GB2310661A

GB2310661A - Production of Acid Halides by Phosgenation

Info

Publication number: GB2310661A
Application number: GB9704047A
Authority: GB
Inventors: Jean-Claude Descorps; Francois Metz
Original assignee: Rhone Poulenc Agrochimie SA
Current assignee: Bayer CropScience SA
Priority date: 1996-02-29
Filing date: 1997-02-27
Publication date: 1997-09-03
Anticipated expiration: 2017-02-27
Also published as: JPH09323953A; FR2745568A1; FR2745568B1; CN1071303C; HUP9700535A2; HU222273B1; DE19707285A1; KR100599065B1; FR2745567A1; FR2745567B1; HU9700535D0; CN1163881A; GB9704047D0; KR970061845A; HUP9700535A3; BR9700326A; GB2310661B; IL120272A0

Description

1 2310661 Phosgenation under pressure of acids andlor anhydrides for the

production of acid chlorides The present invention relates to a novel 5 process for gaining access to acid chlorides by phoagenation of monocarboxylic acids and/or corresponding anhydrides under pressure with or without catalyst, preferably in the absence of catalyst.

The conventional processes with catalyst consist in injecting phosgene into the acid by itself or in solution, at ordinary pressure and at temperatures between 80 and 1500C. An excess of phoogene is generally used. The vent gases, consisting of a mixture of phosgene, carbon dioxide and hydrochloric acid, are not separable at ordinary pressure unless very low temperature condensers are used, which always gives rise to a loss of phosgene.

The chemistry is governed by the following reaction equations:

(1) RCOOH + COC12 RCOC1 + EC1 + C02 (2) RCOOH + RCOC1 (RCO) 20 + EC1 (3) (RCO) 20 + 2COC12 --> 2RCOC1 + 2C02 (kl) (k-21k2) (k3) At ordinary pressure, reaction (1) in limited by the phosgene concentration, which is a function of the temperature. The disappearance of the acid is thus relatively rapid but the acid chloride formed reacts 2 with the acid present to give the anhydride according to--"eaction (2), the subsequent conversion of which anhydride into acid chloride is slow (reaction (3)).

Thus, in order to activate reaction (3), it is necessary to use one or more catalysts, and there is consequently an abundance of literature for such catalysts. However, the use of a catalyst presents many drawbacks. Firstly, their cost and then their influence on the choice of materials, since the catalysts often make the reaction system very corrosive. Next, it promotes the formation of side products (eg. ketene) and the development of colour. Lastly, it involves purification of the acid chloride by distillation or crystallization.

As an example of such a process, mention will be made, for example, of French patent application FR 2,585,351 (EP 213, 976), which describes the preparation of acid chlorides by phongenation of the corresponding carboxylic acid. This document presents as a necessity the use of a catalyst in order to obtain acid chlorides under economically acceptable conditions. One of the subjects of EP 213,976 relates in particular to the catalkst used to-carry out the phosgenation reaction.

Moreover, the Applicant in RP 213,976 cites as a document of the prior art an American patent (USP 2,657,233) which, according to the Applicant, discloses the use of a high pressure combined with a high temperature to produce acid chlorides. However, reading

3 that document shows that the invention relates, in that ca4 to a process for the production of dicarboxylic acid chlorides by phoogenation, under high pressure and temperature, of the corresponding dicarboxylic acid.

This document correctly teaches that for the production of acid monochlorides, the conventional method as described above in entirely satisfactory and that, ultimately, an improvement can only be expected by optimizing the catalysts used, which in confirmed by the abovementioned document PR 2,585,351 and documents FR-2,254,547 or EP 545,774, for example. The invention seeks to avoid the abovementioned drawbacks, in particular those associated with the use of catalysts in the prior art.

