Lubricating oil composition comprising alkylnaphthalene and benzothiophene

A lubricating oil composition comprises an alkylnaphthalene which has one or two alkyl groups each having from 8 to 30 carbon atoms, and at least one member selected from benzo(b)thiophene and derivatives thereof, and naphthalenethiol and derivatives thereof. The composition has good oxidative stability.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a synthetic lubricating oil composition 
having good oxidative stability or oxidation resistance. The present 
invention also relates to a process for preparing such a composition. 
2. Description of the Prior Art 
Lubricating oils which are recycled in use should generally stand long-term 
use. For this purpose, it is usual to employ mineral lubricating oils 
wherein highly refined mineral oils are formulated with appropriate 
antioxidants. However, the mineral lubricating oils undesirably have a 
limitation with respect to the oxidative stability. This makes it 
difficult to subject the mineral lubricating oil to long-term use such as 
in machines whose portions to be lubricated are exposed to severe 
temperature conditions. 
Accordingly, synthetic ester lubricating oils such as diesters, polyol 
esters and the like have been developed and commercialized as having 
better oxidative stability and have now been in general use. Although 
these synthetic ester lubricating oils have good oxidative stability, 
inherent disadvantages are involved in that they suffer hydrolysis to 
produce acids, cause sealing agents to be swollen and are expensive. 
Accordingly, limitation is placed on their range of utility. 
Hydrogenated products of poly-.alpha.-olefins have been widely known as a 
synthetic lubricating oil having high oxidative stability. The oxidative 
stability is better than those of mineral oils but is not so high as those 
of synthetic ester lubricating oils. 
Recently, attention has been drawn to high oxidative stability of 
naphthalene derivatives. There are provided lubricating oil compositions 
which are obtained by mixing alkylnaphthalenes used as a base oil for the 
lubricating oil and specific types of compounds at a defined ratio. These 
are set forth, for example, in Japanese Laid-open Patent Application Nos. 
59-147096 and 59-147097. These compositions are not still satisfactory 
when applied to the fields where high oxidative stability is essentially 
required. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a 
lubricating oil composition which overcomes the disadvantages of the prior 
art lubricating oils or oil compositions. 
It is another object of the present invention to provide a lubricating oil 
composition which has better oxidative stability as never been achieved in 
prior arts and can be applied under severe conditions. 
It is a further object of the present invention to provide a process for 
preparing such a lubricating oil composition. 
The above objects can be achieved, according to one embodiment of the 
invention, by a lubricating oil composition which comprises an 
alkylnaphthalene having one or two alkyl groups each having from 8 to 30 
carbon atoms, and at least one member selected from the group consisting 
of benzo(b)thiophene and derivatives thereof represented by the following 
general formula (1) and naphthalenethiol and derivatives thereof 
represented by the following formula (2) 
##STR1## 
wherein each R.sup.1 and each R.sup.2 independently represent a monovalent 
hydrocarbon group having from 8 to 30 carbon atoms, m is an integer of 
from 0 to 2, n is an integer of from 0 to 4 and p is an integer of from 0 
to 3. 
According to another embodiment of the present invention, there is also 
provided a process for preparing a lubricating oil composition which 
comprises reacting an alkylating agent with naphthalene to obtain an 
alkylnaphthalene having one or two alkyl groups each having from 8 to 30 
carbon atoms, the reaction being effected in benzo(b)thiophene and/or 
naphthalenethiol, and collecting the resultant reaction product.

DETAILED DESCRIPTION AND EMBODIMENTS OF THE INVENTION 
The synthetic lubricating oil composition of the present invention should 
comprise an alkylnaphthalene as a base oil. The base oil is an 
alkylnaphthalene having one or two alkyl groups each having from 8 to 30 
carbon atoms or a mixture of the alkylnaphthalenes as defined above. 
