GB1572076A - Process for producing aromatic carboxylic acid chlorides and 3-chlorophthalide - Google Patents

Description

(54) A PROCESS FOR PRODUCING AROMATIC CARBOXYLIC ACID CHLORIDES AND 3-CHLOROPHTHALIDE (71) We, DYNAMIT NOBEL AKTIENGESELLSCHAFT, a Germany company, of 521 Troisdorf, bez Kiln, Postfach 1209, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a process for forming a product mixture comprising an aromatic carboxylic acid chloride and 3-chlorophthalide.

It is known that aromatic acid chlorides can be obtained with, for example, thionyl chloride, phosphorus pentachloride or similar chlorinating agents. One disadvantage of producing acid chlorides in this way is the presence in the product of residues of sulphur or phosphorus compounds which can only be removed with difficulty. Other synthesis processes start out from the trichloromethyl compounds which are reacted either with water or with the corresponding carboxylic acids in the presence of catalysts to form the acid chlorides. One disadvantage common to these processes is that numerous trichloromethyl compounds are impossible or difficult to obtain. Accordingly, it is generally necessary to react an aromatic carboxylic acid with an aromatic trichloromethyl compound of non-corresponding structure, so that two different acid chlorides, namely the required acid chloride and an unwanted acid chloride, are obtained. Another limitation is that numerous acid chlorides are impossible or difficult to separate from one another.

Readily obtainable trichloromethyl compounds are, in particular, a,a,LZ,a',a',(Y),-hexachloro-m- or p-xylene - m-HCX or p-HCX). These trichloromethyl compounds react for example with 2 moles of benzoic acid to form 2 moles of benzoyl chloride and 1 mole of isophthalic acid dichloride or terephthalic acid dichloride. However, these bifunctional acid chlorides show a tendency towards secondary reactions and are difficult to isolate in pure form from the reaction mixture, i.e. there is the problem that the chlorinating agent (aromatic trichloromethyl compound) is itself transformed into a substance from which the desired acid chloride cannot be effectively and completely recovered and utilised.

If aromatic carboxylic acids are reacted with a,cr,cr,a','-pentachloro-o-xylene (o-PCX) to form carboxylic acid chlorides in accordance with formula (1)

by melting the starting materials in the reaction vessel in the presence of catalysts added in solid form, it has been found that although the carboxylic acid chlorides which form are substantially free from sulphur or phosphorus compounds, the 3chlorophthalide (3-Cp), which is a valuable intermediate product for syntheses, is only formed in a small quantity and generally reacts to form worthless condensates or cannot be recovered. In this process, since one mole of gaseous hydrogen chloride is given off per mole of carboxylic acid during the reaction, the reaction can only be carried out on a very small scale, because otherwise the evolution of HCI cannot be controlled. If it is desired to carry out the reaction on a larger scale, it has been found to be necessary to introduce one of the two reactants in metered form, which is technically difficult to do. On account of the high melting point of many carboxylic acids, they generally have to be metered in powder form, these powders frequently being characterised by poor flow properties. If, on the other hand, the o-PCX is metered, a substantially non-stirrable solid may well be present in the reactor at the beginning of the reaction.

In addition, it has been found that production of the acid chlorides in pure form and recovery of the small amounts of 3-Cp are made difficult by the incomplete reaction and by numerous secondary products, even when the acid chloride and the 3-Cp are basically separable from one another by virtue of their different boiling points. Added to this is the fact that, in many cases, for example in the reaction of toluic acids with o-PCX, the catalyst is consumed by secondary reactions (for example Friedel Crafts reactions) and has to be continuously replenished.

According to the present invention there is provided a process for forming a product mixture comprising an aromatic carboxylic acid chloride and 3 chlorophthalide which comprises reacting o-pentachloroxylene with an aromatic carboxylic acid in a reaction vessel in the presence of a catalyst and removing the hydrogen chloride which is produced, the catalyst being introduced into the reaction vessel separately from the aromatic carboxylic acid and the o pentachloroxylene.

The reaction is preferably carried out at a temperature of up to 1800C.

The process may include an additional step in which the reaction products are separated from one another.

The aromatic carboxylic acid and the o-PCX are preferably introduced into the reaction vessel as an admixture, which permits the reactions to be carried out in homogeneous phase. Addition of the preferably heated starting materials is generally simplified and enables preselected quantitative ratios to be strictly maintained.

