1108
INDUSTRIAL AND ENGINEERING CHEMISTRY
A few tenths of a gram of gummy brown residue was obtained. It was very soluble in water. Analysis showed 3.54y0 sulfur in this residue and 0.53% sulfur in the sample of base oil A used. The potassium soaps of the strong acid fraction of the oxidized oil therefore contained over six times as much sulfur as the original oil. These data can leave little doubt that the strong acid fraction contains considerable quantities of sulfonic acids. They are also a strong indication that the reaction mechanism which has been postulated on the basis of data obtained with synthetic sulfides is also valid for natural-sulfur-containing lubricating oils. CONCLUSIONS
1. The most effective synthetic sulfur inhibitors found for lubricating oil hydrocarbons are monosulfides containing a t least one ali hatic or cycloaliphatic group attached to the sulfur atom. 2. ‘!$he monosulfides react with hydrocarbon peroxides to give sulfoxides. This reaction is relatively rapid, removes peroxides as they are formed, and thus breaks the hydrocarbon oxidation chain. 3. The effectiveness of various types of sulfide inhibitors appears to depend upon the rapidity with which they reduce peroxides. The sulfides themselves autoxidise much less rapidly than ordinary lubricating oils. 4. The sulfoxide formed by the reactions of the sulfide with oil peroxides can react further with peroxides a t a less rapid rate to give a sulfone. I n so doing the sulfoxide also functions as an inhibitor although a less active one than the original sulfide. The sulfone is not an inhibitor. 5. I n addition t o reacting with peroxides, the sulfoxide also reacts or condenses with oil hydrocarbons to give oil-soluble products. These have not yet been identified.
Vol. 37, No. 11
6. Both the sulfoxideand sulfone autoxidise rapidly. Among the oxidation products of each is a strong acid fraction, preaumably consisting of sulfonic acids. 7. The soaps of the strong acid fraction of an oxidized, normally, refined lubricating oil have been isolated and found t o contain sufficient sulfur to substantiate the postulation that this fraction consists of sulfonic acids. LITERATURE CITED
Bilckstrom, H. L. J., and Beatty, H. A., J. Phya. Chem., 35, 2530 (1931): Alyea, H. N., and Bhckstrom, H. L. J., J. Am. Chem. SOC.,51,90(1929).
Bermejo, L., and Jimhez Hewers, J., I X Conqr. inlern. quim. pura abplicado, 4,238(1934).
Denison, G.H.,IND. ENQ,CREM.,36,477 (1944). Dornte, R.W.. 2bid.. 28.26 (1936). Evans, R. N.,-and Davenport, J.‘ E., XND. ENO.CHEM.,ANAL. ED.,9,321 (1937). Flaschentrilger, B., and Wannschaff, G., Ber., 67B. 1121 (1934). Fridau, Ann., 83,16 (1852). Hock, H., and Susemihl, W., Ber., 66,66 (1933). Hunter, B. A.,Iowa State CoZZ. J. Sci., 15,215 (1941). Krafft, F., and Bourgeois, E., Ber., 23B,3045 (1890). McKittrick, D.S.,IND.ENG.CHEM.,21,585 (1929). Piper, J. D.,and Kerstein, N. A., Ibid., 36,1104 (1944). Tschunkur, E.,and Himmer, E., Chem. Zentr., 1933,11, 2457. Wheeler, D. H., Oi2 & Soap, 9,89 (1936). Whitmore, F. C.,“Organic Chemistry”, pp. 162, 164, New York, D. Van Nostrand Co., 1937. Yamada, T., J. SOC.Chem. 2nd. J a p a n , 36,suppl. binding 277 (1933).
Ibid., 40,suppl. binding 44 (1936).
