3,376,313 United States Patent Office Patented Apr. 2, 1968 2 which is employed. The organic radicals of the (SFO) 3,376,313 PROCESS OF PREPARNG ORGANC containing organic compound do not become part of the DSULFDES FROM THOLS disulfide produced in the reaction. Therefore, a wide Thomas J. Wa:Eace, Elizabeth, N.J., assignor to Esso variety of organic compounds containing an (SFO) Research and Engineering Company, a corporation of moiety can be used. Suitable exemplary classes of (SFO) Delaware containing organic compounds which can be employed No Drawing. Filed Nov. 15, 1963, Ser. No. 323,897 include, but are not limited to, the following: organic 19 Claims. (C. 260-327) Sulfoxides; organic sulfones; organic disulfoxides; organic sulfinates; organic thiosulfinates; etc. The following 30 (SFO) containing organic compounds can be listed as ABSTRACT OF THE DISCLOSURE exemplary of those suitable for use in accordance with Organic sulfides are prepared by reacting an organic this invention: phenyl methyl sulfoxide; tetramethylene thiol with an organic compound containing the (SFO) sulfoxide; dimethyl sulfoxide; diethyl sulfoxide; di-n- moiety, the mole ratio of thiol to SFO containing com propyl sulfoxide; cyclohexyl methyl sulfoxide; di-iso 5 propyl sulfoxide; di-n-butyl sulfoxide; benzyl methyl sul pound being about 1:1 when it is desired to form cyclic foxide; dibenzylsulfoxide; phenyl methyl sulfone; dibenz disulfides and about 2:1 when it is desired to form acyclic yl sulfone; tetramethylene sulfone; dimethyl sulfone; di disulfides. The organic disulfides produced are useful as ethyl sulfone; di-n-propyl sulfone; di-iso-propyl sulfone; additives in cosmetic products and depilatory creams. di-n-butyl sulfone; cyclohexyl methyl sulfone; dimethyl -mastessurasam 20 disulfoxide; diethyl disulfoxide; dimethyl sulfinate; dieth This invention is directed to a novel process of prepar yl sulfinate; methyl ethyl sulfinate; dimethyl thiosulfinate; ing organic disulfides which comprises contacting an or diethyl thiosulfinate; methyl ethyl thiosulfinate; etc. ganic thiol with an organic compound containing the It has been discovered that while any organic (S=O) (S=O) moiety. The reactions contemplated herein are containing compound, especially any of the classes of usually conducted in essentially inert atmospheres and compounds listed hereinabove, can be used to selectively preferably in the absence of extraneous oxygen. oxidize the organic thiols to their corresponding organic According to a preferred embodiment of this invention, disulfides, all such (S=O) containing organic compounds the organic thiol and the organic (SFO) containing com are not equally effective in this regard. Preferably, an pounds are reacted in the presence of an organic amine, organic (SFO) containing compound is employed which preferably a primary, secondary or tertiary aliphatic has two organic groups joined to the same sulfur atom amine having from 4 to 12 carbon atoms. The use of an which is doubly bonded to an oxygen atom, viz., the or amine catalyst, especially C4 to C12 aliphatic amines, ganic Sulfoxides and sulfones. Of the organic sulfoxides lowers the temperature of reaction, increases the yield of and sulfones, it has been discovered that those having and selectivity to the disulfide, and greatly increases the both of the organic substituents as aliphatic substituents rate of reaction anywhere from approximately 80 to ap 3 5 yield the best results in preferentially oxidizing the organic proximately 250-fold, and even higher. Acid catalysts, thiols to their corresponding disulfides. The order of as e.g.,acetic acid and other organic acids also have a cata cending selectivity of the organic sulfoxides and sulfones lytic effect, but much less than that of the aliphatic in terms of their comparative ability to preferentially oxi amines. dize organic thiols to their corresponding disulfides is as The temperatures of reaction can range from room tem 40 follows: diaryl, alkyl-aryl, diaralkyl and dialkyl, with di perature or even below up to about 140 C. and even alkyl sulfoxides and sulfones being the most selective and higher. diaryl sulfoxides and sulfones being the least selective on Usually when preparing aromatic disulfides in accord a comparative basis. ance with this invention, the reaction temperatures range Consequently, insofar as obtaining selective oxidation from about room temperature to about 60° C., and from 