ANALYTICAL EDITION
October, 1946 ACKNOWLEDGMENT
The samples of A.P.I.-X.B.S. hydrocarbons were made available by the American Petroleum Institute and the National Bureau of Standards through A.P.I. Research Project 44 on the Collection, Analysis, and Calculation of Data on the Properties of Hydrocarbons. The samples were purified a t the National Bureau of Standards by A.P.I. Research Project 6 on the Analysis, Purification, and Properties of Hydrocarbons, under the supervision of Frederick D. Rossini, from material supplied by the following laboratories: o-xylene, Standard Oil Development Company, Elizabeth, N. J., through the courtesy of William J. Sweeney; 2,2-dimethylbutane, A.P.I. Research Project 6 a t the Sational Bureau of Standards; the four methylnonanes by t,he Ethyl Corporation through the courtesy of George Calingaert; all others by A.P.I. Research Project 45 on
613
the Synthesis and Properties of Hydrocarbons of Low Molecular Weight, a t the Ohio State University under the supervision of Cecil E. Boord.
a
LITERATURE CITED
(1) -4m. SOC.Testing Materials, “A.S.T.M. Standards on Petroleum Products and Lubricants”, p. 398 (1944). (2) Andrade, E. N., Nature, 125,309 (1930). ANAL.ED.,16, 708 (1944). (3) Cannon, M. R., IXD.EXG.CHEM., (4) Cannon, M. R., and Fenske, M.R., Ibid., 10, 297 (1938). ( 5 ) Evans, E. B., J . Inst. Petroleum Tech., 24, 38, 321 (1938). (6) Skrinivasan, M.K., and Prasad, B., Phil. Mag., 33, 258 (1942). PARTof a thesis submitted by J. AI. Geist in partial fulfillment of the requirementa for the degree of master of science in chemical engineering a t T h e Pennsglvania State College.
Chromatographic Resolution of the Quinone Oximes D.
K. GULLSTROM, H. P. BURCHFIELD,
AND
J. N. JUDY
Development Department, Naugatuck Chemical Division, United States Rubber Company, Naugatuck, Conn.
A chromatographic procedure is described for the separation of pbenzoquinone monoxime from p-benzoquinone dioxime and products of side reactions which take place during the nitrosation of phenol and oximation. The sample i s dissolved in acetone and adsorbed on a column of activated alumina. The monoxime forms a brilliant green band which i s removed from the column and eluted with aqueous sodium hydroxide. The concentration is determined b y spectrophotometric mea:urements at 363 and 399 mp. The chromatographic resolution and optical properties of the ortho isomers are also discussed,
I), while that of the neutral molecule in acid solution is a t 301.5 mp. Anderson and Yanke ( 1 ) point out that the absorption spectrum of the system is sensitive to changes in hydrogen-ion concentration between pH 3 and 7 and is independent of this factor in more strongly acid or alkaline solutions. In order to ensure reproducibility of the extinction coefficients,and provide a I
I
I
1
OTH p-benzoquinone dioxime and its derivatives have been used for the nonsulfur vulcanization of rubber (8), and are of current interest for the vulcanization of GR-I. The parent compound is usually formed by the nitrosation of phenol ( l 7 ) , followed by oximation (13).
