June, 1924
I N D USTRIAL A N D ENGINEERING CHEMISTRY
587
The Volatile Yellow Coloring Matter in Cracked Gasolines' By B. T.Brooks and H.0.Parker THEMATHIESON ALKALIWORKS,INC.,h-Ew Y O R XN. , Y.
H E volatile yellow coloring matter of cracked gasolines the absorption is in the visible part of the spectrum, and these is of considerable scientific interest, and at the same hydrocarbons are colored shades of yellow, orange, and red. The writers believe that the volatile yellow coloring matter time constitute! a serious refining problem with the products h a d e by certain cracking processes. The first of cracked gasolines is due to the presence of hydrocarbons thing noted in examining a large number of such distillates containing conjugated unsaturated groups, although they is that the more highly unsaturated the gasoline the more have not yet isolated these coloring matters. It is not due strongly it is colored. The coloring matter in question is to the presence of impurities containing oxygen or sulfur. the bright yellow observed in gasoline distillates when a This is conclusively shown by decomposing a pure, colorless cracked gasoline is freshly distilled through a suitable column paraffin wax in a quartz tube in an atmosphere of methane so that the carrying over of droplets of heavyresidue or as- and other hydrocarbon gases. A well-refined paraffin wax was refluxed over metallic sodium; the metal remained enphaltic matter is entirely prevented. Another type of coloring matter is indicated by the dis- tirely bright and free from scum. The paraffin vapors were coloration of a refined cracked gasoline by air oxidation then passed directly into a quartz tube heated to a cherry-red after slanding for some time. The writers have recently in an ordinary combustion furnace. The gases were passed examined the oil extracted from cracked gasoline by wash- through glass, first in air and then through an ordinary ing with caustic soda prior to treating with acid, and .find watercjacketed glass condenser, the condensate being at that this oil, precipitated from the aqueous alkali by dilute all times protected from the air by the uncondensed gases sulfuric acid, consists chiefly of cresols and phenol. The simultaneously formed in the heated tube. The distillate ease with which phenol and the cresols become discolored was redistilled for the gasoline fraction, and this showed yellow to red by air oxidation is well known, this develop- the same bright yellow color and behavior to acid noted above. ment of color being due to the formation of condensation This experiment was repeated with water-white pharmaceutical oil. The sodium remained bright and uncorroded, products of quinone.2 Still another type of discoloration is produced when a and the cracked gasoline distillate thus obtained showed cracked gasoline that has been refined by sulfuric acid is the same bright yellow color. Further evidence of the nature of this coloring matter allowed to stand without redistillation after refining. The treated gasoline, though originally washed neutral, rapidly is found in the complete parallelism between the known darkem in color and often separates a gummy deposit which methods for polymerizing conjugated diolefins and the beis strongly acid, this change being due to the decomposition havior of this yellow coloring matter. Metallic sodium of alkyl sulfuric esters left in the refined and washed g a ~ o l i n e . ~polymerizes isoprene and its homologs on gentle heating, It seemed remarkable that even the forerunnings of highly and freshly distilled samples of yellow cracked gasoline, cracked gasolines, such as are produced by vapor phase after gently refluxing with sodium for 2 hours, give a colorprocesses, should be colored bright yellow, a tint quite dif- less gasoline fraction. It is well known that fuller's earth ferent irom the dull browns produced by asphaltic matter. and similar materials do not readily remove the coloring The same or a similar volatile yellow coloring matter is present matter from such oils by the ordinary filtration methods. in crude benzene from carbureted water-gas tar and from However, if such a gasoline is heated, or