The type of alkyl group of the alkylnaphthalene greatly influences the 
properties of final lubricating oil compositions. In the practice of the 
present invention, the alkyl group may be linear or branched and should 
have from 8 to 30 carbon atoms, preferably from 12 to 18 carbon atoms. One 
or two alkyl groups should be contained in the alkylnaphthalene. This 
means that the total number of carbon atoms of alkyl group or groups 
ranges from 8 to 60, preferably from 8 to 48 and most preferably from 12 
to 36. With alkylnaphthalenes wherein the total number of the alkyl group 
or groups is less than 8, the resultant lubricating oil composition 
becomes low in flash point. On the other hand, when the total number of 
carbon atoms exceeds 60, the pour point of the resultant lubricating oil 
composition becomes high, unfavorably causing a low temperature pour to be 
deteriorated. 
The alkylnaphthalenes which are especially preferred as a base oil of the 
lubricating oil composition of the present invention include 
monoalkylnaphthalenes which have one linear or branched alkyl group having 
from 12 to 24 carbon atoms, dialkylnaphthalenes which have two linear or 
branched alkyl groups each having from 8 to 24 carbon atoms, and mixtures 
thereof. When these compounds are mixed in an appropriate manner, there 
can be obtained a lubricating oil composition which has a controlled 
viscosity. 
The position of the alkyl group joined to the naphthalene ring is not 
critical. If two alkyl groups are incorporated in the alkylnaphthalene, 
the mutual positions of these alkyl groups are also not critical. 
The lubricating oil composition of the present invention should further 
comprise one or more of benzo(b)thiophene and derivatives thereof 
represented by the following general formula (1) and naphthalenethiol and 
derivatives thereof represented by the following formula (2) 
##STR2## 
wherein each R.sup.1 and R.sup.2 independently represent a monovalent 
hydrocarbon group having from 8 to 30 carbon atoms and preferably a linear 
or branched alkyl group although R.sup.2 may be a naphthalene group or an 
alkylnaphthalene group, m is an integer of from 0 to 2, n is an integer of 
from 0 to 4 and p is an integer of from 0 to 3. In general, m and p are 
each zero and n is 1. 
In the lubricating oil composition of the invention, the amount of the 
compound of the formula (1) or (2) is in the range of from 0.01 to 5 parts 
by weight, preferably from 0.03 to 3 parts by weight, per 100 parts by 
weight of.sup.! the alkylnaphthalene base oil. If the amount is below the 
above range, the effect is not so high that high oxidative stability may 
not be obtained. If the amount exceeds the above-defined range, any 
further significant effect is not recognized with poor economy. In 
addition, there is a tendency that sludge is formed in large amounts. 
In the process for preparing the lubricating oil composition of the 
invention, the compound of the formula (1) or (2) may be added to the 
alkylnaphthalene to obtain a lubricating oil composition. Alternatively 
and, in fact, preferably, it is effective to add benzo(b)-thiophene or 
naphthalenethiol at the time of preparation of the alkylnaphthalene to 
obtain a reaction mixture. This mixture is provided as a lubricating oil 
composition as it is. 
The alkylnaphthalene can be prepared by alkylation of naphthalene with a 
conventional alkylating agent. Examples of the alkylating agent preferably 
include linear .alpha.-olefines which are obtained by low degree of 
polymerization of ethylene or pyrolysis or catalytic decomposition of 
heavy oils and petroleum fractions. By this, there are obtained 
alkylnaphthalenes having a secondary alkyl group whose alkyl moiety has 
one branched methyl, ethyl or propyl group and wherein the number of 
carbon atoms in the alkyl moiety is single or a distribution in the number 
of carbon atoms is very narrow. The resultant alkylnaphthalene has a good 
hue. 
The .alpha.-olefins should preferably be linear in nature and should have 
from 8 to 30 carbon atoms. Specific examples include 1-octene, 1-nonene, 
1-docene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 
1-eicosene, 1-docosene, 1-tetracosene, 1-octacosene, 1-triacontene and 
mixtures thereof. 
