August 15, 1943
ANALYTICAL EDITION
types, but which when dissolved a t a suitable concentration gives a maximum spread between normal and branched paraffns. Tabulated data covering the necessary number of 10' C.-wide fractions can then be taken once, and the viscosity of an unknown sample determined a t a later date concurrently with a control determination on a selected normal paraffin, to correct for resin or polymer aging.
Acknowledgment Opportunity is taken to thank M. Lapeyrouse of the Esso Laboratories, Research Division, for helpful criticism in con-
481
nection with this work. The authors are also indebted t o M. R. Fenske, of the Pennsylvania State College, for supplying the majority of hydrocarbons studied.
Literature Cited (1) Francis, A. W., IND. ENG.CHEX.,33, 554 (1941). (2) Ibid., 35, 442 (1943). (3) McArdle, E. H., and Robertson, A. E., Ibid., 34, 1005 (1942). (4) Thomas, C. L.,Bloch, H. S., and Hoekstra, J., IND. ENG.CHEM., A N A L . ED., 10,153 (1938). P R ~ ~ E N Tbefore E D the Division of Petroleum Chemistry at the 105th Meeting of the AMERICAN CHEMICAL SOCIETY, Detroit, Mich.
N-Methylaniline Point of Viscous Petroleum Oils B. W. GEDDES, L. Z. WILCOX, AND E. H. McARDLE Esso Laboratories, Research Division, Standard Oil Development Co., Elizabeth, N. J.
D
URING the past twenty years, aniline point (1, 9) has become accepted as a reliable quick estimate of the proximate composition of the lighter straight-run petroleum products. It has been widely adopted as a measure of solvency of petroleum distillates for various solutes, and has acquired its popularity largely because among such tests it alone requires no temperature control. For highly aromatic solvent naphthas, it has more recently been modified to "mixed aniline point" (6, 6, 8), wherein the aromatic naphtha is first diluted with an equal volume of a 60" C. aniline point naphtha of 43"/44' API gravity. For testing lubricating oils of relatively high aniline p o i n t 4 e., above 80" C.-a second modification is now suggested, wherein aniline is replaced with N-methylaniline. Preliminary results indicate that the method may also serve in testing other petroleum products. The following simple relation exists between aniline point and N-methylaniline point of petroleum lubricating oils: No. of Oils Tested
Aniline points
15
80-130
O
c.
Range
Aniline Point of Diluted Oil I n an attempt to lower the equivalent aniline point of lubricating oils, a typical 120-viscosity aviation oil was diluted with an equal volume of toluene, and the aniline point of this mixture determined. It was hoped that such dilution would drop the temperature to the half-way point, much as "mixed aniline point" raises the reading for aromatic naphtha3. (Here, the straight aniline point of toluene is assumed to be -40' C., -40' F., based upon its "mixed aniline point"
1
/
LUBRICATING OILS
T
N-Methylaniline points
* c. 3-53
Tem erature Di#erence O
c.
77 =+=I
At present, an important use of this type of test is in estimating the relative tendencies of these oils to attack rubberlike materials. Following the development of several synthetic elastomers which are not ewily soluble in petroleum oils, an increasing proportion of flexible transfer lines and storage equipment has been fabricated from these materials, and correlations have been drawn between the aniline point of petroleum oils and the logarithm of the per cent increase in volume of rubberlike materials (2, 4, '7). The proposed test method was developed because laboratory determinations of aniline point become increasingly difficult and hazardous as one passes from the lighter petroleum fractions to such heavy and highly paraffinic stocks as aviation lubricating oils. At 120" C. (248' F.)a hot oil or hot air bath, or both, is required to obtain an accurate reading. Furthermore, experience shows that the vapor pressure of aniline a t this temperature is sufficient to volatilize enough from the stirred mixture to cause a progressive change in a series of readings. Moreover, the concentration of aniline vapor in the vicinity of a short test tube may be deemed objectionable by sensitive operators.
