D via outlet (12).

Separation unit D comprises separation means having the ability to separate the monohalogenated compounds from the corresponding higher dihalogenated compounds. These separation media may be distillation columns, crystallization units, extraction units or any combination thereof to obtain the required separation. Unit D produces the separated purified monohalogenated product via outlet (14) and a substantially enriched current in the dihalogenated and / or higher product which is introduced into an electrochemical reactor (B) described above through outlet (13).

In the apparatus of the embodiment illustrated in Figure 2, the electrochemical reactor product (B), which is substantially enriched in the monohalogenated product, may be introduced into the chemical reactor (A) through the outlet (15). Optionally, a current containing electrolyte and other components of the physical separation unit (C) is fed into the electrochemical reactor (B) and / or the chemical reactor (A) through the output (10). Optionally, a halide-containing stream (gas or liquid) and a carbonyl-containing compound-containing stream may be introduced into the electrochemical unit (B) also through the inlets (7) and (2), respectively, which may be combined as one entry. In the electrochemical reactor (B) hydrogen gas can be produced at the cathode and separated from the reactor through the outlet (8).

In a preferred embodiment, the process of the invention is carried out in the substantial absence of solvent. "In the substantial absence of solvent" means that a maximum of 5% solvent is present in the reaction mixture. The term solvent is suitable for any substance in which at least the reaction starting materials are soluble but does not include one of the reactants / products. More preferably, in the process of the invention the reaction mixture contains less than 2% solvent. More preferably, about 0% solvent is present.

It should be understood that the liquid chemical reactions occurring in the process of the invention are HX + R-COY XR-COY + H2 R1-X + R-COY XR-COY + R1-H or MXn + η R-COOH (XR -COO) nM + nH2

The compound containing a carbonyl group R-COY or R-COOH to be halogenated may be any compound containing an α-carbon hydrogen atom, preferably liquid at the reaction temperature. The carbonyl group-containing compound R-COY may be an aldehyde, a ketone, a carboxylic acid, a carboxylic anhydride, or an acyl halide. Preferably R-COY and R-COOH are compounds containing the carbonyl group wherein R is an alkyl, alkylene or aryl group which has α-hydrogens and may be linear, cyclic or branched, optionally containing one or more heteroatoms; such as oxygen, nitrogen, chloride, bromide or iodide, and Y is hydrogen, a hydroxyl group, a halide atom, or a group R ", or OCOR", where each R "is independently a hydrogen atom or an alkyl group More preferably, Y is a hydroxyl group, a halide atom, a group R "or OCOR", where R "is a C1-C10 alkyl or C1-C10 alkylene group, and R is a group C1-C26 alkyl or C1-C26 alkylene. Even more preferably, the carbonyl group-containing compound is an unsubstituted C2 -C26 carboxylic acid, most preferably acetic acid, propanoic acid or a fatty acid, and most preferably acetic acid. Fatty acid is defined as a carboxylic acid with hydrocarbyl groups containing 1 to 22 carbon atoms, and preferably 8 to 22 carbon atoms, which may be saturated or unsaturated, linear or branched. Fatty acids derived from natural fats and oils are assumed to have at least 8 carbon atoms. In the present invention, the preferred fatty acids are unbranched C8-C26 carboxylic acids and even more preferred is the group of natural fatty acids as specified, for example, in the CRC Handbook of Chemistry and Physics, 1989 ed. 220

The halide is chloride, bromide or iodide, more preferably chloride or bromide, and most preferably chloride.

Organic halide R1-X can be any compound that can be dehalogenated by an electrochemical step, as indicated, for example, in Lund, Hammerich1 Organic Electrochemistry, 4th ed., Chapter 8, "Halogenated organic compounds" (Mareei Dekker1). 2001). R1-X is preferably a halogenated hydrocarbon compound which may contain other substituents such as nitrogen or oxygen. More preferably, R'-X is a compound containing the dihalogenated and / or higher carbonyl group.

The halide salt Mn + -Xn "is preferably a halide salt wherein M is an alkaline earth metal, alkali metal or metal cation, and more preferably M is a cation of Na, K, Li, Mg. More preferably Ca, Ba, and more preferably an alkali metal cation, and most preferably a lithium, sodium or potassium cation.

