A class of N,N',N"-trisubstituted bis-(p-aminobenzyl)anilines are found to be effective antioxidants in a broad spectrum of petroleum and petroleum related products. Trialkyl, tri(arylmethyl), and tri(heteroarylmethyl) substituted materials of the parent compound are especially effective at concentrations as low as about 0.0005 percent by weight.

BACKGROUND OF THE INVENTION 
A persistant problem common to virtually all petroleum products and 
petroleum-related products is their tendency to undergo oxidative 
degradation. Oxidation may occur even under the relatively mild conditions 
attending storage and transport, and is appreciably accelerated when 
operating conditions are conductive to oxidation processes, for example, 
the elevated temperatures experienced by lubricating oil. Such oxidative 
processes not only cause chemical degradation of the petroleum or 
petroleum-related product, but may also cause appreciable changes in 
desirable physical properties, such as viscosity, which lead to a 
deterioration of product performance characteristics. Additionally, the 
oxidative products themselves may attack materials in contact with the 
petroleum and petroleum-related products, such as metals in contact with 
transmission or lubricating oils, thereby causing inefficient performance 
and, in extreme cases, even mechanical failure. 
It has been found that certain N,N',N"-trisubstituted derivatives of 
bis-(p-aminobenzyl)anilines are effective antioxidants in the 
aforementioned products at relatively low levels. The materials have the 
further advantage of admitting to structural variations within broad, but 
nonetheless well defined, limits thereby permitting optimization of 
antioxidant properties for a particular product in a specified use. 
SUMMARY OF THE INVENTION 
The principal object of this invention is to provide a method of inhibiting 
oxidation in petroleum products and petroleum-related products by the 
addition thereto of effective amounts of additives having antioxidant 
properties, and compositions therefor. An embodiment of this invention 
comprises the use of a N,N',N"-trisubstituted bis-(p-aminobenzyl)aniline 
as an addition in said products. In a more specific embodiment the 
nitrogen substituent is a saturated alkyl moiety containing up to about 20 
carbon atoms. In a further specific embodiment the nitrogen substituent is 
an arylmethyl moiety. In still another specific embodiment the nitrogen 
substituent is a pyridinylmethyl group. Depending upon its intended use, 
the additives are present at a concentration from about 0.0005 to about 5 
wt. %. 
DESCRIPTION OF THE INVENTION 
The invention described herein is a method of inhibiting oxidation in 
petroleum and petroleum-related products selected from the group 
consisting of lubricating oils, greases, plastics and rubbers comprising 
adding to said products oxidation inhibiting amounts of the antioxidant 
materials of this invention, and compositions therefor. The materials of 
this invention which possess the highly desirable antioxidant properties 
claimed have the structure, 
##STR1## 
In one embodiment of this invention A is a saturated alkyl moiety 
containing up to about 20 carbon atoms. In other embodiments A is an 
arylmethyl or heteroarylmethyl moiety of the formula --CH.sub.2 X, where X 
is a monovalent radical whose parent is selected from the group consisting 
of unsubstituted and ring-substituted aromatic and heteroaromatic rings 
(i.e., aromatic heterocycles). A discovery of this invention is that the 
materials herein have potent antioxidant properties and can be effectively 
used as an additive to retard and inhibit oxidation in petroleum products 
and petroleum-related products at concentrations as low as about 0.0005 
wt. %. 
As mentioned previously, the antioxidants of this invention are 
bis-(p-aminobenzyl)anilines. Although all such disubstituted anilines are 
intended to be within the scope of this invention, the 
2,4-bis-(p-aminobenzyl)anilines are particularly preferred materials. 
However, it should be explicitly understood that reference to such 
2,4-disubstituted anilines is not meant to exclude other positional 
isomers. 
In one embodiment of this invention the group represented by A in the above 
structure is a saturated alkyl moiety containing up to about 20 carbon 
atoms. Alkyl moieties containing up to about 10 carbon atoms are 
preferred, with those containing up to about 5 carbon atoms being 
especially preferred. The alkyl group may be linear or branched with 
branched groups being somewhat preferred because of increased solubility 
of the resulting antioxidant in the products to be protected. Examples of 
alkyl moieties which may be used in this embodiment of our invention 
include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, 
decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, 
heptadecyl, octadecyl, nonadecyl, and eicosyl groups. Among the suitable 
branched, saturated alkyl moieties, cited for illustrative purposes only, 
are isopropyl, 2-butyl, tert-butyl, 2-methyl-1-propyl, 2-pentyl, 3-pentyl, 
2-methyl-1-butyl, 3-methyl-1-butyl, 3-methyl-2-butyl, 2-methyl-2-butyl, 
and 2,2-dimethyl-1-propyl. 
