June, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
There is some indication that the products degraded by ultraviolet light follow a law such as Equation 9 but with constants differing from those of heat or mechanically degraded products. However, more data are needed to establish this point. A marked example of the effect of degradation upon homogeneity is illustrated in Figure 2. Degradation of homogeneous fractions A* and A* shows that, as degradation progresses, they move to the left of their original line as defined by Equation 5 and approach the heterogeneity of the other degraded samples. This is shown by the dashed lines of Figure 2. It is by no meana evident that for other heteropolymers, in a aeries aorresponding to stages of procesaing, a definite relation can be found between a viscosity function and the number-average. The usefulneaa of such a relation justifies a search for it. ACKNOWLEDGMENT
We are pleeeed to acknowledge the aid of R. L. Tichenor in carrying out some of the fractionations, of W. F. Walker in determining some of the viscosities, and of L. B. Genung in making eater analyses.
577
LITERATURE CITED
(1) Flory, P. J., J . Am. Chem. SOC.,58, 1877 (1936). (2) Ibid., 62, 3037 (1940). (3) Ibid., 65, 372 (1843). (4) Houwink, R., J . prakt. Chem., 157, 15 (1940). ( 5 ) Huggina, EA. L., IND.ENQ.CHEM., 35, 980 (1943). (6) Kraemer, E.O., Ibid., 30, 1200 (1938). (7) Kraemer, E. O., and Lansing, W. D., J . Phys. Chcm.. 39, 153 (1935).
Kraemer, E. O., and VanNatta, Ibid., 36, 3175 (1932). McNally, J. G., and Godbout, A. P., J . Am. Chem. 8oc., 51, ;WQ5 (1929); Sookne, A. M., Rutherford, H. A., Mark, H . , and Harris, M., J . Rsseurch Natl. Bur. Standards, 29, 123 (1942). (10) Mark, H., “Der feste Korper”, p. 103, Leiprig, 8.Hirrel, 1938. (11) Schull;, G. V., and Dinglinger, A., J . pro& Chem., 158, 153 (8) (9)
(1941). (12)
Sookne, A. M., and Harris, M., J. Reacclrch Natl. Bur. S t w l -
(13) (14)
Spurlin, H. M., IND.ENQ.CHEM.,30,538 (1938). Wagner, R. H., IND.ENQ.CHEM.,ANAL.ED.. 16,620-3 (1944).
ards, 30, 1 (1943).
PRESENTED in part before the Division of High Polymer Physice, American Physical Society. in Rochester, N. Y.,1944. Contribution I001 from Korlnk Research Laboratorieo.
Iron Pentacarbonyl as Antiknock Agent in Alcohol Motor Fuels ISADORE PITESKY AND RICHARD WIEBE Northern Regional Research Loboratory
U,S.Department of Agriculture, Peoria, Ill.
