US2334691A - Treatment of cresylic acid - Google Patents

Description

Patented Nov. 23, 1943 TREATMENT OF GBESYLIC ACID Cari N. Andersen. Weiiesiey Hills, Mala, assignor to Lever Brothers Company, Cambridge, Mara, a corporation of Maine Application April as, 1940. eriai no. 331,151

Claims. (01. 260-827) aromatic compounds, which group of compounds I shall refer to as phenols. These compounds are known to react with caustic in solution to form the corresponding phenolates, and from which the phenols can be regenerated by treatment with an acid. The purest form of cresylic acid is composed entirely of the three isomeric cresols, and has a boiling range of the order of 190 C. to 205 C., the boiling point of the usual mixture of the isomers being in the neighborhood The commercial forms of cresylic acid generally encountered, however, also contain lower boiling phenols, such as phenol, and higher boiling phenols, such as the various xylenols, thymol, isopseudocuminol, pseudocuminol, carvacrol, cateformed by the thermal decomposition of higher molecular weight compounds and comprise, for example, the thiophenes, thiocresols, mercaptans, sulfides, disulildes. pyridine. quinoline and other heterocyclic compounds.

The cresylic acid from petroleum sources is contained primarily in "cracked" products and fractions, and the pyrolytic decomposition of petroleum in the cracking process similarly explains the presence of impurities in the cresylic acid derived from this source.

Coal tar cresylic acid usually contains about 0.05% sulfur, and cresylic acid from petroleum sources contains sulfur in some instances as high as 1%. The nitrogen content is generally about the same in the acids from both sources, and is of the order of about 0.4%. Coal tar cresylic acid chol, durenol, pentamethyl phenol, etc., in varying amounts, and with which are usually associated impurities. This composition of commercial cresylic acid is evidenced by the fact that it has a boiling range of 180 C. to 230 0., and in many instances the major portion of the ingredients boils above 202 C. Cresylic acid is used as a disinfectant and antiseptic and all of the various phenols therein contribute in different degrees to its antiseptic action. However, the cresylic acids containing a larger proportion of the higher boiling phenols have a superior antiseptic action and less toxicity and irritating characteristics. Any

such mixtures of phenols, obtained from either coal tar or petroleum sources may constitute the cresylic acid referred to herein, and may be treated in accordance with my invention.

The cresylic acid of commerce also contains compounds other than the phenols, and these are objectionable constituents of the acid. These compounds generally contain nitrogen and sulfur, and a consideration of the processes by which the cresylic acid is manufactured will explain the presence of these objectionable compounds.

The coal tar from which cresylic acid is derived is known to contain almost an unlimitednumber of compounds, and is obtained by the pyrogenic decomposition of bituminous coal when subjected to distillation in the absence of air. The nitrogen and sulfur containing compounds most likely are is usually high in pyridine derivatives, and petrogum cresylic acid is higher in quinoline derivaves. In the manufacture of cresylic acid by present day methods, the desired petroleum or coal tar fraction containing the phenols, along with hydrocarbons and other compounds, is treated with an aqueous caustic solution. This converts the phenols into alkali metal phenolates, which are soluble in the aqueous liquid; the impurities'are also dissolved in this aqueous portion. The solution is separated from the hydrocarbons and other insoluble ingredients, for example by decantation. The separated aqueous solution is then treated with an acid, such as carbon dioxide or sulfuric acid, which decomposes the phenolates and regenerates the phenols. This treatment does not separate the impurities from the phenols, at least to the desired extent. Such a mixture constitutes the cresylic acid of commerce.

The impurities in the cresylic acid impart an undesirable odor, which is so unpleasant and foul as to make the acid useless for many purposes, particularly where it is to be used in any composition associated with the human body or the household. The impurities in the acid also result in an undesirable color, and the acid of commerce is generally characterized by its reddishbrown appearance. A treatment with caustic and the subsequent regeneration of the phenols does not result in an improvementin the color and the odor,'inasmuch as the impurities are soluble in the aqueous caustic. Distillation is generally used, butthis increases the odor-because heat causes the decomposition of disulfldes into the more odorous monosulfides. The acid derived from petroleum presents a particularly dimcult problem of purification, which has not been satisfactorily solved. This is evidenced by the fact that no method is presently known for refining petroleum cresylic acids to such a degree of purity as to render them useable alone or in any compositions to be used in connection with the human body, or in household use.

