GB1586787A - Process for the preparation of ar-chlormethyl vinyl aromatic compounds - Google Patents

Description

(54) PROCESS FOR THE PREPARATION OF AR-CHLORMETHYL VINYL AROMATIC COMPOUNDS (71) We, EUTECO S.P.A., an Italian Joint Stock Company, of 11, via Galiani, Milan, Italy, 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:- The present invention relates to a process for the preparation of ar-chloromethyl vinyl aromatic compounds and of vinylbenzyl chloride in particular.

Ar-chloromethyl vinyl aromatic compounds form valuable intermediates, useful for the manufacture of ion-exchange resins. For this purpose substitution of the chlorine atoms by functional groups such as amino groups is carried out and the products of such substitution are polymerized.

Alternatively, the said vinyl aromatic compounds are polymerized and the resulting polymer is treated to substitute the chlorine atoms by the said functional groups.

Such a method of operation offers considerable advantages with respect to those known processes for the preparation of ion-exchange resins, which include a chloromethylation treatment. Such treatment is in fact highly risky because of the exceptionally toxic characteristics of some reaction intermediates such as a- chloromethyl methyl ether and a,a'- dichloromethyl ether.

The said ar-chloromethyl vinyl aromatic compounds are also useful as cross-linking agents in the polymerization of vinyl monomers, as well as in the papermaking, in plastic coatings, in flocculants for water treatment and in the textile industry as dye acceptors and antistatic agents.

Several processes are known for the preparation of the said ar-chloromethyl vinyl aromatic compounds and of vinylbenzyl chloride in particular.

Thus, according to U.S. Patent 2,780,604 ethyl-toluene is chlorinated to give achloroethylbenzyl chloride and the latter is dehydrochlorinated to produce vinylbenzyl chloride.

The disadvantages of such a method of procedure consist essentially in the formation of relatively high quantities of byproducts, some of which are difficult to separate from vinylbenzyl chloride.

According to another known process ethylbenzene is submitted to chloromethylation to form the corresponding ortho-and paraethylchlorobenzyl derivatives. These latter are brominated in the ethyl group and finally dehydrobromination is carried out with consequent formation of vinylbenzyl chloride.

Such a method of operation has disadvantages above all due to the chloromethylation treatment. Moreover, the use of several reaction stages renders the process complex and onerous.

According to U.S. Patent 2,981,758 vinylbenzyl chloride is obtained in good yield and with little formation of byproducts by direct chlorination of vinyltoluene at high temperature.

Vinyltoluene is obtained by dehydrogenation of ethyltoluene according to a procedure analogous to that used in the preparation of styrene from ethylbenzene.

Ethyltoluene (mixture of orto, meta and para isomers) is obtained in its turn by alkylation of toluene with ethylene, analogously to the production of ethylbenzene from benzene.

The process of the U.S. Patent under discussion is not completely satisfactory. In fact, the separation of the vinyltoluenes from the ethyltoluenes in the mixture resulting from the dehydrogenation reaction is burdensome and difficult. During the distillation polymerization phenomena in fact occur very easily.

The disadvantages of the prior art are overcome or at least largely reduced by means of the process of the present invention.

Thus, the invention provides a process ror preparing an ar-chloromethyl vinyl aromatic compound of the formula:

wherein the H2Cl substituent is in para or meta position with respect to the H=CH2 substituent and R is a substituent chosen from hydrogen, halogen, cyano, phenyl, tertiary butyl, hydroxy, carboxy and OR1 groups wherein Rl is an aryl group, which comprises preheating to a temperature of at least 400"C a gaseous mixture comprising a halogenated aromatic compound and a gas which is inert under the reaction conditions in a volumetric ratio not exceeding 1:5, said halogenated aromatic compound corresponding to the formula

wherein the -CH3 substituent is in para or meta position with respect to the X-CH-CH3 I substituent, X is a chlorine, bromine or iodine atom and R has the same meaning as in formula (I), contacting gaseous chlorine and the thus preheated mixture in a molar ratio between said chlorine and said halogenated aromatic compound not exceeding 1:1, at a temperature of at least 400"C and for a period of at least 0.1 second, and recovering the ar-chloromethyl vinyl compound from the reaction products.

