916
INDUSTRIAL AND ENGINEERING CHEMISTRY
be interpreted as the values corresponding to each section of the
curve as they approach the point in question. Jn general, the values given for the rate of change in specific numerical index furnish quantitative significance to the dispersion efficiency at the various stages of milling. CONCLUSION
The roller-type fineness of grind gage was found to be an e€fective instrument for both quickly and quantitatively following the course of pigment dispersion in 3-roll milling of conventionaltype printing inks. I t should be clearly understood, however, that the gage method, a t least for the dispersion of printing ink pigments, has the limitation that it evaluates only the oversized range as a criterion of fineness of grind, rather than the entire particle size range. This is justified in the case of printing inks and possibly in other products from the use point of view. An analysis has been madeof thenature of aggregates. Data have been presented leading to the formulation of a general mathematical expression for 3-roll mill pigment dispersion. ACKNOWLEDGMENT
The author wishes to acknowledge J. E. Jacklin, president of the Precision Gage & Tool Company, Dayton, Ohio, for the loan of a gage with which this investigation was accomplished, as well as to his son Everett for the photographs and photomicrographs and in addition for a review of the mathematical treatment.given. Credit is also given to G. L. Roper and C. Maresh of the Calco Chemical Division of American Cyanamid Company for the electron pictures. The gage itself was developed by the author dur-
Vol. 42, No. 5
ing his directorship of the National Printing Ink Research Institute, Lehigh University, Bethlehem, Pa. LITERATURE CITED (1) Arnold, J. E., J . Oil & Colour Chemists’ Assoc., 31, 237 (1948). (2) Beakes, H. L., in “Protective and Decorative Coatings,” Mattiello, J. J., ed., Vol. 4, chap. 2, Kew York, John Wiley & Sons, Inc., 1941. (3) Bernstein, I. RI., Am. I n k Maker, 19, No. 11, 29 (1949). (4) Bernstein, I. XI., U. S. Patent pending (assigned to Satl. Printing Ink Research Inst.). ( 5 ) Bonney, R. D., Ojj’icial Digest Federation Paint &. V(1rnish Py+ duction Clubs, 237, 345 (1944). (6) Bowles R. F., J . Oil & Colour Chemists’ Assoc., 21,25 (1938). (7) Draper, C. R., Paint Manuf., 13, 20 (1943). (8) Fischer, E. K., and Jerome, C. W., IND.ENG.CHEY., 35, 331; (1943). (9) Green, H., J . Applied Phys., 13, 611 (1942). (10) Green, H., J . FrankZinInst., 192, 637 (1921). (11) Green, H., and Weltman, R. N.. ISD.ENG.CHELI..Azar.. I.:D., 15, 201 (1943). (12) Pratt, L. S.,“The Chemistry and Physics of Organic Pigments.” p. 267, New York, John Kiley & Sons, Inc., 1947. (13) Sawyer, R. H., in “Protective and Decorative Coatings ” Mattiello, J. J.,ed., Vol. 4, NewYork, JohnWiley& Sons, Inc.. 1941. (14) Schneider, F. von, Kolloid-Z., 95, 29 (1941). . 14, 382 (15) Smith, D., and Green, H., ISD. ENG.CHEM.,A s . 4 ~ ED., (1942). (16) Sukhikh, 1’. A., and Ushakova, E. D., Chem. Zenfr., 1942, I , 432. (17) U. 9. Federal Specifications TT-T-141 a, Method 441. (18) T‘oet, A , J . Phys. & Colloid Chem., 51, 1037 (1937). (19) Zettlemoyer, A. C., and Walker, W.C., Am. I n k M u k e r , 27, No. 10, 67 (1949). RECEIVED July 20, 1948. Presented before the Division of Industrial and Engineering Chemistry a t the 116th Meeting of t h e AXERICAB C I i E v r c A L SocrErY, Atlantic City, S . J.
Sulfur Compounds from Petroleum Hydrocarbons J
REACTIONS AND DERIVATIVES OF TERTIARY ALIPHATIC MERCAPTANS W. A. SCHULZE, G. H. SHORT, .4ND W. W. CROUCH Phillips Petroleum Company, Bartlesaille, Okla.
T h e tertiary aliphatic mercaptans (thiols) constitute one of the more recent additions to the growing list of organic chemicals synthesized from petroleum. A family of these compounds, including members with four to sixteen carbon atoms, are commercial products of the catalytic addition of hydrogen sulfide to olefinic hydrocarbons of petroleum origin and represent a whole new series of chemical process and raw materials in the field of organic sulfur compounds. This paper reports some of the results of research concerning applications of the tertiary aliphatic mercaptans, and particularly describes some of the more interesting reactions studied and the new compounds w-hich have been prepared. The review of mercaptan reactions covers a range from oxidation and metal salt formation to more complex multistage syntheses which in several cases are novel with respect to successful application i n the aliphatic series. The products include tertiary aliphatic disulfides, polysulfides, trithiocarbonates, sulfenamides, alkylsulfenyl dithiocarbamates, allrylmercapto polyether alcohols, mercaptals, phosphorus thio esters, and various metal mercaptides. The new sulfur
compounds have potential applications in a \ariet> of industrial fields, and examples of commercial or semicommercial developments are cited. Initial evaluations have outlined the extent to which the various types of compounds are of interest for lubricant additives, ore flotation collectors, vulcanization accelerators, fungicides, and nonionic detergents.
