I
. IENRY
GISSER,
OSEPH MESSINA, and JONATHAN SNEAD
Pitman-Dunn Laboratories, Frankford Arsenal, Philadelphia 37, Pa.
Hydroxyarylstearic Acids as Oxidation and Rust Inhibitors in Lubricants In retarding oxidation and rust hydroxyphenylstearic acid performs the functions that required two additives for instrument lubricants
O X I D A T I O N and rust-inhibiting additives are commonly used in modern lubricants. A variety of materials are available as additives in instrument lubricants, typical being the phenols as oxidation inhibitors and the mahogany sulfonates as rust inhibitors. The availability of a compound that is active as both an oxidation and rust inhibitor is desirable as it would make it possible to replace a dual inhibitor system by a single compound, thus simplifying the blending process. A direct approach toward preparation of the desired compound would be the incorporation of groups possessed by oxidation inhibitors into a rust-inhibitor molecule. The rust-inhibiting properties of the long-chain fatty acids have been recognized for some time, and more recently, it was shown that arylstearic acid was effective as a rust inhibitor ( 2 ) . I t appeared probable that the introduction of functional groups on the aryl group might not interfere with the rustinhibiting properties, and this work was therefore undertaken to study the functionally substituted arylstearic acids as combination oxidation and rust inhibitors. A few instances of multipurpose inhibitors have been reported. For example, tris(morpholinomethy1)-phenol has been suggested as a combined rust and oxidation inhibitor in turbine oils (4, and condensation products of chlorinated wax with phenol have been suggested as multipurpose inhibitors in petroleum oil ( 7 7). Although numerous arylstearic acids have been prepared and reported in the chemical and patent literature, only a few contain reactive groups on the aryl ring (3, 7, 9,
10, 74, 75). The latter are the hydroxyphenyl-, methoxyphenyl-, methylhydroxyphenyl-, and halophenylstearic acids. A condensation product of phenol with unsaturated acids has been suggested as a corrosion inhibitor (6).
Preparation of Additives
All the additives were prepared by the condensation of aromatic compounds with oleic acid in the presence of acid catalysts. Oleic acid of 93y0 purity (Emersol 233, Emery Industries) was further purified by fractional recrystallization according to procedures of Swern, Knight, and Findley (76). Iodine and thiocyanogen numbers of the final product were 90.40 and 89.84, respectively, indicating oleic acid of better than 99% purity (5). Mono-tert-butyl-m-cresol, di-tert-butylp-cresol, and p-tert-butyl-catechol (all Matheson practical grade) were purified prior to use, the first by distillation and the latter two by recrystallization from alcohol. Eastman practical grade phenothiazine was recrystallized from alcohol. The benkene was Mallinckrodt thiophene-free reagent grade. The anhydrous aluminum chloride was Baker & Adamson reagent grade and the boron trifluoride was Matheson 9770 purity gas. The bis(2-ethylhexyl) sebacate was a commercial grade from the Rohm and Haas Co. The triiso-octyl phosphate was a commercial grage from the Shell Development Co. Barium petroleum sulfonate rust inhibitor was prepared from Petronate H (H. L. Sonneborn & Sons, Inc.),
which consists of 62yGsodium petroleum sulfonate (average molecular weight 513) and 4% water in a heavy petroleum oil. The commercial sulfonate was dissolved in 50YGisopropyl alcohol and the petroleum oil extracted with C.P. petroleum ether (boiling point 30-65' C,), The isopropyl alcohol was stripped from the solution while being heated under the vacuum of a water aspirator. The aqueous sodium petroleum sulfonate solution was mixed with C.P. benzene, and stirred with an aqueous solution of barium chloride. The benzene layer (which contained the barium sulfonate) was washed free of chloride ion with distilled water and the mixture was distilled under nitrogen until free from water. Bis (2-ethylhexyl) sebacate was then added and the distillation under nitrogen continued until all the benzene was removed. The final product consisted of a 20y0 solution of the barium petroleum sulfonate in bis(2-ethylhexyl) sebacate. This concentrate was used for all blends containing the barium petroleum sulfonate. All other compounds used were Eastman grade or Matheson research grade chemicals. Typical condensation procedures with concentrated sulfuric acid, boron trifluoride, and anhydrous aluminum chloride, are given below. Sulfuric Acid Procedure. Oleic acid (56.5 grams, 0.20 mole) and p-tert-butylcatechol (33.2 grams, 0.20 mole) were weighed into a 500-ml., round-bottomed, three-necked flask, fitted with condenser, dropping funnel, and mechanical stirrer. The mixture was chilled to 0' C. with continuous stirring. Then 29.4 grams (0.30 mole) of concentrated sulfuric VOL. 48, NO. 11
0
NOVEMBER 1956
2001
I !
