HU222273B1 - Process for producing acid chlorides by phosgenation under pressure of acids and/or anhydrides - Google Patents

Abstract

In the method according to the invention for the phosgenation of monocarboxylic acids and/or anhydrides, an acid and/or anhydride is preferably treated with a 2-15 times molar excess relative to phosgenic acid with or without a solvent at 80-200 °C, at a pressure of 2-60 bar, with or without a catalyst, preferably without. In the process, the pressure facilitates the separation of hydrochloric acid, carbon dioxide and phosgene in a column located outside the a-reactor. ŕ

Description

The present invention relates to a novel process for the preparation of acid chlorides by the phosgenation of monocarboxylic acids and / or corresponding anhydrides with or without a catalyst, preferably without a catalyst.

The known catalyst processes consist of injecting phosgene into the acid or its solution at atmospheric pressure and at temperatures between 80 and 150 ° C. Excess phosgene is usually used. Tired gases consisting of a mixture of phosgene, carbon dioxide and hydrochloric acid cannot be separated at atmospheric pressure unless very low-temperature condensers are used, which always results in a loss of phosgene.

The chemistry of the process is represented by the following reaction equations:

(1) RCOOH + COCl ₂ ->

RCOC1 + HC1 + CO ₂ (ki) (2) RC00H + RC0C1o (RC0) ₂ 0 + HC1 (k-2 / k2) (3) (RCO) ₂ O + 2 COCl ₂ ->

RCOC1 + 2 CO ₂ (k3)

At atmospheric pressure, the limitation of reaction (1) is the concentration of phosgene, which in turn is a function of temperature. The disappearance of the acid is thus relatively rapid, but the acid chloride formed reacts with the present acid to form the anhydride according to Reaction (2) and then, according to Reaction (3), slowly converts to the acid chloride.

Thus, one or more catalysts have to be used to activate the reaction (3) and, accordingly, there are numerous literature available on such catalysts. However, the use of a catalyst has several disadvantages. Firstly, its cost and then its influence on the choice of materials, since catalysts often make the reaction system very corrosive. It also promotes the formation of by-products (such as ketene) and the development of color. Finally, the acid chloride has to be purified by distillation or crystallization.

Examples of such processes include French Patent Nos. 2,585,351 and 213,976, respectively, which relate to the preparation of acid chlorides by phosgenation of the corresponding carboxylic acid. This document is about the use of a catalyst to produce acid chlorides under economically acceptable conditions. One of the topics of European Patent Application 213,976 is the catalyst used for the phosgenation reaction.

In addition, Applicant EP-A-213,976 refers to US Patent 2,657,233, which combines high pressure with high temperature to produce acid chlorides. However, reading this document, it will be apparent that the present invention relates to the preparation of dicarboxylic acid chlorides by phosgenation under high pressure and high temperature starting from the corresponding dicarboxylic acid. This document correctly teaches that the known process for the preparation of monochlorides described above is fully satisfactory and that there may be an improvement in the duty upon optimization of the catalysts used. This is confirmed by French Patent Nos. 2,585,351, French 2,254,547 and European Patent 545,774.

The object of the present invention was to overcome the above-mentioned drawbacks, in particular the drawbacks associated with the use of catalysts.

The present invention relates to a process for the phosgenation of monocarboxylic acids and / or anhydrides by treating the acid and / or anhydride in a solvent with or without a molar excess of phosgene, preferably 2 to 15 times more molar than the acid, between 80 and 200 ° C and 2 to 60 bar. pressure (1 bar to 105 bar), with or without catalyst, preferably without catalyst. The process is generally carried out in a closed system under autogenous pressure or in an open system such as under partial pressure degassing. The process is carried out in a continuous or semi-continuous mode, preferably in an open system with partial degassing. The degassing is generally performed with care being taken to maintain excess phosgene. This can either be done by selective elimination of hydrochloric acid and carbon dioxide, while maintaining the excess phosgene and a small amount of hydrochloric acid so as not to produce anhydride, but not too much to slow down the final reaction, or gas, including phosgene, is removed, while the latter is replaced. The temperature is preferably 100-150 ° C, preferably 110-130 ° C, and the pressure is preferably 6-40 bar. The temperature and pressure conditions are determined by the nature of the monocarboxylic acid and / or the anhydride and the corresponding chloride, in particular the critical point and / or the decomposition point.

