INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1931
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Some Copper Mercaptides and Their Reaction with Carbon Disulfide’ W. E. Duncan,2 Emil Ott,a and E. Emmet Reid4 CHEMISTRY
LABORATORY, THEJOHNS HOPKISSU N I V E R S I T Y ,
H.ILTIMOKE,
IfD
The complete series of copper mercaptides from methyl to n-nonyl and sec-propyl to sec-nonyl are prepared by the interaction with copper acetate. Typical mercaptides are analyzed and some of the properties noted. In all cases during the mercaptide formation the cupric salt is reduced to the cuprous state and a corresponding amount of alkyl disulfide is obtained. The cuprous mercaptides are insoluble in water, alcohol, ether, and benzene, with the exception of the sec-amyl, sec-hexyl, sec-heptyl, sec-octyl, and secnonyl cuprous mercaptides, which are soluble in benzene and ether. They are at first light yellow and show decomposition analogous to that observed for lead mercaptides. They also react ,with elementary sulfur in a way similar to that observed for the lead salts. However, he gave no detailed Cuprous mercaptides add carbon disulfide readily proof of this reaction and no to form red-brown alkyl cuprous trithiocarbonates, analysis of the copper merwhich are more soluble in organic solvents than the captide. The only analysis corresponding cuprous mercaptides. is given by Kohler ( 5 ) , who In contrast to the behavior observed for lead, there is obtained CuSCzH5 in the reno indication of the formation of basic copper mercapaction between copper acetotides. Also hydrolysis of the mercaptides is not marked. acetic ester and ethyl sulfoCopper mercaptides are formed by the action of mercyanate: captans in benzene solution on copper metal, copper ~(CH~COCHCO.OCZH~)ZCU sulfide, and copper oxide, also by reaction with butyl 4CzHsSCN = 2(CH&OCcopper phthalate. In this connection some pecu( C K ) C O .O C Z H I ) P C U 4CHsCOCHzCO. OC2H5 liarities observed during the removal of mercaptans (CzHbSh 2CzHsS CU by the above reagents are further explained.
All these compounds are pale yellow when first formed but turn darker on standing even out of contact with air. The derivatives of the secondary mercaptans seem to be affected by light whereas those of the primary mercaptans are not. All are insoluble in water and alcohol. The derivatives of the normal mercaptans and of isopropyl and sec-butyl are insoluble in benzene and ether, but those of the higher secondary mercaptans are soluble. The insoluble mercaptides separate as precipitates, the n-hexyl and n-nonyl being fibrous. The s o l u b l e derivatives of the higher secondary mercaptans are obtained by evaporating the benzene solutions. This leaves the mercaptides mixed with the slightly volatile alkyl disulfides, which can be removed by e x t r a c t i o n with alcohol. If the disulfide is not v o l a t i l e , a n a l y s i s of this mixture gives r e s u l t s An instance of the oxidacorresponding to those calcution of mercaptans to disulfides by cupric salts is given by lated for cupric mercaptide. That the comer derivatives Drummond and Gibson ( I ) , who used cupric chloride for the are cuprous was proved quantitatively by analysis and qualioxidation of thiol camphor to the disulfide. tatively by dissolving specimens in concentrated hydrochloric The present study was undertaken to obtain a, more exact acid and adding excess of caustic soda which precipitated the knowledge of copper mercaptides. The primary and second- yellow cuprous hydroxide. The color deepened but slightly ary mercaptans up t o nonylb were used. It waa of interest on boiling, which showed the absence of cupric compounds. to find whether basic as well as neutral copper mercaptides The formation of the alkyl disulfide was qualitatively are formed, as was found to be the case with lead (8). proved in the case of ethyl and quantitatively for sec-hexyl Some light on the peculiar solutions obtained by treating and sec-nonyl. Hence the reaction takes place as postulated copper or copper sulfide with a solution of a higher secondary by Klason. mercaptan was considered particularly desirable (IO). No evidence could be found for the formation of basic It has been found t,hat both primary and secondary mer- copper mercaptides, though