US2325194A - Manufacture of organic polysulphides - Google Patents

Description

Patented July 27, 1943 MANUFACTURE OF ORGANIC POLYSULPHIDES John F. Olin and Thomas E. Deger, Grosse lle,

Mich.

assignors to Sharples Chemicals Inc., a corporation of Delaware No Drawing. Application March 6, 1941,

Serial No. 381,972

9 Claims.

The present invention pertains to oxidation of organic compounds having an SM radical, M designating an ammonium or substituted ammonium radical, a metal or hydrogen. The invention was developed primarily as a process for obtaining tetra alkyl thiuram disulphides by oxidation of salts of dialkyl dithiocarbamic acids and it will accordingly be described first with particular reference to that problem.

A fairly satisfactory method of manufacturing compounds of this type has been to oxidize salts of dialkyl dithiocarbamic acids with the aid of ammonium persulphate. An object of the present invention has been to produce these compounds by a more economical process providing excellent yields and conversions, thereby effecting considerable economies as compared to the prior art ammonium persulphate oxidation meth od.

In an article in the Canadian Journal of Research, volume 2, pages 144-52 (1930), Cambron and Whitby have described a process by which a salt of diethyl dithiocarbamic acid is oxidized with a nitrous acid salt at C. by addition of a dilute mineral acid to produce the desired tetra ethyl thiuram disulphide, in accordance with the following equation:

2(C2H5)rNCSSNa+2NaNOz+4HCl Cambron and Whitby discussed this reaction on page 151 of their article, describing an experiment involving treatment of a mixture containing 45 grams of the sodium salt of diethyl dithiocarbamic acid and 18 grams of sodium nitrite in 100 cc. of water with 80 cc. of a hydrochloric acid solution. They noted the fact that the crystallized tetra alkyl thiuram disulphide obtained by this process had a melting point of 71 C. and was a relatively pure product, but made no comment with respect to the conversion or yield obtained in the practice of the process.

Experiments made by the present applicants have demonstrated that neither the yield nor conversion obtained in the practice of the Cambron and Whitby process is sufliciently high to warrant commercial adoption of the process in place of the ammonium persulphate oxidation process discussed above.

The present invention rests upon the discovery that excellent yields and conversions may be obtained in the practice of the process described by Cambron and Whitby provided a lower aliphatic alcohol is maintained in substantial quantity in the reaction mixture during the oxidation reaction, or provided a lower alkyl nitrite is substituted for the sodium nitrite which acts as the oxidizing agent.

In the practice of the present invention. methyl, ethyl, propyl, isopropyl, butyl, or a higher alcohol may be mixed with a nitrous acid salt and the salt of the dialkyl dithiocarbamic acid to be oxidized, and the resulting mixture may be cooled to a temperature between 20 C. and 20 C. while a dilute solution of a mineral acid (e. 8., sulphuric, hydrochloric or phosphoric acid) is gradually added. It is believed that the reaction proceeds through two stages, the nitrous acid salt being first converted into the corresponding alkyl nitrite, and this al yl nitrite thereafter serving as the oxidizing agent, as illustrated by the following equations:

As indicated by the above equations, it is preferable to add an amount of alcohol which is at least a molecular equivalent of the quantity of the compound to be oxidized, although smaller amounts of alcohol may be used, with somewhat less satisfactory results.

The hypothesis that the reaction proceeds through the initial formation of an alkyl nitrite is substantiated by the fact that experiments have been made involving initial production of the alkyl nitrite by reaction of the alcohol with the nitrous acid salt, followed by use of the resulting crude nitrous acid ester-containing reaction' mixture as the oxidizing agent in the above reaction.

While we believe that the reaction proceeds as discussed above, we do not wish to be limited by any theory as to the reasons for the results achieved. It may be that the presence of the alcohol, or of the alkyl radical of the alkyl nitrite, assists in the oxidation function of the nitrous acid radical by reason of the fact that we obtain an intermediate alkyl ester of the alkyl dithiocarbamic acid, and that this alkyl ester is more easily oxidized than the corresponding salts. Regardless of theory, however, and regardless of whether an alcohol is separately added or an alkyl nitrite used, the oxidation reaction mixture will contain both the nitrous acid ester and the aliphatic alcohol after the mineral acid is added.

The following examples provide illustrations of the practice of the invention in the manufacture of tetra-alkyl thiuram disulphides.

Example I To a cooled solution of 180 grams of 50% caustic in 850 cc. water is added 146 grams diethylamine in cc. water. grams carbon disulphide are slowly added with stirring at,4-7 C. After the preparation of the sodium diet'nyl dithiocarbamate solution by the above method,

350 cc. water, 152 grams sodium nitrite and 112 grams methanol are added to the resulting crude reaction mixture. A solution of 495 grams of 37% hydrochloric acid in 400 cc. water is then slowly added with stirring at 27 C. The tetraethyl thiuram disulphide precipitates out as a white powder and may be filtered oif and washed with water. The product requires no further treatment than drying. A yield of 90-95% is obtained of material melting between 68 and 72 0., this material being essentially tetraethyl thiuram disulphide.