I
N LINE with the present trend toward increased utilizarion of
the vast supply of compounds of petroleum origin as starting materials in the chemical industry, a commercial process has been described (18) in which olefinic hydrocarbons are combined with hydrogen sulfide to produce tertiarj- aliphatic mercaptans (thiol?) Supplies of both starting materials were developed from refine1I operations. Furthermore, the reaction is effected a t high presures over a solid catalyst in a type of process that waR readd! adapted to operation in a petroleum plant. By varling the olefiii charge, products of different molecular weight ranges are ohtained; consequently, there are now available in conimerciiil quantities various molecular weight fractions of isomeric tertian aliphatic mercaptans of four to sixteen carbon atoms per moleculr
917
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1950
STEAM EVACTOR
r a
w *A>
5s 2
>; 2;
zs
3
s
3
z 0 t z 0
’0 v) 0
c
- 2a U
3 4 3
0
WATER
I
1‘ I
I
+----Figure 1. Schematic Flow Sheet of Disulfide Plant
A number of industrial applications are already known for which aliphatic mercaptans themselves may be used to advantage, and it is expected that the development of adequate supplies of these products in high purity may lead to additional applications. In the production of synthetic rubber, both by the GR-S recipe and in the new “cold rubber” process (19), aliphatic mercaptans of about twelve carbon atoms per molecule are employed as modifiers to control the plasticity of the products. tert-Dodecyl mercaptan is applicable to these processes. The tertiary mercaptans have also given promising results when tested as ore flotation collectors, as shown in Table 111. Of even more interest than uses of the mercaptans themselves] however, are the numerous derivatives that may be obtained from them. This paper reviews research and development work that has been done a t various times during the past 6 years by the authors’ company to study the preparation] properties, and uses of some of the derivatives that are readily obtainable from tertiary aliphatic mercaptans. DlSULFIDES
The primary oxidation products of the commercial mercaptans are di-tert-alkyl disulfides. In a laboratory study of various reagents for use in the oxidation reaction, chlorine gas, chlorine mater, and aqueous solutions of sodium hypochlorite, hydrogen peroxide, nitric acid, potassium permanganate, sodium dichromate, ferric chloride] and cupric chloride were investigated. In addition, tests were made to oxidize the mercaptans with air or oxygen, using various materials as catalysts for the reaction. The most satisfactory laboratory process, from the standpoint of providing a rapid reaction to give a disulfide of high purity, made use of aqueous cupric chloride as the oxidizing agent. The following procedure represents a typical laboratory preparation.:
A sample of 100 grams of tert-butyl mercaptan is dissolved in 300 ml. of toluene and stirred vigorously for 1 hour a t room temperature with 1000 grams of an aqueous solution containing 14.8%
cupric sulfate entahydrate and 13.5% sodium chloride. The spent copper soyution is separated and discarded] and the process is repeated with a second batch of copper solution. The product is recovered and fractionated, first a t atmospheric pressure to remove the solvent and finally at a pressure of 50 mm. to recover di-tert-butyl disulfide boiling in the range of 215 to 223 O F. a t that pressure. The yield is substantially quantitative. In order to supply di-tert-butyl disulfide on a commercial scale as an ingredient of gear lubricants] a manufacturing unit was installed adjacent to the mercaptan plant a t Borger, Tex., in 1945. This unit employs a process in which the mercaptan is oxidized in liquid phase by air over a solid catalyst. A schematic, flow sheet of the disulfide process is presented in Figure 1. The oxidation catalyst is a clay impregnated with copper chloride solution similar to that described previously. The tertbutyl mercaptan which is obtained as a commercial material of high purity from the mercaptan plant is dissolved in a hydrocarbon diluent, admixed with air under pressure, and pumped through beds of this copper reagent to achieve concurrently the conversion of mercaptan to disulfide and the regeneration of the copper catalyst. Water formed in the oxidation is removed continuously from the circulating hydrocarbon-disulfide stream and the product disulfide is recovered and purified by vacuum distillation. The commercial product has a purity above 90%. The impurities usually include traces of other disulfides, resulting from propyl and amyl mercaptans in the mercaptan feed, and small amounts of di-tert-butyl trisulfide. Current specifications include a minimum sulfur content of 35.0% and a Cleveland open cup flash point above 375 O F. for a 2.0% solution in SAE 30 motor oil. The mercaptan-free product has a mild, ethereal odor and is not corrosive to polished copper at temperatures below about 220°F. , Higher disulfides have been produced using corresponding higher mercaptans up to tert-dodecyl mercaptan. Disulfides derived from some of these materials cannot be distilled without decomposition under conditions obtainable in conventional plant equipment, but satisfactory disulfides were recovered as kettle products. Physical properties of typical samples of the commercial disulfides are presented in Table I.
