Critical Solution Temperatures with Cvclic Hvdrocarbons ALFRED W. FRANCIS Socony-Vacuum Oil Company, Inc., Paulsboro, N . J .
Critical solution temperatures are reported for sixty PREVIOUS paper (12) are of little significance, it organic solvents, each with one or several of thirty-five presented a large numseems preferable, as favored ber of critical solution aromatic hydrocarbons and three naphthenes. For each by Gillam ( I d ) and practiced solvent the points agree approximately with a smooth temperatures (C.S.T.) of solby others, t o limit the term function of the total number of paraffinic carbon atoms in vents with nonaromatic hy“aniline point” to the temthe side chains of the hydrocarbons. In the case of alkyldrocarbons, asmeasures of solperature a t which a mixture benzenes the temperatures are nearly parallel with the vent selectivity for the variof equal volumes of aniline ous types of hydrocarbons. boiling points of the hydrocarbons. Moreover, for most and hydrocarbon begins to aliphatic solvents the critical solution temperatures are (In this paper “solvents” are s e p a r a t e i n t o t w o liquid nearly the same for corresponding derivatives of benzene nonhydrocarbons.) Aromatic phases on cooling. This is and naphthalene, so that they may be used to estimate the hydrocarbons were not innearly the same as C.S.T. and paraffinicity of an aromatic mixture. The effects of subcluded in the comparisons becannot exceed it. Attention stituent groups in the solvents upon miscibility are esticause their complete miscishould be called to the fact mated. The hydroxyl, amino, and carboxyl radicals raise bility with most of the solthat Lecat’s “demixing temthe temperatures roughly 200’ C. or more, and the nitro vents, even a t low temperaperatures” (SO) were not all group about 150O. Other radicals have much less effect. tures, prevented the deterC.S.T.; but some were temSelectivities of solvents for aromatic hydrocarbons with mination of C.S.T. The presperature of crystallization. respect to paraffins are about six times as great as those ent paper deals with aromatic About fifty-five of these are for naphthenes. A composite arrangement of solvents hydrocarbons, but necessarily listed incorrectly as C.S.T. in and hydrocarbons is devised showing qualitatively the with a largely different group two books of tables (27,41). mutual solubility of any pair of included substances as of solvents, including many Seven more aniline points of liquids; by use of the relations of this and other papers, of those (Table I11 of the aromatic hydrocarbons are almost any liquefiable organic compound can be included. previous paper) which were presented by Schiessler and only slightly miscible with the co-workers (38) and one by nonaromatic hydrocarbons. Petrov (36). Other observaC.S.T. is valuable in expressing the miscibilities concisely and tions in the literature for aromatic hydrocarbons are given in in pointing out some relations of miscibility with structure and Table I. other properties. It can be used for analysis of mixtures of two DETERMINATION O F C.S.T. individuals or types of compounds aud for characterization of multiple mixtures. As a measure of aromatic content of aromatic I n this investigation the determinations of C.S.T. were made recommended furfural points, which are oils, Rice and Lieber (366) in small test tubes as described previously (12). The reagent8, about 32’ C. higher than aniline points, in preference to “mixed nbout 1 ml. of solvent and 1 to 1.5 ml. of hydrocarbon, were aniline points”. For still more aromatic oils a suitable solvent introduced and stirred with a thermometer while the tubes were such as ethylene diformate can be selected from Table I1 of this Farmed gradually in a bath of water or glycerol or were cooled with ice or a bath of acetone and dry ice; the temperature of paper. Comparatively few observations of C.S.T. are reported in the disappearance or reappearance of the cloud due to two liquid literature for aromatic hydrocarbons (about 125, including aniphases was read three or four times in each direction. If the line points, compared with over 1200 for individual nonaromatics). final position of the interface was not near the middle of the liquid, Observations with aniline can be made only for aromatic hydrothe volumes of the reagents were adjusted to-make it so. Imcarbons having rtt least nine saturated carbon atoms (see Ball, S), proved technique was used recently (66) for C.S.T. at moderate since those with less carbon atoms in the side chains have points temperatures. too far below the freezing point of aniline. Eighty-four aniline About 550 points are recorded in Table 11,including some below points of aromatics are recorded in Doss’ compilation (IO),inthe freezing point of the solvent or hydrocarbon which were cluding thirty-one which are or should be preceded by a < sign. reached by supercooling, and some above one of the boiling points. This applies to m- and p-xylene (IO,page 75) and also probably Some of these were reached by using cork stoppers pierced by to seven dicyclic hydrocarbons (IO,pages 173-9) whose aniline the thermometer and wired in. Others were observed in sealed points are recorded as 0.0’ C. (86). These are ethyl-, propyl-, glass tubes attached t o the thermometer with rubber bands; butyl-, and left-butyl Tetralin and butyl-, tert-butyl-, and octylagitation was obtained by tipping, using the thermometer as a naphthalene. (This holds also for two other butyl Tetralins rehandle. The C.S.T. velues too low to be reached by supercooling ported by Petrov, 36.) The aniline point for Tetralin (IO, page are marked with a < sign; those too high to be reached readily because of decomposition or excessive pressure are marked with a 169) shouId be < -20’ (15) instead of 20.0’ C. Those given for > sign. tetraisopropylbenzene and hexaethylbenzene (IO,page 92) are I n the range 0” to 100’’ C. the temperatures are believed to be called “aniline points” by the original authors (23);but they are temperatures of crystallization of the hydrocarbons and may be accurate to one or two degrees except perhaps with some hygrofar above the C.S.T. Since such crystallization temperatures scopic solvents, since with water miscible solvents a trace of 1096
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1944
TABLE I. LITERATURE OBSERVATIONS OF C.S.T. WIT11 AROMATIC HYDROCARBONS
Solvent Acetamide Acetamide Acetamide Acetamide m-Aminoacetanilide pAminoacet anilide Ammontae Ammonia“. Ammonia“ Ammonia‘ Aniline Ben8 lalcohol Ethyf ether
Hydrocarbon Benzene m-X lene Napgthalene 6 dtcvcltcs Benzene
Formic acid
Bennrene
Benzene Xylene m-Xylene Cumene Cymene Various 2-Phenylhexadecane Chrysene
C.S.T.,
C.
