US2957029A - Purification of thiophenols by treatment with aluminum - Google Patents

Description

'" itd 1 tiara Patented Oct. 18, 1960 PURIFICATION OF THIDPHENOLS BY TREAT- MENT WITH ALUMINUM Donald C. Jones and Robert J1 Earlier, Pittsburgh, Pa, assignors to Consolidation'fioal'Company, Pittsburgh, Pa;, acorporationof'Pennsylvania N Drawing. Filed Nov. 23,1959,- Ser. No. 854,543

7 ciarims; oi; air-soar This invention relates to the art of separating thiophenols from tar acids. More particularly it relates to purifying thiophenols' contaminated with tar" acids by selective reaction of'tlie' tar acids with aluminum to form aluminum salts.

This application" is a continuation-impart of our" copending application Serial No. 807,278, filed April 20, 1959, now abandonedi By tar acids reference'is' made to those constituents present in coal-tar distillates, certain cracked petroleum distillates and the like, often" referred to collectively as phenols, which are soluble in" dilute caustic soda, giving sodium cresylate. We particularly refer to a mixture of the simpler mono'hydric phenols'boiling below about 230 C. and consistingalmost' entirely of a mixture of phenol,- rnethylpheriols ('cresolS) and dimethyh phenols (xylenols), with lesser amounts occasionally present of ethylp'henols and'tiimetliylplien ols. I I

By thiophenols refern eis made to the "a'r'yl mercaptans. Of particularcommercial 'interest'isthiophenol per se and the lower molecular Weight alkylthiophe'nols, such as the thiocresols" andthioxylenols.

At present; thiopheiiols areprincipally obtained from two sources; as a by productfroir'i'the caustic extraction of petroleum distillates and'b'ys'ynthetic methods starting with benzene. In one widel'yused'direct synthesis tech nique, the benzene is converted to benzenesulfonylchloride by treatmenfwitha molar excessofchlorosulfonic acid. The product isth'e'n' converted to thiophenol by reduction in the"p'r'eseiice' of aniet'al-ac'id system: While the resulting'product' is of'li'igh purity andparticularly useful for paint, dyestuifs' and pharmaceutical applica tions, it is relatively expensive. This prevents itswidespread use for niany'applications.

In obtaining thiophenols from petroleumdistillatesresulting from oil crackin'g' processes, the tar acids and thiophenols are recovered by" extracting the petroleum distillate with aqueous ca'ustic'solu'tion' to produce watersoluble tar' a'cid'salts". Inthis"processof'extraction; thio= phenols present are" also removed by the aqueous caustic solution inasmuch as the thiophenols' areeven' stronger acids than' the phenols or tar acids themselves; The quantity of thiophenols in theoriginal source material varies widely, being sometimes as little as'one percent by weight of the phenols and ranging as high'as25'p'ercent and above. The thioph'enolsfound inthe caustic extract consist principally of thiophenol' itself and'mixecl thiocresols and thioxylenols.

In US. Patent'2',767,220, a process is setfortlifor'p'urifying thiophenol-contaminatedtar acids that are substantially free of neutral hydrocarbon oils. In this process, the feedstock, consistingprincipallyof tar acids and thiophenols, is contacted with aqueousmethanoland'with'a low boiling parafi'lnic naphtha fraction in a continuous countercurrent extraction zone. The aqueous methanol solutiondissolves substantially all the tar acids, and the naphtha fractiondissolves the thiophenols. The naphtha fraction" is'distilled' ed to yield the thi'ophen'ols as still bottoms. Inasmuch as the purification of the tar acids is the desideratum of this process, the thiophenols recovered from the paraffinic naphtha fraction invariably contain from 2 to 20 percent tar acids by weight. Complete removal of the tar acids from the thiophenols does not take place even when the thiophenols are fractionally distilled in a highly efiicient column, such-as a 50-plate packed tower. Thiophenol from such a distillation contains approximately 1.5 percent phenol. Eflicient fractional distillation is likewise unsuccessful ineffecting a significant removal of the tar acids from the mixed thiocresols and thioxylenols. These thiophenols contain even higher amounts of close-boiling tar acids.

It is accordingly an object of the present invention to provide a thiophenol of improved purity with respect to tar acid content.