In the alkylation reaction, the molar ratio between the alkylating agent 
and naphthalene is not critical. Preferably, the molar ratio is in the 
range of not less than 2:1, more preferably from 3:1 to 6:1. If the ratio 
is less than 2:1, there may occur the case where polymerization of the 
.alpha.-olefin is not negligible. Over 6/1, the yield of an intended 
product may be lowered. 
For the alkylation reaction, it is preferred that there is used, as an 
alkylating catalyst, hydrogen zeolite Y which is prepared from a silica 
material such as active silicate or active aluminosilicate obtained by 
acid treatment of clay minerals as taught in Japanese Laid-open Patent 
Application No. 63-150231. 
The reaction is preferably effected by gradually dropping an alkylating 
agent in a mixture of molten naphthalene and a catalyst. The dropping time 
may be arbitrarily determined depending on the molar ratio and the amount 
of the reaction system and is preferably in the range of from 1 to 7 
hours. The dropping rate of the alkylating agent is not critical. 
In the preparation of the alkylnaphthalene as described above, when 
benzo(b)thiophene or naphthalenethiol is added to the reaction system, the 
resultant reaction mixture may be used as it is as a lubricating oil 
composition of the present invention. Benzo(b)thiophene or 
naphthalenethiol is preferably added to the mixture of the naphthalene and 
catalyst, followed by dropping of the alkylating agent. The amount of 
benzo(b)thiophene or naphthalenethiol is preferably in the range of from 
0.01 to 5 parts by weight per 100 parts by weight of naphthalene. 
By the addition of benzo(b)thiophene or naphthalenethiol at the time of the 
reaction of the naphthalene, the resultant composition exhibits better 
oxidative stability than those obtained by addition of the compound of the 
formula (1) or (2) to alkylnaphthalenes, with a reduced amount of sludges. 
The synthetic lubricating oil composition of the present invention may 
further comprise additives for lubricating oils ordinarily used for this 
purpose. Examples of such additives include antioxidants, detergent 
dispersants, viscosity index improvers, pour point depressants, oiliness 
improvers, abrasion resistant agents, extreme pressure agents, metal 
inactivating agents, corrosion inhibitors, defoamers, emulsifiers, 
anti-emulsifiers and the like. Details of these additives are set forth, 
for example, in Journals of the Lubrication Society Vol. 15, No. 5 or 
"Additives of Petroleum Products" edited by Toshio Sakurai and published 
by Saiwai Pub. 
The synthetic lubricating oil composition of the present invention can be 
applied as lubricating oils for which oxidative stability is required, 
e.g. turbine oils, gear oils, hydraulic oils, metal machining oils, slide 
guiding oils, bearing oils and the like. 
The present invention is more particularly described by way of examples, 
which should not be construed as limiting the invention. Comparative 
examples are also described. 
EXAMPLE 1 
384 g (3 moles) of purified naphthalene, 3.8 g of benzo(b)thiophene and 
14.0 g of H-Y zeolite (Japanese Laid-open Patent Application No. 
63-150231) were placed in a one-liter four-necked flask equipped with a 
thermometer, an agitating blade, an air-cooling pipe and a dropping 
funnel, followed by setting on a mantle heater. While agitating, the 
mixture was heated from room temperature to 210.degree. C. in about 30 
minutes. This point was taken as an initiation of the reaction, and 234 g 
(1 mol) of a mixture of 1-hexadecene and 1-octadecene at a ratio of 50/50 
was dropped in the mixture for reaction. The reaction time was 7 hours. 
The resultant reaction mixture (lubricating oil composition) was subjected 
to measurement of oxidative stability according to a rotary bomb-type 
oxidative stability testing method prescribed in JIS-K2514-3 and also to 
observations of the copper catalyst used and the amount of sludge formed. 
Evaluation was made according to the following standard. The results are 
shown in Table 1. 