INDUSTRIAL AND ENGINEERING CHEMISTRY
918
Vol. 42, No. 5
Ierovered ab the trisulfide. l'his iivhavior has been observed with o t h r Distillation Specific types of disulfides (7'); under the conRange, F. Pressole, Gravity, Sulfur, .\Iercaptan ditions of the distillation, higher pulyProduct 10% 50% 90% Mm. 60' F./60° F. '% Content Color sulfides are decomposed to sulfur and Dootor sweet Light straw 0.9318 36.5 404 760 389 (C4HsS)s 383 (CsIIuS)r 160 462 466 760 0.9383 31.3 Doctor sweet Light yellow rhe trisulfide which, being volatile, is Doctor sweet Light amber 0.9478 28.5 2F3 5 252 (CsHiaS), 230 removed overhead. On rapid dist,illa22.0 Doctor sweet Yellow 0,9359 5 312 332 ( C S H I ~ S ) ~306 tion in an unpacked column rithout, re!CIZHZSS)I 690 759 dec. 0.8 0,9342 1 4 , 7 Doctor sweet Light amber flux, the trisulfide is recovered in admixture with higher ~" Dolysulfides. Purified di-tert-butyl trisulfide hits tioiling range at 5 inni., 185" to 190" E".; density, 0.991 grain The principal commercial application of the disulfides hns been per ml. a t 60" F.; and refractive index, 1.5208 a t 68" F. The as additives for high pressure gear lubricants. Because of its inercapt'an-free product is almost odorless. higher sulfur content and desirable stability characteristics, diThe polysulfides are chiefly of interest as addit,ives for lubritertbut'yl disulfide usually has been preferred to the higher isocants or cutting oils, as ore flotation collectors, as a sj,nthetic mers, and has been marketed in tank car lots for this use. Other rubber "short stop," or in agricult'ural sprays. For some applicafields in which the disulfides have shown promise are in ore flotations, the mixed polysulfides obtained directly from the reactiori tion, as cutting oil additives, and as chemical intermediates-for of sulfur with the disulfides are preferred to the purified trisulfide. example, for the production of higher polysulfides and sulfenyl These products may have sulfur contents as high as 60%. 4chlorides. though only a small fraction of the total sulfur is uncombined, a HIGHER POLYSULFIDES large proportion is so loosely held t,hat it is readily available for iraction as free sulfur. Primary aliphatic disulfides may react with sulfur at elevated The availability of sulfur from such organic compourids is of temperatures to give mixtures of higher polysulfides ( 2 ) . The interest, particularly when they are considered for use in extreme process was also found to apply to tertiary aliphatic disulfides. pressure lubricant's (15), in tvhich it is usually required that the In a typical reaction, di-tert-butyl disulfide reacted with ~ L I compounds be sufficiently stable not to be corrosive a t ordinary temperatures but sufficiently unstable to decompose under condiequimolar quantity of sulfur in a stirred glass flask at 325 F. At the start of the reaction a separate phase of undissolved molteii tions of temperature and pressure existing a t the contacting sulfur was visible in the flask, but after a few hours the reaction metal surfaces. The stability is reflected by the corrosive nature had proceeded to the point where a homogeneous solution was obof the compounds a t elevated temperatures, as shown in Tahlr I1 tained. After 24 hours the product was distilled at reduced presfor various tertiary aliphatic sulfur compounds. sure in an efficient fractionating column. Based on the weight of the charge to the kettle, there were recovered 30.7% unreacted di-tert-butyl disulfide and 46.6% di-tert-butyl trisulfide; the reTRITHIOCARBONATES mainder was heavy bottoms containing heavier polysulfides and sulfur. Under proper conditions, tertiary aliphatic mercaptaiis react very readily with carbon disulfide and sodium hydroxide to preThe reaction mixture prepared as described above, after repare sodium tert-alkyl trithiocarhonates. moval of unreacted disulfide, is a complex mixture of polysulfides and sulfur, but on careful fractionation the major portion may be
TABLE I. PHYSICALPROPERTIES O F CO>l\lnlERCIAl~TERTI.4RY ALIPHATIC DISULFIDES
I
KSH
TABLE 11. CORROSIVEACTIVITYOF TERTIARY ALIPHATIC SULFUR
COYPOUSDS
210° F.