The pressurized advantages of phosgenation according to the invention can be summarized as follows:

(a) low-temperature condensates may be dispensed with,

(b) solvent and / or catalyst depletion.

This allows the resulting acid chloride to be ultimately purified without the need for simple separation at the end of the reaction, reducing costs, and generally having the benefit of the reaction without the catalysts listed above. The

Example 1 will show that the effect of the addition of the catalyst is substantially eliminated, that is, the increase in productivity of the process according to the invention through the catalyst is very small compared to the same procedure without the catalyst, given the disadvantages of using such a catalyst. It can also be seen that the process of the present invention, without a catalyst, allows all the acids used to be converted to the chloride in less time than would be required by the known process for the catalyst. Finally, the process of the present invention enhances productivity compared to the semi-continuous batch process at atmospheric pressure.

The process of the invention is preferably used to chlorinate acids of formula RCOOH to acid chloride of formula RCOC1, wherein

R is a linear or branched, saturated or unsaturated aliphatic group having up to 22 carbon atoms, optionally

HU 222 273 Bl

(a) with one or more identical or different halogens,

(b) one or more nitro groups; or

c) substituted with one or more aryl, preferably phenyl, aryloxy, or arylthio groups, each of which is unsubstituted or substituted;

C3-C8 cycloaliphatic, unsubstituted or one or more

a) halogen,

b) alkyl or haloalkyl,

(c) with a nitro group; and

d) substituted with aryl, aryloxy and arylthio, the latter being unsubstituted or substituted with aryl, preferably phenyl or aryl derivatives;

and an aromatic carbocyclic group which is unsubstituted or substituted with one or more halogen, alkyl or haloalkyl groups, preferably trifluoromethyl (C 1 -C 12 groups), C 1-6 alkylthio or haloalkylthio; C 1-6 alkylsulfinyl or haloalkylsulfinyl, C 1-6 alkylsulfonyl or haloalkylsulfonyl, C 1-6 alkyloxy or haloalkyloxy; substituted with aryl, aryl, arylthio or aryloxy and nitro;

aromatic or non-aromatic 5 or 6 membered heterocyclic group containing one or more identical or different heteroatoms, namely oxygen, sulfur and / or nitrogen, unsubstituted or substituted with one or more halogen, nitro, alkyl, haloalkyl -, alkyloxy, haloalkyloxy, aryl, arylthio and aryloxy groups and / or fused to an aromatic carbocycle, which in itself is unsubstituted or substituted. Generally, when mentioning an aryl group or derivative thereof, such as an aryloxy or arylthio group, or an aromatic carbocycle, it should be considered, even if not specifically mentioned, that if such a group is present, it may carry substituents such as halogens, alkyl, haloalkyl, alkyloxy, haloalkyloxy, alkylthio, haloalkylthio, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, , haloalkylsulfonyl, aryl, aryloxy, arylthio or nitro.

The process of the invention is preferably used for the chlorination of (RCO) ₂ O anhydrides or (RCO) O (OCR ') anhydrides to the acid chloride RC0Cl and R'COC1, wherein R and R' are not as defined above and R and R 'are not simultaneously means the same group.

Mixtures of acids and anhydrides can also be chlorinated by the process of the invention.

The process of the invention is also characterized in that the pressure is also used to facilitate separation of hydrochloric acid, carbon dioxide and phosgene on a column going outside the reactor and without having to use low-temperature condensers such as already mentioned, they cause a loss of COC1 ₂ . Correspondingly, the separation becomes simpler and therefore more economical than known processes and leads to phosgene, which can be easily recycled to the reaction mixture, and pure hydrochloric acid is obtained.

