IL34281A - Preparation of primary aliphatic mercaptans - Google Patents

Description

34281/2 o**:nvm O»BB»V« o»3B»pno man Preparation of primary aliphatic mercaptana TAUFFER CHEMICAL COMPANY 34281 2 i This invention relates to the process of preparing primary aliphatic mercaptans by reacting hydrogen sulfide with an optionally substituted 0 cc-olefln. Specifically, i relates to the use of trlvaler$ organic phosphorus compounds as promoters in the reaction of hydrogen sulfide with an (x-olefin in the presence of a free radical initiating compound.

The reaction of hydroge sulfide with hydrocarbons containing an olefinlo linkage Is well known in the art. The process is generally characterized by incomplete conversio and low yields of the desired mercaptans. Even though the free radical initiated reaction of hydrogen sulfide with a-olefins produces useful primary mercaptans directly, the poor yields and the production of byr-products such as sulfides and disulfides, have been such that manufacturers have resorted to indirect synthesis routes, for example the synthesis of primary mercaptans from chlorinated hydrocarbons, Various catalyst systems have been employed in the free radical reaction to increase the yields o the desired mercaptans. Free-radical initiating compounds such as organic zo compounds, organic peroxides and organic percarbonates have been used by themselves and together with various promoters ,< such as water and nickel, to increase the conversion of the olefin and the yield of mercaptan.

However , such systems require high temperatures and high catalyst levels and they still leave a large amount of the olefin unconverted.

Actinic light has been employed in the addition of hydrogen sulfide to an olefin. However, this process requires equipment which is expensive, difficult to make and maintain, and the conversions of the olefin are still relatively low when compared to the process of the present invention. Various promoters such as water and organic sulfide have been used to raise the conversion level in the photolytic reaction, but it still does not approach a quantitative conversion. Trialkyl phosphites have been used as a promoter with actinic light but as the conversion of olefin is raised, using progressively longer irradiation times, the mercaptan to sulfide ratio goes down. Thus, although the conversion of olefin is increased, relatively poor yields of mercaptan are still obtained. Further, the reaction times are much shorter and the catalyst levels a much lower in the present invention the-n they are in the photolytic process .

It has now been discovered that quantitative conversions of olefin and greatly increased yields of mercaptan can be obtained by carrying out the reaction of hydrogen sulfide and an eeee¾fc4a-3rlry-^^:_*ee€H?te^ -l-eaei"0«e olefinlro- l-jrftkage ,in the presence of a free radical initiating compound and a promoter consisting of a trivalent organic phosphorus compound. the primary aliphatic mercaptans produced by the ^ process of the present invention have wide utility as raw materials for making insecticides, herbicides, repellants, rubber vulcanizere and surfactants. he present invention is directed to free radical initiated reactions of hydrogen sulfide as distinct from the acid or base catalyzed reactions. In the ionic (acid or base) catalyzed reaction hydrogen sulfide addition across the oleflnic linkage takes place in accordance with the Markownikoff Rule, i.e. "normal" addition in which the sulfhydryl group becomes attached to the unsaturated carbon atom having the fewer hydrogen atoms attached thereto. In the free radical initiated reaction, "abnormal1' addition or anti-Riarkownikoff addition becomes . . d takes place, that is the sulfhydryl group/attaches to the unsaturated carbon atom having the greater number of hydrogen atoms attached thereto. For example when an a-olefin is reacted under acid catalyzed conditions, a secondary mercaptan, namely a 2-thlol, is formed; whereas in the free radical initiated reaction, the a-olefin is converted to a primary mercaptan, namely a 1-hiol.

In accordance with the presen invention, primary aliphatic mercaptans are manufactured b reacting hydrogen sulfide with an a-olefin having from 2-30 carbon atoms optionally substituted with cyano, carboxy, carbamoyl, amino, monoalylamiiio, dialkylamlno, halo, sulfinyl, sulfonyl, hydroxy, aryloxy, alkoxy, cycloalkoxy, alkylthlo, arylthio, ca byloxy, n acyloxy, acylamido, trivalent phosphorus radical and/or pentavalent phosphorus radical, in the presence of a free radical initiatin compound selected from organic azo compounds, peroxyides, peracids and percarbonates, and of a trivalent (Y)¾R» (Z) R"» c wherein X, Y and Z are each an oxygen or sulfur atom, a, h and c are each 0 or If RV, R", and R'1' are each a hydrocarbon radical having from 1 to 20 carbon atoms; said phosphorus compound being present in an amount from about 0.001 to about per mole 1.0 mole/ of said a-olefin.