While known treatments result in some improvements, they do not do so to such a sumcient and critical extent as to achieve the desired improvements in color and odor. Particularly is this so in acids from petroleum sources as available at present, which develop an 'undesirable odor upon heating and develop a color upon standing. The impurities in the acid apparently undergo, enter into, or cause decomposition reactions.

It is an object of my invention to obtain cresylic acid free from undesirable impurities and to produce a water-white acid of the highest grade having a characteristic pure phenol odor suitable for pharmaceutical use and other uses in connection with the human body.

It is a further object 01' my invention to provide a process of treating cresylic acid which can be practiced in connection with the separation of the acid from the coal tar or petroleum fraction containing the same, as well as in the purification of acids previously separated.

It is an additional object of my' invention to provide a simple and economical process which can be carried out readily without detracting in any way from the product or materially enhancing its cost.

In accordance with my invention, I achieve these objects by treating the cresylic acid, either at the time it is regenerated or at any time subsequently, with chemicals that either precipitate or destroy the impurities.

My invention is based at least in part upon the discovery that an alkaline solution of lead may be used to remove the objectionable impurities from cresylic acid, at least to such an extent as to render the resulting product water-white and free from objectionable odors, and that this treatment does not deleteriously affect the phenol constituents of the acid nor interfere with the antiseptic and disinfectant action of the purified product.

I will describe an illustrative embodiment of my invention as applied to cresylic acid of petroleum origin sincethis is the most difiicult to refine, and has not heretofore been refined on a commercial and economical scale for the uses mentioned herein. It is to be understood, however, that my invention is equally applicable to the treatment of cresylic acid derived from coal tar or from other sources.

Referring more particularly to the illustrative embodiment, about 300 parts by weight of cresylic acid of petroleum origin is mixed with a caustic solution of lead, known as sodium plumbite, and the mixture refluxed for about one-half to several hours, after which it is permitted to settle.

The alkaline solution above referred to may be obtained by mixing parts of sodium hydroxide and 3 parts of lead oxide or other lead compound soluble in an alkaline solution. Water is added thereto in a small amount which insures the development of sufllcient heat to cause complete solution of the lead oxide. The amount of the caustic used in making the solution is not critical and may vary between 1 and parts. Enough should be employed to place the lead in solution, but an excess is generally desirable. For economical reasons, too large an excess is to be avoided since the excess converts phenols to phenolates which must be regenerated. The amount of water may vary and any amount that will dissolve the ingredients may be used. Heat is not necessary and is used, merely to speed the reaction.

After the cresylic acid has reacted with the solution as described above, the insoluble compounds formed are removed. This may be facilitatecl by adding water to the cresylic acid mixture which assists in the separation of the insoluble compounds. The alkali is removed by washing, and sufiicient acid, such as sulfuric or carbon dioxide, is added to neutralize the sodium phenolates formed during the treatment with the alkaline solution and to regenerate the corresponding phenols. The mixture may be washed to remove the excess sulfuric acid. In the preferred embodiment the material is heated to about 70 C. as this tends to break down and precipitate any insoluble compounds remaining in solution, and also has the advantage of preventing bumping" during distillation.

It may be desirable at this stage to assure the removal of all basic constituents, and if so the cresylic acid may be thoroughly mixed with a small amount to 1%) of a mineral acid and then heated to C. The mixture is then washed with water to remove any excess acid. The dried cresylic acid is ready for distillation which may be either in vacuum or with steam under reduced pressure. The resulting cresylic acid is waterwhite, and is devoid of the smoky or gassy odor associated with unpurified cresylic acid.

It will be apparent that the exact procedure, that is, the relative length of time of heating, the relative amounts of the ingredients and the neutralizing and washing operation may be varied depending upon the nature of the cresylic acid to be treated and the amounts and types of impurities therein; these factors may be varied over wide limits. Any alkaline solution of a lead, zinc or other metallic compound of the class described may be used in a manner similar to that described. The several acid treating and washing steps may be omitted, if the yield is not important or if a product of the desired purity for the particular use desired can be obtained without them.