I
1
gravity 1.84) in 153 ml. of g l a d acetic acid were added d r o p Wise during a 15-minute period. The -_. ,specific
temperature was not allowed to rise above 10' C. during this addition. After 1 hour, the cooling bath was removed and the reaction allowed to warm gradually to room temperature. It was then heated to 80' C. and maintained a t that temperature for 6 hours. The product was poured into an equal volume of water, and the upper layer was separated, and then taken up in 250 ml. of ether. The ether solution was washed with distilled water until acid-free and dried over anhydrous sodium d a t e , and the ether was removed on a stcam bath. After a preliminary distillation a t 1 mm., the viscous liquid was thrice distilled in a short-path still at 20 microns. Several low temperature fractional reuystallizations were neoessary to obtain a materia pure enough for analysis.
Boron TriUwride Procedure. A solution of 141.2 grams (0.50 mole) of oleic acid and 500 ml. of anhydrous benzene in a lOOO-ml., round-bottomed, three-necked flask was saturated with boron rriffuoride gar, m d u c e d through a gas inlet tube which extended just below the surface of the reaction mixture. During addition of the gas and throughout the reaction period, the solution w a s stirred mechanically. Heat was generated and the reaction mixture turned red. After heating a t 80' C. for 5 hours, the contents of the flask were poured into 1 liter of 20% hydrochloric acid with vigorous stirring. The upper layer w a s separated, washed free of acid, and dried over sodium sulfate. The excelvl benzene was removed on the steam bath with a water pump in a nitrogen ahnosphere. The heavy residual oil was distilled twice a t 0.5 mm.; 92 grams of phenylstearic acid, boiling
I
Table II. Analytical Data Neutroldzrm E*UiSdant % Found Found Calcd. C X 9(m lO)-methoxyphcnylstalric
acid
11.21,11.24
79.9
387.0 390.6 76.73,77.12
10.44,10.69
76.8
373.5 376.6 76.49,76.51
10.55,10.09 76.
360.3 360.6
79.88,79.93
394.7 390.6 76.72.76.73 11.08,lO.W 76. 9(0r 10)-(2,3-dihydrory-5~~~fbutyl) phsqhtestsanc a d d 448.6 448.7 71.07.74.39 10.25,10.45 9(Or IO)-(Z-liPdroiPJ-fort-bu~i5-methyl) bhsn$ateslic ssii 447.8 146.7 77.77.77.67 11.43,11.55 77.97 9(or lD)-(2-meUlyi~-hy&rolg-5fert-butyl) phenylstearic add 445.9 446.7 77.77,77.67 11.33,11.27 77 P0,Sitions of svbititusnts indrcated LIC intended only to show relative *&ti0 substituents and do not necesnarilv indicate mint of attachment of chain to Anr.
I
, .
,2002
IWDU
.AND
I
Y
I
I
p i n t 215-20' C. a t 0.5 nun., were obtained. Alnminum Chloride Procedure. Oleic acid (56.5 grams, 0.20 mole) and ' phenol (131.7 grams, 1.4 moles) were weighed into a 500-ml., round-bottomed, flask, fitted with a rdiux &necked condenser, thermometer, and mechanical stirrer. Then 30.6 grams (0.23 mole) of anhydrous aluminum chloride were added with stirring. Reaction began immediately, with evolution of heat. After about 0.5 hour, the mixtun was heated to 80' C. and held there for 6 to 8 hours with constant s ! h i n g (until evolution of hydrogen chloride fumes subsided). The product was poured into 500 ml. of 20% hydrochloric acid and allowed to separate into two layers. The oily upper layer was separated and the aqueous layer extracted with ether. The extracts were combined with the oily layer and washed with distilled water until acid-free. The ether solution was dried over anhydrous sodium sulfate and the ether was removed on a steam bath. The residue was heated a t 100' C. and 1 mm. for 1 hour to remove excess phenol. The dark viscous oil was thrice distilled in a shortpath still a t 15 to 20 microns. Results of the condensations are given in Table I. The condensations with sulfuric acid were unsuccemi~l,with one exception, that of p-fcr&butylcatechol. Apparently condensation failed to occur, or resulted in mixtures of products which were exceediily di5cult to separate and purify. Variations in procedure, such as higher or lower temperatures during addition of acid, and order of m i x i i of reagents, had no effect. With aniline, the oleic acid was recovered as its isomer, elaidic acid (melting point 44.5O C., neutralization equivalent 283.7), with theoretical carbon and hydrogen content. Boron biRuoride worked well with benzene to give phenylstearic acid in 51% yield. Polymerization to a resinous material occurred with phenol, and with aniline a product was obtained which carbon and hydrogen determination showed to be oleanilide. Aluminum chloride was the most 8uccessful condensing agent. In the condensation with 2,6-di-rcrt-butyl+cresol, it is unlikely that ring attachment will take place unless an alkyl group is removed. The product obtained analyzed best foramethyl-ln?-butylhydroxyphenyIstearic acid, and it was therefore assumed that a fmt-butyl group had split off during the condensation. The dealkylation of hindered phenols in the presence of acid catalysts has been ob-
sewed (8, 72, 73). Table I1 lists analytical data for the arylstearic acids prepared. All the compounds listed w m viscous oils which could not be crystallized on cooling. Methoxyphenylstearic acid, previously
Table 111.