Co ~npound Di-teit-butyl disulfide Di-tert-amyl disulfide Di-tert-hexyl disulfide Di-tert-octyl disulfide Di-tert-dodecyl disulfide Di-tert-butyl trisulfide Mixed tert-butyl polysulfides
1-
3 4
Corrosive Indexu 250' F. 300' F. 5+ 96 10 510
66
10 9 7
2 11
I
11 1l+
11
.
Corrosive indexes were determined with 10% solutions of colllDouuds in neut&-oilheated with a bright copper strip foF3 hours a t indicated ternperaturea. Ratings were assigned from 1 t o 11 based on extent of corrosion of strip: 1 was no discoloration and 11 was solid black with flaking.
TABLE111. SULFUR
COMPOUKDS AS
ORE
FLOTATIOX
COLLECTOR s
Collector Potassium ethyl xanthate Potassium isoamyl xanthate dodium tert-butyl trithiocarbonate Sodium tert-hexyl trithiocarbonate Sodium tert-octyl trithiocarbonate tert-Butyl mercaptan tert-Octyi mercaptan tert-Dodecyl mercaptan Di-tei t-butyl disulfide Di-tert-octyl disulfide tart-Butyl polysulfide
Contact Angle, Degrees 60 88 79 95 90 74 80 100 58 63 70
Copper Recovered.
%
'32.8 81.0
96.0 90.8 82.5 92.5 92.5 86.5 91.0 89.0 96.2
Assay of Concentrate 23.9 26.0 22 0 24.2 23.5 26.0 29.5 30.0 33.0 31.5 27.2
.
+ C S I + S a O H -+ R9
i
SNa
+ H2O
In a typical preparatioii 22 grams of sodium hydroxide are dissolved in 190 grams of water and stirred vigorously in a flask with 45 grams of tert-butyl mercaptan and 40 grams of carbon disulfide. The mixture is stirred for 1.5 hours a t 110' F. As the reaction proceeds, the heavy layer of carbon disulfide dissolves and the clear aqueous solution develops the bright yellow color of the trithiocarbonate. On cooling to 60" F., filtering and drying in an oven a t temperatures below 150' F., there are recovered 68 grams of yellow crystals of sodium tei.t-buty1 trithiocarbonate dihydrate. The two molecules of water of crystallization are not removed on drying for longer periods of time. A4ttemperatures above 160" F. or on long standing in open vessels. the product decomposes wit,h evolution of carbon disulfide and terl-butyl mercaptan. The above procedure was unsuccessful for the preparation of trithiocarbonates from primary butyl mercaptan or from tertiary mercaptans of eight or more carbon atoms per molecule. Trithiocarbonates were prepared succesvfully from the latter, however, by reaction of the mereaptans in solution in diethyl ether with metallic sodium and addition of carbon disulfide to the dispersions of the sodium mercaptides. The chief interest in trithiocarbonates has been for use as collectors in the flotation of sulfide ores. One of the principal types of materials now employed for this process is the xanthates, and the trithiocarbonates are similar in structure to them except that they have even more sulfur in the molecule. Trithiocarbonates derived from tert-butyl, hexyl, and oct'yl mercaptans were evaluated in flotation tests along with t,he t,ertiary mercaptans, disulfides, and a sample of mixed tert-butyl polysulfides. (These tests were performed under the direction of Adolph Legsdin of the
'
May 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
Missouri School of Mines.) Results are presented in Table 111. Contact angles were determined of air bubbles on the surface of a specimen of polished galena ore which had been previously conditioned by treatment with aqueous solutions or dispersions of each sulfur compound. This is a well-known preliminary test for flotation characteristics; the high contact angles shown by the experimental materials indicate potentially effective collectors. Subsequently, tests were made in which these materials were evaluated as collectors in laboratory flotation cells with a sample of copper sulfide ore received from the Utah Copper Company a t Garfield, Utah. Pine oil was used as frother in every case. The data of Table I11 indicate the percentage of the copper present in the original ore that was recovered in the concentrate and middlings. Data are also shown of the assay of the concentrate obtained with each rkagent. The original ore assayed 1.1% copper. The results show all the materials of Table 111to be effective as collectors. Particularly promising results were obtained with sodium tert-butyl trithiocarbonate and the mixture of tert-butyl polysulfides, both of which gave better results in these preliminary tests than either of the well-known xanthate collectors employed as controls. Subsequent tests with other types of sulfide ores used in various flotation procedures confirmed the preliminary results regarding the outstanding flotation characteristics of these two products. Some difficulty was experienced in the use of some of the liquid sulfur compounds, such as the disulfides and polysulfides, because of their insolubility in water. This ww overcome by adding to the material prior to use a small amount of an oil-soluble emulsifying agent which made the reagents readily dispersible when introduced to the flotation cell.
The pure sulfenyl chlorides are highly reactive, unstable compounds which react violently with many reagents. They are of interest chiefly for use as an intermediate in the preparation of a variety of other sulfur compounds, and in these reactions they are used as prepared in solution in isopentane. Following is a list of some of the reactions and products that have been studied: The reaction of tert-alkylsulfenyl chlorides with amines to form sulfenamides (1,6).
