SOLVENT PROPERTIES OF
C, Aromatic Hydrocarbons J
P. D. HAMMOND Heyden Chemical Corporation, Fords, N. J. OMESTIC coal tar light fied by crystallization) probably contain less than 1 per cent imoil sources provide annually E. H, McARDLE purities and possibly less than 0.5 a total of 10 to 15 million Esso Laboratories, Standard Oil per cent. Density and optical gallons of mixed xylenes and CS Development Company, Elizabeth, N. J. data indicate the impurities to be aromatics, in the form of lo, 3", aromatic. The p-xylene appears 5", lo", and industrial pure xylenes, to be less pure than that of Boord together with solvent naphthas and Henne (4); the o-xylene is somewhat purer and equal to and Hi-Flash naphthas (IS). Double this amount of nearly that characterized by the Bureau of Standards "best values" pure toluene and more than ten times as much benzene have annually come from these sources. It is therefore not sur(14). Purity of the ethylbenzene and m-xylene may be estimated at about 99 per cent, again with impurities largely prising that, except for benzene and toluene, no highly aromatic. purified aromatic hydrocarbon has been obtainable until recently a t low cost and in tank car quantities. Freezing points were taken in a Bureau of Standards type Henceforward this balance of supplies may be shifted. apparatus (6),made from two coaxially mounted Dewar While industrial coking favors the formation of benzene, tubes. The inner tube, of 75 ml. capacity, was fitted with a a number of petroleum conversion processes result in a precontrolled-speed motor-driven stirrer. Temperatures were ponderance of the higher aromatics (3, 12). It is not, of taken with a Bureau of Standards standardized platinum course, to be expected that such petroleum stocks may be resistance thermometer. Cottrell boiling points were read taken at the present time for the manufacture of pure arowith a Bureau of Standards standardized Anschutz type matics, either for solvent use or chemical synthesis. Neverthermometer, ranging from 125" to 150" C. and graduated theless, a study of the properties of the individual higherin 0.2' C. Correction was made for barometric pressure. boiling aromatics may be of interest to both the chemical Surface tension was obtained with a du Nouy tensiommanufacturers and the purchasers of solvents. Isoparaffins eter. The ring was mounted on the left-hand side of an have been shown (8) to differ so markedly in solvent properties analytical (Chainomatic) balance, check readings being from the isomeric normal paraffins that one might suspect taken to 0.1 mg. in a constant temperature room a t 25" commercially significant differences to exist within groups of * 0.2"c. isomeric or homologous aromatics. A brief study of the Dielectric constants were determined in a modified four CSaromatics has therefore been made. heterodynebeat apparatus, in conjunction with a platinum The p-xylene used was recrystallized from commercial 1" cell standardized against pure benzene. . xylene. The o-xylene was recrystallized from a commercial o-xylene. The m-xylene was obtained by the reduction of m - x y l i d i n e diazonium chloride. The K: KAURI-BUTANOLVALUE m-xylidine used for diA: ANILINE POINT azotization was purified R:RESIN DILUTION RATIO from commercial m-xyli800 R+\ P: POLYBUTENE-DECANOL VALUE OVER-ALL AVERAGE VISCOSITIES: dine by crystallization of META = D O % the acetate salt. A samPARA =loo% ple of the m-xylidine in I ETHYL BENZENE = 106% dilute hydrochloric acid ORTHO =153% ' 500 gave no turbidity when cn boiled with formaldehyde 0 5i j400 solution; this indicated a t h e a b s e n c e of o t h e r z xylidines. s
D
1
-e
t
DEGREES OF PURITY