0 OH + HNO~-+
c-)OH I , Y O H = ( ==-~=O + H~NOHHON = CT - = SOH ON
During the course of work on the preparation of this material it was of interest to follow the rate of oximation, and determine the concentration of unreacted monoxime in the final product. As this substance is tautomeric with p-nitrosophenol, a method described by Clauser (5) for the determination of the nitroso group by reaction with phenylhydrazine and measurement of evolved nitrogen was investigated. However, under these conditions a large volume of gas is obtained from the dioxime. Both compounds are reduced by potassium iodide in hydrochloric acid solution (e),but the reduction of the monoxime proceeds more rapidly. This suggested the possibility of a polarographic analysis. At a pH of 7.0 in a phosphate buffer, the half-wave potential of the monoxime was found to be 0.15 volt more positive than that of the dioxime, and on solut,ions of the pure compounds, the diffusion currents are well defined. However, an unresolved wave is usually obtained on the crude product, owing to an unfavorable concentration ratio and the presence of other electroreducible materials in the mixture. p-Benzoquinone monoxime is readily soluble in dilute sodium hydroxide with the formation of the sodium salt, Fhich is believed to exist largely in the ionized quinone oxime form ( 1 , 10). The principal absorption maximum of the ion is a t 399 mp (Figure
I
‘540
460
38 0
300
220
MILLIMICRONS
Figure 1. Absorption Spectra of Quinone Oximes in 0.1 N Aqueous Sodium Hydroxide Solution 1. p-Benzoquinone monoxime II. p-Benzoquinone dioxime
medium in which the product is sufficiently soluble, the quantitative measurements described in this paper were made in 0.1 N sodium hydroxide solution. Quinone dioxime behaves in an analogous manner. The principal maximum attributable to the free ion is a t 363 mp (Figure l),while that of the neutral molecule occurs a t 317 mp (Figure 2). As both compounds obey the BeerLambert law within experimental error, a direct calculation of the composition of a binary mixture is possible from optical readings made a t 363 and 399 mg on solutions of the sodium salts, providing no interfering substances are present and the concentration ratio is favorable. As these conditions cannot be predicted, and in general are not satisfied, it is necessary to remove the products
Vol. 18, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY
614
of side reactions which take place during the nitrosation of phenol and concentrate the monoxime a t the expense of the dioxime xvithout loss of the former. Khen a solution of the crude oximation product in acetone is percolated through a column containing activated alumina, the constituents of the mixture adsorb in easily distinguishable zones which can be further resolved by washing the column with a more polar solvent. The monoxime forms a green zone, while the dioxime forms a brilliant yellow zone. The schematic diagram (Figure 3) illustrates the separations normally obtained. Band I is dark brown in color, and contains an amorphous material of indefinite composition produced by resinification of the monoxime ( 1 7 ) . Band I1 contains p-benzoquinone monoxime, and Band 111, p-benzoquinone dioxime. In the lower section of the column, narrow blue, red, and yellow bands appear which are completely removed from the column during development with solvent. The initial fraction of the percolate is orange yellow in color, and contains substances not readily adsorbed from acetone by alumina. On evaporation of the solvent and readsorption from petroleum ether, these materials can be further resolved. The green zone containing quinone monoxime initially forms directly below the brown resinous material and is not readily separated from it by continued washing. Complete resolution is achieved by treatment of the column with a dilute solution of acetic acid in acetone. The acid is adsorbed less strongly than the resinous material, and more strongly than the monoxime which results in the formation of a colorless zone between the two materials. The development of the column is completed by washing w i t h 300 ml. of a 5% solution of methanol in acetone. The effect of this solvent is to wash the lower zones and part of the dioxime into the percolate, and improve the separation of the oximes. A4tthe end of this treatment the green zone contains all of the monoxime but is contaminated with 20 t o 3570 dioxime tvhich is not readily removed by further washing. As a spectrophotometric correction can be made for residual dioxime, a complete separation is unnecessary. The analytical values in Table I show that after 300 ml. of solvent have been used the results are independent of the volume of solvent used in developing the chromatogram and the purity of the zone.
BROWN 6AND STRONGLY ADSORBED RFSINOUS MATERIALS
I
GREEN BAND p . BENZOQUINONE
YELLOW BAND . 6ENZOOUINONE
O ,
BLUE RED AND Y E L L & + BANDS WEAKLY ADSORBED I " ~ I R I T I E S
i3r-E
YELLOW ORANGE -!?LOLATE N ON-A DSORBA BL E '.'WRI TIES
m Figure 3.
Chromatographic Resolution of Crude p-Benzoquinone Dioxime
Table I . Effect of Volume of Solvent Used in Development of Chromatogram on Results of Monoxime Analysis and Purity of Zone Monoxime Found
Solvent
%
%
4.9
72
MI. 0 1.no ..
