PHYSIC-IL COSSTANTS DBT-4 FOR HTDROCARBOSS
387
GAPS IN PHYSICAL COSSTANTS DATA FOR HYDROCARBOSS' S . % S C Y C O R M S , NARY BLEXASDLR,
ASU
GCYTAY LGLOFF
L7rzzversal 021 Products Companu, Chacayv, Illaimas
Recencd .luglist 90, 1947
In the course of studying data from a complete liteiature survey of the physical constants of hydrocarbons, it became apparent that numerous gaps exist. Many of the possible hydrocarbons are not linon-n, and many known compounds have not been investigated from the standpoint of their physical constants. Our study showed that of the astronomical number of possible hydrocarbons only about fifty-two hundred have been investigated. The problem of the correlation of physical properties with structure is one which has engaged the attention of an ever-increasing number of scientists. From the time of Kopp, in the middle of the nineteenth century, to the present time numerous correlations have been proposed, varying broadly in scope and accuracy. Many of the early attempts covered a wide field and included both hydrocarbons and compounds v-ith functional groups. In recent years, as more data became available, the tendency has been t o narrow the field in the interests of greater accuracy. The questions may be asked: TVhy is so much effort expended in developing correlations? K h a t purpose do they serve? On the practical side, correlations make it possible to predict the physical constants of unknon-n compounds and, in addition, inaccuracies in existing data may be located and corrected. From the more theoretical point of vieiv, correlations play an important rGle in the evaluation of structural effects and provide a basis for the interpretation of chemical and physical phenomena. It is apparent that an indispensable condition, without which no correlation is possible, is the availability of reliable data on whatever property is under consideration. Data used in correlations must be for pure compounds of definite and known structure. The importance of purity cannot be overemphasized; many of the older physical constants data are unreliable because of the presence of impurities. Recent developments in hydrocarbon chemistry have improved this situation, and it is now more feasible to prepare and purify a desired compound. A study of the literature n-ill usually reveal whether synthesis or isolation from a natural source will be more satisfactory from the standpoint of ease of purification. Once the compound has been prepared, its purification depends on the amount and nature of the impurities. The time-honored method of fractional distillation is being supplemented by other techniques, such as azeotropic distillation, extraction, fractional crystallization, and the method of percolation through adsorbents. In addition to techniques of purification, new methods are available for testing the purity of the product. These incliide Presented before the Division of Petroleum Chemistry a t the 112th Meeting of the American Chemical Society, vhich x-as held in S e w Tork City September 15-19, 1947
388
N. CORBIX, \I. .iLIX.iSDCR
ISD G . L;GI.OFF
quantitative study of time-freezing curves (12), analysis of ultraviolet and infrared absorption spectra, and use of the mass spectrometer. By employing onr or more of these methods the nature of the impurities as \Tell as their amount is revealed, and further purification is facilitated. Khen the desired purity has been attained, the determination of the physical constants should be carried out with equal care. Accurately calibrated apparatus and rigid control of conditions are necessary. Preferably, each constant should be determined over a range of conditions,-for example, the boiling point a t varying pressures, and the density and refractive index at a number of temperatures. Among the hydrocarbons, the number and accuracy of the physical constants data vary widely from one class of compounds to another. In order to illustrate these variations, an analysis of the data appearing in the four volumes of Physical Constants of H~drocarbons( 7 )has been made. Table 1shows the total number of hydrocarbons in each class, and the percentage of compounds for which each physical constant has been recorded. These figures indicate only the percenTdBLE 1 C o m p o u n d s f o r which phusical corislants hare been recorded __
CLASS O F HSDROCARBONJ ~
Alkane. . Unsaturated aliphatic Alicyclic Mononuclear aromatic Polynuclear aromatic -
__
~___
196 601 1242 1400 1728 ____
___
p e r cent
per cent
60 2 19 6 22.3 43 2 82.6
88 8 96 2 87.2 68.2 32.8
___
_~__
-___ p e r cent
per cent
85 81 79 18
2 5
8 9 15 4
,
76.5 73.4 73.9 13 9 13 0
- -
tages of compounds for which at least one value of a physical constant has been recorded. They give no clue as to the quantity and reliability of the data. Taking the alkanes as a basis for comparison, differences among the classes may be readily analyzed. It should be noted that the state of aggregation a t normal temperatures is an important factor influencing the determination of physical constants. For example, data on melting points are more numerous for solid compounds and on boiling points for liquids. For the unsaturated aliphatic hydrocarbons, the proportion of compounds for which melting points have been recorded is far smaller than for the alkanes, that of boiling points somewhat greater, and that of density and refractive index about the same. The alicyclic and mononuclear aromatic compounds have a smaller proportion of all four constants, and the polynuclear arcmatics exceed the alkanes only in the percentage of melting points, the other three constants being distinctly ferrer. The cause of the distribution of percentages for the polynuclear aromatics is that for a large proportion of thcsc compounds the melting point is the only constant which has been determined.