The mixture of the reactants, i.e. aromatic carboxylic acid and o-PCX, may be present in basically any form, for example even in the form of a mixture of solid powders of both substances. Ideally the quantitative ratios selected for the reaction of the two reactants, possibly with allowance for impurities, should be maintained.

This quantitative ratio preferably only deviates by at most 10 mole% from the ratio of 2 moles of carboxylic acid per mole of o-PCX, the best results generally being obtained by the strictest possible maintenance of the molar ratio. Although there is no harm in using an excess of o-PCX, this excess has to be removed on completion of the reaction, whereas a deficiency of o-PCX is unfavourable in that it leads to the formation of worthless condensation products which reduce the yield.

Admixtures of the aromatic carboxylic acid and the o-PCX generally have a much lower melting point than the acid alone; it is very much preferred to perform the process by forming the melt of reduced melting point from the admixture of reactants and to introduce it into the reactor from a storage vessel. The temperature of the melt formed from the starting materials may be for example a few degrees centigrade above the melting temperature of the admixture up to about 180"C and preferably up to 1600C.

In some cases, it is also possible, although not particularly preferred, to react the admixture of starting materials in an inert high boiling solvent such as hexachlorobutadiene or 1,2,4-trichlorobenzene.

The process according to the invention may be carried out continuously by running the molten admixture preferably continuously or, optionally, in portions into a preferably mutiple-stage reactor into which the catalyst is simultaneously introduced either continuously or in portions, and removing the reacted product mixture at a constant rate from the last stage of the reactor. Production of the molten mixture of o-PCX and aromatic carboxylic acid may be carried out in a separate apparatus, which means that the problems conventionally associated with simultaneously metering two substances in the correct ratio disappear; further, the evolution of HCI takes place at a constant rate and creates few problems for subsequent units of apparatus, for example an absorber.

Aromatic carboxylic acids preferred for use in the process according to the invention are aromatic carboxylic acids whose substituents do not enter into any secondary reactions with the o-PCX, for example unsubstituted carboxylic acids and carboxylic acids substituted by one or more alkyl and/or chlorine and/or nitro groups. Non-inert carboxylic acids, such as hydroxy carboxylic acids, for example salicyclic acid, or methoxy carboxylic acids, form complex mixtures of condensation products and, for this reason, should preferably not be used.

The use of aromatic carboxylic acids which, in admixture with 1/2 mole of o PCX, have a melting point above 200"C, as is the case with terephthalic acid for example, in the form of a mixture of the starting materials or in the form of a melt is not recommended, although the melting points of the mixtures can usually be sufficiently reduced by adding a high-boiling inert solvent or the particular acid chloride, for example in the case of p-chlorobenzoic acid.

Accordingly, it is particularly preferred to use monocarboxylic acids, of which mononuclear and also binuclear and, in some cases, trinuclear and polynuclear carboxylic acids are in turn particularly preferred. It is possible, although not preferred, to use dicarboxylic acids, such as terephthalic acid or isophthalic acid, however the reaction of these acids is generally less smooth and is accompanied by the formation of secondary products and acid chlorides, some of which are difficult to separate from 3-Cp in a later stage.

Particularly preferred aromatic carboxylic acids are readily obtainable compounds such as benzoic acid, o, m- and p-toluic acid, o-, m- and pchlorobenzoic acid and m-nitrobenzoic acid. However, other carboxylic acids, for example ethylene benzoic acids, dichlorobenzoic acids or dinitrobenzoic acids may also be used.

In pure form, these aromatic carboxylic acids remain substantially stable for several hours in admixture with o-PCX in the melt. Technical aromatic carboxylic acids occasionally contain traces of iron, however, and in this case, a gentle reaction accompanied by the evolution of HCI takes place slowly in the melt, even in the absence of added catalyst. If this reaction causes problems, it may be stopped by the addition of a small quantity of a complex former, for example ethylene diamine tetraacetic acid or caprolactam. These small quantities of complex former do not interfere with the later deliberately catalysed reaction. The quantity in which the complex former is used need not exceed from 20 to 200 mg and preferably amounts to from 20 to 120 mg per g/mole of aromatic carboxylic acid.

The stabilities of admixtures of aromatic carboxylic acids and o-PCX, and the effect thereon of complex formers are exemplified in Table 1.