is The invention provides a process for the phosgenation of monocarboxylic acids andlor anhydrides characterized in that the acid and/or the anhydride is treated, in the presence or absence of solvent, with a molar excess of phoagene, preferably 2 to 15 times (molar) an much phougene as acid, at a temperatures from 80 to 2000C and at a pressure from 2 to 60 bar (1 bar = 10' Pa), with or without catalyst, preferably in the absence-of any catalyst. The process is generally performed in a closed system (autogenous pressure) or in an open system (pressure adjusted by eg partial degassing).The process is generally carried out as a continuous or semi-continuous process. Preferably, the process is performed in an open system by partially 4 degassing. The degassing is generally carried out while taking care to ensure that an excess of phosgene remains. This occurs either by selective elimination of the hydrochloric acid and the carbon dioxide, while at the same time retaining the excess phoagene and a little EC1 (so as not to make anhydride, but not too much, so as not to slow down the final reaction too much), or by a degassing including phougene, the latter. being resupplied at the same time. The temperature is advantageously chosen from 100 to 1500C, preferably from 110 -to 13CC, whereas the pressure is preferably chosen from 6 to 40 bar. The temperature and pressure conditions are determined by the nature of the monocarboxylic acid andlor the anhydride and the corresponding chloride, in particular the critical point andlor the point of decomposition.

The advantages of the phosgenation under pressure according to the invention are to be able a) to dispense with the low temperature condensers and b) to dispense with solvent andlor catalyst. This makes it possible to avoid the final purification of the acid chloride obtained and allows a simple separation at the end of the.reaction and a reduction in the utilities cost, and in general the advantages are those already discussed above associated with the absence of catalyst. It will be seen in Example 1 that the effect of adding a catalyst is virtually removed, that is to say that the gain in productivity obtained by the use of the process according to the invention with a catalyst compared with the same process without a catalyst in very low with regard to the drawbacks entailed by the use of such a catalyst. It will also be scan that the process according to the invention without a catalyst makes it possible to convert all of the acid employed into chloride in less time than a conventional process with.catalyst would take. Lastly, the process according to the invention allows an increase in productivity when compared with the semicontinuous hatch process at ordinary pressure.

The process according to the invention is advantageously used.for the chlorination of acids of formula RCOOM into acid chloride RCOC1, R being defined as:

- a linear or branched, saturated or unsaturated aliphatic.radical having up to 22 carbon atoms, optionally substituted a) with one or more identical or different halogen atoms, b) with one or more nitro groups or c) with one or more aryl (preferably phenylb aryloxy or arylthio groups, each of which is unsubstituted or substituted; ---acycloaliphatic radical having from 3 to 8 carbon atoms, which is unsubstituted or substituted by one or more substituents chosen a) from halogen atoms, b) alkyl or haloalkyl radicals, c) nitro groups and d) aryl, aryloxy and arylthio radicals, these aryl (preferably phenyl) or aryl derivatives being 6 unsubstituted or substituted; - an aromatic carbocyclic radical which is unsubstituted or substituted by one or more substitutents chosen from the group consisting of halogen atoms, alkyl or haloalkyl radicals (preferably CF3) having from 1 to 12 carbon atoms, alkylthio or haloalkylthio radicals having from 1 to 6 carbon atoms, alkyloulphinyl or haloalkyloulphinyl radicals having from 1 to 6 carbon atoms, alkyloulphonyl or haloalkylsulphonyl radicals having from 1 to 6 carbon atoms, alkyloxy or haloalkyloxy radicals having from 1 to 6 carbon atoms, aryl, arylthio or aryloxy radicals and the nitro group; - an aromatic or non-aromatic 5- or 6-membered heterocyclic radical, having one or more identical or different heteroatoms chosen from oxygen, sulphur and nitrogen atoms and being unsubstituted or substituted by one or more substituents chosen from halogen atoms, nitro groups and alkyl, haloalkyl, alkyloxy, haloalkyloxy, aryl, arylthio and aryloxy radicals andlor optionally being fused to an aromatic carbocycle which is itself unsubstituted or substituted; in general, when an aryl group (or one of the derivatives thereof such an aryloxy or arylthio) or an aromatic carbocycle is mentioned, it should be considered, even if this is not stated at the time when such a radical appears in order to abridge the present 7 account, that this group may bear substituents chosen finw-the group consisting of halogen atoms and alkyl, haloalkyl, alkyloxy, haloalkyloxy, alkylthio, haloalkylthio, alk3rloulphinyl, haloalkyloulphinyl, alkylsulphonyl, haloalkylaulphonyl, aryl, aryloxy, arylthio and nitro radicals.