The substituent R of formulae (I) and (II) is preferably hydrogen.

The halogenated aromatic compound (II) is preferably a-chloroethyltoluene.

a-chloroethyltoluene is conveniently obtained by hydrochlorination of vinyltoluene. The latter is obtained by dehydrogenation of ethyltoluene.

Therefore, ethyltoluene is first prepared by alkylation of toluene with ethylene, in the presence of a Friedel-Crafts catalyst.

The mixture of ortho, meta and para isomers thus obtained is submitted to rectification to remove the ortho isomer.

This ortho isomer in fact gives rise to the production of indenes in the subsequent dehydrogenation reaction.

The ethyltoluene isomers are therefore obtained by a process similar to that of ethylation of benzene with ethylene to produce ethylbenzene.

The mixture of meta and para ethyltoluene isomers is dehydrogenated at a temperature of 600700 C and in the presence of water vapour, in similar conditions to those used for the production of styrene from ethylbenzene. The resulting dehydrogenation product typically contains about 40% vinyltoluene and about 600/, of unaltered ethyltoluene. This mixture is generally directly sent to the hydrochlorination treatment of the vinyltoluenes.

Said hydrochlorination is conveniently carried out by contacting hydrogen chloride with the mixture containing the vinyltoluenes, at a temperature of from -1000 to 0 C and preferably from -30" to -10"C, possibly in the presence of a catalyst such as zinc, antimony or tin chloride.

The a-chloroethyltoluenes are then separated from the ethyltoluenes in the reaction mixture by rectification, operating at subatmospheric pressure in order to avoid possible dehydrochlorination phenomena. The ethyltoluenes are conveniently recycled to the dehydrogenation stage.

By operating in accordance with the above procedure the problems relating to the separation of the reaction products are more easily resolved.

In particular, those losses of vinyltoluene due to polymerization during distillation with resultant fouling of the apparatus which are experienced in the processes of the prior art, are avoided.

The a-chloro ethyltoluenes in fact have boiling temperatures very different from those of the ethyltoluenes and can thus be easily separated from the latter.

Moreover, the hydrochlorination reaction is almost complete, heavy byproducts being formed only in small amounts. Therefore, the separation operation may be reduced to a simple distillation of the reaction mixture, without further rectification of the hydrochlorinated fraction. All this permits a considerable simplification with the resultant advantages.

According to another embodiment the vinyltoluenes are submitted to a hydrohalogenation treatment, using hydrogen bromide or iodide. This last treatment may be carried out in the presence of a catalyst chosen from bromides and iodides of zinc, antimony and tin.

The a-bromo, or a-iodoethyltoluenes thus obtained are treated in a similar manner to the corresponding chlorinated compounds.

It is however preferable to use hydrogen chloride as the halogenation agent as it is more readily available and less expensive.

Moreover, the a-chloroethyltoluenes are more stable than the corresponding brominated and iodated compounds. The hydrogenated aromatic compounds (II) in which R is different from hydrogen may be prepared by similar processes.

In the preparation of vinylbenzyl chlorides (non-substituted or having a substituent R different from hydrogen) according to the process of the present invention the a-haloethyltoluenes of formula (II) (non-substituted or having a substituent R different from hydrogen) are mixed in the gaseous phase with an inert gas selected for example from steam, carbon dioxide, nitrogen, helium and hydrogen chloride.

The volumetric ratio of the ahaloethyltoluene to the inert gas is conveniently maintained at a value of from 1:5 to 1:50 and preferably of from 1:10 to 1:20. The mixture thus obtained is sent to a preheater and heated to a temperature of at least 4000C and preferably to a temperature equal to or near to that of the subsequent reaction stage with chlorine.

The preheating temperature is conveniently from 400 to 5500 C, depending on the preselected temperature for the subsequent reaction with chlorine.

The preheated mixture is then sent to a mixer into which is also fed chlorine, possibly diluted with an inert gas.

The molar ratio between chlorine and the a-haloethyltoluene is conveniently maintained at a value of from 1:1 to 1:10 and preferably from 1:1.5 to 1:4.

In general a molar excess of a haloethyltoluene with respect to the chlorine is maintained so as to ensure complete conversion of the chlorine and to reduce to a minimum the formation of polychlorinated compounds.