45 of the organic thiols to their corresponding organic di about 90 to 150° C. when preparing aliphatic disulfides. sulfides is concerned, the preferred organic sulfoxides are When amine catalysts are employed, reaction tempera those having the formula: tures usually range from about 40 to 70° C. for pre O paring aliphatic disulfides from aliphatic thiols. The re actions are conducted at atmospheric pressure in closed 50 R--R system reactor vessels so that the pressures developed wherein R is selected from the group consisting of alkyl, during reaction are the autogenous reaction pressures aralkyl and alkaryl. caused by the reactants, themselves. Suitable preferred organic sulfoxides and sulfones The preparation of organic disulfides according to this which can be listed as exemplary of those included by invention can be performed at acid, neutral or basic pH the above formula: dimethyl sulfoxide; diethyl sulfoxide; with or without solvents, which can be either organic or tetramethylene sulfoxide; cyclohexyl methyl sulfoxide; di inorganic. Of course, when a solvent is employed, an inert benzyl sulfoxide; benzyl methyl sulfoxide; diisopropyl solvent should be used, viz., one which does not interfere sulfoxide; di-n-butyl sulfoxide; dimethyl sulfone; tetra with the oxidation of thiols to disulfides. Examples of methylene sulfone; cyclohexyl methyl sulfone; dibenzyl suitable inert solvents are toluene, Xylene, cetane, dimeth 60 sulfone; etc. ylformamide, sulfur dioxide, etc. Usually the disulfide When it is desired to form linear (acyclic) disulfides, synthesis is conducted at a pH ranging from about 4 to organic monothiols are reacted with a suitable (SFO) 14. The employment of an aliphatic amine catalyst usual organic compound, e.g., an organic sulfoxide, employing ly results in a basic pH during reaction. approximately a 2:1 mole ratio of organic monothiol to Both linear and cyclic disulfides can be prepared in 65 organic sulfoxide. The reaction stoichiometry is shown accordance with the process of this invention. The present in Equation 1 below: invention is based upon the discovery that organic com Equation 1 pounds containing the (SFO) moiety selectively oxidize organic thiols (organic mercaptans) to their correspond In essence the organic monothiol is oxidized to the cor ing disulfides. The specific organic disulfide produced is 70 responding organic disulfide, and the organic sulfoxide is independent of the (SFO) containing organic compound reduced to the corresponding monosulfide with the elimi 3,376,313 4. 3 It has been discovered that the preparation of organic nation of water. Of course, a mixed organic disulfide can disulfides in accordance with this invention is general both be prepared readily by employing a mixture of organic insofar as the organic thiol and the organic (SFO) con monothiols, but the mole ratio of organic thiol to organic pounds are concerned. Thus, in the preparation of acyclic (SFO) containing compound is still maintained at 2:1. organic disulfides in accordance with this invention, the The production of a mixed organic disulfide, viz., one organic monothiol can be alkyl or mixed alkyl; aryl or having different organic R groups is illustrated in Equa mixed aryl; alkaryl or mixed alkaryl; aralkyl or mixed tion 2 below. aralkyl; alkylaryl; alkyl-alkaryl; alkyl-araikyl; aryl Equation 2 alkaryl; aryl-aralkyl; and alkaryl-alkyl. R-SH -- R'SO - R-S-S-R -- R'S -- HO Suitable organic dithiols which can be employed in the R-SE 10 practice of this invention to produce cyclic organic di sulfides by (S=O) selective oxidation include those in As noted from Equation 2, the mixed disulfide produced the following exemplary classes of organic dithiols: alkyl has two different organic groups, R1 and R. dithiols; esp. C. to Ca alkyl dithiols; alkyl trithiols; aryl Moreover, the organic (SFO) containing compound dithiols; alkaryl dithiols and aralkyl dithiols wherein the can have a plurality of different organic radicals. For alkyl moiety has at least two carbon atoms. Of course, in example, a mixed organic sulfoxide can be used to oxidize cases where the alkyl moiety has more than two carbon either a single organic monothiol, a mixture of organic atoms, e.g., three or four carbon atoms or more, a trithiol, monothiols or an organic dithiol. Equation 3 below illus tetrathiol, etc. can be used in place of the dithiol. Further, trates the products obtained by reaction of a mixed