The reaction of the present invention can be carried ou with or without a diluent.

The hydrocarbon radicals RV, R" and R* ' ' can each be alkyl, aryl, cyeloalkyl, alkaryl or arylalkyl. In the preferred embodiment of this invention, these radicals are each a lower alkyl having from 1 to 4 oarbon atoms or aryl having from 6 to Θ carbon atoms.

These trivalent organic phosphorus compounds are illustrated b the alkyl and aryl phosphines, phosphites, phosphonites and phosphinites such as: trimethyl phosphine, tributyl phosphine, triphenyl phosphine, trimethyl phosphite, tributyl phosphite, trihexyl phosphite, trltolyl phosphite, trimethyl phosphonite, triphenyl phosphonites tributyl phosphonlte, trimethyl phosphinite, triphenyl phosphinlte.

These compounds are further illustrated by the thio analogs of phosphites, phosphonites and phosphinites such as triphenyl thiophosphite, trimethyl thiophosphite, trimethyl thiophosphonite, triphenyl thiophosphinite and tributyl thiophosphite.

The preferred promoters for this reaction are the trimethyl, triethyl, trlpropyl, tributyl and triphenyl phosphites and phoephines.

The free radical initiating compounds which can be employed in the present invention include peroxide compounds, organic azo compounds, peracids and percarbonates . Thus the various azo initiators which cause the addition of hydrogen sulfide to an olefin by way of a free radical mechanism can be used. For instance, the azo initiators which have an acyclic azo group, -N=N, bonded to different non-aromatlcs, that is aliphatic or cycloaliphatic carbons, at least one of which is tertiary can be used in the process of this invention. . These azo compounds are described in U.S. Patent 2,551,815, and are illustrated by azo-bisiso-butyronitrile , azobis- (< , -dimethylvaleronitrile ) , azobis- (^-methyl- <?-carboxybutyronitrile) ,. azobis-fisobuty-ramidine hydrochloride), azobicyclohexanecarbonitrile, O^(carbamylazo) isobutyronitrile,c^ (carbamylazo)c^ , -dimethylvaleramide , hexyl-c^(carbamylazo) ,o{, Y-dlmethyl-valerate , of , c 1 -azobis (o{-methyleneanthonitrile ) , ,θ -azobis (c^-ethylbutyronitrile) ,o,o{-azobis ((7^-cyclo-propylpropionltrile) , c , C(-azobis- (c - -dlmethylcapro-nitrile) and 1, 11 -azobicycloheptanecarbonitrile . The preferred azo compounds are azo -bisisobutyronitrile and azobis (o,^ dimethylvaleronitrile). While di-tertiary alkyl peroxides, such as di-tertlarybutyl peroxide, are highly effective initiators for the present invention, the other dialkyl peroxides, alkylhydroperoxides, alkyl peroxy esters and diacyl peroxides are also effective Initiators for this process. Illustrative of the peroxide compounds which can be employed in the present invention are di-tertiarybutyl peroxide, benzoyl peroxide, lauroyl peroxide, caprylyl peroxide, acetyl peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, pinane hydroperoxide, cumene hydroperoxide, t-butiyl hydroperoxide, p-methane hydroperoxide, p-chloro- benzoyl peroxide, 2 4-dichlorobenzoyl peroxide, hydroxy- heptaldehyde peroxide, dibenzal diperoxide, methyl isobutyl . ketone peroxide and cyclohexanone peroxide . The preferred peroxide compounds are dl-tertiary butyl-peroxide and tert- butyl hydroperoxide. The "hot catalysts", such as percarbonates , peracids and peracid esters can also be used in this Invention. By the use of the term "hot catalyst", it is meant those catalysts having a 10 hour half-life at a temperature below 6o° C.

The percarbonates can be illustrated by isopropyl percarbonate, diisopropyl peroxydicarbonate and t-butyl- peroxy isopropyl percarbonate. The peracids and peracid esters are exemplified by t-butyl perbenzoate, t-butyl. peroxypivalate, di-t-butyl diperphthalate, t-butyl permaleic acid, t-butyl peracetate, t-butyl per oxyisobutyrate and t-butyl perphthalic acid.