Comparative Oxidation Data on Additive-Containing Oils"'b Change i n Neutralization
Additive None Oleic acid (99%) 9(or 10)-phenylstearic acid 9( or 10)-methoxyphenylstearic acid 9(or 10)-hydroxyphenylstearic acid 9(or 10)-methylhydroxyphenylstearic acid 9(or 10)-dihydroxy-tert-butylphenylstearic acid 9(or 10)-hydroxy-tert -butylmethylphesylstearic acid 9(or 10)-methylhydroxy-tert-butylphenylstearic acid Barium petroleum sulfonate (1.4%) and phenyl1-naphthylamine (0.5%) Barium petroleum sulfonate (0.7%) Phenyl-1-naphthylamine (0.5%) Barium petroleum sulfonate (1.4%) and 2,6-ditert-butyl-4-methy'phenol (0.5%) Barium petroleum sulfonate (0.7%) and phenothiazine (0.5%) Oxidation and rust inhibitors" Oxidation and rust inhibitorsd a
NO.^
+ 4.06
f31.64 $22.02 7.04 0.06 0.30 4- 0.38
+ + +
4- 0.38
+ 0.54 + 0.10 + 9.48 + 0.12 + 0.07 + 0.37 + 0.08 + 0.30
Change in Volatile Viscosity Acids Formed, Eq. Mg. o j K O H Cs. at looo F. 2.1 +0.84 13.5 4-9.92 12.2 f6.45 4.9 +1.76 1.2 +O.Ol 0.7 4-0.24 f0.38 0.4 2.6
+0.28
3.0
4-0.50
14.9 169.2 -0.8
4-0.58 +1.45 +O. 13
10.13
$0.28
24.15 9.56 1.87
+O. 18
$0.23 fO.09
Change i n wt. o j Metal Strips$M g . Copper Steel
3.2
0 4-0.5 $0.5 -0.1 -0.1 +0.2 $0.1
Condition of Metal Scrips Copper Steel Clean Clean Darkened Clean Clean Etched Clean Clean Clean Clean Clean Clean Clean Clean
4.2
+o.
Darkened
Clean
0.2
$0.4
Clean
Clean
2.6 1.a 2.4
0 $0.2 0
Darkened Darkened Darkened
Clean Clean Clean
0
Darkened
Clean
Darkened Darkened Darkened
Clean Clean Clean
0 -10.4 -74.8 - 0.8 - 0.3
-
0.5
- 2.1 0.2 -- 2.1 - 2.2
0 -0.3 -0.2
1
Oxidation at looo C. for 168 hours. All oils tested, except the last two, consisted of bis(2-ethylhexyl) sebacate containing 2% of additive unless otherwise indicated. Neutralization number a s determined by ASTM method D 974-54T. Last two oils were commercial diester instrument oils which contained oxidation and rust inhibitors.
reported as a para-substituted product (74), was converted to hydroxyphenylstearic acid with hydriodic acid. The conversion of methoxyl was 96.3y0, the neutralization equivalent was 376.8, and the analysis agreed with the theoretical carbon and hydrogen content. This material was compared with the phenol condensation product by infrared spectroscopy. Identical curves were obtained with characteristic hydroxyl peaks a t 2.85 to 3.2 microns.