The following examples illustrate the invention. The examples illustrate the advantages of the process according to the invention.

Example 1

Preparation of stearoyl chloride by phosgenation of stearic acid (Test 413)

Stearic acid (0.615 mmol, 0.175 g, 0.41 mol) and chlorobenzene (0.92 g, 8.171 mmol) were weighed in a microcrystalline sapphire swab (1) having an outside diameter of 10 mm and an inside diameter of 8 mm. A 5 mm diameter sealed tube (2) containing deuterated benzene is also introduced into tube (1) to ensure the presence of an external sluice necessary for subsequent NMR analysis. The tube (1) is then sealed, immersed in an acetone and cardice carbon dioxide bath at -78 ° C and connected to a phosgene bottle. Phosgene (0.606 g, 6.127 mmol, 4.08 mol) was then condensed in tube (1). After warming to room temperature, the reaction medium is in the form of a suspension of stearic acid in a colorless, homogeneous liquid. The tube is then introduced into a cryo magnet of an NMR spectrometer, previously heated to 117 ° C. A first spectrum is recorded 11 minutes after introduction into the cryo magnet, that is, after a period corresponding to tuning the spectrometer and after the reactor has stabilized at the set temperature. An automated program then allows the spectra to be recorded at regular intervals, usually every 5 minutes.

The molar percentage of each compound is determined by integrating triplets corresponding to alpha-methylene protons with the carbonyl group. The following results are obtained:

test Number Temperature C Acid M [COC12 ₂ ] M Volume ml Observed k * h 11/2 min P ** gh-11-1 413th 117 0.41 4.08 1.5 2.4 18 210

♦ The pseudo-first order k-kinetic constant is calculated by linearization as follows: -Ln (1 -DC) = kt, where DC is the degree of acid conversion and t = time.

** P = Productivity at DC = 50%.

HU 222 273 BI

Following the example above and varying the various parameters (temperature, pressure, etc.), the results are shown in the table below.

(a) Effect of temperature:

test Number Temperature C Acid M [cocy M Volume ml Observed k h-l 11/2 min P g-h-1-1-1 415th 83 0.42 4.3 1.5 0.44 94 40 421st 101 0.39 4.94 1.6 1.18 35 100 413th 117 0.41 4.08 1.5 2.4 18 210 416th 121 0.39 4.69 1.6 3.2 13 270

b) The presence of the catalyst described in Example 1 of French Patent No. 2,585,351:

test Number Temperature C Acid M [cocy M Volume ml Observed k h-l 11/2 min P gh-11-1 413. * 117 0.41 4.08 1.5 2.4 18 210 414th ** 115 0.415 4.57 1.5 3.7 11 340

* without catalyst ** with catalyst (hexane-n-butylguanidinium chloride) (0.02 mol%)

As mentioned above, the addition of the catalyst by the process according to the invention essentially eliminates the effect of the catalyst, that is to say, very low yields or, by the same process, the gain in productivity growth.

(c) Effect of phosgene concentration:

test Number Temperature C Acid M [COClj] M Volume ml Observed k h-l 11/2 min P gh-11-1 413th 117 0.41 4.08 1.5 2.4 18 210 420th 114 0.47 3.15 1.3 2.1 20 185

(d) Effect of the solvent:

test Number Temperature C Acid M (COC1 _2] M Volume ml Observed k h-l 11/2 minute P gh-11-1 415 * 83 0.42 4.3 1.5 0.44 94 40 425th ** 80 0.885 10 1.4 0.63 66 50

* Solvent = chlorobenzene ** Solvent = COCl ₂ .

(e) Effect of degassing:

In Test 417, gas is used, in Test 413, gas is depleted, and the effect thereof is shown in Figure 1. Test 413 has already been described and Test 417 uses the same but 0.16 g, 0.56 mmol acid, 0.875 g chlorobenzene and 0.88 g 8.9 mmol phosgene. For test 417, when 90% of the acid is ca. After 45 minutes of conversion, the tube was allowed to cool to degass 60 and then reheated to 117 ° C after re-introduction of 0.99 g of phosgene.

