The invention pertains to a method for converting an aromatic aldehyde or a mixture of aromatic aldehydes to an aromatic acyl halide or a mixture of aromatic acyl halides.

Methods for converting an aromatic aldehyde to aromatic acyl halide are known in the art. For instance in US 3,274,242 the preparation of aromatic acyl chlorides by vapor phase chlohnation of aromatic aldehydes was described at temperatures of 225 ⁰ C or higher. This method has the disadvantage that high temperatures must be used, which makes the process expensive and for terephthaldehyde only a low yield was obtained.

In BE 647037 a method was disclosed wherein neat chloro-substituted aromatic aldehydes were brought in contact with chlorine gas at moderate temperatures. This method only worked for chloro-substituted aromatic aldehydes and rendered yields around 80%. In US 3,894,923 the conversion to benzoyl chloride was described by chlorinating neat liquid benzaldehyde using UV light and/or peroxides as catalyst.

This method was only claimed for the conversion of benzaldehyde to benzoyl chloride.

In US 2,791 ,608 phthaloyl chloride was prepared from oxidation of xylene in the presence of an oxidation catalyst followed by chlorination of the oxidation product. Inert solvents may be used, including aromatic dicarbocylic acid chlorides. The reaction mixture may contain toluic acids, phthalic acids, methyl and carboxy benzaldehydes and methylbenzyl toluates. This preparation method has several disadvantages. Part of the product will be ring chlorinated due to the presence of oxidation catalysts. Accurate control of the equimolarity of methyl and acid groups in the mixture is essential. Any unbalance in the presence of these functional groups will lead to formation of significant amounts of side products that are difficult to remove from the reaction mixture. Furthermore, it is also required to remove water that is formed during oxidation to avoid formation of side products during the chlorination step. Finally, the complexity of the method, comprising oxidation, chlorination and fusion steps, is disadvantageous as well.

The best method for making terephthaloyldichloride from an aromatic aldehyde was disclosed in US 3,950,414 wherein the preparation of aromatic diacyl chlorides was described by chlorination of aromatic dialdehydes in an inert solvent, such as carbon tetrachloride or another fully halogenated aliphatic hydrocarbon. Terephthaldehyde was converted by reaction with chlorine in carbon tetrachloride

(CTC) as solvent in high yields at moderate temperatures. According to this method TPAL can be moderately dissolved in CTC at temperatures of about 35 ⁰ C, and can be chlorinated with high conversion and high selectivity by subjecting the solution or slurry to chlorine gas. The reaction rate, conversion and selectivity of the reaction are not influenced by the presence of light. The reaction goes perfectly well in complete darkness.

However, due to more stringent environmental requirements the use of carbon tetrachloride and other halogenated aliphatic hydrocarbons is not longer acceptable, and industrial processes using this solvent no longer can count on governmental license due to its detrimental effects on the ozone layer. Therefore it was required to search for a novel process having similar high yields and selectivity, whereas the reaction conditions in terms of reaction time and reaction temperature are equally favorable.

According to the present invention it has now been found that TPAL can be converted to TDC under similar reaction conditions giving similar yields and selectivity, without using toxic halogenated solvents. It was also found that the present method could advantageously be used for other aromatic aldehydes as well.

To this end the invention relates to a method for converting an aromatic aldehyde or a mixture of aromatic aldehydes to a reaction product which is an aromatic acyl halide or a mixture of aromatic acyl halides in a reaction medium which is free from xylene, comprising bringing the aromatic aldehyde or mixture of aromatic aldehydes in contact with a halogen to obtain the reaction product, wherein the reaction medium optionally comprises a co-solvent selected from the group consisting of any aromatic acyl halide and mixtures thereof.

This reaction for TPAL and chlorine is given by the reaction equation

O H O // // ^ Cl

C (TPAL) + 2 Cl ₂ - -C (TDC) + 2 HCI

H \ / ) ^C

O ^c \

Cl ⁷ O

The present method uses the reaction product as solvent, optionally in the presence of a co-solvent.

