US3071364A - Isomerization of olefins with thioacetic acid - Google Patents

Description

3,071,364 Patented Jan. 1, 1963 3,071,364 ISOMEMZATION F OLEFINS WITH THIOACETIC ACID William J. Bailey, University Park, Md. University of Maryland, College Park, Md.) N0 Drawing. Filed Apr. 4, 1960, Ser. No. 19,501 Claims. (Cl. 260-666) The present invention is concerned with the isomerization of olefins, particularly of internal olefins to terminal olefins.

An object of this invention is to provide a new and novel process for the isomerization of olefins. A particular object is to provide a method for the conversion of internal olefins to terminal olefins. These and further objects of the invention will be evident as the discussion proceeds.

It has now been found that olefins can be converted into isomers thereof with the unsaturation' in a different position by reacting them with thioacids and then subjecting the reaction mixture to pyrolysis to release the desired olefin. The unsymmetrically substituted olefins, especially internal olefins, are preferred starting materials. The lower alkyl thioacids, especially thioacetic acid, are preferred thioacids. Additionally, the olefin and thioacid are reacted at temperatures preferably between about 20 to 50 C. and the resulting product subjected to pyrolysis at temperatures preferably between about 450 to 550 C. A particularly preferred embodiment of this invention comprises the reaction of 2-methyl-2-butene with thioacetic acid at 0 to 50 C. and then subjecting the reaction mixture to pyrolysis at 450 to 550 C. to obtain B-methyIbutene-l. These and other embodiments of the invention will be evident from the discussion hereinafter.

The present invention will be more readily understood from the following examples.

Example I Z-methyl-Z-butene was mixed with thioacetic acid controlling the temperature at essentially room temperature. The reaction was essentially instantaneous and the yield obtained was 82 percent. Then the reaction mixture was passed through a hot tube maintained at 520 C. to efiect pyrolysis. The yield of olefin product thus obtained was 83 percent which consisted of 59 percent 3-methylbutene-1 and 41 percent of Z-methyl-Z-butene.

Example 11 Employing the procedure of Example I, l-methylcyclohexene-l was reacted with thioacetic acid and a 93 percent yield of predominantly the cis isomer was obtained. The resulting mixture was then passed through the hot tube again maintained at 520 C. in which manner a 77 percent yield of olefin product was obtained of which 80 percent was 3-methylcyclohexene-l and 20 percent was l-methyl-l-cyclohexene.

The above examples are presented by way of illustration and other examples -will now be evident to those skilled in the art.

As illustrated by the above examples, the olefins employed are preferably unsymmetrically substituted olefins, especially internal olefins. Generally, such olefins will contain up to and including 30 carbon atoms. Typical examples of such olefins include Z-methyI-Z-butene, 2- methyl-Z-pentene, 2-methyl 2hexene, 3-methyl-2-hexene, 2-methyl-2-octene, Z-methyl octadecene-Z, l-methylcyclohexene-l, l-ethylcyclohexene-l, and the like. Thus, when these or other unsymmetrically substituted olefins are substituted in the above examples, similar results are obtained.

The acids which are employed in the process of this invention are the thioacids. Included in this definition are also th dithioacids. Thus, such compounds are organic compounds in which divalent sulfur has replaced some or all of the oxygen atoms of the carboxyl group. Typical examples of such thioacids include thioacetic acid, thiopropionic acid, thiobutyric acid, thiobenzoic acid, dithioacetic acid, and the like. In general, such thioacids will contain up to about 18 carbon atoms in the hydrocarbon moieties. The alkyl thioacids in which the alkyl groups contain up to and including about 8 carbon atoms are preferred. Accordingly, when the above and other thio and dithio acids are substituted in the above examples, equally satisfactory results are obtained.

The temperature at which the reaction of the thioacid with the olefin is conducted is generally between about 0 to C. For best results and practical operation, it is desirable to maintain the temperature between 20 and 50 C. This reaction is essentially instantaneous and external cooling is employed, if necessary, to maintain the reaction temperature. The pyrolysis of the resulting non- Markownikofi addition product is conducted at temperatures sufiicient to effect the dissociation or pyrolysis and generally above about 350 C. For best results in order to avoid side reactions, it is preferable to conduct the pyrolysis between about 450 to 550 C.