The process according to the invention is also advantageously used for the chlorination of anhydrides of formula MC0)20 or mixed anhydrides MCOMOCRI) into acid chloride RCOC1 and RICOC1, R and R,-being defined as R above and R and R' not representing the same radical at the same time.

The process according to the invention is also suitable for the chlorination of mixtures of acids and anhydrides.

This process according to the invention is also characterized in that.the pressure is moreover used to facilitate the separation of any hydrochloric acid, the carbon dioxide and the phoagene, in a column which is external to the reactor, without using low temperature condensers which, as we have already seen, are a cause of loan of COC12. The separation consecluently becomes simpler, and therefore more economical, than with the known processes, and leads to phongene which can be readily recycled and to pure hydrochloric acid.

The examples which follow illustrate the invention. They show the advantages associated with the 8 process according to the invention.

Example 1. Production of stearoyl chloride by the action of phougene on stearic acid (test No. 413).

0.175 g (0.615 - 1, concentration 0.41 M) of stearic acid and 0.920 g (8. 171 =nol) of chlorobenzene are weighed out into a monocrystalline sapphire tube (1) with outside and inside diameters of 10 and 8 mm respectively, this tube being designed to withstand high pressures. A scaled tube (2) of diameter 5 mm containing deuterated benzene in also introduced into tube (1) to ensure the presence of an external lock, required for the subsequent NMR analysis. The tube (1) is then closed, Imm rued in an acetonelcardice bath (-78'C) and then conn cted to a phougene bottle. 0.606 g (6.127 mmol) of phosgene (concentration 4.08 M) is 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 colourless, homogeneous liquid. The tube is then introduced into the cryomagnet of an NMR spectrometer preheated to 117'>C. A first spectrum is recorded 11 min after introduction into the cryomagnet, i.e. a period corresponding to tuning of the stectrometer-and to stabilization of the reactor at the set temperature. An automatic programme then allows the spectra to be recorded at regular intervals (typically every 5 min).

The molar percentage of each compound is determined by integration of the triplets corresponding 9 to the methylenic protons alpha to the carbonyl fur=tion.

The foll i- result- a- thus obta4neA Tent Temp. [Acidl [C0C121 Vol. k observed t 112 P NO. OC m 1 m =l h_l inin. g-h-1-1-1 413 117 0.41 4.08 1.5 2.4 18 210 The kinetic constant k of pseudo-first order is calculated by linearization according to the formula: -Ln(l-DC) kt with DC = degree of conversion ofthe acid and t time.

P = Productivity calculated at DC = 50%.

By working an in the above example and varying different parameters (temperature, pressureffl etc.), the results given in the tables below are obtained.

a influence of e temDerature:

Test Temp. [Acid] ECOC121 Vol. k observed t 112 p NO. OC m m ral h_l min. g-h-1-1-1 415 83 0.42 4.3 1.5 0.44 94 40 421 101 0.39 4.94 1.6 1.18 35 100 413 117 0.41 4.08 1.5 2.4 18 210 121 0.39 4.69 1.6 3.2 13 270 15.. b) Presence of the catalyst described in examnle 1 o FR 2 585 351:

Test Temp. [Acid] [C0C121 Vol. k observed t 112 p NO. OC m m Ial h_l min. g-h-1-1-1 413 117 0.4 4.08 1.5 2.4 18 210 414 115 0.415 4.57 1.5 3.7 11 340 Without catalyst.

With catalyst (hexa n-butylguanidinium chloride)(0.02 mol%).