Citations
142.6 148.b 206 a
188 12.2 14.7
(18, 47)
1%
83)
ss,
Furfural Toluene < -00.7 Furfural X lene 66 Nitromethane n-htylbeneene 4 Nitromethane aec-Butylbenzene -1 88) -4 Nitromethane p-Cymene Nitromethane m-Diethylbenaene -a Nitromethane pDiethylbenzene -6 Nitromethane tert-Amylbenzene 14 ss Nitromethane Tetralin I6 Nitromethane 6 higher aromatics 24-70 47) m-Phenylene- Benzene 09 diamine Phmphotus Naphthalene 202.7 200 Phosphorurr Phenanthrene t8Ol Proptonamide Naphthalene 7b 108*9-110 s7* 44* Reaoroinol Benzene 60 65) Reaorcinol Eth lbenzene 1bl.b 18, ko, Rssoroinol m-2ylene 140.7 :?84 66 65 Sulfur Benrcne 10s 17&80 Toluene Sulfur 64:663681 190 {lb; Xylene auifur Water Benzene > aoo 10 8?] 48 A 0.6 T. for xylene would be expected to be much hi@= than those for benzene abd na bthalene (compare the observation 200 C., in Table 11). Perha 7 9 O C. the freezing point of the acetamiddlayer. b T& h not reliable because it wan observed wlth “monoacetyl-mendiqmine” me!tinp at 279O C., wherean the m. IS about 87“ Sid wok and Neil1 (47) apparently wed the hydroc%loride,m.P. about 280
-
-
%!
if: %{
‘’ l’
8
8%;;
c.ctie). De Carli (s,87) indicated that liquid ammonia hsll only a aught bolvent
power for nineteen aromatic hydrocarbons including benzene, xylene, cumene. and o mene. The inconsistmay with the above data, and with obaervatioty thin paper may be due to the preaence of wate; in bb ammonta. HIS observations of complete mtsctbtiity of sulfur dioxide with liquid aromatic h drocarbono are consistrnt with others. d This iu desoriied as a “lower C.S.T.”, but it may be the temperature of separation of gas and solid.
h
water affects the C.S.T. greatly. Determinations a t very low temperatures are less accurate because the mjxtures become so viscous that there may be some supercooling of C.S.T. (forming a onephase supersaturated liquid mixture) and because the pentane thermometer used had less precision. Determinations a t high temperatures are increasingly less accurate because of thermometer stem corrections and more rapid heating and cooling. For those over 200” and below -40’ C. and for those followed by a * sign the uncertainty is about 6” to 10’. h e of these uncertainties are due to supercooling below the freezing point of one reagent, since in such experiments rapid cooling and gentle stirring were sometimes necessary to prevent crystallization. Thirty-five aromatic hydrocarbons and three naphthenes were used, The latter and fifteen of the former were available in our stock. The other twenty aromatics were made by alkylation of bemene, toluene, ethylbenzene, naphthalene, or Tetralin with ethylene, propylene, %butene, isobutene, or pentene, using aluminum chloride an catalyst. The products were separated by fractional distillation. Those boiling below 220’ C.were collected over a 2” distillation range or less. The monoalkyl derivatives ethylbenzene, cumene, sec-butylbenzene, tertbutylbenzene, 8ecamylbenzene, isopropylnaphthalene, and sec-amylnaphthalene showed satisfactory agreement in properties with those recorded in the literature. The properties of the dialkylbenzenes agreed with those recorded for the meta and para isomers, which differ only slightly from each other. No attempt made to separate isomers or to establish their exact structure, since results indicated that the C.S.T.would be substantially independent of the relative
1097
positions of the side chains. Some of the higher alkyl derivatives had the properties given in Table 111, in comparison with those in Doss’ compilatiop (IO)for the same or related hydrocarbons. Some of the observations in Table I11 are more consistent with the properties of other related hydrocarbons than are those quoted. For example, di-isopropylnaphthalene would be expected to boil nearly 50” higher than isopropylnaphthalene instead of only 15’ higher, as given in Doss’ compilation (IO); and with six paraffinic carbon atoms it should have a lower density. The two trialkylbenzenes are so closely related that there should be only a moderate difference in density. Hexaethylhenzene was recrystallized from alcohol. It melted at 127” C. The samples of di-tertbutylnaphthalene and diamylnaphthalene were not of high purity, but are included merely to have high-boiling aromatic individuals. Their boiling points in Table I1 are average. Most of the solvents used were substantially pure, but were not specially purified except to dry those miscible with water, since traces of other probable impurities are unlikely to affect C.S.T. seriously. The presence of an impurity which raisea the C.S.T. is usually apparent in an observation, since it causes a persistent slight cloudiness over a wide temperature range instead of a sudden appearance or disappearance of a heavy cloud. The solvents were not all tried with dl the hydrocarbons, which would have required a prohibitive number of observations. In many cams it was evident from other determinations that the C.S.T. could not be reached. Sometimes they were omitted because of a limited supply of a reagent, and because C.S.T. could be estimated fairly closely from the table aa discussed below. Table 11the hydrocarbons we approximately in increasing order of “paraffinicity”. This is measured primarily by the total number of carbon atoms in the side chain or chains. However, in the c&8e of styrenewith a double bond, and of fluorene, Tetralin, and isopropyl-Tetrdn with saturated additional rings, the paraffinicity is determined by the C.S.T. itself, higher temperature corresponding to higher ParaffinicitY. Anthracene, phenanthrene, and diphenyl show a slight pardinicity by this test. It has been suggested that the unexpectedly high C.S.T. €or these hydrocarbons is due to their high melting points. While this poeaibility should not be neglected, the absencae of such an effect with naphthalene makes it unlikely. Ball (3)states: “As no solid w&8present, the energy of melting did not influence the experiment” in an analogous case. In his Table 13, Ball found similar indications for anthracene. The criterion of C.S.T.
