US2753378A - Process for alkylating thiophenols in the para position with a tertiary alcohol or mercaptan - Google Patents

Description

United States Patent PROCESS FOR ALKYLATIN G THIOPHENOLS IN THE PARA POSITION WITH A TERTIARY ALCO- HOL 0R MERCAPTAN Kenneth L. Kreuz, Fishkill, N. Y., assignor to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application March 2, 1953, Serial No. 339,901

7 Claims. (Cl. 260-609) This invention relates to a process for preparing alkyl thiophenols. More particularly, it involves a process whereby para-t-alkyl thiophenols are prepared by an alkylation procedure.

In contrast with phenolic compounds, which are simply alkylated to produce alkyl phenols, previous eiforts to alkylate thiophenols have resulted in alkylation exclusively of the sulfur atom with the resulting production of aryl alkyl sulfides. Since efforts to effect carbon alkylation of thiophenols in the past have resulted in the production of aryl alkyl sulfides, it has been necessary to resort to means such as zinc dust reduction of alkyl benzene sul fonyl chlorides, the reaction of diazotized alkaryl amines with hydrogen sulfide, catalytic hydrogenation of aryl sulfonic acids and the action of sulfur on Grignard reagents in order to produce alkyl-substituted thiophenols. In addition to the tendency towards thioether formation, attempted alkylation of thiophenols has also been complicated by the fact that common alkylating catalysts such as anhydrous aluminum chloride and concentrated sulfuric acids have tended to cause desulfurization and condensed ring formation at relatively mild operating conditions.

This invention involves the discovery that para-t-alkyl thiophenols are produced in substantial yield by alkylation of thiophenol and its homologs with a particular alkylating agent at prescribed conditions. This invention provides the first means of producing alkyl thiophenols by an alkylation process which is adaptable to commercial exploitation.

In accordance with the process of the invention, para-taliphatic-substituted thiophenols are prepared by reacting thiophenol or one of its homologs containing a hydrogen atom in para-position with a tertiary aliphatic alcohol or mercaptan containing 4 to 16 carbon atoms in the presence of an aluminum halide catalyst. Para-t-aliphaticsubstituted thiophenols include para-t-alkyl thiophenols and para-t-alkenyl thiophenols. The alkylation proceess of the invention is advantageously elfected at a temperature between 20 and 75 C. and at atmospheric pressure. Alkylation of thiophenols under the prescribed conditions results in the formation of a substantial yield of C-alkylate and in many cases the C-alkylate product is substantially larger than the S-alkylate, alkyl aryl sulfide.

The advantage of the process of this invention over previously employed procedures for preparing alkyl thiophenols is that it is adaptable to continuous operation and to commercial development. The complex procedures heretofore described are laboratory methods which are useful to prepare small research quantities of alkyl thiophenols, but are not feasible for commercial development because of their prohibitive cost. The instant process utilizing an alkylation reaction moves para-t-alkyl thiophenols into the realm of low-cost commercial chemicals. Low-cost alkyl thiophenols are of interest as lubricating oil additives because of the anti-oxidant and detergent properties of their metallic salts.

The thiophenol compounds employed in the process "ice of the invention must have a hydrogen substituted in paraposition to the --SH group on the benzene nucleus. Since the process of the invention is specific to the preparation of para-alkyl thiophenols, it is necessary that the para-position be unsubstituted in order to obtain carbon alkylation. Examples of thiophenol homologs that may be employed in the process of the invention are 0- thiocresol, o-ethylthiophenol, o-butenylthiophenol, mbutylthiophenol and o-hexylthiophenol. In general, 0- and m-substituted alkyl thiophenols in which the alkyl group contains from about 1 to 10 carbon atoms are usable in the process of the invention to prepare para-t-alkyl thiophenols.

Alkylation of para-substituted thiophenols by the process of the invention results in the introduction of an aliphatic group solely on the sulfur atom. Reaction of parathiocresol with tertiary butyl alcohol in the presence of aluminum chloride resulted in the formation of almost theoretical yields of the sulfur alkylation product, namely, tolyl-t-butyl sulfide. It is also significant that once an alkyl group has entered into the para-position, further substitution on the carbon atoms of the benzene ring by alkyl groups is not effected by this invention.