=
2oLLL IO
180
200
ANILINE
220 240 POINT,OI
260
FIGURE 1
of 10.0" C.) Unfortunately, however, instead of lowering the aniline point of the aviation oil (255" F.) to the half-way point (107.5' F.)-i. e., by 147.5" F.-the drop amounted to only 85' F.,from 255" to 170". When the oil was diluted with two volumes of commercial 10' xylene, to make 10 ml. of mixture, the critical solution temperature with 10 ml. of aniline became 140" F., much more than one third the way from -40' (assumed for xylene, from its mixed aniline point of 10" C.) up to 255". Thus no simple correlation between aniline point and a blended aniline point appeared likely to exist when dealing with such dissimilar materials as lowboiling aromatics and viscous lubricating oils. When N-
INDUSTRIAL AND ENGINEERING CHEMISTRY
488
TABLE I. INSPECTIONS OF N-METHYLANILINE USED Specific gravity a t 25' C. Initial n6 20' boiling C.. point, O C. 5 7 dia$!ed, ".C. 10% dutdled, C.
.
0.981 195.1 1.5682 196.4 196.7
50% distilled,
99502~
Dry point,
~,"
O
C.
c.
$
::::: ~
197.0
198.4
ethylaniline was substituted for aniline and no diluent was present, complete miscibility occurred with the aviation oil a t room temperature.
N-Methylaniline Point N-Methylaniline was accordingly tried. The ideal temperature range of a satisfactory substitute test for the aniline
Vol. 15, No. 8
point of lubricating oils would (1) be exactly as wide as the corresponding temperature range of their aniline pointsi. e., about 50" c. (90" E'.)-and (2) for practical convenience, ~ begin ~ just~ above ; melting ice temperature for the lowest values ordinarily encountered, and not extend above 60" C. (140" F.), easily obtainable with running hot water. Table I1 shows how ideally N-methylaniline meets these requirements. With the wide variety of lube oils tested, it drops the aniline Point by 77" * 1" c., 01 139" * 2" Beginning with 3" c. for an SAE 10 Coa&al (naPhthenic) Oil, N-methYlaniline values parallel aniline values upward to 53" C., for a treated Pennsvlvania 120-viscositv aviation lube oil, as indicated in the last column of Table 11. The correlation between aniline point and N-methylaniline point is shown in Figure 1, and the relationship between these values and swelling tendency is indicated in Figure 2.
TABLE 11. ANILINEPOIXTS AND N-METHYLANILINE POI~VTS
N-Methylaniline Points Aniline Operator Operetor Operator Pointa 1 2 3 Av. F. C. c. c. O C. C. 2 9 40 30 176 80.0 2.6 2.8 2.8 SAE 10 coastal 35 198 9 2 . 2 69 14.6 14.3 14.3 SAE 40 coastal 14.0 102 212 100.0 45 23.2 24.0 23.2 23.5 Penn. 180 neutral 221 105.0 80 47 29.0 29.4 29.1 29.2 Nujol 231 110.6 44 113 34.8 34.7 34.3 34.6 SAE 10 extracted mid-continent 236 113.4 65 36.0 190 36.5 36.4 Coastal bri h t stock 36.7 244 117.8 96 40 8 41 2 100 41.0 41.0 SAE 50 mi -continent 247 119.4 87 120 41.5 40.8 41.0 41.1 Calif. aviation 120 252 1 2 2 . 1 150 98 44.9 45.0 45.0 Penn. bright stock 45.0 103 253 1 2 2 . 8 100 46.0 46.2 45.7 46.8 Extracted mid-continent av. 100 257 125.0 103 120 48.0 47.7 47.3 Extracted mid-continent av. 120 257 125.0 104 123 4 7 . 78 48 0 47.7 47.6 Treated Penn. aviation 120 261 127.2 102 145 49.0 49.0 49.0 49.0 Extracted mid-continent 150 bright st,ock 265 129.4 9.5 160 52.3 52.7 52.0 52.3 160 viscosity extracted bright stock 264 128.9 105 120 53.0 53.0 53.0 53.0 Treated Penn. aviation 120 a Taken by operator 1, in A. S. T. M. eteam emulsion tubes; believed equal t o strict A. S. T. M. aniline point (1). Viscosity
at 210° F.