Dioxime in Monoxime Zone
28 ~.
6 5
34 23 25 35 20
200 300
500 800
1000
I
I
I
I /
Table Compound p-Benzoquinone monoxime p-Benzoquinone dioxime
2ml1 1 ; I
_5 A 0_
460
380
300
220
MILLIMICRONS
Figure 2. Absorption Spectra of Quinone Oximes in 0.1 N Aqueous Sulfuric A c i d Solutions 1. p-Benzoquinone monoxime II. p-Benzoquinonedioxime
The analysis is completed by separating the adsorbent containing monoxime from the rest of the column and eluting i t with aqueous sodium hydroxide. A yellow-brown solution is obtained on which the monoxime content is determined by absorption measurements a t 399 and 363 m p . In making the analysis as outlined, low results are obtained owing t o incomplete elution of the material from the adsorbent. Experiments made on the pure compound indicate that the average recovery is 95.0 =t 0.870',. When this factor is incorporated into the calculations, mwlts close t o theory are Obtained.
II. Analytical Constants
K at 399
mp
Slit Setting
224
Mm. 0.10
283
0.10
K a t 363 109 65.7
nip
Slit Setting A4 m 0.15
.
0.15
where D A and ~ Dx2 arc the measured optical densities a t 399'and 363 mu, G is the sample weight, V is the volume in liters to which the solution is diluted, K'xl and K Aare ~ the specific extinction coefficients of the monoxime a t 399 and 363 mp, K ' A and ~ K'x2 are the specific extinction coefficients of the dioxime at 399 and 363 mp, and F is the decimal per cent monoxime recoverable after adsorption on alumina. This equation is a modification of the type generally used in the spectrophotometric analysis of binary mixtures where the absorption bands overlap. Details concerning the derivation are given b x Ashley (3). Spectrophotometric constants determined on solutions of the pure compounds in 0.1 3 sodium hydroxide are shown in Table 11. The optical measurements were made with a Beckman RIodel DU spectrophotometer in 1-cm. quartz cells, using a tungsten lamp and a red purple filter. Both compounds obey the Beer-Lambert law within experimental error a t concentrations corresponding to a density range of 0.4 t o 1.0. APPARATUS
Adsorption columns are conveniently made from 35-cm. lengths of 18-mm. outside diameter Pyrex tubing constricted t o an internal diameter of about 0.5 cm. about 10 cm. from the end.
ANALYTICAL EDITION
October, 1946 Table
111.
Analyses of Synthetic Mixtures
Monoxime Added
Monoxime Found
%
%
%
5,5 4.3 4.5 4.6 6.5 4.9 5.8 6.0 7.8 4.8 4.8 7.0
5.7 3.9 4.3 4.4 6.7 5.5 5.5 6.2 8.0 5.0 4.8 6.9 5.58
+0.2 -0.4 -0.2 -0.2
A\‘. 5 . 54
Table
Deviation
+o. 2
+O. 6 -0.3 +0.2 +0.2 +0.2 0.0 -0.1 t0.23
IV. Analysis of Crude Reaction Products
hIonoxirne,% Dioxime, yo Resinous in&terial, % Inorganic, % Total
4.9 90.7 2.6
5.6 84.5 4.5
3.5 79.4 14.6
0.8
2.9 97.j
1.6
99.0
4.8 77.8 10.9
4.4 91.3 3.1
1.1
0.1
94.6
98.9
The shorter end is connected to a suction flask and the constriction plugged with glass wool. The column is filled t o a height of 15 cm. with a mixture of 90 parts by weight of grade F-1 €%mesh activated alumina (Aluminum Company of America) and 10 parts of Hyflo Super-Cel (Johns Manville Company) which is included to increase the percolation rate, The adsorbent is added to the column in 2- to 3-cm. portions and tamped firmly into place with a wooden dowel. Solvent is delivered continuously to the head of the column from a 500-ml. separatory funnel. REAGENTS
Anhydrous analytical reagent grade solvents are used for the preparation of the chromatogram. The column is developed wit,h a 1% by volume solution of acetic acid in acetone and a 5% solution of anhydrous methanol in acetone. The adsorbent is eliitJed with aqueous N sodium hydroxide. PROCEDURE
A I-gram sample is dissolved in 100 ml. of acetone under reflux and filtered through a tared Selas crucible to remove acetoneinsoluble resin and inorganic constituents. If desired, the amounts of these materials can be determined by the usual gravimetric procedures. The filtrate is reduced t o half its original volume on a steam bath and after cooling percolated through a column containing the adsorbent. The column is then washed with 10 ml. of acetic acid solution, followed by 300
