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CONSTITUTION OF THE BENZENE NUCLEUS | Werner the present writer has based the following generali WITH REFERENCE TO THE PHENOMENON OF DI-SUBSTITUTION. By BERNHARD FLÜRSCHEIM. sation:-When an unsaturated atom (tervalent nitrogen, bivalent oxygen, monovalent halogen, &c.) takes the place of hydrogen linked to carbon, the demand thereby made on the affinity of the carbon atom is increased (not reduced) in amount. That substitution of methyl-hydrogen in toluene by unsaturated atoms must gradually lead to inversion of orientation is a postulate of this theory, and does not require any special hypothesis. Which of these two diametrically opposed views on carbonyl and similar bonds is correct may be deduced from independent evidence. If, for instance, C in CO were, in accordance with Thiele, more unsaturated than C in -CH2, carbon monoxide might be expected to have a greater tendency to polymerisation than methylene; the other view leads to foresee the opposite, and this, of course, corresponds to fact. UNDER the above title Mr. Cecil L. Horton recently (CHEM. NEWS, 1914, cix., 157) published certain theoretical views. In discussing these it is only necessary to deal with the last eight lines; for-although Mr. Horton appears to have overlooked the fact-everything else in his article had previously appeared in publications by the present writer (Journ. Prakt. Chem., 1902, lxvi., 321; 1905, lxxi., 497; 1907, lxxvi., 165, 185; Ber., 1906, xxxix., 2015; Journ. Chem. Soc. Trans., 1909, xcv., 718; 1910, xcvii., 84), and can now already be found in some textbooks and other publications (for instance, Hans Meyer, "Analyse und Konstitutionsermittlung Organisher Verbin- Again, if C in-CO were unsaturated, the effect which dungen"; Richard Meyer, Jahr. der Chemie; "Annual the latter radicle would have on the mobility of certain Reports on the Progress of Chemistry," 1909, vi., 61, &c.). atoms in side-chains would lie in the same direction as the According to the present writer's theory, an unsaturated action of other radicles with admittedly unsaturated atoms atom in direct combination with the benzene nucleus in corresponding positions. Thus a phenyl- or methoxylcauses an increase of free affinity in the ortho- and para-group in the ortho- or para-position is known to increase positions with regard to itself, and therefore substitution in these positions. In applying this principle to carbonyl the mobility of x in compounds of the type C6H5C and similar groups, Mr. Horton, in the last eight lines of his article, finds it necessary to make a supplementary assumption:-Since these radicles are unsaturated and still do not mainly direct into the ortho- and para-positions, it is, in his opinion, necessary to assume that such groups are first transformed by addition of the reagent, whereupon the latter migrates into the meta position. If it were necessary to have recourse to additional hypotheses of this nature, the whole theory would have no value whatever. There would obviously be no reason why some other groups, for instance, methoxyl, should not also first add, say, nitric acid, and then be substituted in the meta-position. We should not have a comprehensive generalisation permitting to foresee anything, but simply a series of "explanations" ad hoc. Mr. Horton's assumption is, however, wholly unnecessary. If a carbonyl or similar group is unsaturated, it does not follow that the particular atom by which it is linked to the nucleus is also unsaturated. It would be so according to Thiele's theory of partial valencies; but it would not be so according to the views advanced by Werner ("Beiträge zur Theorie der Affinität und Valenz," Zürich, 1891) in connection with the carbonyl-group in aliphatic acids. Werner argued that this group is linked to the neighbouring carbon atom with an abnormally low amount of affinity, because the bulk of the carbonyl-carbon atom's affinity is saturated by oxygen. On this idea of (x = halogen, hydroxyl, &c.). According to the view first advanced by the present writer, and now accepted by most authors, this is due to a shifting of the distribution of affinity in the molecule, caused by the increased amount of benzene-carbon affinity taken up by the unsaturated substituting atom, and resulting in a decrease of the affinity available for linking x. It can be expressed graphically by Formulæ I. and II., the thick lines representing increased, and the thin lines decreased, amounts of affinity. If these substituents are replaced by carbonyl radicles, Formula III. (or III.a which has the same meaning) would result according to Thiele's theory, IV. according to the writer's; by the former theory the mobility of x would be greater than in the unsubstituted compound, by the latter theory it would be less. As a matter of fact, Staudinger, Clar, and Zcako (Ber., 1911, xliv.. 1640), and Staudinger and Clar (Ber., 1911, xliv., 1632) have found that the mobility is less. Steric conditions cannot be made to account for these results, since they are practically the same in IV. as in I. Neither can the electro-negative nature of the carbonylgroup be adduced, since this would even tend to increase the mobility of x, according to universal experience concerning the mutual influence of electro-negative groups on each other. Neither can the "explanation" given by Staudinger-an adherent of the Thiele theory-that OCH, The reactions of "conjugated double bonds" had not lent themselves to an experimental decision between the two theories. The reduction of ketones to pinacones had, even on the basis of the Thiele theory, necessitated the assumpion that it was the oxygen which reacted first. But if these reactions had not given any indication of free affinity at the carbon atom of a carbonyl-group, they also had not disproved it. It is in the aromatic series that a crucial test has now been possible, and the verdict is against an unsaturated carbonyl-carbon atom as postulated by Thiele's theory of partial valencies, and therefore against that theory itself. GAS ANALYSES BY FRACTIONAL DISTILLATION AT LOW TEMPERATURES.