Redwood Products as Inhibitors of Oxidation in Petroleum Hydrocarbons INHIBITION OF OXIDATION IN CYCLOHEXENE AND GASOLINE’
S
H. F. LEWIS, M. A. BUCHANAN, acteristics t o a s u r D r i s i n n O M E ninety years ago Chevreul (9) called attenE. F. KURTH2, .&D D. FRONMULLER3 d e g r e e (6). I n t h i s ’ e a r l i e i tion to the ability of oakwood The I m t i t u t e of Paper Chemistry, Appleton, Wis. work t h e t a n n i n s a n d t h e Droducts of destructive distillato retard the drying of linseed kon of the tannins and of redoil. Poplar and pine were found wood were tested as inhibitors of acid formation in mineral to have these characteristics to a much smaller degree. oils. In view of their activity in this field, it was decided This DroDertv of oakwood was ascribed bv Moureu and to investigate the products as inhibitors of gum formation. The Dufraisse‘ ( S i to the presence of tannin -in the wood. characteristics of redwood tannin have already been described The latter investigators studied a long list of organic compounds from the standpoint of their activities as “antioxygenic cata(.a). The autoxidation of gasoline has been the subject of many relysts” and “autoxidizable substances”. Under the former they searches since, as a result of this autoxidation, a nonvolatile listed catechol, pyrogallol, the naphthols, and tannins. No gum is formed which is objectionable in any motor fuel. Dimention wm made of the tannin type in the article cited (8). olefins present in the gasoline will oxidize readily to form this Among the “autoxidizable” substances were aliphatic aldehydes, gum. The autoxidation of petroleum distillates was reviewed substituted aliphatic aldehydes, and cyclic aldehydes; unsatusome years ago (4). The reaction has been studied in detail by rated hydrocarbons, such as styrol, phenylbromoethylene, diMorrell, Dryer, Lowry, and Egloff (6), who oxidized gasoline phenylethylene, and turpentine; complex organic substances under carefully regulated conditions in steel bombs and measured such as caoutchouc, fats, and oils; and finally sodium sulfite and the period before serious absorption of oxygen occurred with reinorganic salts. A patent (9) described the use of “tannic arid” sultant formation of gum. The addition of antioxidants to the in 1930. gasoline serves to increase this “induction period”, which is deEarlier experiments showed that the tannin obtained from the pendent on the nature and concentration of the antioxidant. redwood tree (Sequoia sempervirens) possesses antioxidant charThe evaluation of these various inhibitors was studied exten1 The first article in this aeries appeared in October issue (6). sively by the same investigators (7). They suggested the term Present address, Oregon State College, Corvallis, Oreg. “cyclohexene number” or the number of minutes the induction 8 Present address. Scott Paper Company, Chester, Pa.
November, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
1109
period of pure cyclohexbe will be retarded by 0.002% of the antioxidant. Instead of using cyclohexene directly, Morrell et al. recommended the use of reference fuels. In our study of the inhibiting action of the redwood products purified cyclohexene was employed. The test units were similar to those described by Winning and Thomas (11) and were made by the Tagliabue Manufacturing Company (10). The explosionproof cabinets were manufactured locally. Figure 1shows the assembly of three units. EXPERIMENTAL PROCEDURE
A long period was required for establishing a standard and readily reproducible test with cyclohexene. In the preliminary experiments, the cyclohexene purchased from Eastman Kodak Company was freshly distilled before each use. In spite of this precaution, the induction period of a given antioxidant appeared to diminish gradually with time. Investigation indicated that the cyclohexene sample was contaminated with peroxides which partially distilled with it. The peroxides were removed by shaking the cyclohexene with solid potassium hydroxide and then washing with aqueous ferrous thiocyanate. The product was stored over potassium hydroxide in a refrigerator, and s c c i e n t was withdrawn each day for the required test. Before use i t was washed with ferrous thiocyanate and with water, dried over calcium chloride, and distilled. A test for peroxides by the method of Young, Vogt, and Nieuwland (18) ehowed that only small amounts of peroxide remained in the eyclohexene. It should be pointed out that the bomb test is empirical; except for Table V, the results reported are averages of two or more tests. The data show a maximum variation in most cases of less than 10%. The redwood tannin was prepared in a pilot plant large enough to extract 100 pounds of wood, which was chipped and run through a hammer mill. Tannin was extracted either with hot water or with 95% ethyl alcohol. When the latter was used as solvent, the extract was first distilled in a twenty-plate column vacuum still until most of the ethyl alcohol had been removed. The residual water in the still waa sufficient to keep the tannin in solution. Phlobaphenes and other water-insoluble, alcoholsoluble extractives precipitated on removal of the alcohol and were