I
N CONNECTION with work on knock suppressors for agricultural motor fuels, an investigation waa made of iron pentacarbonyl, since it is an excellent antiknock agent for ethyl alcohol. The term “ethyl alcohol” is used here in the chemical sense and is equivalent to anhydrous ethyl alcohol. Tetraethyllead is not only totally ineffective in ethyl alcohol but actually depresses the octane rating. That the two metallic compounds, tetraethyllead and iron pentacarbonyl, both extremely effective in gasoline, should have diametrically opposite effeeata in ethyl alcohol is somewhat surprising. Since this laboratory is interested in the development of motor fuels derivable from agricultural products, it was considered desirable to obtain any pertinent information. The purpose of this paper is to present experimental data conoerning its action on alcohol motor fuels. I n these tests a commercial product better than 99% pure waa used which waa further purified by repeated distillations either in vacuo or in a countercurrent of nitrogen. All operations were
carried out either in the dark or in red illumination. The physical and chemical properties were described by Blanchard and others (S,4,IS, t3,l.I). ENGINE TESTS
Knock ratings were made according to the A.S.T.M. Tentative Method of Test for Knock Characteristics of Motor Fuels (D357-43T). Tables I and I1 give some of the results obtained. Two difficulties were encountered in rltting fuels containing iron pentacarbonyl, and therefore the highest accuracy cannot be claimed for the data. Usually after a few runs the knockmeter readings became erratic because of a deposit of iron oxide on the diaphragm of the bouncing pin. This was partially overcome by making only three to five octane number determinations before overhauling the engine. The other difficulty WBS the persistence of action of iron pentacarbonyl in the engine, probably because of an active deposit of iron oxide on the rylinder walls which
Iron pentacarbonyl is an effective antiknock agent for ethyl alcohol fuels; however, caution must be observed when it is used in motor fuels, since the iron oxide deposit may seriously interfere with engine operation. The action of light changes iron pentacarbonyl to iron enneacarbonyl which is practically insoluble in hydrocarbon fuels. Iron enneacarbonyl, however, is soluble in ethyl alcohol, at least to the extent tested, and no obnoxious precipitate occurs in this fuel. Small amounts of oleic, palmitic, and stearic acids and of triethanolamine oleate are effective stabilizers for the h n pentacarbonyl in some hydrocarbon fuels; however, no generalizationcan be made at present. For solutions in anhydrous ethyl alcohol and in ethyl alcohol containing 5% water by volume, no stabilizer is necessary. If reasonable precaution6 are observed, working iron pentacarbonyl is probably no more dangerous from a health standpoint than tetraethyllead.
578
affected, at least for a time, the octane number of the reference fuels. This factor was variable, and the extent of its influence on the data would depend to some extent on the operator’s judgment. A comparison of Tables I and I1 shows the significant differences between the action of iron pentacarbonyl and tetraethyllead on ethyl alcohol as a fuel, While 0.25% by volume of iron pentacarbonyl will raise the octane number from 90 to 99, 1 ml. of tetraethyllead depresses the rating to 85; further amounts of lead up to 3 ml. have no effect.
TABLEI.
Vol. 37, No. 6
INDUSTRIAL A N D ENGINEERING CHEMISTRY
IRON PENTACARBONYL SUSCEPTIBILITY OF
EXPRESSED AS OCTANENLTMBERS
FUELS
Fe(CO)a Added, % by Vol. (Ml./Gal.) 0 0.1(3.8) 0.25(9.6)
Fuel Ethyl alcohol 7 5 q ethyl dcohol 257’ benz alcohol 60+ acet’ L ethyl 90 wtane 10% a&
90
+ ++
96
99
0 When the knock value of the fuel is greater than that of iso-octane, it is ex ressed in term of iso-octane milliliters of tetraethyllead. !Ootane number of F-4ia 99. and that of C-13 ie 71.2.
+
Iron pentacarbonyl seems to have a slightly higher antiknock influence on gasoline than on alcohol, at least in the case of the reference fuel noted. The effect of lead on gasoline is considerably greater. In fuels containing stabilizers, iron enneacarbonyl might exist in molecular aggregates rather than in single units, and since it is known that the state of subdivision of an antiknock is important, it is conceivable that such solutions would show a decrease in octane rating. Any nonvolatile antiknock agent will also be partially lost in a carburetor engine; however, this loss may be very small.
TABLE11. LEAD SUSCEPTIBILITY OF FUELSEXPRESSED AS OCTANISNUMBERS Tetraethyllead. Ml./Gal. 1 2 3 Ethyl alcohol 90” 86 86 86 Eth 1 alcohol 2 ml. Fe(C0)dgal. 93s 91 89 9 0 d e t h y l alcohol 107 anilrne 96 91 Qi Reference gasoline (76.7 If-4in C-la)a 90 98 0:bQml.d a The octane number of ethyl alcohol haa been variously reportad from 90 to 99; however, we believe the oorrect value lies between 90 and 91. b Inter olnted value * See ‘?able I, footnote b . d See Table I, footnote 0 , Fuel
+ +
0
..