In addition, as shown in Fig. 1, stearic acid can be converted to 100% conversion in less than 2 hours, at ca. 75 minutes when the process is degassed at 117 ° C (Test 417). This makes our own invention comparable in French Patent No. 2,585,351 ka4

EN 222 273 Β1 results. In fact, in this document, stearic acid is completely converted to chloride when carried out in the presence of 0.02 mol% catalyst at 120-125 ° C for 4 hours. It is therefore clear that, as already mentioned, the process of the present invention, without a catalyst, enables all the measured acids to be converted to chloride in a shorter period of time than in the known catalyst process.

Example 2

Phosgenation of pivalic acid

a) First, phosgenation with pure acid under pressure. In the same manner as in Example 1, using a 10 mm multinuclear tube, but using deuterated pyridine instead of deuterated benzene for the sluice, it is seen that pivalic acid is phosgenated under acid pressure to the acid chloride. The results are as follows:

al) At 81 ° C, the rate constant = 0.28 h ¹ (conditions: 0.75 g, 7.3 mmol acid and 1.5 g, 15.2 mmol phosgene).

a2) At 115 ° C, the rate constant = 3.00 h ^-1 (conditions: 0.692 g, 6.78 acid and 1.25 g, 12.7 mmol phosgene).

b) A second experiment was carried out to observe the kinetics of the phosgenation reaction of pivalic acid in chlorobenzene, i.e. the reaction with a crude acid. In contrast to the pure acid experiment, it is no longer possible to distinguish between the CH3 protons of the acid and the chloride, so that we cannot trace the reaction in chlorobenzene.

However, attempts have been made to distinguish between acid and chloride by carbon NMR, since the chemical shifts of carbon atoms of carbonyl groups relative to tetramethylsilane (TMS) and the chemical shifts of quaternary carbon atoms of tert-butyl groups are very different. Chemical shifts for COOH

185.8 ppm, COCl 180.8 ppm, acid quaternary carbon 38.9 ppm and acid chloride quaternary carbon 49.5 ppm. A 75 MHz AMX 300 spectrometer is used for carbon 13 equipped with a 10 mm multinuclear tube. Chemical shifts (δ) of carbon resonance lines relative to tetramethylsilane (TMS) were expressed. As in (a), deuterated pyridine (outer lock) is used.

Observation is then carried out to show that the acid chloride predominates at 80 ° C after 1 hour 45 minutes, although little acid remains (conditions: 0.06 g, 0.06 mmol acid, 0.943 g chlorobenzene and 0.735 g). , 7.43 mmol phosgene).

Example 3

Phosgenation of pivalic anhydride

Proton NMR analyzes were performed under pressure on an AMX 300 spectrometer operating at 300 MHz on a proton equipped with a 5 mm QNP 1H / 13C / 19F / 31P gradient Z tube. Chemical shifts (δ) of proton resonance lines are expressed relative to tetramethylsilane (TMS). Here and in Figures 4-6. Even in the examples, the microcrystalline sapphire has an outer diameter of 5 mm and an inner diameter of 4 mm.

As in the phosgenation reaction of pure acid under pressure by Ή-NMR analysis [cf. 2a), pivalic anhydride could be distinguished

CH3 protons (δ = 1.24 ppm) and acid chloride CH3 protons (δ = 1.31 ppm).

The reaction was carried out at 80 ° C with 3 molar excess of phosgene relative to the anhydride.

Plotting a minus negative logarithm of the relative molar ratio of pivalic anhydride as a function of time gives a straight line. Obviously, the preparation of pivaloyl chloride from pivalic anhydride is a first order reaction. The slope of this straight line is the same as the reaction rate constant: k = 1.6 IO- ² min- ¹ . The half-life, i.e., t 1/2, which is the time required for the concentration of the anhydride to halve, is equal to a logarithm of 2 / k (t 1/2 = about 40 minutes).