Aluminum chloride, aluminum bromide and aluminum iodide can be employed as catalysts to effect replacement of a hydrogen atom by a tertiary aliphatic group in the para-position on a thiophenol compound. Aluminum chloride, of course, is the preferred reagent because of its low cost and ready availability.

The alkylating agent used in this invention is a tertiary aliphatic alcohol or mercaptan containing between 4 and 16 carbon atoms; t-alkyl and t-alkenyl alcohols and mercaptans of prescribed chain length are included Within this definition. It is preferred to use alcohols and mercaptans containing between 4 and 12 carbon atoms because separation of higher molecular Weight alkylated thiophenols from the reaction product is not simply effected. Tertiary aliphatic alcohols and mercaptans are by definition compounds wherein the hydroxyl group or sulfhydroxyl group is attached to a carbon atom which is attached to three carbon atoms. Tertiary butyl alcohol, 1,1-dimethyl-1-hydroxy butene-Z (a t-hexenyl alcohol), t-butyl mercaptan, t-amyl alcohol and t-amyl mercaptan are particularly preferred alkylating agents.

The substitution of primary and secondary alcohols for tertiary alcohols as alkylating agents results in the production of a sulfur alkylation product exclusively. The high specificity of the process to tertiary alcohols and mercaptans is particularly surprising in view of the high yields of C-alkylate obtained therewith.

The preparation of para-alkyl thiophenols is effected at a temperature between 20 and C. with temperatures between 35 and 65 C. being preferred. The temperature is maintained within the prescribed limits by effecting the alkylation in a low boiling hydrocarbon solvent such as petroleum ether.

The reaction is also normally effected at atmospheric pressure because the use of elevated pressures does not materially improve the yield of p-alkyl thiophenol.

It has also been found that the highest yields of parat-alkyl thiophenol are obtained when the mol ratios of reactants and catalyst are maintained within particular, well-defined limits. The use of thiophenol, alkylating agent and catalyst in ratios between 1:121 and 1:03:03 results in the production of maximum yields of C-alkylate. Outside of the prescribed mol ratios of reactants and catalyst, lower yields of C-alkylate are obtained and the S-alkylation product, an aryl alkyl sulfide, is the major component of the reaction product. Use of excessive or minute amounts of aluminum halide catalyst causes substantial reduction in the yield of C-alkylate; for example,

when the mol of aluminum chloride is either equivalent to or less than one sixth of the mol sum of the thiophenol and alkylating agent, the yield of C-alkylate is very small. It has been discovered that particularly high yields of para-alkyl thiophenol are obtained when thiophenol, alk ylating agent and catalyst are employed in a ratio of 3 mols of thiophenol, 2 mole of alkylating agent and 1 mol ofcatalyst.

The process of the invention is similar to commercial alkylation processes, and is effected either batch-wise or continuously. In batch operation, the thiophcncl con.- pound containing a hydrogen substituted in the paraposition, the alkylating agent and a hydrocarbon solvent such as petroleum ether are added to a reaction vessel; the aluminum halide catalyst is added to the reaction mixture in small increments; after addition of all the catalyst, the mixture is refluxed or stirred without refluxing for a period of the order of 1 to 5 hours at which time the reaction is substantially complete. In the event that acontinuous process is employed, it is recommended that the reactants be in contact with the catalyst for a period of 30 to 60 minutes.

The process of the invention is illustrated in the following examples which demonstrate that para-t-alkyl thiophenols are produced in substantial yield by the reaction of the thiophenol compound containing a hydrogen atom in the para-position with tertiary butyl alcohol or mercaptan in accordance with the process of the invention.