It is a further object to provide a method for obtaining thiophenols free from tar acids that is readily adaptable to existing techniques for extracting tar acids from petroleum distillate fractions.

The process of the present invention provides a thiophenol of improved purity with respect to tar acid content. lt further provides a method for enriching a mixture of thiocresols with respect to o-thiocresol content.

In accordance with this invention, a mixture containing thiophenols and tar acids is reactedwith aluminum, preferably in finely divided form, at a temperature at which the tar acids present selectively react to formaluminum phenoxides. The thiophenols are then separated from the relatively nonvolatile aluminum p'henoxide, preferably by distillation. It is particularly preferred, andfor certain purposes essential because of process operability and product purity requirements, that the aluminum used be aluminum metal per se free from activators or promoters, such as inorganic mercury salts, which are used to stimulate or enhance its reactivity;

Commercially available finely divided aluminum foil of 99+ percent purity is preferred for. use in'practicing' this invention. This finely divided aluminum foil in approximately A-inch squares is ordinarily usedas a pigment in aluminum paint. It has a protective film of. a cutting oil which prevents'oxidation of'the aluminum without interfering with the purification of the thiophenols- While aluminum in granular form or aslathe turnings is also suitable, the reaction is generally slower, presumably because of the reduced surface available compared with the aluminum foil.

It has been found that this method is suitable for rendering an individual thiophenol'or mixtures of thiophenols containing tar acids in amounts up to 50 percent by weight substantially free from tar acid contamination.

The method is particularly preferred where the thiophenol has a tar acid content of up to 20 percent by weight of the mixture. In general, where thiophenol itself'is to be purified, the contaminant present is usually phenol. 7 It is believed that an azeotrope is formed thereby preventing a separation of the thiophenol and phenol by conventional distillation techniques. Alkylthiophenols are generally contaminated by corresponding alkylphenols. Thus mixed thiocresols are usually contaminated with o-cresol, o-ethylphenol and other tar acids. The thioxylenols generally contain contaminating amounts of close-boiling cresols and xylenols. for purifying tar acid-contaminated thiophenol and lower alkylthiophenols such as thiocresols and thioxylenols.

As a preferred method of practicing this invention, the thiophenol containing a minor portion of tar acid'is conveniently charged to a batch still along with at least one third of a gram atom of aluminum foil per gram mole of tar acids present in the charge. Additional aluminum is required to reactwith any moisture present. An excess This process is particularly useful of aluminum above the stoichiometric amount is ordinarily not required for substantially complete removal of the tar acids if moisture is not present. Excess aluminum, depending upon the reaction temperature and specific thiophenol, may react with the thiophenols, thereby lowering their yield. The charge is heated at atmospheric pressure to a temperature between 100 and 220 C., depending on the thiophenol and the phenolic contaminant present. The lower molecular weight phenols and thiophenols react at the lower temperatures.

A preferred reaction temperature range for a thiophenol-phenol mixture in which evolution of hydrogen at a satisfactory rate occurs with the aluminum is between 135 and 170 C. For mixed thiocresols, a range between 140 and 185 C. is preferred. The mixed thioxylenols have a preferred reaction range between 160 and 200 C. Where the purified thiophenol is subsequently distilled off at atmospheric pressure, a preferred upper limit for the reaction temperature range is the reflux temperature of the thiophenol being purified. Where substantial amounts of tar acids are present, in excess of 20 per cent by weight, a satisfactory rate of evolution of hydrogen occurs at the lower end of the range or even at lower temperatures. The evolution of hydrogen is usually com.- pleted within 5 to 30 minutes depending on the rate at which the pot temperature rises. The reaction with aluminum is exothermic. Therefore, in a situation requiring rather large amounts 0.5 percent) of aluminum, the reaction, once initiated, may boost the temperature by 20 C. or more, thus speeding the reaction rate considerably. When the vigorous evolution of hydrogen has ceased, the pressure is then reduced and the purified thiophenols are recovered as an overhead distillate. The residue contains the aluminum salts of tar acids and may also contain some aluminum salts of the thiophenols, depending on reaction conditions and on the excess quantity of aluminum employed. The residue may be hydrolyzed by aqueous acid such as dilute hydrochloric acid and the organic materials recovered if desired.

