US 3318949 A
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United States Patent 3,318,949 PROCESS FOR CHLORINATING ORTHO-CRESOL Robert Roberts and George Henry Francis Walker, Widnes, England, assignors to Imperial Chemicals Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed Jan. 29, 1962, Ser. No. 169,663 Claims priority, application Great Britain, Feb. 3, 1961, 4,125/61 9 Claims. (Cl. 260521) This invention relates to a chlorination process, more particularly for the manufacture of chlorinated phenols. It is known to chlorinate phenols by means ofchlorine or other chlorinating agents for example sulphuryl chloride, and to carry out the reaction in the presence of added I catalysts in order to increase the yield of chlorinated products, or, in those instances in which more than one chlorinated product can be for-med, to increase the yield of a desired product at the expense of other possible products. In particular, it has been proposed to produce an enhanced yield of the para-halo phenol from a phenol which reacts with a sulphuryl halide to produce a mixture of ortho and para halophenols by carrying out the reaction with the sulphuryl halide in the presence of a metal halide at a temperature not in excess of 75 C' The metal halides useful for this purpose include those of aluminium, iron, tin, titanium and zinc, and particularly aluminium chloride, ferric chloride, stannic chloride, titanium tetrachloride and zinc chloride.
In the chlorination of ortho-cresol, the two principal products formed are 4-chloro-2-methylphenol and 6- chloro-Z-methylphenol. Of these two compounds, the 4-chloro isomer is the more valuable as an intermediate for the manufacture of herbicidal com-pounds, so that methods of reducing the proportion of the undesired 6- chloro isomer are of commercial value.
In order to obtain a product containing a satisfactory proportion of the 4-chloro isomer, it is usually necessary to subject the crude chlorinated cresol t-o fractional distillation before further use.
The proportion of 4-chloro-2-methylphenol in the prodnot formed by chlorinating ortho-cresol can be increased by chlorinating the ortho-cresol with sulphuryl chloride in the presence of a metal chloride. Unfortunately, when chlorocresol made in this way is used directly, without distillation, for the manufacture of other products, highly coloured impurities in the chlorocresol are retained in the final product. Consequently, the full value of this improvement in the yield of the 4-ch1oro isomer cannot be realised in practice because the product still requires distillation before it can be used further for the manufacture of saitsfactorily light-coloured products, particularly 2-methyl- 4-chlorophenoxy acetic acid and its derivatives. Moreover, when distillation of the chlorocresol is carried out in the presence of the metal chloride, tarry materials are formed with corresponding loss of chlorocresol. It would be a considerable economic advantage if this intermediate distillation could be avoided, but no satisfactory substitute for it has so far been found, particularly since the chlorocresol product tends to crystallise if kept for any length of time at or near atmospheric temperature.
We have now found that a surprisingly high purifying effect, suificient to enable the resulting chlorocresol to be used satisfactorily without distillation, can be attained by carrying out the chlorination process by means of sulphuryl chloride in the presence of fullers earth in addition to the metal halide. This purifying effect is obtainable with-out detriment to the catalytic effect of the metal chloride, and indeed the fullers earth appears to have some contributive catalytic elfect. An alternative adsorbent, charcoal, has been found to be quite unsuitable as a replacement for the fullers earth in our process, since it causes the yied of chlorocresol to fall and decreases the proportion of 4-chloro cresol in the product; Also, the fullers earth does not exert the same cleaning effect if it is added after the chlorination instead of being present during the chlorination.
Thus according to our invention we provide an improved process for the chlorination of ortho-cresol by interacting ortho cresol and sulphuryl chloride in the presence of a metal halide catalyst, wherein the interaction is carried out in the presence of fullers earth. The proportion of fullers earth to be used is preferably between 0.5% and 1.0% by weight of the ortho-cresol.
Larger proportions tend to produce little additional effect and smaller proportions tend to be less efficient, but they may be used if desired. Proportions of 1.5% or more tend to be less satisfactory however, since there is a tendency then for the proportion of undesirable 6-chloro- Z-methylphenol in the product to increase. When the chlorination reaction is completed, the fullers earth can be removed from the chlorinated cresol product by any convenient means, for example by settling and decantation.
The fullers earth may be a commercial natural or activated grade, and is preferably dried before use to minimise the adverse effect of water on the metal halide cata-' yst.
and conditions of the process are those ah'eady known and used in the art and no substantial modification is necessary. In particular, the reaction temperatures and the proportions of ortho-cresol, metal halide catalyst and sulphuryl chloride to be used remain substantially unchanged.