State of Copper Catalyst 
.largecircle.: the copper catalyst suffered little change in color 
.DELTA.: the copper catalyst suffered a change in color to brown .times.: 
the copper catalyst suffered a change in color to black 
Occurrence of Sludge 
.largecircle.: little occurrence 
.DELTA.: some deposits found on the test container .times.: deposits found 
entirely on the test container 
EXAMPLES 2 AND 3 AND COMATIVE EXAMPLE 1 
The general procedure of Example 1 was repeated except that 5.7 g and 7.6 g 
of benzo(b)thiophene were, respectively, used to obtain reaction mixtures 
(lubricating oil compositions) of Examples 2 and 3 and that 
benzo(b)thiophene was not used to obtain a reaction mixture (lubricating 
oil composition) of Comparative Example 1. These mixtures were subjected 
to similar tests as in Example 1. The results are shown in Table 1. 
EXAMPLE 4 
The general procedure of Example 1 was repeated except that 3.8 g of 
naphthalenethiol was used instead of benzo(b)thiophene, thereby obtaining 
a reaction mixture (lubricating oil composition). The mixture was tested 
in the same manner as in Example 1. The results are shown in Table 1. 
TABLE 1 
______________________________________ 
Oxidative 
State of 
Amount 
Amount stability 
copper of 
Additive (g) (minutes) 
catalyst 
sludge 
______________________________________ 
Example 1 
benzo(b)- 
3.8 1300 .largecircle. 
.largecircle. 
thiophene 
Example 2 
benzo(b)- 
5.7 2000 .largecircle. 
.largecircle. 
thiophene 
Example 3 
benzo(b)- 
7.6 2800 .largecircle. 
.largecircle. 
thiophene 
Example 4 
naphtha- 3.8 2800 .largecircle. 
.largecircle. 
lene-thiol 
Com- no -- 400 .largecircle. 
.largecircle. 
parative 
additive 
Example 1 
______________________________________ 
EXAMPLES 5 to 10 AND COMATIVE EXAMPLES 2 AND 3 
1 part by weight of benzo(b)thiophene or naphthalenethiol was added to 100 
parts by weight of the reaction mixture of Comparative Example 1 to 
provide mixtures of Examples 5 and 6, respectively. Similarly, 
hexadecylbenzo(b)thiophene was added in amounts of 0.5 and 1 part by 
weight, thereby providing mixtures of Examples 7 and 8, respectively. One 
part by weight of octadecylbenzo(b)thiophene was added, thereby obtaining 
a mixture of Example 9. One part by weight of hexadecylnaphthalenethiol 
was added, thereby obtaining a mixture of Example 10. These composition 
were each subjected to an oxidative stability test in the same manner as 
in Example 1. The results are shown in Table 2. 
Additives other than those used in the invention were also used to obtain 
synthetic lubricating oil compositions for comparison. These compositions 
were subjected to an oxidative stability test in the same manner as in 
Example 1. The results are also shown in Table 2. 
TABLE 2 
______________________________________ 
Oxidative 
State of 
Amount 
Amount stability 
copper of 
Additive (parts) (minutes) 
catalyst 
sludge 
______________________________________ 
Example 
benzo(b)- 1 1050 .largecircle. 
.largecircle. 
5 thiophene 
Example 
naphtha- 1 1400 .largecircle. 
.largecircle. 
6 lene-thiol 
Example 
hexadecyl- 
0.5 1800 .largecircle. 
.largecircle. 
7 benzo(b)- 
thiophene 
Example 
hexadecyl- 
1 2200 .largecircle. 
.largecircle. 
8 benzo(b)- 
thiophene 
Example 
octadecyl- 
1 1900 .largecircle. 
.largecircle. 
9 benzo(b)- 
thiophene 
Example 
hexadecyl- 
1 2000 .largecircle. 
.largecircle. 
10 naphtha- 
lene-thiol 
Com- dibenzyl 0.5 900 X X 
parative 
disulfide 
Example 
Com- triphenyl 1 100 X .largecircle. 
parative 
phosphate 
Example 
3 
______________________________________ 
As will be apparent from the above results, the lubricating oil 
compositions of the invention exhibit better oxidative stability and can 
be appropriately used in fields where high oxidative stability is required 
.