389
PHTGICAI, COXSTASTS DATA FOR HTDROCARDOSS
Evidence of the amount of reliable data may be gained from an analysis of the “best values” appearing in the Physical Constants volumes ( 7 ) . In order to calculate a “best value” it was necessary to have data sufficiently numerous and consistent to form a basis for statistical treatment to find the most probable correct x-alue for a given constant. The figures representing the percentages of “best values” are shonn in table 2. The most striking fact brought out by this table is the paucity of reliable data for the known hydrocarbons. Even among the alkanes, the data for almost 60 per cent of the compounds are insufficient for the calculation of any “best values” whatscever. About 85 per cent of the unsaturated aliphatics and 95 per cent of each of the other three classes of hydrocarbons have been so superficially studied that no “best values” can be computed. From table 2 it is apparent that the data for the allianes are more nearly complete than for any other class of hydorcarbons. The data on the alkanes have been further amplified by the authoritative values recently determined a t the Kational Bureau of Standards ( 2 7 ) . This investigation included all the paraf-
.
TXRLE 3 C ‘ o m p o ~ t n d sJar w h i c h “best m l u e s ” hare O e e z compirted
CLASS OF HPDROCARBOXS .
~
..
..
-
,
I
su~$~oF ’
YELTIXG
COXPOUNDS’
BOILING POIST
’
.. .- .
DESSITY
EPRACTIVE ISDEX
~
~ _ _ _ ____
Alkane . . . . . . . . . . . . . . . . . . . . . . . I - m a t u r a t e d aliphatic. . . . . . . . . . . . . . . . Alicyclic . . . . . . . . . . . . . . . . . . . . Mononuclear aromatic.. . . . . . . . . . . . . . . Polynuclear aromatic.. . . . . . . , . . . . . . . . . ~
.I ~
196 601 1242 1400 1728
p e r cen:
per c e d
p e r cent
fier cent
28.1 4.0 0.2 4.9 4.5
35.7 16.5 2.7 5.6 0.8
41.8 15.5 5.1 6.3 0.3
32.6 13.0 3.5 4.3 0.05
___
fin isomers from the pentanes through the octanes. Among higher alkanes the proportion of isomers which have been investigated decreases sharply, owing in part to the large number of possible compounds. All of the normal alkanes through pentatetracontane, Cd5Hg2, are known, and a t least one physical constant has been determined for each compound. Above this, nine normal alkanes have been investigated, the highest being heptacontane, C70H142. From propane through normal dodecane “best values’’ of all four constants have been calculated. For the tu-enty-four compounds from CI3 through C36, ‘lbest values” for all four constants have been determined on only five compounds. Xbove C36the data are insufficient to calculate any “best values”, and often the only recorded physical constant is a melting point. For the normal alkanes higher than tetracosane, C24H60, boiling points have been determined only a t pressures below atomospheric, if at all. The completeness of the alkane data relative to other classes of hydrocarbons is reflected in the large number of correlations for these compounds. Relationships covering melting points, boiling points, densities, and refractive indices
390
S . CORBIK, 11. A L E X l S D E R . i S D G . EGLOFF
have been ~ o r k e dout by l\libashan (23). Boiling points, densities or molecular volumes, and refractive indices or molal refractions have been covered by Egloff and coworkers (8, lo), Francis ( l l ) ,and Roasini and con-orkers (21). Densities and refractive indice3 have been treated by Huggins (13) and Iiurtz and Lipkin (21, 22). Calingaert and Hladky (2) have derived relationships for molecular volume. Boiling-point relations have been v-orked out by Burnop (l), Kinney (16, 18), Klages (20), and Kiener (25). Ivanorsky and Brancker (15) have treated melting points of alkanes. The data for the other hydrocarbons present a sharp contrast to those for the alkanes. For the unsaturated aliphatic compounds the percentages of “best values” are far lon-er than for the alkanes in spite of the fact that the percentage of compounds for which a constant has been recorded (table 1) is nearly the same. In the case of boiling points, even more have been recorded for the unsaturated