separated from the tannin by filtration. Residual water was evaporated in stainless steel pans in a vacuum pan evaporator a t temperatures which never exceeded 60' C. Three types of redwood waste were available-conveyor waste, (which is a reject from the sawmill operation and is entirely heartw d ) s t u m p w d , and rootwood. The particular tannin samples were tested either directly or after further purification. During each day's operations, blanks were run on the cyclohexene without any inhibitor; at intervals, checks were made using benzy1-p-aminophenol as a control. A study was made of tannins purified in a number of ways with the hope of concentrating the active principle of the tannin. Dry crude tannin extracted from the rootwood (run 37) was first treated with 12 volumes of acetone at room temperature, which diesolved about 86% of the crude tannin. The insoluble and soluble fractions were tested. I n another experiment a part of the rootwood tannin (run 41) was extracted with 10 volumes of acetone, and the acetone-soluble product was tested. In a third experiment a sample of the same tannin was dissolved in 3% sodium bicarbonate solution, and the solution extracted with ethyl acetate. Removal of the solvent from the extract gave an ethyl soetat%eoluble fraction which amounted t o 49% of the original
Figure 1. Bombs Used in Tests
Solvent-purifiedredwood tannins are effective in preventing the oxidation of cyclohexene but are of little value in protecting gasolinebecause of their solubility characteristics. Products prepared by reacting the tannin with benzoyl chloride, caproyl chloride, chloroacetic acid, formaldehyde,and amines appear to have little interest as antioxidants. Condensation of tannin with acetone or other ketones results in a good yield of ether-soluble products which are good inhibitors for cyclohexene. However, the addition of water to the treated cyclohexeneresults in the loss of approximately half of the inhibiting action. The acetone-tannin condensation products have poor solubility in gasoline and are of questionable value as gasoline antioxidants. Products obtained by condensing catechol with acetone have excellent inhibiting properties for cyclohexene and appear somewhat promising as antioxidants for gasoline. In using cyclohexene in the WinningThomas breakdown test, it is necessary to remove the peroxides in order to obtain duplicate results.
tannin. Other samples were prepared by extracting similar sodium bicarbonate-tannin solutions with methyl amyl ketone and with amyl isobutyl ketone; these solvents gave yields of 43 and 53% tannin, respectively. Table I shows the induction times of the tannin samples. It is apparent that the inhibitor is concentrated in the acetone-soluble tannin, since the acetoneinsoluble material has no antioxidant activity. Shortly after these tests were run, a sample of the crystalline material found in the green cones of the redwood was received. This material contains about 85y0of material soluble in methanolacetone; the other 15% is largely fibrous material, cone scales, dirt, etc. About 15% of the fraction soluble in methanol-acetone was insoluble in acetone; the acetone-soluble fraction is chiefly tannin. The tannin fraction was a satisfactory tanning agent, but neither the crude cone tannin nor its acetone-soluble and -insoluble fractions showed any antioxidant activity. Experiments were conducted to determine the effect of storage conditions on the stability of redwood tannin itself in terms of its
I N D U S T R I A L' A N D E N G IN E E R I N G C H E M I S T R Y
1110
Vol. 37, No. 11
product was purified by dissolving in ether. The data in Table TABLEI. EFFECTOF SOLVENTPURIFICATION OF REDWOOD I1 show that tannin treated with 0.2 mole of caproyl chloride had TANNIN ON INDUCTION PERIOD good antioxidad activity, but the yield was low. None of the (0.005% antioxidant, treated to remove peroxides and distilled) other esterification products had sufficient activity to be of further Induction interest. All these products had low solubility in water. Period, Min. Run No. Description 35 No antioxidant Control AMINES. Experiments made to neutralize the acid material 37 Crude tannin 225 had shown that the addition of tributylamine to an aqueous 245 Acetone-sol. tannin 35 Acetone-insol. tannin tannin solution caused the separation of an insoluble product. Acetone-sol. tannin 255 Accordingly, redwood tannin was reacted with a variety of amines 41 Ethyl acetate-sol. tannin 260 Methyl amyl ketone-sol. tannin 235 (such as tributylamine, aniline, p-aminophenol, ethylenediHexone-sol. tannin 285 amine, and 2-amino-1-butanol) to form products which in some cases have fair antioxidant activity. I n most cases the yields TABLE 11. INHIBITINQ ACTIVITYOF CONDENSATION PRODUCTS were small and further work was dropped. OF TANNIN WITH ORGANIC ACID (0.005% antioxidant in oyclohexene treated to remove peroxides and
distilled)
Description of Tannin Beneoylated crude product) Bensoylated {ether-extracted) Treated with 2.7 moles caproyl chloride Treated with 0.2 mole caproyl chloride Treated with crude chloroacet 1 chloride TreateG with chloroacetyl chforide. ether-sol. fraction
Yield,
Induction Period, Min.