The mixture containing chlorine is then rapidly conveyed to a reactor in which the reaction is generally carried out at a temperature of from 400 to 6500C and preferably from 450 to 5500C. It is not convenient to operate at temperatures above 650"C as at such temperatures there is a sensible formation of carbon with resultant fouling of the apparatus and loss of useful products. On the other hand, reaction temperatures of less than 400"C in general afford only partial conversion of the chlorine.

The reaction times are conveniently from 0.1 to 10 seconds and preferably of the order to 0.2-2 seconds.

In practice it is found that by operating within the preferred temperature range, complete or nearly complete conversion of the chlorine is obtained with contact times of the order of 0.5 seconds.

The vinylbenzyl chlorides may be recovered from the gaseous mixture discharged from the reactor by rapidly cooling said gaseous mixture, with separation of the products which are liquid under normal conditions, and distilling the liquid organic phase thus obtained.

When steam is used as the inert gas, the condensate is formed of an organic layer and an aqueous layer of hydrochloric acid.

When a non-condensable gas is used as the inert gas, after cooling of the reaction products, an organic liquid phase saturated with hydrochloric acid and a gaseous phase containing hydrogen chloride and saturated with said organic phase are separated.

Rapid neutralization of the liquid phase is therefore carried out.

The organic compounds are removed from the gaseous phase and the residual gaseous flow is then scrubbed by means of a liquid to separate the hydrogen chloride contained in it. To this end a mixture of ethyltoluene and vinyltoluene may conveniently be used, thus recovering the hydrogen chloride necessary for the hydrochlorination.

Lastly, when hydrogen chloride is used as the inert gas, on cooling of the reaction products an organic liquid phase saturated with hydrochloric acid and a gaseous hydrogen chloride phase saturated with the said organic phase are separated. The liquid phase is rapidly neutralised.

The gaseous phase is treated to remove the organic products contained in it and the residual hydrogen chloride may be recycled partly to the hydrochlorination stage and partly as the inert gas to the reaction stage in which the vinylbenzyl chloride is formed.

In each case the liquid organic phase thus obtained contains predominantly vinyltoluene from the dehydrochlorination of a-haloethyltoluene and vinylbenzyl chloride from the chlorination and dehydrochlorination of a-haloethyltoluene.

This organic phase is therefore distilled to separate the vinylbenzyl chlorides (which are recovered) and the vinyltoluenes (which may be recycled to the hydrochlorination stage, or to the reaction stage in which the vinylbenzyl chlorides are formed, upon dilution and mixing with the inert gas and with fresh a-haloethyltoluenes).

By operating in accordance with the process of the present invention vinylbenzyl chlorides are obtained with yields equal to or generally greater than those of the processes in which vinyltoluenes are directly chlorinated at high temperature, while avoiding the disadvantages peculiar to the said known processes.

Example I A mixture of meta- and para ethyltoluenes is dehydrogenated on a metal oxide catalyst at a temperature of 600"C and in the presence of steam to give a reaction product containing 41.5% by weight of meta- and para-vinyltoluenes with a ratio between the two isomers equal to 60:40, the remaining percentage consisting essentially of unreacted ethyltoluenes.

0.5 kg of this dehydrogenation product, maintained under agitation at -400C, are reacted with gaseous hydrogen chloride at atmospheric pressure. The hydrogen chloride is gradually added in an overall amount slightly greater than that stoichiometrically necessary for the hydrochlorination reaction, over a period of 90 minutes. At the end of this addition the temperature is maintained at -400C for a further 30 minutes, the mass being kept agitated.

The temperature is than brought slowly over about one hour to 200C, while removing by scrubbing the unaltered hydrogen chlorine which is evolved.

The hydrochlorination product is then washed with deionized water, dehydrated and then distilled at a pressure of 2-3 mm Hg. Thus 258 grams of cr-chloro ethyltoluenes are recovered in which the ratio of the meta- and para-isomers is 60:40, with a yield of 95 /" with respect to the vinyltoluenes loaded in.

Said a-chloroethyltoluenes are fed at a rate of 0.5 moles/hour into an environment maintained at 2500--3000C to induce vaporization, and water vapour, provided by a boiler in which measured quantities of demineralized water are vaporized, is also fed into said environment.