Example I 93 g. (0.75 mol) of o-thiocresol, 37 g. (0.5 mol) of t-butyl alcohol and 400 cc. of petroleum other were charged to a three-neck flask fitted with a stirrer and refiux condenser. 34 g. (0.25 mol) of aluminum chloride was added to the stirred reaction mixture in small proportions such that the heat of reaction caused gentle refluxing. After addition of the aluminum chloride was complete, the reaction mixture was stirred for a period of 2.8 hours and then allowed to stand overnight at room temperature. The reaction product consisting of a clear supernatant liquid and an orange colored solid phase was hydrolyzed by pouring on a mixture of ice and hydrogen chloride. The hydrolyzed mixture was extracted with ether which was, in turn, extracted with per cent sodium hydroxide to efiect separation of the product into neutral and acidic fractions; the neutral fraction contains the S-alkylate, and the acidic fraction comprises unreacted thiocresol and the C-alkylate. The caustic extract was acidified with hydrochloric acid, and the acidified mixture g 51 g. (0.41 mol) of o-thiocresol, 21.3 g. (0.27 mol) of t-butyl alcohol and 200 cc. of petroleum ether were charged to a three-neck flask, and 18.5 g. (0.14 mol) of aluminum chloride was added thereto with stirring. The reaction conditions were those described in Example I with the exception that the reaction mixture, after all the aluminum chloride had been added thereto, was heated under reflux for one hour prior to standing overnight. From the reaction product which was worked up in accordance with the procedure described in Example I, there was obtained g. of para-t-butyl-o-thiocresol which is a theoretical yield of 52 per cent basis the t-butyl alcohol charged. There was also obtained 15.2 g. of t-butylo-tolyl sulfide which is a yield of about 31.2 per cent basis of the t-butyl alcohol charged.

Example III 55 g. (0.50 mol) of thiophenol, 37 g. (0.50 mol) of t-butyl alcohol and 200 cc. of petroleum ether were charged to a three-neck flask, and 68 g. (0.50 mol) of aluminum chloride was added to this mixture with stirring. The mol ratio of thiophenol, t-butyl alcohol and aluminum chloride catalyst was 1:1:1. The reaction conditions described in Example I were followed with the exception that the reaction mixture, after addition of aluminum chloride, was heated under reflux for one hour prior to standing overnight. From the reaction. product which was worked up in accordance with the procedure described in Example I, there was obtained 27.4 g. of para-t-butyl thiophenol, which is a yield of 33 per cent basis the t-butyl alcohol charged. There was also obtained 28 g. of t-butyl phenyl sulfide which is a theoretical yield of approximately 33.6 per cent basis t-butyl alcohol charged.

Example I V 83 g. (0.75 mol) of thiophenol, 37 g. (0.5 mol) of t-butyl alcohol and 200 cc. of petroleum ether were added to a three-neck flask; 68 g. (0.5 mol) of aluminum chloride was added slowly to the stirred reaction mixture. The mol ratioof reactants and catalyst was 3:212. The reaction conditions were those used in Example III. From the reaction product, which was treated in accordance with the procedure described in Example I, there was isolated 29.9 g. of para-t-butyl thiophenol which is the theoretical yield of 36 per cent basis t-butyl alcohol charged. There was also obtained 29.2 g. of t-butyl phenyl sulfide which is a yield of approximately 35.2 per cent basis t-butyl alcohol charged.

Example V 83- g. (0.75 mol) of thiophenol, 37 g. (0.5 mol) of t-butyl alcohol and 200 cc. of petroleum ether were added to a three-neck flask; 34 g. (0.25 mol) of aluminum chloride was slowly added to the reaction mixture with stirring. The reaction conditions were those used in Example IV. The mol ratio of thiophenol, t-butyl alcohol and catalyst was 3:2:1. From the reaction product which was worked up in accordance with the procedure described in Example I, there was obtained 37.7 g. of para-t-butyl thiophenol which is a yield of 45 per cent basis of t-butyl alcohol charged. There was also obtained 32.8 g. of t-butyl phenyl sulfide, which is a yield of 38 per cent basis t-butyl alcohol charged.

Example VI 50 g. (0.4 mol) of o-thiocresol, 29 g. (0.24 mol) of t-amyl mercaptan and 200 cc. of petroleum ether were added to a three-neck flask; 19 g. (0.14 mol) of aluminum chloride was slowly added with stirring to the reaction mixture. The reaction conditions were similar to those employed in Example I with the exception that the reaction mixture was stirred wihout refluxing for six hours prior to standing overnight. From the reaction product which was worked up in accordance with the procedure outlined in Example I, there was recovered 12 g. of parat-amylmercapto-o-thiocresol, which is a yield of 25 per cent basis t-amyl mercaptan charged. There was also obtained 25.8 g. of t-amyl-o-tolyl sulfide which is a yield of approximately 53.6 per cent basis the t-amyl mercaptan charged.