Example II To a cooled solution of 180 grams of 50% caustic soda in 600 cc. water is added 361 grams of 25% dimethylamine in 200 cc. water. 160 grams carbon disulphide are slowly added with stirring at 4-7 C. After the preparation of the sodium dimethyl dithiocarbamate by the above method, 400 cc. water, 152 grams sodium nitrite and 112 grams methanol are added. A solution of 495 grams 37% hydrochloric acid in 400 cc. water is slowly added with stirring at 1-7 C. The tetramethyl thiuram disulphide is filtered off, washed with water and dried. It is a white,

crystalline powder, melting between 136 and 138 C. and obtained in 98% yield.

Example III To a cooled solution of 270 grams of 50% caustic soda in 1250 cc. water is added 387 grams dibutylamine. 235.6 grams carbon disulphide are then slowly added with stirring at 49 C. To this sodium dibutyl dithiocarbamate solution is added 224.5 grams sodium nitrite and 160 grams methanol. A solution of 666 grams 37% hydrochloric acid in 500 cc. water is then slowly added at 2-8 C. The tetrabutyl thiuram disulphide separates as a yellow oil which is extracted with naphtha, washed with water and vacuum distilled to remove the naphtha. It is obtained in quantitive yields.

Example IV To a cooled solution of 0.30 gram mol. sodium di-isopropyl dithiocarbamate in 175 cc. water is added 22.1 grams sodium nitrite and 12.8 grams methanol. A solution of 51.8 cc. 37% hydrochloric acid in 48 cc. water is slowly added with stirring at 3-7 C. Th solid tetra isopropyl thiuram disulphide is filtered off and washed with water. 34.2 grams of product melting between 80 and 90 C. is obtained.

Example V To a cooled solution of 0.30 gram mol. sodium diethyl dithiocarbamate in 150 cc. water 3 aMed 22.1' grams sodium nitrite and 19.4 grams ethanol. A solution of 51.8 cc. of 37% hydrochloric acid in 48 cc. water is slowly added with stirring at 4-7 C. The tetraethyl thiuram disulphide is obtained in 95% yield having a melting point between 69 and 72 C.

Example VI The same procedure was followed as in Example V except that 24.1 grams isopropanol were substituted for the ethanol. The tetraethyl thiuram disulphide was obtained in 90% yield and had a melting point between 69 and 70.5 C.

Example VII To 67.5 grams sodium diethyl dithiocarbamate in 250 cc. water is added 22.4 grams sodium nitrite and 16 grams methanol. A solution of 17.6 cc. 95.5% sulphuric acid in cc. water is slowly added with stirring at 48 C. A 92% yield of tetraethyl thiuram disulphide is obtained melting between 68.5 and 71 C.

Example VIII 23 grams carbon disulphide were slowly added with stirring to a cooled solution of 12 grams sodium hydroxide, 22 grams diethylamine and cc. water. To the sodium diethyl dithiocarbamate thus formed were added 22 grams sodium nitrite and 31 grams normal butyl carbinol. A solution of 51.5 cc. 37% hydrochloric acid and 48 cc. water are then slowly added at 1 to 8 over a period of 1.75 hours. The unreacted alcohol and possibly some of the amyl nitrite was removed from the precipitated tetraethyl thiuram disulphide by treatment of the mixture under vacuum with a slow stream of air. The solid was then filtered and washed with water. 18 grams tetraethyl thiuram disulphide of excellent purity were obtained, melting 70-715.

Example IX *solid. 598 grams or 90.4% yield of the thiuram disulphide melting at 54 to 58 are obtained.

While the invention has been described above with reference to the specific problem of oxidizing salts of dialkyl dithiocarbamic acids to produce tetra alkyl thiuram disulphides, it is applicable to the oxidation of all of the many compounds having an SM radical as discussed above, including aliphatic, cycloaliphatic, aromatic and heterocyclic compounds. The following are a few examples of such compozmds:

1. Dithiocarbamic acid salts to produce thiuram disulphides.

2. Xanthates to produce xanthogen disulphides.

3. Mono-, di-, and tri-thiocarbonic acids to produce the corresponding dithiocarbonic acid, di-dithiocarbonic acid and di-tri-thiocarbonic acid, respectively.

4. Mercaptans and mercaptides to produce disulphides.

In the practice of the invention in oxidizing organic acids, such as the thiocarbamic and thiocarbonic acids, we prefer to treat these acids in the form of their alkali metal or ammonium salts, since improved yields are obtained by treating the salts instead of the free acids; i. e., oxidizing the acids in their nascent state as they are liberated from their salts. In oxidation of mercaptans, on the other hand, there is no particular advantage in converting the mercaptans into mercaptides before oxidizing them.

