noticeable positive errors even a t p H 2.0 (compare Tables I and 11). This might be thought to be due to a n increase in the B factor for iron. However, as this increase is small and accurate titrations for iron alone a t p H 2 to 3 are easily accomplished, the blame for erroneous iron results must rest on the aluminum. Although the concentration of alumi-, num-hydroxy complexes is believed to be negligible below pH 3 (8),the establishment of equilibria is notoriously slow. I n addition, mixed complexes of aluminum, hydrogen ion, and EDTA can esist in the p H range under consideration ( 2 ) . For these reasons aluminum is apparently able to compete with the iron to a slight extent for complexation above pH 2 but not a t p H 1. Flaschka and Abdine (5) have devised a procedure for the determination of aluminum alone or the sum of iron and aluminum by titrating a boiling solution of the metal ions with EDTA to a copper-PAX end point a t p H 3.0. This method may be applied to the determination of aluminum directly following the spectrophotometric titration of iron. Ammonium acetate vias used to adjust the pH to 3.0. Several
Table II. Determination of Iron-Aluminum Mixtures a t pH 1.0 b y Titration with EDTA
(End point found spectrophotometrically) -41 PresFe Fe ent, Present, Found, Error, Ng. Mg. 70 Mg. 0 60.9 60.Ta -0.3” 5-~1
60.7
ACKNOWLEDGMENT
The authors thank Hermann Flaschka for his many helpful discussions and suggestions. LITERATURE CITED
-0.3
60.5 -0.7 60.9 0 121.8 121.2 -0.6 55 80 -0.12 55.87 55.77 -0.18 55.83 -0.07 55.77 -0.18 5.59 5.64 $0.9 5.74 +2.7 5.76 +3.0 5.79 $3.6 iiverage of 9 determinations.
51 102 51 0 50 100 150 0 5 25 50 (1
be necessary rather than the direct titration of Flaschka and Abdine.
typical iron-aluminum mixtures were determined by the combined procedures with an accuracy to 0.3%. Slightly more than enough EDTA to complex all the iron must be added to establish the base line of the spectrophotometric titration curve. If the amount of aluminum is smaller than the excess, a back-titration method would
(1) Agren, Allen, Acta Chem. Scand. 8 , 266 (1954). (2) Bjerrum, Jannik, Schwarzenbach, G., Sillin, L. G., “Stability Constants,” Part I, Chemical Society, London, 1957. (3) Cheng, K. L.,Bray, R. H., Kurtz, T., ANAL.CHEM.25,347 (1953). (4) Flaschka, H.A., “EDTA Titrations,” Pergamon Press, London, 1959. (5) Flaschka, H.A , , Abdine, H., 2.anal. Chem. 152, 77 (1956). (6) Schwarzenbach, Gerold, “Complexometric Titrations.” Interscience. New York. 1957. (7) Sweetser, P.B.,Bricker, C. E., ANAL. CHEM.25,253 (1953). (8) Wanninen, Erkki, Ringbom, A,, Anal. Chim. Acta 12,308 (1955). (9)Welcher, F. J., “Analytical Uses of Ethylenediaminetetraacetic Acid,” p. 209, Van Nostrand, Princeton, N. J., 1958. (10) Ibid., p. 222.
RECEIVEDfor review July 29, 1959. Accepted November 6,1959.
Carbon-Hydrogen Stretching Frequencies STEPHEN E. WIBERLEY, STANLEY C. BUNCE, and WALTER H. BAUER Department o f Chemistry, Rensselaer Polytechnic Instifufe, Troy, N. Y. b A correlation chart of the carbonhydrogen stretching region is presented and discussed. Spectra of 10 cyclobutyl compounds and 60 aromatic compounds in the region of 2700 to 3 1 00 cm.-l are shown. This information should prove of value in spectrastructure correlation studies of related materials.