Evaluation of Inhibitor Activity The additives were evaluated in bis(2-ethylhexyl) sebacate. Two per cent solutions were prepared and the solutions subjected to accelerated oxidation and rust tests. Oxidation stability was determined by means of a dynamic oxidation test similar to one previously described (7). Duplicate tests were run on 50-gram samples of each blend. Clean, dry air, 5 i 0.5 liters per hour, was bubbled through the oil in the presence of weighed copper and steel catalyst strips immersed in the oil. These strips were 1.750 X 0.375 X 0.025 inches and were prepared by successive polishing with l / O , 3/0, and 5/0 emery paper, washing in boiling benzene, wiping with absorbent cotton, and finally washing in boiling petroleum ether. They were flash-dried over a hot plate and stored in an evacuated desiccator until used. The metal strips were not touched by hand after polishing. Tests were run a t 100' =I= 0.1' C. for 168 hours, during which time volatile acids were trapped in potassium hydroxide solution. After oxidation, the metal strips were weighed, and oil viscosity
and neutralization number were determined. I n Table I11 a comparison is made among the prepared hydroxyarylstearic acids and selected inhibitor systems currently used in instrument lubricants. Oleic and phenylstearic acids were included to obtain data on compounds with similar structures which are poor antioxidants. The materials tested also include base fluid with barium petroleum sulfonate only, and phenyl-1-naphthylamine only, to obtain comparative data on oils containing a rust inhibitor and an oxidation inhibitor alone. One of the best oxidation inhibitors prepared was hydroxyphenylstearic acid, although the amount of volatile acids formed was slightly higher than with dihydroxy-tert-bu tylphenylstearic acid or methylhydroxyphenylstearic acid. In comparing hydroxyphenylstearic acid with the established antioxidants in Table 111, such as phenyl-l-naphthylamine, phenothiazine, etc., it should be noted that the concentration of the former is four times that of the latter compounds. This was done to achieve a certain level of rust inhibition and the actual comparison is made in terms of a single compound to replace both antioxidant and rust inhibitor. Rust-inhibitor properties were evaluated by means of a cyclic humidity cabinet which has been used by the authors for several years. In this test, specimens are exposed for 4 hours a t 110' F. and 80% relative humidity, followed by 4 hours at 130' F. and 95% relative humidity. The test specimens were rods of WD 1020 steel, 4 inches long and 0.375 inch in diameter. They were prepared by successive abrasion
Table IV. Humidity Cabinet Rust Test Data on Additive-Containing Oils
Oil
Additive
HOUTS to Failure
A
None 24 Oleic acid (99%) 84 9(or 10)-phenylstearic acid 24 9(or 10)-methoxyphenylstearic acid 24 9(or 10)-hydroxyphenylstearic acid 192 9(or lO)-methylhydroxyphenyl stearic acid 180 9(or 10)-Dihydroxy-tert-butylphenylstearic acid 96 9(or 10)-hydroxy-tert-butylmethylphenylstearic acid 96 9(or 10)-methylhydroxy-tertbutylphenylstearic acid 72 Barium petroleum sulfonate (1.4%) and phenyl-l-naphthylamine (0.5%) 204 Barium petroleum sulfonate (0.7%) 132 Phenylrl-naphthylamine (0.5%) 24 Barium petroleum sulfonate (1.4%) and 2,6-di-tert-butyl4-methylphenol (0.5 %) 198 Barium petroleum sulfonate (0.7%) and phenothiazine (0.5%) 132
B
Oxidation and rust inhibitors Oxidation and rust inhibitors
C None 9(or 10)-hydroxyphenylstearic acid
216 168 48 222
A. Bis(2-ethylhexyl) sebacate containing 2% of additive unless otherwise indicated. B. Commercial diester instrument oils which contain oxidation and rust inhibitors. C. Triiso-octylphosphate. Last oil contains 2% of additive.
VOL. 48, NO. 1 1
NOVEMBER 1956
2003
7c
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BIS (2-ETHYLHEXYL) SEBACATE
( INHIBITED)
0 BIS (2-ETHYLHEXYL 0 81s ( 2 - ETHYLHEXYL
0 BIS (2-ETHYLHEXYL) SEBACATE (UNINHIBITED) TRI-ISO-OCTYL
PHOSPHATE (UNINHIBITED)
) SEBACATE
I
(INHIBITED) SEBACATE (UNINHIBITED1
0 T tl-ISO-OCTYL
PHOSPHATE
m
PHOSPHATE L UNINHIBITED
TRI-ISO-OCTYL
( INHIBITED
I
200
400
600
1000
800
1200
200
Acid formation during oxidation
with 1/0, 3/0, and 5/0 sandpaper while being rotated at approximately 1700 r.p.m., then washed in boiling benzene, wiped with clean cotton, washed in boiling petroleum ether, and finally flash-dried. The rods were immersed in the test oil overnight. They were removed, supported upright in wooden blocks, and allowed to drain in a dustfree atmosphere for 4 hours before being placed in the humidity cabinet. The metal rods were observed every 24 hours, and time for failure was taken as the first appearance of rust, if this rust increased in extent during the next 24 hours. Four rods were used for each test oil and the values shown in Table I V are means of time to failure. I n Table I V the rust-inhibitor properties of the compounds are compared with inhibitor systems such as barium petroleum sulfonate combined with various antioxidants and two commercial diester lubricants which are oxidation- and rust-inhibited. Among the hydroxyarylstearic acids, hydroxyphenylstearic and methylhydroxyphenylstearic acids are the best rust inhibitors, the former being slightly better than the latter. The results compare favorably with barium petroleum sulfonate (one of the better current rust inhibitors for instrument lubricants) and two inhibited commercial instrument oils. Hydroxyphenylstearic acid was blended with bis(2-ethylhexyl) sebacate and triiso-octyl phosphate in 2% ccncentrations and subjected to oxidation for 1000 hours a t 100' C. Samples (11 to 13 grams) were withdrawn periodically
2004
400
600
8 00
1000
I200
TIME ( H O U R S )
TIME (HOURS)
Figure 1.