Example 4

Phosgenation of octanoic acid

Example 2a) shows that phosgenation of pure octanoic acid into acid chloride is a first-order reaction under pressure. The results are as follows:

At 1.79 ° C, the rate constant = 0.25 h ^-1 (conditions: 0.79 g, 6.9 mmol acid and 1.68 g, 17 mmol phosgene).

2. At 124 ° C, the rate constant = 1.28 h ^-1 (conditions: 0.78 g, 6.85 mmol acid and 1.35 g, 13.7 mmol phosgene).

Example 5

Phosgenation of trifluoroacetic acid

Fluorescence NMR analysis was performed on a ΑΜΧ-300 spectrometer operating at 300 MHz on a proton equipped with a 5 mm QNP 1H / 13C / 19F / 31P gradient Z tube. Chemical shifts of fluorescence resonance lines are expressed relative to trifluoroacetic acid (TFA).

The reaction is monitored when the resonance appears at 0.3 ppm, which corresponds to trifluoroacetyl chloride and the acid to 0 ppm as a reference.

The reaction is slow because the degree of conversion to chloride is approx. 20% after heating at 107 ° C for 4 hours. However, this phosgenation reaction is carried out under pressure with the pure acid (conditions: 0.22 g, 1.93 mmol acid and 0.464 g, 4.7 mmol phosgene).

Example 6

Phosgenation of Benzoic Acid ¹³ C NMR analysis was performed under pressure on an AMX 300 spectrometer operating at 75 MHz on carbon 13 and equipped with a 5 mm QNP 1H / 13C / 19F / 31P gradient Z tube. Chemical shifts (δ) of carbon resonance lines are expressed relative to tetramethylsilane (TMS).

It is very difficult to distinguish benzoic acid from acid chloride by Ή-NMR. Therefore, the test was carried out with carbon-13-enriched benzoic acid (carbon atom of the carbonyl group) to observe the reaction of the pure acid at 90 ° C under the influence of carbon 13 NMR.

EN 222 273 B1. Indeed, the carbon resonance lines of the acid occur at δ = 170 ppm and the acid chloride at δ = 167 ppm.

Placing the minus negative logarithm of the relative molar gold of benzoic acid over time gives a straight line (conditions: 0.077 g, 0.63 mmol acid and 0.422 g, 4.27 mmol phosgene, 90 ° C). The preparation of benzoyl chloride from benzoic acid is a primary reaction. The slope of the straight line corresponds to the reaction rate constant ·. k = 0.28 h ^-1 . The half-life, i.e. 11/2, required to halve the acid concentration is equal to a log of 2 / k (t 1/2 = about 2 hours 30 minutes).

General test procedure in larger operation than in previous cases:

The following tests were conducted in a 2 liter autoclave reactor equipped with a condenser and a pressure control system. The total volume of the autoclave and accompanying devices is 2.25 liters. Monochlorobenzene and organic acid were introduced into the completely anhydrous reactor which was purged with argon and ca. Phosgene was added at 20 ° C. The air valve is closed and the control valve is adjusted to adjust the orifice to the desired pressure. The reaction medium is then heated to 120 ° C as quickly as possible. Percentages of the acid anhydride and chloride in the reaction medium were determined by proton NMR analysis.

Example 7

Phosgenation of pivalic acid

Pivalic acid (61.3 g, 0.6 mol) and monochlorobenzene (890 g) were introduced into the reactor and 597 g (6 mol) of phosgene were added over 30 minutes while maintaining the reaction temperature to max. Keep at 25 ° C. The set pressure is adjusted to a relative pressure of 10.5 bar and the reaction medium is heated. During the first 30 minutes, approx. 0.3% anhydride is formed. The resulting anhydride is phosgenated. The reaction was completed in 2 hours. The resulting acid level is less than 0.5 mol%, the residual anhydride level is 0, and the pivaloyl chloride level is more than 99.5 mol%.