( 1
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9
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-
-
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1
PARAFFINIC CARBON ATOMS
~i~~~~ 1. Critical Solution Temperature of Aromatic Hydrocarbons as a Function of Number of Paraffinic Carbon Atoms
1098
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 36, No. 12
is used also to arrange hydrocarbons with an equal number of aliphatic carbon atoms, such as ethylbenzene and xylene. RELATION OF C.S.T. TO PARAFFINIC CARBON
The relation of C.S.T. to the number of paraffinic carbon atoms is illustrated in Figure 1 in which the ordinates are the C.S.T. values of the aromatic hydrocarbons with diethylene glycol. This solvent was chosen for illustration because its series of observations with the aromatic hydrocarbons is complete except for anthracene, whose melting point is too high to permit observation. If the abscissas of Figure 1 had been total carbon atoms, two curves would have resulted with a spread of 4 carbon atoms for the same temperature between curves for benrene and naphthalene homologs. Similar curves for aniline (3,31) show a spread of 6 to 8 carbon atoms, since aniline is more selective than diethylene glycol. 3exaethylbeneene alone ehows an appreciable discrepancy from the curve, having a point correaponding to only about 9.5 paraffinic carbon atoms instead of the actual 12. This may be due to ita very symmetrical structure. Tilicheev (48)gave a similar discussion with respect t o aniline C.S.T. with certain aromatics and drew somewhat different conclusions. On the baais of this plot certain hydrocarbons have approximately the following paraffinicities: styrene, 0.4; anthracene, phenanthrene, diphenyl, Tetralin, and fluorene, each 1; isopropyl-Tetralin, 5 ; this would be expected to be only 3 greater than for Tetralin. The saturated ring of Tetralin seems to be largely aromatic in character (3,SI), but in the alkyl derivative it is less so. It is curious that the "mixed aniline point"of toluene is often found to be slightly lower than that of benzene (5, 36, 63) and that of o-xylene lower still (16A), although the reverse would be expected from Table I1 and Figure 1. Plots of solution temperature-hydrocarbon composition for toluene and benzene would show increasing curvature as compared with those for xylene ($6)
1
The relation of Figure 1 can be used to characterize an aromatic
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INDUSTRIAL AND ENGINEERING CHEMISTRY
1099
INDUSTRIAL AND ENGINEERING CHEMISTRY
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SIDE CHAINS
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Vol. 36, No. 12
observed, since in general the temperatures in one column decrease continuously down the column. There are numerous exceptions, aa the solvents are not uniformly responsive to differences in structure of the hydrocarbons. This waa indicated in the previous paper (1.2). Conspicuous in this respect is methanol, which haa much higher C.S.T. values with naphthalene derivatives than with benzene derivatives of equal paraffinicity. This solvent is unusually sensitive to molecular weight of hydrocarbons and relatively unaelective to type of hydrocarbon. RELATION OF C.S.T. TO BOILING POINT
22
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If boiling points of alkylbenzenes were plotted against total number of paraffinic carbon atoms, the plot would resemble Figure 1. This suggests another related generalization from Table I1 llustrated in Figure 2. The axis of ordinates measures the difference between the C.S.T. and the boiling point of each alkylbenzene, which.is identified by the alkyl groups at the top. The zigzag lines are not true plots, since the axis of abscissas does not represent any quantity, although the hydrocarbons are arranged in order of increasing parafinicity. The purpose of the lines is primarily to identify the points with the solvents. However, they do show a rough correlation between boiling point and C.S.T. The latter for p-phenylenediamine, for example, are ali within 20' C. below the boiling points of the hydrocarbons, respectively, and those of diethylene glycol are mostly a little above the boiling points. The boiling points used in Figure 2 are listed in Table 11, and in some casea are intermediate between those observed and the literature values. Some solvents are omitted from Figure 2 to avoid excessive congestion. Sometimes different types of points are used, merely to distinguish between different solvents. The incompleteness
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1944
~~~~~~
than the average for ita isomers. The line for maleic anhydride is especially erratic, perhaps because of its pronounced affinity for conjugated double bonds, which may be of varying vulnerability in different aromatics. The low point for benzene-triethylene glycol is hard to explain. The mean ordinates of Figure 2 for each solvent and the corresponding means for some other solvents are given in Table IV, which is useful in estimating C.S.T. values not listed in Table 11. This is done by adding At for the desired solvent to the boiling point of the alkylbenaene. The other solvents in Table I1 are omitted because too few C.S.T: values were observed for them with alkylbenzenes. The order in Table I V is slightly different from that in Table I1 because naphthalene derivatives and other aromatics are not considered. These are excluded from Figure 2 since, for the same paraffinicity, they would have much higher boiling points. Among themselves naphthalene homologs might show similar relations, but there are too few available with both C.S.T. and accurate boiling point to justify a separate plot.
