however, to the number of branches or the molecular weight. SUMMARY
The correlations a t present available for determining the carbon-type composition of lubricating oil, in general, show satisfactory agreement with data for pure compounds. Their disagreement for mononuclear aromatic compounds, and for pure compounds containing nonfused aromatic rings, when considered together with the data on the lubricant portion of Ponco Oklahoma crude studied by API Project 6, suggests that single benzene rings, unfused with naphthene rings or other aromatic rings, do not occur in lubricating oil in large quantities. The range of physical properties encountered in highly aromatic oils suggests that the preparation of kata-condensed polynuclear structures containing associated cycloparaffin rings and a multiplicity of short chains is highly desirable. While this work confirms the general validity and utility of available correlations, further advances in our knowledge of the viscous fractions of petroleum may have
to come from a thorough comparison of complete composition data for narrow fractions separated from lubricating oil with data for pure compounds. ACKNOWLEDGMENT
The authors acknowledge the valuable assistance of M. E. Peterkin and M. F. Brown with calculations conducted with the IBM 650. LITERATURE CITED
(1) Am. Petroleum Inst., Research Project 42, Pennsylvania State University,
University Park, Pa.
( 2 ) Andre, M. L., O’Neal, M. J., Jr., ANAL.CHEM.31, 164 (1959). (3) Boelhouwer, C., Waterman, H. I., J. Inst. Petrol. 40, 116 (1954). (4) Cornelissen, J., Waterman, H. I., Anal. Chim. Acta 15, 401 (1956). (5) Cornelissen, J., Waterman, H. I., J . Inst. Petrol. 43, 48 (1957). (6) Greenshields, J. B., Rossini, F. D., J . Phys. Chem. 67, 271 (1958). (7) Hastings, S. H., Johnson, B. H., Lumpkin, H. E., Williams, R. B., Am.
SOC.Testing Materials, Spec. Tech. Publ. 224, 250 (1958). (8) Kurtz, S. S., Jr., King, R. W., Stout, W. J., Partikian, D. G., Skrabek, E. 8., ANAL.CHEM.28, 1928 (1956).
(9) Kurtz, S. S., Jr., King, R. W., Stout, W. J., Peterkin, M. E., Ibid., 30, 1224 (1958). (10) Kurtz, S. S., Jr., King, R. W., Sweely, J. S., Ind. Eng. Chem. 48, 2232 (1956). (11) Kurtz, S. S., Jr., Martin, C. C., India Rubber World 126, 495 (1952). (12) Kurtz, S. S., Jr., Sankin, A., Ind. Eng. Chem. 46, 2186 (1954). (13) Martin, C. C., Sankin, A., ANAL. CHEM.25, 206 (1953). (14) Rossini, F. D., Mair, B. J., Streiff: A. J., “Hydrocarbons from Petroleum, Reinhold, New York, 1954. (15) Schiessler, R. W., Herr, C. H., Rytina, A. W., Weisel, C. A., Fischl,
F., McLaughlin, R. L., Keuhner, H. H., Proc. Am. Petrol. Inst. 26 (III), 254
(1946). (16) Schiessler, R. W., Whitmore, F. C., Ind. Eng. Chem. 47, 1660 (1955). (17) Smith. E. E.. Ohio State Universitv. ‘ Eng. Expt. Stat:, Bull. 152 (May 1953): (18) Stout, W. J., King, R. W., Peterkin, M. E., Kurtz, S. S., Jr., Am. SOC.Test-
ing Materials, Spec. Tech. Publ.
224,
230 (1958). (19) van Nes. K.. van Westen. H. A.. ‘
“AAspects of ’the eonstitution of Mineral Oils,” Elsevier, New York, 1951.
RECEIVEDfor review July 22, 1959. Accepted February 12,. 1960. 24th Mid-
year Meeting, Division of Refining, American Petroleum Institute, New York, May 1959.
Reducing Properties of Cerous Ion in Alkaline Media N. H. FURMAN and A. J. FENTON, Jr.’ Princeton University, Princeton,
N. J.
,The stoichiometric reactions of fer& cyanide and permanganate with cerous ion in strong carbonate solutions are described. Ferricyanide can b e titrated accurately in an inert atmosphere. An indirect method for determining glucose was developed in which the excess ferricyanide in a carbonate reaction mixture was determined with standard cerous sulfate. This method should b e applicable to the indirect determination of many substances that react slowly with ferricyanide.
