small endothermic peak beginning at about 100’ C. in both thermograms is the glass transition. Curve A shows no peaks after the glass peak until the large peak of thermal degradation begins at 300’ C. Curve B, however, shows a n exotherm beginning a t about 240’ C. This peak continues until the endothermic degradation peak becomes dominant. This exotherm is possibly the reaction of oxygen from the air with polystyrene to form polystyrene hydroperoxide as described by Boundy. The samples both weighed about 10 mg. and therefore degradation peaks of approximately the same size should be expected. Since the degradation peak of curve B is smaller, it appears that the exothermic oxidation is present a t higher temperatures and reduces the size of the endothermic degradation peak. Conclusions
Some of the factors affecting glass transitions of polystyrene have been examined with a series of commercial and standard samples using a modern DTA instrument. Thermal degradation was also observed. These observations indicate that DTA is a useful tool for studying glass transitions and thermal deg-
radation characteristics. Present equipment is sensitive enough to permit more extensive study of the variables affecting these phenomena, and the ease in conducting the tests suggests all the more strongly the routine use of DTA in quality control. Acknowledgment
We are most grateful to W. C. Brasie, Dow Chemical Co., Midland, Mich., for furnishing commercial samples of polystyrene. We are indebted to Robert L. Stone for the use of DTA equipment of the Robert L. Stone Co. literature Cited Boundy, R., Boyer, R. F., “Styrene,” Reinhold, New York, 1952. Bueche, F., “Physical Properties of Polymers,” Interscience, New York, 1962. Fox, T. G., Flory, P. J., J . Polymer Sci.14, 315 (1954). Kauzmann, W., Chem. Rev. 43,219 (1948). Keavney, J. J., Eberlin, E. E., J . Appl. Polymer Sci. 3,47 (1960). Madorsky, S. L., “Thermal Degradation of Organic Polymers,” Interscience, New York, 1964. Spencer, R. S., Boyer, R. F., J . Appl. Phys. 17,398 (1946).
RECEIVED for review November 14, 1966 ACCEPTEDMarch 13, 1967
SUBSTITUTED B I P H E N Y L S A N D T E R P H E N Y L S A S OXIDATIVELY AUTOINHIBITIVE COMPOUNDS H E L E N E. M E R T W O Y AND H E N R Y GISSER Pitman-Dunn Research Laboratories, Frankford Arsenal, Philadelphia, Pa. 19137
In a study of oxidatively autoinhibitive biphenyls and terphenyls, sec-butylbenzenes having phenyl, methoxyphenyl, sec-butylphenyl, or tert-butylphenyl substituted in the ring, either singly or in combination, were prepared, and their autoxidation rates measured a t 100’ C. Whereas sec-butylbenzene oxidized in less than 2 4 hours, all of the substituted compounds except 4-sec-butyl-4’-tert-butylbiphenyl, were stable for a t least 100 hours. The latter compound, however, oxidized at a much slower rate than sec-butylbenzene. The stability of these compounds was attributed to autoinhibition. This is the resultant when the tendency to increase oxidation rate by electron-donating substituents is outweighed by the effectiveness of the inhibitor formed. The inhibitors are presumably hydroxybiphenyls or terphenyls and are a decomposition product of the hydroperoxide produced via autoxidation a t the tertiary carbon. As confirming evidence that inhibitors are formed, it was found that 4-sec-butylbiphenyl and 4-sec-butyl-4’-methoxybiphenyl in mixtures with sec-butylbenzenes exerted a distinct oxidation-inhibiting effect on the latter. Most of the compounds were found to b e nonspreading fluids.