An has already been stated above, the effect of adding a catalyst is virtually erased, that is to say that the gain in productivity obtained by the use of the process according to the invention with catalyst compared with the same process without catalyst is very low.

c ) Influence of he Dhoscene concentration:

That T [Acid] (C0C121 Vol. k observed t 112 p No. OC m m zal h-1 min. g-h-1-1-1 413 117 0.41 4.08 1.5 2.4 18 210 420 114 0.47 3.15 1.3 2.1 20 185 cl 1 influence of the solvent:

Test Temp. [ACid] [C0C121 Vol. k observed t 112 p No. OC m m M1 h-1 min. g-h-1-1-1 415 83 0.42 4.3 1.5 0.44 94 40 425 80 0.885 1.0 1. 3 66 50 is Solvent = chlorobenzene. Solvent = COC12.

e) influence of degassing:

The influence of working with (test 417) or 20 without (test 413) degassing is shown in the attached Figure 1. Test 413 is already described and test 417 is 11 the same but using 0.16 g (0.56 mmole) of acid, 0875 g of-- ehlorobenzene and 0.88 g (8.9 mmol) of phosgene. For test 417, when 90% of acid is transformed (after about 45 min), the tube is allowed to cool in order to achieve degassing and then heated again up to 1170C after 0. 99.g of phosgene are again introduced. moreover, according to this Figure 1, it is observed that a 100% degree of conversion-of the stearic acid is obtained in less than 2 hours (about 75 min when the processIs performed with degassing at 1170C (test No. 417)). This makes it possible to compare our invention with the results given in FR 2,585,351. indeed, in that document, the stearic acid is completely converted into chloride when the process is performed in the presence of 0.02 mol% of catalyst at a temperature of 120-1250C but in 4 hours. it is therefore clearly seen, as has already been stated, that the process according to the invention without catalyst makes it possible to convert all of the acid employed into chloride in less time than a conventional process with catalyst would take. Exa=le 2. Phosgenation of pivalic acid: a) A first approach was made by performing a phosgenation reaction under pressure on this neat acid.

By working as in Example 1 with a 10 mm multinuclear probe but using deuterated pyridine for the lock in place of the deuterated benzene, it in seen that the phoagenation reactions under pressure of pivalic acid 12 into acid chloride are first order. The results are as f 0-1-1-Ows:

al) at WC, a rate constant equal to 0.28 h-1 was found (conditions: 0.75 g of acid (7.3 mmol) and 5 1.5 g of phosgene (15.2 mmol)).

a2) at 1150C, a rate constant equal to 3. 00 h1 was found (conditions: 0. 692 g of acid (6.78 mmol) and 1.25 g of phongene (12.7 wm M.

b) A second study is performed to monitor the kinetics of the phougenation reaction of pivalic acid in-chlorobenzene rather than with neat acid. in contrast with the study with neat acid, it is no longer possible to distinguish the CH3 protons of the acid and the chloride and, consequently, it in not possible to monitor the progress of the reaction in chlorobenzene.

We have, however, attempted to distinguish the acid and the chloride by carbon NMR since the chemical shifts (relative to tetramethylsilane, TMS) of the carbons of the carbonyl groups and the quaternary carbons of the tert-butyl groups are very different. Chemical shifts are obtained at 185.8 ppm for COOR, 180.8 for COC1, 38.9 pp= for the quaternary carbon of the aidid and 49.3 ppm for the quaternary carbon of the acid chloride. An AMX 300 spectrometer operating at 75 MHz for the carbon 13 and equipped with a 10 mm multinuclear probe was used. The chemical shifts (3) of the carbon resonance lines are expressed relative to tetramethylsilane (TMS). As in a), deuterated pyridine 13 is used (external lock).

After that, monitoring was carried out which shows that, at 800C, after 1 hour 45 minutes the acid chloride is predominant although a little acid remains 5 (conditions: 0.06 g of acid (0.6 mmol), 0.943 g of chlorobenzene and 0.735 g of phosgene (7.43 mmol)).

