I
ELLIS K. FIELDS Research Department, Standard Oil
Co. (Indiana), Whiting, Ind.
Preparation of Lubricating Oil Additives from Dimercaptothiadiazole In addition to inhibiting corrosion of copper-lead bearings, most dimercaptothiadiazole derivatives prevent corrosion of silver by active sulfur compounds
ONE
important class of lubricating oil additives is bearing-corrosion inhibitors. Compounds containing a high percentage of sulfur have been useful as inhibitors for copper-lead bearings, but may be corrosive to silver bearings. Certain derivatives of 2,5-dimercaptothiadiazole (DMTD) are excellent corrosion inhibitors for copper-lead bearings. They are not corrosive to silver bearings, and, in addition, prevent the corrosion of silver bearings by corrosive sulfur compounds. 2,5-Dimercaptothiadiazole, readily prepared by reaction of hydrazine and carbon disulfide (Z), has the structure:
N-N H-S-C
II
II
C-S-H
It behaves as a dibasic acid in water, with dissociation constants Kal, 1.1 X and Ka2, 1.8 X 10-8. The first ion seems to be stabilized by the resonance structures:
N-N
N=N
converted by reactions a t one or both -SH groups to oil-soluble derivatives. Thirty-nine such derivatives have been prepared and evaluated as corrosion inhibitors.
HS.
N=N
I
N-N-
1
HS-C
I1
I C=S
‘S/
N=N I
HS-C
I C=S
-\s/
The largest contributions to stability are probably from the first three structures, with the fourth and fifth contributing little. The tremendous difference between Kal and Kas indicates the inability of the doubly charged ion to acquire any further resonance stabilization. Although 2,5-dimercaptothiadiazole itself is insoluble in oil, it can easily be
Preparation of Derivatives
The 2,5-dimercaptothiadiazole derivatives fall into five general classes: thioethers, amine salts, thioesters, thioacetals, and polysulfides. T h e yields, properties, and analyses are given in Table I. For the sake of completeness the thioether from a-methylstyrene, described together with 13 other thioethers in an earlier work (3),is also listed. All other compounds are new. Thioethers. Thioethers were made either by alkylation of dipotassium 2,5-dimercaptothiadiazolewith alkyl bromides or by reaction of 2,5-dimercaptothiadiazole with olefins (2). Two other thioethers were prepared by condensation with hydroxymethylphenols. Hydroxymethylnonylphenol was prepared by reaction of 220 grams (1 mole) of nonylphenol, 40 grams (1 mole) of sodium hydroxide in 250 ml. of water, VOL. 49, NO. 9
SEPTEMBER 1957
1361
and 77.81 ml. of 35.5% (1 mole) of formaldehyde a t 25' for 72 hours; the free phenol was liberated with 1 mole of acetic acid. 2,5-Dimercaptothiadiazole 75 grams (0.5 mole), was stirred with 1 mole of hydroxymethylnonylphenol at 110' for 4 hours while a slow stream of nitrogen was bubbled through the mixture to remove water as it formed. The yield of the bis(2-hydroxy-4-nonylbenzyl) thioether was 292 grams (95%). Analysis: Calcd. for C34HS~N2S302: h-,4.56; S, 15.62. Found: AT, 4.30; S, 15.60. I n another preparation, the hydroxymethylphenol was not isolated, but reacted as it formed. T o a stirred solution of 22.5 grams (0.15 mole) of 2,5-dimercaptothiadiazole and 91.2 grams (0.3 mole) of 3-pentadecylphenol in 100 ml. of dioxane was added 24 ml. (0.3 mole) of 37.5% aqueous formaldehyde dropwise. The mixture was refluxed for 4 hours, evaporated under vacuum, and filtered through Celite, giving 108 grams (92%) of the bis(2hydroxy-6-pentadecylbenzyl) thioether. Analysis: Calcd. for C4&N2S$02: N, 3.58; S, 12.27. Found: K, 3.45; S, 12.40. These two thioethers probably have the structure :
Table I. Yields, Properties, and Analyses of DMTD Derivatives Yield,
yo
M.P.,
C.
n2k
Nitrogen, yo Sulfur, 7a Calcd. Found Calcd. Found
THIOETHERS Hydrocarbon group Bis-( 1-n-octyl)
98
Bis-2-(4-methyl-3-cyclohexeny1)isopropyl" Bis-2-phenylpropyl
74 88
... ...
...