The initiators used in this invention have heretofore been employed at temperatures sufficiently high enough - to decompose the initiator into free radicals and yet sufficiently low enough to control the half-life of the initiator so that said initiator can sustain the reaction for abou 1 to about 6 hours . The optimum temperature varies with the particular initiator and pressure used, Therefore, prior to this invention, azobisisobutyronitrile (AIBN) was employed at temperatures in the range from about 80° C. to about 110° C. in the addition of hydrogen sulfide to an olefin. Likewise di-tertiarybutyl peroxide was employed at 150° C. to l6o° C, whereas tertiarybutyl 120 ° C. -to about 150 ° C. When the process of the present . invention is employed, however, lower temperatures may be used without substantially -effecting the conversion of olefin and yield of the mercaptan. Therefore azobisiso-butyronitrile can be used at temperatures ranging from about a 40° C. to about 110 ° C. without substantially effecting the yield and is still effective at temperatures down to 20 ° C, whereas without the promoters of this invention the minimum temperature applicable for using azobislsobutyrohitrlle under the same pressure was about 70 ° C. The temperatures at which the initiator can be used in the present invention will vary with that particular initiator and the pressure employed but each can be . used at a lower temperature than was previously feasible without the promoter of this invention.. The normal reaction temperatures will be in the range from about 30° C. to about.200 ° C. The preferred range for this invention is from about 6o ° C. to about 130 ° C. Another advantage of the process of this invention is that substantially lower initiator a levels can be used without -effecting the conversion of the olefin or the yield of the mercaptan. This will be further exemplified in examples which follow.

Although water may be present in the system,' better yields are obtained when an anhydrous reaction. is carried out .. To maximize the formation of mercaptans and minimize the formation of thioethers, ratios of hydrogen sulfide. to hydrocarbon of at least one or greater,, that is from about 1 to about 20 moles H2S/mole of hydrocarbon should be used, the higher the mole ratio, the higher is. the molar ratio of mercaptan to sulfide in the product. -fefe-e--g»¾ e*s-of--the--p»es©tt£--tavettfe-t^H-¾¾-»&- The α-olefins suitable for use in the process of the present Invention include such a-olefins containing subs ituents which do not affect the basic nature of the method and/or containing two or more olefinic linkages, for example, 1,3-butadiene, lsoprene, 1,5-hexadiene, 1,7-ootadiene, inylcyclohexene. Illustrative of these substituents are: cyano, carboxy, oarbamayl, amino, monoalkylamino, dialiqrlainino, halo, sulflnyl, sulfonyl, hydroxy, arylpxy, alkoxy, cycloalkoxy, alkylthio, arylthio, n carb^Loxy, acyloxy, acylami&o, and the like. The hydrocarbon can also have trivalent and pentavalent phosphorus compounds attached thereto. Suitable olefins for this invention include ethylene, propylene, 1-butene , Isobutene, l-pentene, 1-hexene, 1-octene, 1-nonene, styrene, l-dodecene, 1-decene, 1-tridecene, 1-undecene, l-heptadecene, 2-methylhexene-l, 3-methyl-2~ethyl-i-pentene,'5t3-dimethyl-l-heptene, 4-methyl-2-propyl-l-pentene .vinyl oyclohexahe, 3-phenyl-l-pentene, 1,3-butadiene', 1,3-pentadiene ,5-hexadlen©^l,6-octadiene, 3»4-dlethyl-l,5-hexadlene, otyrono» 3-chloro-l-hexene , 5-nitro-l-pentene and -cyano- -pe'ntene, vinyl chloride , vinyl bromide, 34281 2 3-βthoxy-pe tene~l, 2-chloro-eicosene-l, methyl vinyl ether, divlnyl ether, acrylic acid, ethyl acrylate , methyl methacrylate , 2-cyano-l-propene and the like.

The reaction can be run in a batch system, ; a continuous operation, or in a series of reactors.