While the above discussion has been concerned primarily with the step-wise addition reaction and subsequent pyrolysis, it is to beunderstood that both operations can be conducted in one step by merely mixing the olefin and acid and then rapidly passing through a hot tube or some suitable means to effect the pyrolysis in essentially simultaneous operations. Generally, however, it has been found more advantageous to employ the stepwise addition and pyrolysis operations.

Although such are not required, various organic solvents can be employed, particularly to effect heat control of the addition reaction. For this purpose, the hydrocarbons, ethers, and amines, especially tertiary amines, are well suited. Typical examples of the hydrocarbons include the hexanes, octanes, nonanes, decanes, benzene, toluene, and the like. Typical examples of the ethers include diethyl ether, dipropyl ether, dibutyl ether, diamyl ether, tetrahydrofuran, dioxane, and the polyethers such as the dimethyl and diethyl ethers of ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. In general, such solvents are preferably inert in the reaction and liquid under the addition reaction conditions. The aforementioned ethers, particularly the polyethers, are especially preferred organic solvents. Other examples of organic solvents which can be employed in the process of this invention will now be evident. Such solvents can be employed in varying amounts as between about 0.01 to 100 parts per part by weight of the olefin.

While not essential, advantage is achieved in faster reaction and higher yields when the process of this invention is conducted in the further presence of free radical catalysts or light, such as ultra-violet light. The organic peroxides are particularly suitable free radical catalysts as, for example, benzoyl peroxide, lauroyl peroxide, stearoyl peroxide, acetyl peroxide, succinoyl peroxide, and the like. When employed, such can be present in minor amount as, for example, 0.001 part per part by weight of the olefin and up to about 0.1 and higher parts by Weight per part by weight of the olefin.

The products produced according to the process of this invention are of considerable utility. By way of example, the terminal olefins such as 3-methylbutene-l and 4- methylpentene-l are admirably suited for polymerization reactions to produce fibers. They can also be added to diborane, particularly in the aforementioned ethers, at room temperature to produce the corresponding organoborane compounds. For example, when diborane is reacted in. the dimethyl ether of diethylene glycol at room temperature with 3-methylbutene-1, tri(3-methylbutyl)- borane is obtained in good yield. The olefins can also be hydrated by known techniques to form the corresponding alcohols. Additionally, they can be oxidized to form the corresponding epoxides by known techniques. These and other uses of the products of this invention will now be evident.

Having thus described the process of this invention, it is not intended that it be limited except as set forth in the following claims.

I claim:

1. The process which comprises reacting an unsymmetrically substituted internal olefin with an organic thioacid and then pyrolyzing the resultant product to form an alpha isomer of said olefin wherein the unsaturation is non-adjacent to the substituted carbon atom.

2. A process for the production of 3-rnethylbutene-1 which comprises reacting 2-methylbutene-2 with thioacetic acid and then subjecting the resulting product to pyrolysis at a temperature between about 450 to 550 C.

3. The process of claim 2. wherein the reaction of 2- methyl butene-2 and thioacetic acid is conducted at about room temperature.

4. The process of claim 2 wherein the reaction of 2- methyl butene-Z and thioacetic acid is conducted at about room temperature and the subsequent pyrolysis is conducted at a temperature of about 520 C.

5. A process for the production of 3-rnethy1 cyclohexene-l which comprises reacting l-methyl cyclohexene-l with thioacetic acid and then subjecting the resultant product to pyrolysis at a temperature of about 520 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,128,971 Snow Sept. 6, 1938 2,425,858 Beach Aug. 19, 1947 OTHER REFERENCES Ipatiefl et al.: Journal of American Chemical Society, 1939, vol. 61, pages 71-74.

Advanced Organic Chemistry (Wheland), published by John Wiley & Sons, Inc., second ed., 1949, (pages 666 and 667 relied on. (Copy in Div. 31.).

Advanced Organic Chemistry (Royals), published by Constable and Company, Ltd., 1956 (page 371 relied on). (Copy in Div. 31.)

Claims (1)

1. THE PROCESS WHICH COMPRISES REACTING AN UNSYMMETRICALLY SUBSTITUTED INTERNAL OLEFIN WITH AN ORGANIC THIOACID AND THEN PYROLYZING THE RESULTANT PRODUCT TO FORM AN ALPHA ISOMER OF SAID OLEFIN WHEREIN THE UNSATURATION IS NON-ADJACENT TO THE SUBSTITUTED CARBON ATOM.