40
136 26 92
...
45 30 105 215 65
93
130
%
antioxidant activ?ty. Conditions investigated included the effect of high and low temperature, sunlight and ultraviolet light, and moisture. I n general, there was little indication of deterioration of the tannin stored under widely varying conditions. Previous work has shown that tannin can be prepared from redwood having about the same degree of inhibiting action with cyclohexene as does benzyl-p-aminophenol. These products were prepared in a number of ways and were stable over a 4month test period. The next problem was to improve the solubility of the tannin in cyclohexene or gasoline and lower its solubility in water without, at the same time, altering its inhibiting activity.
.
CONDENSATION PRODUCTS WITH ACIDS AND AMINES
BENZOIC ACID. Ethyl-acetate-soluble stumpwood tannin was treated with 1.1 moles (assuming a molecular weight of 510 for the tannin) of benzoyl chloride in the presence of pyridine. The crude product was insoluble in ether and was purified by extraction with ether to remove the benzoic acid. CRLOROACETIC ACID. Acetone-soluble rootwood tannin was heated on the steam bath with 2 parts of chloroacetyl chloride for 8 hours; the product was largely ether soluble. CAPROIC ACID. Ethyl-acetate-soluble stumpwood tannin was treated with 2.7 moles of caproyl chloride in the presence of pyridine. The product was ether soluble and was purified by dissolving in ether. A second product was prepared using only 0.2 mole of caproyl chloride in the presence of pyridine. The
CONDENSATION WITH FORMALDEHYDE AND CATECHOL
Redwood tannin was reacted with formaldehyde in an effort to obtain water-insoluble and gasoline-soluble products having antioxidant activity. The solubility of these products was very poor, and they had little or no antioxidant activity. Since catechol may be recovered in good yield from the destructive distillation of redwood phlobaphene, tests were run both with catechol and with a number of its condensation products. Catechol was found to have good antioxidant activity but is not used for protecting gasoline because of its high solubility in water. Baker ( I ) described the preparation of a water-insoluble product by the condensation of catechol with acetone in the presence of acids. This product was prepared and found to have considerable promise as an antioxidant. Several experiplents were made to study the conditions necessary to plloduce a satisfactory antioxidant in good yield. The gencral procedure was to heat the catechol, acetone, and acid mixture on the steam bath under reflux. The reaction product separated as a tar when poured into water. AfteriYashing with water, this tar was either recrystallized from alcohol-acetic acid or was purified by dissolving in ether and washing the ether free of acid. I n most cases the product was completely soluble in ether. The data in Table I11 indicate that large amounts of acids or long periods of heating are necessary for high yields of the product. Substitution of anhydrous aluminum chloride for the acid resulted in poor yield. These products have good antioxidant activity and appear to have reasonably good solubility in cyclohexene and gasoline, with low solubility in ,w&ter. CONDENSATION WITH KETONES