For example, all of the hydrogen sulfide, a-olefin, initiator and promoter can be added at once or the a-olefin and hydrogen sulfide can be added as separate streams to a continuous reactor system wit an appropriate addition of the initiator and promoter in the desired proportions, either separately or along with the olefin or hydroge sulfide. If desired, a coil reactor can also be employed with injection of the initiator along the coil at various points. Is another embodiment of the present invention, the trivalent phosphorus promoters can be generated in situ by adding phosphine to the olefin to yield the trivalent organic phosphorus compounds which can then act as the promoter. , The amount of the novel organic phosphorus reaction promoters used in this invention will vary over a wide range and will depend upon various factors such as the particular promoter used, the amount of initiator used, and the temperature employed. The amount of phosphorus compound used will be the. amount sufficient to promote the reaction and increase the conversion of the unsaturated compound without reaction substantially with mercaptan formed. For most applications, the fH^ef-esfsped- amount of reaction promoter will be in the range of 0 .001 to 1 .0 mole of promoter per mole of ea-e-h-c^»olefin4« -1-iRk-ag-e.. At concentrations higher than 1 .0 mole, the formation of mercaptan drops off/considerably due to interaction between the promoter and product. The amount of initiator can be varied and will ^depend upon the type of. initiator, the amount of promoter and the reaction temperature used. For most normal applications the preferred amount of initiator will J e in the range from about 0 .0001 to about 0 .25 mole of initiator/mole of olefinto—l-i»kag©., As stated above, /Φϊιβ reaction of the present invention can be run with or without a diluent. The diluent should be inert S with respect to the reactants and the products .s-uitable diluents include saturated and aromatic hydrocarbons . These diluents, can be illustrated by pentane, hexane, octane, cyclo- hexane, benzene, toluene and xylene.

The following examples serve to illustrate the practice of the invention. The experimental procedure followed comprised placing the catalyst and if a solvent Is to be employed, 50 ml of inert solvent such as benzene or hexane into a stainless steel autoclave equipped with a gas inlet, thermocouple well, 3000 p.s.l. pressure gauge and a glass liner was frequently used; however, it has been demonstrated that the reaction proceeds : without the liner. The autoclave was then sealed and evacuated; however, it has been demonstrated that evacuation is not necessary . After cooling the autoclave in a nitrogen bath, the olefin and hydrogen sulfide were added. The autoclave was then heated to the desired reaction temperature in 1 to 3 hours and maintained at the reaction temperature for a specific time. The maximum pressure developed for the ethylene experiments at 9Q° -100° C. was 1200' p. s.i.; the propylene reactions usually reached a maximum pressure of 800 p. s.i. Pressures diminished as the number of carbon atoms in the olefin increased. Table 1 contains the results when 0.1 gram, of azobisisobutyronitrlle (AEBN) was employed as the initiator in 50: milliliters of solvent (benzene) at temperatures between 90° C. and 100° C. Example No. 1 was the control using no promoter.

Table 1 Example No. 1 2 3 4 5 6 7 8 Charge (moles): ethylene 0.2 0.2 0.2 propylene 0.2 0.2 0.2 dodecene-1 0.2 octene-1 0.2 H2S 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Promoter (grams): triphenyl phosphine 2.0 triphenyl phosphite 2.0 2.0 2.0 trlbutyl phosphine 2.0 trlmethyl phosphite 2.0 2.0 yield { ) of mercaptan 22 74 67 71 84 76 70 72 conversion of olefin 36 100 97 92 100 100 87 91 The increase in the yield of products which is provided by the phosphorus compounds employed as promoters Ιό obvious from the above data! · Examples 9-11 were made using peroxide initiators instead of AIBN. The results of these examples are contained in Table II. Temperatures varied with the peroxide used but were in the range of 110° C. to l40° C. Example 9 is the control, using no promoter.

Table II The above data shows that the promoter is also very effective in peroxide initiated addition of H2S to an olefin. The promotional effect of these compounds is also present in the peracid and percarbonate initiated reaction. Temperature ranges will vary with the particular initiator.

Examples 12-18 were conducted using varying amounts of initiator and promoter. In these examples the initiator was AIBN and the promoter was trimethyl phosphite (T P) . The hydrogen sulfide in 50 milliliters of inert solvent, in this case benzene. Temperatures were in the range of from about 85° C. to 95° C. and reaction times were about 6 hours .