1.5924
7.48
7.28 25.67
25.50
1.5995 1.6750
6.64 7.25
6.46 22.73 22.60 7.33 24.87 24.70
Am NE SALTS Amine Dioctadecyl Di-Armeen 2 H T Di-Primene 81-R Mono-4-n-amylpyridine Di-Primene JM-R Mono-Primene JM-R"
98 100 100 96 100 100
... ... ... ...
7.11 4.94 10.72
1.5333 1.5648
7.24 7.24
115-116 71-84 80-87 134
... ...
14.05
7.29 4.71 10.66 13.84 7.05 6.98
12.18 8.47 18.03 32.10 12.40 16.55
11.97 8.30 18.10 32.30 12.70 16.30
ESTERS Acyl group Dicaprylyl Monolauroyl Dilauroyl Distearogl
84 71 87 94
... ....,
52 113 73 66
,.+
6.96 8.44 5.45 4.11
6.80 23.89 23.83 8.31 28.95 28.80 5.68 18.68 18.90' 4.24 14.08 14.10
.*a
8.05
7.89 36.78 36.60
6.93
6.8I
T H I O \ m T $13
AIdehyde P-(tert-octylthia)butyraldehyde 8-(n-dodecylthia) butyraldehyde p- (teTt-dodecy1thia)butyraldehyde n-Hexanal
94
B
97
d
92 94
d d
... ... ...
31.68 31.40
6.93 6.66 31.68 31.50 12-06 12.16 41.38 41.20
hfIXlCD ' r H I O A C E T I L S
Both were viscous red oils.
R" H
Amine Salts. To prepare the amine salts, 2,5-dimercaptothiadiazole was stirred with 1 or 2 moles of amine a t 110' to 140' C. until a clear liquid resulted. Armeen 2 HT was obtained from Armour; Primene 81-R and JM-R amines from Rohm & Haas; 4-amylpyridine from Reilly. The solid salts were crystallized from n-heptane. 4-nAmylpyridine is such a weak base that it forms only the monobasic salt, even when present in excess. Esters. Carboxylic acids other than formic acid and esters do not react with 2.5-dimercaptothiadiazole. Acid chlorides, however, react smoothly to liberate hydrogen chloride and give thioesters. The monothioester is easily formed by reaction with 1 mole of acid chloride. As in the case of the olefin adducts, much longer reaction times are needed to force the second -SH group to react. For preparation of esters, a mixture of 1 mole of 2,5-dimercaptothiadiazole,2 moles of acyl halide, and 375 ml. of dry benzene was stirred and refluxed. After about 24 hours hydrogen chloride was no longer evolved and all 2,5-dimercaptothiadiazole had gone into solution.
1 362
H R n-CBH18
EtBuCH CeH6
R'e n-Butyl tert-Octyl tert-D o d ecyl CKHS tert-Octyl tert-Octyl
91 86 87 78 84 92
... ... ...
... ...
...
1.6209 1.5850 1.5535 1.6168 1.5475 1.6257
7.75 6.02 4.63 4.74 4.16 4.79
45.21 34.32 27.68 28.47 24.19 25.90
45.00 34.50 27.90 28.50 24.00 25.70f
11.76 11.61 9.52 9.70 8.00 7.87 10.85 10.62
53.80 43.54 36.58 49.60
53.60 43.50Q 36.70 49.50h
7.91 6.03 4.84 4.98 4.23 4.53
MONODTSULFIDES tert-Butyl fert-Octyl n-Dodecyl Phenyl
83 86 81
64
125 106-106.5 80
140.5-141
... ... ... ...
BISDISTJLFIDES
Re?< la-Hexyl tert-Octyl n-Dodecyl tert-Dodecyl
e f
t'
INDUSTRIAL AND ENGINEERING CHEMISTRY
94 95 94 95
...
... 31-33
...
1.5787 1.5800
...
1.5591
7.33 6.39 5.09 5.09
7.60 6.30 5.23 4.80
41.89 41.60 36.53 36.603 29.09 28.90 29.09 29.23
From dl-limonene. Salt of 1:1 adduct of 2,5-dimercaptothiadiazoleand a-methylstyrene. Calcd.: C, 60.70; H, 8.95. Found: C, 60.54; H, 8.78. Glass. Refers t o appropriate formula in text. Molecular weight: Calcd., 618; found, 584. Calcd.: C , 40.82; H, 5.12; mol. n-t., 292. Found: C, 40.97; H,5.99; mol. wt., 295. Molecular weight: Calcd., 258; found, 268. Prepared by both methods in text. Calcd.: C , 49.31; H , 7.56; mol.wt., 438. Found: C,49.10; H, 7.54; mol. wt.,428.
