Procedure for the Photochlorination of Alkyl-Aromatic Compounds

~™ llll III II II II I II I II III II 1 1 (19) J European Patent Office

Office europeen des brevets (11) EP 0 612 707 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int. CI.6: C07C 17/14, C07C 22/04, of the grant of the patent: C07C 25/02 18.06.1997 Bulletin 1997/25

(21) Application number: 94200350.0

(22) Date of filing: 16.02.1994

(54) Procedure for the photochlorination of alkyl-aromatic compounds Verfahren zur Photochlorierung von alkylaromatischen Verbindungen Procede pour la photochloration de composes alkylaromatiques

(84) Designated Contracting States: • Contardi, Giuseppe AT BE CH DE DK ES FR GB GR IE IT LI LU MC NL 1-20161 Milan (IT) PTSE • Messori, Vittorio 1-20129 Milan (IT) (30) Priority: 24.02.1993 IT MI930346 (74) Representative: Fusina, Gerolamo et al (43) Date of publication of application: Ing. Barzanb & Zanardo Milano S.p.A, 31.08.1994 Bulletin 1994/35 Via Borgonuovo, 10 20121 Milano (IT) (73) Proprietor: ENICHEM SYNTHESIS S.p.A. 1-90139 Palermo (IT) (56) References cited: DE-A- 3 320 020 DE-B- 2 530 094 (72) Inventors: GB-A- 928 693 • Ribaldo, Carlo 1-20131 Milan (IT)

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Csl Note: Within nine months from the publication of the mention of the grant of the European patent, give CO any person may notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in ^ a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. Q. 99(1) European Patent Convention).

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Description does not form an explosive mixture with the organic compound to be chlorinated. Other problems related to The present invention relates to a procedure for the photochlorination methods of the known art consist in selective photochlorination in the side chain of alkyl-aro- the difficulties of thermal exchange, in that the heat of matic compounds. 5 the reaction is only exchanged through the reactor It is known that the chlorination in the side chain of jacket; the difficulty of regulating the temperature and alkyl-aromatic compounds is generally favored by rais- the ratio between chlorine and aromatic compound during the reaction temperature or, more commonly, by ing the reaction; the dirtying of the lamp immersed in the operating in the presence of free radical initiators such reaction mixture; the limited operating pressures due to as light radiation or peroxides. 10 the glass seal of the lamp-holder; and the difficulty in Particularly known in the art is the chlorination in providing a system which completely satisfies security the side chain of toluene, and its chlorine-substituted regulations. derivatives in the nucleus, to benzyl chloride, benzal The purpose of the present invention is to over- chloride and benzotrichloride. These compounds are come the disadvantages of the known art related to pro- useful intermediates which can be transformed into 15 cedures for the photochemical chlorination of alkyl- other chemical products, especially by reactions involv- aromatic compounds. ing chlorine substituents in the side chain. In this way In particular it has been found, in accordance with benzyl chloride can be used in the production of benzyl the present invention, that it is possible to photochlorin- butyl phthalate, a plasticizer for vinylic resins, benzal ate alkyl-aromatic compounds with practically total con- chloride can be hydrolyzed to benzaldehyde and benzo- 20 versions of the reagents and with a high selectivity in trichloride can be transformed into benzoyl chloride. In the useful reaction product, operating with a batch circu- addition also some chlorine-substituted derivatives in lation system with the progressive chlorination of the the nucleus of the above compounds have a commer- alkyl-aromatic compound. It has also been found that cial value; for example p-chlorobenzotrichloride is an this photochlorination system is extremely safe and suit- important intermediate in the production of dinitroaniline 25 able for overcoming the disadvantages and limitations weed-killers. of the known art mentioned above. The basic problem related to procedures for the In accordance with this the present invention thermal and photochemical chlorination of alkyl-aro- relates to a procedure for the selective photochlorina- matic compounds consists in the limited selectivity of tion in the side chain of an alkyl-aromatic compound by the desired reaction product. For example in the produc- 30 contact with chlorine under the action of light radiation, tion of benzyl chloride there is normally only a partial characterized in that: conversion of the toluene, in order to minimize the formation of products with a degree of chlorination which is said alkyl-aromatic compound is continuously higher than that required. The same happens in the pro- removed from a container, mixed with chlorine in a duction of benzal chloride. Finally in the preparation of 35 static mixer, to obtain a homogeneous mixture, con- benzotrichloride, the product with a higher degree of taining from 0,02 to 2 parts by weight of chlorine for chlorination in the side chain, the selectivity of the reac- every 100 parts by weight of the alkyl-aromatic tion is reduced by the presence of by-products. All of compound, mixture which is fed to the foot of a this involves difficult operations for the separation and tubular-shaped reactor, without any mechanical purification of the useful products and for recycling the 40 stirring equipment, at least partially composed of unaltered reagents. material which is transparent at light radiation and With respect to the known photochlorination meth- externally equipped with a supply of light radiation, ods of organic compounds, either batch or continuous, said reactor being maintained under photochlorina- basically two types of reactors are used and more spe- tion conditions, to almost completely use up the cifically: a vessel reactor with one or more immersed 45 chlorine, and recover a mixture of the chlorinated lamps and a film reactor with an internal lamp. In the tra- alkyl-aromatic compound and hydrochloric acid by- ditional vessel reactors the stirring which is necessary product at the head of the reactor, to allow the chlorine to flow near the lamps and the said reaction mixture being continuously recycled organic compound to be effectively exchanged, is pro- to the container where the gaseous hydrochloric vided by bubbling the chlorine itself and hydrochloric so acid is separated from the chlorinated alkyl-aro- acid which is developed as a reaction by-product. This matic compound, causes a limited feeding flexibility of the chlorine which the alkyl-aromatic compound being partially chlo- can be partially remedied by connecting several reac- rinated at each recycling in the reactor, the number tors to each other in series, mainly to use up as much of recycles depending on the degree of chlorination chlorine as possible discharged from the photochlorina- 55 required, and further characterized in that in said tion. In the film reactor, this problem does not exist, but photochlorination reactor the linear rate of the reac- as the process is carried out in the presence of a radi- tion mixture is from 0,4 to 4 m/s, with a temperature ated gaseous phase, the use of these reactors in photo- at the inlet ranging from 0 to 150°C and maintaining chlorination is restricted to cases where the chlorine a difference of temperature between the inlet and