In an even more preferred embodiment, the reaction mixture comprises essentially only reagents, products, and auxiliaries, i.e. more than 95% by weight of the reaction mixture consisting of starting materials, products , and auxiliary agents, and more preferably more than 99% by weight comprise the same. Auxiliary agents are defined as agents that may be functionally present in the process of the invention, such as catalyst and carrier electrolyte.

In principle, a support electrolyte is not required in the process as long as sufficient current can be passed through the fluid under the process conditions. In a preferred embodiment, a support electrolyte is present in the reaction mixture. This electrolyte is a non-aqueous compound (a mixture) that is sufficiently soluble and provides sufficient conductivity in the applied reaction mixture, can be easily separated and recycled, and is sufficiently stable versus oxidation and reduction. Examples of such support electrolytes may be any combination of ions provided, for example, in F. Beck, Elektroorganische Chemie, Verlag Chemie GmbH, Weinheim, 1974, chapter 3.3, pages 104 to 110 or D. Pletcher, A First Course in Electrode Processes, The Electrochemical Consultancy, Alresford Press Ltd., 1991, chapter 2.3, pages 57 to 72, and may include ions such as OH ", Γ, Br", Cl ", F", NO3 ", SO42", HCO3 ", Fe (CN) 63", CIO4 ", BF4", PF6 ", H +, Li +, Na +, K +, Rb +, Ca2 +, Mg2 +, Al3 +, La3 +, Ag +, NH4 +, [N (CH3) 4] +, [N (C2H5) 4] +, [N (C4H9) 4] +, [N (C2H5) H] + More preferably, the electrolyte is a salt that is soluble in the carboxylic acid to be halogenated and does not participate in the reaction. halogenation or otherwise participates but then contains the same halogen anion as the halogen source in the reaction to prevent the formation of compounds containing different halogenated carbonyl groups.In an even more preferred embodiment, the electrolyte is a halide salt such as NaCl, NaBr, NaI, KCl, KBr, Kl, LiCl, LiBr, Lil, MgCl2, MgBr2, Mgl2, caCl2, CaBr2, Cal2, BaCl2, BaBr2, Bal2. In the aforementioned embodiment, the MXn metal salt acts as a supporting electrolyte.

In another preferred embodiment, an accelerating compound

The reaction reaction (also referred to herein as a "catalyst") is present in the reaction mixture. In a more preferred embodiment, this compound is the carboxylic acid anhydride (derivative) to be halogenated or the acid halide thereof. In the embodiment comprising a two-stage process, i.e. a chemical halogenation step followed by an electrochemical step, the above-mentioned acid halide catalyst may be formed in the reaction mixture, and thus need not be added when using a product such as PCI3 or SOCI2 or SO2Cl2, COCl2, acid or sulfur anhydride (as catalyst) in the chemical step. As already indicated briefly above, these types of acid halide and acid anhydride compounds have as an added advantage that they purify water to obtain carboxylic acid and can thereby render the reaction conditions totally anhydrous. The catalyst is used in typical amounts between 2 and 30% by weight in the total reaction mixture.

An additional advantage of the process of the invention is that since the electrochemical reaction is carried out in a non-aqueous environment, the catalyst compound is not degraded by the water present in the reaction mixture.

Used electrodes may be selected from any material as long as they do not degrade in the reaction mixture under the reaction conditions to result in unwanted by-products. In this regard, in particular the selection of anode material is of importance because the anode is the most susceptible to degradation during process conditions. In a preferred embodiment, the anode is carbon (such as boron-doped diamond, graphite, glassy carbon), ceramic (such as magnetite, ie Fe304 or Ebonex®, ie mixed titanium oxides), a metal alloy (such as platinum / ruthenium) or a noble metal (such as Au, Ag, Pd, Pt, Ti), optionally containing a mixed metal oxide such as Ir02 / Ru02 (e.g. Ir02 / Ru02 in titanium , Dimension Stable Anodes: DSA® electrodes), and the cathode is carbon (such as boron-doped diamond, graphite, glassy carbon), metals (such as nickel, lead, mercury, titanium, iron, chrome) , a metal alloy (such as stainless steel (Cr-Ni-Fe), Monel (Cu-Ni), bronze (Cu-Zn) or metal oxides (such as Pb / Pb02) or any other electrode, as long as it is stable in the system and does not produce significant amounts of unwanted by-products. Examples of electrode materials are mentioned in AJ Bard and M. Stratmann, Eds., Encyclopedia of Electrochemistry, Organic Electrochem., Vol. 8, Chapter 2.4.1, page 39, to which reference is made.