the conditions known to give captans in benzene solution react with a water solution basic lead mercaptides were simulated. of cupric acetate to give cuprous mercaptides. The cuprous mercaptides react with sulfur, as do the lead The cuprous derivatives of ethyl, n-propyl, n-butyl, mercaptides, but more slowly. I n the case of sec-hexyl n-hexyl, n-nonyl, isopropyl, sec-butyl, sec-amyl, sec-hexyl, mercaptide the dark brown reaction product was analyzed, and sec-nonyl mercaptans have been prepared and analyzed. though it did not appear to be entirely uniform and was found to approximate cupric sulfide in composition, but 1 Received February 9,1931. Presented before the Division of Petrofrom its formation it should be cuprous disulfide. The leum Chemistry a t the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931. This paper (contains results reaction might be (compare 9 ) :
T
HE literature concerning copper mercaptides is scanty. Zeise, who discovered mercaptans, mentions the formation of a light yellow copper mercaptide as a precipitate on mixing a solution of copper sulfate and ethyl mercaptan. The formulawas given as Cu(SCsHJ2 until Klason (4) showed that c u p r o u s mercaptide is obtained according to the reaction:
+
+ + +
A
obtained in an investigation on a study of the “Reactions of a Number of Selected Sulfur Compounds” listed as Project 28 OF the American Petroleum Institute Research. Financial assistance in this work has been received from a research fundof the American Petroleum Institute donated by John D. Rockefeller. This fund is being administered by the institute with the cooperation of the Central Petroleum Committee of the National Researc Council. 2 ilmerican Petroleum Institute summer assistant. 8 A . P. I. research ft:llow for the summer of 1930. 4 Director, Project 28. 6 Prepared by L. M. Ellis, Jr., as part of A. P. I. Project 28.
+ S ---f Cu. S.SR +Cu.S Cu.SR + S Cu.S.SR Cu.d Cu.SR
I
SR
+ JR
When the soluble secondary copper mercaptides are left standing in benzene solution, the originally yellow solutions become deeper and deeper colored regardless of the presence of light, and eventually turn deep brown. A sealed sample
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of sec-hexyl mercaptide solution which was left standing for more than 6 weeks yielded, after evaporation and treatment with alcohol, a small amount of a dark brown precipitate which gives a red-brown solution in benzene. This contained 56.16 per cent copper (Cu. SCSHI,= 35.17 per cent Cu; CuS = 66.47% Cu). Nothing definite can therefore be said about the reaction as yet, but evidently a marked change in composition has occurred. Reaction of Carbon Disulfide with Cuprous Mercaptides
It has long been known that carbon disulfide combines with sodium mercaptides to form sodium alkyl trithiocarbonates. Thus Mylius ( 7 ) prepared sodium butyl trithiocarbonate and Holmberg (3) the corresponding potassium ethyl salt. From these the heavy-metal salts were obtained by double decomposition. The copper salt was described as a reddish brown precipitate, but neither it nor other salts of its kind have been thoroughly studied. The present writers have found that the cuprous mercaptides combine with carbon disulfide readily to form reddish brown products which are considerably more soluble in benzene-carbon disulfide mixtures than the mercaptides are in benzene. The higher members of the normal and secondary series are quite soluble in benzene and only the methyl and ethyl compounds are insoluble. I n the normal series from amyl mercaptan upward the solutions often thicken to jellies upon standing. This is not so likely to occur in the secondary series, but has been observed for sec-amyl after prolonged standing. The reaction products are still more soluble in carbon disulfide. The investigation of these products leaves no doubt that they are the alkyl cuprous thiocarbonates formed according to the reaction: CU-SR
+ CS~+CU-S R-S
\
/c=S