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outlet at values of 1 to 35°C. namic conditions in the reactor, regardless of the quantity of chlorine fed; The alkyl-aromatic compounds which can be sub- the source of radiation external to the reactor and jected to the photochlorination process of the present the fact that the chlorine is dissolved or at least uni- invention are preferably toluene, monochlorotoluene s formly dispersed in the liquid phase enable the isomers, dichlorotoluene isomers trichlorotoluene, operation to be carried out without hot points, thus xylene isomers and mesitylene. The photochlorination avoiding the formation of explosive mixtures which products are those which are mono or polychlorinated are typical in the gaseous phase; in the side chain. For example in the case of toluene, the possibility of independently regulating the feed- benzyl chloride, benzal chloride or benzotrichloride can 10 ing of the chlorine and the reaction temperature, be obtained, depending on the reaction conditions. makes it possible to operate under excellent condi- According to an embodiment of the present inven- tions in relation to the depletion of the chlorine and tion, the alkyl-aromatic compound is removed from a selectivity of the reaction product desired, with a container and fed to the photochlorination reactor by a practically complete conversion of the alkyl-aro- suitable pump, after mixing with chlorine and homoge- is matic compound subjected to photochlorination; nizing the mixture by passing it through a static mixer. In there is no limitation relating to the thermal this phase of the procedure the ratio between chlorine exchange as the temperature of the reagent mix- and the alkyl-aromatic compound is such that the chlo- ture can be regulated to the most suitable value for rine, or a substantial quantity of this, is dissolved in the the particular reaction, with the consequent possi- liquid phase at the inlet of the photochlorination reactor. 20 bility of exploiting the fast kinetics to the utmost; Suitable concentrations of chlorine generally vary from there are no problems of the radiation lamps being 0.02 to 2 and preferably from 0.1 to 1 parts by weight for dirtied thus facilitating maintenance operations; every 100 parts by weight of the alkyl-aromatic com- finally there are no limitations deriving from the pound. operating pressures. The photochlorination reactor used in the present 25 invention is generally a long, tubular shaped reactor, for Figure 1 of the enclosed drawing schematically example with a ratio between length and diameter of shows suitable equipment for the embodiment of the about 50/1 , without any stirring devices and composed procedure of the present invention. In particular this fig- of a material which is transparent at light radiation or ure shows with (1) a container of the alkyl-aromatic having one or more windows which are permeable to 30 compound subjected to chlorination and with (2) the said radiation. At least one source of light radiation is photochemical reactor, having a long tubular shape, placed outside the reactor in a suitable position, and the made of material which is transparent to light radiation, light is either a visible or an UV radiation, for example at least in the part next to the source (3) of light radia- with a wave-length of 1 50-600 nm and preferably 300- tion. The alkyl-aromatic compound subjected to chlorin- 400 nm. Sources of radiation normally used are mer- 35 ation is continuously removed from the container (1) by cury arc lamps (with high, medium or low pressure), or means of line (6) and fed, through the pump (7) to the xenon lamps, which emit in a UVTvisible range. These bottom of the reactor (2). The chlorine is continuously devices are available on the market. fed through line (8) to the bottom of the reactor. The In the photochlorination reactor the linear rate of the alkyl-aromatic compound and the chlorine are mixed mixture varies from 0.4 to 4 meters/second and prefera- 40 and homogenized in the static mixer (4) and the homo- bly from about 0.5-2 meters/second, with an inlet tem- geneous mixture is subjected to photochlorination con- perature ranging from 0 to 150°C and maintaining a ditions in the reactor (2). The reaction mixture difference of temperature between the outlet and inlet at composed of the chlorinated alkyl-aromatic compound values of 1 to 35°C. The inlet temperature of the mixture and hydrochloric acid is removed from the head of the is conveniently regulated by means of a heat 45 reactor (2) and sent to the container (1) by line (9). The exchanger. hydrochloric acid is discharged from the reactor (1) Operating under these conditions the chlorine is through line (10), after passing through the exchanger completely or almost completely used up and the reac- (11). In the form of embodiment shown in figure 1, the tion mixture is sent to the container where the hydro- exothermal effect of the reaction is controlled by contin- chloric acid, a reaction by-product, is separated from so uously recirculating the contents of the container (1) the liquid phase. through the exchanger (5). This exothermicity however The alkyl-aromatic compound is then subjected to can be controlled by the exchangers situated on line (6) progressive chlorination, the number of recycles and/or on line (9), instead of or in addition to exchanger depending on the desired degree of chlorination. (5). The procedure of the present invention has the fol- ss A single photochlorination reactor (2) can be used lowing effects and advantages: or two or more reactors, placed in series or parallel to each other, thus improving the productivity of the sys- the means of feeding the reagent mixture to the tem. photochlorination reactor ensure excellent fluodi-