615
ml. of methanolin acetone. The top brown layer is removed with a spatula and discarded. The green segment is transferred quantitatively t o a 250-ml. beaker and eluted with successive portions of sodium hydroxide. A total volume of about 100 ml. is required. The separation of the yellow zone need not be complete, as a correction for residual dioxime is made in the calculations. After filtration, the elutriate is diluted to 1 liter with distilled water and then rediluted t o a concentration a t which optimum optical density readings can be obtained. The measurements are made a t 399 and 363 mii. with a Beckman spectrophotometer. PRECISION AND ACCURACY
The appearance of the adsorption column is subject to variation, depending on the composition of the sample and differences in the techniques used in preparing and developing the c,hromatograms. Impurities in the solvents and changes in the adsorptive capacity of the alumina may alter the widths ,>f the bands formed from equal amounts of monoxime. Although a measurement of the band width will not give a quantitative estimate of the concentration, the appearance of a green zone provides direct visual evidence of the presence of the monoxime. -1band widt,h of 2 to 6 mm. is obtained on samples containing 10 nig. of this compound. Thus, the method is sufficiently sensitive to establish the presence of this substance in mixtures in which it occurs Do the extent of less than 1%. I n order to evaluate the accuracy of the method under the conditions normally encountered in the analysis of crude reaction products, weighted quantities of the pure monoxime were added t o a sample on which a preliminary analysis of 5.6% was obtained. This value was then subtracted from the analytically determined results. This information is shown in Table 111. The average deviation is +0.23%, while the average of the analytically determined values is 0.04% higher than theory. The precision of the method as determined by the analysis of 64 samples in duplicate by a routine analyst is *3.6% of the materid present. This series included samples containing from 2 to 55% quinone monoxime. The use of t.his method for the analysis of crude reaction products is illustrated by the data in Table IV. The quinone dioxime content of the materials was determined by a gravimetric procedure based on it’s oxidation to polymeric “p-dinitrosobenzene” (IS) with potassium ferricyanide in a carbonate buffer. The materials in bands IV t o VI and the percolate are not included in the analyses. These values are not representative of the yielda obtained on nitrosation and odmation, as the determinations w,ere made on samples which were partly purified by separation from the mother liquor. While the results obtained by the chromatographic procedure are not comparabk in precision to those obtained by direct spectrophotometric methods under favorable conditions, in this application the removal of interfering impurities and the concentration of the minor constituent permits a reasonably accurate analysis which would otherwise be impossible to obtain. DISCUSSION
2 540
460 380 MILL 1MlCRONS
300
220
0,
Figure 4. Abror tion Spectra of Quinone Oximes in 0.1 N /&ueous Sodium Hydroxide
Solution I.
0-Benzoquinone monoxime II. o-Bcnzoaulnone dioxlmc
The para isomer is the principal reaction product formed in the nitrosation of phenol. However, Veibel (17) has shown that as much as 10% of the o-nitrosophenol may be formed under certain conditions. As this compound is tautomeric, oximation would result in the presence of o-benzoquinone dioxime in the crude product. In order to investigate the possibility of interference from this source, the chromatographic behavior and optical p r o p erties of the ortho isomers were investigated. The experiment,al data are outlined in Table V. Both ortho isomers adsorb above p-benzoquinone dioxime, and if present, can be mechanically removed from the column before elution. I n the reaction products examined, these bands were not evident, probably owing to loss by solubility of the o-monoxime in the mother liquor.