TABLE I Stability of mixture of 1 mole of a carboxylic acid and 0.5 mole of o-PCX

M.p. of the Complex Stability mixture former Heating temperature % HCl carboxylic acid C (mg) and time 1) Benzoic acid 1025) - 5 hours, 160 C ~0.05 0-toluic acid 89 5) - 3 hours, 160 C ~0.1 m-toluic acid ~100 - 1 hour, 140 C; 1.5 hours, 170 C 0.8 p-toluic acid 2) ~140 EDTA 3) (100) 4 hours, 170 C 0.7 p-toluic acid 2) ~140 CL 4) (25) 7 hours, 150 C 0.07 o-chlorobenzoic acid 120 5) - 1 hour, 140 C; 1 hour, 160 C 0 o-chlorobenzoic acid 120 5) EDTA (100) 1 hour, 140 C; 1 hour, 180 C 1.0 m-nitrobenzoic acid 125 - 1 hour, 140 C; 1 hour, 180 C ~2 1) Quantity of HCl formed in % of the theoretical quantity with complete conversion.

2) Contains 20 ppm of iron.

3) Ethylene diamine tetraacetic acid.

4) Caprolactam 5) As measured by differential thermoanalysis.

It has been found that metering of the catalyst to the reaction vessel is easy to carry out by using the catalyst in the form of its aqueous solution. This is surprising because Lewis acids are generally deactivated by water.

Lewis acids may be used as catalysts for the reaction. It is immaterial whether the catalyst is present in its active form (generally the chloride) or in another form from which the chloride can be formed under the reaction conditions. Other forms such as these are, for example, the oxides or hydroxides of the associated metals of the Lewis acids, optionally the metals themselves or the metal acids. In a preferred embodiment, the catalyst is used in the form of an aqueous solution, the watersoluble salts selected being of the readily obtainable type which form stable aqueous solutions.

The preferred catalysts are zinc chloride and iron (III) chloride, both preferably used in the form of aqueous solution. However, it is also possible to use aqueous solutions of salts of divalent iron, such as FeCl2.4H2O, FeSO47H2O and also salts of trivalent iron. Molybdenum chlorides are also suitable catalysts, the readily obtainable ammonium heptamolybdate preferably being used instead of the expensive MoCI5. However, other Lewis acids, such as for example bismuth (II)chloride and antimony(V) chloride, are also suitable.

The aqueous solution of the metal chlorides may generally contain from 3 to 60% by weight and preferably from 10 to 45% by weight of metal chloride, although these quantities do not have to be strictly observed. The inclusion in the aqueous solution of hydrochloric acid (5 to 20 wt% aqueous), for example in a quantity of 10 to 30% based on the amount of the aqueous solution, or even direct dissolution of the catalyst in aqueous hydrochloric acid is extremely favourable.

The quantity in which the catalysts are used may be comparatively small so that, for a general range from 0.001 to 2% by weight, it is preferred to use from 0.001 to 0.1% by weight, expressed as metal, of the catalyst, based on the mixture of starting materials. In the case of catalyst solutions, it is preferable to use from 0.001 to 0.03% by weight. It is preferred to add the catalysts continuously, although they may also be added in portions.

It may be assumed that the water in the aqueous catalyst solution is taken up by reaction with already formed acid chloride, which reaction of course produces the original aromatic carboxylic acid; this carboxylic acid formed is preferably compensated for by a small excess of o-PCX. By virtue of the small quantities of water used, however, this correction is generally within the normal process fluctuations, for example in the purity of the materials used.

In addition to the fact that it can readily be metered, the catalyst added in aqueous form is also preferred because some of the catalysts, when in solid form, are hygroscopic and unstable. Thus, anhydrous FeCI3 often contains insoluble fractions, such as hydroxides, which reduce its activity. Accordingly, it should be freshly sublimated. By contrast, the catalysts formed from aqueous solution have been found to be highly active, presumably because they accumulate in finer distribution after the water has reacted and, for this reason, dissolve in the melt more easily than catalysts added in solid form. This is particularly noticeable in the case of zinc chloride which, in aqueous solution, represents an excellent catalyst but which, in solid form, is slow in starting the reaction on account of its poor solubility in the reaction medium.

The reaction of the o-PCX/carboxylic acid admixture in the presence of catalyst is preferably carried out at temperatures above the melting point of the mixture, for example up to 1800C and preferably at 120 to 1800C, the choice of the most favourable temperature being determined by the carboxylic acid used, by the catalyst and by the type of reactor.

In the case of melts of some carboxylic acid/o-PCX starting mixtures the lowest reaction temperature is 90"C, as for example in the case of melts containing o-toluic acid, or 105"C as in the case of melts containing benzoic acid, although in their case, too, the preferred temperature is above 120"C for reasons of the reaction velocity. In the continuous embodiment of the process, the residence time in the reactor represents another variant. In most cases, it is favourable to combine the highest possible temperature in the range from 140 to 1800C with a short residence time in the reactor, although this is by no means a condition.