+ Clp +RSCl + HCl RSSR + C1, --+ 2 RSCl
RSH
In practice, the chlorination of the disulfide is preferred, because less chlorine is required and there is no by-product to be separated for disposal. Di-tert-butyl disulfide on chlorination in isopentane solution a t temperatures of 80" to 90" F. gives t e r t butylsulfenyl chloride in 85% of the theoretical yield. The higher tertiary mercaptans and disulfides, as well as primary and secondary mercaptans of four to twelve carbon atoms, also may be converted to sulfenyl chlorides, usually with somewhat lower yields for higher molecular weights. A typical preparation of tert-butylsulfenyl chloride is as follows: Di-tertbutyl disulfide (0.75 mole) is dissolved in 1000 ml. of isopentane and the solution is heated to reflux temperature (80O to 90 F.). While the solution is stirred, 0.75 mole of chlorine is added a t the maximum rate possible to permit complete condensation of the boiling isopentane. A reddish-yellow solution of the sulfenyl chloride in isopentane is obtained for use as an intermediate. Yield is 85% based on the disulfide charged.
R'
R'
RSCl
\
+
NH
/
+
+ HCI
R S d
(1)
R'E
R"
With sodium alkyldithiocarbamates to give alkylsulfenyl dithie carbamates.
S
R'
RSCl
+
S
R'
'NJSNa
/
--+
\NdSSR
/
+ NaCl
(2)
R"
R"
With xanthates to form alkylsulfenyl xanthates.
S RSCl
+ R'O8SNa
S
+R'OASSR
+ NaCl
(3)
With sodium trithiocarbonates, yielding alkylsulfenyl trithiocarbonates.
S NaSdSNa
S /I
+ 2RSCl + RSSCSSR + 2XaC1
(4)
or
d
ALIPHATIC SULFENYL CHLORIDES AND DERIVATIVES
The reactions of mercaptans with chlorine have been studied for many years. The use of chlorine as an oxidizing agent for conversion of mercaptans to disulfides was once a conventional step in petroleum refqning and natural gasoline treating. Another possible action of chlorine is the replacement of the hydrogen of the sulfhydryl group, yielding sulfenyl chlorides. The chemistry of sulfenyl chlorides from aromatic mercaptans has been investigated extensively (6), but little success was reported in the earlier literature in the preparation of the corresponding derivatives of aliphatic mercaptans ($1). As reported by Schulze (16),however, the tertiary mercaptans form sulfenyl chlorides readily under proper conditions. Under proper conditions the direct chlorination of tertiary aliphatic disulfides gives high yields of the alkylsulfenyl chlorides.
919
R'S SNa+RSCl
+
B
R'S S S R + NaCl
With sodium cyanide to give alkyl thiocyanates ( 6 )
+
+
RSCl NaCN +RSCN NaCl (5) With sodium thiocyanate, yielding alkylsulfenyl thiocyanates (61 819).
RSCl
+ NaSCN +RSSCN + NaCl
(6)
With mercaptans to give unsymmetrical disulfides. RSCl
+ R'SH -+
RSSR'
+ HCl
(7)
The sulfenyl chlorides react readily with aliphatic primary and secondary amines to give the corresponding sulfenamides, as shown in Equation 1. A variety of these prqducts has been made from various types of amines including open-chain aliphatic amines, polyamines such as triethylenetetramine, and heterocyclic amines such as piperidine and morpholine. A number of the sulfenamides of suitable molecular weight are effective antioxidants and bearing corrosion inhibitors when employed as additives for lubricating oils. Of particular interest are the sulfenamides obtained from secondary amines with from about eight to about-twelve carbon atoms per alkyl group and
TABLEIV. ENGINETESTSON SULFENAMIDES AS LUBRICATINQ OIL ADDITIVES *
1.
2.
3. 4.
5.
6.
Bearing Weight Loss 9 viscosity Sample Mg. % reduction Increasea Blended SAE 30 oil 296 .. 135 No. 1 1.0% N,N-di-a-ethyl49 84 48 hexyl- tert-butylsulfenamide No. 1 1.0% tetraethyleqepent- 120 59 57 amine-tert-butylsulfenamide Solvent refined SAE 30 base stock 870 .. 59 No. 4 1.5 tetraethylenepent136 84 24 amine- tert-?utylsulf enamide No. 4 5.0% commercial antioxi64 93 18 dant-inhibitor-detergent a Measure of oxidation occurring in oil sample during testing.
+ +
+ +
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
920
undergo the same tjpes of reaction as those described for sulfenyl chlorides, to give an additional series of compounds having one more sulfur atom per molecule than those mentioned above, Thus, amines react to form thiosulfenamides, and sodium alkyldithiocarbamates give alkylthiosulfenyl alkyldithiocarbamates which are effective vulcanization accelerators.