Oil
Viscosity Index
'3
Dilference between Aniline and N-hl ethylaniline Points (Operator 1)
Av. deviation O C. F. 0.1 0.2 0 . 3 0.5 0.4 0.7 0.2 0.4 0.2 0.4 0.3 0.5 0.1 0.2 0.3 0.5 0.1 0.1 0.4 0.8 0.2 0.0 0.2 0.0
c.
77.1 77.6 76.0 76.0 75.8 77.4 76.6 77.9 77.2 76.8 77.0 77.0 78.2 77.1 75.9
0 . 34 0.0
0.4 0.0
TABLE IIT. POSSIBLEERRORS Effect of Incorrect hleasurement Critical Solution Temperature
Mixture
0
m 0 z m D
SAE 40COASTAL
9 ml. 10 ml. 11 ml. 9 ml. 10 ml. 11 ml.
c.
4.1 2.9 1.6 46.8 44.9 43.5
of SAE 10 coastal, 11 ml. of N-methylaniljne of SAE 10 coastal 10 ml. of N-methylaniline of SAE 10 coastal' 9 mi. of iV-methglaniline Pennsylvania bright stock, 11 ml. of h'-methylanjline Pennsylvania bright stock 10 ml. of .V-methylanlline
Pennsylvania bright stock: 9 ml. of N-methylaniline Effect of Redistillation
v, ,z
Six Weeks Freirhly Old Sample Distilled
ro 0
G)
9::
Equal volumes of SAE 10 coastal and N-methylaniline Equal volumes of Pennsylvania bright stock and N methylaniline
c.
c.
2.9
2.6
44.9
44.6
Effect of Added Water
Px "f
SAE IO EXT'D. MID-CON
O
N-methylaniline point Same, lus 0 04 ml. of N-metgylaniiine point Same, plus 0.04 ml. of
COASTAL BRT.
96 VI. SAE 50 MID-CON
of SAE 10 coastal oil water of Pennsylvania bright stock water
c.
2.9 3.0 44.9 45.4
I
CALIF. AVIATION I 2 0
FIGUBE 2
The K-methylaniline employed was the Eastnian grade labeled "free of aniline and dimethylaniline". It was six weeks old when used, Pertinent inspections are shown in Table I. A double redistillation, discarding light and heavy ends, caused a negligible change in the N-methylaniline points of the light coastal oil and a Pennsylvania bright stock (Table 111). Presumably, like aniline, N-methylaniline should be handled in the laboratory as a toxic reagent, although accord-
August 15, 1943
ANALYTICAL EDITION
489
ing to one authority (3) "introduction of a n alkyl group such as methyl (CHJ . . makes (N-methylaniline) less poisonous than aniline, for dimethylaniline is less poisonous than aniline." Like aniline, N-methylaniline is an established intermediate in the dyestuff industry.
cumulative 10 per cent errors in measuring the componentsfivefold those indicated as the average of the three operatorsis about 1.5" C. over the range of oils tested; and the presence of water raises the S-methylaniline point, as it does the aniline point.
Performance of the Test
Conclusions
The current A. S. T. M. method for aniline point (A. S. T. M. D611-41T) calls for pipetting the aniline, and pipetting or weighing the sample t o be tested. Since the room-temperature pipetting of a 120-viscosity a t 210" or heavier aviation oil is practically impossible, the sample and test tube must each be weighed, a time-consuming process. Hence resort was made to the utilization of A. S. T. M. steam emulsion tubes (A, S. T. M. D157-36) of Pyrex, 200 mm. long and of 23-mm. bore (8 X 1 inch test tubes), graduated in milliliters beginning at 10 ml. The tubes had been previously calibrated by the Standard Inspection Laboratory, Standard Oil Development Company, Bayonne, K. J. Correct placement of the bottom line of the graduated range, at 10 ml., is as important to the N-methylaniline point test as are the other graduations. Selected tubes were rechecked for the accuracy of this marking against a 10.0ml. pipet, and were all found correct. The reagent, being heavier than lubricating oils, is poured into the tube first. The bottom of its meniscus is tangential to the marking, which encircles the tube. Oil to be t,ested is poured atop the reagent, again with the meniscus tangential to the top of the 20-ml. marking. Interfacial tension between glass and N-methylaniline is apparently much lower than in the case of anilinr, since the former flows smoothly down the wall of the tube, leaving fener and smaller droplets above the body of the liquid.