aliphatics than for the alkanes (96.2 per cent as compared to 88.8 per cent), but the percentage of “best values” is only about half of that for alkanes (16.5 per cent as compared to 3 5 . i per cent). This relative dearth of “best values” shorn that the data for the individual compounds are often scarce and unreliable. In many cases only one or tTyo values for a constant are available in the literature,!and in other cases the values recorded by different authors do not agree. The alkenes or monoolefins have been more extensively studied than the other types of unsaturated aliphatics. Even for these, *‘bestvalues” are very scarce above (210. From Clz through C’h the only “best values” are those for the normal olefins with the double bond in the l-position, and above this only one “best value”, the melting point of l-octadecene, has been calculated. Correlations for unsaturated nliphatics are less numerous than for alkanes. Rossini and coworkers (24) have presented a method for calculating boiling points, densities, and refractive indices of monoolefins. Molecular volumes and molal refractions of unsaturated aliphatics have been treated by Huggins (14), and boiling points by Burnop ( l ) ,Klages (ZO), Kinney (16), and Egloff, Sherman, and Dull (10). Alicyclic compounds have been even less thoroughly investigated than the unsaturated aliphatics. Although the percentages of compounds for which constants have been recorded are of the same order of magnitude as for the unsaturated aliphatics, the percentages of “best values” are very much smaller. The greater proportion of compounds for which “best values” have been calculated are the alkyl derivatives of cyclopentane and cyclohexane. The boiling point and the density or molecular volume are the only alicyclic constants which have been related to structure. Boiling points are used in the correlations of Burnop (l), Klages (20), and IGnney (16, 18), and molecular volumes in those of Iiurtz and Lipkin (21) and Egloff and Kuder (9). Among the mononuclear aromatics, the percentage of compounds for which each constant has been recorded is significantly less than for the alkanes. Often only one or two different properties have been determined for a compound. For example, many compounds are represented only by a melting point or a boil-
PHYSICAL COSSTA1NTS DATA FOR HYDROCARBOKS
391
ing point, lvhereas most of the lower alkanes are represented by a t least three and often all four constants. The low proportion of “best values” s h o w that many compounds have been the subject of such a small number of investigations that no evaluations can be made. For the alkylbenzenes through the Cg compounds, all possible isomers are 1ino11-n and have been studied extensively enough so that “best values” have been O twentycalculated for three or four of the physical constants. In the C ~group one of the tu-enty-tn-o possible isomers are known, but only forty-five of a possible total of eighty-eight “best values” can be calculated. The CII group is represented by only thirty-six out of fifty compounds, with only eighteen out of a possible tn-o hundred “best values”. As the number of carbon atoms increases, the proportion of knon-n isrmers decreases rapidly. The normal alkylbenzenes have been more n-idely investigated than any of the other isomers, and all of these are known through normal docosylbenzene (CzsH~o),with the exception of C16H2F,C21H36,C&Hd4,and C27H48.Of the other series of mononuclear aromatics, such as alkenylbenzenes, alkynylbenzenes, and polyphenyl aliphatics, only the first few members are known. The boiling-point calculations of Burnop (l),Klages (20), and Kinney (17,19) can be applied to mononuclear aromatics, and correlations of boiling point, molecular volume, and molal refraction have been worked out for several homologous series by Corbin, Alexander, and Egloff (3, 4,6). The polynuclear aromatics have been investigated even less than the mononuclears. For many of the polynuclears the only recorded physical constant is the melting point, and frequently only one or two values for this constant are