Example 3.. Phoagenation of pivalic anhydride:

The proton NMR analyses under pressure were carried out on an AM 300 spectrometer operating at 300 MHz for the proton and equipped with a 5 mm QNP 1B/13C/I9F/31P gradient-z probe. The chemical shifts (3) of the proton resonance lines are expressed relative to tetramethylsilane (TMS). Here and for example 4 to 6 as well, the monocrystalline sapphire tube has outside and inside diameters of 5 and 4 mm respectively.

As for the 1H NMR analysis under pressure of the phosgenation reaction of the neat acid (cf. 2a), it was possible to distinguish the CE3 protons of pivalic anhydride (8=1.24 ppm) and of the acid chloride (8=1.31 ppm).

The reaction was carried out at 800C with a 3 molar'excbsg of phosgene relative to the anhydride.

When minus the natural logarithm of the relative molar proportion of pivalic anhydride is plotted as a function of time, a straight line is obtained. The apparent order of the reaction for the formation of pivaloyl chloride from pivalic anhydride 14 is therefore 1. The slope of this straight line is e to the rate constant for the reaction: k = 1.6-102 min-l. The half-life t 112, representing the time required for the concentration of anhydide to decrease by one-half, is equal to ln 21k (t 112 = about 40 minutes).

Example 4. Phoogenation of octanoic acid:

Working an in Example 2a), it is seen that the reactions for the phoagenation under pressure of neat octanoic acid into the acid chloride are first order. The results are as follows:

1) at 790C, a rate constant equal to 0.25 h-1 was found (conditions: 0.79 g of acid (6.9 mmol) and 1.68 g of phongene (17 ==1)).

2) at 1240C, a rate constant equal to 1. 68 h-1 was found (conditions: 0. 78 g of acid (6.85 mmol) and 1.35 g of phosgene (13.7 mmol)).

Example 5. Phoogenation of trifluoroacetic acid:

Fluorine NM analyses under pressure were carried out on an AM 300 spectrometer operating at 300 MHz for the proton and equipped with a 5 = QNP IM/13C/197131P gradient-z probe. The chemical shifts of the fluorine resonance lines are expressed relative to 25 trifluoroacetic acid (TPA).

The reaction is monitored by the appearance of a resonance line at 0.3 ppm, which corresponds to trifluoroacetyl chloride, the acid being at 0 ppm since is it is the reference.

The reaction is slow since the degree of conversion into chloride is about 20% after heating at 1070C for 4 hours. However, this phougenation reaction under pressure with neat acid does take place (conditions: 0.22 g of acid (1.93 ==l) and 0.464 g of phongene (4.7 ==1)).

Examole 6. Phosgenation of benzoic acid:

13C NMR analyses under pressure were carried out on an AMX 300 spectrometer operating at 75 MHz for carbon 13 and equipped with a 5 r= QNP 1H/13C/19P/31P gradient-z probe. The chemical shifts (5) of the carbon resonance lines are expressed relative to tetram thylailane (TMS).

is it is very difficult by 1H NMR to distinguish benzoic acid from the acid chloride. For this reason, the test was carried out with benzoic acid enriched with carbon 13 (carbon of the carbonyl group) in order to carry out kinetic monitoring at 900C of the reaction under pressure of the neat acid by NMR on this carbon 13. indeed, the carbon resonance lines of the acid and of the acid chloride are at 8=170 ppm and 8=167 PPM risp6ctively.

When minus the natural logarithm of the relative molar proportion of benzoic acid is plotted as a function of time, a straight line is obtained (conditions: 0.077 g of acid (0.63 mmol) and 0.422 g of phoagene (4.27 mmol)-Temperature: 90OC). The 16 apparent order of the reaction for the formation of bez=yl chloride from benzoic acid is therefore 1. The slope of this straight line is equal to the rate constant for the reaction: k = 0.28 h-1. The half life t 112, representing the time required for the concentration of acid to decrease by one-half, is equal to ln 2/k (t 1.12 = about 2h 30).