Since catechol condenses with acetone to form a product having good antioxidant activity with improved solubility characteristics, an investigation was made of the effect of acetone on redwood tannin under similar conditions. Tannin was found to react with acetone and other ketones in the presence of concentrated hydrochloric acid and glacial acetic acid or in the presence of anhydrous aluminum chloride to form water-insoluble products. The product from the tannin always consisted of both ether-soluble and ether-insoluble fractions. The ether-soluble fraction had good antioxidant activity and was nearly insoluble TABLE111. YIELD AND INDUCTION PERIOD OF CATECHOLPRODUCTS ACETONE CONDENSATION in water. The ether-insoluble fraction had poor antioxidant (0.005% antioxidant in cyclohexene treated to remove peroxides and properties and was somewhat soluble in water. distilled) Apparently the acetone or other ketone is essential to the reReagent8 Used/lO action, because tannin heated under similar conditions without Grams Catechol Ace- Acetic Concd. Induction acetone resulted in a low yield of inactive material. Other keCondensation tone; acid, HCI, Hours Yield, Period, tones can be substituted for acetone in this reaction, but no adProduct CC. cc. cc. Heated % Min. vantage was found in their use, particularly since the high-boiling Recrystallized 16 27 22 25 390 Tar from mother ketones were difficult to remove from the product. The various liquor 16 27 22 25 .. 300 Recrystallized 16 27.5 22 25 28 260 conditions used in preparing the condensation products, the yield Crude 16 27.5 22 24 113 290 data, and the induction periods of the products are summarized 5 8 30 Ether soluble 20 6 200 8 Ether soluble 15 12 10 57 310 in Table IV. Ether soluble 16 27.5 22 8 290 90 Ether soluble .. 8 200 .. 315 50 The most satisfactory of the condensation products were then 20 6 5 25 Ether aoluble 255 105 tested for solubility behavior. The general procedure was to Catechol .. .. 410 shake 100 cc. of cyclohexene, to which had been added the anti0 One gram AlClr used. oxidant, with two 25-cc. portions of water and determine the in-
...
November, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE IV. YIELD AND INDUCTION PERIOD OF CONDENSATION PRODUCTS OF REDWOOD TANNIN WITH KETONES (0.006% antioxidant in cyclohexene treated to remove peroxides and distilled) Tannin
(10 G.)
Acetic Concd. Acid, HCl Cc. Cc.’
Ketone, Cc. Acetone 20 6 5 Acetone: 20 6 Acetone 20 6 55 Acetone: 20 6 5 Cone Acetone, 20 6 5 Rootwood Acetone 20) Acetone’ 20) ~ c e t o n e :IO 3 2.5 Acetone 6 5 Acetone’ 20 10 3 2.5 Acetone: 10 3 2.5 Stumpwood Acetone, 10 3 25 Rootwood Hexone 20 6 5 C clohdxanone 20 6 5 $ethyl ethyl kktone, 20 6 5 Mesityl oxide, 5 6 5 Isophorone, 5 6 5 Acetophenone, 20 6 5 5 60 cc. acetic acid and 50 cc: hydrochlqric acid added b One gram anhydrous aluminum chloride used. C Heated to 50° C. only. Rootwood
... ...
... ...
Hours Heated
22.5‘‘
Ether-Sol. Reaotion, Products, %
.
Induction Period, Min.
215 8 ‘ 210 160 10 6 255 8 170 6 60 275 6 43 240 10 54 250 lod 57 215 8 26 255 8 29 310 8 28 245 8 78 250 225 8 120 8 80 270 8 65 250 8 25 250 8 54 150 and heating continued for 2 hours. 60 44 41 66 41
results were essentially the same as those obtained in the absence of surface-active materials. TESTS ON GASOLINE
From the beginning of this investigation it was known to be impossible to obtain and keep a standard gasoline for test. Different samples of gasoline have widely different oxidation stabilities and, in addition, the stability of an unprotected gasoline undergoes considerable change under normal storage conditions. However, a few tests were made on different gasolines. In general, the results indicated that the tannins and their condensation products are much less effective than benzyl-p-aminophenol in preventing the oxidation of gasoline. This may be due to the poor solubility of the tannins in gasoline, but there are some indications that the redwood products protect a considerably narrower field of chemical structures than is the case with the substituted aminophenols.
TABLE v.
SOLUBILITY BEHAVIOR OF CONDENS.4TION PRODUCTS (Cyclohexene treated to remove peroxides but not distilled. 0.005% used in eaoh case; water washed after addition of antioddant) Induotion Condensation Product Period, Min.