TABLE 111. PROPERTIES OF ALKYLATED AROMATIC HYDROCARBONS
Hydrocarbon
B.P..
C.
d,Oo
194.8 190-2
0.8616
Meth ldiethylbensene 1,3,6-~ethyldiathyIben~ene (IO)
204-6 200
0.8737 0.879
Trieth Ibenzene l,3,6-?Yriethylbensene (10)
2 17-8 211.2
0.8673 0.86080
Isopro 1 Tetralin P r o p y f h r a l i n (10)
256-66 266-8
0.9636 0.9396
Di-aec-amylbenzene Diamylbenaene (10) 1,4-Di-aso-amylbenzene (10)
260-70 261-7 127-8s
0.8642 0.8520 0.8619
Di-iao ropylnaphthalene "2 2-&-iaopropylnaphthalene'' (10) ?should be 2,7-)
306-16 278-80
0.9641 0.9683
7.
.
O
Eth lis0 ropylbenzene 1,3-&thy isopropylbenzene (10)
Corrected to 20° C.
b
..
A t 14 mm.
EFFECTS OF SUBSTITUENTS IN ORGANIC SOLVENTS
TABLE Iv. AVERAGEDIFFERENCES BETWEEN C.S.T. AND BOILINGPOINT FOR ALKYLB~NZBNES Solvent Ethylene $yo01 Ethanolamine Reaorcinol Diethylene glycol -Phenylenediamine actic acid Trieth lene glycol Bendne p N i troaniline EAminoacetophenone thylene diformate Sdioyl alcohol Maleic anhydride pAminoeth ylacetanilide Aeetoacetanilide
e
At $. 100
++i-21 18 -1; -13 -22 --22 --40 79 90 --92 98 -112
-118
TABLEV. Solvent
Solvent Catechol Ammonia Phenylethanolamine Methyl sulfate Nitromethane Phenylhydrazine Furfuryl alcohol Methanol Furfural Ethylene ohlorohydrin Acetonitrile Acetiaanh dride Eth lene dacetate Aniine
... ... ...
60
...
At
-119 130 167 181 182 186 192 - 196 -216 -219 222 -226 238 -249
----
Increment, O
c.
374 274 201 > 168 313 368 198 123 212 267 183 208 23 162 36 30
36; b9 166 Amino Group Ethanolamine Ethanol 290 27.47 udminophenol Phenol 192 69 Phenol 217 69 pAminophenol pAminoacetophenone Acetophenone 231 46 Acetanilide 23 1 21,86,36 Aminoacetanilide p-Aminodiphenyl Lidina 196 26,45 o-Nitrotolueneb 166 8,4-Nitroaminotoluenel(18) Nitrobensene 172 o-Nitroanijine (18) Nitrobensene 261 pNitroaniline 53' ' Aniline 134 o-Phenylenediamine 50 Aniline 220 gPhen lenediamine 60 Aniline henydydraaine 60 Hydroxyl Group ua. Amino Group Ethanolamine 82 Ethylene glycol Ethylenediamine (0) 328 Ethanolamine 2j: 52 Diethylene $1 col ... Diethanolamine 62 Triethanolamine 107 Triethylene col ... < -160 Formamide F W c acid ({able I) 7 Acetamide -322 27,62 Acatac acid ( I d ) 97 p-Aminophenol 22 Hydroquinone -34 p-Phenylenediamine 22 2x-12 o-Phenylenediamine ... 2 x 20 m-Phen ylenediamine horcinol Correaponding anilines -1l*6 Lux monophenols (1d )
.. .
...
,
--
E$.;;phenoI
.... ..
Table V of the previous paper (29) summarized the effects of substituents in organic solvents on the C.S.T. with nonaromatio hydrocarbons. Similar effects are now presented in Table V for solvents with aromatic hydrocarbons. Those of the hydroxyl and amino groups are so great that they cannot be derived from either set of data alone, but can be computed from the combination of data by indirect methods as in the following example. The C.S.T.values of ethylene glycol should be compared with those of ethanol to get the effect of the second hydroxyl group. The comparison should be made with the same hydrocarbon; but the temperature range of this investigation (-78' to +262' C.) is too small to include the points of any single hydrocarbon.
EFFECTS OF SUBSTITUENTS IN ORQANIC SOLVENTS ON C.S.T:
Intermediates0 Precursor Hydroxyl Group (Aliphatic) Ethanol 13 Cellosolve 27,47 Carbitol 27,47 Propylene glycol 13 Propanqls 27,47 Propionic acid 27,47 o-Creaol 60 Hydroxyl Group (Aromatic) 89 36 69 36: 69
1101
Solvent Lactic acid o-Nitrobenzoic acid
WITH
HYDROCARBONS
Inter mediates' Precursor Carboxyl Group 27.47 Ethanol 69 Nitrobenzene Nitro Group Nitrobenzene o-Nitrochlorohenrnne 59 * +Nitro henyl 45 Acetopienone Aniline Phenol 60 Acetyl Group so Acetanilide p-Phenylenediamine Aniline 2i'. Ethylene glycol Glycerol Nitrobenaene Methyl or -CH:- Group
Increment
'c.' 265 266
147 99 146 127 208 150
.