General procedure for tests on a larger scale than the previous ones:

The following tests were performed in a two- litre..autoclave reactor equipped with a condenser and a pressure-control system. The total volume of the autoclave and the accessories in 2.25 litres. Monochlorobenzene and the organic acid are introduced into the totally anhydrous reactor which has been flushed with argon, and phoagene is then added at about 200C. The valve set to air is closed and the control valve is adjusted to the set opening for the desired pressure. The reaction medium is then brought to 1200C as quickly as possible.

The percentages of acid, of anhydride and of chloride in the reaction medium are determined by proton NMR monitoring.

Example 7. Phosgenation of pivalic acid:

61.3 g (0.6 mol) of pivalic acid and 890 g of monochlorobenzene are introduced into the reactor and 597 g (6 mol) of phosgene are then added over about 30 minutes while maintaining the temperature of the 4 17 reaction medium at a maximum of 250C. The set pressure is-adjusted to 10.5 bar relative and the reaction medium is heated. About 0.3% anhydride forms in the first 30 minutes. The anhydride formed becomes phoogenated. The reaction is complete after two hours. The level of residual acid is less than 0.5 mol%, the level of residual anhydride is zero and the level of pivaloyl chloride obtained in greater than 99.5 mol%.

Exa=le 8. Phoogenation of 2-ethylhexanoic acid:

87 g (0.6 mol) of 2-ethylhexanoic acid and 890 g of monochlorobenzene are introduced into the reactor and 607 g (6.14 mol) of phosgene are then added over about 30 minutes, while maintaining the temperature of the reaction medium at a maximum of 250C. The set pressure is adjusted to 10.5 bar relative and the reaction medium in heated. The reaction is complete after one hour 30 minutes. The levels of residual acid and anhydride are zero and the level of 2-ethylhexanoyl chloride obtained is greater than 99.8 molso,.

Example 9. Phosgonation of octanoic acid:

86.6 g (0.6 mol) of octanoic acid and 890 g of mohochlorobenzene are introduced into the reactor and 600 g (6.07 mol) of phoagene are then added over about 30 minutes, while maintaining the temperature of the reaction medium at a maximum of 250C. The set pressure in adjusted to 10. 5 bar relative and the reaction medium in heated. After two hours, the level 18 of residual acid is about 1 mol%, the level of residual adride is zero and the level of octanoyl chloride obtained is 99 mol%.

Exanmle 10 Phosgenation of stearic acid:

170.4 g (0.6 mol) of stearic acid and 890 g of monochlorobenzene are introduced into the reactor and 594 g (6 mol) of phongene are then added over about 30 minutes, while maintaining the temperature of the reaction medium at a maximum of 250C.. The set pressure is adjusted to 10.5 bar relative. The reaction medium is heated to 1200C and in maintained at this temperature for 1 hour 30 minutes and is then heated to ISO'C and maintained at this new temperature for 1 hour. The level of residual acid is then about 1.4 mol%, the level of residual anhydride is zero and the level of stearoyl chloride obtained 98.6 mol%. The maximum pressure reached was 9 bar relative.

Example 11. Phongenation of oleic acid:

g (0.7 mol) of oleic acid and 725 g of monochlorobenzene are introduced into the reactor and 574 g (5.8 mol) of phoagene are then added. The set pressure is adjusted to 11.2 bar relative and the react Ion medium-is heated. The reaction is complete after 1 hour 30 min. The level of residual acid is 0.5 zLol% and the level of oleoyl chloride obtained is 99.5 molso,.

Example 12. Phosgenation of p-toluic acid:

81.4 g (0.6 mol) of.p-toluic acid and 892 g 19 of monochlorobenzene are introduced into the reactor and-82 g (5.9 mol) of phosgene are then added. The set pressure is adjusted to 11.2 bar relative and the reaction medium is heated. The reaction is complete after 3 hours. Analysis of the final reaction medium is carried out by gas chromatography. The level of residual acid is 0.3 mol% and the level of toluoyl chloride obtained is 99.7 mol%.