Since the melting point of ortho-cresol is about 31 C., there is a tendency for crystallisation to occur if the chlorination is carried out much below this temperature, at least in the early stages, As the yield of 4-chloro-2- methyl phenol is better at lower temperatures, it is preferred to carry out the reaction at as low a temperature as possible while avoiding crystallisation, though the actual temperature to be employed may vary for different raw materials. Usually, it is best to maintain the reaction mixture at approximately 30 C. at the start of the chlorination and to cool it progressively during the reaction to about 20 C. Higher temperatures may be used if desired, however.
The metal halide catalysts which may be used are in general, volatile metal halides, and particularly the halides of aluminum, iron, tin, titanium and zinc. The preferred metal halide catalyst is aluminum chloride, as it is a cheap material which is a very active catalyst and enables a chlorocresol of light colour and good quality to be obtained by our process with the least difficulty of operation.
Apart from the use of fullers earth, the general features ther catalysts which may be used include ferric chloride, .annic chloride, titanium tetrachloride and zinc chloride. he proportion of metal halide catalyst to be used is prefrably between about 0.5% and 2% of the weight of the rtho-cresol, as greater proportions tend to produce little dditional effect. Smaller proportions are usually suitble only when the reactants are thoroughly dried. lnert Jlvents or diluents may be added if desired.
The metal halide should be substantially anhydrous if s beneficial effect on the formation of the para chloro tomer is to be obtained. Likewise, the adverse effect of ater on the isomer ratio of the product is preferably iinimised by using substantially anhydrous materials, specially the ortho-cresol, and by excluding moisture tom the reaction vessel.
Our process has the advantage of giving a chlorocresol aixture which can readily be used directly for the manuacture of other products Without the need for expensive urification for example by intermediate distillation. In articular, the chlorinated cresol is very suitable for direct onversion into 2-methyl-4-chlorophenoxy aliphatic acids for example 2-methyl-4-chlorophenoxyacetic acid, by :ondensation with caustic soda and monochloroacetic .cid) and compositions derived therefrom, and yields a elatively light-coloured product. For this purpose it is [011 essential to remove the fullers earth before conversion 2-methyl-4-chlorophenoxyacetic acid, and removal after :ondensation is satisfactory.
The invention is illustrated but not limited by the folowing example in which the parts and percentages are \y weight.
Example 1 297 parts of sulphuryl chloride are added over a period )f 30 minutes to a mixture of 216 parts of ortho-cresol, I.4% (i.e. 0.86 part) of anhydrous aluminum chloride 1nd 0.5% (i.e. 1.08 parts) of activated fullers earth (a :alcium montmorillonite) which is initially at a temperaure of 30 C. and is cooled gradually to C. during he addition. When the addition of sulphuryl chloride s complete, the mixture is stirred for a further 2 hours, tfter which time stirring is stopped and the mixture is alowed to stand overnight. The resulting mixture, which nay be liquid or solid, is heated during 1 hour to 70 C. and then a slow stream of nitrogen is blown through it for 2 hours to remove the acidic gases formed in the reaction. the crude chlorocresol product is then separated by dezantation from most of the fu-llers earth, which settles 'apidly. The product is obtained in a yield of 280.9 parts and contains 92.3% of 4-chloro-2-methylphenol, 6.1% of 6-chloro-2-methylphenol, 1.5% of 4:6-dichloro-2- methylphenol and no detectable proportion of ortho- :resol (corrected infra-red analytical results). The ratio of 4-chloro isomer to 6-chloro isomer is 15, and the yield at 4-chloro-2-methylphenol is 91% of theory based on the artho-cresol used.
Conversion of this chlorinated ortho-cresol into 4- chloro-2-methyl phenoxyacetic acid is carried out as follows:
A mixture of 142.5 parts of the above-described chlorinated ortho-cres-ol and 72.7 parts of monochloroacetic acid is heated to 100 C. and stirred while a slow stream of nitrogen is passed through it. 283.2 parts of an aqueous solution of caustic soda are then added rapidly with continued stirring to the above mixture, the rate of addition being such that the temperature of the reaction mixtures does not exceed about 109 C. and stabilises itself when the addition is complete at about 100-103 C. The mixture is maintained at 100-103" C. for 1 hour more and then 40 parts of an aqueous 25 solution of caustic soda and 21.7 parts of molten monochloroacetic acid are added, separately and simultaneously, and the whole is stirred for a further hour at l00103 C. while the nitrogen steam is maintained. The mixture is filtered to remove the small quantity of fullers earth present, is then acidified to approximately pH 6 by the addition of a small quantity of concentrated hydrochloric acid, and steam distilled to remove uncondensed materials (mainly chlorocresols). This distillation is continued until about 200 parts of distillate have been produced. The hot mixture is then acidified to approximately pH 2 by the addition of more hydrochloric acid (about 116 parts of hydrochloric acid of specific gravity 1.16 are required), and the molten layer of crude 4-chloro-2-methylphenoxy-acetic acid which is thereby formed is separated off from the aqueous layer. The aqueous layer is cooled to atmospheric temperature, and the further quantity of organic acid thus precipitated is collected, combined with the molten organic layer previously separated, and the whole is then partially dried by heating at 100110 C. for minutes.