I n order to obtain a rough idea regarding the effect or iron oxide deposit within the engine during operation, tests were run in a Lauson RLC 152, to horsepower, single-cylinder, aircooled engine, using a fuel consisting of 0.1% by volume of iron pentacarbonyl in ethyl alcohol. The engine stopped after 78 hours because deposits on the exhaust valve seat prevented compression; it is suggested that since sleeve valve engines have less lead trouble, they may also be more suitable for use with fuels containing iron pentacarbonyl. After the initial soft film of iron oxide had been deposited on the walls, there seemed to be no tendency for the amount of deposit to increase. Tests also included additions of small amounts (0.1 to 1%) of butyl borate which is reported to make the iron oxide film nonconductive through possible formation of iron monoboride and in general to have a “favorable influence” (9). Under the condition of the experiment no such advantage was found. It must be emphaabed that the work was done with only one type of engine, which may have been particularly unsuited for fuels containing car-
bonyl. Tests extending over two years (8) have shown that iron pentacarbonyl can, apparently without detriment, be used as antiknock in fuels; however, its use has been practically discontinued. Harrington (6) mentioned the fact that iron pentacarbonyl is being sold as an antiknock under the trade name “Ferroline”. Another instance of its use in motor fuels has also come to the attention of the authors. STABILITY TESTS
Iron pentacarbonyl, alone and in dilute solution, is very unstable towards blue light and changes to iron enneacarbonyl (diferrononacarbonyl) and carbon monoxide according to the following equation: fzFe(C0)~= Fer(C0)g
+ CO
The rate of formation of iron enneacarbonyl is a function of light intensity and will proceed rapidly in direct sunlight. In the cwe of a 0.1% solution of iron pentacarbonyl in iso-octane, for example, the above reaction is indicated first by a deepening of color, followed by the appearance of a precipitate of goldenyellow to orange-colored thin plates of iron enneacarbonyl, since the latter compound is practically insoluble in hydrocarbons. Iron enneacarbonyl is partially soluble in ethyl alcohol, and an identical solution of iron pentacarbonyl in this solvent will, on exposure to light, show only a gradual change from very pale yellow to dark orange, no precipitate being formed. In the absence of air such a solution will remain stable; however, if it is fully exposed to air, dissolved oxygen may gradually react with the dissolved enneacarbonyl and give rise to a finely divided precipitate of ferric oxide or hydroxide. Leahy (11) not only made an extensive survey of the literature but also performed some experiments with certain stabilizing agents for the purpose of preventing the formation of iron enneacarbonyl. (The word “stabilizer”, as used in this article, refers to a substance which, presumably through peptization or otherwise, prevents the precipitation of iron enneacarbonyl.) He claimed some success but does not disclose the nature of the substances he used. I t WBS impossible to test the many claims made in various patents and articles, and no attempt, therefore, was made to cover the field. Many substances were tested, but the results obtained in only a few typical cases are given in Table 111. Twelve samples of each of the various stabilizers were observed over a period of two weeks. S i of the samples were kept in the dark, and six were exposed to light except where otherwise stated. Three of each of the two sets were open to the atmosphere: the other three were kept in tight-stoppered test tubes. No difference was observed between the samples in stoppered and in open containers. The time recorded in Table I11 gives the interval which elapsed before a precipitate was observed. Samples were exposed to light from the north during August. All solutions remained stable in the dark. None of the substances tested was found to inhibit the action of light, although several were effective in preventing the precipitation of iron enneacarbonyl for the duration of the test. Since, as previously mentioned, enneacarbonyl is soluble in ethyl alcohol, at least to the extent of its equilibrium concentration present in fuels, no .precipitate was formed, and only a darkening of the solution was observed. The solubility of enneacarbonyl in ethyl alcohol decreased with increasing water content, and measurements are now in progress in this laboratory to determine the solubility of iron enneacarbonyl in various solvents. Solutions of pentacarbonyl in leaded gasoline appear to be slightly more stable, although no reason can be given. Palmitic acid, stearic acid, and triethanolamine oleate appear to be good stabilizers; however, the behavior of commercial iso-octane and particularly that of ethyl alcohol show that no generalization should be made. It was also observed that the purity of the reagents-e.g., triethanolamine o l e a t e w a s important, and that
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
June, 1945
579
under a hood. After a, time a, dull sound was heard: investigation showed that the enneacarbonyl had been oxidized to iron oxide apparently with somewhat explosive violence. Both Mittasch (f9) and Blanchard (9)mentioned this reaction but are not in total agreement 85 to its cause. Mittasch states that iron enneacarbonyl is very sensitive to atmospheric oxygen and will ignite when rapidly dried; Blanchard found that the enneacarbonyl is very stable in dry air but, when moistened with iron pentacarbonyl, may ignite spontaneously. Either explanation was applicable in this c a e , and no attempt was made to investigate the real cause.