LUBRICATING OIL ADDITIVES
4
aldehyde by warming 1 mole of mercaptan(thiol), 1 mole of crotonaldehyde, and 2 ml. of diethylamine a t 8 5 O for 10 hours, then distilling. Yields, properties, and sulfur analysis of the p-alkylmercaptobutyraldehydes are shown in table
The benzene solution was diluted with an equal volume of n-heptane and chilled to -5'. The thioester which crystallized was recrystallized from nheptane. One mole of lauroyl chloride with 1 mole of 2,5-dimercaptothiadiazole gave the monoester. Formic acid alone of the carboxylic acids gives esters with 2,5-dimercaptothiadiazole. Trithioformates have been made from formic acid and mercaptans in the presence of hydrogen chloride. No catalyst is needed for the reaction of formic acid with 2,5-dimercaptothiadiazole and tert-octanethiol. Three products are formed in this reaction: the trithioformate, the mixed trithioformate with tert-octanethiol, and a product which is probably
11. Equimolar quantities of aldehyde and 2,5-dimercaptothiadiazole were warmed a t 75' to 80' until all solid dissolved, then heated for 6 hours a t 110' to 120' under vacuum in a slow stream of nitrogen. All three mercaptobutyraldehydes gave products which had molecular weights corresponding to trimers. Another aldehyde, n-hexanal, gave a tetramer. The absence of acidity in these thioacetals and the molecular weights indicate that the products are cyclic, possibly, in the case of the mercapto butyraldehyde condensates : N - N I1 II R-HC
To prepare the trithioformates, a solution of 45 grams (0.3 mole) of 2,5dimercaptothiadiazole, 43.8 grams (0.3 mole) of tert-octanethiol, and 13.8 grams of 100% formic acid in 200 ml. of dioxane was refluxed 6 hours. The solution was evaporated under vacuum to a total volume of 125 ml. and cooled to precipitate 27 grams of solid melting at 177' with decomposition. Analysis : Calcd. for CsH&TBSp: N, 17.86; S, 61.27; mol. wt., 473. Found: N, 17.63; S, 61.10; mol. wt., 458. The filtrate was diluted with 100 ml. of heptane and chilled to -5', then filtered; the 6 grams of light yellow crystals were collected, washed with 50 ml. of cold heptane, and crystallized from heptane to melt a t 74-5'. Analysis: Calcd. for C I I H I ~ N Z S N, ~ : 9.13; S, 42.60. Found: N, 8.95; S, 41.50. The filtrate was evaporated under vacuum to give 38 grams of a light yellow oil which contained 33.80% sulfur and 7.5Oy0 nitrogen. Thioacetals. T o prepare thioacetals which would be freely soluble in oils, tert-octanethiol, fert-dodecanethiol, and n-dodecanethiol were added to croton-
-c\s/c- s\
CH-R
R
Mixed thioacetals R
R
\/ are easily formed without catalysts from formaldehyde or other aldehydes and mercaptans. To a solution of 0.5 mole of 2,5-dimercaptothiadiazole and 1 mole of mercaptan in 350 ml. of dioxane at 70' was added 1 mole of aldehyde dropwise over 1 hour. The solution was stirred a t 90' for 2 hours, evaporated under' vacuum, and filtered through Celite. In the purification of the thioacetal from 2,5-dimercaptothiadiazole, 2-ethylhexaldehyde, and tert-octanethiol, there was
Table II. Yields, Properties, and Analyses of /3-Mercaptobutyraldehydes R-S-CH-CH2-CHO
I
obtained an 8% yield of the monothioacetalnnelting a t 106' from hexane. Analysis: Calcd. for C18H34N&: N, 6.90; S, 31.53; mol. wt., 406. Found: N, 6.62; S,31.40; mol. wt., 411. Polysulfides. 2,5-Dimercaptothiadiazole, mercaptans, and sulfur give monodisulfides : N-N R-S-S-C
I1
II
C-S-H