* By G. A. BURRELL and F. M. SEIBERT. THIS paper describes experiments that resulted in the separation of a natural-gas sample into the individual paraffin hydrocarbons present. This had not been accom plished hitherto. Natural gases may contain only methane as the combustible constituent or may be mixtures that contain large quantities of the higher gaseous paraffins. In some samples the latter predominate. In addition, there may be vapours of the liquid paraffin hydrocarbons present, sometimes enough to warrant the installation of a plant for their extraction. The natural gas used in Pittsburgh, Pa., is a complex mixture, and is typical of gas that is supplied to many cities to the extent of billions of cubic feet per year. The exact composition of this gas is of importance to the Paper presented before the Spring Meeting of the American Chemical Society, April 7-10, 1914, by permission of the Director of the Bureau of Mines, U.S.A. Bureau of Mines, because it is used in testing explosives, safety lamps, electrical mining machinery, and other mining appliances. By the scheme shown herein it is also possible to determine more closely the quantity of the vapours of the liquid paraffins in a natural gas mixture than has been possible heretofore. Gases that contain enough of these vapours are compressed and cooled at many plants and the condensate sold as gasoline. It is generally known that ordinary combustion gas analyses give but little indication regarding the individual hydrocarbons present in a natural gas mixture. Only the two predominating paraffins are shown. In the experiments reported herein, natural gas was first liquefied by means of liquid air, and the different paraffin hydrocarbons separated by properly adjusting temperatures and removing the various fractions with a mercury pump. These fractions were analysed by the ordinary slow combustion methods. Advantage was taken of the work of P. Lebeau and A. Damiens (Comptes Rendus, 1913, clvi., 325), who prepared various mixtures of the gaseous paraffins, liquefied them, and partially separated them. This work is an advance over their work in that the separation was made into single constituents. The important part of this paper, however, is the application of the work to the determination of the constituents of natural gas. Such a separation is possible because in the liquid condition the boiling points of the gaseous paraffins are rather widely separated. These boiling-points follow:Methane, 160 C.; ethane, 93° C. ; propane, -45° C. ; N-butane, +1° C., and isobutane -10° C. The two butanes were not separated. In order to finish the work with fractions large enough for accurate analyses the experiment given herein was started with about 1 litres of gas (1531 cc.). Other experiments were performed with various natural gases in which smaller quantities were used. The sample as analysed by ordinary slow combustion methods contained the following constituents : There is also about o'03 per cent of carbon dioxide in the gas mixture. Carbon monoxide, hydrogen, and olefine hydrocarbons are not present. The experimental procedure follows: Fig. 1 shows the general arrangement of the apparatus. The Topler pump is on the left of the photograph. (A) is a small glass vessel used for holding the liquefied gases. It could be enclosed in the Dewar flask (B). Surrounding this Dewar flask is shown another and larger one. This arrangement was adopted in order to provide better insulation than was afforded by only one flask. The gas sample prior to liquefaction was measured in the glass vessel (c), then transferred to the gas burette (D), and from there passed into the liquefying bulb (A). At (E) is shown a mercury manometer for registering pressures in the pump. At the base of the Topler pump are shown the glass vessels for trapping the different gas fractions over mercury as they were removed. The entire sample was first liquefied by means of liquid air or liquid oxygen. With the gas in the liquid condition, connection was made between it and the mercury pump, and as much of the gas removed with the pump as possible. This process divided the original quantity into two portions; first, a gaseous portion; and second, a liquid residue. In other words, the vapour pressure of liquid ethane (boiling-point - 93° C.) is so small at the temperature of liquid air that none could be detected in the distillate within the experimental error of making the analysis. It was found that when liquid air was used that had stood for some time so that its boiling-point had risen to a point FIG. 1.