Aromatic carboxylic acid chlorides are known to be highly reactive starting materials for syntheses. 3-Chlorophthalide is an intermediate product, for example for the production of phthalide, o-phthalic aldehyde acid and 3-bromophthalide and for introducing the phthalidyl radical into organic molecules, for example in accordance with J. Org. Chem. 37 (1972), 1375.

The invention is illustrated by the following Examples. Example I (Comparison Example) shows that it is difficult to obtain a complete conversion by metering the carboxylic acid and adding the FeCI3 in solid form. Examples 2 and 3 describe batch-type tests, whilst Examples 4 to 10 describe continuous tests.

EXAMPLE 1 (Comparative).

In a I litre capacity four-necked flask equipped with a stirrer, thermometer, metering funnel and reflux condenser with gas vent, 278.5 g (1 mole) of o-PCX were heated to a temperature of 1400C. 0.4 g of anhydrous FeCI3 were then introduced at that temperature, followed by the addition over a period of 30 minutes of 272 g (2 moles) of m-toluic acid in solid form. The hydrogen chloride produced was absorbed in water on leaving the reflux condenser. After another 60 minutes, the evolution of HCI had stopped and the conversion was calculated from the hydrochloric acid formed as 71% of the theoretical. Working up by distillation gave a distillate boiling at 95--148"C/13 Torr and a distillation residue of 28%. Analysis of the distillate by gas chromatography showed a yield of 95% of the theoretical for m-toluic acid chloride and of 25% of the theoretical for 3-Cp.

Repetition of the Example produced similar results i.e. incomplete conversion, distillation residues between 26% and 40% and a low yield of 3-Cp.

EXAMPLE 2.

613 g (2.14 moles) of 97% pure o-PCX and 544 g (4 moles) of m-toluic acid were melted and mixed in a 2 litre flask equipped with a bottom outlet. The resulting mixture was introduced over a period of 1 hour into a 2 litre capacity four-necked flask equippled in the same way as in Example 1, which flask was kept at a temperature of 150"C. At the same time, 6 g of aqueous ZnCl2-solution (17%) were added in three portions. The mixture was left to react for 2 hours, after which time the conversion was calculated from the hydrochloric acid formed as being approximately 100% of the theoretical. Working up by distillation gave 94% of a distillate boiling at 95--1450C/14 Torr and 6% of a distillation residue. Analysis of the distillate by gas chromatography showed a yield of 95% of the theoretical of m- toluic acid chloride and of 92% of the theoretical of 3-Cp. Separation of the acid chloride from the 3-Cp by fractional distillation did not involve any difficulties.

EXAMPLE 3.

In an enamelled 500 litre capacity stirrer-equipped vessel equipped with a double jacket, stirrer drive, reflux condenser, filling spout and bottom outlet, 225 kg of m-toluic acid and 240 kg of 96% pure o-PCX were melted and kept at a temperature of 140"C. The reaction vessel which was used was in the form of an approximately 30 litre capacity recirculation reactor equipped with an insertiontype heater and reflux condenser. Approximately 20 litres of the mixture of mtoluic acid and o-PCX were run off from the stirrer equipped vessel into the reaction vessel and the reaction was started at 180"C by the addition of 30 ml of 40% aqueous ZnCl2-solution. After 20 minutes, another 10 litre of the mixture and 15 ml of ZnCl2-solution were run in. The HC1-gas escaping from the reflux condenser was monitored by a flow meter and absorbed in an absorber to form 30% hydrochloric acid. Approximately 15 litres of fully reacted crude product mixture were pumped off from the recirculation reactor every 20 minutes and the original volume of material in the reactor was restored by the addition of further toluic acid/o-PCX-mixture. 15 ml of 40% by weight of ZnCl2-solution were added per cycle, giving a total input of 350 ml. After 12 hours, the entire contents of the stirrer equipped vessel had been reacted. The crude product was collected in another 500 litre capacity enamel vessel and subjected to distillation. Fractional distillation through a 20 cm diameter 150 cm long column filled with ceramic saddles yielded 244 kg (95% of the theoretical) of 99.5% pure (gas chromatography) m-toluic acid chloride at b.p. 820C/5 Torr and 98 kg (70% of the theoretical) of 3-Cp at b.p.

130"C/6 Torr.