The resulting product consists of 189.4 parts of material which is found by analysis to contain 82.8- '-3% of 4- chloro-2-methylphenoxyacetic acid, 89.3:3% of total chloro-2-methylphenoxyacetic acids. The yield corresponds to a yield of total acids of 84.4% of theory, of which 92.7% is the 4-chloro isomer, assuming the mean value of the analyses.
The mixed acids are then neutralised with aqueous potassium hydroxide solution, 1.5% of potassium citrate is added as sequestering agent, and the solution is adjusted to pH 11.0 and to contain 32.2% of total acids (3l.0i0.5% of 4-chloro-2-methylphenoxyacetic acid). This solution is slightly darker in colour than a solution prepared in a similar manner from distilled 4-chloro-orthocresol. Comparison of the two solutions by means of a spectrophotometer measuring the extinction coefficiencies at comparable dilutions (tenfold dilution), shows that the product produced by the procedure of this example is darker than the product derived from distilled 4-chloroortho-cresol by a factor of only 2.2.
Comparison in similar manner of (a) the product pro-' duced by the procedure of this example with (b) the product prepared using the aluminum chloride but omitting the fullers earth, shows that the latter is darker by a factor of approximately 4.
When the conversion of the chlorocresol to 4-chloro-2- methyl-phenoxy acetic acid in the manner described in this example is repeated using chlorocresol from which the fullers earth has not been removed, no significant difference in the colour of the product is observed.
Example 2 The procedure of Example 1 is repeated except that the anhydrous aluminum chloride is replaced by an equal weight of anhydrous zinc chloride. The procedure is also repeated using the zinc chloride but omitting the fullers earth.
Comparison of the colour intensities of solutions of the potassium salt of 2-methy-l-4-chloro phenoxyacetic acid derived from the chlorocresols so prepared shows that the product made from ortho-cresol chlorinated in the presence of zinc chloride alone is twice as dark as the product made from ortho-cresol chlorinated in the presence of zinc chloride and fullers earth.
What We claim is:
1. A process for the chlorination of ortho-cresol which comprises reacting ortho-cresol and sulphuryl chloride at a temperature within the range of approximately 2075 C. in the presence of from 0.5% to 2% by weight of a metal halide catalyst selected from the group consisting of the halides of aluminum, iron, tin, titanium and zinc, and from 0.5% to 1.5% by weight of fullers earth to produce chlorinated ortho-cresol, the amounts of catalyst and fullers earth being based on the weight of ortho-cresol.
2. Process as claimed in claim 1 wherein the fullers earth is dried before use.
3. Process as claimed in claim 1 wherein the metal halide catalyst is aluminum chloride.
4. Process as claimed in claim 1 wherein the reaction mixture is maintained at approximately 30 C. at the start of the chlorination and is cooled progressively during the reaction to about 20 C.
5. Process as claimed in claim 1 wherein the chlorinated ortho-cresol product is subsequently converted into a 2- methyl-4-chlorophenoxy aliphatic acid.
6. Process as claimed in claim 5 wherein the chlorinated ortho-cresol product is converted into 2-methyl-4-chlorophenoxyacetic acid, by condensation with caustic soda and monochloroacetic acid.
7. Process as claimed in claim 5 wherein the fullers earth is not first removed from the chlorinated orthocresol product.
8. A process for the chlorination of ortho-cresol which comprises reacting ortho-cresol and sulphuryl chloride at a temperature Within the range of approximately 20-30" C. in the presence of from 0.5% to 2% by weight of a metal halide catalyst selected from the group consisting of the chlorides of aluminum, iron, tin, titanium and zinc, and from 0.5% to 1.0% by weight, of fullers earth, to produce chlorinated ortho-cresol, the amounts of catalyst 6 and fullers earth being based on the weight of orthocresol.
9. The process of claim 8 wherein the chlorinated orthocresol product, containing some fullers earth, is condensed with caustic soda and monochloroacetic acid to produce a 2-rnethyl-4-chlorophenoxy acetic acid.
References Cited by the Examiner I UNITED STATES PATENTS 1,247,516 11/1917 Ellis 260-409 2,511,784 6/1950 ONeal 260-521 2,777,002 l/1957 Sullivan 260-623 OTHER REFERENCES Gregory: Uses and Applications of Chemicals and Related Materials, vol. II, pp. 144-147 (1944).
LORRAINE A. WEINBERGER Primary Examiner.
C. B. PARKER, L. ZITVER, S. B. WILLIAMS, D. P. CLARKE, G. P. DANGELO, Assistant Examiners.