Additionally, in the process of the invention the electrodes are preferably selected such that their specific surface area is as large as possible and the distance between the cathode and anode is as small as possible. An element skilled in the art will have no problem selecting the appropriate electrodes for this purpose. Non-limiting examples of electrodes meeting one or more of the above criteria may include concentric electrodes, porous electrodes, parallel plate electrodes, packing bed electrodes, and fluidized bed electrodes. The electrode arrangement can be monopolar or bipolar.

The density of electric current during the inventive process is typically from 0.1 to 7 kA / m2, preferably from 0.5 to 4 kA / m2, and more preferably from 1 to 2 kA / m2. The cell voltage typically ranges from 1 to 10 volts, depending mainly, but not exclusively, on the current density applied, the conductivity of the reaction fluid, and the distance between the electrodes.

The process of the invention may be combined with a UV treatment step whereby halogen gas is added to the reaction system, converted to a halogen atom by UV irradiation, and also capable of reacting with the compound. containing a carbonyl group to obtain the compound containing a desired halogenated carbonyl group.

The process of the invention may be a batch, semi-batch or continuous process; preferably it is a continuous process. The process may be carried out at a pressure typically ranging from 1 to 10 barA; preferably the pressure is between 0.9 and 5 barA, more preferably about 1 to 2 barA. BarA stands for absolute bar.

The process is generally carried out at a temperature of from 11 to 200 ° C, preferably from 20 to 150 ° C, more preferably from 75 to 140 ° C, more preferably from 80 to 120 ° C.

The invention is also illustrated by the following examples and comparative examples.

EXAMPLES

Example 1 - Acetic Acid Chlorination Using HCI

In a reaction vessel containing graphite effective anodes and cathodes (material type 6503) with an effective anode area of 580 cm2, Le Carbonne Lorraine1 Rotterdam1 Netherlands, and 530 cm2 of an effective cathode area, an amount of 800 grams of a mixture containing 7% by weight of anhydrous calcium chloride (JT Baker1 No. 0070, min. 95% by weight), .60% acetic acid (Fluka, No. 45731,> 99.8 % by weight), and 24% by weight of acetyl chloride (Fluka, No. 00990,> 99%) was preheated to 70 ° C and submerged to electrolysis at an average current of 20 amps. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture.

Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC).

Table 1 shows the concentrations of monochloric acid (MCA) and dichloroacetic acid (DCA) measured by HPLC (in% by weight relative to the sum of the amounts of acetic acid (HAc), MCA and DCA) versus amount of electrical charge transferred during the process. Table 1. Monochlorochloric acid (MCA) and dichloroacetic acid (DCA) concentrations versus the amount of electrical charge transferred during electrolysis of a mixture that initially contains acetic acid, acetyl chloride, calcium chloride, and chloride of hydrogen (Example 1)

<table> table see original document page 17 </column> </row> <table> <table> table see original document page 18 </column> </row> <table>

Example 2 - Acetic Acid Chloride Using CaCl2 (in the absence of HCO

In the reactor as mentioned in Example 1, 650 grams of a mixture of 72 wt% acetic acid (Fluka, No. 45731,> 99.8 wt%), 21 wt% acetyl chloride (Fluka, no. 00990,> 99%), and .7 wt.% Anhydrous calcium chloride (JT Baker, No. 0070, min. 95 wt.%) Were preheated to 70 ° C and subjected to electrolysis at an electric current of 5 ° C. and 20 amps. Unlike Example 1, in the present example no hydrogen chloride gas was added to the reaction mixture. Samples taken for electrolyte examination during the electrolysis process were analyzed by high performance liquid chromatography (HPLC).

Analytical results show that MCA can be produced from the mixture also in the absence of hydrogen chloride.