Cross reference between t h e values given i n Table I and those obtained by previous authoritative investigators reveals that the present samples of 0- and p xylenes (both finally puri-
Figure 1. Median Solvency Trend and Over-All Viscosity Average for Represen tative Solutions
809
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
810
TABLE I. COMPARISON OF PHYSICAL PROPERTIES OF MATERIALS USEDWITH PREVIOUS VALUES
Freezing point, C. Plateau time, Din. Bath composition
Ethylo-Xylene m-Xylene p-Xylene benzene Present Materials -25.30 -48.56 +13.00 -95.30 21.5 8 7.5 11 iso- Commercial CO1 iso- Commercial COz nitrogen nitrogen propyl propyl alcohol alcohol
+
+
Gr35ent at F. P., 55 144 U. Cottrell spread, ini139.1 to ti,al B. P. to 50% 144.4 t o 144.4 139.1 distd.. C. d25a 0.8759 0.8600 dz0 b 0.8809 0.8650 28.3 31.2 G:avityb A.P.I. 7.39 7.26 Lb./gal. kt 60' F. 1.4970 1.5053 n '3-0 Dyspersionat 20' C. 158.2 155.8 Sp. dispersion at 20' C. 179.6 180.1 D u Nofiy surface tension at 25O C., d nes/cm. 31.56 30.46 Diecctric oonstant at 30.05' C. 2.571 2.351 Bureau of Standards Values -25.30 -47.55 Freezing point. ' C. Boiling point, C. 144.4 139.3 0,86401 d20 0.88040
93
97
138.5 to 138.6 0.8576 0.8626 31.6 7.24 1.4959 156.5
136.3 to 136.5 0.8624 0.8674 30.7 7.28 1.4958 151.3
181.4
174.4
29.95
30.50
2.264 (14) +13.36 138.4 0,86100
2.382
., . .. .. ..
Boord and Heme Values (4) -25.5 -48.9 4-13.19 -94.96 144.5 139.2 138.5 136.5 1.4968 1.4959 1.4971 1.5054 0.8609 0.8661 0.8799 0.8639 d? 0.026 A 0.0010 d. 0.006 d. Estd,impurities,mole 0.010 d. 0.003 0.009 fraction 0.0005 0.002 a 10-cc. pycnometer a t 25' ==, 0.002' C. b Coefficient of cubical expansion of all four Cs aromatics taken as 0.0010 (20).
Thus o-xylene suggests itself as a doubly desirable solvent. Not only may i t answer a demand for critically high solvency, but i t appears able to serve with representative solutes where a higher viscosity is needed a t a stipulated solids content, or a lower solids content is desirable a t a k e d viscosity-e. g., in the mechanical application of adhesives or saturants. Ethylbenzene, which may or may not eventually become available a t a price competitive with commercial xylenes, appears to offer little advantage as a solvent over a meta-para mixture, the bulk component of present-day narrow-cut fractions. Figure 1 illustrates a median solvency trend and an overall viscosity average for representative series of solutions. Divergencies are regarded as effects of structural relations since past experience (1,2, 6-9) has shown that the experimental errors involved in running dilution ratios and determining viscosities (under carefully controlled conditions) are of the order of 1-3 per cent. I n the present instance weighings and volume readings were made to 0.1 per cent, and all operations were carried out in a constant temperature room a t 25' * 0.2' C. TABLE 111. SOLUTION VISCOSITIESAT 25" C.
Freezing ppintbo C. Boiling point, C. n SO
Gardner-Holdt/Centipoisesa +Xylene 50% wt. cut of Beckosol No. 3 50% aolids wt.b cut of 25-gal. tung oil-Beckacite No. 3000 varnish solids 20% wt. s o h . of 125-oentipoise
DILUTION RATIO VALUES
Solvent properties, such as kauri-butanol solvency, aniline point, and other dilution ratio values, have been characterized (8) as estimates of affinity or relative structural similarity between solute and solvent, and may thus be regarded as measuring the ability of a solvent to dissolve a certain solute, or an intrarelated class of solutes. That such values do not necessarily predict viscosity effects has been demonstrated in the case of certain isomeric paraffins (8); this behavior is strikingly evident among the Cs aromatics.
Vol. 35, No. 7
m-Xylene
p-Xylene
Ethylbenzene
v+l/av+l/av ! ! 6 907 M E O
945
840
I 225
H/I .~
2 j
100 grems/liter soln. of milled pale crepe rubber
5
I/.