EXAMPLES 4 TO 10.

For each of these Examples there was provided a continuous laboratory reactor consisting of three reaction vessels, a mixing vessel, a collecting vessel for the crude product, an absorption vessel for the gaseous hydrogen chloride, a controlled magnetic valve for metering the mixture and a metering unit for the catalyst solution. The reaction vessels were in the form of heated 500 ml capacity four-necked flasks each equipped with a stirrer, reflux condenser, contact thermometer, product inlet and product outlet, through which a predetermined filling level was maintained. The first reactor stage additionally had an inlet for the catalyst solution. The mixing vessel was a heated four litre capacity flask equipped with a stirrer, reflux condenser, bottom outlet and contact thermometer, whilst the collecting vessel was a 4 litre capacity flask equipped with a reflux condenser and product inlet. Outlet pipes for HCI extended from the heads of all the reflux condensers to the absorption vessel.

The benzoic acid and o-PCX were introduced into the mixing vessel in the ratios indicated in Table 2 and were melted at 1400C. While the reactor was in operation, the reatants, premixed in solid form, could be continuously replenished as required. To start up the reactor, all the reactor stages were initially filled with fully reacted product (obtained for example from previous batches). After the prescribed reaction temperature had been reached, the mixture was introduced into the first stage of the reactor through the controllable magnetic valve, the catalyst solution being separately introduced at a constant rate. It was found necessary to heat the inlet pipe for the o-PCX/acid mixture. From the first stage, the product flowed into the second stage, from there into the third stage and from there into the collecting vessel from which it was removed as required. The conversion could be followed by titrimetric analysis of the hydrochloric acid formed in the absorption vessel. The reaction conditions were varied until the conversion amounted to approximately 100% of the theoretical under the conditions specified in Table 2. The yield of crude product then also amounted to approximately 100% of the theoretical. The yield of acid chloride and 3-Cp was determined by distilling a sample and subsequently separating the components by gas chromatography. In Examples 7 and 9, the two reaction products were quantitatively separated by fractional distillation and the yields determined in this way.

The pure components could be obtained from the acid chloride/3-Cp mixtures of Examples 4 to 10 by fractional distillation in vacuo through packed columns. The acid chlorides were obtained in a purity of from 99.0 to 99.8%, whilst the 3-Cp had an average purity of 97 to 99% (as determined by gas chromatography).

Thus in accordance with the process exemplified above, when reacted in pure form with o-PCX, even in the melt, the aromatic carboxylic acids in question only react very slowly with one another, if at all, in the absence of catalysts. Melt mixtures of the type in question advantageously remain stable for several hours.

These mixtures have a much lower melting point than the carboxylic acids and, for this reason, are technically easy to meter, for example with heated pumps. Further, these mixtures react quickly and completely following the addition of a catalyst of the Lewis acid type, in accordance with equation (1) in a reactor at temperatures above 100"C or above the melting point, the reaction being controllable by the rates at which the melt mixture and the catalyst are added.

TABLE 2 Continuous production of aromatic acid chlorides and 3-chlorophthalide

Carboxylic acid/o-PCX Catalyst Yield (% of mixture theoretical) 5) Ratio by % by weight of Through- weight Through Example Carboxylic acid to o- put in put Temp. Acid No. acid PCX g/hour Formula H2O ml/hour C chloride 3-Cp 4 o-toluic acid 1:1.077 2) 1010 ZnCl2 40 1.16 170 94 (GC) 71 1)(GC) 5 m-toluic acid 1:1.077 2) 758 (NH4)6Mo7O24.4H2O 20 4.86 170 91 (GC) 72 (GC) 6 p-toluic acid 3) 1:1.044 4) 796 ZnCl2 40 2.36 170 95 (GC) 80 (GC) 7 p-toluic acid 3) 1:1.044 4) 884 FeSO4.7H2O 20 8.1 170 96 (D) 66 (D) 8 benzoic acid 1:1.164 4) 799 ZnCl2 40 2.55 160 94 (GC) 94 (GC) 9 o-chlorobenzoic 1:0.898 4) 1059 FeCl3.6H2O 67 1.75 140 96 (D) 85 (D) acid 10 m-nitrobenzoic 1:0.842 4) 1400 " " 67 2.21 160 ~90 (GC) ~90 (GC) acid 1) GC: calculated from analysis (gas chromatography).

D: from distillation (quantitative separation of acid chloride and 3-Cp).

2) 95% o-PCX.

3) Addition of 0.5 g of caprolactam per kg of toluic acid 4) 98% o-PCX.