... ...
Aoetoacetanilid?. p-Aminoacetanilide EAminoacetophenone thylene diacetate Monoacetin m-Nitroacetophenone
Sebacic acid Phenylethanolamine
2,4-Dinitrochlorobenzene
. .. .... ..
.
Ethylene. lycol 29 Adipic ac13 Phenyl Group 20 Ethanolamine Chlorine Atom , m-Dinitrobenzene homeric Effects
..
.,. ... .. . ...
60
a-Phenylenediamine Catechol o-Nitroaniline
31
> so
167 2X--168 < - 172 113
< -81 2 X -75 2 x -43 237 -366 4 X -61
-
-210
-23 82 134 83
26 Resorcinol m-Aminophenol I-Aminophenol 46 Iydro runone Me ta-ort%o 124 60 o-Nitrophenol nn-Nitrophenol 0 Numbers refer to solvents in Table 11. b Com arison should be made with the meta isomer, but the t w o probably diEer on& ilightly in C.S.T.
i
INDUSTRIAL AND ENGINEERING CHEMISTRY
1102
Vol. 36, No. 12
cursor" I n selecting inttwnediatc solvents for such :I comparison, care was taken to use those which are as similar in structure as possible, or at least to have thc v same type with respect to selectivity (aliphatic alcohols ow160 and esters are of one type, aromatic solvents are of a difDI + 13 ferent type). The intermediates used are indicated in B I20 Table V by numbers referring to the numbered solvents in Table 11. A blankineans that the comparison is W direct. Ia0 z The effects of hydroxyl, amino, and carboxyl groups in 0 c the solvents are all great. They are comparable with = 40 one another and generally greater when the substituents /%' are attached to smaller molecules than to larger ones, a 0 o ALKYLBENZENES , s and when attached to aliphatic carbons than to aromatic * ALKYL NAPHTHALENES c a V ones. This is apparent in the effects of the two hydroxyl X NON-AROMATICS -a groups in salicyl alcohol. The effect of hydroxyl in o/ x/ nitrophenol and in 2,4-dinitrophenol is masked because / I d X I I I I I it is ortho to a nitro group, and so forms a latent ester a0 5 IO I5 20 25 30 with abnormally - high - miscibility. Salicyl aldehyde beNON-AROMATIC CARBON ATOMS haves similarly, and so does catechol to a slight extent. Fiaure 3. Critical Solution Temperature as a Function of The effect of amino group in phenylhydrazine also is - Nonaromatic Carhn Atoms low because it is ''piled on" another amino group. I n certain cases the relative effect of hydrgxyl and amino groups varies enormously. Thus ethylenediamine is None is incompletely miscible with ethanol a t -78' C. and far more miscible with hydrocrtrbons than is ethanolamine, with sufficiently miscible with ethylene glycol a t high temperatures so indications that the hydroxyl group raises the C.S.T. over 300" C. that the comparative temperatures can be observed. However, more than the amino group. At the other extreme is acetic acid, Table I1 lists other solve'nts of somewhat similar structure, which which is far more miscible than acetamide, with the reverse conhave intermediate miscibilities with the hydrocarbons. Since clusion. On the other hand, pix monophenols and also catechol the C.S.T. values of ethylene glycol exceed those of ethylene have C.S.T. values only slightly below those of the correspontldiformate by an average of 186" C. in the case of five aromatics ing amino derivatives. (benzene, 01- and p-methylnaphthalene, Tetralin, and toluene), it is reasonable to supposc that they would also be about 186' R I higher in the case of the higher aromatics, which cannot be observed directly with ethylene glycol. Since the C.S.T. values of methanol with fourteen of these higher aromatics average 93" lower than those of ethylene diformate, respectively, they should be about 279" lower than those of ethylene glycol. Similarly, there is an average difference of 95" between C.S.T. of methanol and ethanol for six aliphatic hydrocarbons respectively (12). This indicates a total of 374" C. by which C.S.T.of ethylene glycol should exceed corresponding ones of ethanol; this increment is due to the second hydroxyl group'. This comparison is illustrated also in Figure 3 in which C.S.T. values with the four solvents are plotted against the number of nonaromatic carbon atoms (including the side chains of aromatic hydrocarbons and all the carbon atoms of paraffins and naphthenes). Tetralin and its homolog are omitted because of uncertainty about their proper abscissas. Three points of methanol with alkylnaphthalenes are high because of the unusual sensitivity of this solvent to molecular weight. The abscissas of the last two points for methanol and ethanol, with lube oils, were taken Figure 4. Mutual Solubility of Liquids from the molecular weights. They may be too far to the right because of the presence of some aromatics. Assuming that the Complete mimcibility ---High solubility four curves have approximately uniform differences in ordinate, L o w solubilit NO line Very low mol%ility the difference for the top and bottom curves is the sum of the 5. Ethyl ether 1. Water three intermediate differences taken at convenient points. 