616 Table
INDUSTRIAL AND ENGINEERING CHEMISTRY V. Chromatographic and Spectrophotometric Properties of Quinone Oximes o-L!onoxime
Position of band Color of band Am-. (ion) (mp) ernax. (ion) Amax. (molecule) ( m r ) tmiix.(molecule) Dipole moment ( p X
I
Red 470 6,130 400 1,110
o-pioxinie
p-hlonoxime
p-Dioxime
I1
I11
IV
Orange 433.5 5,600 396 5,720 3.84
Green 399 27,570 301.5 16,620 4.72
Yellow 363 39,010 317 23,300 2.37
10’8)
The isomeric dioximes are adsorbed in the order of their dipole moments, the ortho isomer with a moment of 3.84 D (11) forming the upper orange band, and the para isomer with a moment of 2.37 D forming the lower yellow band. This behavior is analogous to that of the position isomers of benzene, and to the cistrans isomers of azobenzene in which the compound n-ith the higher dipole moment is usually most strongly adsorbed ( 2 , 15). The moment of p-benzoquinone monoxime in dioxane solution has been reported to be 4.72 D (7). This compound is adsorbed between the 0- and p-dioximes. Data on the electric moment of the o-monoxime are not available. However, a direct correlation between dipole moment and adsorbability should not necessarily be expected in this case, owing to possible shifts in the tautomeric equilibria. The o-monoxime is adsorbed as a red band a t the top of the column, while the para isomer appears as a green band. This suggests that the ortho compound is adsorbed in the quinoid form, while the para isomer is adsorbed as p-nitrosophenol, for the green color is similar to that of compounds containing the free nitroso group (14). The proximity of the functional groups in the ortho compound, on the other hand, might lead to chelation with the adsorbent. This would tend to shift the equilibrium to the quinoid modification. A more direct correlation is observed between the order of adsorption and the wave lengths of the spectrophotometric maxima in alkaline solution. In this case the compounds which absorb light of longer wave length are bound mor: tightly. It is evident that the compounds are polarized by contact with the alumina, for the free acids are pale yellow to almost colorless. While the formation of colored bands is not requisite to a good separation, it is of great practical convenience in locating and distinguishing between the adsorbed compounds. Owing to restricted rotation about the C=N bond, the exisb ence of cis-trans isomers of the benzoquinone dioximes was considered possible. However, under the experimental conditio& described, the bands appear homogeneous and no differences in properties can be detected between materials eluted from the upper and lower portions of the columns. The choice of the solvent, adsorbent, and eluant was guided by a consideration of the physical properties of the compounds. Acetone is the only solvent readily available in which they are easily soluble and from which they can be adsorbed by alumina. However, it is difficult to free from traces of water and alcohol and undergoes a condensation reaction in contact Kith the adsorbent which results in the presence of a high-boiling liquid in the percolate (18). These factors may cause variations in the widths of the bands, and complicate recovery of the impurities found in the percolate, but otherwise do not interfere with the analysis. Alumina, magnesia, talc, silica gel, and a number of other materials were tested as adsorbents, but, aside from alumina, magnesia was found to be the only one of potential value. Of the possible eluants, aqueous sodium hydroxide is the most effective. The compounds are readily removed from the adsorbent and optical measurements can be made directly on the filtered and diluted solutions without further adjustments. The chromatographic adsorption method of Tswett (16) has found extensive use in the purification and estimation of naturally occurring substances. However, applications in the field of in-
Vol. 18, No. 10
