US2973391A - Method for chloromethylating aromatic hydrocarbons - Google Patents

Description

2 Sheets-Sheet 1 INVENTORS. HAROLD w. EARHART WILLIAM G. DEPIERRI,JR., BY )3 ATTORNEY.

UNREACTED TOLUENE TIME, MIN.

I H. W. EARHART EI'AL METHOD FOR CHLOROMETHYLATING AROMATIC HYDROCARBONS Feb. 28, 1961 Filed July 14, 1959 FIG.

FIG. 2

Feb. 28, 1961 VOLUME PERCENT ul METHOD FOR CHLOROMETHYLATING AROMATIC HYDROCARBONS Filed July 14, 1959 2 Sheets-Sheet 2 FIG. 3.

DIPHENYLMETHANES RUW./ .//I 1 PM RUN TIME, MIN.

INVENTORS.

HAROLD W. EARHART, WILLIAM G. DEPIERRLJR,

ail/2% ATTORNEY.

METHOD FOR CHLOROMEATING AROMATIC HYDRGCARBGNS';

Harold W. Earhart and William G. De Pierri, Jr., Baytown, Tex, assiguors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N..l., a corporation of Delaware Filed July 14, 1959, 'Ser. No. 826,994

9 Claims. Cl. 250-651) This invention relates to a process for the chloromethylation of aromatic hydrocarbons. More particularly, this invention relates to a process for the substantially selective chloromethylation of benzene and alkyl substituted benzenes.

This application is a continuation-in-part of our copending application Serial No. 717,225, filed February 24, 1958, and entitled Chloromethylation Process, and now abandoned.

In the chloromethylation of aromatic hydrocarbons, serious problems are encountered with respect to the selectivity of the chloromethylation reaction and the achievement of a reasonable conversion rate. Thus, when aromatics are treated with formaldehyde and hydrochloric acid, the products that are normally formed include not only chloromethyl derivatives but also alkyl diphenyl methanes formed by the reaction of unconverted feed stock components with chloromethylated products. Moreover, the tendency for the formation of undesired alkyl diphenyl methane by-products is normally enhanced under conditions which favor a maximized rate of conversion of the feed stock.

It has now been discovered in accordance with the present invention that these and similar problems may be overcome by reacting an aromatic hydrocarbon with bydrochloric acid and formaldehyde in the presence of at least 0.5 mol of a water solublechloride of an alkali metal or alkaline earth metal, such as sodium chloride, potassium chloride, etc. and mixtures thereof.

Representative compounds which may be chloromethylated in accordance with the present invention either alone or in admixture with each other include benzene; methyl benzenes (e.g., toluene, ortho-, meta-, or paraxylene; trimethyl benzenes such as pseudocumene or mesitylene; tetramethyl benzenes such as durene, prehni-- tene, and isodurene; and pentamethyl benzenes); propyl and isopropyl benzenes; butyl benzenes; tertiary butyl benzenes; isobutyl benzenes, etc.; as well as polynuclear aromatics such as diand triphenyl methanes, naphthalenes, phenanthrenes, anthracenes, etc. The feed stock may consist of the aromatic hydrocarbon to be chloromethylated or may comprise a mixture of such aromatic hydrocarbons with non-reactive hydrocarbons such as paraffins, naththenes, etc. r y

The amount of formaldehyde to be employed will be dependent, in large part, on the extent to which the aromatic hydrocarbon feed stock is to be chloromethylated. Thus, when it is desired to maximize the production of monochloromethylated derivatives, it is preferable to utilize from about 0.5 to about 1.5 mols of formaldehyde per mol of aromatic hydrocarbon feed stock. If it is desired to prepare a trichloromethyl derivative, as disclosed in copending Earhart and De Pierri application Serial No. 826,926, entitled Trichloromethylated Aromatic, filed on an even date herewith, it is preferable 7G to utilize from about 2.5 to about 6 mols of formaldehyde per mol of aromatic hydrocarbon feedstock.