This process is particularly applicable to the purification of mixtures of thiophenols and tar acids as recovered from the paraffinic naphtha fraction obtained from the double-solvent extraction method of treating caustic-extracted petroleum distillates, as set forth in US. Patent 2,767,220. However, the process is also applicable to refining thiophenols contaminated with other substances in addition to tar acids in that these other contaminants are removed by fractionation either before or after treatment of the thiophenol with aluminum.

The procms is also considered applicable to the removal of trace amounts of moisture and alcohols, as well as phenols, from aromatic thiols, i.e., thiophenols. Excessive amounts of moisture, however, particularly Where non-amalgamated aluminum is used, require too long an induction period for reaction to commence. It has been found that, in general, aluminum becomes selectively less reactive in going from water to phenols, to alcohols to thiophenols. Thus an equilibrium involving Al(OR) and Al(SAr) should very strongly favor the former. Distillation would not affect the equilibrium position significantly if the alcohol involved were of a similar volatility to the thiophenol; if the latter situation were not involved, then the separation would, in any event, ordinarily be carried out by distillation.

Somewhat surprising is the finding that magnesium cannot be used to practice this invention, despite reports in the literature of the formation of magnesium phenoxides. The reaction proceeds very satisfactorily with aluminum, which is preferably in granular, flake or foil form. For granular aluminum, a 20- to 30-mesh U.S. standard sieve size is suitable. Finely divided aluminum foil or flake is particularly preferred.

As will be hereinafter described, it has been found that the use of aluminum amalgam or aluminum added oo- 4 jointly with an inorganic mercury salt such as mercuric chloride greatly accelerates the rate of reaction, which generally may be conducted at lower temperatures, compared with use of aluminum alone. However, for many applications, problems of mercury contamination are of consequence, and the use of aluminum amalgam must be avoided. Thus the use of aluminum that has not been treated with a mercury salt avoids difliculties frequently encountered when mercuric chloride that is initially present is reduced to mercury metal and, during distillation of the thiophenol, carried over in the overhead distillate. Thereby the thiophenol is contaminated, and the distillation column may also require to be cleaned. Thus it has been found that in such a reaction system although the use of aluminum-mercuric chloride leads to a more vigorous reaction, entrained mercury generally appears in the overhead distillate. Unless highly eflicient fractionating columns are used where the distillate fractions are taken off at a high reflux ratio, the obtaining of mercury-free distillate is difficult. Distillation at lower reflux ratios frequently results in a cloudy distillate being obtained, the resulting sediment eventually coalescing to mercury. Thus for most commercial applications, the use of aluminum amalgam or aluminum-mercuric chloride is to be avoided in order to eliminate the necessity for frequent column cleanup and also to eliminate requirements for redistillation of the distillate fractions obtained in order to render them free from mercury.

In addition to the freedom from contamination obtained by using aluminum metal without a mercury salt activator such as mercuric chloride, other advantages are also present. Eliminating use of a mercury salt obviously permits a cost saving. In addition, the reaction of aluminum metal alone with a mixture of thiophenols and tar acids at well below the atmospheric boiling point of the mixture is highly selective because aluminum is essentially unreactive with respect to thiophenol except at elevated temperatures. In the usual situation, in which the tar acid is a minor component, the reaction with essentially pure aluminum of 20-30 mesh granular size, or even in foil form, proceeds quite slowly compared with the reaction rate when an aluminum amalgam or aluminum mercuric chloride combination is used.

When the rate of gas evolution has diminished greatly relative to its maximum value, the pressure may be reduced and the purified thiophenols readily recovered by distillation. Further, the slower reaction rate occurring with aluminum alone permits charging all of the alumi num metal to the still pot simultaneously with the thiophenols. In the event that the charge contains relatively small or trace amounts of moisture, no hydrogen evolution will ordinarily occur until an overhead distillate fore-cut has been removed. Thus it may not be necessary to completely dry the thiophenols prior to the addition of the aluminum, where relatively small amounts of moisture are present, provided a sufficient excess of aluminum is used to first react with the moisture present.