In another embodiment of this invention the group represented by A in the 
above structure is an arylmethyl or heteroarylmethyl moiety. That is to 
say, A represents the group --CH.sub.2 X, where X is a monovalent radical 
whose parent is an aromatic or heteroaromatic ring and which is derived 
from said parent by removal of a hydrogen from a carbon atom of said ring. 
By "heteroaromatic ring" is meant an aromatic heterocycle, that is, a 
heterocyclic system commonly identified as having aromatic properties 
because of a (4n+2) delocalized electron system in its ring, n being an 
integer, most commonly 1. Because of such rings include benzene, 
naphthalene, anthracene, chrysene, pyridine, thiophene, pyrrole, furan, 
imidazole, oxazole, thiazole, quinoline, carbazole, pyrimidine, purine, 
and so forth. Where X is the univalent radical from the benzene ring, 
viz., a phenyl group, it will be recognized that the resulting material is 
N,N',N"-tribenzyl-2,4-bis-(aminobenzyl)aniline. In other cases, it will be 
recognized that the resulting materials are aromatic and heteroaromatic 
analogs of the foregoing aniline. The heteroaromatic analogs often are 
especially desirable materials in this invention, and among these analogs 
the compounds where the parent of X is pyridine, furan, or thiophene are 
particularly preferred. 
In some cases it is advantageous to have the aromatic or heteroaromatic 
ring bearing at least one substituent. Among those substituents often 
leading to enhanced desirable properties are halogen, especially chlorine, 
nitro, cyano, carboxyl, and hydroxyl moieties. Another class of 
substituents which may be effectively used in the materials described 
herein comprises alkyl, alkoxy, and alkylmercapto where the carbonaceous 
portion contains up to about 18 carbon atoms. Examples of the latter 
include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, 
decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, 
heptadecyl, and octadecyl. The carbonaceous portion is saturated and may 
be either a straight or branched chain, although a branched chain is 
preferred because of increased solubility in products where their use is 
intended. 
The following are examples of suitable oxidants according to the invention 
herein and are cited for illustrative purposes only. The designation of 
the disubstituted aniline as the 2,4-isomer is for convenience only; other 
positional isomers are intended to be subsumed by the designated isomer, 
although not necessarily with equivalent results. 
N,N',N"-trimethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-triethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tripropyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"tributyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tripentyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trihexyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"triheptyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trioctyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trinonyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tridecyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tritetradecyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trioctadecyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trieicosyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tribenzyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trinaphthalenylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trianthracenylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-pyridinylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trithienylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tripyrrolylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trifuranylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trioxazolylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-trithiazolylmethyl-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tri(methoxybenzyl)-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tri(ethoxybenzyl)-2,4-bis-(aminobenzyl)aniline; and so on; 
N,N',N"-tri(chlorobenzyl)-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tri(methylbenzyl)-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tri(ethylbenzyl)-2,4-bis-(aminobenzyl)aniline; 
N,N',N"-tri(hexylbenzyl)-2,4-bis-(aminobenzyl)aniline; and so forth. 
The preparation of these materials is not novel and suitable methods will 
be recognized by those skilled in the art. One preparative route is the 
condensation of the bis-(p-aminobenzyl)aniline with an aromatic or 
heteroaromatic aldehyde or ketone, or mixtures of such aldehydes or 
ketones, to afford the Schiff base, or imine, followed by reduction. 
Typically, such a reaction is conducted in an inert solvent, such as an 
aliphatic or aromatic hydrocarbon or ether, especially ethers of glycols 
and polyglycols, in the presence of an acid as catalyst, frequently 
p-toluenesulfonic acid or a similar acid, or Lewis acids, such as boron 
trifluoride, with subsequent recovery of the imine as product. Catalyst 
concentration may vary from about 0.1 to about 10 mole percent based on 
the least abundant reactant. Reaction temperatures from about 100.degree. 
to about 150.degree. C. are common. Subsequent hydrogenation may be 
effected with platinum group metal catalysts, nickel, and so on. 
Alternatively, the materials of this invention may be prepared by reductive 
alkylation of the bis-(p-aminobenzyl)aniline by aromatic and 
heteroaromatic aldehydes or ketones. Usually an inert solvent, such as an 
aromatic hydrocarbon or an alcohol, or some combination of them, is used 
to dissolve the parent amine and the carbonyl compound. A small amount of 
a hydrogenation catalyst as previously described, but usually less than 20 
mole percent, is added. The resulting mixture is then heated at 
125.degree.-150.degree. C. under about 100 atm hydrogen for several hours. 