-APPARATUS FOR FRACTIONAL DISTILLATION OF GASES AT LOW TEMPERATURES. near to the boiling-point of oxygen (-183° C.), that the methane and nitrogen were removed from the original mixture more quickly than when newly made liquid air was used. This is to be expected. The residue from this first fractionation was allowed to volatilise, measured, and again liquefied at the temperature of liquid air. Connection was again made to the pump, and more methane removed. In other words, although the residue from the first fraction was treated in exactly the same manner as the original sample more methane was obtained. Upon volatilising the entire residue, however, and again liquefying a re-arrangement of the solution occurred, and chance for faster evaporation of this last methane portion was afforded. In no case could the last minute portions be recovered, so the attempts at complete recovery were stopped when it was found that only such a small propor tion was being left behind as did not sensibly affect the results. To this point the first series of fractionations had reached a stage where the larger portion of the methane had been removed by the first fractionation and where the first residue had been volatilised, re-liquefied, and pumped to obtain another small portion of methane. The residue from the second liquefaction was treated again in the same identical manner, and more methane obtained. A further identical treatment resulted in no additional recovery of methane. No indication of methane was found in the ethane portion within the error of making the analysis. The distillate obtained by the above scheme undoubtedly contained a trace of ethane, but so small that it could not be detected by analysis. The analysis of a portion of the total methane and nitrogen fraction follows: TABLE I.-Analysis of a Portion of the Total Methane and Nitrogen Fraction. cooled to a temperature of - 145° C., and pumping started and continued until the temperature had risen to 125°C. By this process there was obtained a distillate consisting of ethane and propane. In other words, some propane (boiling-point -45° C.) is removed at - 125° C. as well as the ethane (boiling point - 93° C.). The residue was then treated twice in the same manner, the final separation of the ethane being made at a temperature of -155° to 140°C. The temperature was purposely lowered to - 125° C. to obtain practically all of the ethane as well as some propane, because it was found easier to separate the ethane from that part of the propane that came over than to attempt to pull off all of the ethane from the original residue. All the ethane was obtained, there being only small quantities of propane remaining as a residue. The analysis of a portion of the total ethane fraction follows: 70'10 Cc. Cc. 59'40 cooled The next step in the process involved the separation of the ethane from the methane free residue. This necessi tated the employment of a temperature such that practically all of the ethane could be separated from the still higher paraffins, propane, the butane, &c. The temperature used could not be too low, else the ethane itself could not be separated, nor so high as to also remove all the propane. A natural gas condensate obtained from a natural gas gasoline plant by subjecting natural gas (casing head gas) from an oil well to a pressure of 250 lbs. per square inch, and then cooling it to ordinary temperature, proved excellent when by liquid air for obtaining temperatures higher than the temperature of liquid air. This condensate is known in the natural gas gasoline trade as "wild" gasoline. It contains large quantities of liquid propane and the butanes (especially the latter), as well as some of the ordinary gasoline constituents, the pentanes, hexanes, &c. Other substances tried for obtaining low temperatures, such as alcohol, ether, methyl, and ethyl chloride, &c., jellied so much at low temperatures that they could not be used satisfactorily. The mass did not remain of uniform temperature from top to bottom. In order to obtain a temperature of 145° C., for instance, the condensate was placed in a Dewar flask and stirred with a test-tube into which liquid air was run until - 145° C. was reached. Upon removal of the liquid air the condensate warmed up very slowly, about 5° to 10° C. per hour, thereby affording sufficient time for the withdrawal of the vapour from the liquefaction bulb. In separating ethane from the methane free residue the latter was first According to the equation C2H6 + 3'5O2 = 2CO2 + 3H2O, the contraction should be equal to the CO2 × 1.25. In No. I analysis the contraction then becomes 51'I CC. X I.25 63.87 cc. This corresponds well with the contraction actually observed, 63 80 cc. In No. 2 analysis the contraction is equal to 40 50 cc. XI'25=50 €2. The contraction actually observed is 50 50 cc. In calculating the ethane from the carbon dioxide and contraction use was made of equations that correct for the deviations of carbon dioxide and ethane from the ideal conditions as follows ("Errors in Gas Analysis Due to Assuming that the Molecular Volumes of all Gases are Alike," by G. A. Burrell and F. M. Seibert, Technical Paper 54, U.S. Bureau of Mines; CHEM. NEws, cix., 188, 196): No. 1 Analyses. O'990 C2H6+3°5O2 = 1·992 CO2 + 3H2O. cc. ethane 0 396 x contraction = 25.26. cc. ethane = 0'497 × CO2 = 25*39. No. 2 Analyses. 0.990 C2H6+3′502=1·994 CO2+3H2O. cc. ethane = 0.397 × contraction = 20.05. cc. ethane 0'496 × CO2 = 20.09. Third Series of Fractionations. The final residue from the second series of fractionations then contained propane and higher paraffins. The ethane free residue was next liquefied and pumped at a temperature that started at - 125° C. and ended at - 110° C., the object being to remove practically all of the propane (boiling-point - 45°), and also some of the butanes (boiling points + 1° C. and -10° C). The residue from this operation was again treated in the same manner to obtain any propane that still remained behind. It was thought that if a temperature was used that would permit the distillation of an appreciable quantity of butane, practically all of the propane should come over. The total distillate obtained in this manner was then liquefied, and pumped at a temperature ranging from 135 C. to 120°. There resulted a distillate that consisted of propane only. In other words, propane can be separated from the butanes at a temperature between - 135° and 120° C. The analysis of a portion of the total propane fraction follows: |