Herein below throughout the description of the invention the terms "compound", "reaction product", "aromatic aldehyde", and "aromatic acyl halide" have the meaning "compound or compounds", "reaction product or reaction products",

"aromatic aldehyde or mixture of aromatic aldehydes", and "aromatic acyl halide or mixture of aromatic acyl halides", respectively. Preferably, the same compound as the reaction product is selected as co- solvent. This makes isolation of the reaction product very simple and makes it possible that no other solvents have to be isolated and regenerated. In another embodiment another than the reaction product is selected as co-solvent to lower the reaction temperature. In this embodiment it is preferred to use as co-solvent a compound that has a different crystallization behavior than the reaction product, in order to facilitate isolation of the reaction product. It is possible to dispense from any co-solvent and to start with neat aromatic aldehyde. The reaction product thereby formed acts as solvent. In the reaction medium of aromatic aldehyde and the optional co-solvent, the amount of co-solvent is 0- 95% by weight, preferably 40-90% by weight. It is preferred that the co-solvent exclusively or virtually exclusively (i.e. about 98-100%) contains the reaction product, or is a mixture of reaction product and another aromatic acyl halide that can easily be separated by crystallization. If a co-solvent is used this may be added to the mixture prior to the reaction or during the reaction. For the conversion of TPAL with chlorine TDC is the reaction product, optionally in the presence of TDC and/or IDC as co-solvent. A suitable amount of TDC (as co- solvent) in the mixture is about 90% by weight with regard to TPAL. For the conversion of other aromatic aldehydes, preferably similar amounts of co-solvent are used. Although preferred to use the same compound as co-solvent, as the product that is obtained by converting the aromatic aldehyde, also other aromatic acyl halides, or mixtures of aromatic acyl halides may be used as co-solvent.

The method does not longer make use of xylenes, such as para-, meta- or ortho- xylene or other alkylarenes, and does not make use of heavy metal catalysts.

Although not necessary, it may be advantageous to enhance the reaction rate by irradiating the reaction medium with actinic light. Irradiation can be done during the whole reaction period or during part of the period that the aromatic aldehyde is brought in contact with the halogen.

The term "co-solvent" relates to the aromatic acyl halide that is present in the reaction medium before the reaction has started and/or that is added during the reaction, and which is not a reactant of the reaction. At the end of the reaction the mixture contains reaction product, which is the solvent, and optionally co- solvent. The reaction product may be the same or a different compound as the co-solvent, and as such acts as a solvent for the aromatic aldehyde reactant. However, the reaction product, whether or not the same compound as the co- solvent, is not included in the definition of the term "co-solvent".

The term "aromatic acyl halide" stands for the reaction product that is obtained from the aromatic aldehyde. The term "any aromatic acyl halide" stands for the reaction product or any other aromatic acyl halide. IDC (isophthaloyldichlohde) and TDC are the most common aromatic acyl halides that can be made as reaction product or used as co-solvent, but their corresponding bromides and iodides, and their substituted analogous compounds, including annealed compounds such as naphthaloyldichlohde can also be used. It was found that IPAL (isophthaldehyde) or TPAL can easily be dissolved in isophthaloyldichloride (IDC) or TDC, or in a mixture thereof and can be chlorinated at temperatures above the melting point of IDC (42-43 ⁰ C) or TDC

(79-81 ⁰ C), by subjecting the mixture to chlorine gas. If mixtures of solvents and co-solvents are used, eutectic mixtures are preferred. A eutectic mixture in the sense of this invention is a mixture at such proportions that the melting point is as low as possible, or at least is not more than 10 ⁰ C, preferably not more than 5 ⁰ C higher than the minimum melting point.

In general a co-solvent is selected wherein the aromatic aldehyde dissolves at low temperatures, preferably below 90 ⁰ C, most preferably at room temperature. The co-solvent may be any aromatic acyl chloride, such as TDC, IDC, benzoyl chloride, and the like, and mixtures thereof.