Example 13. Phoagenation of 2-furoic acid:

g (0.98 mol) of 2-furoic acid and 900 g of-monochlorobenzene are introduced into the reactor and 615 g (6.2 mol) of phoogene are then added. The set pressure is adjusted to 11.2 bar relative and the reaction medium is heated. The pressure is adjusted by addition of argon. The reaction is complete after 3 hours. The level of residual acid is 5.5 mol% and the level of 2-furoyl chloride.obtained is 94.5 mol%.

-LC-1 Key to Figure 1 Figure 1 illustrates the phosgenation of stearic acid with (Test No. 413) and without (Test No. 417) intermediate degassing.

The ordinate gives the percentage of stearic acid- The abscissa gives the time of reaction in minutes.

Test No. 417 is the upper curve and Test No. 413 the lower.

1 1-k

Claims

1. Process for the phosgenation of monocarboxylic acids andlor anhydrides, characterized in that the acid andlor the anhydride is treated, in the presence or absence of solvent, with a molar excess of phoogene at a temperatures from 80 to 20CC and at a pressure from 2 to 60 bar, with or without catalyst, to obtain a monocarboxylic acid chloride.

2. Process according to claim 1 in which a 2 to 15 times molar excess of phoogene to acid is used.

3. Process according to claim 1 or 2 in which the reaction is carried out in the absence of a catalyst.

4. Process according to claim. 1, 2 or 3 characterized in that the process is performed in an open system by partially degassing.

5. Process according to any one of the preceding claims, characterized in that the temperature is from 100 to 1500C.

6. Process according to claim 5 in which the temperature in from 110 to 1300C.

7.. Process according toany one of the preceding claims, characterized in that the pressure is from 6 to 40 bar.

8. Process according to any one of the preceding claims, characterized in that a monocarboxylic acid of formula RCOOE is converted into identical or different halogen atoms, b) with one or more nitro groups or c) with one or more aryl (preferably phenyl), aryloxy or arylthio groups, each of which is unsubstituted or substituted; - a cycloaliphatic radical having from 3 to 8 10 carbon atoms, which in unsubstituted or substituted by one.or more substituents chosen a) from halogen atoms, b) alkyl or haloalkyl radicals, c) nitro groups and d) aryl, aryloxy and arylthio radicals, these aryl (preferably phenyl) or aryl derivatives being 15 unsubstituted or substituted; - an aromatic carbocyclic radical which is unsubstituted or substituted by one or more substitutents chosen from the group consisting of halogen atoms, alkyl or haloalkyl radicals (preferably 20 CP3) having from 1 to 12 carbon atoms, alkylthio or haloalkylthio radicals having from 1 to 6 carbon atoms, alkyloulphinyl or haloalkyloulphinyl radicals having from 1 to 6-carbon atoms, alkylsulphonyl or haloalkylsulphonyl radicals having from 1 to 6 carbon atoms, alk-yloxy or haloalkyloxy radicals having from 1 to 6 carbon atoms, aryl, arylthio or aryloxy radicals and the nitro group; - an aromatic or non-aromatic 5- or 6-m emb ered heterocyclic radical, having one or more idical or different heteroatoms chosen from oxygen, sulphur and nitrogen atoms and being unsubstituted or substituted by one or more substituents chosen from halogen atoms, nitro groups and alkyl, haloalkyl, alkyloxy, haloalkyloxy, aryl, arylthio and aryloxy radicals andlor optionally being fused to an aromatic carbocycle which is itself unsubstituted or substituted.

9. Process according to any one of claims 1 to-7, characterized in that an anhydride of formula (RCO)20 or mixed anhydride (RCO)O(OCRI) is converted into acid chloride RCOC1 and RICOC1, R and R' being def ined as P. in claim 8 and R and R I not representing the same radical at the same time.

10. Process according to any one of claims 1 to 7, characterized in that a mixture of acids and anhydride is converted to monocarboxylic acid chloride.

11. Process according to one of the preceding claims characterized in that the separation of hydrochloric acid and carbon dioxide formed in the reactions and phosgene, is conducted in a column which is external-to the reactor.

12. Process according to claim 1 substantially as hereinbefore described in any one of Examples 1 to

13.