given in the literature. This is shown by a comparison of the figures in table 1 and table 2. Melting points have been recorded for 82.6 per cent of the known polynuclear aromatic hydrocarbons-a greater percentage than for the alkanesbut the data are suitable for calculation of “best values” in only 4.5 per cent of the compounds. The percentages of “best values” for the other constants are so low as to be almost negligible. The most extensively investigated group of polynuclears is that of naphthalene and its alkyl derivatives. Hoir-ever, the data are scattered and sparse, and even the normal alkylnaphthalenes are completely represented only as high as 1- and 2-butyl derivatives. The only correlations which include the polynuclears are the boiling-point calculations of Burnop ( l ) , Klages (20), and Kinney (19), ancl these are very general in nature. It must be emphasized that the above citations are not intended to be a complete coverage of published correlations, but simply representative examples. Even so, it is apparent that the alkanes have been studied more extensively than the other classes of hydrocarbons. S o t only are the alkanes treated in a greater number of studies, but the proportion of compounds t o which the relations may be applied is larger. In fact it may be said that the boiling point, density, and refractive index of any alkane may be calculated with a fair degree of accuracy. The method of calculation developed by Taylor, Pignocco, and
392
N. CORBIN, h l . ALEXASDER AND G. EGLOFF
Rossini (24) can be applied to all alkanes. Likewise the structural determination of boiling points set forth by Kiener (25) can be applied to unknown alkanes. This method of calculation can also be extended to other physical properties (26). The good agreement of values calculated by these methods with the experimental data among the lower alkanes indicates that extrapolations to higher members should be reliable. Calculations according to Taylor, Pignocco, and Rossini (24) are applicable to all monoolefins, but the average deviation of the calculated from the experimental values is appreciably greater than for the alkanes; estimations of properties of unknown olefins will therefore be less reliable. For the alicyclic hydrocarbons the correlations are few, and cover only a small proportion of the possible isomers; extrapolations are possible only for limited types of compounds. h similar situation exists for the mononuclear aromatics. The work of Kinney (12, 13) on boiling points includes different types of aromatic hydrocarbons, but the average deviation is rather large. Correlations based on homologous series of mononuclear aromatics may be extrapolated to other compounds of a particular series, but the majority of compounds are not included in any series for which relations have been worked out. In addition, these correlations do not represent the experimental data as \Tell as the correlations of aliphatics; the average deviations are appreciably larger. The decrease in accuracy of most aromatic correlations as compared to those for aliphatics is a reflection of the relative quality of the data for these two classes of compounds. For polynuclear aromatics no predictions of physical constants can be made except for a limited number of boiling points, because of the lack of sufficient data on which to base any conclusions. The alkanes are the only compounds for which the data permit extensive correlations, and even here authoritative values are lacking for the majority of compounds. In order to correct this situation, more and better data on physical constants are necessary. The constants should be carefully determined on pure compounds. To facilitate the calculation of relationships either of tiyo approaches will be helpful: First, to determine the constants of a number of hydrocarbons in one homologous series, or second, to determine the properties of all possible isomers of a given number of carbon atoms. Investigations of physical constants will be more immediately helpful if they supplement existing data, rather than open up entirely new