I
Figure 2.
for determination of viscosity and neutralization number. The data are illustrated in Figures 1 and 2. Hydroxyphenylstearic acid is effective in retarding oxidation, prolonging the induction period beyond 1000 hours. Acid formation is considerably decreased and the viscosity is remarkably constant over the entire oxidation period. Thus it is apparent that this compound performs the functions that hitherto required two additives for instrument lubricants. Summary and Conclusions
Hydroxyarylstearic acids were prepared by condensation of phenols with oleic acid, using aluminum chloride. The compounds were found to be active as oxidation and rust inhibitors in instrument oil compositions. The most effective compound prepared was hydroxyphenylstearic acid, which in 270 solution was an effective antioxidant (at 100' C.) and rust inhibitor in bis(2-ethylhexyl) sebacate and triiso-octyl phosphate. Acknowledgment
The authors wish to express their appreciation to the Ordnance Corps, Army Department, for permission to publish this report. Literature Cited (1) .4tkins, D. C., Jr., Baker, H. R., Murphy, C. M., Zisman, W. A.,
IND.ENG.CHEM.39, 491 (1947). (2) Baker, H. R., Zisman, W. A., Zbid., 40, 2338 ( I 948).
INDUSTRIAL AND ENGINEERING CHEMISTRY
Viscosity increase during oxidation ( 3 ) Gleason, A. H. (to Standard Oil Development Co.), U. s. Patent 2,380,305 (July 10, 1945). (4) Herlocker, R. D., Kleinholz, M. P., Watkins, F. M. (to Sinclair Refining Co.), Ibid., 2,413,972(April 24,
1943).
(5) Irvin, W. H., Bailey,R. W., Law,T. C., Long, C. P I Morrison, H. J., Sheely, M. L., Tolman, L. M., Trevithick, H. P., Vollertsen, J. J., IND.ENG. CHEM.,ANAL.ED.8, 233 (1936). (6) Jahn, E. J. (to Shell Development Co.), U. S. Patent 2,349,044 (July
21, 1941). (7) McGrew, F. C. (to E.I. du Pont de Nemours & C o . ) , Ibid., 2,396,715 (March 19, 1946). (\ 8 ,) Morrell. C. E.. Swanev. M. W. (to Standard Oil Develbpment Co.), Ibid..2,370,810(March 6, 1945). . - J.- B., ~ ~Ibid.,2,082,459 (June (9) Niederl, 1, 1936).
(10) Niederl, J. B., Liotta, C., J . Am. Chem.Sac. 55, 3025 (1933). (11 Reiff. 0. M.. Otto. F. P.. Giammaria. J. J., Obcmight; E. A: (to Socony: Vacuum Oil Co.), U. S. Patent 2,198,275 (Oct. 18, 1939). Stevens, D. R., Livingstone, C. J. (to Gulf Research and Development C o . ) , Ibzd., 2,297,588 (Sept. 29, 1942). Stevens, D. R., McKinley, J. B. (to Gulf Research and Development Co.), Ibid., 2,290,602, 2,290,603 (July 21, 1942), 2,327,938 (Aug. 24, 1943). Stirton, A. J., Peterson, R. F., IND. ENG.CHEM.31, 856 (1939). Stirton, A. J., Schaeffer, B. B., Stawitzke, A. A,, Weil, J. K., Ault, W. C., J. Am. Oil Chemists' SOC., 25, 365 (1948). Swern, D., Knight, H. B., Findley, T. W., Oil and Soup 21, 133 (1944). RECEIVED for review October 18, 1955 ACCEPTED June 12, 1956 First Delaware Valley Regional meeting, ACS, Philadelphia, Pa., February 16, 1956.