HE phenomenon of autoinhibition was previously explored T i n the autoxidation (100’ C.) of methoxy- and alkylsubstituted phenyldodecanes, hexadecanes, and phenylbutyl adipates having an aryl group attached to a tertiary carbon (7). Autoinhibition was attributed to the formation of an inhibitor, presumably a phenol, from the decomposition of the hydroperoxide initially formed via autoxidation a t the tertiary carbon. I n the case of both the diesters and hydrocarbons, the p-methoxyphenyl compounds were found to be much more stable than the corresponding phenyl compounds. This was expected, since it was assumed that p-methoxyphenol, a better oxidation inhibitor than phenol, was formed. I n earlier work, the stability of l-methyl-l-p-methoxyphenyl-
108
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
butane to autoxidation was also attributed to the formation of p-methoxyphenol ( 8 ) . The oxidation rates of the alkyl-substituted compounds were variable. Differences in oxidation rates were explained from the standpoint of effectiveness of oxidation inhibitors formed and increased oxidation rate as a function of increased electron density a t the tertiary carbon due to the electron-donating alkyl and methoxy groups. This work has now been extended to the synthesis and autoxidation of substituted biphenyls and terphenyls having an aryl group adjacent to a tertiary carbon. When subjected to autoxidation, these compounds should form phenylphenols which would probably be more effective inhibitors than the
phenols formed by the previously studied aromatic hydrocarbons and diesters. Phenylphenol is known to be a better antioxidant for paraffin than phenol (5). Fluids of this type which are autoinhibitive to oxidation, like the previously studied compounds, should be highly advantageous as stable lubricants. This property eliminates the need to formulate a fluid with an added antioxidant which might have an adveide effect on the physical properties of the base fluid. Furthermore, these compounds should have the added property of thermal stability, since biphenyls and terphcnyls and many of their derivatives are known to be thermally stable a t elevated temperatures over long periods of time ( 7 7 ) . Experimental
Preparation of Compounds. All of the compounds studied \\.ere prepared by direct alkylation of a biphenyl or terphenyl via a Friedel-Crafts reaction. I n all of the preparations, both mono- and disubstitution occurred, and these products were separated by fractional distillation in vacuo. I n some cases, it \vas not determined on which ring or in what position on the rings substitution occurred. T h e predominant points of attachment \ \ o d d probably be in the para rather than the ortho positions because of steric factors; however, in all the compounds, an aryl group would be adjacent to a tertiary carbon \vhich would behave in a similar manner in autoxidation. it'ith the exception of 4-sec-butylbiphenyl, 4,4'-di-secbutylbiphenyl, and 2- and 4-methoxy-p-terphenyl, the compounds prepared have not previously been reported. T h e microanalyses were determined by Schwarzkopf Microanalytical Laboratory, Ll'oodside, N. Y . Molecular weights \\ere determined by vapor pressure osmometry. 4-stc-Butylbiphenyl (I) a n d 4,4'-Di-sec-butylbiphenyl (11). To a stirred solution of 77 grams (0.5 mole) of biphenyl in 150 ml. of carbon disulfide cooled to 0 ' C. was added 7 grams (0.05 mole) of anhydrous aluminum chloride. Main' C., 44 grams (0.53 mole) of taining the temperature a t 0 2-chlorobutane \vas added dropwise over a period of 3 hours. After addition \vas completed, the ice bath was removed, and stirring \vas continued for 24 hours. T h e reaction mixture was then poured over a n equal volume of crushed ice. T h e organic layer was washed free from acid with lOy0 potassium carbonate. Ivashed \vith distilled water until neutral to p H paper, dried over anhydrous sodium sulfate, and filtered. Carbon disulfide \vas removed under reduced pressure. The products \irere separated by fractionation in vacuo using a Vigreux column to yield two liquid products, which were identified as compounds I and I I ? and a ivhite solid. I t was necessary to run steam through the condenser until all the solid, identified as unreacted biphenyl, had distilled over. The lo\ver boiling liquid fraction distilling a t 102-03' C . (0.70 mm.) [lit. (73) 6 2 117.5' C . ] was obtained in 32% yield (33.8 grams) ( ~ I ~1.57493, ~ O d42j0.97004). Elemental analysis identified i t as compound I . Calculated for C16H18: C, 91.37; H. 8.63; M ? . \ V . ,210. Found: C, 91.00; H, 9.03; M . W . , 210. Theliquid distilling at 145' C . (0.72 mm.) [lit. (2) b20222°C.] \vas obtained in 9.2y0 yield (12.3 grams) and identified as compound 11 (nIIZo1.55474, d4*50.93996). Calculated for C20H26: C, 90.16; H , 9.84; M.\Y., 266. Found: C, 90.30; H, 9.83; M.\t'., 264. If the reaction time was only 10 hours, a 25.6% yield of compound I and a 970 yield of compound I1 were obtained. 4-sec-Butyl-4'-tert-butylbiphenyl (111) a n d 4-sec-Butyl-ditert-butylbiphenyl (IV). A solution of 31.5 grams (0.15 mole) of compound I in 200 ml. of petroleum ether was saturated with anhydrous hydrogen chloride for 45 minutes with stirring. T h e gas inlet tube was then removed, and 3.5 grams (0.026 mole) of anhydrous aluminum chloride was added. Isobutylene gas was then bubbled through the solution a t such a rate that the heat of reaction maintained the temperature between 45' and 50' C. After 12.9 grams (0.22 mole) of isobutylene had been added, the gas inlet tube was removed and the reaction mixture stirred a t room temperature for 3 hours. 'The reaction mixture was then handled in the same manner as the above compounds. Compound I11 [b.p.