or it is also clear that polymeric dithiols can be oxidized by ganic sulfoxide with a mixture of different organic mono 20 this technique provided that a suitable molar ratio of thiols. sulfoxide to thiol group is employed, viz., one (SFO) Equation 3 group per two (SH) groups. Ri-SH. R. The alkyl groups of the organic thiols can be substi tuted or unsubstituted C, to Cao aliphatic alkyls, espe -- DS-o - R-S-S-R -- R-S-R' + H2O cially C to C aliphatic alkyls. The aryl group (or R-SI R' groups) of the organic thiols can be substituted or uri substituted, homo or heterocyclic rings containing at least When the present invention is employed to produce one benzene ring with monocyclic or polycyclic, especially cyclic disulfides, an organic dithiol is reacted with an mono- and di-benzene rings containing, aryl groups. The (SFO) containing organic compound, e.g., an organic alkaryl and aralkyl groups of the organic thiols can be Sulfoxide, employing approximately a 1:1 mole ratio of substituted or unsubstituted groups having combinations dithiol to sulfoxide. Equation 4 below, stoichiometrically of the alkyl and aryl groups set forth hereinabove. illustrates the preparation of a cyclic disulfide in accord The following organic thiols can be listed as exemplary : ance with this invention. organic thiols for use in accordance with this invention: 3 1-hexadecanethiol; 1-dodecanethiol; 1-octadecanethiol; a Equation 4 toluenethiol, 4-methyl-benzenethiol; 2 - napthalenethiol; SH R S benzenethiol; 2 - methylbenzenethiol; 1,4-butanedithiol; R -- Ss O - R -- R'-S-R'' - HO 1,3-propanedithiol; 1,2-ethanedithiol; 1,8 - octanedithiol; / N 2 40 2 - dodecanethiol: 4 - hexadecanethiol; cyclohexanethiol; S R S 1,1-di-n-butyl- 1 - butanethiol; 2 - pyridinethiol; 2 - thio phenethiol; diphenylmethanethol; a,c-orthoxylenedithiol. Accordingly, from the foregoing it can be seen that, The organic thiol can be a substituted organic thiol. in one embodiment, the present invention has provided Suitable substituents which can be present on the organic a process for preparing organic disulfides which comprises thiol include: amino groups; hydroxyl groups; carboxyl reacting at least one organic monothiol with an organic . 5 groups; halogens, e.g., chloro, bromo, iodo and fluoro; Sul Sulfoxide at a temperature of from about 25° C. to about fur groups; nitro groups; acetamido groups; amido groups; 150° C. and a pH of from about 4 to 14, the mole ratio acyl groups; etc. Suitable exemplary substituted organic of monothiol to sulfoxide being about 2:1. thiols which can be employed to form the corresponding videdIn anothera process embodiment, for preparing the present organic invention disulfides has which pro substituted organic disulfides include, but are not limited comprises contacting at least one organic monothiol with to, the following: 4-chloro-benzenethiol: 4-nitrobenzene an organic sulfoxide and a catalytic amount of an organic thiol; 2-carboxybenzenethiol: 4-bromo-2-napthalenethiol, amine at a temperature of from about 25° C. to about panethiol;2-amino-benzenethiol; 3-chloro-1-propanethiol: thiolacetic acid; 3-nitro-1-propanethiol; 3 -amino - 1 - pro 150 C. and a pH of from about 4 to 14, the mole ratio of monothiol to sulfoxide being about 2:1. 5 5 etc. In a further embodiment, the present invention has As mentioned hereinabove, it is preferable to employ an provided a process for preparing acyclic organic disulfides organic amine catalyst when producing organic disulfides which comprises contacting at least one organic mono in accordance with this invention. The use of an organic thiol with an organic sulfoxide and a catalytic amount amine catalyst is especially preferred when preparing ali of an organic amine at a temperature of from about 25° 60 phatic disulfides, whether acyclic or cyclic, from aliphatic C. to about 150° C. and a pH of from about 4 to 14, thiols and dithiols. The organic amine catalyst can be a the mole ratio of monothiol to sulfoxide being about 2:1. primary, secondary or tertiary amine having one, two or In still another embodiment, the present invention has three organic groups which can be substituted or unsub provided a process for preparing cyclic organic disulfides stituted. Aliphatic amines, especially C-C aliphatic which comprises reacting an organic dithiol with an or amines, constitute the preferred class of organic amine. ganic sulfoxide at a temperature of from about 25° C. catalysts