2 Disthylenegl 001 6. Benzene 3: Triethylena grycol 7. Cyclohexane The use of the same curve for aromatic and paraffin hydro4. Furfural 8. n-Heptane carbons (e.g., the one for methanol) is possible for aliphatic solvents but not for aromatic ones such as aniline, since the spread The effect of the njtro group is about the same as that reported for equal aniline points is 15 to 20 carbon atoms (&SI) instead of in the c a m of nonaromatic hydrocarbons (fa). That of the acetyl six (as i t would be if total carbon atoms were plotted in Figure 3). group seems erratic, but it is negative in esters because i t covers a I n Table V the solvent without the radical concerned (taken free hydroxyl group. That of -CHIis equivalent to thst of from citation 1.2 in most cases) is given under the heading "prethe methyl group and is still uniformly negative. It is much s If an increment of similar order were subtracted from the C.S.T. of greater when i t covers a free hydroxyl group, forming ethers, as methanol or ethanol with any hydrocarbon, so as to eliminate the effect of the first hydroxyl group, those of methane or ethane would seem to be in the in methyl Carbitol and methyl Cellosolve. The phenyl radical neighborhood of absolute zero. The same conclusion resulta from similar lowers the C.S.T.in phenylethanolamine much more than in preelimination of effect of carboxyl from acetic acid. This supporta the author's vious cases b6cause it partly covers a free amino group. As be,opinion (Table I1 of citation 18) that no wholly hydrocarbon system will fore, a chlorine atom shows only slight effect. separate into two liquid phsaea. 2w
3
d
-p
-
I
--------
_
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1944
HYDROT A B L E VI. SELECTIVITIES OF SOLVENTS FOR AROMATIC CARBONS AS COMPARED WITH CORRESPONDING NAPHTHENES Tetkhydrofurfuryl alcohol Furfural Ethylenechlorohydrin m-Dinitrobensene Ani1ine Sulfur dioxide Aoetonylacetone mcNitroacetophenone Acetonitrile Methyl sulfate
207 207 20b 204 200 198 191 191 191 186
Acetic anhydride Furfuryl aloohol Nitromethane Triphenyi hosphite Ethylene d?acetate Phenylhydrazine Phenyl hthalate Catecho? Methanol Ammonia
184 178 172 168 167 167 169 1b6 147 61
The "isomeric effects" are consistent with the previous indications (19) that ortho isomers among solvents are much more miscible than meta and para isomers with the same hydrocarbons. With respect to the hydrocarbons, no direct comparison is available in this paper between o-, m, and p-dialkylbenzenes; but the trivial differences between C.S.T. for isomeric alkylbenzenes (e.g., sec-butylbenzene and diethylbenzene) with the same solvent suggests that the effect of position likewise would be negligible for nonpolar groups, as contrasted with the polar groups of the solvents. This is supported hy observations of JIulliken and Wakeman (33) recorded in Table I. I t was noted previously (fd) that the position of the nonpolar methyl group in cresols and toluidines had little effect on C.S.T. AROMATIC SELECTIVITIES
The previous paper (12) estimated selectivities of solvent8 for olefins, naphthenes, and branched-chain paraffins with respect to paraffins, but did not evaluate those for aromatic hydrocarlions. The selectivities mentioned were measured by the difference in C.S.T. for the same solvent with appropriate pairs of hydrocarbons. For example, naphthene selectivity is the difference between the C.S.T. values of n-hexane and cyclohexane or between those of n-heptane and methylcyclohexane, or a mean of both differences. The aromatic selectivity of ammonia with respect to naghthenes is so low that it can be found directly by subtracting its C.S.T. with toluene from that with methylcyclohexane. For some other solvents i t can be computed approximately by an indirect method similar to that used in Table IV, as in the following example with methanol. Its C.S.T. values with ten alkylbenzenes average 106' C.2 lower than the corresponding ones of ethylene diformate. I t is reasonable to suppose, therefore, that its C.S.T. values with benzene and toluene likewise would be about 106" below those of ethylene diformate, or -111' C.8 and -91', respectively. These are subtracted from the C.S.T. veJues of methanol with cyclohexane (45') and methylcyclohexane (47'), giving as a mean 147' for the selectivity of methanol for aromatics with respect to naphthenes. The aromatic selectivities of the ot,her eighteen solvents whose C.S.T. values are recorded in Table I1 for either cyclohexane or methylcyclohexane were computed by similar methods and are arranged in Table VI in order of selectivity. Each value is a n adjusted mean of several such calculations so that neighboring Rolvents in the list are compared with one another. For example, methyl sulfate is rated a little less selective than acetonitrile because the mean difference in their C.S.T. value6 with the two naphthenes, 35' C., is slightly lower than the mean difference, 40', for the ten alkylbenzenes tried with each solvent. I n other words, acetonitrile has relatively a little more affinity for aromatics than has methyl sulfate. This difference is trifling. The exact order of Table VI may not be significant, especially since there seems to be little relation to structure. For selective The larger value for this increment than that uaed previously in a similar cornparison is due to the omission of four dicyclic hydrocarbons. The preaent oaloulation is aeleotivity for monocyclic aromatior. A high value for this point, 29O C. ( 6 ) found by extrapolation is disproved also by several others (4,64,4O, 46). f
1103
extraction of light aromatics, a solvent much higher in Table I1 (e.g., triethylene glycol) would be preferable, so as to have a more limited miscibility. These solvents would have selectivities comparable with those in Table VI, but are not assigned numbers because their C.S.T. with naphthenes cannot be observed readily. The selectivities for aromatics with respect to naphthenes in Table V1 average 184' C. (neglecting ammonia) as compared with an average of 35" for naphthene Relectivity in Table I V of the previous paper (fa). The sum of these is the order of magnitude of aromatic selectivity with respect to paraffins, which is thus over six times that for naphthenes. This ratio is not uniform, however. Sulfur dioxide, for example, has good selectivity for aromatic hydrocarbons but prartically none for naphthenes (1.8.