T
of cerous ion as a reductant in carbonate solutions were studied. The titration of ferricyanide was chosen for extensive experimentation because of its nearly perfect reversibility, simple single-electron change, solubility of reactants and products, and utility as an oxidant in alkaline solutions. Ferricyanide under alkaline conditions is a suitable oxidant for the direct determination of manganous (I6),vanadyl (6),and cobaltous (14) HE PROPERTIES
Present address, Analytical Methods Research, The Procter & Gamble Co., Cincinnati 17, Ohio.
salts. It can a1 so be used for determining chromic ion, sodium arsenite, hydrogen peroxide, h j drazine (S),and reducing sugars (3) if an excess of reagent is used. Excess ferricyanide may be backtitrated with mercurous nitrate (4) in alkaline solutio is or with thiosulfate after acidificaticn and addition of zinc sulfate and potr ssium iodide. Cerous ion call be determined quantitatively by oxidation with ferricyanide in strong carbcnate solutions (2,18). Tomicek ( I S ) dc termined the end point potentiometrically, reporting satisfactory results deslite the small change in potential a t thrm end point. Leonard, Keily, and Huine (IO) have recently developed an arnperometric procedure and report exce lent results with sensitivity superior to the potentiometric method. During this work derivative, classical, and current inpiit potentiometry, titration to the precet potential, and solid electrode voltammetry were investigated as end point prccedures. The effect of atmospheric oxygen was increasingly deleterious as the concentration of reagents was owered. As little as 1.8 peq. (0.6 mg.) of potassium ferricyanide can be titrated with good ac-
curacy if a stream of inert gas is passed over the deaerated test solution. An indirect method for determining glucose was dereloped in which the excess ferricyanide in the carbonate reaction mixture was determined with standard cerous sulfate. A linear calibration curve was obtained over a reasonably large range of glucose concentrations. Because permanganate ion is also useful for alkaline oxidations, a few titrations were performed using cerous sulfate as titrant in carbonate solution. The reaction product of permanganate under the conditions employed is hydrated manganese dioxide. The precipitation of this gelatinous materisl on the indicating electrodes slowed electrode response so that 10 to 15 minutes were required per titration. The results are included only as an indication of accuracy and stoichiometry. APPARATUS AND REAGENTS
Potassium Ferricyanide. Solutions were prepared daily by dissolving accurately weighed quantities of an assayed reagent grade salt in distilled water. Assay was by the iodometric procedure to a starch end point in the presence of zinc sulfate. The result of VOL. 32, NO. 7, JUNE 1960
745
Table 1.
Determination of Ferricyanide"
Added
Av Dev. in Trials, P.P.T. k0.4 2.7 0.4 0.6
Found
Meq. Mg. Meq. Mg. 2.553 840.6 2.553 840.6 1,023 336.9 1.025 337.5 1,258 414.3 1.258 414.3 0.2530 83.31 0.2528 83.25 0.1027 33.82 0.1028 33.85 0.09800 32.27 0.09800 32.27 0.08133 26.78 0.08125 26.76 0.04082 13.44 0.04075 13.42 0.009544 3.143 0.009544 3.143 0.004082 1.344 0.004087 1.346 0.001801 0.5931 0.001798 0.592 a Results calculated as KaFe(CN)6. P = potentiometric, A = amperometric, DS potential, D = derivative potentiometric.
No. of
T.ype.b Indication D DbP
4 4
D DS, A , P P, DS
Trials 4 5 4
1.0 0.9
6
1. R
3.1 0
3.1 1.7
=
dead stop, T
=
titration, to preset
i3 k,; I
I
I
25
i 24 2s
Table II.
Adamson crystals (sp. rotation 52.5 to 53.0"). hloisture was removed by vacuum drying a t 38" to 40" C. for 12 hours. Solutions were prepared daily by weight. All other reagents were of reagent or analytical grade purity. Pipets and burets were calibrated. Apparatus. The potentiometric titrations were performed with a Leeds & Northrup vacuum tube voltmeter (Catalog No. 7664). A platinum foil electrode was used as indicator and a saturated calomel electrode as reference.
Titration of Permanganate"
Av. Dev. between Trials, P.P.T.
Taken, Found, No. of Meq. Trials Meq. 2.890 2.890 4 f0.7 2.901 2.901 2 0.5 0.5806 0.5801 4 2.6 0.2901 0.2898 4 0.5 0.05806 0.05797 5 3.5 Potentiometric end point procedure used throughout.
Table 111.
Determination of Glucose
Av. Net Meq. Cerous Used
Glucose Av. Dev. Taken, between Mg. ( X102)Q Trials, 0.538 1.79 =to. 57 . ~ . 1.026 3.42 0.30 1.613 5.37 0.19 1.974 6.54 0.18 2.460 8.10 0.37 2.962 9.66 0.30 Average of 3 or 4 determinations.
746
ANALYTICAL CHEMISTRY
C N M.
Figure 1. Derivative and potentiometric titration data A.
Derivative
8.