E
I/J
Parlon (chlorinated rubber)
840
I- 210 218
136
0
+. l / s
470 382 Solutions made at 25' C., by tumbling at 15 r. back-tared. b Phenol-modified alkyd resin.
p.
-
I
-
I/(
191 0 P 370 4m m.; corked bottles
, ACKNOW LEDGME-NT
Opportunity is taken to thank R. H. Decker, A. E. Robertson, and J. V. Sommer, of the Esso Laboratories, and s. B. Beddow, of the Standard Alcohol Company, for determining physical properties. LITERATURE CITED
TABLE 11. SOLVENCY PROPERTIES o-Xylene 106.8 97.7 85.5 101.9 8.4
m-Xylene 102.8 94.0 80.8
p-Xylene 97.3 89.2 76.4 93.2 10.6
Ethylbenzene 98.6 90.3 77.8 94.5
Kauri-butanol value, CC. Kauri-butanol solvent power" Solvent power by wt.a 98.4 Kauri-butanol solvency b Mixed aniline oint C. e 10.0 10.0 Pclyhutene n-zecank value, 12.40 11.72 ml. d 12.38 11.70 44.0 42.2 Maleic resin solvency, ml. e 37.5 36.7 a Beneene 100; n-heptane = 25.4 (!. 8 ) . b Toluene = 100; primary reference mineral spirits = 40 (9). e Critical solution temperature of 10 ml. ,anhydrous aniline, 5 ml. of Cs aromatic.,and 5 ml. of a 60' C. aniline point naphtha of 43'/44' A.P.I. gravity-i. e., a naphtha which gives a 10.Oo C. mixed aniline point with pure toluene (7 11) d Toler&!e,'to cloud point a t 25' C., of a solution of 2.0 grams of 5500 molecular weight polybutene in 10 ml. of Cs aromatic (8). e M1. of 60' C. aniline point naphtha tolerated a t 25' C. by a solution of 10.0 grams hmberol801 in 40 grams Cs aromatic ( 7 ) .
-
(1) Baldeschmieler, E. L., Morgan, M. D., and Troeller, W. J., IND. ENQ.CHEM.,ANAL.ED., 9, 540 (1937). (2) Baldeschwieler, E. L., Troeller, W. J., a n d Morgan, M . D., Ibid., 7, 374 (1935). (3) Bates, J. R., Rose, F. W., Kurt,, S. S., Jr., a n d Mills, I. W., IND. ENQ.CHEM.,34, 147 (1942). (4) Boord, C. E., and Henne, A. L., Div. Petroleum Chem., A. C. S., Detroit, 1940. (5) Mair, B. J., Glasgow, A. R., Jr., a n d Rossini, F. D., Ibid.. St. and Baldeschwieler, E .
(9) (10)
The data in Table I1 show that o-xylene has a 4-20 per cent superiority over the meta and para isomers in ability to dissolve one natural resin and one synthetic resin. Table I11 indicates, however, that solutions made with the highersolvency o-xylene are, with one exception, 8 to 75 per cent more viscous than the corresponding meta and para solutions.
(11) (12)
(13) (14)
L., IND.ENQ. CHEM.,
a n d Baldeschwieler, E. L., IND.ENCI.CHEM., ANAL.ED.,13, 301 (1941). McBrdle, E . H . , a n d Robertson, A. E., IND.ENQ.CHEM..,34, 1005 (1942). Philadelphia 'Paint and Varnish Production Club, Natl. Paint, Varnish, Lacquer Assoc., Sci. Sect. Circ., 546, 273 (1937). "Science of Petroleum". Vol. 11, I). 1136, New York. Oxford Univ. Press, 1938. Shoemaker, B. H., and Bolt, J. A., IXD.EHQ.CHEM.,ANAL.ED., 14, 200 (1942). Sweeney, W. J., and McArdle, E. H., IND. ENQ. CHEM.,33, 787 (1941). U. S. Tariff Comm., Report 148, 2nd series, Synthetic Organic Chemicals Production and Sales 1940, p. 6. White, J. D., and Rose, F. Wr., Bur. Standards J.Research, 9, 711 (1932).