It the reaction mixture is cooled to room temperature or lower, a gelatinous precipitate of aluminum phenoxides is formed. This may then be partially separated from the thiophenols by filtration or centrifugation. However, it is ordinarily preferred to separate the thiophenols from the relatively nonvolatile aluminum phenoxides by distilling off the thiophenols from the mixture without any prior cooling of the mixture.

The following examples illustrate this invention but are not intended as limitations thereof.

EXAMPLE 1 Reaction of aluminum with thiophenol-phenol mixture A 504.4-gram sample of thiophenol containing 1.8 percent by weight phenol was reacted with 5.0 grams (a 456% excess) of 20-30 mesh granular aluminum at the atmospheric reflux temperature. Reaction commenced 5 after a small amount of moisture had been removed in a distillate fore-cut. Hydrogen evolution practically ceased after 2.5 hours, even though a considerable amount of aluminum remained unreacted. The pressure was then gradually reduced and an 87% recovery of phenol-free thiophenol was obtained.

EXAMPLE 2 Reaction of aluminum with thiocresol-o-cresol mixture Treatment of 500 grams of mixed thiocresols containing 24.5 grams (0.227 mole) of o-cresol with 4.15 grams of 20-30 mesh granular aluminum (a 100% excess) at a reflux temperature'of 192194 for 0.2 hour yielded 140% of the theoretical hydrogen which would be formed by complete reaction of the o-cresol present. The pressure was then reduced, and an 88% recovery of o-cresol-free thiocresols was obtained.

EXAMPLE 3 Reaction of aluminum with thiophenol-tar acid mixture Approximately /3 of a gram atom of aluminum in the form of shredded aluminum foil per gram mole of phenol plus o-cresol present was reacted with the thiophenol-tar acid mixture by refluxing at 169170 C. at one atmosphere in a 1" x 3' Vigreaux column. About 4 to 5 hours was required for completion of the reaction. The thiophenol was distilled overhead until boilup fell off and pot temperature started to increase rapidly. The thiophenol distillate was found to contain no phenol or o-cresol as determined by gas chromatographic analysis.

EXAMPLE 4 Purification of xylenol-containing thioxylenols A-commercially obtained thioxylenol sample was reacted with excess aluminum flake at a temperature between 190 and 210 C. for 4 hours. The excess amount of aluminum used in two different runs represents the excess over the stoichiometric requirements for reacting with the tar acids present in the thioxylenols. After cessation of gas evolution, the reaction mixture was cooled and decanted. The decanted phase was fractionated through a packed column, and a heart-cut distillate, boiling 12l125.5 C./50 mm. Hg, corresponding to 91 weight percent of the still charge, was obtained. Analysis by gas chromatography showed the thioxylenols to be substantially free of tar acids. The results obtained were as follows (in weight percent):

100% excess Aluminum 150% excess Aluminum Feed Neutral oil m-p-Cres ols Thiocresols 2,4-2,5-Xylenls Thioxylenols Trace Trace 0. 4 0. 4 0. 3. 6 Trace 0. 96. 0 99. 6 99.

Trace Trace EXAMPLE (a) Removal of neutral 0ils.-Crude thiophenol, 67 pounds, which contained about 6% neutral hydrocarbon oils, 7.5% phenol and some o-cresol was charged to an evacuated kettle and blanketed with nitrogen. Then 120 pounds of 20 weight percent sodium hydroxide was added, which resulted in an increase in kettle temperature from 11 to'40" C. After stirring, an additional 25 pounds of water was added. With the overhead system set up for total take-off, the kettle was heated and neutral hydrocarbon oils and water were distilled off at a 95 C. head temperature and at atmospheric pressure. The first material recovered overhead consisted of 52 weight'percent water and 48 percent neutral oil. At a boil-up rate of 13-14 liters per hour, all the neutral oil which could be recovered came over within one hour. Of the 27.8 pounds of total overhead product, 2.8 pounds was neutral oil. An additional 20.4 pounds of water was then taken overhead.