2,973,391 C I Patented Feb. 1,

As adduced from the foregoing, therefore, at least about'0.5 mol of formaldehyde per mol of aromatic is utilized in accordance with the present invention and, more particularly, from about 0.5 to about 6 mols of formaldehyde are employed per mol of aromatic. The formaldehyde may be charged as a solution of formaldehyde or a water-soluble polymer thereof (cg. formalin), etc.

The amount of hydrochloric acid to be utilized in accordance with the present invention should generally be within the range of about 1 to 2 mols of hydrochloric acid per mol of formaldehyde. It is preferable to utilize, about 1.5 mols of hydrochloric acid per mol of formaldehyde.

of an alkali metal or alkaline earth metal hydroxide such as sodium chloride, potassium chloride, calcium chloride, lithium chloride, magnesium chloride, etc. At least 0.5 mol of the chloride salt ion per mol of hydrochloric acid should be employed. Preferably, 1 mol or more of chloride salt ion is employed per mol of hydrochloric acid. Thus, for example, from about 1 to 9 mols of chloride salt ion may be utilized per mol of hydrochloric acid.

Acidic chloromethylation catalysts such as zinc chloride, stannic chloride, boron trichloride, phosphoric acid, sulfuric acid, etc. are preferably utilized although it is not absolutely essential to use a catalyst with respect to relatively highly reactive aromatics such as metaxylene and mesitylene. In the case of comparatively low reacting aromatics such as benzene toluene, ethylbenzene,.

isopropylbenzene, t-butylbenzene, etc., it is necessary to use a catalyst if reasonable reaction rates'are to be obtained. It is preferable to employ from about 0.5 to 2 mols of catalyst per mol of aromatic hydrocarbon feed stock. A preferred catalyst is zinc chloride.

Normally, the utilization of acidic chloromethylation catalysts not only promotes the chloromethylation reaction but also promotes the reactions leading to alkyl diphenyl by-products.

methylation catalyst is utilized in the process of the present invention.

The reaction temperature to be utilized may be varied within comparatively wide limits but is preferably conducted at temperatures within the range of about F. to about 300 F., the temperature level employed depending to a great extent on the reactivity of the aromatic being treated.

The process of the present invention is preferably conducted at atmospheric pressure in liquid phase with agitation and, still more preferably, in a two phase system employing aqueous solutions of formaldehyde and hydrochloric acid. When this is done, the chloromethylated derivatives remain in the oil phase and are readily separated from the aqueous phase at the end of the reaction by decantation. easily separated from the other components of the oil phase by simple distillation; however, itis preferable to wash the oil prior to distillation with water, followed by for a wide variety of purposes. They are primarily use- In addition, there is employed a Water soluble chloride However, it has been discovered, that this problem is minimized when an acidic chloro-- The chloromethylated products are ful as raw materials for the preparation of a wide variety of aromatic intermediates such as alcohols, aldehydes, acids, amines, ethers, diesters, nitriles, isocyanates, mercaptans, etc.

The invention will be further illustrated by the following specific examples which, togethenwiththe drawings, are given by way of illustration and not intended as limitations on the scope of this invention.

In the drawing, Figures 1, 2 and 3 are plots of the results obtained in Example 1.

In conducting the following described experiments, the procedure used was as follows. The aromatic hydrocarbon to be treated and a predetermined amount of formalin (37 percent CH O) were added to a glass-lined reaction flask and heated to the desired temperature. A predetermined amount of 37 percent hydrochloric acid containing, where appropriate, the desired amount of zinc choride catalyst was preheated to a temperature of about 5 to F. below the desired reaction temperature and then added to the heated reaction mixture. Reaction time was measured from the time of addition of the hydrochloric acid. Agitation was: employed in all runs.