129-32' C. (0.19 mm.), 7 2 1.56445; ~ ~ ~ dd2j0.96641 was obtained in 7.3y0yield (3.5 grams). Calculated for C?OH2,$: C: 90.22; H, 9.78; M.W., 266. Found: C, 90.56; H , 9.39; M.W., 256. Compound I V [b.p. 169-71' C . (0.6 mm.), nD25 1.55521 was obtained in 1.7% yield (1 gram). Calculated for CPbH34: C, 89.44; H, 10.56; M.W., 322. Found: C, 89.86; H, 10.31 ; M.W., 304. 4-sec-Butyl-4'-methoxybiphenyl (V) a n d Di-sec-butyl-4'methoxybiphenyl (VI). To a stirred solution of 46 grams (0.25 mole) of p-phenylanisole (insoluble in carbon disulfide) in 700 ml. of hot n-heptane was slowly added 14 grams (0.11 mole) of anhydrous aluminum chloride. While maintaining the temperature between 75' and 85' C., 25 grams (0.27 mole) of 2-chlorobutane was added drop\vise over a 2- to 5hour period, after which time the reaction mixture was stirred for 8 hours. After cooling to room temperature and standing overnight, the reaction mixture was poured over ice and the organic layer washed and dried in the manner described for compounds I and 11. n-Heptane was removed under reduced pressure, and the remaining reaction mixture was distilled in a pot still a t 10 microns. A waxy solid believed to be unreacted p-phenylanisole sublimed up the sides of the pot into one.of the receiving flasks, followed by a liquid which was collected in another receiving flask. T h e liquid was distilled twice in the pot still to separate it from all traces of the white solid. It was then fractionated in vacuo using a Vigreux column to yield two liquid products, compounds V and VI. These compounds, in turn, were fractionated twice in order to ensure a good separation of the mono- and disubstituted products. Compound V was obtained in 2OY0yield (11 grams) [b.p. 137-38' C . (0.65 mm.), nD20 1.56842, d425 1.00521. Calculated for CliH,oO: C, 84.95; H, 8.39; 0, 6.66; M . W . , 240. Found: C,85.11; H , 8 . 3 9 ; 0 , 6 . 7 0 ; M.\V.,246. T h e compound distilling at 162-63' C . (0.75 mm.), obtained in 9.6% yield (6 grams), was identified as compound V I (nD20 1.55428). Calculated for C 2 1 H 2 8 0 :C. 85.08; H, 9.52; 0, 5.39; M.W., 296. Found: C, 85.38; H , 9.65; 0, 5.55; M.W., 284. sec-Butyl-o-terphenyl (VII) a n d Di-sec-butyl-o-terphenyl (VIII). T h e reaction was performed in the same manner and a t the same temperature as for the preparation of compounds I and 11, employing 100 grams (0.43 mole) of o-terphenyl, 40 grams (0.43 mole) of 2-chlorobutane, 7 grams (0.05 mole) of anhydrous aluminum chloride, and 100 ml. of carbon disulfide. Addition of 2-chlorobutane )vas done over a 1.5hour period, and the total reaction time was 7 hours. Compound V I 1 [b.p. 183-85' C. (0.30 mm.), db25 1.01841 was obtained in 20.992 yield (27 grams). Calculated for Cw"22: C, 92.26; H, 7.74; M.\V., 286. Found: C, 92.22; H , 7.85; M.W., 295. Compound (VIII) [b.p. 219' C. (0.5 mm.), d425 0.99841 wasobtained in 7.0% yield (10 grams). Calculated for C26Hm: C, 91.17; H, 8.83; M.W., 342. Found: C, 91.53; H , 8.81; M.W., 340. 