for use in accordance with this invention. Suit to about 150° C. and a pH of about 4 to 14, the mole able exemplary Ca-C12 aliphatic containing amines in ratio of said dithiol to sulfoxide being about 1:1. clude: n-dodecylamine, tri-n-butylamine; di-n-butylamine; In yet another embodiment, the present invention has tri-n-hexylamine; benzyl-dimethylamine. Other less pref provided a process for preparing cyclic organic disulfides 70 erable organic amine catalysts include, but are not limited which comprises contacting an organic dithiol with an to, the following: 2,6-lutidine, pyridine, N,N-dimethyl organic Sulfoxide and a catalytic amount of an organic aniline, diphenylamine, benzylamine etc. The ratio of or-. amine at a temperature of from about 25° C. to about ganic amine catalyst to organic thiol should be sufficient 150 C. and a pH of about 4 to 14, the mole ratio of to result in from about 2 to about 40 mole percent or said dithiol to sulfoxide being about 1:1. 75 ganic amine catalyst based on organic thiol. Usually, 3,376,313 5 6 however, the mole percent of amine catalyst based on or ganic thiol should range from about 4 to 30%, and pref Example 1-Preparation of a typical acyclic disulfide erably 5 to 15%, especially when C-C12 aliphatic amines without catalyst are employed as catalysts. Bis (n-dodecyl) disulfide was prepared by reacting 0.2 Acids also have a catalytic effect on the disulfide syn mole of 1-dodecanethiol and 0.1 mole of dimethyl sulfox thesis performed according to this invention. However, 5 ide for 19 hours at 160° C. in a nitrogen atmosphere in the catalytic effect obtained by acids is mild compared to a glass reactor vessel at atmospheric pressure. The yield that secured with aliphatic amines. Suitable organic acids of bis (n-dodecyl) disulfide was 72 percent based on which can be listed as exemplary are: acetic acid; pro 1-dodecanethiol. pionic acid; butyric acid; valeric acid; benzoic acid; ben Example 2-Preparation of a typical acyclic disulfide zene sulfonic acid; 1-butane sulfonic acid; etc. O It is preferable to employ an organic (SFO) containing using various organic amines as catalysts compound whose end product (reduction product) has a Bis (n-dodecyl) disulfide was prepared by reacting 0.1 lower boiling point than that of the organic disulfide pro mole of 1-dodecanethiol and 0.2 mole of tetramethylene duced. For example, when an organic sulfoxide is em Sulfoxide at 100° C. in a nitrogen atmosphere in a glass ployed as the organic (SFO) containing compound, it is reactor vessel at atmospheric pressure using ten mole per greatly preferred to use an organic sulfoxide whose mono cent amine catalyst based on thiol in the various runs. sulfide has a much lower boiling point than the organic di The pseudo first order rate constants (k, sec.) and rel sulfide prepared. When this process condition is observed ative reaction rates for the various catalysts are tabulated and the organic thiol is an aliphatic thiol and the catalyst hereinbelow. is a C-C12 aliphatic amine; the organic disulfide synthesis 20 constitutes a highly desirable cyclic, catalytic process. That is to say that when the preferred class of reaction products Amine First order rate Relative Rate are used, the only regeneration required (except for the (k, sec.-)

None------8.00x10-0 ... O addition of more organic thiol) is the regeneration of the 25 N,N-dimethylaniline.------1.15X10-5 1.4 organic (SFO) containing compound. For example, when 2,6-lutidine------1.64x10-5 2.1 the organic thiol is 1-dodecanethiol and the organic 1-dodecylamine--- - - 6.42XO- 80.2 (S=O) containing compound is dimethyl sulfoxide and Tri-n-butylamine------2.04x10-3 258.0 the organic amine catalyst is 1-dodecylamine; the Sulf oxide reduction product is dimethylsulfide (B.P. 34° C.) 30 which has a much lower boiling point than the organic As will be observed from the above rate data, aliphatic disulfide, viz., bis(n-dodecyl) disulfide (M.P. 32° C.). amines are the most active catalyst under these pseudo Consequently, the monosulfide (reduced sulfoxide) is dis first order reaction conditions. tilled off from the reaction leaving the product and wa ter remaining in the reactor vessel. The removed dimethyl Example 3.