Table 2 shows the concentrations of monochloric acid (MCA) and dichloroacetic acid (DCA) as measured by HPLC (wt.% Versus the sum of the amounts of acetic acid (HAc), MCA and DCA) versus the amount of charge. transferred during the process. Table 2. Concentrations of monochloroacetic acid (MCA) and dichloroacetic acid (DCA) versus the amount of electric charge transferred during electrolysis of a mixture that initially contains acetic acid, acetyl chloride and calcium chloride (Example 2 )

<table> table see original document page 18 </column> </row> <table> <table> table see original document page 19 </column> </row> <table>

Example 3 - Acetic Acid Chlorination Using Dichloroacetic Acid

In the reactor as mentioned in Example 1, 700 grams of a mixture of 60 wt% acetic acid (Fluka, No. 45731,> 99.8 wt%), 19 wt% acetyl chloride (Fluka, no. 00990,> 99%), 5 wt.% Anhydrous calcium chloride (JT Baker, No. 0070, min. 95 wt.%), And 16 wt.% Dichloroacetic acid (Acros Chemicals, batch A0220473 99 +%) were preheated to 70 ° C and subjected to electrolysis to a 20 amp electrical current. Hydrogen chloride gas was added to the reaction mixture.

Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC).

Analytical results show that, compared to Example 2, the MCA production rate is almost twice as high in the present example. Acetic acid is chlorinated and DCA is hydrogenated in MCA.

Table 3 shows the concentrations of monochloric acid (MCA) and dichloroacetic acid (DCA) as measured by HPLC (wt.% Versus the sum of the amounts of acetic acid (HAc), MCA and DCA) versus the amount of charge. transferred during the process. Table 3. Concentrations of acetic acid (HAc), monochloroacetic acid (MCA) and dichloroacetic acid (DCA) versus the amount of electrical charge transferred during electrolysis of a mixture that initially contains acetic acid, acetyl chloride, monochloric acid , dichloroacetic acid and calcium chloride (Example 3)

<table> table see original document page 19 </column> </row> <table> <table> table see original document page 20 </column> </row> <table>

Example 4 - Propionic Acid Chlorination Using HCI

In the reactor as mentioned in Example 1, 840 grams of a mixture of 65 wt% propionic acid (Fluka, lot no. 1241470,> 99 wt%), 30 wt% propionic anhydride (Aldrich, lot no. 05003 HC-026, 97%), and 5% by weight of anhydrous calcium chloride (JT Baker, No. 0070, min. 95% by weight) were preheated to 70 ° C and electrolyzed to a stream. between 1 and 9 amps. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture.

Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC).

Analytical results show that 1-chloropropionic acid can be produced from the mixture.

Table 4 shows the concentrations of propionic acid and 1-chloro-propionic acid as measured by HPLC (% by weight relative to the sum of the amounts of propionic acid and 1-chloropropionic acid) versus the amount of electrical charge transferred during the process. . Table 4. Propionic acid and 1-chloropropionic acid concentrations versus the amount of electrical charge transferred during electrolysis of a mixture that initially contains propionic acid, propionic anhydride and calcium chloride (Example 4)

<table> table see original document page 20 </column> </row> <table> <table> table see original document page 21 </column> </row> <table>

Example 5 - Acetic acid chlorination in aqueous environment

In a 1 liter beaker, a mixture containing 500 ml hydrochloric acid (10 wt% HCl in water) was charged and electrolized at room temperature in a 2 amp stream to produce chlorine gas. After two hours of electrolysis, 150 ml of acetic acid (70% by weight) was added to the reaction mixture, which was electrolyzed for an additional one and a half hours at 2 amps at room temperature.

Samples taken during the process were measured with 1 H-NMR. Only trace amounts of MCA could be detected by NMR, the amount of DCA was below the detection limit (the detection limit of MCA and DCA with this NMR instrument is about 50 ppm).

Example 6 - Preparation of Bromoacetic Acid Using LiBr

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with .580 cm2 effective anode area and 530 cm2 effective cathode area, an amount of 900 grams The mixture containing 11% anhydrous lithium bromide, 33% acetyl bromide and 56% acetic acid (Fluka No. 00990,> 99%) was preheated to 70 ° C and subjected to electrolysis at a medium current. 20 amp. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). After passing an 83 amp-hour charge through the electrodes, 12.97% bromoacetic acid and 0.017% dibromoacetic acid are formed. Example 7 - Acetic Acid Chloride Using HCI and Sodium Chloride as Electrolyte

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with. 580 cm2 of anode effective area and 530 cm2 of cathode effective area, an amount of 808 grams of the mixture containing 11% anhydrous sodium chloride, 33% acetic anhydride and 56% acetic acid (Fluka ns. 00990, > 99%) was preheated to 70 ° C and subjected to electrolysis at an average current of 3.8 amps. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). After the passage of 15.9 amp-hours of charge through the electrodes, 3.66% MCA and 0.043% DCA are formed.