The materials described herein may be used as antioxidants in a wide 
variety of petroleum and petroleum-related products, and are particularly 
useful in inhibiting oxidation in hydrocarbon oils. For example, the 
materials may be used in lubricating oils and greases, either of synthetic 
or petroleum origin. Examples, cited for illustrative purposes only, 
include aliphatic esters, polyalkylene oxides, silicones, 
fluorine-substituted hydrocarbons, and the like. Lubricating oils of 
petroleum origin include motor lubricating oil, railroad type lubricating 
oil, marine oil, transformer oil, transmission oil, turbine oil, gear oil, 
differential oil, diesel lubricating oil, hydraulic oil, cutting oil, 
rolling oil, etc. Greases include petroleum grease, whale grease, wool 
grease, grease from inedible and edible fats, synthetic greases, such as 
those from mineral or synthetic oils containing hydrocarbon-soluble metal 
salts of fatty acids, and so forth. The materials of this invention also 
are suitable for the stabilization of plastics and rubbers obtained from 
polymerization of various petroleum-derived materials, such as 
polyethylene, polypropylene, polybutadiene, polystyrene, copolymers of 
ethylene and butadiene, and the like, polyacrylonitrile, polyacrylates, 
and so forth. 
The antioxidants described within also find use as oxidation inhibitors in 
fuel oils. Among the latter are included gasoline, diesel fuel, jet fuel, 
other aviation fuel, burner oil, furnace oil, kerosene, and naphtha. Of 
the compositions comprising a major amount of fuel oil and a minor amount 
of the additives herein, sufficient to inhibit oxidation, those 
compositions where the fuel oil is gasoline are especially preferred. 
The materials may be effective as an antioxidant at levels as low as about 
0.005 by weight. Higher concentrations, up to about 5% by weight, may be 
used if desired, although it will be recognized that it is economically 
advantageous to use these materials at as low a concentration as will be 
effective. The particular ranges of concentration depend somewhat on the 
particular use. For example, in lubricating oils the antioxidants herein 
may be used in the range from about 0.005 to about 5% by weight, with the 
range 0.05 to about 3% being more desirable, and the range 0.1 to about 2% 
being still more preferred. When the materials herein are used in fuel 
oils their concentration is reduced, being generally in the range from 
about 0.0005 to about 1% by weight, with the preferred range being from 
about 0.005 to about 0.5%.

The materials described in the examples are merely illustrative of this 
invention. It is to be understood that this invention is not to be limited 
thereto. 
EXAMPLE 1 
Preparation of N,N',N"-pyridinylmethyl-2,4-bis-(aminobenzyl)aniline. To a 
300 ml glass liner was added 4.6 g (15.2 mmol) 
2,4-bis-(4-aminobenzyl)aniline, 5.0 g (46.7 mmol) of 2-pyridine 
carboxaldehyde, 0.7 g Pt.Al.sub.2 O.sub.3 and 60 ml toluene. Reaction 
mixture was a red-brown opaque mixture. After standing for 15 mins., it 
became a red-brown solution with water condensed on the sides and catalyst 
on the bottom. A pressure change of 6 atm H.sub.2 was observed after 
heating for 10 h under 100 atm H.sub.2 at 172.degree.-8.degree. C. After 
cooling to room temperature, the mixture was decanted; the residue was 
rinsed with toluene and added to the decantate. Concentration on a flash 
evaporator yielded a thick golden brown oil. Heat treatment under vacuum 
(10 mm Hg) produced a viscous oil (6.3 g). Spectral techniques were 
consistent with the assigned structure. 
EXAMPLE 2 
Preparation of N,N',N"-tribenzyl-2,4-bis-(4-aminobenzyl)aniline. In a 300 
ml glass liner was dissolved 10.5 g (99.0 mmol) based on 
2,4-bis-(4-aminobenzyl)aniline in 50 ml THF. Freshly distilled 
benzaldehyde (11.5 g, 108.5 mmol) was added, followed by 1 g of 
Pt/Al.sub.2 O.sub.3. Reaction mixture became darker as it was heated to 
170.degree.-80.degree. C. for 10 h under 100 atm H.sub.2. After a pressure 
decrease of about 10 atm the reaction mixture was cooled to room 
temperature. Most of the material was a clear, golden brown liquid with a 
lower phase of catalyst and moisture. The reaction mixture was decanted to 
remove catalyst and concentrated on the flash evaporator. The thick, brown 
oily residue was azeotroped with toluene (3.times.30 ml) to a thick oil. 
Heat treatment under vacuum (0.3 mm Hg) removed residual traces of alcohol 
and unreacted benzaldehyde. The residue was a viscous brown oil (17.3 g). 
NMR & IR support the structural assignment. 
EXAMPLE 3 
Preparation of N,N',N"-tri-(2-butyl)-2,4-bis-(aminobenzyl)aniline. 