In particular the feeds are regulated in such a manner as to ensure a volumetric ratio between the vaporized a chloroethyltoluenes and the water vapour equal to about 1:10.

The gaseous mixture thus obtained is continuously fed to a preheater where the temperature is raised to 50()5200C in a period of the order to 0.5 seconds.

The mixture thus preheated is continuously conveyed to a tubular reactor together with gaseous chlorine, said chlorine being fed in an amount such as to ensure a molar ratio between the a chloroethyltoluenes and the chlorine equal to 3.2:1.

The residence time in this reactor is 0.5 seconds and the temperature about 540"C.

The gaseous flow leaving the reactor is rapidly cooled in a cooler and two liquid phases, one organic, the other aqueous, are collected. The residual gases are scrubbed in a packed column with a 1 N aqueous sodium hydroxide solution.

After 3 hours working an organic phase is recovered containing 55.5 grams of vinylbenzyl chloride, with a yield of 77.5% evaluated on the chlorine fed in.

Example 2 The run of Example 1 is repeated maintaining the volumetric ratio between the water vapour and the vaporized achloroethyltoluenes at a value of 15:1.

Vinylbenzyl chloride is obtained with a yield equal to 82% with respect to the chlorine fed in.

Example 3 The run of Example 1 is repeated maintaining the volumetric ratio between the water vapour and the vaporized a- chloroethyltoluenes at a value of 20:1.

Vinylbenzyl chloride is obtained with a yield equal to 90% with respect to the chlorine fed in.

Example 4 The run of Example 1 is repeated maintaining the volumetric ratio between the water vapour and the vaporized achloroethyltoluenes at a value of 20:1 and the molar ratio between said c- chloroethyltoluenes and the chlorine at a value of 2.4:1.

Vinylbenzyl chloride is obtained with a yield of 81% with respect to the chlorine fed in.

WHAT WE CLAIM IS: 1. A process for preparing an archloromethyl vinyl aromatic compound of the formula:

wherein the --CH,CI substituent is in para or meta position with respect to the H=CH2 substituent and R is a substituent chosen from hydrogen, halogen, cyano, phenyl, tertiary butyl, hydroxy, carboxy and OR1 groups wherein R1 is an aryl group, which comprises preheating to a temperature of at least 4000C a gaseous mixture comprising a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. yields equal to or generally greater than those of the processes in which vinyltoluenes are directly chlorinated at high temperature, while avoiding the disadvantages peculiar to the said known processes. Example I A mixture of meta- and para ethyltoluenes is dehydrogenated on a metal oxide catalyst at a temperature of 600"C and in the presence of steam to give a reaction product containing 41.5% by weight of meta- and para-vinyltoluenes with a ratio between the two isomers equal to 60:40, the remaining percentage consisting essentially of unreacted ethyltoluenes. 0.5 kg of this dehydrogenation product, maintained under agitation at -400C, are reacted with gaseous hydrogen chloride at atmospheric pressure. The hydrogen chloride is gradually added in an overall amount slightly greater than that stoichiometrically necessary for the hydrochlorination reaction, over a period of 90 minutes. At the end of this addition the temperature is maintained at -400C for a further 30 minutes, the mass being kept agitated. The temperature is than brought slowly over about one hour to 200C, while removing by scrubbing the unaltered hydrogen chlorine which is evolved. The hydrochlorination product is then washed with deionized water, dehydrated and then distilled at a pressure of 2-3 mm Hg. Thus 258 grams of cr-chloro ethyltoluenes are recovered in which the ratio of the meta- and para-isomers is 60:40, with a yield of 95 /" with respect to the vinyltoluenes loaded in. Said a-chloroethyltoluenes are fed at a rate of 0.5 moles/hour into an environment maintained at 2500--3000C to induce vaporization, and water vapour, provided by a boiler in which measured quantities of demineralized water are vaporized, is also fed into said environment. In particular the feeds are regulated in such a manner as to ensure a volumetric ratio between the vaporized a chloroethyltoluenes and the water vapour equal to about 1:10. The gaseous mixture thus obtained is continuously fed to a preheater where the temperature is raised to 50()5200C in a period of the order to 0.5 seconds. The mixture thus preheated is continuously conveyed to a tubular reactor together with gaseous chlorine, said chlorine being fed in an amount such as to ensure a molar ratio between the a chloroethyltoluenes and the chlorine equal to 3.2:1. The residence time in this reactor is 0.5 seconds and the temperature about 540"C. The gaseous flow leaving the reactor is rapidly cooled in a cooler and two liquid phases, one organic, the other aqueous, are collected. The residual gases are scrubbed in a packed column with a 1 N aqueous sodium hydroxide solution. After 3 hours working an organic phase is recovered containing 55.5 grams of vinylbenzyl chloride, with a yield of 77.5% evaluated on the chlorine fed in. Example 2 The run of Example 1 is repeated maintaining the volumetric ratio between the water vapour and the vaporized achloroethyltoluenes at a value of 15:1. Vinylbenzyl chloride is obtained with a yield equal to 82% with respect to the chlorine fed in. Example 3 The run of Example 1 is repeated maintaining the volumetric ratio between the water vapour and the vaporized a- chloroethyltoluenes at a value of 20:1. Vinylbenzyl chloride is obtained with a yield equal to 90% with respect to the chlorine fed in. Example 4 The run of Example 1 is repeated maintaining the volumetric ratio between the water vapour and the vaporized achloroethyltoluenes at a value of 20:1 and the molar ratio between said c- chloroethyltoluenes and the chlorine at a value of 2.4:1. Vinylbenzyl chloride is obtained with a yield of 81% with respect to the chlorine fed in. WHAT WE CLAIM IS:

1. A process for preparing an archloromethyl vinyl aromatic compound of the formula:

wherein the --CH,CI substituent is in para or meta position with respect to the H=CH2 substituent and R is a substituent chosen from hydrogen, halogen, cyano, phenyl, tertiary butyl, hydroxy, carboxy and OR1 groups wherein R1 is an aryl group, which comprises preheating to a temperature of at least 4000C a gaseous mixture comprising a

halogenated aromatic compound and which is inert under the reaction conditions gas in a volumetric ratio not exceeding 1:5, said halogenated aromatic compound corresponding to the formula:

wherein the -CR3 substituent is in para or meta position with respect to the X-CH-CH3 substituent, X is a chlorine, bromine or iodine atom and R has the same meaning as in formula (I), contacting gaseous chlorine and the thus preheated mixture in a molar ratio between said chlorine and said halogenated aromatic compound not exceeding 1:1, at a temperature of at least 400"C and for a period of at least 0.1 second, and recovering the ar-chloromethyl vinyl aromatic compound from the reaction products.

2. A process according to claim 1, wherein said substituent R is hydrogen.

3. A process according to claim 1 or 2, wherein X is chlorine in formula (II).

4. A process according to any one of the preceding claims, in which said volumetric ratio between said halogenated aromatic compound and said inert gas is from 1:5 to 1:50.

5. A process according to any one of the preceding claims, in which said inert gas is chosen from steam, carbon dioxide, nitrogen, helium and hydrogen chloride.

6. A process according to any one of the preceding claims, in which said gaseous mixture is preheated to a temperature of from 400 to 5500 C.

7. A process according to any one of the preceding claims, in which said molar ratio between chlorine and halogenated aromatic compound is from 1:1 to 1:10.

8. A process according to any one of the preceding claims, in which said molar ratio between chlorine and halogenated aromatic compound is from 1:1.5 to 1:4.

9. A process according to any one of the preceding claims, in which said chlorine and preheated gaseous mixture are contacted at a temperature of from 400" to 6500C for a period of from 0.1 to 10 seconds.

10. A process according to any one of the preceding claims, in which said chlorine and preheated gaseous mixture are contacted at a temperature of from 450" to 5500C for a period of from 0.2 to 2 seconds.

11. A process according to any one of the preceding claims, in which said archloromethyl vinyl aromatic compound is recovered from the reaction products by cooling the latter and distilling the liquid organic phase thus obtained.

12. A process according to claim 1, substantially as hereinbefore described with reference to the Examples.

13. Ar-chloromethyl vinyl aromatic compounds, whenever obtained by the process according to any one of claims 1 to 12.