2-Methoxy-p-terphenyl (IX) a n d 4-Methoxy-p-terphenyl (X). These compounds were prepared by a diazo reaction similar to that described for 2-methoxy-4'-bromobiphenyland 4-methoxy-4'-bromobiphenyl (7), employing 21 1 grams (1.25 moles) of 4-aminobiphenyl and 497 grams (4.6 moles) of anisole. Since a previous attempt to steam-distill compound X, as described for 4-methoxy-4'-bromobiphenyl, was unsuccessful, the brown oily mixture of products was treated in the following manner. T h e brown oil was washed with water until neutral, dried over anhydrous sodium sulfate, and filtered. Unreacted anisole was removed under reduced pressure. T h e remaining oil was dissolved in the minimum amount of hot heptane, and upon cooling, a broivn compound crystallized out. I n a n attempt to remove the brown color, the product was dissolved in benzene and percolated through a column of activated alumina. Only some of the color was removed. Elimination of this step might result in a larger yield. Benzene was then removed under reduced pressure. I n order to remove the brown color and partially to separate the products, the remaining mixture of solids was distilled in vacuo using a steam condenser. Since the products are high melting solids, they could not be easily fractionally distilled. Compound IX distills first at 95' to 103' C. (0.9 mm.), then VOL. 6
NO. 2
JUNE 1 9 6 7
109
the temperature rises, and between 190' and 200' C. (0.9 mm.), compound X distills. At this point, both compounds are yellowish white solids. I n order to obtain pure products, the compounds were completely separated in the following manner. Boiling cyclohexane was added to compound IX, which is much more soluble than compound X, until all the solid dissolved. An excess of about 40 ml. of boiling cyclohexane was then added. T h e solution was cooled, and the small amount of compound X which crystallized out was filtered off and added to the crude compound X. The filtrate was concentrated until it became cloudy and more boiling cyclohexane was added until the cloudiness just disappeared. O n cooling, white crystals of compound I X were isolated. Upon recrystallization, a 10% yield (31.4 grams) was obtained, m.p. 223' C . [lit. (4) m.p. 22324' C . ] . Calculated for CI9Hl6O: C, 87.36; H, 6.51; 0, 6.13; M.W., 261. Found: C, 87.52; H, 6.35; 0, 6.40; M.\Y., 258. Compound X, a white solid, was crystallized from cyclohexane twice to give a 5% yield (15.8 grams) [m.p. 118' C. (lit. (4) m.p. 118-19' C.]. Calculated for C19H160: C, 87.36; H, 6.51; 0, 6.13; M.W., 261. Found: C, 87.45; H, 6.30; 0, 6.40; M.W., 255. sec-Butyl-2-methoxy-pterphenyl (XI) (Liquid Isomer), sec-Butyl-2-methoxy-p-terphenyl (XII) (Solid Isomer), and Di-sec-butyl-2-methoxy-p-terphenyl (XIII). The reaction was performed in the same manner and a t the same temperature as for the preparation of compounds V and VI employing 24 grams (0.092 mole) of compound IX, 8.7 grams (0.094 mole) of 2-chlorobutane, 5 grams of anhydrous aluminum chloride, and 500 ml. of hot n-heptane. Addition of 2-chlorobutane was done over a 1-hour period, and the total reaction time was about 2 days. Completion of the reaction was indicated by the fact that hydrogen chloride stopped evolving rapidly, and, upon cooling to room temperature, unreacted compound I X no longer crystallized out of solution. Fractionation of the reaction mixture yielded three products. Compound X I [b.p. 181' C. (0.16 mm.)] was obtained in 23.9% yield (7 grams). Calculated for C23H240: C, 87.30; H, 7.64; 0, 5.05; M.W., 316. Found: C, 86.99; H , 7.69; 0, 5.09; M.LY., 306. Comuound X I 1 1b.D. 174' C. (0.22 mm.)l which solidified on stanhing, was obtiined in 27.2% yield (7.9 grams). Calculated for C23H240: C, 87.30; H, 7.64; 0, 5.05; M.W., 316. Found: C, 87.80; H: 7.30; 0 , 4 . 