--Preparation of a typical acyclic disulfide sulfide can then be cycled to a regeneration step wherein at various temperatures with and without an aliphatic it is converted from dimethyl sulfide back to dimethyl amine catalyst sulfoxide by oxidation employing a suitable oxidizing Bis (n-dodecyl) disulfide was prepared by reacting 0.1 agent, e.g. NO2 or a metal oxide, e.g. manganese dioxide, mole of 1-dodecanethiol and 0.2 mole of tetramethylene chromic oxide, etc. The regenerated dimethyl sulfoxide 40 sulfoxide at the temperatures listed below in a nitrogen can then be recycled back to the reactor. When the or atmosphere using a glass reactor vessel and atmospheric ganic disulfide is continuously removed as a product pressure. 1-dodecylamine was the aliphatic amine used, stream, new organic thiol can be continuously charged to and the mole percent of aliphatic amine based on thiol the reactor. The organic amine catalyst is essentially a was 10 percent. The various reaction temperatures and true catalyst since the initial amount of organic amine the corresponding reaction rates at these temperatures, catalyst added does not decrease substantially regardless with and without catalyst, are tabulated hereinbelow. It of the length of time over which it is used. Therefore, the should be noted that excess sulfoxide was employed to only additional materials added are the organic thiol and simplify the kinetic measurements, i.e., pseudo first order the regenerated organic (SFO) containing compound. reaction conditions were used. Hence, according to this preferred embodiment of the in vention, the organic disulfide synthesis is truly a cyclic, catalytic process. Temperature First Order Relative Reaction As mentioned previously, the reactions contemplated . Catalyst (° C.) Rates (k, sec.-) Rates herein are usually conducted in essentially inert atmos 00 7.58X10-6 1.0 100 6.42X10-4 r84 pheres especially when forming aliphatic disulfides from 75 3.88X10-8 .0 aliphatic thiols. Preferably, the disulfide synthesis is con 75 2.18x10-4 ru60 ducted essentially in the absence of molecular oxygen, 55 8.63X10-7 ... 0 e.g. gaseous oxygen, air (which contains gaseous oxygen), 55 6,39X10-5 -73 as the presence of such extraneous oxygen during reac tion (1) reduces the selectivity and rate at which organic 60 thiols are oxidized to disulfides and (2) poisons the As noted from the above table, the use of an aliphatic amine catalyst. Hence, the selective oxidation of aliphatic amine catalyst allows the attainment of excellent reaction thiols to their disulfides is preferably conducted in essen rates at lower temperatures than possible when no catalyst tially inert atmospheres, viz., atmospheres containing little is used. Thus the use of an aliphatic amine catalyst results or no extraneous oxygen, e.g. nitrogen, argon, helium, etc. in a more economic synthesis of organic disulfides since In addition to the preparation of organic disulfides, less heat is required. this invention can be used to sweeten petroleum fractions, esp. gasoline fractions, containing reactive aromatic thiols. Example 4-Preparation of a typical acyclic disulfide The present invention will be understood in greater using a typical acid catalyst detail by the examples which follow. However, it should 70 Bis (benzyl) disulfide was prepared by reacting 0.1 be understood that the present invention in its broadest mole of ox-toluenethiol and 0.2 mole of tetramethylene aspects is not necessarily limited to the specific organic sulfoxide at 100° C. in a nitrogen atmosphere at atmos thiols, organic (SFO) containing compounds, catalysts, pheric pressure in a glass reactor vessel using varying reaction temperatures and times as shown in the examples amounts of acetic acid as a catalyst. The mole ratio of below. 5 acid catalyst to thiol and the corresponding first order 3,376,313 7 8 iratA.estants for the variouss reactionsd are tabulated here Example 6-Preparation of typicalo cyclic disulfides The below indicated cyclic disulfides were prepared by Acid Catalyst/thiol First Order Rate reacting the given mole amounts of organic dithiols with (mole ratio) (kX10, sec.-) 5 the given amounts of the below indicated organic sul 8 10 3. foxides at the reaction temperatures listed. All syntheses 5.16 5. were conducted at atmospheric pressure in a nitrogen at 3. f mosphere using glass reactor vessels. The pertinent yields ------and other data are tabulated hereinbelow. The listed cyclic The above data establishes that acetic acid is a mild to disulfide yields are based on initial quantities of the or catalyst in the preparation of organic disulfides to this ganic dithiol.