The n-butyl cuprous trithiocarbonate was prepared in this way and also by precipitation from an aqueous solution of sodium n-butyl trithiocarbonate and cupric acetate. Both preparations were alike in color, solubility, and general behavior. Analysis showed them to have approximately the same composition, though both were low in sulfur. They are not so stable as the sodium alkyl trithiocarbonates are reputed to be. They decompose slowly on standing; one sample contained 36.49 per cent sulfur when first analyzed and only 35.19 per cent 2 days later. Although a cupric salt was used in its precipitation, the salt obtained is cuprous butyl trithiocarbonate. This does not seem to have been noted previously, but it is well known that cuprous xanthate is similarly formed. The butyl cuprous thiocarbonate becomes soluble in alcohol when butyl sodium thiocarbonate is added, probably owing to formation of a complex CuRCSa. NaRCS3. Addition of copper acetate will again precipitate out the previous product. A similar observation has been made for cellulose xanthate (6), where i t was found that the deep red-brown copper salt became very soluble when an excess of the sodium salt was added. The peculiar behavior observed by Slagle and Reid (IO) for some mercaptans during their “adsorption” measurements on copper sulfide now finds a ready explanation. They observe the formation of copper compounds, soluble in benzene, which were suspected to be the mercaptides, exactly in the cases where we find the cuprous mercaptides to be soluble. If to such a solution carbon disulfide is added the color changes to a red-brown, as was found to be typical
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for the cuprous mercaptides. Also the darkening of the benzene solution by itself upon standing is characteristic. Experimental
ANALYTICAL PROCEDURE-The sulfur was determined with the Parr bomb, by the same procedure as described in a previous article (8). The copper was determined electrolytically by the method of Hillebrand and Lundell ( 2 ) . Special pains were taken to decompose the compound entirely and to boil off all mercaptan. PREPARATION O F COPPERMERCAPTIDES-The mercaptides were usually prepared by shaking 0.3 N aqueous copper acetate solution with a dilute solution of the desired mercaptan in benzene, washing the precipitate thoroughly with different solvents, and drying in high vacuum. However, the mercaptides can also be obtained by the interaction of mercaptans with copper butyl phthalate solutions. Usually the first method was employed, but in the case of ethyl mercaptan several different methods were used giving essentially the same results, as may be seen from the following analyses : CUPROUS
ETHYL MERCAPTIDE
COPPER
SULFUR
cu:s
Samgle A . The benzene solution was shaken with excess of copper acetate solution, copper acetate solution drained o f f ,precipitate plus benzene shaken with water and water drained off; repeated three times. The precipitate was filtered off, washed with benzene, 95 per cent alcohol, and ether, and desiccated to constant weight in vacuum (10 minutes). Somple B. The two solutions were shaken as before, same volume of alcohol added: precipitate filtered off, washed with benzene, alcohol, and ether, and dried as before. Sam& C. The mercaptan solution was added to a very slight excess of copper butyl phthalate in benzene. The gelatinous precipitate waa washed well with benzene and dried. This sample darkened more than the others. Samples D and E. A 100-cc. solution of CIH~SH(2 cc. CaHd3-I) waa shaken with 76 cc. 0.3 N copper acetate solution. The separated benzene layer plus precipitate was shaken with 3 portions of water (100 cc. each), alcohol added, and filtered. The precipitate was washed with benzene, alcohol, water, alcohol, ether, and dried as before.
The Cu:S ratio is very nearly the same in all cases, which shows that hydrolysis is not important as was previously assumed. This behavior differs, therefore, from that of the lead mercaptides. The color observed is light yellow only a t first and rapidly changes to a light orange-brown. OTHERINSOLUBLE COPPERMERCAPTIDES-All the other insoluble copper mercaptides were prepared essentially according to the procedure for samples D and E. Often free mercaptan was added to the wash water to check possible hydrolysis. The desiccation was often prolonged for higher mercaptides. I n the case of sec-amyl mercaptan part of the mercaptide remained dissolved and only part formed a precipitate. The precipitated fraction alone was analyzed. sec-HExYL AND sec-NoN.ra COPPER MERCAPTIDES WITH REMOVAL OF ALKYLDIsuLFIDE-These mercaptides, which are very soluble in benzene, had to be prepared in a different manner. A solution of 2 cc. of the mercaptan in 50 cc. of benzene was shaken with 50 cc. of copper acetate solution; the benzene layer was separated, filtered, and evaporated with dry air down to about 10 cc. The addition of 75 cc. of alcohol (95 per cent) caused the formation of a fine precipitate, which was filtered off, washed well with alcohol, and dried as usual. The mercaptides prepared and their analyses are given in t h e following table:
IA-DUSTRIAL A X D ENGINEERING CHEMISTRY
=Ipril, 1931
SORMAL
SERIES
Ethyl
40.84
50.90
25.94
25.i2
1:1.03
I’ropyl Biutyl
45.60 41.00
45.84 41.63
22.77 20.92
23 1 2 21.00 17.74 14.39
1 : 0 99 1:1.01 1:0.98 1:0.99
Hexyl Sonyl
35.60 28.96
35.17
17.57
28.53
14.45
Light orangebroq-n Deep yellow Nearly white Yellow-white Light yellow
SECONDARY SERIES
Propyl Butyl Amyl
Hexyl Nonyl
45.40 40.93 37.85 35.14 28.61
45.84
41.63 38.13 35.17 28 5 3
22.56 20.79 18.84 17.70 14.57
23.12
21.00 19.23 17.74 14.39
1:0.99
1:1.01 1:0.99 1:l.OO 1:1.01
T.ight yellow Nearly white Yellow-white Light yellow Amber
REACTIOKPRODUCTS FROM SeC-IIEYYL .45D SeC-S0XI-L &IERCAPTAKS WITHOljT REMOVAL O F DISULFIDES-In the case of sec-hexyl mercaptan, where the corresponding disulfide is non-volatile a t moderate temperatures, the benzenr solution was evaporated to dryness. The residue, which was a mixture of 2 molecules of cuprous mercaptide with 1 of the disulfide, gave analytical results corresponding to cupric mercaptide as shown by the analyses below. Sample 1 was prepared by shaking the benzene solution of the mercaptan with cupric acetate. Sample 2 was prepared under conditions which should have given a basic mercaptide, were the formation of such possible. The benzene solution of the mercaptan was shaken with a suspension of cupric hydroxide in 4 caustic soda. In both cases the resulting benzene solution was separated, filtered, and two equal portions were evaporated with dry air, for the copper and sulfur determinations. The analyses show that no basic copper mercaptide was formed and that there is no hydrolysis of the salt. s4\IPI 5
cu 1
2
FOU~D S
70
%
20 53 20 67
20 96 21.48
RATIO cu:s 1:2.02 1:2.06
CALCD. F O R
cu
CuSzCinHx S
%
%
21.34
21.53 21 53
21.34
Analysis of the mixed reaction product from sec-nonyl mercaptan, prepared as sample 1, gave 16.60 per cent copper, calcd. 16.64 for C U S ~ C ~ ~InH all ~ ~these . cases the cuprous mercaptides could be obtained from the mixtures by washing out the disulfides with alcohol. PROOFOF PRESENCE OF ETHYLDISULFIDE--A benzene solution of ethyl mercaptan was shaken with cupric acetate, then several times with water, separated, and filtered to get rid of the insoluble cuprous ethyl mercaptide. The clear benzene solution was shown to be free of mercaptan by the doctor test. This solution was refluxed with zinc dust and acetic acid for 2 hours and then gave all the tests for the mercaptan. This shows that ethyl disulfide had been formed in the original reaction. REACTIONO F SULFUR WITH A COPPER h k R C A P T I D E A solution of 1 cc. sec-hexyl mercaptan in benzene was shaken with 50 cc. of 4 N caustic soda solution containing an excess of suspended copper hydroxide, separated, filtered, and 100 cc. of saturated benzene solution of sulfur added. After 30 minutes the precipitate was filtered off, washed carefully with benzene, and dried to constant weight.
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some suspended solid. After an hour this was filtered and the filtrate evaporated to dryness under vacuum in a desiccator. The analysis of the dark red-brown product is given below. Preparation from sodium salt. A solution of the n-butyl sodium thiocarbonate was obtained by dissolving 3.6 grams of sodium hydroxide in 100 cc. of absolute alcohol, adding 10 cc. of n-butyl mercaptan and then 6 cc. of carbon disulfide. To this solution aqueous copper acetate solution was added in excess to yield a heavy red-brown precipitate of butyl cuprous thiocarbonate. The precipitate was filtered off, washed well with alcohol, dried as before in vacuum, and analyzed. The dark red-brown powder was soluble in henzene and carbon disulfide, but J-ery slightly so in ether. I’REPARATIUS
++
CuS(C