7 1 ; M.W., 305. Compound XI11 [b.p. 182' C. (0.25 mm.)], a n extremely viscous liquid, was obtained in 10.9% yield (3.9 grams). Calculated for C2+&20: C, 87.05; H, 8.66; 0, 4.29; M.W., 372. Found: C, 87.50; H, 8.28; 0, 3.80; M.W., 351. Oxidation Techniques. Oxygen consumption a t 100' C. was measured by using standard Warburg manometry as previously described ( 3 ) . One milliliter of compound was introduced into the main compartment of the Warburg flask. After flushing with oxygen for approximately 15 minutes, the system was closed to the atmosphere and excess oxygen pressure was bled off so that 0.1 to 0.5 cm. above atmospheric pressure remained. Oxygen consumption was calculated as moles of oxygen per mole of compound. Spreading Determination. A drop of fluid 1 to 2 mm. in diameter was placed on a 1-inch diameter W.D. 52-100 steel disk hardened to Rockwell C-62, which had been cleaned and polished by a method described i n the literature (9). T h e degree of spreading was determined by measuring the change in diameter after 7 and 30 days, respectively. Results and Discussion
The work presented here is a study of the relative effect on the oxidation rate (100' C.) of sec-butylbenzene by electrondonating groups such as phenyl, methoxyphenyl, and secbutylphenyl substituted in the ring either singly or in combination, forming biphenyls or terphenyls. Structures of these compounds are illustrated in Figure 1. The compounds prepared are unsymmetrical and liquids. T h e higher the symmetry of a substituted biphenyl or terphenyl, the higher 4,4'-di-sec-butylbiphenyl is a the melting point (70)-e.g., 110
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
Figure 1. phenyls
Structural formulas of the biphenyls and ter-
liquid, yet 4,4'-dibutylbiphenyl (m.p. 137' F.) and 4,4'tert-butylbiphenyl (m.p. 263' F.) are solids ( 7 7 ) . Oxidation studies were not made of all the compounds prepared. Some of the compounds, notably di-sec-butyl-2methoxy-pterphenyl, had such high viscosities that they were not suitable for oxidation studies using a Warburg apparatus. The oxidation curves are in Figures 2 and 3. I n replicate runs, the rates, as in previous work (7), did not in most instances vary more than 27,, and the maximum rate range was 10%. The curve for sec-butylbenzene (oxidized for comparative purposes) is shown only up to 12 hours, since the results were erratic beyond this point, because the volatile decomposition products formed exerted a pressure in the Warburg flask and caused erroneous manometer readings. Beyond 100 hours, reproducibility was not as good for the compounds because of progressively increasing leaks in the Warburg apparatus. The leaks were believed to be caused by oxidation products of low molecular weight and high temperature, resulting in removal of the lubricant from the ground-glass joints. Compounds with extremely low oxidation rates were oxidized up to 150 hours, and little, if any, leakage was observed. T h e initial and final oxidation rates of the compounds are calculated from the slopes of the curve during the time intervals given in Table I . In most instances, the curve is a straight line during the oxidation time interval; otherwise the rate is an average over the time interval given.
Table 1.
Oxidation Rates of Aromatic Hydrocarbons at 100' c.
Compound
4-sec-Butylbiphenyl 4,4 '-Di-sec-bytylbiphenyl 4-sec-Butyl-4 -methoxybiphenyl 4-sec-Butyl-4 '-tert-butylbiphenyl sec-Butyl-o-terphenyl Di-sec-butyl-o-terphenyl sec-Butyl-2-methoxy-p-terphenyl 2-Phenylhexadecane ( 7 ) sec-Butylbenzene
2-p-Met hoxyphenylhexadecane
0.03 0.13 0.00 1, 5 0 0.00 0.03 0.00 1.97
7.20"
(7) 0.00 a Oxidation rate during 5 to 70 hours.