Even if 2 or more moles of sulfur and mercaptans are used per mole of 2,5dimercaptothiadiazole, monodisulfides are the major products. They are crystalline compounds and strong acids, readily soluble in aqueous carbonate. When excess sulfur and mercaptans are used, the other products are mixtures, possibly of 2,5-dimercaptothiadiazole bisdisulfides and monopolysulfide. Specific monodisulfides were prepared by stirring a mixture of 0.2 mole of 2,5-dimercaptothiadiazole, 0.3 mole of mercaptan, 0.23 gram-atom of sulfur and 100 ml. of Cellosolve at 125' to 130' for about 6 hours, until hydrogen sulfide no longer was evolved. The bright yellow solution was stirred 5 minutes with 500 ml. of water a t 80°, and the lower layer was separated, diluted with ' . 250 ml. of n-heptane, and chilled to 0 The crystals were collected on a filter, washed with a little cold n-heptane, and recrystallized from n-heptane or a mixture of benzene and n-heptane. 2,5Dimercaptothiadiazole mono-trrt-octyl disulfide was also formed, in 60% yield, from 2,5-dimercaptothiadiazole, sulfur, and excess tert-octanethiol without added solvent. 2,5-Dimercaptothiadiazole tert octyl monodisulfide is also formed by oxygen oxidation of a Cellosolve solution of 2,5-dimercaptothiadiazoleand the mercaptan. Oxygen was passed through a solution of 22.5 grams (0.15 mole) of 2,5-dimercaptothiadiazole and 21.9 grams (0.15 mole) of tert-octanethiol in 100 ml. of Cellosolve a t 100' for 7 hours, then treated as above. This reaction gave 23 grams (53y0) of the mono-ttrtoctyl disulfide. None of the disulfide product was formed in the absence of Cellosolve, even when ferric citrate or sodium hydroxide was added to the mixture. Pure bisdisulfides
-
-
CHs Yield,
R t ert- 0ctyl
n-Dodecyl tert-Dodecyl
%
ng
47 88 41
1.4800 1.4168 1.4031
Boiling Point "C. Mm. 95-97 146-149 138-144
1.7 0.95 2.4
Sulfur, Calcd. 15.53 11.76 11.76
7, Found 15.40 11.90 11.60
N-N R-S-S-C
/I
/I
C-S-S-R
can be prepared in good yields eithe.r by the reaction of the sulfenyl chloride VOL. 49, NO. 9
SEPTEMBER 1957
1363
RSCl with 2,5-dimercaptothiadiazole, or by formation of 2,5-dimercaptothiadiazole dichloride N--N
Cl-s-c
/I
>’
I1
c-s-c1
and subsequent reaction with mercaptans. The second method is generally preferable, as the dichloride is more stable a t higher temperatures than the alkyl sulfenyl chlorides, especially those derived from tertiary mercaptans. In carrying out the first method, chlorine (0.4 mole) was slowly bubbled into a stirred solution of 0.4 mole of mercaptan in 300 ml. of dry carbon tetrachloride a t -10’. After all the chlorine was in, the solution was stirred at - IOo for 20 minutes, then treated with 0.2 mole of 2,5-dimercaptothiadiazole in 2gram portions. When all the 2,5-dimercaptothiadiazole had been added, the solution was slowly warmed to 4 5 O , stirred a t that temperature for 2 hours, cooled to room temperature, and washed successively with water, 5% sodium carbonate solution, and water. I t was then dried and evaporated under vacuum. The chlorination involved in the second method was carried out with either chIorine or sulfuryf chloride. Chlorine (0.4 mole) was slowly bubbled into a stirred suspension of 0.2 mole of 2,5-dimercaptothiadiazole in 300 moles of dry carbon tetrachloride a t 5’ to IOo; the suspension of bright yellow solid was stirred a t 10’ for 30 minutes, then treated with the mercaptan dropwise a t lo’, Alternatively, sulfuryl chloride
Table 111.