TABLEV. TESTSOF ALKYLSULFEXYL DITHIOCARBAMATES AS VULCANIZATIOX ACCELERATORS
krceleratoi Santocurea Compound Ab Compound A CoinpoundBC Compound B
$mount, Part/100 0 80 0 25 0 50 0 25 0 50
cure,
Min. a t
307O F. 45 45
30 45
30
Tensile, Lb /Sa. Inch a t 80' F. 300% 400% Break 1670 2210 2514 1430 1950 2510 1750 2400 2695 1290 1680 2320
1360
1785
%
Elongation
%
Compyesvon Set
450
13
2320
516
16
460
13
575 530
18
22
(' Trade b C
mark. Wonsanto Chemical Co.; N-cyolohexyl-2-mercaptoth~aaylsulfena~~~ide. tert-Butylsulfenul dimethyldithiocarbamate. tert-Butylsulfenul diethyldithiocarbamate.
from the polyamines. Test results for two experimental compounds are shown in Table Ii7. The preparation of sulfenamides from polyamines may be controlled to result in either complete or partial substitution of the amino hydrogens by an alkylsulfenyl chloride. thereby varying the sulfur content and the water dispersibility of the products. Of equal interest are the alkylsulfenyl dithiocarbamates prepared from the reaction of sulfenyl chlorides with sodium alkyldithiocarbamates as shown in Equation 2. The latter compounds are crystalline products of the well-known reaction of aliphatic amines with carbon disulfide and sodium hydroxidr. Examples of this process that have been studied include the preparation of sodium alkyldithiocarbamates from dimethyl, diethyl, di-n-propyl, di-n-butyl, di-n-dodecyl, ethyl, and isopropylamines and their reaction with sulfenyl chlorides derived from ethyl, isopropyl, and tert-butyl mercaptans. The stability of these compounds depends apparently on both the amine and mercaptan components. Secondary amines give more stable dithiocarbamates than primary amines, and the tertiary mercaptans give more stable derivatives than the primary and secondary mercaptans tested. Most of the compounds are rather easily purified, either by distillation a t reduced pressure or by crystallization, Two of the normally liquid products that have been isolated by distillation are tert-butylsulfenyl dimethyldithiocarbamate, boiling point, 250" F. a t 0.7 mm., and tert-butylsulfenyl di-n-butyldithiocarbamate, boiling point, 311-316' F. a t 1.0 mm. Ethylsulfenyl dimethyldithiocarbamate, isopropylsulfengl dimethyldithiocarbamate, and tertbutylsulfenyl ethyldithiocarbamate could not be distilled without decomposition and were purified by loK-temperature crystallization. Laboratory tests indicate that the alkylsulfenyl alkyldithiocarbamates are ultra-accelerators for the vulcanization of synthetic and natural rubber. Outstanding activity was shown by products derived from dimethylamine, diethylamine, and piperidine with tert-butylsulfenyl chloride. I n Table V physical properties are shown of a GR-S nlcanizate prepared from a recipe including: GR-S, 100 parts; Philblack A, 50 parts; zinc oxide, 3 parts: asphaltic softener, 6.0 parts; sulfur, 2 parts; and accelerators. These preliminary data indicate the effectiveness of the experimental accelerators in providing rapid rates of cure a t Ion concentrations in the mixture. ALKYLTHIOSULFENYL CHLORIDES
When tertiary aliphatic disulfides react with chlorine a t low temperatures, the reaction takes a different course from that described in the preceding section and alkylthiosulfenyl rather than alkylsulfenyl chlorides are formed. RSSR
+ C1,
RSSCl
+ RCl
At temperatures below 0 F. the reaction to sulfenyl chlorides is almost completely suppressed and tert-alkylthiosulfenyl chlorides are obtained in yields of 80 to 90% of theoretical. The alkylthiosulfenyl chlorides are reactive compounds that
Vol. 42, No. 5.