EXAMPLE I Three comparative runs were made in order to demonstrate the advantages to be obtained through the process of the present invention. The runs were made under reaction conditions which were maintained constant in order to provide a suitable basis for comparison. The feed stock was toluene and the catalyst was zinc chloride. In the third run, 1 mol of hydrochloric acid per mol of toluene was employed, in the first run 2 mols of hydrochloric acid were employed, and in the second run 1 mol of hydrochloric acid and 1 mol of sodium chloride were employed.

The reaction conditions employed and the results obtained are set forth in Table I and graphically plotted in Figures 1 to 3.

The temperature for the three runs was 176 F.

TABLE I In the second run, conducted in accordance with the present invention, diphenyl methane formation was drastically reduced to 10 percent whereas monochloromethylbenzene formation was substantially enhanced to provide about percent of monochloromethyl toluene.

It will be seen, therefore, that the use of sodium chloride (a water soluble chloride of an alkali metal or alkaline earth metal chloride) substantially inhibited diphenyl methane formation.

In addition, the yield of desired product (monochloromethyl derivative) was increased even by the use of a shorter reaction time. Thus, in run No. 1, about 33% was obtained after minutes whereas in run No.2, about 40% was obtained after 30 minutes.

When potassium chloride is substituted for sodium chloride and run 2 is otherwise repeated, substantially equivalent results are obtained in that diphenyl methane formation is again suppressed and in that the desired monochloromethylated product is obtained in larger yield.

EXAMPLE II A 12-liter Morton stirring flask was fitted with a reflux condenser, a Trubore stirrer and thermometer. Into the flask was placed the following materials:

4200 ml. (51.2 mols) concentrated hydrochloric acid. 1080 g. (36.1 mols) of paraformaldehyde.

818.2 g. (5.9 mols) of anhydrous zinc chloride.

185.2 g. (3.2 mols) of sodium chloride.

The contents of the flask were heated to C. with stirring and 721.1 g. (6.0 mols) of mesitylene were added. The reaction mixture was heated at the reflux temperature for ten hours, at the end of which period reaction was stopped. The maximum temperature, 99 C., was attained at the end of about 5 hours, and was maintained for the remainder of the reaction period.

The product was separated into beads by the use of a shock-chilling technique (as disclosed in copcnding De- Chlaromethylation of toluene to test effect of added sodium chloride Run 3 Run 1 Run 2 1 M01 Toluene, 1 M01 Zinc Chloride, 1 M01 Formaldehyde (37%) 1 M01 Hydrochloric 2 Mols Hydrochloric 1 M01 Hydrochloric Acid (37%) Acid (37%) Acid (37%) plus 1 M01 Sodium Chloride Temperature, 80 0.

Reaction Time, Min i0 30 60 10 30 60 10 30 60 Product Composition, Vol.

Percent:

Toluene 22. 6 14. 9 7. 1 75. 2 62. 7 28.0 58. 4 52. 2 41- 6 Chloromethyltoluene 21. 7 21. 7 16.0 19. 3 27. 7 33. 3 35. 6 41.2 45. 0 Di (ehloromethyl) toluene 2.3 2.4 2.3 0.6 0.8 3.0 1.2 1.5 2.2 Tri (chlorornethyl) toluene- 0.4 0.2 0.2 0.3 0.2 0.2 0.2 0.2 0.2 Diphenylmethanes 53.0 60. 8 74. 4 4. 6 8. 6 35. 5 4. 6 4. 9 10.0

Total 100 100 100 100 100 100 100 100 100 monochloromethyl toluene was still only about 33 per-v cent.

Pierri and Earhart application Serial No. 827,087, filed of an even date herewith, and entitled Method for Recovering Solid Chloromethylation Products") and was removed from the reactionmixture by filtration through a sintered-glass filter. The product, which remained on the filter, was washed with about 4 liters of water and was air-dried.

The product was analyzed by the following procedure. A sample was reduced with lithium aluminum hydride and lithium hydride in toluene solvent, and the reduced sample was-analyzed.by allow voltagemass spectrometer. The product was found to contain the following distribution of materials:

The product was recovered by recrystallization from toluene. A total of 604 g. of trichloromethylmesitylene was recovered. This corresponds to a recovery of 76 percent of the trichloromethylmesitylene present in the product and to a yield of trichloromethylmesitylene of 38 percent of the theoretical amount.