Example VII 104 g. (0.75 mol) of o-ethyl thiophenol, 37 g. (0.5 mol) of t-butyl alcohol and 200 cc. of petroleum ether were added to a three-neck flask; 34 g. (0.25 mol) of aluminum chloride was slowly added with stirring to the reaction mixture. The reaction conditions were similar to those employed in Example I with the exception that the reaction mixture, after addition of aluminum chloride, was heated under reflux for 1.3 hours prior to standing overnight. From the reaction product, which was worked up in accordance with the procedure outlined in Example I, there was recovered 28 g. of para-t-butyl a1- cohol charged. There was also obtained 57.3 g. of t butyl-o-ethyl phenyl sulfide which is a yield of approximately 59 per cent basis the t-butyl alcohol charged.

Examples I and II illustrate the high yields of carbon alkylate that can be obtained in the process of this invention at the preferred mol ratio of reactants and catalysts, namely, 3 mols of thiophenol, 2 mols of tertiary alcohol or mercaptan and 1 mol of catalyst; yields of carbon alkylate higher than 50 per cent are obtained in both of these examples. Comparison of Examples II, III and IV definitely proves that the 3:2:1 mol ratio of thiophenol, tertiary alcohol and catalyst gives the optimum yields of carbon alkylate; the preferred 3:2:1 mol ratio employed in Example V gives a carbon alkylate yield of 45 per cent, whereas the 12121 mol ratio employed in Example II gives a yield of 33 per cent carbon alkylate and the 322:2 mol ratio employed in Example III gives a 36 per cent yield of carbon alkylate.

Example VI demonstrates the use of tertiary alkyl mercaptans in the process of the invention. Example VII applies the process of the invention to higher homologs of thiophenol.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for preparing para-t-aliphatic-substituted thiophenols which comprises reacting a thiophenol containing a hydrogen atom in para-position with an alkylating agent selected from the group consisting of tertiary alkyl and alkenyl alcohols and mercaptans containing four to sixteen carbon atoms, effecting said reaction in the presence of a catalyst selected from the group consisting of aluminum chloride, aluminum iodide and aluminum bromide at a temperature between 20 and C. so that substantial carbon alkylation in the para position occurs.

2. A process according to claim 1 in which aluminum chloride is employed as the catalyst.

3. A process according to claim 1 in which thiophenol, an alkylating agent and aluminum halide catalyst are employed in a mol ratio in the range of 1:1:1 to 1:03:03.

4. A process according to claim 1 in which the process is efiected at atmospheric pressure.

5. A process according to claim 1 in which the alkylating agent contains four to twelve carbon atoms.

6. A process according to claim 1 in which the reaction is elfected in a low boiling hydrocarbon solvent.

7. A process for preparing para-t-butyl-o-thiocresol which comprises reacting thiocresol with t-butyl alcohol and effecting said reaction in the presence of aluminum chloride in a petroleum ether solvent at a temperature between 20 and 75 C.

Recueil des Travaux Aux Chirniques, 69, page 644. Huston et al: 58, J. A. C. S. (1936) pages 439-441.

Claims (1)

1. A PROCESS FOR PREPARING PARA-T-ALIPHATIC-SUBSTITUTED THIOPHENOLS WHICH COMPRISES REACTING A THIOPHENOL CONTAINING A HYDROGEN ATOM IN PARA-POSITION WITH AN ALKYLATING AGNET SELECTED FROM THE GROUP CONSISTING OF TERTIARY ALKYL AND ALKENYL ALCOHOLS AND MERCAPTANS CONTAINING FOUR TO SIXTEEN CARBON ATOMS, EFFECTING SAID REACTION IN THE PRESENCE OF A CATALYST SELECTED FROM THE GROUP CONSISTING OF ALUMINUM CHLORIDE, ALUMINUM IODIDE AND ALUMINUM BROMIDE AT A TEMPERATURE BETWEEN 20 AND 75* C. SO THAT SUBSTANTIAL CARBON ALKYLATION IN THE PARA POSITION OCCURS.