fields. For example, a study of some higher alkanes and alkenes would provide a means for testing the validity of extrapolations of existing correlations. In the alicyclic group only the hydrocarbons of lower molecular weight have been thoroughly investigated, and studies of higher members, especially cyclopentane and cyclohexane derivatives, would make possible the extension of correlations which have already been proposed. Among aromatic compounds the number of possible isomers of a given molecular Tyeight increases rapidly with the number of carbon atoms, and studies based on homologous series will probably be most useful for correlations. Several series of mononuclear aromatics hare been studied, but in most cases they are short, and data on higher members are necessary. In addition, many series hare not been
PHYSIC.1L CONSTASTS DATA FOR HYDROCARBONS
393
investigated a t all. Along another line, the data on dialkylbenzenes are inconsistent, and a comparison of ortho, meta, and para compounds above the xylenes mould clarify the effect of position of substitution on the physical constants. An apparent discrepancy in physical constants data has been noted for the pentylbenzenes ( 5 ) . Both the normal boiling points and the change of boiling points with pressure are greater than n-ould be expected for these compounds. Accurate vapor-pressure data would make it possible to determine whether these compounds really are anomalous, or whether the present experimental data are at fault. The polynuclear aromatics have been so little investigated that almost any reliable data n-ould be welcome. In order to supplement existing data, however, the study of homologous series of alkyl derivatives oi naphthalene and indene would be a good starting point. X a n y of the compounds of higher molecular vieight for which data are inadequate have boilingpoints too high to be easily determined at a pressure of 760 mm. -41~0, many of the compounds are solid at 20” or 25”C., and their densities and refractive indices hare not been determined at btandard conditions. These difficulties may be alleviated by determining the boiling point over a sufficient pressure range and the density and refractive index over a sufficiently large temperature range YO that extrapolation to standard conditions is possible. Khen this procedure is not feasible, correlations may be based on the boiling point at a specified low pressure, or on density or refractive index at some temperature other than 20°C. Supplementing existing data. by the wcurate determination of physical constants of pure compounds is necessary in order to serve both practical and theoretical nerds, and it is to be hoped that the next few years will produce an increasing amount of research along this line. \Vhile excellent results hax-e already been attained, the amount of rese-irch so far completed is infinitesimal compared to the whole, despite more than a century of eflort. SUJIhlhKI
The importance of correlations betn-een the physical properties and the structure of hydrocarbons is stressed. The quality and quantity of data needed for such correlations is discussed, and the available data analyzed. The analysis shows the percentage of knoirn alkanes, unsaturated aliphatics, alicyclics, mononuclear aromatics and polynuclear aromatics for which each of four physical constants (melting point, boiling point, density, and refractive index) has been recorded. Further analysis shows the percentage of compounds in each class for which the data were adequate to calculate a “best value.” .I comparison of correlations covering the different classes of hydrocarbons shows that the quality and quantity of data are reflected in correlations. Suggestions are made for further research on physical constants. REFERESC’ES (1) HLRSOP,J-. C ~ .k:.:
.J. Cheni. Soc. 1938, 826. G.. ~ S DH L A D h Y . J. W.:J . . h i . Cheni. Soc 68, 133 (1936). (2) CALINGAERT, (3) CORBIS,S , A L E X I ~ D E RJl., , A I Z D EGLOFF, G : Ind. Eng. Clieni. 36, 156 (1916). (4) CORBIS,S . ,A I X X ~ S D E RM, . , ASD EGLOFF, G . : Ind. Eng. Chcm. 38, 610 (1916).