The following example will illustrate the practice of the invention as applied to the oxidation of mercaptobenzothiazole to produce benzothiazyl disulphide, according to the following equation:

2RoH+2Nac1+2No+2mo Ewample X 50.1 grams (0.30 gram mol.) mercaptobenzothiazole, 22.1 grams (0.32 gram mol.) sodium nitrite, 600 cc. water and 19.2 grams (0.60 gram mol.) methanol are charged into a flask equipped with thermometer well, mechanical stirrer and dropping funnel. A solution of 26.8 cc. (0.323 gram mol.) of 37% hydrochloric acid in 100 cc. water is slowly added at 2-5 C. with vigorous stirring. The precipitate which is now benzothiazyl disulphide is filtered off and dried in a current of air at 50-70 C. The yield is practically quantitative.

The following examples also illustrate the practice of the invention as applied to the oxidation of sulphur-containing organic compounds.

Example XI To a cooled solution of 56 grams sodium amyl xanthate (sodium amyl sulphothiocarbonate), 22 grams sodium nitrite and 15 grams ethanol in 200 cc. water were added with stirring a solution of 52 cc. 22 Baum hydrochloric acid in 50 cc. water over a period of 1.5 hours while holding the temperature below 5 C. After reaction the oil layer was extracted with ether, washed with water and dried under vacuum on a water bath. 32 grams amyl xanthogen disulphide were obtained as a deep yellow slightly viscous oil.

Example XII To a stirred, cooled mixture of 37 grams benzyl mercaptan 12 grams sodium hydroxide, 22 grams sodium nitrite, 15 grams ethanol and 200 cc. water was slowly added a solution of 52 cc. 37% hydrochloric acid in 50 cc. water in 1.5 hours at 3 to 7 C. A red oil layer settled out which on slowly warming to 35 was decomposed to benzyl disulphide with the evolution of nitrogen oxides. 35 grams of white, crystalline benzyl disulphide were obtained which melted at 67-68 C.

Example XIII To show that the metallic salt was not necessary in the oxidation of a mercaptan by the alkyl nitrite process the above Example XII was repeated with the exclusion of the sodium hydroxide. About the same results were obtained. 31.5 grams white benzyl disulphide melting 6'7-63 C. were produced.

Somewhat higher temperatures may be employed in the treatment of mercaptans and mercaptides than in the treatment of thio-acids. The temperature range depends on the stability of the compounds treated, higher temperatures being permissible'in treatment of the more stable compounds. In general, we prefer to maintain thio-acids and their salts at temperatures between and +20 C., and mercaptans and mercaptides between 5 and 35 C., during the oxidation reaction.

As indicated by the above examples, we prefer to maintain a considerable quantity of water in the reaction mixture, although the presence of water is not a necessity. The most important advantage of having water present is that the oxidation products of the reaction are usually soluble in water and may therefore be separated as aqueous solutions from undesired lay-products .by simple decantation.

A number of modifications will be evident to those skilled in the art and we do not therefore wish to be limited except by the scope of the following claims.

We claim:

1. In the manufacture of organic polysulphides, the process comprising oxidizing an organic compound containing an SM radical, in which S designates sulphur and M designates a. member chosen from the group consisting of ammonium and substituted ammonium radicals, metals and hydrogen, which comprises mixing said compound with a mineral acid in the presence of an alkyl nitrite.

2. In the manufacture of organic polysulphides, the process comprising oxidizing an organic compound containing an SM radical, in which S designates sulphur and M designates a member chosen from the group consisting of ammonium and substituted ammonium radicals, metals and hydrogen, which comprises mixing said compound with a mineral acid in the presence of a nitrous acid salt and an aliphatic alcohol.

3. In the manufacture of organic polysulphides, the process comprising oxidizing an organic compound chosen from the class consisting of mercaptans and mercaptides by mixing the compound to be oxidized with a mineral acid in the presence of an alkyl nitrite.

4. In the manufacture of organic polysulphides,

the process comprising oxidizing an organic compound chosen from the class consisting of mercaptans and mercaptides by mixing the compound to be oxidized with a mineral acid in the presence of a nitrous acid salt and an aliphatic alcohol.

5. In the manufacture of organic polysulphides, the process comprising oxidizing an organic compound chosen from the class consisting of organic thio-acids and salts thereof by mixing the compound to be oxidized with a mineral acid in the presence of an alkyl nitrite.

6. In the manufacture of organic polysulphides, the process comprising oxidizing an organic compound chosen from the class consisting of organic thio-acids and salts thereof by mixing the compound to be oxidized with a mineral acid in the presence of a nitrous acid salt and an aliphatic alcohol.

7. A process as defined in claim 3 in which the temperature of the reaction mixture is maintained between 5 and 35 C. during the oxidation reaction.

8. A process as defined in claim 5 in-which the temperature of the reaction mixture is maintained between 20 C. and -20 C. during the oxidation reaction.

9. A process as defined in claim 1, in which water is also maintained in the reaction mixture.

JOHN F. OLIN. THOMAS E. DEGER.