General miscibility relations are illustrated in Figure 4, which is somewhat similar to that of Jdnecke (21) but with a definite arrangement. To diminish the number of diagonals, the figure has only eight points instead of twenty. The compounds listed are selected as typical of various groups, and are arranged in an order indicated by solubility relations so that any two adjacent points, except the extremes, are connected by snlid lines which signify complete misribility. Compounds represented by points once removed also are miscible, but those farther removed usually have lower solubility, as indicated by dashed or dotted lines oi no line a t all. The last are practically immiscible. The only departure from symmetry is the solid-line diagonal, 5-8. Perhaps ethyl ether should be nearer to point 6. The scope of Figure 4 can he extended as follows: The various solvents of Table I1 can be arranged in the order given, around the right-hand side of the figure, mostly between points 1 and 4. The solvents of Table IV of the preceding paper (12) would be mostly between points 3 and 5. Those of Table I1 of that paper would be in the neighborhood of point 5 or between 5 and 6. The aromatic hydrocarbons of this paper would be in the order given, between points 6 and 7; and the naphthenes and olefinn, in order of increasing molecular weight for each class, between points 7 and 8. The paraffins would be near point 8. Appropriate position8 can be found (using relations of Tables IV and V and Figures 1 and 2) for points representing other liquefiable compounds. With such an arrangement the miscibility as liquids of any pair of compounds is approximately a function of their distance apart on the resulting, nearly complete circle, measured around the circumference. Usually higher solubility with water corresponds to lower solubility with hydrocarbons, but there are numerous irregularities. Alcohols, for example, are more miscible than aniline with each extreme. Such a n extension of Figure 4 is nearly the graphical equivalent of the class arrangement proposed by Ewell, Harrison, and Berg (IOA). LITERATURE CITED
(1) Alekseev, V.,Ann. physik. Chem., [2]28, 305 (1886). (2) Angelescu, E., and co-workers, Bull. sect. sci. acad. roztmaine. 29, 515 (1941). (3) Ball. J. S.,U. S. Bur. Mines, Rept. Investigation 3721 (1943); Natl. Petroleum News, 36, R297 (1944). (4) Barbaudy, J., Compt. rend., 182, 1279 (1926). (5) Buchner, E. H.,2.physik. Chem., 54, 668 (1906). (6) Butaric, A.,end Corbet, G.,Compt. rend., 184, 1446 (1927). (7) Campetti, A., Atti a d . sci. Torino. 52. 114 (1917). (8) Cornish, R.E.,and co-workera. IND.ENG.CHEM.,26,399(1934). (9) De Carli, F.,G a m d i m . ital., 57, 347 (1927). (10) DOSE, M.P., "Physical Constants of Principal Hydrocarbons", 4th ed., Texas Go., 1943. (10A) Ewell, R.H.,Harrison, J. M., and Berg, L., IND.ENO.CHEM., 36, 871 (1944). (11) Ewins, A. J.,J. Chem. Sac., 105, 357 (1914). IND.ENO.CHEM.,36,764 (1944). (12) Francis, A. W., (13) Garner, F.H., J . Znel. Petroleum Tech., 14, 716 (1928). (14) Gillam, N. W.,Austrdian Chem. Znst. J . & Proc., 9, 230 (1942). (15) Zbid., 11, 67 (1944). (16) Hammiok, D.L.,and Holt, W . E., J . Chem. SOC.,1926, 2003. (16A) Hammond, P.D.,and McArdle, E. H.,IND.ENO.CAIDM., 35, 810 (1943).
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(17) Hildebrand. J. H., and Buehrer, T. F., J . Am. Chem. SOC.,42, 2216 (1920). (18) International Critical Tables, Vol. 111, pp. 394-7, New York, McGraw-Hill Book Co.,1928. (19) Jacobs, W. A., and Heidelberger, M., J . Am. Chem. Soc., 39,1448 (1917). (20) Jaeger, A.,Brennstoff-Chem., 4,259 (1923). (21) Janecke, E., 2. Elektrochem., 38,860 (1932): 2. physik. Chem., 184, 61 (1939). (22) Koch, H., and Steinbrink, H., Brennstoff-Chem., 19,282 (1938). (23) Kraus, C.A.,and Zeitfuchs, E. H., J . Am. Chem. SOC.,44,1250 (1922). (24) Kruyt, H.R., 2. physik. Chem., 65,497 (1909). (25) Landolt-Bornstein-Roth-Scheel,Tabellen, pp. 760-1. (26) Zbid., Erg. I, 301. (27) Zbid., Erg. IIa, 474-8. (28) Zbid., Erg. IIIa, 678-9. (29) Lecat, M., J . chim. phys., 27,79 (1930). (30) Lecat, M., Rec. trau. chim., 46,244 (1927); 47,16 (1928); Ann. soc. sci. Bruzelles, 45,284 (1926); 47B,i, 149 (1927); 49B,ii, 17,109 (1929). (31) Mair, B. J., Willingham, C . B., and Streiff, A. J., J . Research Natl. Bur. Stanclards, 21,599 (1938). (32) Moles, E.,and Jimeno, E., Anales soc. espufi. fds. qudm., 11, 393 (1913). (33) Mulliken, 5. P.,and Wakeman, R. L., IND. ENG.CHEM.,ANAL. ED., 7,276 (1935);Rec. true. chim., 54,370-1 (1935). (34) Ormandy, W. R., Pond, T. W. M., and Davies, W. R., J . Znst. Petroleum Tech., 20,324,328 (1934). (35) Petrov, A. D , and Andreev, D. N., J . Gen. Chem. (U.S.S.R.), 12,95 (1942). (36) Rice, H. T., and Lieber, E., IND. ENG.CHEM.,ANAL.ED., 16, 109 (1944).