At moderate temperatures (90 ⁰ C) the reaction rate is low and a limited conversion is obtained (30-50%) at commercially acceptable reaction times, although at high selectivity. Side products other than the intermediate product 3- or 4-formylbenzoylchloride (3-FBC or 4-FBC) could not be detected. Irradiation with actinic light was found to enhance the reaction rate considerably, rendering

TPAL conversions of more than 90%. It was further found that halogen light gave the best results in terms of suppressing formation of CI-TDC (chloro- terephthaloyldichloride) as side product. IPAL can easily be converted to IDC in TDC as co-solvent. The mixture at the end of the reaction then contains IDC as the reaction product and TDC as the co- solvent. IDC can easily be separated from TDC by crystallization. In another embodiment IPAL can be converted to IDC in IDC as co-solvent, not requiring any further crystallization. If the lowest possible conversion temperatures are important, a eutectic mixture of IDC and TDC can advantageously be used, and the reaction product can be separated from TDC by crystallization. A practical method for making TDC is dissolving TPAL in a eutectic mixture of IDC and TDC, adding chlorine, and after finishing the conversion of TPAL to TDC separating TDC from the co-solvent IDC by crystallization.

Suitable amounts of aromatic aldehyde with regard to the amount of reaction medium at the start of the reaction are 5 to 100 wt%, preferably 10 to 60 wt%, based on the reaction medium weight. Amounts lower than 10 wt% are economically unattractive and amounts higher than 60 wt% require high reaction temperatures.

Obviously, the present method for making TDC from TPAL has major advantages over the known route, because it is a simple one-step process and the chlorine demand and hydrochloric acid formation are 33% less than the method of US 2,791 ,608.

The invention is illustrated by the following non-limitative examples

General

A 1 liter Schott bottle was used as reaction vessel, equipped with a temperature sensor and a gas inlet sparger. Mixing was achieved with a magnetic stirrer. The reactor, fixed to a metal frame, was hung in a pan filled with hot water which was used to establish the desired reaction temperature.

Chlorine was fed to the reactor vessel from a small sized Cb cylinder. The gas flow was controlled by a beforehand calibrated mass flow controller and led through a filter to remove moisture. Before and after CI2 dosing, the reactor content was purged with nitrogen gas. The reaction mixture was subjected to a mixture of N ₂ (g) and Cl ₂ (g). The off-gas from the experiments is a mixture of N ₂ , Cl ₂ and HCI, which was led through an off-gas 'street' of three absorption bottles in series filled with water/caustic soda (bottle 1 ), water (bottle 2) and water/caustic soda (bottle 3). The off-gas was led over the content of bottles 1 and 2 and led through the content of bottle 3. Cl ₂ will preferably absorb in caustic soda and HCI in both caustic soda and water.

By measuring the weights of the absorption bottles before and after the experiment, one obtains an indication of the total amounts of Cl ₂ and HCI in the off-gas. A distinction between HCI and Cl ₂ can be made when bottle 1 is filled with water.

For the irradiation experiments, either a 20 W or 50 W halogen light source was used or a 150 W high-pressure mercury light source (emitting predominantly in the UV part of the light spectrum).

IDC (isophthaloyldichloride), IPAL and TPAL were purchased from Sigma-Aldrich (purity > 99%); Cl ₂ was obtained from a small sized cylinder (12.5 Kg) with purity 2.8 (equivalent to > 99.8 vol%). TDC was obtained from the TDC plant of Teijin Aramid, Delfzijl, the Netherlands

Example 1

14.9 gram TPAL (111 mmole) were dissolved in 600 mL of TDC. About two times the stoichiometrically required amount of chlorine was bubbled through the mixture while the mixture was kept at a constant temperature of 90 ⁰ C. During the first 53 minutes, 346 mmole of Cl ₂ were added to the mixture (at a constant rate of 6.5 mmole/min) followed by an extra 66 mmole of Cl ₂ in 2 hours and 17 minutes (0.5 mmole/min).

Gas chromatographic analysis of a sample of the final reaction mixture showed 50% conversion of TPAL while obtaining a significant amount of 4-formyl benzoyl - chloride (4-FBC). Example 2

Experiment 1 was continued while irradiating the reaction mixture with a high- pressure mercury UV light source (150 W), positioned outside the reactor. During 56 minutes 362 mmole of Cb were dosed (at a constant rate of 6.5 mmole/min) followed by another 66.5 mmole of CI2 in 2 hours and 18 minutes

(0.5 mmole/min).

TPAL was almost fully converted into TDC while a small amount of ring chlorinated TDC was formed as well.