Example 8

Phosgenation of 2-ethylhexanoic acid G, 0.6 moles of 2-ethylhexanoic acid and 890 g of monochlorobenzene were introduced into the reactor, followed by ca. Phosgene (607 g, 6.14 mol) was added over 30 minutes while maintaining the reaction temperature to max. Keep at 25 ° C. The set pressure is brought to a relative pressure of 10.5 bar and the reaction medium is heated. The reaction was completed in 1 hour 30 minutes. The level of residual acid and anhydride is 0 and the resulting 2-ethylhexanoic acid chloride is greater than 99.8 mol%.

Example 9

Phosgenation of octanoic acid

86.6 g (0.6 moles) of octanoic acid and 890 g of monochlorobenzene are introduced into the reactor and 600 g (6.07 moles) of phosgene are added over 30 minutes while maintaining the reaction temperature to max. Keep at 25 ° C. The set pressure is adjusted to a relative pressure of 10.5 bar and the reaction medium is heated. After 2 hours the residual acid was 1 mol%, the residual anhydride 0% and the resulting octanoyl chloride was 99 mol%.

Example 10

Phosgenation of stearic acid

Stearic acid (170.4 g, 0.6 mol) and monochlorobenzene (890 g) were introduced into the reactor and 594 g (6 mol) of phosgene were added over 30 minutes while maintaining the temperature of the reaction mixture to max. Keep at 25 ° C. The set pressure is adjusted to a relative pressure of 10.5 bar and the reaction medium is heated to 120 ° C for 1.5 hours and then heated to 150 ° C and maintained at this new temperature for 1 hour. The level of residual acid is approx. 1.4 mol%, the remaining anhydride 0 and the resulting stearoyl chloride 98.6 mol%. The highest pressure achieved is 9 bar relative.

Example 11

Phosgenation of oleic acid

200 g (0.7 mol) of oleic acid and 725 g of monochlorobenzene are introduced into the reactor and 574 g are added,

5.8 moles of phosgene. The set pressure is adjusted to a relative pressure of 11.2 bar and the reaction medium is heated.

After 1.5 hours, the reaction was complete. The residual acid was 0.5 mol% and the resulting oleoyl chloride was 99.5 mol%.

Example 12

Phosgenation of para-toluic acid

81.4 g (0.6 mol) of para-toluic acid and 892 g of monochlorobenzene are introduced into the reactor and 582 g are added,

5.8 moles of phosgene. The pressure is then adjusted to a relative pressure of 11.2 bar and the reaction medium is heated. After 3 hours, the reaction was complete. The final reaction mixture was analyzed by gas chromatography. The remaining acid was 0.3 mol% and the resulting toluoyl chloride was 99.7 mol%.

Example 13

Phosgenation of 2-furan carboxylic acid

2-Furanecarboxylic acid (110 g, 0.98 mol) and monochlorobenzene (900 g) were introduced into the reactor, followed by addition of 615 g (6.2 mol) of phosgene. The set pressure is relative

The reaction mixture was adjusted to 2 bar and the reaction mixture was heated. The pressure is adjusted with argon. The reaction is complete within 3 hours. The remaining acid was 5.5 mol% and the resulting 2-furoyl chloride was 94.5 mol%.

Claims (11)