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EXAMPLE 1 (2) with a rate of 200 liters/hour, feeding 1 ,058 g of chlorine gradually and uniformly. The temperature at the Preparation of p-chlorobenzotrichloride from p- inlet of the reactor is 30°C and at the outlet 32°C, and chlorotoluene. 3,595 g of a chlorinated product are obtained having the With reference to figure 1 , 3,400 g of p-chlorotolu- following analysis: ene treated to eliminate metallic and inorganic impuri- ties are charged into container (1). The p-chlorotoluene - 2,4-dichlorobenzylchloride absent is removed from container (1) and fed, by pump (7) to - 2,4-dichlorobenzalchloride 95% w/w the bottom of the reactor (2), with a rate of 200 lit- - 2,4-dichlorobenzotrichloride 5% w/w ers/hour. Chlorine is also fed through line (8) to the bot- 10 tom of the reactor, with an average rate of 1,432.5 The reaction is continued for a further 2.5 hours cir- g/hour. The liquid and gaseous reagents are homoge- culating the liquid between the container (1) and reactor nized in the static mixer (4) and reacted in the reactor (2) with a rate of 300 liters/hour, feeding 1 ,050 g of chlo- (2). This reactor has a long cylindrical shape (length rine gradually and uniformly. The temperature at the 300 mm, diameter 14 mm) and is made of nickel, except 15 inlet of the reactor is 1 20°C and at the outlet 1 21 °C, and for the areas near the lamp (3), which are made of 4,105 g of a chlorinated product are obtained having the DURANSO material which is transparent with radiation. following analysis: Lamp (3) is a commercial Heraeus TQ 150 lamp, with a power of 150 Watt, which emits radiations having a - 2,4-dichlorobenzalchloride 0.2% w/w wave-length within the range of 240-579 nm, and is sit- 20 - 2,4-dichlorobenzotrichloride 99.8% w/w uated at a distance of about 1 0 cm from the transparent - chlorinated products in the nucleus absent. wall of the reactor. The reaction products are sent, by line (9) from the reactor (2) to the container (1) where Claims the liquid product is separated from the gaseous hydrochloric acid. The liquid flow is fed to the bottom of the 25 1 . Procedure for the selective photochlorination in the reactor at a temperature of between 40°C and 70°C and side chain of an alkyl-aromatic compound by con- the flow leaving the reactor is at a temperature of tact with chlorine under the action of light radiation, between 50 and 75°C. characterized in that: The operation is carried out for a period of 4 hours feeding a total of 5,730 g of chlorine and 6,180 g of p- 30 said alkyl-aromatic compound is continuously chlorobenzotrichloride are obtained with a 100% con- removed from a container, mixed with chlorine version of the p-chlorotoluene and a yield of p-chlorotol- in a static mixer, to obtain a homogeneous mix- uene which is higher than 99.8%. The analysis of the ture, containing from 0,02 to 2 parts by weight reaction product is as follows: of chlorine for every 1 00 parts by weight of the 35 alkyl-aromatic compound, mixture which is fed - p-chlorotoluene absent to the bottom of a long tubular-shaped reactor, - p-chlorobenzotrichloride 99.9% w/w without any mechanical stirring equipment, at - p-chlorobenzalchloride 0.1 %w/w least partially composed of material which is - products chlorinated in the nucleus absent transparent to light radiation and externally 40 equipped with a supply of light radiation, said EXAMPLE 2 reactor being maintained under photochlorination conditions, to almost completely use up the The same procedure is carried out as for example chlorine, and recover a mixture of the chlorin- 1 , charging 2,500 g of purified 2,4-dichlorotoluene into ated alkyl-aromatic compound and hydrochlo- the container (1). During the first hour of the reaction, 45 ric acid by-product at the head of the reactor, the liquid is circulated between the container (1) and said reaction mixture being continuously recy- reactor (2) with a rate of 200 liters/hour, whereas 1,119 cled to the container where the gaseous hydro- g of chlorine are gradually and uniformly fed through chloric acid is separated from the chlorinated line (8). The temperature at the inlet of the reactor is alkyl-aromatic compound, 60°C and at the outlet 65°C, and 3,082 g of a chlorin- 50 the alkyl-aromatic compound being partially ated product are obtained having the following analysis: chlorinated at each recycling in the reactor, the number of recycles depending on the degree of ■ 2,4-dichlorotoluene < 0.1% w/w chlorination desired, and further characterized ■ 2,4-dichlorobenzylchloride 90% w/w in that in said photochlorination reactor the lin- ■ 2,4-dichlorobenzalchloride 10% w/w 55 ear rate of the reaction mixture is from 0.4 to 4 ■ 2,4-dichlorobenzotrichloride absent. meters/second, with a temperature at the inlet ranging from 0 to 150°C and maintaining a dif- The reaction is continued for a further 2.5 hours cir- ference of temperature between the inlet and culating the liquid between the container (1) and reactor outlet at values of 1 to 35°C.