0.03 0.17 0.00 1.30 0.00 0.23 0.00 2.84 ...
0.00
0 0 0 A
x
Q
w.-BUTYLBENZENE 4~-BUTYL-I'-~BUTYtBIPHENYL
N 0
2.0-
2 L
e~-BUTYL-4~METHOXYBlPHENYL
4-=-BUTYLBIPHENVL 4,4!01-~-BUTYLBlPHENYL
Y
d
:
0" l o 2 d
e
0
20
40
60
80
100
TIME-HOURS
Figure 2.
Oxidation of the biphenyls a t 100" C.
0
2S.BUTYLBENZENE
0 aec-BUTYL-g-TERPHENVL DI-~-BUTYL-~.TERPHENYL
A
Figure 3.
~.BUTn.Z.METHOXY.9-ERPHENYL
Oxidation of the terphenyls at 100" C.
T h e presence of electron-donating substituents such as phenyl or methoxyphenyl on the ring of sec-butylbenzene, which increase the electron density a t the tertiary carbon, should facilitate oxidation of the compound. However, as can be seen in Figures 2 and 3, there is a considerable decrease in oxidation rate, probably resulting from inhibitor formation. Whereas sec-butylbenzene oxidizes in less than 14 hours, the substituted compounds were stable to a t least 100 hours. T h e stability of these compounds indicates the formation of substituted phenolic inhibitors as oxidation products which are expected to be hydroxybiphenyl or terphenyl, hydroxymethoxybiphenyl or terphenyl, dihydroxybiphenyl or terphenyl, and hydroxy-tert-butylbiphenyl. It can be seen in Table I that almost all the biphenyls and terphenyls rival the stability of 2-p-methoxyphenylhexadecane (3),one of the most stable autoinhibitive compounds previously prepared. 4-sec-Butyl-4'-tert-butylbiphenyl, although relatively unstable compared to the other biphenyls and terphenyls, was much more stable (Figure 2 and Table I) than sec-butylbenzene. Its maximum oxidation rate u p to 100 hours was 1.5 X mole of 0 2 per mole per hour (all oxidation rates in the following are expressed in these units). Disec-butylbiphenyl, having two tertiary carbons subject to oxidation, is much more stable than 4-sec-butyl-4'-tert-butylbiphenyl which contains only one tertiary carbon. This indicates that the former compound is forming a very effective inhibitor, presumably 4,4 '-dihydroxybiphenyl. Similarly, the stability of di-sec-butyl-o-terphenyl is probably the result of the formation of a dihydroxyterphenyl. I n the case of 4-sec-butyl4 '-tert-butylbiphenyl, the deleterious effect of the increased
electron density a t the tertiary carbon due to the electrondonating tert-butyl group outweighs the effectiveness of the inhibitor formed, presumably 4-hydroxy-4'-tert-butylbiphenyl. T h e latter compound, however, is a better inhibitor than phenol, as indicated by the fact that 4-sec-butyl-4'-tert-butylbiphenyl is a more stable compound than either sec-butylbenzene or 2-phenylhexadecane (7) (Table I). Hydroxybiphenyls and terphenyls, with or without electrondonating substituents on a ring, since they are substituted phenols, are expected to be better inhibitors than phenol itself. I t has been reported that in most cases the activity of phenol, which is a relatively poor antioxidant, can be greatly improved by substitution which increases electron density of the hydroxyl oxygen, thereby increasing the effectiveness of the phenol (6). A phenyl group or a phenyl group containing electron-donating substituents would increase the electron density. Furthermore, phenylphenol is far superior to phenol as an inhibitor in the oxidation of paraffins ( 5 ) . Values given for inhibitive periods (hours) for paraffins oxidized a t 170' C. with 0.05% antioxidant were as follows: pure paraffin 0.17, phenol 0.42, and phenylphenol4.67. Previous work showed that phenolic inhibitors formed during oxidation could not be detected by infrared spectroscopy or gas and paper chromatography, presumably because they reacted