The'material remaining in the kettle was cooled to 50 C., and pounds of 40% sulfuric acid was added in 10-pound portions with stirring. The temperature rose to 64 C. during this operation, thereby requiring cooling of the kettle under a nitrogen blanket to a temperature of 50 C. Inspection of the lower (aqueous) phase revealed that it was still basic (pH of 8) so that a small additional amount of sulfuric acid was added and stirred in. This was suflicient to render the aqueous phase acidic. It was then withdrawn (183 pounds), and 2.5 pounds of 10 weight percent sodium hydroxide was stirred in. After a bottom basic phase of 2 pounds was recovered, 4 pounds of water was stirred in and the kettle contents were then drained. The lower organic phase weighed 62 pounds, and the aqueous top phase weighed 6 pounds. This procedure was also repeated for a second batch so that 117.5 pounds of substantially neutral oil-free thiophenol containing phenol and o-cresol was available. The 117.5 pounds of thiophenol (lower organic phase) Was recharged to the kettle and dried by distilling off water present together with low-boiling contaminants at 150 mm. Hg pressure to a head temperature of C. The 6.2 pounds of material recovered overhead was mostly thiophenol (dark).

(b) Reaction with aluminum.After the kettle was cooled to 78 C., 1.8 pounds of flake aluminum was added, and heating was resumed. At 158 C. the reaction became sufficiently exothermic so that the heat input was reduced temporarily. Evolution of hydrogen continued for about 1% hours, the hydrogen being diluted with nitrogen in the vent line before it was released to the atmosphere. During the aluminum phenoxide formation, 5.5 pounds of thiophenol (dark) was distilled off and/ or entrained overhead.

The kettle temperature was then raised slowly and the thiophenol was taken overhead. Approximately 90 pounds of thiophenol (clear, water-white) was recovered at a head temperature of 161 C. with a maximum pot temperature of 188 C. The kettle was then cooled preparatory to placing the system under vacuum, and the receiver was drained. Another 4.6 pounds of thiophenol (dark) was then recovered at about 75 mm. Hg pressure. The kettle was finally cooled to permit the addition of tar acids to render the residue less viscous for withdrawal.

The starting thiophenol for reaction with aluminum contained approximately 92% thiophenol, 8% phenol and o-cresol, after it had been freed from substantially all of the neutral oil. The analysis of the final product was: 0.4% neutral oil, 98.4% thiophenol, and 1.2% mixed thiocresols. No phenols could be detected. The yield of pure thiophenol obtained is approximately 67% based on the initial crude thiophenol starting mixture, and 90% based on the actual thiophenol content of the crude mixture.

EXAMPLE 6 Large-scale purification of phenol-contaminated thiophenol A 125-gallon reaction kettle was charged with approximately 1.5 drums (621 totalpounds) of a thiophenol mixture containing 96.4% thiophenol, 2.74% phenol and 0.86% neutral oil. Because of the deleterious elfect of water on the aluminum catalyst, residual water present in the distillation unit was first removed. To accomplish this, vacuum was applied (1l5 mm. Hg pressure) followed by steam heat, and the kettle contents and system were dehydrated to an overhead vapor temperature of 97 C. The heat was then turned oif and'the 7 vacuum was released with nitrogen purging. The dis.- tillate, weighing 67 pounds, contained approximately 85% water, 14% thiophenol, 0.4% phenol and 0.1% neutral oil. The dehydration residue weighing 611 pounds, contained 96% thiophenol, 3% phenol, and 1% neutral oil. 2.13 pounds of flake aluminum was then added to the residue (2.13 pounds; 0.35% of the total weight of the charge, 33% stoichiometric excess). The total time to this point was 100 minutes.

Heat was again applied, and after 95 minutes the kettle contents reached a temperature of 157 C., at which point the aluminum reaction became quite vigorous. The temperature in the kettle was maintained at 155160 C. for a period of two hours. The kettle was then cooled to 70 C. and the reaction residue transferred under vacuum to the distillation unit. The distillation was carried out at a pressure of 70 mm. Hg and was completed in 3 hours. All overhead material was clear and light in color. The final distillate product weighed 490 pounds and analyzed as 99.1% thiophenol and 0.9% neutral oil. No phenol whatsoever could be detected in the distillate. The residue contained thiophenol, neutral oil, aluminum phenoxide and aluminum thiophenoxide. The recovery of the thiophenol, based on the initial charge, amounted to 96.3%. The percent of excess aluminum for the aluminum reaction amounted to 33%.