refluxed, with a Pintsch gas condensate. The behavior of such gasolines small quantity of fuller's earth, the bright yellow color will when tieated with sulfuric acid has already suggested to one change to a darker brown shade, but on redistilling a colorof the writers that such highly cracked yellow gasolines less gasoline fraction is obtained; the volatile yellow coloring contain conjugated diolefins. The simple olefins, contain- matter has been polymerized to higher boiling substances. ing onr double bond, give no tars with ordinary sulfuric Moreover, if the vapors of such a gasoline, on distilling, acid a t 15" to 20' C., and very little rise in temperature. are passed through a small column of fuller's earth, kept Such highly cracked yellow gasolines, on the other hand, hot to prevent too much condensation, the distillate is react energetically with sulfuric acid, giving black, tarry colorless. Such a method of refining was tried industrially products, reduction of the acid, and considerable rise in in England by Hall and has been patented in this country temperitture-all of which effects are known to result when by Grey. Heat alone will also affect this polymerization, conjugated diolefins are treated with sulfuric acid. Thus just as in the case of isoprene and its homologs. I n this pure cy clohexadiene and cyclopentadiene react with sulfuric case several experiments were carried out by heating the acid with explosive violence. cracked gasoline in a steel autoclave for about 3 hours to All known simple olefins are colorless, and therefore a temperatures of about 316" to 360" C. (600" to 680" F.) or cracked gasoline may have a substantial percentage of un- below the temperatures ordinarily employed in cracking. saturated hydrocarbons and yet be nearly colorless. Such After cooling, the cracked gasoline fraction was distilled off olefins, however, show an absorption band in the ultra- and entirely colorless distillates were obtained up to 205" C. violet, and diolefins show two such bands. I n the fulvenes, (400' F.). This colorless fraction no longer reacted energetically with sulfuric acid. In order to compare this effect with sulfuric acid, the gasoline fraction, up to 205" C., of a very yellow gasoline made by a vapor phase process was treated with a relatively large proportion of sulfuric 1 Presented under the title "The Coloring Matter of Cracked Gasolines" before the Division of Petroleum Chemistry a t the 65th Meeting of t h e acid (10 per cent by volume). On agitating a liter of such American Chemical Society, hTew Haven, Conn., April 2 to 7, 1923. Regasoline with 100 cc. of acid the rise in temperature was ceived December 19, 1923. 46" C., but the same fraction of the colorless gasoline from 1 Gibbs, P h i h p p i n e J. Sci., 4, 133 (1909). 9 Brooks and Humphrey, J . A n . Chem. SOL, 40, 822 (1918). which the diolefins had been removed by polymerization
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by heat showed a rise in temperature of only 13” C. with acid under the same conditions. Since fuller’s earth is known to polymerize even simple olefins such as amylenes, and since heating such yellow gasolines with fuller’s earth evidently causes polymerization of these yellow hydrocarbons, it has been assumed that whatever hydrocarbons could be recovered from the fuller’s earth would very probably not be the original diolefins, but their polymers. Observation of the boiling points of the diolefins present
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also makes it very uncertain whether the oils retained by the fuller’s earth and which can be recovered from it represent the original colored hydrocarbons. Two methods for the isolation of these colored hydrocarbons appear to give some promise of success-namely, fractional separation by means of solvents, and the use of mercuric acetate. It is intended to continue work in this direction along the lines just indicated, with the expectation that these colored hydrocarbons may be isolated in a sufficient state of purity to prove their identity.
T h e Sodium Plumbite or Doctor Test of Gasolines’ By B. T. Brooks THEMATHIESON ALKALIWORKS, INC.,N a w YORK, N. Y.