PRODUCTS OF REACTION WITH ETHYLENE OXIDE
Another group o' f derivatives of tcitiaij' aliphatic mercaptans which have promise of widespread applications for both commercial and household use are the surfaceactive alkylmercapto polgether alcohols obtained from the reaction of the mercaptans with several moles of ethylene oxide. RSH
+
TL
CHtCH2 --+ RS(CHzCH*O),H
'd
The reaction occurs readily on controlled addition of the required amount of ethylene oxide to a mercaptan in an autoclave a t 200" to 250" F. A basic catalyst such as sodium methoxide or sodium hydroxide in methanol is employed ( 1 5 ) . The most valuable products for use as nonionic detergents an& wetting agents are obtained from tertiary mercaptans of about twelve carbon atoms per molecule reacting with eight to fifteen moles of ethylene oxide. The oxide combines in steps, and products of varying properties are obtained as the reaction proceeds. The first step of the process occurs more readily than the subsequent steps, and after addition of one mole of ethylene oxide, led-dodecylmercapto ethanol, a water-insoluble oil distilling a t 248' to 257" F. a t 2-mm. pressure, is obtained in high yield. As additional moles of the oxide are added, products of increasing solubility in water, increasing viscosity, and more useful surfaceactive properties are produced. The alkylmercapto polyether alcohols derived from long-chain tertiary mercaptans may be used in solutions containing dilute acids, alkali, or salts and are particularly adapted for use in hard water areas. This, in addition to the fact that they are outstandingly effective detergents ( 5 )that can be made from readily available Iow-cost ingredients, assures them an excellent prospect for worth-while markets in the fields of detergents, wetting agents, and emulsifiers. MERCAPTALS
Mercaptans are known to react with aldehydes in the presence of hydrogen chloride to produce mercaptals ( 2 ) . The reaction is presumed to occur through the formation of the hemimercaptal as an intermediate product, but except Kith certain aldehydes it usually cannot be isolated from the reaction
-
+ R'CHO HC1 R'CH(0H)SR + RSH RSH
R'CH( 0H)SR R/CH(SR)z
+ HzO
The reaction is applicable to the commercial tertiary mercaptans, and mercaptals have been prepared from various mercaptans with acetaldehyde, butyraldehyde, heptaldehyde, and benzaldehyde. The preparation consists in mixing the ingredients in the ratio of 2 moles of mercaptan per mole of aldehyde and passing dry hydrogen chloride through the mixture a t room temperature. Heat is evolved and water separates from the mixture. After 2 hours the flow of hydrogen chloride is stopped and the product is washed to remove hydrochloric acid. The reaction product usually contains the mercaptal in high purity.
,
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 19%
Products from low-boiling mercaptans may be purified further by fractionation a t reduced pressure. Mercaptals produced from the reaction of mercaptans with chloral have been reported ( 3 )to be effective additives for extreme pressure lubricants, and a test was made of the reaction of the various tertiary mercaptans with this aldehyde. When tert butyl mercaptan was mixed with chloral or with chloral hydrate containing hydrochloric acid catalyst, a rapid reaction occurred to produce a crystalline product which, after recrystallization from carbon tetrachloride] melted a t 190" F. Analyses showed conclusively that the product was the hemimercaptal, CClsCH(0H)SCdHs. The yield of the crystalline product was above 90% of theoretical, and the reaction apparently shows no tendency to proceed further to give the expected mercaptal. This is in contrast to the reported behavior of primary mercaptans with chloral, from which the mercaptals were obtained (8). The reaction of chloral with higher tertiary mercaptans apparently also goes only to the hemimercaptal, with no separation of water on longer treatment. These products are liquids that decompose during distillation to evolve the starting materials. PHOSPHORUS COMPOUNDS
The thio esters of acids containing phosphorus have worthwhile applications as lubricant additives] flotation agents, and insecticides] and numerous promising reactions can be suggested for their synthesis from tertiary mercaptans and readily available inorganic phosphorus compounds. A preliminary laboratory study has been made of a few of these reactions. The reaction of mercaptans with phosphorus trichloride produces alkyl trithiophosphites with evolution of hydrogen chloride. 3RSH
+ PCli +P(SR), + 3HC1
Acid acceptors are frequently employed in the reaction (IO), but under proper conditions they are not required. Tri-tertbutyl trithiophosphite was prepared in good yields from this reaction, as a white solid having a melting point of 198" to 199 O F. It is insoluble in water but dissolves readily in organic solvents. A similar reaction occurred with higher mercaptans] but the products were not crystalline and were not characterized. The tertiary mercaptans may also be reacted with phosphorus pentasulfide to produce alkyl tetrathiophosphates (14). 6RSH PPSS+2(RS)a PS 3HzS
+
+