Example 8 - Acetic Acid Chloride Using HCI and Lithium Chloride as Electrolyte

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with an effective anode area of .580 cm2 and a cathode area of 530 cm2, an amount of 808 grams of the mixture containing 1.3% anhydrous lithium chloride, 6.6% acetyl chloride and 92.1% acetic acid (Fluka ne. 00990,> 99%) was preheated to 70 ° C and submitted to electrolysis at an average current of 20 amperes. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). After 112 ampere hours of charge through the electrodes, 22.76% MCA and 0.108% DCA are formed.

Example 9 - Acetic Acid Chlorination Using HCI and Potassium Chloride as Electrolyte

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with .580 cm2 effective anode area and 530 cm2 effective cathode area, an amount of 808 grams The mixture containing 10% anhydrous potassium chloride, 24% acetyl chloride and 66% acetic acid (Fluka No. 00990,> 99%) was preheated to 70 ° C and subjected to electrolysis at 100 ° C. an average current of 10 amps. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). After 57.7 amp-hours of charge through the electrodes, 13.39% MCA and 0.57% DCA are formed.

Example 10 - Acetic Acid Chlorination Using Trichloroacetic Acid and HCI In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with .580 cm2 effective anode area and 530 cm2 effective area of the cathode, an amount of 808 grams of the mixture containing 11,9% trichloroacetic acid (TCA), 4,8% anhydrous lithium chloride, 11,9% acetyl chloride and. 71.4% acetic acid (Fluka No. 00990,> 99%) was preheated to 70 ° C and subjected to electrolysis at an average current of 30 amperes. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (H-PLC).

The results in Table 5 show that at the end of the process the DCA and TCA contents decreased and the MCA content increased. Table 5: Concentrations of monocloroacetic acid (MCA), dichloroacetic acid (DCA) and trichloroacetic acid (TCA) from Example 10 measured by HPLC (% by weight relative to the sum of the amounts of acetic acid (HAc), MCA, TCA and DCA) versus the amount of electrical charge transferred during the process

<table> table see original document page 23 </column> </row> <table> <table> table see original document page 24 </column> </row> <table> Example 11 - Reducing the mother liquor with chloride of lithium as electrolyte (acetic acid chlorination when using dichloroacetic acid and HCI)

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with .580 cm2 effective anode area and 530 cm2 effective cathode area, an amount of 1,007 grams of the mixture containing 30% dichloroacetic acid (DCA), 5% anhydrous lithium chloride, 15% acetyl chloride, 30% monochloracetic acid (MCA) and 20% acetic acid (Fluka No. 00990, > 99%) was preheated to 70 ° C and subjected to electrolysis at an average current of 30 amperes. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture.

Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). The results in Table 6 show that at the end of the process both HAc and DCA contents decreased, while MCA content increased.

Table 6: Concentrations of monocloroacetic acid (MCA), dichloroacetic acid (DCA) and acetic acid (HAc) from Example 11 as measured by HPLC (wt.% Versus sum of HAc, MCA and DCA) versus amount of electrical charge transferred during the process

<table> table see original document page 24 </column> </row> <table> <table> table see original document page 25 </column> </row> <table>

Example 12 - Reduction of the mother liquor with calcium chloride as electrolyte (acetic acid chlorination using dichloroacetic acid and HCl)

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 580 cm2 effective anode area and 530 cm2 effective cathode area, 1,007 grams of the mixture containing 30% dichloroacetic acid (DCA), 5% anhydrous calcium chloride, 15% acetyl chloride, 30% monochloracetic acid (MCA) and 20% acetic acid (Fluka no. 00990,> 99%) was preheated to 70 ° C and subjected to electrolysis at an average current of 30 amperes. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture.

Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). The results in Table 7 show that at the end of the process both the HAc and DCA contents decreased, while the MCA content increased. Table 7: Concentrations of monocloroacetic acid (MCA), dichloroacetic acid (DCA) and acetic acid (HAc) from Example 12 as measured by HPLC (wt.% Versus sum of HAc, MCA and DCA) versus amount of electrical charge transferred during the process

<table> table see original document page 25 </column> </row> <table>

Example 13 - Reduction of mother liquor with magnesium chloride as an electrolyte (acetic acid chlorination using dichloroacetic acid and HCl)

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with .580 cm2 effective anode area and 530 cm2 effective cathode area, an amount of 1007 grams of the mixture containing 30% dichloroacetic acid (DCA), 5.2% anhydrous magnesium chloride, 15% acetyl chloride, 30% monochloracetic acid (MCA) and 20% acetic acid (Fluka 10000,> 99%) was preheated to 70 ° C and subjected to electrolysis at an average current of 30 amperes. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). The results in Table 8 show that at the end of the process the HAc and DCA contents decreased while the MCA content increased.

Table 8. Concentrations of monocloroacetic acid (MCA), dichloroacetic acid (DCA) and acetic acid (HAc) from Example 13 as measured by HPLC (wt.% Versus sum of HAc, MCA and DCA) versus amount of electrical charge transferred during the process. <table> table see original document page 26 </column> </row> <table>

Example 14 - Acetic Acid Chlorination Using HCI and Zinc Chloride as Electrolyte

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with .580 cm2 effective anode area and 530 cm2 effective cathode area, an amount of 1,607 grams The mixture containing 5% anhydrous zinc chloride, 13% acetyl chloride and 82% acetic acid (Fluka No. 00990,> .99%) was preheated to 70 ° C and subjected to electrolysis under a current. average of 25 amps. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). After 162 ampere hours of charge through the electrodes, 15.67% MCA and 0.10% DCA are formed.

Example 15 - Chlorination of acetic acid with iron (III) chloride as an electrolyte

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 580 cm2 effective anode area and 530 cm2 effective cathode area, an amount of 1,607 grams of The mixture containing 5% anhydrous iron (III) chloride, 13% acetyl chloride and 82% acetic acid (Fluka ns. 00990,> 99%) was preheated to 70 ° C and subjected to electrolysis to a average current of 30 amps. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). After passing 192 ampere hours of charge through the electrodes, 4.73% MCA and 0.10% DCA are formed.

Example 16 - Acetic Acid Chloride Using HCI and Aluminum Chloride as Electrolyte

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 580 cm2 effective anode area and 530 cm2 effective cathode area, an amount of 1,607 grams of The mixture containing 5% anhydrous aluminum chloride, 13% acetyl chloride and 82% acetic acid (Fluka No. 00990,> 99%) was preheated to 70 ° C and subjected to electrolysis to a color. - average close to 30 amps. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by high performance liquid chromatography (HPLC). After passing 119 amp-hours of charge through the electrodes, 12.29% MCA and 0.02% DCA are formed.

Example 17 - Dimethyl Pentanone Chlorination Using HCI

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 47 cm2 effective anode area and 16 cm2 effective cathode area, an amount of 61 grams of the mixture containing 6% anhydrous lithium chloride, 94% 2,4-dimethyl pentanone was preheated to 70 ° C and electrolyzed to an average current of 0.3 amp. During the electrolysis process, hydrogen chloride gas was added to the reaction mixture. Samples taken from the electrolyte during the electrolysis process were analyzed by NMR.

The results in Table 10 show that at the end of the process 2-chloro-2,4-dimethyl pentanone is formed.

Table 10: Concentrations of 2,4-dimethyl pentanone and 2-chloro-2,4-dimethyl pentanone from Example 17 measured by NMR in mole%

<table> table see original document page 28 </column> </row> <table>

Comparative Example 18 - Acetic Acid Fluoridation Using Trifluoroacetic Acid (TFA)

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 47 cm2 effective anode area and 16 cm2 effective cathode area, an amount of 99 grams of the mixture containing 4% anhydrous lithium chloride, .35.4% TFA1 35.4% acetic acid and 25.2% acetyl chloride were preheated to 70 ° C and electrolysis 2 amp average current. Samples taken from the electrolyte during the electrolysis process were analyzed by NMR. In the samples, no evidence was found regarding the formation of monofluoroacetic acid or difluoroacetic acid. Only MCA and small amounts of DCA were found. Comparative Example 19 - Acetic Acid Fluoridation Using KF

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 47 cm2 anode area and 16 cm2 cathode area, an amount of 99 grams of the mixture containing It contains 4.3% anhydrous potassium fluoride, 68.5% acetic acid and 27.2% acetyl chloride was preheated to 70 ° C and electrolyzed to an average current of 0.4 amp. Samples taken from the electrolyte during the electrolysis process were analyzed by NMR. In the samples no evidence was found regarding the formation of monofluoroacetic acid or difluoroacetic acid. Only MCA and small amounts of DCA were found.