Reaction Cyclic Organic Moles of Organic Moles of Reaction Time Disulfide Yield Dithiol Dithiol Sulfoxide Sulfoxide Temp. (C.) (hrs.) Produced (percent) 1,4-butane.------0. Dimethyl sulfoxide------0. 130 18 1,2-dithia cyclohexane---- 68 Do----- 0.1 Tetramethylene sulfoxide.------0. 125 71 ----- do------89 1,3-propane------0.1 ----- do------0.1. 125 17 1,2-dithiacyclopentane.-- 75

invention. Apparently acids catalyze by protonation of The cyclic disulfides produced are known, and their sulfoxide oxygen whereas amines catalyze by increasing presence was verified by melting point and boiling point the amount of RS' available for attack on the Sulfur determinations and by gas chromatographic comparison atom. Of course, the important fact is that both acids 25 to authentic samples. it. it. gitive catalytic effects regardless of the Example 7-Preparation of typical disulfides in inert eory of catalySIS. solvent medium

O Percent Organic Thiol MolesThiol of Sulfoxide (noles) Solventcentimeters) (cubic Terpgrature(° C.) Time(hrs.) DisulfideYield O-Toluene.------0031 Dimethyl (.0031).------. Toluene (20)------100 72 50 DO.------.003 -----do------Cetane (20)--- 100 70 72 1-dodecane------0063 Dimethyl (.0032).------Toluene (20)------00 67 96 cy-Toluene. ------.0068 ----- do------Dimethyl formanide (20)------100 68 60

Example 5-Preparation of various typical acyclic disul E.E.E.E.ganic monothiols and various preparedBis (tolyl) by reactingdisulfide the and appropriate bis (n-dodecyl) thiol withdisulfide dimethyl were The below indicated organic disulfides were prepared sulfoxide in the presence of the various solvents listed by reacting their corresponding monothiols with the vari- above. The reactions were performed in glass reactors by ous organic sulfoxides or sulfones noted below in the dissolving the dimethyl sulfoxide in the solvent and then mole amounts, set forth below in the table. The appropri- adding the thiol thereto. The respective reaction tempera ate reaction temperatures, times and yields (based on 45 tures, times and obtained yields of disulfides are tabulated thiol) are listed; and all syntheses were conducted in a hereinabove. The above data clearly demonstrate the nitrogen atmosphere at atmospheric pressure in closed feasibility of preparing both aliphatic and aromatic di glass reactor vessels. sulfides in inert organic solvent medium.

Moles of Moles of Reaction Reaction Organic disulfide Yield a Organic Monothiol Monothioi Organic Sulfoxide or Sulfone orSulfoxide Sulfone Temp. (C.) (hrs.)time Produced (Percent).2, 2 b 1-hexadecane------.05 Dimethyl Sulfoxide------.025 , 150 12 Bis (n-hexadecyl)------82 Do------. .25 Diisopropylsulfoxide 125 50 4 -----do------36 Do-- - .25 Di-n-butyl sulfoxide------.25 50 5 -----do--- 20 Do.---- .25 Tetramethylene sulfoxide. ..125 150 4 -----do------52 1-dodecane- - . . .05 Dimethylsulfoxide------.025 50 9 Bis (n-dodecyl)------72 D0------.00625 Tetramethylene sulfoxide. - .0032 100 17.5 ----- do------100 1-octadecane--- - .05 Dinnethylsulfoxide-...----- 025 150 7 Bis (n-octadecyl)- - 72 oz-Toluene.------.05 -----do------.025 50 3.5 Bis (benzyl)------52 Do-- - 0.063 Tetramethylene sulfoxide.-- 0.032 100 21 -----do----- 100 Do.------. 0.063 Methyl phenylsulfoxide- .0032 100 44 70 4-methylbenzene.----- .05 Dimethylsulfoxide.------.025 150 19 82 2-methylbenzene .0063 Tetramethylene sulfoxide- .0032 100 20 00 Benzene. 