Table III Examples 12-14 demonstrate that by using a promoter of the present invention we may decrease the initiator level considerably, here by ten times, and yet still get complete conversion of the olefin with only a small decrease in the yield of mercaptan. Examples 15 and l6 demonstrate that at the low initiator level, we can decrease the amount of promoter by one-half and still obtain complete conversion and good yields. However, example 17 shows that when the promoter level is reduced below 1.0 grams/0.2 moles of ethylene the promotional effect begins to decrease with the resulting lower conversions of ethylene and lower yields of mercaptan. Examples 18 and 19 demonstrate that even at these levels of promoter, we can get quantitative conversion by very slight increases in the amount of initiator employed. However, the promotional effect is still quite evident even at this low promoter level. When 0.01 grams of AIBN was employed in the absence of the promoter as in Example 20 less than 10^ conversion of olefin and a negligible amount of the desired mercaptan was obtained. It is obvious from this data that the promoters of the present invention not only increase conversion of the olefin and yield of the mercaptan but they also allow unexpected and drastic reduction of initiator levels.

Examples 21-23 were run at varying temperatures . Example 21 was the control using no promoter while Examples 22-23 use 1.0 gram of TMP, 0 .01! gram of ΑΓΒΝ, 0.2 moles of ethylene and.1 mole of hydrogen sulfide in 50 milliliters of benzene. The results are contained in Table IV. Examples 24-25 were run using 0.01 gram of AIBN, 1.0 gram of trlmethyl phosphite, 0.2 moles of ethylene and 1 mole of. hydrogen sulfide hile reaction.time was varied. Examples 26-27 were run under the same condition as 24-25 except that the olefin used was propylene. The results of these examples are also contained in Table IV.

Table IV No promoter used.

Examples 21-23 demonstrate that when the promoter be used at temperatures below those at which they can be used without these promoters,. Examples 24-27 show that the process of the present Invention gives quantitative conversions and high yields even at reaction times as short as one hour.

Further examples (examples 28-30 ) were run using extremely short reaction times. These reactions were run at 95 ° C. using a hydrogen sulfide to ethylene molar ratio of 5: 1 and employing 0 .008 mole of TMP and 0 .00006 mole of AIBN/0 ..2 mole of ethylene . The results of these examples are contained in Table V.

Table V Examples 28-30 demonstrate that we can greatly decrease reaction times and still obtain quantitative conversion of the olefin while only slightly decreasing the yield, of .mercaptan. Thus by using the present invention. we can decrease reaction times by tenfold over the prior art and still obtain quantitative conversion and higher yields of ercaptans .

Examples 31 and 32 were run without a diluent . . Both were run at 90 ° C. for about 1 hour using 1 mole of hydrogen sulfide . The results of these examples are con Ta l VI Examples 31 and show that the reaction of the present invention can be run with or without a diluent to give substantially quantitative conversion of the olefin; however, slightly higher yields of mercaptan are usually attained using diluents.

From.all of the preceding examples it has been demonstrated that employing the reaction of the present invention we obtain unexpected increases in mercaptan yield while decreasing initiator level, reaction time and reaction temperature.. . . . . . . 34281/3

Claims (1)

1. CLAIMS A process for manufacturing primary mercaptans which comprises reacting hydrogen sulfide with an having from carbon atoms optionally substituted with trivalent phosphorus radical pentavalent phosphorus in the presence of a free radical initiating compound selected from organic peracids and perearbonates and of a trivalent organic phosphorus compound having the formul wherein Y and Z are each an oxygen or sulfur b and c ar each 0 or and are each a hydrocarbo radical having from 1 to 20 carbon atoms said phosphorus compound being present in an amount from per mole about to about mole said process according to Claim wherein said is selected from group consisting of and 18 A process according to Claim wherein said is vinyl A process according to Claim wherein said organic phosphorus compound a trialkyl the groups of which each contain from 1 to 4 carbon process according to Claim wherein said organic phosphorus compound la a trialkyl phoaphine A process according to Claim wherein trivaient organic phosphorus compound is a triaryl A process according to Claim wherein said trivaient organic phosphorus compound is a triaryl A process according to Claim wherein said free radical initiating compound is benzoyl ditertlary tertiary utyl Isopropyl percarbonate or tertiarybutyl A process according to any one of the preceding wherein the process is carried out in an For the Applicants insufficientOCRQuality