(0.4 mole) was added dropwise to a stirred suspension of 0.2 mole of 2,5dimercaptothiadiazole in 300 ml. of dry carbon tetrachloride at 28’ to 30’; the suspension was stirred at 25’ for 1 hour, and treated with the mercaptan. The product was worked up as in the first method. Evaluation
Test results for typical derivatives of each of the five classes are listed in Table 111. The bench test for corrosion of copper-lead bearings (the SSCT) is a modification (4) of the original test described by Loane and Gaynor ( 5 ) . A modified Electromotive Diesel (EMD) test ( 4 ) was used to measure the ability of 2,5-dimercaptothiadiazole derivative to prevent corrosion of silver by corrosive sulfur compounds. As Table I11 indicates, the thioethers vary considerably in ability to inhibit bearing corrosion. Alkyl thioethers, whether made by addition of 2,5-dimercaptothiadiazole to alkenes or by reaction of dipotassium 2,5-dimercaptothiadiazole with alkyl halides, are ineffective. Thioethers derived from terpenes such as a-pinene and dl-limonene are intermediate ; the styrene and a-methylstyrene adducts are the best inhibitors of all the thioethers. The reason for these differences is not known. The trithioformate from 1 mole of 2,5-dimercaptothiadiazole and 1 mole of tert-octanethiol is an exceptionally powerful inhibitor. The ability of these derivatives to inhibit corrosion is not limited to lubricating oils alone. Aviation gasolines having a copper strip rating of 3a (7)
2,5-Dimercaptothiadiazole Derivatives as Corrosion Inhibitors
Literature Cited
(All tests run in soIvent-extraction SAE 30 oil) SSCP,
wt. Loss
in 48 Hours,
Derivative None Mono-4-n-amylpgridinium salt Di- JM-R amine salt Di-Armeen 2 HT salt Bis-( 1-n-octyl) thioether Bis-2-(4-methyl-3)-cyclohexenyl isopropyl thioetherC Bis-2-phenylpropyl thioether 3-tert-Dodecylthiathiobutyral Bisthioformal with tert-octane thiol Bisthio-2-ethylhexanal with tert-octanethiol Bislauroyl ester Mono-tert-octgltrithioformate Mono-tert-octyl disulfide Bis-tert-octyl disulfide Bis-tert-dodecyl disulfide Bis-n-dodecyl disulfide
E M D Test Wt. loss Concn., in 24 Hour* %b
580 30 110
49 549
...
0.15 0.15 0.20 0.20
110 3
5 11 95
155 66 65 29
0.20
14
0.10
14
0.15 0.10
2
11 120 0
0.15 0.20
7 0 2 0 8 0
... 75 50 80
0.10
0.15 0.20 0.10 0.20
From dl-limonene.
INDUSTRIAL AND ENGINEERING CHEMISTRY
(1) Am. SOC. Testing Materials, Philadelphia, Pa., D 130-55T, ASTM Standards, 1955. ( 2 ) Bambas, L. L., “Chemistry of Heterocyclic Compounds,” vol. IV, pp. 177-98, Interscience, New York, 1952. (3) Fields, E. K., J. Org. Chern. 21, 497 (1956). ( 4 ) Fields, E. K., Scanley, C. S., Linsk, J., U. S. Patent 2,719,126 (Sept. 27, 1955). ( 5 ) Loane, C. M., Gaynor, J. W., IND. ENG. CHEM., ANAL. ED. 17, 8 9 (1945). (6) Roberts, E. N., Fields, E. K., Brown, J. S., U. S. Patent 2,703,785 (March 8, 1955). ~
4
0
RECEIVED for review September 28, 1956 ACCEPTEDFebruary 6, 1957
0.75% inhibitor f 3.3% barium-neutralized reaction product of phosphorus pentasulfide and polybutene. Plus 0.75% of sulfurized olefin.
1 364
are dropped to a rating of l a by the addition of O.1y0 of bis-JM-R amine salt of 2,5-dimercaptothiadiazole,and to 2a by O . O O l ~ o of the salt. Soluble-oil compositions containing 0.09% 2,5dimercaptothiadiazole prevent rusting of iron chips in water; in these compositions the thioformals also prevent the growth of fungi and bacteria ( 6 ) . The silver corrosion data show that the bisdisulfides are among the most effective inhibitors. I t is easy to see haw they inhibit the corrosion of silver by sulfur or active sulfur compounds. These bisdisulfides can react with large quantities of sulfur to give compounds which are noncorrosive to silver. Specifically, 2,5dimercaptothiadiazole bis-n-dodecyl disulfide was made to react with 16 gramatoms of sulfur. The resulting product was noncorrosive in the modified EhfD silver-strip test. This ability to act as a ‘(sulfur sink” is peculiar to the 2,S-dimercaptothiadiazole disulfides, as alkyl o r aryl polysulfides containing as few as three sulfur atoms are already corrosive to silver. No such simple explanation will serve for the other derivatives. The mechanism of bearing-corrosion inhibition is not well understood. An inhibitor may function in a t least three ways: as an antioxidant, either by preventing the formation of peroxides o r hydroperoxides, or by breaking oxidation chains; as a chelating agent, in forming tightly adhering organic coatings on bearing surfaces; and as a steady source of enough sulfur under severe conditions to form a protective sulfide layer on the bearing surfaces without releasing enough to cause corrosion. Whatever the requirements for effective bearing-corrosion inhibitors, the 2,5dimercaptothiadiazole derivatives seem to be especially qualified.
-
Division of Petroleum Chemistry, Symposium on Additives in Lubricants, 130th Meeting, ACS, Atlantic City, N. J., Septemlxr 1956.