Potentiometric
potential employed in each case was chosen from potentiometric titration data and was +SO mv. us. S.C.E. when ferricyanide was titrated. The titration cell consisted of a beaker or large weighing bottle of suitable size fitted with a rubber stopper drilled with holes t o accommodate electrodes, deaeration tube, and the tip of a 50- or 10-ml. semimicroburet. A magnetic stirrer supplied the necessary agitation. PROCEDURES
M g . from
Equation
___
C).FlR(i - .
1.030
1.619 1.976 2.248 2.927
Difference, % ' -0.37 +0.39 +O .37 +o. 10 -0.45 -1.2
@
six determinations showed the punty to be 99.83 =t0.07%. Cerous Sulfate. A stock O.1N solution was prepared from the octahydrate (G. Frederick Smith Chemical Co., Columbus, Ohio) and contained enough sulfuric acid to make the resulting solution 0.2N in the acid. The stock solution was standardized by the persulfate method (1'7). The strength of the ferrous solution employed in the back-titration was obtained by titration with 0.02N ceric sulfate which had been standardized against NBS arsenious oxide. Aliquots of the stock solution were diluted to the desired concentrations. The persulfate method was used to assay the original cerous solution. Potassium Carbonate. A stock 60% (ca. 4M) solution was prepared from the anhydrous reagent grade salt. Potassium Permanganate. A 0.2N solution was prepared and standardized against NBS sodium oxalate in the usual manner. Glucose. Standard solutions were prepared by weight from the Baker &
O I N C E R O U S $0."-
For derivative titrations two identical platinum electrodes (1 sq. cm.) were employed. A 45-volt radio B battery and 22-megohm resistor were used to supply the necessary small constant current. The voltage changes were followed by the vacuum tube voltmeter (17 ) . Amperometric titrations were performed with the saturated calomelplatinum electrode pair with no external source of current. A microammeter (0 to 50 pa.) was used to indicate current. Dead stop titrations employed a polarizing voltage of 200 mv. tapped from a 1.5-volt dry cell by a radio potentiometer. Two identical platinum foil electrodes (1 sq. cm.) were used and the current was read from the microammeter. Titration to a preset potential was accomplished with the platinum-calomel electrode pair. The current was measured with a reflecting galvanometer (G. M. Laboratories, No. 2564B) with a sensitivity of 0.033 A. per mm. equipped with an Ayrton shunt. The preset
Determinations of Ferricyanide and Permanganate. The amount of 60% potassium carbonate added to the titration cell a t the start was so chosen that the carbonate concentration a t the end point was 20 to 25y0',. The contents of the cell were deaerated for 5 to 10 minutes with carbon dioxide, and the sample was added and titrated in a stream of carbon dioxide with the acidified cerous solution to the end point. The general end point procedures employed are described in detail elsewhere (6, 9, 11, 19); only the titration curves are giren here (Figures 1 and 2). The error due to an oxidation of cerous ion a t the 1-meq. level was 0.1 to 0.2%, whereas a t the 0.01-mea. level it was 3%. Determination of Glucose. 9 standard procedure was employed. Twenty milliliters of 4M potassium carbonate, 5.00 ml. of 0.025N potassium ferricyanide, and 5.00 ml. of glucose solution containing 0 to 3 mg. of glucose were added in this order to a 50-ml. beaker. The beaker was placed in a boiling water bath for exactly 15 minutes. After the heating period the beaker was cooled in a water bath maintained a t room temperature (23-4" C.) for 3 minutes, the sides of the beaker were rinsed with 2 ml. of distilled water, and the magnetic stirring bar was placed in the beaker. The solution was then titrated under a carbon dioxide atmosphere with 0.01N cerous sulfate to a potential of $0.076 volt (us. S.C.E.)
1
Figure 2. A.
Amperometric
0
Titration curves E. Dead stop
or until the galvanometer read zero, No pretitration was necessary. A blank conltaining distilled water was treated in the same manner as above to obtain the blank of the ferricyanide solution under these test conditions. The calibration curve was prepared by plotting the titration difference (milliliters of blank - milliliters for titration) X N cerous against milligrams of glucose taken. The linear relationship obtained is shown as curve A in Figure 3. To extend the range of glucose concentration to 5 mg., the concentrations of the reagents employed was increased twofold. Curve B of Figure 3 shows the nonlinear relationship obtained. RESULTS
Table I contains results for the determination of ferricyanide, Table I1 those for the determination of permanganate. The calibration curves for the glucose determinations are represented in Figure 3. An equation was derived from data for the determination of glucose (Table 111),to estimate the nonlinearity of the calibration curve. The equation used was, g = 0.303, x - 0.0007, where y = milligrams of glucose and 2 = net milliequivalents of cerous sulfate consumed. DISCUSSION
End Point Detection. The method for determining the end point in the titration of ferricyanide with cerous ion depends upon the concentration of titrant. Derivative potentiometric detection was insensitive when the cerous concentration was less than 0.02X. This insensitivity was evidenced by a rounded maximum a t the point of inflection and by the slow rise in potential preceding it. Potentiometric end point detection was useful and accurate over the whole concentration range studied. At titrant concentrations lower than 0.005N the
Figure 3.