310 105 75
so
60
.4cetone-condensed catechol Acetone-condensed catechol
45 35 60 50 300 250
duction period on 25 cc. of the washed cyclohexene. In some cases 25 cc. of the washed cyclohexene were evaporated, and the residue was weighed in an attempt to determine the amount of antioxidant left in solution. This washing procedure was probably more drastic than would be encountered in commercial practice but, since the condensation products are ether soluble and water insoluble, it was originally believed that they would easily withstand such a test. This treatment of cyclohexene protected with tannin condensation products caused the separation of a sludge between the two layers, and a decrease of more than 50% in the induction period. The water treatment had much less effect on the induction period of cyclohexene protected with the catechol condensation product, and had no apparent effect on cyclohexene protected with benzyl-paminophenol or with isobutyl-p-aminophenol. The tests made to determine the amount of antioxidant left in solution indicate that the water treatment removed a considerable amount in each case. The quantity of the tannin condensation products left in solution was approximately equal to that left in solution with substituted aminophenols and the catechol condensation product. In one test the addition of about 0.5% water was sufficient to decrease the induction period more than 50%. On the other hand, the use of cyclohexene which had been shaken with water before addition of the antioxidant did not resul$ in any loss in protection. The experimental data are given in Table V. The extraction of the treated cyclohexene with water appears to cause the antioxidant to separate a t the interface. It was believed that the presence of small amounts of some surface-active material might prevent this separation. Accordingly, the treated cyclohexene was waahed with water containing varying amounts of NOPCO 2090-M (sulfonated toaseed oil), Surpasol 630 (double sulfonated castor oil), and Vel (glyceryl lauryl sulfate). The
1111
SUMMARY
1. The Winning and Thomas breakdown test involvin the use of cyclohexene has been standardized. Satisfactory cgecks are obtained when the cyclohexene is treated to remove peroxides, followed by distillation. 2. Satisfactory antioxidants for use with cyclohexene are made by extracting redwood with 95% alcohol, precipitating the phlobaphene with water after the alcohol is mainly removed, and evaporating. The active fraction is removed from the residue by extraction with acetone or ethyl acetate. 3. Such tannins are too soluble in water to be satisfactory for use in water-sealed gasoline tanks. A variety of condensation roducts have therefore been made. Of greatest interest is that Formed by condensation with acetone. Caproyl chloride and p aminophenol can also be used as condensin agents. 4. Although the solubilities of these jerwatives have been greatly improved, there is a concentration of the antioxidant at the interface when solutions in cyclohexene are washed with much water; antioxidant effectiveness is thus. lost. Surfaceactive oils have been added in the hope of reducing the concentration of the antioxidant a t the interface. The results have not been successful. 6. The solubility of the redwood products in several asolines is less than in cyclohexene. Poorer protection is afforfed than with benzyl+-aminophenol. Tests with gasolines have only directional value. 6. Some interest in catechol condensation products is indicated; this is in line with the possible production of catechol from the destructive distillation of redwood phlobaphene. ACKNOWLEDGMENT
The authors are indebted to the Standard Oil Company of New Jersey for aid in setting up the testing equipment and to Carlton Ulmen for running many of the tests, Appreciation is expressed to The Pacific Lumber Company for permission to publish this work and for the redwood samples used. LITERATURE CITED
Baker, J . Chem.Soc.. 1934, 1678. Buchanan, Lewis,and Kurth. IND. ENQ.CEEM.,36,907 (1944). Chevreul, Ann. chim. ph,hys., [3],47,209 (1856). Ellis, “Chemistry of Petroleum Derivatives”, Vol. I, pp. 889913 (1934): Vol. 11, pp. 905-41 (1937). Lewis, Buohanan, Fronmder, and Kurth, I ~ D ENQ. . CHBY.. 37, 988 (1945).
Morrell, Dryer, Lowry, and Egloff, Ibid., 27, 315 (1935). Zbid., 28,465 (1936). Moureu and Dufraisse, Chem. Rev., 3,113 (1926). Pure Oil Co., French Patent 701,340 (1930). Tagliabue Mfg. Co., Catalog No. 6690D,Item 55,940. Winning and Thomas,IND. ENQ.C H ~ M25, . , 511 (1933).
Young, Vopt, and NieuwIand, IND.ENG.CHEM., ANAL.ED.,8, 198 (1936).