Example 20 - Chlorination of HCI using dodecanoic acid and LiCI as electrolyte

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 47 cm2 anode area and 16 cm2 cathode area, an amount of 92 grams of the mixture containing contains 4.9% anhydrous lithium chloride, 35.3% acetic acid, 35.3% dodecanoic acid and 24.5% acetyl chloride was preheated to 70 ° C and subjected to electrolysis at an average current of 1 amp. Samples taken from the electrolyte during the electrolysis process were analyzed by NMR. After 3.4 ampere hours of charge through the electrodes, 1.3 mol% of 2-chloro dodecanoic acid is formed. Example 21 - HCl Chlorination Using Octadecanoic Acid

In a reaction vessel containing graphite anodes and cathodes (material type 6503 Le Carbonne Lorraine, Rotterdam, the Netherlands) with 47 cm2 effective anode area and 16 cm2 effective cathode area, an amount of 92 grams of the mixture containing 4.7% anhydrous lithium chloride, .38.3% acetic acid, 33.6% octadecanoic acid and 23.4% acetyl chloride was preheated to 70 ° C and subjected to electrolysis at an average current of 1 amp. Samples taken from the electrolyte during the electrolysis process were analyzed by NMR. After 3.2 ampere hours of charge through the electrodes, 1.3 mol% of 2-chloro octadecanoic acid is formed.

Claims (15)

Process for the preparation of a compound containing a halogenated carbonyl group by electrochemical reaction of the corresponding carbonyl containing compound with an H-X hydrogen halide, an R1-X organic halide and / or a Mn + -Xn halide salt. under substantially water-free conditions, wherein X is a chlorine, bromine or iodine atom, R 'is an alkyl or aryl group which may be straight or branched, optionally containing one or more heteroatoms such as oxygen, nitrogen , chloride, hydride, fluoride or iodide, from which the halogen atom X may be electrochemically separated, Mn + is a quaternary ammonium, alkaline earth metal, alkali metal or metal cation, and η is a positive integer from 1 to 5, depending on the valence of the metal cation Mn +. The process according to claim 1, wherein the organic halide R1-X is a compound containing the dihalogenated and / or higher carbonyl group. A process according to claim 1 or claim 2 wherein the compound containing a halogenated carbonyl group which is prepared is a monohalogenated compound. Process according to any one of claims 1 to 3, wherein the compound containing a halogenated carbonyl group which is prepared is halogenated to the α-carbon atom. 5. Process for the preparation of a compound containing a halogenated carbonyl group first by chemical reaction of the carbonyl group containing compound with chlorine, bromine or iodine molecules and subsequently electrochemical treatment of the reaction mixture according to the process according to claim 1. The process according to claim 2, wherein the starting mixture is the mother liquor which is obtained when a compound containing a monohalogenated carbonyl group is separated from a reaction mixture containing a compound containing a carbonyl group. monohalogenated and a compound containing a dihalogenated and / or higher carbonyl group. A process according to claim 6 wherein further compound containing a carbonyl group is added to the starting mixture. A process according to any one of claims 1 to 7, wherein X is a chlorine atom. A process according to any one of claims 1 to 8, wherein the carbonyl group-containing compound is acetic acid or propanoic acid or a fatty acid. A process according to any one of claims 1 to 9, wherein a support electrolyte is also present in the reaction mixture. A process according to any one of claims 1 to 10, wherein the electrolyte is a chlorine salt. A process according to any one of claims 1 to 11, wherein a catalyst selected from the group of acyl halides and carboxylic anhydrides is also added to the reaction mixture. Process according to any one of claims 1 to 12, carried out in the substantial absence of any solvent. Apparatus suitable for the process as defined in any one of claims 1 to 13, comprising a chemical reactor (A) connected to an electrochemical reactor (B) via an outputs (5) and optionally outputs (2), (3) and (4), with reactor (B) being connected to a physical separation unit (C) via an output (9). The apparatus of claim 14 further comprising a separation unit (D) for separating monohalogenated compounds from the corresponding higher dihalogenated compounds.