What is claimed is:

l. A method for chloromethylating an aromatic hydrocarbon which comprises contacting said aromatic hydrocarbon with formaldehyde and hydrochloric acid in the presence of at least about 0.5 mol of a chloride salt per mol of hydrochloric acid, said chloride salt being selected from the group consisting of water soluble chlorides of alkali metals and alkaline earth metals.

2. A method which comprises contacting a hydrocarbon feed stock containing an aromatic hydrocarbon selected from the group consisting of benzene and alkylsubstituted benzenes with an aqueous medium having dissolved therein from about 0.5 to about 6 mols of formaldehyde per mol of aromatic hydrocarbon, from about 1 to 2 mols of hydrochloric acid per mol of formaldehyde and from about 0.5 to mols of a metal chloride per mol of hydrochloric acid and from about 0.5 to about 2 mols of zinc chloride per mol of aromatic hydrocarbon, said contacting being conducted at a temperature within the range of about 0.5 to about 5 hours, whereby at least a portion of said aromatic hydrocarbon feed stock is substantially selectively converted to a chloromethyl derivative thereof, said metal chloride being selected from the group consisting of water soluble chlorides of alkali metals and alkaline earth metals.

3. A method as in claim 2 wherein the metal chloride is sodium chloride.

4. A method as in claim 2 wherein the aromatic hydrocarbon is toluene.

5. A method in accordance with claim 3 wherein the aromatic hydrocarbon is mesitylene.

6. In a chloromethylation reaction wherein an aromatic hydrocarbon is reacted with formaldehyde and hydrochloric acid to form a chloromethylated aromatic product, the improvement which comprises conducting said chloromethylation reaction in the presence of at least about 0.5 mol, per mol of hydrochloric acid, of a water soluble chloride of a metal selected from the group consisting of alkali metals and-alkaline earth metals.

7. In a catalytic chloromethylation reaction wherein an aromatic hydrocarbon is reacted with formaldehyde and hydrochloric acid in the presence of a catalytically effective amount of a .chloromethylation catalyst, the improvement which comprises conducting said chloromethylation reaction in the presence of from about'0.5 to 10 mols, per mol of hydrochloric acid, of a water soluble chloride of a metal selected from the group consisting of alkali metals and alkaline earth metals.

8. In a method for chloromethylating a methyl benzene wherein each mol of methyl benzene is reacted with about 0.5 to 6 mols of formaldehyde, from about 0.5 to about 2 mols of an acetic chloromethylation catalyst and from about 1 to 2 mols of hydrochloric acid per mol of formaldehyde in liquid phase at a temperature in the range of about to about 300 F., the improvement which comprises conducting said chloromethylation reaction in the presence of about 0.5 to about 10 mols of a water soluble chloride of a metal selected from the group consisting of alkali metals and alkaline earth metals.

9. A method as in claim '8 wherein the water soluble chloride is sodium chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,469,334 Hartough et a1. May 3, 1949 2,859,253 Snow Nov. 4, 1958 2,862,980 Muench et a1. Dec. 2, 1958 OTHER REFERENCES Ginsburg et aL: Ind. Eng. Chem., vol. 38. pages 478- (1946).

Claims (1)

1. A METHOD FOR CHLOROMETHYLATING AN AROMATIC HYDROCARBON WHICH COMPRISES CONTACTING SAID AROMATIC HYDROCARBON WITH FORMALDEHYDE AND HYDROCHLORIC ACID IN THE PRESENCE OF AT LEAST ABOUT 0.5 MOL OF A CHLORIDE SALT PER MOL OF HYDROCHLORIC ACID, SAID CHLORIDE SALT BEING SELECTED FROM THE GROUP CONSISTING OF WATER SOLUBLE CHLORIDES OF ALKALI METALS AND ALKALINE EARTH METALS.

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