further as soon as they were formed (7). I n order to obtain evidence that a n inhibitor was formed as a product of oxidation, experiments a t 100' C. were run on mixtures of oxidatively unstable compounds and compounds believed to be autoinhibitive. T h e results showed a distinct inhibiting effect by the autoinhibitive compounds. Similar experiments were run in this work on mixtures of the Oxidatively unstable sec-butylbenzene and some of the compounds believed to be autoinhibitive. As can be seen by Figure 4, 6.8 mole % of 4-sec-butyl-4'-methoxybiphenyl used as an additive decreased the oxidation rate of sec-butylbenzene. Its oxidation rate between 5 and 10 hours was reduced from 7.2 X to 1.4 X and remained 1.4 x up to 40 hours, beyond which time no oxidation was observed for a t least 80 hours. T h e addition of 4-sec-butylbiphenyl also reduced the oxidation rate of sec-butylbenzene ; however, the effect was not as pronounced. By adding 7.4 mole % of 4sec-butylbiphenyl, the oxidation rate of sec-butylbenzene was reduced to 5.0 X 10-4 between 5 and 10 hours. I t is not expected that 4-hydroxybiphenyl would be as good an inhibitor as 4-hydroxy-4 '-methoxybiphenyl. A methoxyphenyl group would increase the electron density at the hydroxyl group of phenol more than a phenyl group. I t was previously reported (7) that between 5 and 35 hours, 13 mole 70of 2-p-methoxyphenyldodecane reduced the oxidation rate of 2-phenylhexadecane from 2 X lo-' to 0.4 X 1O-4. Apparently 4-sec-butyl-4 '-methoxybiphenyl forms a more effective inhibitor, since it takes only 6.8 mole % of this compound to reduce the oxidation rate of sec-butylbenzene 5 times, but it takes 13 mole % of 2-p-methoxyphenyldodecane to reduce the oxidation rate of 2-phenylhexadecane, a more stable compound than sec-butylbenzene (Table I), by the same amount. I t is expected that 4-hydroxy-4'-methoxybiphenyl would be a better inhibitor than p-methoxyphenol. Methoxyphenyl should activate the hydroxyl oxygen of phenol more than a methoxy group alone. Stabilization of compounds to oxidation by inhibitorgenerating arylstearic acids has been recently observed (72). These compounds also form inhibitors via autoxidation a t a tertiary carbon-e.g., hydroxyarylstearic acid forms hydroquinone. VOL. 6
NO. 2
JUNE 1 9 6 7
111
0
NO ADDITIVE
A
6.8 Yo b~-BUTYL-4’-METHOXYBIPHENYL
ZO0/o 4-Jec-BUTYLBIPHENYL
A-A-M-
$
a Y
90 --
A0
60 .-
TIME-HOURS
Figure 4. Oxidation of mixtures of benzene and biphenyls at 100’ C.
sec-butyl-
With the exception of 4-sec-butyl-4 ‘-tert-butylbiphenyl and sec-butyl-2-methoxy-p-terphenyl, the compounds were found to be nonspreading fluids (Table 11). 4-sec-Butylbiphenyl appeared to be nonspreading ; however, despite its high boiling point (107’ C. a t 0.7 mm.), it completely evaporated within 4 days, leaving no residue. While the drop of 4-sec-butyl-4’methoxybiphenyl spread only 0.9% after 30 days, its contact angle had noticeably decreased, indicating that this compound (b.p. 146’ C. a t 0.7 mm.) was also evaporating but a t a much slower rate. Evaporation of high boiling liquids such as 1methylnaphthalene (b.p. 240’ C.) and tert-butylnaphthalene (a nonspreading fluid) has been reported ( 3 ) .
Table II. Spreading Data for Aromatic Hydrocarbons (Room temperature, anhydrous conditions) yo Spreading after Compound 7 days 30 days 4-sec-Butylbiphenyl Evaporated ... 4,4 ’-Di-sec-butylbiphenyl 0.0 0.3 4-sec-Butyl-4 ’-methoxybiphenyl 0.4 0.9 4-sec-Butyl-4’-tert-butylbiphenyl 12.0 24. O n 1.2 1.5 sec-Butyl-o-terphenyl Di-sec-butyl-o-terphenyl 0.0 0.5 sec-Butyl-2-methoxy-p-terphenyl 9.5 22.0 a After 20 davs.