%) Distillation residues 4-6% of the theoretical.

Claims (33)

WHAT WE CLAIM IS:

1. A process for forming a product mixture comprising an aromatic carboxylic acid chloride and 3-chlorophthalide which comprises reacting o-pentachloroxylene with an aromatic carboxylic acid in a reaction vessel in the presence of a catalyst and removing the hydrogen chloride which is produced, the catalyst being introduced into the reaction vessel separately from the aromatic carboxylic acid and the o-pentachloroxylene.

2. A process according to claim 1 wherein the aromatic carboxylic acid and the o-pentachloroxylene are introduced into the reaction vessel as an admixture.

3. A process according to claim 2 wherein the admixture is introduced into the reaction vessel in melt form.

4. A process according to claim 3 wherein the melt includes a complex former to render ineffective trace amounts of catalyst incidentally present in the reactants.

5. A process according to claim 4 wherein the complex former is present in a concentration of from 20 to 200 mg/gmol of aromatic carboxylic acid.

6. A process according to claim 5 wherein the complex former is present in from 20 to 120 mg/g mol of aromatic carboxylic acid.

7. A process according to claim 4, 5 or 6 wherein the complex former is ethylene diamine tetra acetic acid or caprolactam.

8. A process according to any one of the preceding claims wherein the opentachloroxylene and the aromatic carboxylic acid are reacted in a molar ratio of 1:2.

9. A process according to any one of claims 1 to 7 wherein the opentachloroxylene is reacted in an excess of up to 10 mole %.

10. A process according to any one of the preceding claims wherein the aromatic carboxylic acid is a mono carboxylic acid.

11. A process according to any one of the preceding claims wherein the aromatic carboxylic acid is mono nuclear or bi nuclear.

12. A process according to claim 10 or 11 wherein the aromatic carboxylic acid is benzoic acid, o- m- or p-toluic acid, o- m- or p-chlorobenzoic acid, or mnitrobenzoic acid.

13. A process according to any one of the preceding claims wherein the catalyst is present in an amount of from 0.001 to 2% by weight (expressed as metal) based on the combined weight of the aromatic carboxylic acid and the opentachloroxylene.

14. A process according to claim 13 wherein the catalyst is present in from, 0.001 to 0.1% by weight (expressed as metal) based on the combined weight of the aromatic carboxylic acid and the o-pentachloro xylene.

15. A process according to any one of the preceding claims wherein the catalyst is a Lewis acid or a metal or metal compound which is converted into a Lewis acid under the conditions of the process.

16. A process according to claim 15 wherein the catalyst is zinc chloride or ferric chloride.

17. A process according to claim 15 wherein the catalyst is FeCl2.4H2O, FeSO4.7H2O, molybdenum pentachloride, bismuth (II) chloride, antimony (IV) chloride or ammonium heptamolybdate.

18. A process according to any one of the preceding claims wherein the catalyst is introduced into the reaction vessel in the form of an aqueous solution.

19. A process according to claim 18 wherein the solution contains from 3 to 60% by weight of metal chloride catalyst.

20. A process according to claim 19 wherein the solution contains from 10 to 45% by weight of metal chloride catalyst.

21. A process according to claim 18, 19 or 20 wherein the aqueous solution additionally includes hydrochloric acid.

22. A process according to any one of the preceding claims wherein the reaction is carried out at a temperature which is greater than the melting point of the reactants when in admixture.

23. A process according to any one of the preceding claims wherein the reaction is carried out at a temperature of up to 180eC.

24. A process according to claim 23 wherein the reaction is carried out at a temperature of from 120 to 180"C.

25. A process according to claim 24 wherein the reaction is carried out at a temperature of from 140 to 180"C.

26. A process according to any one of the preceding claims when carried out continuously.

27. A process according to claim 26 when appendant to any one of claims 3 to 25 wherein the reactants are introduced into the reaction vessel in melt form continuously or in portions.

28. A process according to claim 26 or 27 wherein the catalyst is introduced into the reaction vessel continuously or in portions.

29. A process according to any one of the preceding claims which includes the additional step of separating the product mixture into the aromatic acid chloride and 3-chlorophthalide.

30. A process according to claim 1 substantially as described in any one of Examples 2 to 10.

31. A process according to claim 1 substantially as hereinbefore described.

32. An aromatic acid chloride whenever produced by the process according to any one of the preceding claims.

33. 3-Chlorophthalide whenever produced by the process according to any one of claims 1 to 31.