Lubricating oils are protected against oxidation by the addition of a stabilizing amount of at least one n-alkyl substituted 2-thiazoline disulfide.

This invention relates to improved additives for lubricants. In one aspect, 
this invention relates to lubricating compositions containing as an 
additive at least one n-alkyl substituted 2-thiazoline disulfide. In 
accordance with another aspect, this invention relates to a method of 
stabilizing lubricating oils against oxidative degradation by the addition 
of at least one n-alkyl substituted 2-thiazoline disulfide. In accordance 
with a further aspect, this invention relates to improved lubricants 
containing at least one n-alkyl-2-thiazoline disulfide. 
Advances in the design and construction of internal combustion engines to 
produce improved and more efficient and economical engines have presented 
many problems in the lubrication of the modern internal combustion engine. 
To meet the increased severe demands upon engine lubricants many types of 
lubricant additives have been developed to obtain certain desired 
characteristics thereof. Among the more effective addition agents which 
have been developed for compounding with lubricants are many 
sulfur-containing organic compounds. However, few of these compounds have 
been considered entirely adequate for the purpose for which they were 
intended because they did not sufficiently improve one or more of the 
lubricating properties. For example, they did not improve the resistance 
to oxygen and the like. The present invention resides in providing an 
additive that will stabilize lubricating compositions against oxidative 
degradation. 
An object of this invention is to provide improved additives exhibiting 
reduced oxidative degradation tendencies in lubricating oils. 
Another object of this invention is to provide improved lubricating 
compositions utilizing the additives of the invention. 
A further object of this invention is to provide novel compounds useful as 
ashless lubricant additives. 
A further object is to lower the phosphorus content of automobile engine 
oil. 
Other objects, aspects, as well as the several advantages of the invention 
will be apparent to those skilled in the art upon reading the 
specification and the appended claims.

Thus, according to the invention there is provided lubricating compositions 
exhibiting improved characteristics containing at least one n-alkyl 
substituted 2-thiazoline disulfide. 
In accordance with another embodiment of the invention lubricating 
compositions are provided containing an effective stabilizing amount of at 
least one n-alkyl substituted 2-thiazoline disulfide. 
Further, according to the invention, there is provided a method of 
stabilizing lubricating compositions against oxidative degradation which 
comprises incorporating therein a stabilizing amount of at least one 
n-alkyl substituted 2-thiazoline disulfide. 
The additives of the invention are n-alkyl-2-thiazoline disulfides wherein 
the n-alkyl group can range from 1 to about 20 carbon atoms, inclusive, 
per alkyl group. The disulfides of the invention can be represented by the 
formula 
##STR1## 
wherein R is a normal alkyl group having from 1 to 20, inclusive, carbon 
atoms. 
Representative examples of suitable compounds that can be used falling 
within the scope of the above-described formula include 
methyl-2-thiazoline disulfide, n-propyl-2-thiazoline disulfide, 
n-butyl-2-thiazoline disulfide, n-hexyl-2-thiazaline disulfide, 
n-octyl-2-thiazoline, disulfide n-decyl-2-thiazoline disulfide, 
n-dodecyl-2-thiazoline disulfide, n-eicosyl-2-thiazoline disulfide, and 
the like, and mixtures thereof. 
The lubricating oils to which the invention compositions can be added 
include any suitable mineral oil of lubricating viscosity such as those 
used for compounding lubricating oils of SAE 10 to SAE 50 viscosity. These 
oils can be derived from suitable naphthenic, paraffinic, and mixed base 
crudes as well as mixtures of one or more types. The additives of the 
invention has special advantages when employed with paraffinic types of 
oil such as are obtained by solvent extraction of a suitable refinery 
stream. Many suitable lubricating compositions are available as commercial 
products such as those used as motor oils, fuel oils, gear oils, automatic 
transmission oils, and the like. A lubricating oil can also contain other 
additives such as thickeners and the like. 
Lubricating oil for internal combustion engines generally contain an 
antioxidant-antiwear zinc additive, such as zinc dialkyldithiophosphate, 
with the concentration of zinc being in the range 0.1-0.15 weight percent 
of the finished oil. The zinc and the phosphorus can be detrimental to 
other parts of the engine operation as it is desirable to have a 
non-metal, non-phosphorus substitute to permit the use of a lower 
concentration of zinc and phosphorus in motor oil. The compounds of the 
instant invention, since they are antioxidants, permit the use of lower 
concentrations of the zinc compound in the range 0.04-0.07 weight percent 
zinc in the finished oil. Use of 0.04-0.07 weight percent zinc without the 
inventive additive would result in excessive thickening of the oil during 
normal engine operations. 
Generally speaking the additives of this invention can be added to a base 
lubricating oil in any amount sufficient to produce the desired degree of 
improvement. More specifically, an amount of additive used according to 
the invention will be an antioxidant stabilizing amount which is 
sufficient to stabilize the lubricating composition against oxidative 
degradation. For example, the additives can be used in amounts ranging 
from 0.05 to about 10 weight percent of the finished oil. The presently 
preferred concentration of product additive is in the range of about 0.1 
to about 5 weight percent of finished oil. 
Other agents than those which are mentioned can be present in the lubricant 
composition, such as dyes, pour point depressants, heat thickened fatty 
oils, sulfurized fatty oils, sludge dispersers, foam suppressants, 
thickeners, viscosity index improvers, oiliness agents, resins, rubber, 
molten polymers and the like. 