I 40
I
I
1
I
2.0
8 0 C E l i l l I M I L L I E Q U I V XIO‘
EC
Calibration curves for glucose-ferricyanide titration
exact end point had to be ascertained graphically or by calculating the differential, dE/dV. Amperometric titrations made with either one or two polarized electrodes were equally effective. More trials were carried out using a single electrode and reference cell because the response Kas generally more linear. The method of choice, however, is titration to a preset end point potential. This method is extremely simple-requiring no graphing or volume correction-and titration continues until the current or galvanometer changes sign. Even with cerous solutions as dilute as 0.0005N the current change was extremely sharp. Determination of Glucose. The results for the titration of glucose show an accuracy about equivalent to that reported by Whitmoyer (16). The reduction equivalents or number of moles of ferricyanide reacting per mole of glucose is somewhat larger than that reported by Whitmoyer (16) or Hulme and Narain (7). This increase may be attributed to the greater ionic strength of the reaction mixture used here. The effect of ionic strength is discussed in some detail by Adams, Reilley, and Furman (1). Other Uses. The following substances did not react with cerous ion in 30% potassium carbonate solution: arsenic acid, potassium bromate, potassium iodate, potassium periodate, potassium perchlorate, potassium chlorate, quinone, hydroxylamine, and hydrazine. Hypochlorite, hypobromite, and hypoiodite reacted with cerous ions under these conditions but the over-all reaction was so slow as to be unsuitable for analytical purposes. Cerous ion reacted slowly with manganese dioxide if cerous ion was in great excess. The relative unreactivity of cerous ion in carbonate solutions can be attributed to its relatively high alkaline reduction
potential, zk0.085 volt us. N.H.E. in 25% potassium carbonate. Thus it reacts only with oxidants having high alkaline reduction potentials. It should be possible to determine ferricyanide selectively in the presence of some strong oxidants without prior separation. REFERENCES
(1)TAdams,R. N., Reilley, C. N., Furman, h. H., ANAL,CHEM.24, 1200 (1952). (2) Brauner, B., Chem. News 71, 283 ( 1895). (3) Brown, C.A., Zerben, F. W., “Physi-
cal and Chemical Methods of Sugar Analysis,” Wiley, New York, 1941. 14’1 Burriel. F.. Anal. Chzm. Acta IO, 301 \
1
,
,
(1954). (5) Cooke, W.D.,Reilley, C. N., Furman, N. H., ANAL. CHEW23, 1662 (1951). (6) Del Freeno, C.,Valdes, L., Anales SOC. espaii,f;?s.y quim. 27, 368 (1929). (71 Hulme. A. C.. Karain, R., Biochem. J. is, i051‘(193ij. (8) Job, A , , Ann. chim. et phys. 20, 205 ~
(1900’1. \ - - - - ,
(9) Knowles, G., Lowden, G. F., Analyst 78, 159 (1953). (10) Leonard, G. W., Keily, H. J., Hume, D. N., Anal. Chim. Acta 16, 185 (1957). (11)Reilley, C. N., Adams, R. N., Furman, N. H., ANAL.CHEM.23, 1223 (1951). (12) Stamm, H., “Die Reduktion des
Permanganats zu Manganat als Grundeines massenanalytischen Verfahrens,” Neuere massanalytische Methoden, G. Jander, ed., F. Enke Verlag, Stuttgart, 1956. (13) Tomicek, O.,Rec. trav. chim. 44, 410 lage
(1920). (14) Tomicek, O.,Freiberger, F., J. Am. Chem. SOC.57,801 (1935). (15)Tomicek, O., Kalny, J., Ibzd., 57, 1209 (19351. (16) Whitmoyer, R. E., IND. ENQ.CHEM., ANAL.ED.6, 268 (1934). (17)Willard, H. H., Young, P., J . Am. Chem. SOC.50, 1379 (1928). (18) Winkler,. C.,, J. prakt. Chem. 79, 261 (1860) (19)Wooster, W. S., Farrington, P. S., Swift, E. H., ANAL. CHEM.21, 1457 (1949). ~
RECEIVED for review December 21, 1959. Accepted March 18, 1960. Taken from Ph.D. dissertation of A. J. Fenton, Jr., Princeton University, 1958. VOL. 32, NO. 7, JUNE 1960
747