The foregoing example demonstrates the large-scale commercial feasibility of this process wherein phenol-free thiophenol of 99.1% purity was obtained in a yield of 96.3%. The use of aluminum metal to remove tar acids from tar acid-contaminated thiophenols is hence of considerable commercial interest.

Although it is generally preferred for the purposes of this invention to use aluminum that has not been treated with mercury, for certain specific purposes mercurated aluminum may be used, i.e., a preformed aluminum amalgam or an aluminum-mercury complex formed in situ by the addition of aluminum and a mercury salt. A preferred mercurated aluminum reactant for use in the present invention is aluminum together with a minor quantity of mercuric chloride. Other inorganic mercuric salts are also suitable for use with the aluminum, such as the bromide, nitrate, cyanide, or the like, which salts are readily available. In general, for in situ amalgamation, any mercury salt somewhat soluble in the thiophenol being treated is considered suitable. The mercuric halides, specifically mercuric chloride, are particularly preferred'because of their efiectiveness and ready availability. It is believed that actual amalgamation of the aluminum occurs in situ. However, the exact composition of the amalgam or complex formed is not known.

An active aluminum amalgam may be prepared by contacting granular aluminum (2030 mesh) with a saturated ethereal solution of mercuric chloride for 0.5 minute at the boiling point of the solution. The supernatant liquor is then quickly decanted, and the aluminum is washed by decantation with two portions of dry ether. The amalgamated aluminum should be prepared just prior to use. Other methods of preparing a preformed aluminum amalgam are also suitable.

During the course of the reaction the amalgam or the mercury salt used, such as mercuric chloride, is converted to mercury metal. The mercury is generally recovered in a finely divided colloidal state. Depending on the type of equipment employed, greater or less amounts of the mercury will be recovered with the thiophenol distillate. Thus where previously fractionated contaminated thiophenol was treated with mercuric chloride and aluminum at its atmospheric reflux temperature and the pressure was then reduced, it was found that the phenol-free thiophenol recovered by rapid distillation through a Vigreaux column contained mercury. Only the initial drops of distillate were cloudy due to the presence of finely divided mercury. The mercury appeared to have been transported mechanically up the walls of the column by the rising ring of condensate. The remainder of the distillate was clear. It has also been observed that where a packed column is used in place of a Vigreaux column, most of the distillate fractions will contain mercury metal. Apparently because of the fine state of subdivision of the mercury, its presence in the overhead distillate appears indigenous to the various procedures used. However, the amount present will depend on the type of equipment employed. Also, after a short period of storage the colloidal mercury will tend to coagulate and hence be more readily separated from the distillate which then may be obtained essentially free of mercury.

In general, the use of mercurated aluminum introduces problems of column cleanup and distillate contamination. Further, for most commercial applications removal of the mercury is a desideratum. The mercury may be removed by concentrating it in the early distillate fraction; settling and centrifugation techniques are also feasible.

Where a greater than a stoichiometric amount of mercurated aluminum is used in the reaction, after the tar acids have been converted to the corresponding aluminum phenoxides, and traces of water and alcohols have been reacted with, in the presence of mercury salt the excess aluminum will react at substantially the same reaction temperature with the thiophenols present. It has been observed that where mixed thiocresols are present, in the presence of the mercury salt the excess aluminum, in an amount sufficient to combine with only a portion of the thiocresols, selectively reacts with the metaand para-thiocresols present so as to enrich the o-thiocresol content of the mixture. Thus mercurated aluminum finds further applicability for concentrating a mixture of thiocresols with respect to its o-thiocresol content.

The following examples illustrate the use of mercurated aluminum in this invention but are not intended as limitations thereof.

EXAMPLE 7 Reaction 0 aluminum-mercury salt with synthetic thiophenol-phenol mixture A synthetic sample of commercially available reagentgrade phenol and 99+ percent thiophenol was prepared. This composite synthetic sample contained 97.5 percent thiophenol and 2.5 percent phenol. Of the mixture, 350 grams (0.093 mole phenol) was treated with 1.80 grams aluminum (0.067 gram atoms aluminum) and 1.05 grams of mercuric chloride. This corresponded to 0.51 weight percent aluminum based on the feed. The temperature was raised to 169 C. and a vigorous reaction ensued during which hydrogen gas was generated and vented. The thiophenol was then distilled off at reduced pressure and the product was analyzed by vapor-phase chromatography. Ninety-four weight percent recovery of thiophenol free from any phenol was obtained. No phenol could be detected in the chromatogram.