The effectiveness of the herein described thiazoline disulfides stabilizing 
oxidative degradation of lubricating oils is demonstrated by the following 
examples. 
EXAMPLE I 
The following inventive and comparative runs were conducted to demonstrate 
the oxidative stabilization achieved by the inventive additive. 
In the following bench test 1500 ppm nitrous oxide/air mixture was used as 
the oxidizing agent on a fully formulated 10W30 engine oil. The only 
difference on the two formulations was the oxidation inhibitor as shown in 
Table I. 
TABLE I 
______________________________________ 
hours elapsed before 
Run# oxidation inhibitor oxidation break point 
______________________________________ 
1 1.0 vol % Lubrizol 1395.sup.a 
49 
2 0.5 vol % Lubrizol 1395 
&gt;80 
+ 1.0 vol % 
n-dodecyl-2-thiazoline disulfide 
______________________________________ 
.sup.a Commercial zinc dialkyldithiophosphate (antioxidant and antiwear 
additive) 
For each run, 30 g of test oil in a test tube was heated to 150.degree. C. 
with an immersed copper electric wire while the above oxidizing agent 
bubbled through the oil at a rate of 100 cc gas per min. At about 20 hr 
intervals the level of oxidation was determined by differential infrared 
analysis. The intensity of the 1720 cm.sup.-1 carbonyl stretching band was 
used in the measure of oxidation. A plot of the band intensity versus time 
in each run showed a break point at which oxidation sharply increased. 
This break point is a measure of the antioxidative capacity of the test 
oil. 
The test results in Table I show that n-dodecyl-2-thiazoline disulfide is 
an effective antioxidant, and can replace some of the zinc 
dialkyldithiophosphate used in all automobile motor oils. 
EXAMPLE II 
The n-alkyl-2-thiazoline disulfide additive was further evaluated for 
antioxidant properties in a Sequence III-D high temperature oxidation and 
engine wear test for evaluating automobile engine oils as described in 
ASTM Special Technical Publication 315 H. 
For comparative purposes tert-octyl-2-benzothiazyl disulfide (disclosed in 
U.S. Pat. No. 3,878,117) was also tested. 
The formulations tested were as follows: 
______________________________________ 
FORMULATIONS 
Volume Percent 
A B C 
______________________________________ 
Mid-continent SAE 10 stock 
33.1 33.1 33.1 
Mid-Continent SAE 20 stock 
33.0 33.0 33.0 
Phil-Ad 300.sup.a 2.2 2.2 2.2 
Edwin Cooper E 686.sup.b 
1.5 1.5 1.5 
Lubrizol 934.sup.c 4.1 4.1 4.1 
Phil-Ad VII solution.sup.d 
23.0 23.1 23.0 
Exxon ECA 5118.sup.e 
0.6 0.6 0.6 
Lubrizol 1395.sup.f 0.5 0.5 0.5 
n-octyl 2-thiazoline disulfide 
1.5 -- -- 
tert-octyl-2-thiazoline disulfide 
-- 1.5 -- 
tert-octyl-2-benzothiazyl disulfide 
-- -- 1.5 
______________________________________ 
.sup.a Overbased calcium petroleum sulfonate 
.sup.b Commercial calcium phosphonate phenate 
.sup.c Commercial alkyl succinic ester 
.sup.d Commercial butadienestyrene copolymer viscosity index improver 
diluted in oil 
.sup.e Commercial pour depressant 
.sup.f 0.5 vol % of 1395 is equivalent to 0.05 wt % zinc 
A summary of the Sequence III D test results is presented in Table II 
TABLE II 
__________________________________________________________________________ 
pass 
specification 
Formulation A B C for S.F. grade 
__________________________________________________________________________ 
Viscosity Increase, % at 40.0.degree. C. 
at 16 hr 50.9 
76.9 
32.1 
32 hr 75.6 
109.1 
508.5 
48 hr -- 290.9 
a 
56 hr 112.2 
1584.2 
b 
64 hr 124.5 
a b 375 max. 
average engine sludge (10 = clean) 
9.8 9.3 9.3.sup.b 
9.2 min. 
average engine varnish (10 = clean) 
9.3 9.3 9.3.sup.b 
9.2 min. 
average cam plus lifter wear 
0.00016 
0.0023 
0.0018.sup.b 
0.0040 max. 
(inches) 
average bearing weight loss (mg) 
2.87 
203.0 
283.0.sup.b 
number of sluggish rings 
0 14 21.sup.b 
__________________________________________________________________________ 
.sup.a too viscous to measure 
.sup.b at 42 hr. test terminated as oil too viscous to operate engine. 
These data show oxidative thickening of the oil is controlled in inventive 
formulation A, containing n-octyl-2-thiazoline disulfide while control 
formulation B with tert-octyl 2-thiazoline disulfide failed (exceeded 375% 
viscosity increase) in less than 56 hrs and control formulation C failed 
in less than 32 hrs. Also control formulations B and C gave excessive 
bearing weight loss. The data also show that the formulation containing 
the n-alkyl group in the inventive additives passes the above III-D test 
while the formulation containing the tert-alkyl group attached to 
2-thiazoline fails in excessive viscosity. Thus the n-alkyl group is 
essential for the inventive additive.