394
K . L. SUTHERLASD
(5) CORBIN,s., ALEXANDER, AI., AXD EGLOFF,G.: J. Phys. Colloid Chem. 51, 528 (1947). (6) CORBIK, S., ALEXANDER, hI., A N D EGLOFF, G.: Ind. Eng. Cheni. 39, 1147 (1947). (7) EGLOFF,G. : Physical C o m t a n t s of Hydrocarbons, Reinhold Publishing Corporation, Yew 1-ork: Vol. I. P a r a g i n s , Olejins, Acetylenes, and Other A l i p h a l i c Hydrocarbons (1939) ; T-01. 11. Cyclanes, C'yclcnes, C'yclynes, and Other Alicyclic Hydrocarbons (1940); Vol. 111. Mononuclear Aromatic Hydroca&ons (1946) ; 1701. IV. Polynuclear Aronialic Hydrocarbons (1947). (8) EGLOFF,G., ASD K U D E RR.: , J. Phys. Cheni. 45, 836 (1941); 46, 296 (1942); Ind. Eng. Cherii. 34,372 (1942). (9) EGLOFF,G., ASD K G U E RR.: , J. I'liys. Chem. 46, 28 (1942). (10) EGLOFF,G., SHERXIS, J., ASD DULL,R. B.:J. Phys. Chem. 44, 730 (1940). (11) FRASCIS, A . W.:Ind. Eng. Chern. 33, 554 (1941); 35, 442 (1943); 36, 256 (1944). (12) GLASGOK, A . R.,JR.,STREIFF, h. J . , . ~ S D ROSSINI,F . D.: J. Research S a d . Bur. Standards 35,355 (1945). (13) HUGGISS, 11.L.: J. din. Clieni. Sac. 63, 116 (1941). (14) HUGGISS,AI. L.: J. h i i . Cheni. SOC.63, 916 (1941). (15) IVANOVSKI-, L., ASD B R - ~ X C K EAR. ,T-.: Petroleum 5, KO.10, 169 (1942). (16) KIKNEY, C. R.: Ind. Eng. Cheni. 32, 550 (1940). (17) I~ISSEY, C. R.: Ind. Eng. Chern. 33, 791 (1941). (18) RISSEY,C. R.: J. Ani. Cheni. h e . 60, 3032 (1935). (19) KIXXEY, C . R.: ,J. Org. Chem. 6, 220 (1941). F.: Ber. 76, 7bS (1943). (20) KLAGES, (21) KURTZ, S.S., J R . , ASD LIPKIX,11. R.: Ind. Eng. Chem. 33, 779 (1941). (22) KURTZ, S.S., ,JR,, A N D LIPKIN,AI. R.: J . Am. Chem. Soe. 63, 2158 (1941). (23) MIBASHAN, -4.:Trans. Faraday Soc. 41, 374 (1945). (24) T.LYI.ort, W.J . , I'IGXOCCO, J. 11.,ASD ROSSINI,F. D.: J. Research Natl. Bur. Standards 34, 413 (1945). (25) WIESER, H . : J. Am. (:hem. SOC.69, 17 (1947). (26) WIESER, IT. : Private communication (April 25, 1947). (27) WILLINOHAM, C . B., TAYLOR, W. J., PIGNOCCO, J. M., AND ROSSINI,F. D.: J. Research Natl. Bur. Standards 35, 219 (1945).
PHYSICAL CHEMISTRY OF FLOTATION. XI
KIYETICSOF
THE
FLoTa.rroN
PROCESS
T i . I,. d U T H E R 1 , h S D 1)irzszon of Induotrial Cheinzsiry, Comnionweulth Council for Scientific and Industrial Research, Melbourne, A u s t r a l i a Received A u g u s t 27. 1947 I . ISTRODL7C'l'IOh-
To detrimiiie tlw tliroretical rate of flotation of mineral in a cell, it is necessary t o make 1i.e of ;I Yimplified model of the -!.stem, nhich ignores unimportant variables u-liile retaining e*sentinl teatiire-. Theories of air-mineral adhesion are discussed and tlic directt enc~oiinterhypothesis is chosen for detailed investigation. .lny fiiilure of the subsequent theory t o describe tlie kinetics of the process is certainly due t o oversimplification of the encounter hypothesis and some attempt is made to a the importance of the simplifications.