excem of either oleic acid or triethanol amine caused the form& tion of a precipitate in ethyl alcohol. Basic solutions of iron pentacarbonyl are very susceptible to oxidation, and it was found that additions of 0.001% of formic or acetic acid to ethyl alcohol prevent any possible formation of ferric hydroxide. Bowen and Tietz (9) observed the effect of small quantities of various antiknock substances on the photochemical oxidation of acetaldehyde. Both iron and nickel carbonyl inhibited the reaction; tetraethyllead had no effect on the reaction rate. I n the case of iron pentacarbonyl, inhibition was proportional to the amount added, and the reaction proceeded normally after the
TABLE 111. EFFECTOF STABILIZERS ON FUELS CONTNNINQ 0.1%
BY VOLUME OF IRON PENTACARBONYL (The time given is t h a t required for the formation of a precipitate of iron enneaoarbonyl) 0.1% O~srraACXD(7) 0.1% STEARICACID (7) CONTROL Dark Light FUEL Dark Light Dark Light Dark Light Ethyl alcohol No change Clear browno, No change Turbidity in 16 No change Turbidity i n 16 No change Turbidity in 16 no ppt. min.: heavy a n . : heavy min heavy ppt. i n 2 hr. ppt. in 2 hr. ppt.*\n 2 hr. No change Same No change Same No change Same Ethyl alcohol 557 H:O No change Same No change Same No change Same No change Same Ethyl alcohol 10% HxO No change Sli.ght turbidity In 1 hr.b, no
.
++
Benzene, thiophene-free
No change
3
E?*
No change
Gasoline V-80leaded Iso-actark commercial Reference ’ruel, M-3
No change No change No change
2 days
No change
No change No change
Clear brown, no PPt. Same Same Same
No change No change
Reference fuel A-6 Reference fuel: C-13 Skellysolve C
No change No change No change
3 hr. 3 hr. 3 hr.
No change No change No change
Same Same Same
No change No change
3 hr. 3 hr.
0.1% AMMONIUM OLEATE(7)
No change
No change No change
Clear brown, no PPt. Same 2-3 days Clear brown, no PPt. Eame Same Same
0.1% T R I ~ H A N O L A M I N E1,4-P-TOLUIDOANTHRAOLEATE(7) QUINONE, 0.01% ( 1 )
No change No change No change No ohange
No change No change No change
Clear brown, no PPt. Same 2-3 days Clear brown, no PPt. Same Same Same
Dark No change
Light Clear brown, no PPt.
Dark No change
Light No change0
OIL BROWN DYE(I), 0.01% Dark L i g h t No change Deeper brown, no ppt.
No change No ahange
Same Same
No change
No changeC
No change No change
No change Benzene, thiophene-free No change 2 days No change Gasoline, V-80 leaded No change 6 days No change Iso-octane, commercial No change 2 daya No change 2 days No change Reference fuel M-3 Reference fuel: A-6 No change 2 days No ohange Referenre fuel, C-13 No change 2 days No change No change Skellvsolve C No change 2 d a m a These tests were carried on for one month; b Became opalescent within I hour, hut no precipitate formed. C Color change, if any, masked by dye: color remained green.