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2. Procedure according to claim 1, characterized in Reaktionsmischung von 0,4 bis 4 m/sec that said alkyl-aromatic compound is selected from betragt, bei einer Temperatur am EinlaB im toluene, monochlorotoluene isomers, dichlorotolu- Bereich von 0 bis 150°C und daB ein Unter- ene isomers, xylene isomers and mesitylene. schied der Temperatur zwischen EinlaB und 5 AuslaB mit Werten von 1 bis 35°C aufrechter- 3. Procedure according to claim 1, characterized in halten wird. that a mixture containing from 0.1 to 1 parts by weight of chlorine for every 1 00 parts by weight of 2. Verfahren nach Anspruch 1 , dadurch gekennzeich- the alkyl-aromatic compound is fed to the chlorina- net, daB die alkyl-aromatische Verbindung ausge- tion reactor. 10 wahlt ist aus ToluoP Monochlortoluol-lsomeren, Dichlortoluol-lsomeren, Xylolisomeren und Mesity- 4. Procedure according to claim 1, characterized in len. that in said photochlorination reactor the linear rate of the reaction mixture is from 0.5-2 meters/second. 3. Verfahren nach Anspruch 1 , dadurch gekennzeich- 15 net, daB eine Mischung dem Chlorierungsreaktor 5. Procedure according to claim 1, characterized in zugefiihrt wird, welche 0,1 bis 1 Gewichtsteil Chlor that several photochlorination reactors are used, pro jede 100 Gewichtsteile alkyl-aromatischer Ver- arranged in series or parallel to each other. bindung enthalt.