A process for the preparation of monocarboxylic acid chloride by phosgenation of monocarboxylic acids and / or anhydrides, characterized in that the acid and / or anhydride is treated in a solvent with or without a molar excess of phosgene at 80-200 ° C and a pressure of 2-60 bar. 2. The process of claim 1, wherein the molar excess of phosgene is 2 to 15 times the molar excess of acid. Process according to claim 1 or 2, characterized in that the reaction is carried out without a catalyst. HU 222 273 Bl 4. A process according to any one of claims 1 to 5, characterized in that the process is carried out by partial degassing in an open system. 5. Process according to any one of claims 1 to 3, characterized in that the reaction is carried out at 100-150 ° C. Process according to claim 5, characterized in that the reaction is carried out at 110-130 ° C. 7. Process according to any one of claims 1 to 3, characterized in that the reaction is carried out at a pressure of 6 to 40 bar. 8. A process according to any one of claims 1 to 3, wherein a monocarboxylic acid of formula RCOOH is converted into an acid chloride of formula RCOC1, wherein R is a straight or branched, saturated or unsaturated aliphatic group having up to 22 carbon atoms, optionally substituted (a) with one or more identical or different halogens, (b) one or more nitro groups; or c) one or more aryl, preferably phenyl, aryloxy, or arylthio groups, each of which is unsubstituted or substituted; a cycloaliphatic C 3 -C 8 group which is unsubstituted or substituted with one or more groups, namely a) halogen, b) alkyl or haloalkyl, (c) with a nitro group; and d) aryl, aryloxy and arylthio, these aryl, preferably phenyl, or aryl derivatives are unsubstituted or substituted; an aromatic carbocyclic group which may be unsubstituted or substituted with one or more substituents selected from the group consisting of halogen, alkyl or haloalkyl, preferably trifluoromethyl, having from 1 to 12 carbon atoms, C1 to 6 alkylthio or halogen; alkylthio, C 1-6 alkylsulfinyl or haloalkylsulfinyl, C 1-6 alkylsulfonyl or haloalkylsulfonyl, C 1-6 alkyloxy or haloalkyloxy aryl, aryloxy or nitro; aromatic or non-aromatic 5 or 6 membered heterocyclic group containing one or more identical or different heteroatoms, namely oxygen, sulfur and / or nitrogen, and unsubstituted or substituted with one or more halogen, nitro, alkyl, haloalkyl, alkyl substituted with oxy, haloalkyloxy, aryl, arylthio or aryloxy and / or optionally fused with an aromatic carbocycle, which in itself may be unsubstituted or substituted. 9. A process according to any one of claims 1 to 6, wherein an anhydride of formula (RCO) ₂ O is converted into an acid chloride of formula RCOC1 or a mixed anhydride of formula (RCO) O (OCR ') into an acid chloride of formula RCOC1 and R'COC1. R and R 'represent a straight or branched, saturated or unsaturated aliphatic group having up to 22 carbon atoms, which is optionally substituted (a) with one or more identical or different halogens, (b) one or more nitro groups; or c) one or more aryl, preferably phenyl, aryloxy, or arylthio groups, each of which is unsubstituted or substituted; a cycloaliphatic C 3 -C 8 group which is unsubstituted or substituted with one or more groups, namely a) halogen, b) alkyl or haloalkyl, (c) with a nitro group; and d) aryl, aryloxy and arylthio, these aryl, preferably phenyl, or aryl derivatives are unsubstituted or substituted; an aromatic carbocyclic group which may be unsubstituted or substituted with one or more substituents selected from halogen, alkyl or haloalkyl, preferably trifluoromethyl, having from 1 to 12 carbon atoms, C1 to 6 alkylthio or haloalkyl; thio, C 1-6 alkylsulfinyl or haloalkylsulfonyl, C 1-6 alkylsulfonyl or haloalkylsulfonyl, C 1-6 alkyloxy or haloalkyloxy aryl, aryloxy or nitro; aromatic or non-aromatic 5 or 6 membered heterocyclic group containing one or more identical or different heteroatoms, namely oxygen, sulfur and / or nitrogen, and unsubstituted or substituted with one or more halogen, nitro, alkyl, haloalkyl, alkyl substituted with oxy, haloalkyloxy, aryl, arylthio or aryloxy and / or optionally fused to an aromatic carbocycle which may be unsubstituted or substituted in itself, with the proviso that R and R ' is a different group. 10. Process according to any one of claims 1 to 4, characterized in that the mixture of acids and anhydride is converted to the monocarboxylic acid chloride. 11. Process according to any one of claims 1 to 3, characterized in that the hydrochloric acid and carbon dioxide formed during the reaction and the phosgene are separated on a column located outside the reactor.