EXAMPLE 8 Reaction of aluminum-mercury salt with petroleum dis tzllate fraction containing thiophenol and phenol '9 EXAMPLE '9 A sample obtained from the naphtha fraction of a petroleum distillate was found to contain 972 percent mixed thiocresols and 2.8 percent ofcreso'l. Upon-treatment with 0.72 weight percent aluminum and 0.3 percent mercuric chloride, based on feed, following the procedure as set forth in Example 8, 91 weight percent of thio'cresols free from tar acid was obtained. No tar acids could be detected by vapor :phase chromatography.

EXAMPLE Reaction of aluminum-mercury salt'with petroleum distillate fraction containing thiocresols and cresols An excess of aluminum was used to treat a 435-gram sample containing 94.5 percent mixed thiocresols. Analysis of the sample showed the following to be present:

o-thiocresol34.4 percent (36.4 percent of mixed thiocresol-s) m-thiocresol-45.1 percent (47.7 percent of mixed thiocrcsols) p-thi-ocresol-15.0 percent (15.9 percent of mixed thiocresols) o-cresol2.2 percent m-p-cresol-3.3 percent The mixed thiocresol and cresol content was determined by vapor-phase chromatography. The specific distribution of isomers was found by infrared spectrophotometry. Fifteen grams of aluminum was used, corresponding to 3.4 weight percent aluminum based on the total feed; 2.5 grams HgCl was added. The aluminum was added in several portions to control the reaction. Thi batchwise addition is preferred where relatively large proportions of aluminum are used, as in this example. Following distillation, 54 weight percent of thiocresols free from tar acids was recovered. Analysis of the distillate by vapor-phase chromatography and infrared spectrophotometry showed 50.8 percent o-thiocresol, 36.8 percent m-thiocresol, and 12.4 percent p-thiocresol. No tar acids could be detected.

As shown in this example, the aluminum selectively reacts with the metaand para-thiocresol-s, since these are diminished relative to the ortho-isomer in the recovered thiocresols.

EXAMPLE 11 Reaction of aluminum-mercury salt with petroleum distillate fraction containing thiocresols and o-cresol A sample containing 97.2 percent mixed thiocresols and 2.8 o-cresol was treated with mercuric chloride and 3.4 weight percent aluminum, as described for Example 10. No tar acids could be detected in the thiocreso-l product. The thiocresols originally present were o-thiocresol 32.1 percent, m-thiocresol 51.9 percent, and p-thiocresol 13.2 percent (97.2 percent). The analysis of the recovered product showed o-thi'ocresol 43.2 percent, m-thiocresol 44.0 percent, and p-thiocresol 12.8 percent (100 percent).

EXAMPLE 12 Reaction of aluminum-mercury salt with thiophenolphenol-neutral oil mixture Thiophenol, 750.4 grams, containing 3.2 weight percent phenol and 0.7 weight percent neutral oil (non-acidic hydrocarbons) as obtained from a petroleum distillate fraction was reacted with 27 gram of granular aluminum in the presence of 3.3 grams of mercuric chloride as in previous examples. Distillation at 50 mm. Hg pressure yielded 270 grams of phenol-free thiophenol oontaining 1.2 weight percent neutral oil.

. 10 t EXAMPLE '13 Attempted reaction of magnesium-mercuric :chloride with thiophenol-phenol mixture -A mixture consisting of 377.7 grams of thiophenol and 5.4 grams of phenol was heated to 168 C. with 2.00 grams of magnesium turnings. No gas evolution occurred.

Then 1.2 grams'of HgCl was added and the temperature wa maintained at "C. for 22 minutesstill no gas evolution. Finally, 1.00 gram of granular aluminum (2030 mesh) was added. Reaction occurred within 13 minutes. on completion of the Vigorous reaction, the supernatant liquor was decanted and, after washing with toluene and petroleum ether, 2.6 grams of unreacted magnesium and mercury metals were recovered. 'No aluminum remained unreacted.