dustrial organic analysis have been comparatively few. This may in part be ascribed to the relatively poor precision obtained when compared to standard gravimetric and volumetric methods, and to the small quantities of materials which can be isolated on columns of convenient size. However, when used in conjunction with absorption spectrophotometry, the usefulness of both methods is greatly extended, for the small amounts of materials recovered from the column can often be measured conveniently, while frequently compounds can be separated which would otherwise produce unresolved absorption spectra. While optical methods have been proposed in xhich a number of constituents are determined from a series of measurements made on a complex reaction mixture, it is evident that they are completely valid only in cases where the qualitative composition of the mixture can be predicted with certainty. If the properties of the materials permit, a preliminary separation will frequently augment the reliability of the analysis. EXPERIMENTAL
p-Benso uinone monoxime was prepared by the nitrosation of phenol, ana purified by repeated recrystallizations from water until a pale yellow product was obtained with a melting point of 1%”c. o-Benzoquinone monoxime was prepared by the oxidation of phenol with hydrogen peroxide in the presence of cupric acetate and hydroxylamine hydrochloride (4). The reaction mixture was acidified and extracted with petroleum ether and the monoxime concentration determined iodometrically (6). Spectrophotometric measurements were made on a solution obtained by extracting an aliquot of the petroleum ether with aqueous sodium hydroxide. p-Benzoquinone dioxime was prepared by oximation of the monoxime with hydroxylamine acid sulfate. The crude product was adsorbed on alumina the zoves containing impurities removed and discarded, and the dioxime displaced by treatment with a solution of acetic acid in acetone. After evaporation of the solvent, the product was further purified by precipitation from acetone solution by the addition of petroleum ether. A pale yellom product was obtained with a decomposition point of 239’ C. o-Benzoquinone dioxime was prepared by the oxidation of 0nitraniline with sodium hypochlorite (9),followed by reduction of the benzfurazan oxide with sodium hydrosulfide. The crude product was dissolved in aqueous ammonia, filtered and precipitated by the addition of acetic acid. Yellow needles with a melting point of 145” C. were obtained. ACKNOWLEDGMENTS
The methods for the gravimetric determination and purification of p-benzoquinone dioxime were devised by H. P. C. Burrell. Many of the spectrophotometric measurements were made by Virginia S. llartin. LITERATURE CITED
(1) Anderson, L. C., and Yanke, R. L., J . Am. Chem. SOC.,56, 732 I1 934). \ - - - - I
(2) Arnold, R. T., Ibid., 61, 1611 (1939). (3) Ashley, S.E. Q., IND.ENG.CHEM.,ANAL.ED.,11, 72 (1939). 14) . . Baudisch, 0.. and Smith, S. H., .~aturwissenschuften, 27, 769 (1939). (5) Clauser, R., Ber., 34,889 (1901). (6) Cooper, E. A., and Forstner, G. E., J . SOC.Chem. I n d . , 45, 94T - - - (1926). \----,-
(7) Cowley, E. G., and Partington, J. R., J . Chem. S O ~ 1933, ., 1252. (8) Fisher, H. L., U. S.Patent 2,170,191(1939). (9) Green, A. G., and Rowe, F. M.,J . Chem. SOC.,101,2452 (1912). (10) Hodgson, H. H., I b i d . , 1937,520. (11) . . Milone. M., and Tappi, G., Atti X’ Congr. I n t e r n . Chim.,2, 352 (1938). (12) Nietzki, R., and Guiterman, A. L., Ber., 21, 428 (1888). (13) Nietzki, R., and Kehrmann, Fr., Ibid., 20, 613 (1887). (14) Sidgwick, N. V., and Taylor, T. W.J., “Organic Chemistry of Nitrogen”, p. 206, London, Oxford University Press, 1937. (15) Strain, H. H., “Chromatographic Adsorption Analysis”, p. 18, New York, Interscience Press, 1942. fit? - _,Tqwptt,. - - - ., M.. Ber. deut. botan. Ges.. 24. 384 (1906). . . (17) Veibel, S.,Ber., 63B, 1577 (1930). (18) Zechmeister, L., and Cholnoky, L., “Principles and Practice of Chromatography”, p. 5, New York, John Wiley & Sons, 1941. ~