RACTICALLY all gasoline refined today is treated to be negative to this well-known test. Though the chemistry of it is not understood, positive doctor tests have become associated with more or less malodorous gasoline and most gasolines high in sulfur give heavy precipitates in this test. It is well known that gasolines that have been treated so that they are negative to this reaction may still contain substantial proportions of sulfur derivatives. The types of sulfur derivatives which react in this test are not known, but that in the great majority of cases, some sort of sulfur derivatives are responsible for a positive reaction seems practically certain, and this is the prevailing opinion. Inasmuch as a negative doctor test is a common commercial requirement and is also legally required in some states, the writer believes it advisable to call attention to a reaction with sodium plumbite solution which very closely resembles the positive results obtained with unrefined or “sour” gasoline. The resemblance is so close that when shown the test many experienced petroleum chemists have pronounced it a positive and characteristic doctor reaction. A positive. result in the test in question may be obtained with oils absolutely free from sulfur, and since the results are due to peroxides, it will be referred to as the “peroxide reaction.” I n a typical doctor test the oil is agitated with a solution of litharge in caustic soda; a yellow discoloration results, usually without the formation of any visible precipitate. A very small proportion of sulfur is then added and the mixture agitated again, when the color is much intensified and a flocculent precipitate begins to form, the color passing through a dull orange, rapidly becoming darker, to brown, and finally assuming a brownish black or black color. (When free hydrogen sulfide is present, black lead sulfide is immediately formed,) I n ‘rapid routine testing the initial orange tints are usually all that are noted, these being obtained in a few seconds. A sample of cracked gasoline that had been treated until entirely negative to the alkaline plumbite test showed a very positive test after standing several months; the usual color changes were noted, but the brownish black precipitate suggested that it might be lead peroxide. When the gasoline was tested for organic peroxides by shaking with a little starch-iodide solution, a very positive reaction was obtained. Another sample of cracked gasoline was then refluxed over metallic sodium for about 6 hours and then distilled over
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1 Presented under the title ”Note on the Doctor Reaction for Sulfur” before the Division of Petroleum Chemistry at the 65th Meeting of the American Chemical Society, New Haven, Conn., April 2 to 7 , 1923. Received December 19, 1923.
this metal. The distillate was entirely negative to alkaline plumbite and the addition of sulfur caused no discoloration; any sulfur derivatives not reacted upon by the metallic sodium were certainly very stable and at any rate showed not the slightest reaction with alkaline plumbite and sulfur. After standing 3 weeks in a partially filled and loosely stoppered bottle, this gasoline showed the lead peroxide test with alkaline plumbite and the peroxide test with starchiodide solution. A sample of turpentine was then refluxed over sodium and then distilled, the distillate collected a t 156” to 158” C. and tested for sulfur by all known methods, with entirely negative results. It was also entirely negative to alkaline plumbite, but after standing in a partially filled bottle soon acquired a peroxide reaction and with alkaline plumbite showed the yellow-orange-brown color changes. After standing about 3 months, the reaction was so pronounced that to simulate a very sour gasoline it was necessary to dilute i t ten times with a doctor negative gasoline. When a few drops of aqueous hydrogen peroxide, about 0.5 per cent, are added to a mixture of sweet gasoline and alkaline plumbite, the dark brown precipitate of lead peroxide is produced almost immediately. When a trace of benzoyl peroxide is added to sweet gasoline and then agitated with alkaline plumbite, the yellow-orange-brown color changes are observed, indicating that organic peroxides are responsible for these color changes in this peroxide test, with the ultimate formation of lead peroxide. It was noted that the addition of sulfur did not intensify the color and its addition was not necessary to bring about the formation of the precipitate; in parallel tests the amount of precipitate was not visibly increased by the addition of sulfur. This difference helps to distinguish this peroxide test from the true doctor test, which is almost certainly due to sulfur ‘derivatives. Moreover, the precipitate in the latter case, if allowed to stand a few hours, becomes quite black, whereas the lead peroxide retains its distinct dark brownish shade. Another difference that may sometimes be noted is that cracked oils which have become oxidized by air during storage may show considerable discoloration when treated with alkali, due probably to the presence of aldehydes formed by the air oxidation, Oxidation of cracked gasoline by air is, like all such processes, much accelerated by sunlight, and such a peroxide test as described above is much more likely to be developed in glass sample bottles than in iron storage tanks, from which light is excluded and which have relatively little surface, compared with the volume, exposed to air.