Example 3

12.6 g of TPAL (94 mmole) were dissolved in 560 mL of TDC. About two times the stoichiometrically required amount of chlorine was bubbled through the mixture at a constant temperature of 90 ⁰ C. The mixture was irradiated by a 50 W halogen light source. During the first 59 minutes, 382 mmole of CI2 were added to the mixture (at a constant rate of 6.5 mmole/min) followed by an extra 71 mmole of CI2 in 2 hours and 28 minutes (0.5 mmole/min). Gas chromatographic analysis of a sample of the final reaction mixture shows almost full conversion of TPAL while obtaining a much better selectivity as compared to experiment 2.

Example 4

10 gram TPAL and 10 gram IPAL (isophthalaldehyde) (both 74.5 mmole) were dissolved in 500 mL of TDC. The mixture was irradiated by a 20 W halogen light source and kept at 90 ⁰ C during the experiment. During the first 50 minutes, 323.5 mmole of CI2 were added to the mixture (at a constant rate of 6.5 mmole/min) followed by an extra 79.5 mmole of CI2 in 2 hours and 45 minutes

(0.5 mmole/min).

TPAL and IPAL were fully and high selectively converted into TDC and IDC (isophthaloyl dichlohde) respectively.

Example 5 10 g of TPAL and 10 g of IPAL (both 74.5 mmole) were dissolved in a 500 mL of TDC/IDC mixture with a TDC content of 30 mass%. The mixture was irradiated by a 20 W halogen light source and kept at 50 - 55 ⁰ C during the experiment. During the first 45 minutes, 291 mmole of Cb were added to the mixture (at a constant rate of 6.5 mmole/min) followed by an extra 75 mmole of CI2 in 2 hours and 35 minutes (0.5 mmole/min).

TPAL and IPAL were fully and high selectively converted into TDC and IDC respectively. Already after the first 45 minutes, TPAL and IPAL were vanished completely, though peaks could be identified representing the half products 4- FBC and 3-FBC.

Example 6

10.29 g of TPAL (76.7 mmole) and 5.42 g of IPAL (40.4 mmole) were dissolved in a 500 mL of TDC/IDC mixture with a TDC content of 30 mass%. The mixture was not irradiated and kept at 45 - 50 ⁰ C during the experiment. During the first

45 minutes, 291 mmole of CI2 were added to the mixture (at a constant rate of

6.5 mmole/min) followed by an extra 128 mmole of CI2 in 3 hours and 45 minutes

(0.56 mmole/min).

The final product showed a full and highly selective conversion of TPAL and IPAL in TDC and IDC respectively.

Example 7

9.9 g of TPAL (73.8 mmole) and 3.32 g of IPAL (both 24.8 mmole) were dissolved in a 500 mL of TDC/IDC mixture with a TDC content of 30 mass%. The mixture was irradiated by a 20 W halogen light source and kept at 43 ⁰ C during the experiment. During 30 minutes, 194 mmole of CI2 were added to the mixture (at a constant rate of 6.5 mmole/min).

The final product showed a full and highly selective conversion of TPAL and IPAL in TDC and IDC respectively. Example 8

189 g of TPAL (1409 mmole) were dissolved in a 355 ml_ of TDC/IDC mixture with a TDC content of 30 mass%. The mixture was irradiated by a 20 W halogen light source and kept at 75 ⁰ C during the experiment. During 3 hours and 6 minutes, 1522 mmole of Cb were added to the mixture (at a constant rate of 8.2 mmole/min). TPAL was only partially converted into 4-FBC and TDC.

Example 9 10.32 g of TPAL (76.9 mmole) were dissolved in 500 mL of benzoylchloride.

The mixture was irradiated by a 20 W halogen light source and kept at room temperature (22 ⁰ C) during the experiment. During 30 minutes, 194 mmole of CI2 were added to the mixture (at a constant rate of 6.5 mmole/min).

The final product showed a full and highly selective conversion of TPAL in TDC.

Example 10

34.4 g of TPAL (257 mmole) and 46.6 g of IPAL (348 mmole) were molten.

The viscous mixture (without co-solvent) was irradiated by a 20 W halogen light source and kept at 90 ⁰ C during the experiment. During 4 hours, 1440 mmole of CI2 were added to the mixture (at a constant rate of 6 mmole/min).

Due to the high viscosity the conversion was only 43% and the selectivity was

44%.