Patentanspruche 20 4. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, daB in dem Photochlorierungsreaktor die 1. Verfahren zur selektiven Chlorierung in der Seiten- lineare Geschwindigkeit der Reaktionsmischung kette einer alkyl-aromatischen Verbindung mittels von 0,5 bis 2 m/sec betragt. Kontakt mit Chlor unter der Einwirkung von Licht- strahlung, dadurch gekennzeichnet, daB: 25 5. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, daB verschiedene Photochlorierungsreaktoren die alkyl-aromatische Verbindung kontinuier- verwendet werden, welche in Reihe oder parallel lich aus einem Behalter entnommen wird, mit zueinander angeordnet sind. Chlor in einem statischen Mischer gemischt wird, urn eine homogene Mischung zu erhal- 30 Revendications ten, welche von 0,02 bis 2 Gewichtsteile Chlor fur jede 100 Gewichtsteile der alkyl-aromati- 1. Procede de photochloration selective dans la schen Verbindung enthalt, wobei die Mischung chame laterale d'un compose alkylaromatique par dem Boden eines langen rohrenformigen contact avec le chlore sous I'effet de la lumiere Reaktors ohne mechanische Ruhrmittel zuge- 35 caracterise en ce que : fuhrt wird, welcher mindestens teilweise aus Material zusammengesetzt ist, welches fur ledit compose alkylaromatique est elimine en Lichtstrahlung transparent ist und welcher continu d'un conteneur, melange au chlore auBen mit einer Quelle fur Lichtstrahlung aus- dans un melangeur statique en vue d'obtenir geriistet ist, wobei der Reaktor auf Photochlo- 40 un melange homogene contenant de 0,02 a 2 rierungsbedingungen gehalten wird, urn das parties en poids de chlore pour 100 parties en Chlor fast ganzlich zu verbrauchen, und wobei poids du compose alkylaromatique, on ali- eine Mischung der chlorierten alkyl-aromati- mente en ledit melange le fond d'un reacteur schen Verbindung und Chlorwasserstoffsaure tubulaire fagonne en longueur, ne comportant als Nebenprodukt am Kopf des Reaktors 45 pas de dispositif mecanique d'agitation, consti- gewonnen wird, tue, au moins en partie, d'une matiere transparent^ au rayonnement lumineux et equipe a die Reaktionsmischung kontinuierlich zu dem I'exterieur d'une alimentation en rayonnement Behalter zuruckgefiihrt wird, wo gasformige lumineux, ledit reacteur etant maintenu sous Chlorwasserstoffsaure von der chlorierten 50 conditions de photochloration jusqu'a une con- alkyl-aromatischen Verbindung getrennt wird, sommation presque complete du chlore, et on recupere un melange du compose alkylaroma- die alkyl-aromatische Verbindung bei jedem tique chlore et du sous-produit I'acide chlorhy- Zuruckfiihren in den Reaktor teilweise chloriert drique a la tete du reacteur, wird, wobei die Zahl der Zyklen von dem Grad 55 ledit melange reactionnel etant recycle en con- der gewiinschten Chlorierung abhangt, tinu au conteneur ou I'acide chlorhydrique und daB das Verfahren ferner dadurch gekenn- gazeux est separe du compose alkylaromati- zeichnet ist, daB in dem Photochlorierungsre- que chlore, aktor die lineare Geschwindigkeit der le compose alkylaromatique etant chlore par-

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tiellement a chaque recyclage au reacteur, le nombre d'operations de recyclage depend du degre de chloration voulu, et, en plus, caracterise en ce que, dans ledit reacteur de photochloration, le taux lineaire du melange 5 reactionnel etant de 0,4 a 4 m/s, avec une temperature a I'entree comprise entre 0 et 1 50°C et en maintenant une difference de temperature entre I'entree et la sortie d'une valeur comprise entre 1 et 35°C. ro

2. Procede selon la revendication 1 , caracterise en ce que ledit compose alkylaromatique est pris dans le groupe comportant le toluene, les isomeres de monochlorotoluene, les isomeres de dichloroto- is luene, les isomeres de xylene et le mesitylene.

3. Procede selon la revendication 1 , caracterise en ce qu'on alimente le reacteur de photochloration en un melange contenant de 0,1 a 1 partie en poids de 20 chlore pour 100 parties en poids de compose alkylaromatique.

4. Procede selon la revendication 1 , caracterise en ce que dans ledit reacteur de photochloration, le taux 25 lineaire du melange reactionnel est de 0,5 a 2 m/s.

5. Procede selon la revendication 1 , caracterise en ce qu'on utilise plusieurs reacteurs de photochloration disposes en serie ou en parallele. 30

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