Reductive alkylation of 2,4'-bis-(4-aminobenzyl)aniline (3.0 g, 28.3 mmol) 
in 50 ml of 2-butanone was accomplished using 0.5 g Pt.Al.sub.2 O.sub.3 
and heating for 10 h at 160.5.degree. C. under 67 atm H.sub.2. After a 
pressure drop of 14 atm, the golden brown homogeneous solution was cooled 
to room temperature, filtered by suction to remove catalyst and 
concentrated on a flash evaporator. The viscous orange brown residue is 
azeotroped with cyclohexane and concentrated under reduced pressure to 
yield a thick orange brown oil. Spectral assignments are consistent with 
the structure. 
EXAMPLES 4-13 
A standardized test was used to screen the suitability of particular 
compounds as a stable antioxidant. Air at a constant rate of 50 ml per 
minute was bubbled through the test oil (a bright stock) which was held at 
275.degree. F. in a thermostatically heated aluminum block. The test oil, 
to which was added the potential antioxidant, was contained in a large 
test tube with metal coupons of aluminum, brass, copper, and steel. 
Heating time for the test was a minimum of five days, but was continued 
until the oil spot test indicated that the test sample had significantly 
decomposed. Upon termination of the test the acid number (AN), change in 
the viscosity expressed as a percentage change (.DELTA.V%), weight gain 
and weight loss of the coupons were determined. It has been found that the 
latter data are most significant for copper coupons, thus only these are 
reported herein. 
The oil spot test consists of placing a drop of oil on a chromatography 
sheet. The appearance of the brown spot with a distinct perimeter or a 
spot with material at the center or with a definite ring indicates 
significant decomposition of the base oil. This was used to determine the 
length of the test subject to a five-day minimum time. 
The results of testing are summarized in the accompanying table. 
TABLE 1 
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PERFORMANCE OF ADDITIVES AS ANTIOXIDANTS - 
HIGH TEMPERATURE 
Example 
Additive.sup.a,b 
OS.sup.c 
L.sup.d 
AN.sup.e 
Cu.sup.f 
V %.sup.g 
______________________________________ 
4 None 3 124 4.62 7.3 27.0 
5 A = CH(CH.sub.3).sub.2 
5 144 0.60 4.1 10.9 
6 A = C.sub.6 H.sub.5 CH.sub.2 
5 144 0.39 2.1 8.8 
7 None 4 124 5.56 9.3 37.7 
8 Ethyl 702.sup.h 
6 172 2.83 3.8 17.3 
9 A = 7 172 0.12 0.12 
3.4 
2-pyridinylmethyl 
10 None 3 124 4.96 29 
11 Ethyl 702.sup.h 
7 190 3.56 26 
12 A = 11 266 0.52 4 
3-pyridinylmethyl 
13 A = 11 262 0.42 5 
4-pyridinylmethyl 
______________________________________ 
.sup.a All additives are at 0.5 weight percent. 
.sup.b Additives have formula shown, vide supra, with A being designated 
in this column. 
.sup.c Oil spot test; time in days to onset of sludging. 
.sup.d Duration of test in hours. 
.sup.e Acid number, ASTM D974. 
.sup.f Weight loss in milligrams. 
.sup.g Percent change in kinematic viscosity at 100.degree. F. 
.sup.h A commercial product from Ethyl Corporation. 
EXAMPLES 14-16 
The effectiveness of materials as antioxidants in fuel oils was determined 
by measurement of the induction period prior to oxidation, ANSI/ASTM 
Method 525-74. The liquid petroleum product was a base washed, blended 
full range gasoline. Test results for various compositions are listed in 
Table 2. As a comparison, there is included an antioxidant of wide 
commercial utility which consists of 2,6-di-t-butylphenol (75%), 
2,4,6-tri-t-butylphenol (15%), and 2-t-butylphenol (10%) and which we 
designate by the symbol E733. 
TABLE 2 
______________________________________ 
Concentration, 
Induction period.sup.a 
Example 
Additive.sup.a 
ppm in minutes 
______________________________________ 
14 None 340 
A = 2-pyridinyl 
5 355 (390) 
10 355 (425) 
20 365 (495) 
15 None 380 
A = benzyl 5 335 (345) 
10 385 (380) 
20 445 (450) 
16 None 425 
A = isopropyl 
5 430 (470) 
10 425 (520) 
20 390 (570) 
______________________________________ 
.sup.a Additives have formula shown, vide supra, with A being designated 
in this column. 
.sup.b Figures in parenthesis refer to results with E733 at the same 
concentration. 
Thus the data of Table 2 clearly show that some antioxidants of this 
invention are comparable to the material which is used as the commercial 
benchmark for fuel oil antioxidants.