Tri-teit-butyl tetrathiophosphate was obtained in fair yield after reaction of the mercaptan with phosphorus pentasulfide for 52 hours in refluxing toluene. This product is also a waterinsoluble crystalline material that melts a t 264" to 273" F. Many other reactions of phosphorus compounds with primary aliphatic or aromatic mercaptans or sodium mercaptides are known (11, l a ) , and a study of the corresponding products from commercial tertiary mercaptans is a promising field for development of lower-cost phosphorus thio esters. METAL MERCAPTIDES
The commercial tertiary mercaptans may react with various salts (8)to form insoluble metal mercaptides, some of which have important potential applications. The methods of preparation vary, depending on the molecular weight of the mercaptan and the mercaptide required. Usually, the insoluble cuprous, mercuric, zinc, cadmium, silver, or lead salts of tert-butyl mercaptan may be prepared by stirring aqueous solutions of soluble inorganic salts of the metals with tert-butyl mercaptan and subsequently filtering to recover the mercaptides. Higher mercaptans may be employed as solutions in alcohols or in hydrocarbons such as toluene, in which the mercaptides are soluble and from which they may be precipitated subsequently by adding methanol. Cuprous mercaptides of primary and secondary mercaptans have been prepared previously by reaction of mercaptans with cupric salts, but one half of the product was converted to the di-
921
sulfide and only the remainder was recovered as the salt ( 4 ) . The authors prefer to make the mercaptides directly from cuprous salts-for example, cuprous chloride in water containing sodium chloride and a small amount of hydrochloric acid to give a clear solution. Yellow, crystalline cuprous mercaptides are formed in good yields. With increase in the molecular weight of the mercaptide, oil solubility increases and the products tend, to precipitate as amorphous gums rather than crystals. The cuprous mercaptides usually decompose slowly in storage. Tests have shown that oil-soluble cuprous mercaptides made from heavy tertiary mercaptans are excellent secondary accelerators for vulcanization of synthetic rubber (17). These materials are also suggested for use in fungicide and in antifouling paints or similar applications in which an oil-soluble copper compound is required. Mercuric salts are another well-known group of derivatives of mercaptans (80), and mercuric tert-butyl mercaptide is a white, crystalline material melting a t 318" F. I t is insoluble in water, but is sufficiently soluble in benzene to be recrystallized from that solvent. It is a powerful fungicide when used as a powder or as an aqueous dispersion. Zinc and cadmium mercaptides are white, crystalline products that are formed readily when methanolic solutions of the metal acetates are added to the mercaptans in the same solvent. These compounds have been found to be applicable for use as modifiers in synthetic rubber, hydrolyzing slowly during the polymerization reaction to provide a continuous supply of mercaptan to the reaction. ACKNOWLEDGMENT
The authors gratefully acknowledge the assistance of their co-workers who participated a t various times in this research program; particularly to C. M. Himel, formerly with the Research Department of Phillips Petroleum Company, who was connected with the work on sulfenyl chlorides, and to J. P. Lyon, who was associated with the commercial disulfide plant development. Acknowledgment is also made to George Wash and Adolph Legsdin, the latter from the Missouri School of Mines, who cooperated in the evaluation of the products in ore flotation. LITERATURE CITED (1) Billman, J. H., and O'Mahony, E., J . Am. Chem. SOC.,61, 2340 61,2340 (1939). (2) Connor, R., in Gilman's "Organic Chemistry," 2nd ed., Vol. I, p. 865, New York, John Wiley & Sons, 1943. (3) Davey, W., J.Inst. Petroleum, 33,527 (1947). (4) Duncan, W. E., Ott, E., and Reid, E. E., INB. ENG.CHEM.,23, 381 (1931). (5) Griesinger, W. K., Nevison, J. A., and Gallagher, G. A., J . Am. Oil Chemists' SOC.,26, No. 5, 241 (1949). (6) Kharasch, N., Potempa, S. J., and Wehrmeister, H. L., Chem. Rev., 39,269 (1946). (7) Klason, P., Bo., 20,3413 (1887). (8) Lecher, H., and Simon, K., Ibid., 54, 632 (1921). (9) Lecher, H., and Wittwer, M., Ibid., 55, 1474 (1922). (IO) Lippert, A,. and Reid, E. E., J . Am. Chem. SOC.,60, 2370 (1938). (11) Michaelis, A., and Linke, G. L., Ber., 40, 3419 (1907). (12) Pishchimuka, P., J . Russ. Chem. SOC.,44, 1406 (1913). (13) Prutton, C. F., Turnbull, D., and Dlouhy, G., J . Inst. PetioZeum, 32, 90 (1946). (14) Rosnati, L., Gazz. chim. itaZ., 76, 272 (1946). (15) Schuette, H., Schoeller, C., and Wittwer, M. (to I. G. Farbenindustrie), U. S. Patent 2,129,700 (Sept. 13, 1938). (16) Schulre, W. A. (to Phillips Petroleum Co.), Ibid., 2,123,082 (July 5, 1938). (17) Schulze, W. A,, and Crouch, W. W. (to Phillips Petroleum C o . ) , Ibid., 2,487,074 (Nov. 8, 1949). (18) Schulze, W. A.. Lson, J. P.. and Short.,G. E., IND. ENG.C H m f . . 40,2308 (1948); (19) Shearon, W. H., McKenzie, J. P., and Samuels, M. E., Ibid., 40, 769 (1948). (20) Wertheim, E., J . Am. Chem. SOC.,51, 3661 (1929). (21) Zincke, T., and Eismayer, K., Ber., 51, 751 (1918). RECEIVED December 29, 1949. Presented at the Fifth Southwest Regional Meeting of the AMERICANCHEMICAL SOCIETY, Symposium on Chemicals from Petroleum, Oklahoma City, Okla., December 10, 1949. Report 778-49R, Phillips Petroleum Company.