Despite the less acid nature of phenols compared with thiophenols, aluminum phenoxides are ordinarily formed with greater ease and at lower temperatures than the corresponding aluminum thiophenoxide's. However, when all the phenols present are combined with aluminum, the presence of a mercury salt allows the further rapid reaction of aluminum with the thiophenols to form an aluminum thiophenoxide. This is of particular utility Where it is desired to selectively concentrate a mixture consisting only of mixed thiophenols. Also, where the phenol is relatively low-boiling, the presence of a mercury salt activates the aluminum metal so that the phenoxide reaction may take place at a lower temperature at atmospheric pressure, which might otherwise not be feasible.

The formation of the aluminum phenoxide has been found to proceed satisfactorily at atmospheric pressure when a preformed aluminum amalgam is used. The use of the preformed amalgam may be preferred where relatively low reaction temperatures are desired. However, where it is desired to use mercurated aluminum, it is generally preferable and more convenient to activate the aluminum metal in situ by adding it to the thiophenolphenol mixture together with a suitable mercury salt, such as mercuric chloride, cyanide, bromide or the like.

The mechanism that occurs in the reactions of thi in vention is considered a highly complex one. While it is not desired to have the scope of this invention restricted by any explanation profiered, it is considered apparent that the formation of aluminum phenoxide proceeds at a very much more rapid rate than that of aluminum thiophenoxide. Hence under the conditions used, the reaction is highly selective. This selectivity phenomenon occurs despite the fact that thiophenol is a considerably stronger acid than phenol, and hence the thiophenol might ordinarily be expected to be more reactive than the phenol. However, as is shown herein, not only is the selective reaction with phenol favored, but apparently the aluminum will react with the phenol to the complete exclusion of the thiophenol as long as any phenol is present.

While this invention has been described with respect to specific preferred embodiments, it is not desired to be limited by the illustrative examples given or by the speculative mechanisms postulated for this reaction. The scope thereof should be determined in accordance with the objects and claims herein set forth.

We claim:

1. The process for purifying a tar acid-contaminated thiophenol which comprises reacting a mixture containing a thiophenol and a tar acid with aluminum to selectively form an aluminum salt of the .tar acid, and separating the thiophenol from said salt.

2. The process for recovering a thiophenol in substantially pure form from a mixture containing a thiophenol and a tar acid which comprises adding to said mixture aluminum in an amount sufiicient to provide at least /3 gram atom of aluminum per mole of tar acid present to react selectively with the tar acid to form an aluminum 11 salt thereof, and distilling ofi the thiophenol substantially free from tar acid.

3. The process for recovering a thiophenol in substantially pure form from a mixture containing a major portion of a thiophenol and a minor portion of a tar acid which comprises adding at least /3 gram atom of aluminum per mole of tar acid present to said mixture, heating said mixture to a temperature between 100 and 220 C. at which a reaction occurs and hydrogen is evolved, continuing said heating until evolution of said hydrogen has substantially ceased, and distilling off a thiophenol from the mixture in substantially pure form free from tar acid.

4. The process according to claim 3 wherein said thiophenol is a thiocresol and said tar acid includes a cresol.

5. The process according to claim 3 wherein said thiophenol is a thioxylenol and said tar acid includes a xylenol.

6. The process according to claim 3 wherein the aluminum consists of finely divided aluminum foil having a purity of at least 99 percent by weight.

7. The process for recovering thiophenol per se in substantially pure form from a mixture containing a major portion of thiophenol and a minor portion of phenol which comprises adding at least /3 gram atom of aluminum per mole of phenol present to said mixture, heating said mixture to a temperature between 135 and 165 C. at which a reaction occurs and hydrogen is evolved, continuing said heating until evolution of hydrogen has substantially ceased, and distilling off the thiophenol from the mixture in substantially pure form free from phenol.

No references cited.

Claims (1)

1. THE PROCESS FOR PURIFYING A TAR ACID-CONTAMINATED THIOPHENOL WHICH COMPRISES REACTING A MIXTURE CONTAINING A THIOPHENOL AND A TAR ACID WITH ALUMINUM TO SELECTIVELY FORM AN ALUMINUM SALT OF A TAR ACID, AND SEPARATING THE THIOPHENOL FROM SAID SALT.