125 Dimethylsulfoxide.---- ... 625 50 5 70 DO--- 0028 Tetramethylene sulfoxid .004 25 20 00 Do.-- 0.0625 Tetramethylene sulfone .25 00 34 - 65 2-naphthalene.--4-chlorob .05.025 -----Dimethylsulfoxide---do------.025.0125 15050 76 Bis(2-naphthalienyl).------.- e 68 Bis(2-naphthyl)-- 98 O-Toluene.------.00625 Tetramethylene sulfone------.0125 100 22 Bis-(benzyl)------35 a Based on the total initial moles of thiol employed. bn all cases the reaction is 100% selective to the disulfide. The above disulfides are all known disulfides whose Example 8.-Effect of sulfoxide structure on rate of oxida presence was verified by their respective melting points 70 tion-no catalyst inand the boiling literature. points, The all above of which disulfide are knownsyntheses and all available involve Bis (tolyl) disulfide was prepared by reacting .0063 the use of organic sulfoxides or sulfones whose reduction mole of a-toluene thiol with .0125 mole of various organic products (monosulfides or sulfoxides, respectively) have a sulfoxides at 100° C. in nitrogen atmosphere using glass lower boiling point than the disulfide prepared. 75 reactor vessels and atmospheric pressure. The varying 3,376,313 10 rates of Oxidation obtained using the varied types of 2. A process according to claim 1 wherein said sulf sulfoxides are listed hereinbelow. Oxide is of the formula: Organic Sulfoxide Type Rate of Oxida- Compara tion (k, sec.) tive Rate O Dimethylsulfoxide----- Alkyl------4. 10x10-5 33.3 R-S-R. Phenyl methylsulfoxide. Alkyl-aryl----- 7.76X10-8 6.3 Diphenylsulfoxide------Aryl------1.23X10-6 1.0 where R is selected from the group consisting of alkyl, The above tabulated data are typical and illustrate the aralkyl and alkaryl. comparative superiority of alkyl sulfoxides to alkyl-aryl 3. A process for preparing organic disulfides which sulfoxides and aryl sulfoxides in their ability to oxidize O comprises contacting at least one organic monothiol with thiols at a rapid rate. an organic sulfoxide and a catalytic amount of an organic amine at a temperature of from about 25 C. to about Example 9.-Comparative ease of uncatalyzed oxidation 150 C. and a pH of from about 4 to 14, the mole ratio of various types of organic thiols of monothiol to sulfoxide being about 2:1. The below indicated disulfides were prepared by react 4. A process for preparing acrylic organic disulfides ing their corresponding thiols with tetramethylene sul which comprises contacting at least one organic monothiol foxide at 55 C. in nitrogen atmosphere in glass reactor with an organic sulfoxide and a catalytic amount of an vessels. The respective rate of oxidation (k, sec.), energy organic amine at a temperature of from about 25 C. to of activation (Ea, kcal./mole) and other pertinent in about 150° C. and a pH of from about 4 to 14, the mole formation are tabulated hereinbelow. 20 ratio of monothiol to sulfoxide being about 2:1.

Thiol Type of Disulfide Oxidation Rate Activation Energy, Thiol, pKa Disulfide Produced (k, sec.-) Ea (kcal.fmole) Benzene thiol------Aryl.-- 1.73X10-2 4.9 6-7 Bis (benzene) disulfide. o-Toluene thiol (2-methylbenzene) thiol---- Alkary 2.65X10-3 6.2 7-8 Bis (o-toluene) disulfide. ov-Toluene thiol (phenyl methane thiol) Araikyl 2,50X10-5 13.7 10- Bis (o-toluene) disulfide. 1-dodecane thiol------Alkyl---- 8.63x10-7 19.4 13-14 Bis (l-dodecy) disulfide.