Conclusions
The biphenyls and terphenyls, having an aryl group adjacent to a tertiary carbon, are, in general, more stable than the arylhydrocarbons and diesters previously studied (7). This is attributed to the fact that the hydroxybiphenyls and terphenyls, presumably formed upon autoxidation, are more
112
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
effective inhibitors than the corresponding phenols-e.g., p-phenylphenol and 4-hydroxy-4’-methoxybiphenylare more effective inhibitors than phenol and p-methoxyphenol, respectively. Being inherently stable to autoxidation and thereby eliminating the need for antioxidant additives, these compounds would be advantageous as potential lubricants. Furthermore, they also have a potential use as antioxidants, since they were found to inhibit the oxidation of an unstable compound, secbutylbenzene. Since they are liquids, they could be more easily blended into lubricant compositions than most inhibitors, which are generally solids and difficultly soluble in the usual base fluids-e.g., hydrocarbons, esters, etc. The fluids which are nonspreading would be useful as lubricants in such mechanisms as watches and clocks, where a continual supply of lubricating substance cannot be provided, and where the lubricant film is placed between components having low relative speeds such that the resistance of the lubricant to spreading governs their accuracy. literature Cited
(1) Adams, R., Bachman, W. E., Fieser, L. F., Johnson, J. R., Snyder, H. R., “Organic Reactions,” R. Adams, ed., Vol. 11, p. 246, Wiley, New York, 1944. (2) Boedtker, E., Bull. SOC.Chim. 45, 645-50 (1929). (3) Fox, H. W., Hare, E. F., Zisman, \Y. A., Naval Research Laboratory, Washington, D. C., “Wetting Properties of Organic Liquids on High-Energy Surfaces,” NRL Rept. 4569 (July 1955). (4) France, H., Heilbron, I. M., Hey, D. H., J . Chem. SOC. 1937, 1283-7 (1937). (5) Goftman, M. V., Kharlampovich, G. D., Zh. Priklad. Khim. 30,439-46 (1957). (6) Lundberg, W.O., “Autoxidation and Antioxidants,” W. 0. Lundberg, ed., Vol. 11, pp. 726-8, Wiley, Kew York, 1962. (7) Mertwoy, H. E., Gisser, H., IND. ENG. CHEM.PROD.RES. DEVELOP. 3, 180-6 (1964). (8) Mertwoy, .4.,Trachman, M., Gisser, H., J . Phys. Chem. 64, 1085 (1960). ( 9 ) Portnoy, S., Verderame, F., Messina, J., Gisser, H., Chem. Eng. Data Ser. 3, 287 (1958). (10) Schmidt, J . J. E., Krimmel, J. A., Farrell, T. J., Jr., Denver Research Institute, Univ. of Denver, Denver, Colo., “ ‘Chain Type’ Polyphenyl and Polynuclear Aromatic Compounds as Base Materials for High Temperature Stable and Radiation Resistant Lubricants and Hydraulic Fluids,” Office of Technical Services, U. S.Dept. Commerce, AD151166 (April 1958). (11) Schmidt, J. J. E., Krimmel, J. A., Hobaugh, J. R., Denver Research Institute, Univ. of Denver, Denver, Colo., “Development of ‘Chain Type’ Polyphenyl Compounds for Use as High Temperature Lubricants and Hydraulic Fluids,” Office of Technical Services, U. S.Dept. Commerce, AD110420 (October 1956). (12) Snead, J. L., Messina, J., Gisser, H., IND.ENG.CHEM.PROD. RES.DEVELOP. 5 , 222 (1966). (13) Zavnorodini, S. V., Sidelnikova, V. I., Dokl. Akad. Nauk SSSR 118, 96-9’( 1958): RECEIVED for review October 18, 1966 ACCEPTED February 1, 1967
Division of Petroleum Chemistry, First Middle Atlantic Regional Meeting, ACS, Philadelphia, Pa., February 1966.