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(37) Rothmund, V.,2. physik. Chem., 26,467,475(1898). (38) Schiessler, R. W., and co-workers, Petroleum Refiner, 22, 392 (1943);Proc. Am. Petroleum Inst., 24,111,50 (1943). (39) Seidell, A., “Solubilities of Organic Compounds”, 3rd ed,, Vol. 11,p. 27,New York, D.Van Nostrand Co., 1941. (40) Zbid., Vol. 11, pp. 46,47,53. (41) Zbid., Vol. H, pp. 66,92,121. 198,341,342,346,355,356,367, 389,516,551,584,667,700. (42) Zbid., Vol. 11, p. 121. (43)Zbid., Vol. 11, p. 365. (44)Zbid., Vol. 11,p. 394. (45) Shepherd, F. M.E., J . Inst. Petroleum Tech., 20,299 (1934). (46) Shtkkarev, A,, 2. physik. Chem., 71,94 (1910). (47) Sidgwick, N. V., and Neill, J. A., J . Chem. SOC.,123,2813 (1923). (48) Tilicheev, M,D., Khim. Tverdogo Topliva, 9,No. 2, 181 (1938). (49) Tilicheev, M. D., and Kuruindin, K. S., Neftyunoe Khoz.,’lS, 686 (1930); Chem. Zentr., 1931,I, 2561. (50) Timmermans, J., J . chim. phys., 20,506 (1923). (51) Timmermans, J., thesis, Brussels (1911); Proc. A d . Sci. Amsterdam, 13,507 (1910). (52) Timmermans, J., and Hennaut-Roland, Mme., Zbid., 27, 420 (1930). (53) Tropsch, H., and Simek, B. G., Mitt. Kohlenforsch. Inst. Prug., 1931,62. (54) VrevsW, M. S., Held, N. A., and Shchukarer, S. A., J . RUE. Phys. Chem. Soc., 59,625 (1927); Z.physik. Chem., 133,386 (1928). (55) Woodburn, H. M., Smith, K., and Tetewsky, H., IND.ENQ. CHEM.,36,588 (1944). (56) Wratschko, F.,Pharm. Presse, 34,143 (1929). PRESENTED before the Division of Petroleum Chemistry at the 108th MeetYork, N. Y.
ing of the AMERICAN Cxshrrcar. SOCIETY, New
OIL-PAPER DIELECTRICS Power Factors and Related Properties of Impregnated Cable and Filter Papers JOHN D. PIPER AND N . A. KERSTEIN The Detroit Edison Company, Detroit, Mich.
I
N SERVICE, oil-impregnated paper dielectrics often deteriorate with resultant increase in power factor and conductivity. 1n.this respect they are similar to oil dielectrics. As Clark (6) pointed out, however, the oils that are most resistant to deterioration in themselves do not necessarily produce the most resistant oil-paper dielectrics. The reason for the apparent difference in behavior is probably twofold. First, the paper acts as a catalyst that partially determines the types of degradation products formed; second, the same type of degradation product affects the power factor, conductivity, and other dielectric properties of oils differently from the corresponding properties of oil-impregnated papers. To these must be added the third possibility that the type of degradation undergone by the paper depends on the type of degradation product (from oil) with which it is in contact. There is evidence, however, that the latter is unimportant a t service temperatures below 100” C. , It ispossible that both oil and paper may sometime be displaced by materials that are intrinsically more stable. However, continuous efforts are still being made by manufacturers of insulating oils, equipment, and cables, and by utility companies to select and improve insulating oils in order to obtain superior stability in both liquid dielectrics and oil-impregnated paper dielectrics. These efforts have been expended principally in various service and accelerated life tests on finished insulation, and in tests designed to subject experimental samples of oil or oil-impregnated paper to controlled deterioration treatments such as oxidation,
corona discharge, high temperature, catalysts, and combinationa of these. Significantly more stable dielectrics have resulted from such efforts; but reasonably accurate predictions based upon the degree to which one oil resists given treatments cannct be made concerning the degree to which a different oil will resist the same treatment or the degree to which the same oil will resist altered treatments. Results of such tests are often chaotic. It is probable that this condition will persist until the fundamentals of the changes that take place in dielectrics are better understood. ADDITIVE STUDIES
For a number of years the authors and their colleagues (7-18) have been endeavoring to obtain fundamental data for the limited field that concerns the physicochemical nature of substances that can cause significant increases in the power factors and conductivities of insulating oils and impregnated papers. The kinds of materials studied have been limited to those that could conceivably be formed by the deterioration of oil and paper in contact with materials with which they are used in service; the maximum concentrations have been limited to those that cauld be formed during severe service conditions. The method used consists simply of adding to an oil with a very low conductivity, various concentrations of highly purified materials of the types selected to’represent constituents or deterioration products of commercial insulating oils, and of determining