As will be noted from the above data, the aryl and 5. A process according to claim 4 wherein said sulf alkaryl thiols oxidize at a much faster rate than the alkyl oxide is a compound of the formula: thiol with the comparative decreasing oxidation rate order being: aryl thiols, alkaryl thiols, aralkyl thiols and alkyl 35 thiols. These data are typical for the above listed types of organic thiols when selectively oxidized with an organic where R is selected from the group consisting of alkyl, (SFO) containing compound; and aryl and alkaryl thiols aralkyl and alkaryl. are usually oxidized at a rate of 103 times faster or more 6. A process for preparing cyclic organic disulfides than alkyl thiols when organic sulfoxides are employed 40 to effect oxidation to the corresponding disulfides. For this which comprises reacting an organic dithiol with an or reason, the use of an aliphatic amine catalyst can usually ganic sulfoxide at a temperature of from about 25 C. to be dispensed with in the case of aryl and alkaryl thiol about 150° C. and a pH of from about 4 to 14, the mole oxidations. This example also stresses the point that even ratio of dithiol to sulfoxide being about 1:1. when aliphatic thiols are present, the selective oxidation 7. A process according to claim 6 wherein said sulf of aromatic thiols to their disulfides may well proceed oxide is a compound of the formula: preferentially compared to the selective oxidation of ali phatic thiols to their disulfides. In other words while both aromatic and aliphatic thiols are selectively oxidized to their disulfides by uses of this invention, the uncatalyzed where R is selected from the group consisting of alkyl, rate of oxidation of the former is so much faster than that 50 aralkyl and alkaryl. of the latter that for all practical purposes when no amine 8. A process for preparing cyclic organic disulfides catalysts are present in the reaction almost all of the which comprises contacting an organic dithiol with an or aromatic thiols present will be oxidized before any sub ganic Sulfoxide and a catalytic amount of an organic stantial oxidation of aliphatic thiols occurs. This discovery amine at a temperature of from about 25° C. to about is put to use in selectively sweetening gasoline petroleum 55 150° C. and a pH of from about 4 to 14, the mole ratio fractions where oxidation of aromatic thiols is not really of dithiol to sulfoxide being about 1:1. objectionable (due to the reasonably inert nature of aro 9. A process according to claim wherein the reduc matic disulfides) but oxidation of aliphatic thiols is con tion product of said sulfoxide has a lower boiling point sidered objectionable since aliphatic disulfides are more than that of said disulfide. reactive and lead to the formation of objectionable color 60 10. A process according to claim 1 wherein said re producing compounds and insoluble residues (sludge). action is conducted essentially in the absence of extraneous The organic disulfides produced according to the proc OXygen. ess of this invention are useful as additives in cosmetic 11. A process according to claim 4 wherein said amine products and depilatory creams. is an aliphatic amine. While the foregoing examples have illustrated this in 65 12. A process according to claim 11 wherein said vention in great detail, it should be realized that the present aliphatic amine is a C4 to Caliphatic amine. invention in its broadest aspects is not necessarily limited 13. A process according to claim 4 wherein said mono to the specific materials, temperatures, contact times, etc., thiol is selected from the group consisting of aryl mono as set forth therein. thiols, aralkyl monothiols, aliphatic monothiols, and mix What is claimed is: 70 tures thereof. 1. A process for preparing organic disulfides which 14. A process according to claim 6 wherein said thiol comprises reacting at least one organic monothiol with an is selected from the group consisting of aryl dithiols, organic sulfoxide at a temperature of from about 25 C. aralkyl dithiols, aliphatic dithiols, and mixtures thereof. to about 150° C. and a pH of from about 4 to 14, the mole 15. A process according to claim 6 wherein said amine ratio of monothiol to sulfoxide being about 2:1. 75 is an aliphatic amine. 3,376,313 16. A process scorin. claim 1 wherein said thiol re. Cited EE"E"E.thereof. y 2,893,952. UNITED7/1959. STATESChenicek PATENTS------208-204 17. A process according to claim 2 wherein said sulf- 5 3,052,626 9/1962 Ferrara. ------208-204 oxide is selected from the group consisting of dimethyl 3,130,149 4/1964 Hoover ------208-204 sulfoxide and tetramethylene sulfoxide. 3,213,155 10/1965 Schriesheim et al. -- 208-204 oxide18. isA selectedprocess accordingfrom the togroup claim consisting 4 wherein of saiddimethyl sulf- DELBERT E. GANTZ, Primaryo Examiner. sulfoxide19. A processand tetramethylene according to sulfoxide. claim 6 wherein said sulf- 10 R. H. SHUBERT, G.J. CRASANAS. t Examiners, oxide is selected from the group consisting of dimethyl SSSF eS. sulfoxide and tetramethylene sulfoxide.