N-Methylaniline point has practical advantages as a qualitative test instead of aniline point for the proximate composition of petroleum oils. Aniline points may be obtained from N-methylaniline points by adding 77" C. or 139' F. A. S. T. M. steam emulsion tubes offer a convenient and precise means of performing the test.
.
The precision of the test is seen from Table I1 t o be ==0.2" C., or ==0.4" F, Table I11 shows that the effect of
Literature Cited SOC.Testing
hlaterials, Standards on Petroleum Products and Lubricants, Philadelphia, October, 1942. (2) Carman, F. H., Powers, P. O., and Robinson, H. A., IND.ENQ. CHEM.,32, 1069 (1940).
(1) Am.
(3) Hamilton, Alice, "Industrial Poisons in the United States", p. 490, New York, AMacmillanCo., 1925. (4) Hanson, A. C., IND. ENG.CHEM., 34, 1326 (1942). ( 5 ) Holabird Ordnance Motor Base Tentative Specification ES-No. 680a, p. 19 (August 10, 1942). (6) McArdle, E. H., and Baldesohmieler, E. L., IND. ENQ. CHEM., ANAL.ED., 13, 301 (1941). (7) Powers, P. O., and Robinson, H. A., IND. ENO. C H ~ M 34, . , 614 (1942).
(8) Shoemaker, B. H., and Bolt, J. A., IND.EXQ.C H ~ MANAL. ., ED., 14, 200 (1942). (9) Tizard, H. T., and (1921).
Marshall, A. G., J. SOC.Chsm. I d . ,
40. 20T
Determination of Free Gossypol in Cottonseed Meal A Colorimetric Method CARL M. LYRIAX, BRYANT R. HOLLAND, AND FRED HALE Texas Agricultural Experiment Station, A. & RI. College, College Station, Texas
I
T HAS been shown by Lyman, Holland, and Hale (4) that
cottonseed meal can be processed in such a manner that it no longer has any toxic qualities whatsoever, and that the procedure is a practical one from the standpoint of oil mill operation. It has also been shown that the free gossypol content of cottonseed meal is a reliable index which mill determine whether any given sample of meal will prove toxic in animal feeding tests. In the authors' experience, accurate results for the determination of free gossypol by the precipitation of the dianiline compound from extracts of cottonseed meal have been obtained only with considerable difficulty. I n attempting to follow the procedure of Halverson and Smith (2, 6) duplicate determinations often gave satisfactory checks but the precipitates were not always sufficiently pure to give the accuracy desired, and preripitates which had the color of dianiline gossypol were never obtained. This paper reports a quantitative method for the determination of gossypol, based on the change in color which occurs when aniline reacts with gossypol in an organic solvent.
Experimental The absorption spectra data on which the method is based were obtained with a Cenco Sheard spectrophotelometer. For
purposes of routine analysis any good photoelectric colorimeter with a filter transmitting light of 440-millimicron wave length is satisfactory. The procedure used for the isolation of gossypol to be used as a standard was the same as that given by Campbell, Morris, and Adams ( 1 ) . Figure 1 shows the comparison of the absorption of light by pure gossypol and by dianiline gossypol (formed by the addition of anibine to the solvent), both measured against a reference cell containing pure solvent. Dianiline gossypol exhibits a maximum of absorption at 440 millimicrons while pure gossypol absorbs very little light at this wave length. B y measuring the absorption of a solution of gossypol plus aniline (freshly distilled, water-white) against a reference cell containing the same amount of gossypol but no aniline, the change in absorption due to the reaction with aniline can be measured. This procedure makes it possible to apply the measurement to solutions containing other colored materials besides gossypol, provided that gossypol is the only substance present which reacts with aniline to produce a color change. Figure 2 s h o w this type of measurement applied to solutions of gossypol a t two concentrations and to a diluted ether extract of cottonseed meal. The close similarity in the shapes of the absorption curves suggests that the change in absorp-