Same Eame Same Same Same Same Same
No change No change No change No change No change
2 hr. 2 hr. 2 hr.
2 hr. 3 days
No change No change No change No change No chanee No change No change
Ethyl alcohol
Dark No change
Ethyl alcohol Ethyl alcohol
No change ++ 510%7 Hz0 €110No change
Light Turbidity in 15 min.: heavy ppt. in 2 hr. Same Same
close of the induction period, The results with nickel carbonyl, however, were inconclusive, since the amount added was so large as to inhibit the reaction completely, and no induction period ws9 observed. The strikingly different behavior of iron and lead in this reaction might give some clue regarding their equally different behavior in alcohol fuels, particularly since acetaldehyde has been shown to influence the ignition temperature-pressure relation of ethyl alcohol-air mixtures (10). Egerton and Gates (6) found that, although tetraethyllead raised the self-igniting temperatures of various hydrocarbon fuels, m well as of acetaldehyde, normal alcohols were little affected. This, incidentally, was true also for benzene which, in actual operation, shows a low to zero lead susceptibility. All that can be said at present is that lead and iron compounds in ethyl alcohol show a distinct difference of behavior both in the laboratory as well as in the engine; however, experimental evidence, such as the’addition of 10% of acetaldehyde without effect on the knock rating, is too contradictory. I n order to maintain existing theories of intermediate compounds-.g., the formation of peroxides-recourse must be had to assumptions which cannot or have not yet been verified. To illustrate that precautions must be observed when working with pure iron pentacarbonyl, one incident should be recorded: After filtering a residual amount of iron pentacarbonyl which had been left in a shipping container t o separate the enneacarbonyl formed, the filter paper with precipitate was left in the funnel
No change No change No change
No changec
2 hr. 2 hr.
Same Turbidity, ppt. in 2 rnin. 4 hr. 2 days 4 hr. 4 hr. 4 hr. 4 hr. 4 hr.
ACKNOWLEDGMENT
The writers wish to thank C. F. Elder and F. R. Truby for conducting the engine tests, and C. B. Kretschmer for help in the preparation of iron pentacarbonyl. LITERATURE CITED
(1) Badische Anilin- & Soda-Fabrik, Brit. Patent 260,639 (Nov. 2, 1926). (2)’ Blanchard, A. A., Chem. Rev.,21, 3 (1937); Science, 94, 311 (1941). (3) Bowen, E. J., and Tietz, E. L., J . Chem. SOC.,1930, 234. (4) Dewar, J., and Jones, H.O., Proc. Roy. boo. (London), 76A, 558 (1906). (5) Egerton, A., and Gates, 5. F., J . Znsl. Petroletcm Tech., 13, 244 (1927). (6) Harrington, M. T., Thesis, Iowa State College, 1941. (7) Hocking, J. W., U. 8. Patent 2,140,627 (Dec. 20, 1938). (8) I. G. Farbenindustrie. A.-Q., Auto-Tech., 15, 7 (April 4, 1926). (9) I. G. Farbenindustrie, A+-G., Brit. Patent 252,018 (April 7, 1927). (10) Kane, 0.P., Chamberlain, E. A. C., and Townend, D. T. A., J. C h m . Soc., 1937, 436. (11) Leahy,M. J.,RelSnerNaturala~olineMfr.,14,82 (1935). (12) Mellor, J. W., “Comprehensive Treatise on Inorganio and Thebretical Chemistry”, Vol. V, pp. 967-61, New York, Longmans, Green and Co., 19.24. (13) Mittsach, A., 2. ongm. C h . ,41,827 (1928). (14) Trout, Wm. E., J . Chem. Eduaa6ion, 14, 463, 676 (1937); 15, 77, 113 (1998).