It has been observed that upon the distillation of cresylic acid that has not been purified to the requisite extent, the distilled cresylic acid is sometimes not as sweet or clean as it was prior to distillation. This is no doubt due to the fact that certain pyrogenic decomposition products are formed from the sulfur compounds during the distillation and these impart the undesirable odor to the finished product. Such a product is generally referred to as "gassy.

It may be desirable, therefore, in instances where the cresylic acid contains certain types of impurities, or in excess amounts, to distill the acid prior to the plumbite treatment in order to decompose such products and render them more readily removable during the plumbite treatment.

My invention as described above may b utilized in the treatment of cresylic acid at any stage in its manufacture, in which event the extraction of the acids from any other ingredients associated with the same is accomplished by means of an alkaline solution of one of the herein mentioned metals as described. If desired.

, move all trace of acid and distilled either in vacuum or with steam at reduced pressure. The resulting product is water-white and of excellent odor.

It will be apparent that my process is capable of any minor alterations and adaptations as to the exactnature and sequence of the various operations described, and I intend all such variations and adaptations to be included within my invention.

I claim: 1. In a process of treating impure cresylic acid,

5. In a process of purifying cresylic acid having an undesirable color and odor, the step which comprises heating said acid in admixture with a caustic soda aqueous solution oi sodium plumbite and removing the impurities rendered insoluble thereby. g

8. In a process of purifying cresylic acid having an undesirable color and odor, the steps which comprise distilling said acid to decompose at least some of the impurities, heating said acid in admixture with a caustic aqueous solution of an alkali metal plumbite, and removing the impurities rendered insoluble thereby.

the step which comprises treating the mixture with an alkaline aqueous solution of an alkaline soluble lead compound to remove impurities from said cresylic acid.

2. In a process of treating impure cresylic acid,'the steps which comprise heating the mixture with a caustic soda aqueous solution of sodium plumbite, removing the separated undesirable compounds, acidifying the resulting mixture, removing the excess acid, and distilling the purified mixture.

3. In a process of treating impure cresylic acid to obtain a purified cresylic acid, the steps which comprise scrubbing the mixture with a caustic aqueous solution of an alkali metal plumbite, separating the solution from the residue, acidifying the solution to regenerate any phenols converted into phenolates by said caustie, and distilling the resulting mixture under reduced pressure.

4. In a process of treating impure cresylic acid to obtain a purified cresylic acid, thesteps which comprise scrubbing the mixture with a caustic soda aqueous solution of sodium plumbite, acidifying the solution to regenerate any phenols converted into phenolates by said caustic, removing any acid remaining in the resulting mixture, and distilling the purified cresylic acid.

7. ma process 01' purifying cresylic acid having an undesirable color and odor, the step which comprises treating said cresylic acidwith an alkaline aqueous solution of an alkali metal plumbite, adding water to the mixture and removing the impurities, acidifying-the mixture to regenerate any phenols converted into phenolates by said alkali, washing the resulting mixture to remove acid, and distilling the mixture.

8. In a process of purifying cresylic acid having an undesirable color and odor, the step which comprises heating said cryslic acid with caustic aqueous solution of an alkali metal plumbite, adding water to the mixture and removing the impurities, acidifying the mixture to regenerate any phenols converted into phenolates by said caustic, heating the mixture to further precipitate the insoluble compounds, treating the resulting mixture with an acid, washing the mixture to remove the acid, and distilling the mixture under reduced pressure.

9. In a process of treating impure cresylic acid, the steps which comprise treating the mixture with an alkaline solution of an alkaline soluble lead compound to precipitate impurities from said cresylic acid, separating the undesirable precipitated compounds, and acidifying the resulting mixture to regenerate phenols from any phenolates formed by the treatment with the alkaline solution.

10. In a process of treating impure cresylic acid, the steps which comprise treating the mixture with an alkaline solution of an alkaline soluble lead compound to separate impurities from said cresylic acid, removing the separated undesirable compounds, acidifying the resulting mixture, removing the excess acid, and distilling the Purified product.

' CARL N. ANDERSB.