length region are summarized in Figure 1. The range for the various groups is shown, the average value for the group being indicated by a short line over the range. The maximum and minimum values are based on current spectra and undoubtedly as more data become available these ranges will broaden. ALIPHATIC C-H COMPOUNDS
B
lithium fluoride prisms free of the hydrogen fluoride absorption band are now generally available, and with the advent of commercial infrared spectrometers which have a grating attachment for a sodium chloride prism, it seems pertinent to review the information which can be obtained by studying spectra measured with such a prism or a grating attachment. In addition, new data on cyclopropyl, cyclobutyl, and 60 aromatic compounds are presented. In particular the region involving carbon-hydrogen stretching frequencies -namely, from 2700 to 3100 cm.-’-is covered. The correlations in this wave ECAIJSE
Bellamy ( 2 ) has reviewed thoroughly the work of Fox and Martin (6) on hydrocarbons and Pozefsky and Coggeshall (22) on compounds containing sulfur and oxygen. As shown in Figure 1, the CH, bands occur a t 2960 and 2870 cm.-’ and the CH2 bands a t 2930 and 2860 cm.-l. In many cases only one band in the region of 2860 to 2870 cm.-’ can be resolved. In a given straight-chain homologous series such as the fatty acid series, the CHBband a t 2960 is stronger than the CH2 band a t 2930 when the ratio of methylene to methyl groups is 4 to 1 or less (8). With larger ratios the 2930 band is more intense. TT7ith branched-
chain acids the ratio need only be 3 to 1 before the relative intensities reverse. However, exceptions to this rule occur when the methyl group is adjacent to the carboxyl group, as is shown by the comparison of 2-methylhexanoic acid with 3-methylhexanoic acid (9). In Figure 1 the frequency range for the methyl and methylene groups in compounds containing oxygen and sulfur has been determined from the data of Pozefsky and Coggeshall ( 2 2 ) . For oxygenated and sulfur-containing compounds the methyl and methylene bands are approximately 7 cm.-l higher and the extinction coefficients are greater than for the corresponding hydrocarbons. .A single methyl group attached to-a nitrogen atom gives rise to a band in the 2780- to 2805-cm.-l range when the group is in an aliphatic or a nonaromatic heterocyclic system ( I S ) . In an aromatic system the band is between 2810 and 2820 cm.-l. Two methyl groups attached to a nitrogen atom yield two bands: one between 2810 and72825 crn.-l and the other between 2765 and VOL. 32, NO. 2, FEBRUARY 1960
217
2775 cm.-l. However, if the nitrogen is directly connected to an aromatic system, only one band occurs near 2800 cm.-l. This correlation applies only to amines and not to amides. The methoxy group (fa) absorbs in the same region-namely, 2815 to 2832 cm.-l. The CH group in aliphatic aldehydes (19, 22) gives rise to two bands: one at 2720 cm.-l and the other a t 2820 cm.+. I n the case of compounds containing
CM." 3m
I
I
3000 12972-2S52
ASYM- CH,
2992 -2955
2900 I
HYDROCARBONS
2800 I
2700
SULFUR,OXYGEN
SYM ASY M
- CH,
\
the -CH group there is a weak band a t
/
2890 cm.-' for hydrocarbons, but this assignment does not hold for oxygenated materials. Compounds containing =CHs and =CHR groups have been studied in some detail by Tallent and Siewers (25). Bellamy (2) states that the RHC=CH:! groups exhibit two bands, one between 3077 and 3092 cm.-' and one between 3012 and 3025 cm.-l. The high frequency band is assigned to the =CHI group and the low frequency band to the =CHR group. ALIPHATIC RING COMPOUNDS
Plyler and Acquista (20) have studied the location of the CH, vibrational bands for three-, five-, and six-membered ring systems. For cyclopropane they report values of 3103 and 3024 crn.-l, for cyclopentane 2952 and 2866 cm.-l, for cyclopentene 2959 and 2853 cm.-l, for cyclohexane 2927 and 2854 crn.-l, and for cyclohexene 2927 and 2851 cm.-'. Thus, the sixmembered ring system has bands coincident with the usual CH, range. I n addition, the presence of a double bond in the ring has little effect on the CHI frequencies. Although the symmetrical CH2 band lies in the normal CH2 range for the five-membered rings, the unsymmetrical CH2 band occurs a t a higher value than the maximum shown for the range even for oxygenated compounds. This fact has been re-emphasized by Hastings
Table I.
2812 d Z 6 l 5
Figure 1 .
Correlation chart of carbon-hydrogen stretching frequencies
et al. (10) in their quantitative analysis of hydrocarbon functional groups. Actually this band a t approximately 2952 cm.-1 just overlaps the symmetrical CHI range. The cyclopropyl CH2bands are easily distinguished from the straight-chain CHI bands, as has been demonstrated by Wiberley and Bunce (26). The band a t approximately 3020 cm.-l is the symmetrical stretching and the one a t 3085 cm.-' is the unsymmetrical CHI stretching vibration. In this laboratory (3, 17, 21) the spectra of more than 60 monosubstituted cyclopropanes, including those with alcohol, amine, azide, carbonyl, carboxylic acid, ester, ether, halide, and nitrile functional groups, have been obtained. The range for the first band was 2995 to 3033 cm.-' and for the second band 3072 to 3099 cm.-'. Allen et al. (I) question not the validity
Infrared Frequencies of Cyclobuty! Derivatives in the Carbon-Hydrogen Stretching Region
Compound4 Cyclobutane (gas) Cyclobutanecarboxylic acid Cyclobutylamine
Wave Numbers, Cm.-l 3190
Cyclobutyl bromide Cyclobutylcarbinol Diethyl cyclobutane-1,l-dicarboxylate Ethyl 2-cyanocyclobutane-1-carboxylate 1-Phenyl-1-cyanocyclobutane
2900 2946 2862 3067 3035 Bandun- 2962 2925 2888 resolved 2855 2987- 2946 2920 2863 2977 2929 2858 2983 2955 2902 2870 2987 2970 2910 2874 3441
ANALYTICAL CHEMISTRY
2999
5914
2886 2874 2859 1-Phenyl-1-cyano-2-methylcyclobutane 3088 3061 3030 2963 2924 2865 1-Phenyl-1-cyano-3-methylcyclobutane 3081 3061 3027 2980 2953 2866 4 The first six compounds, excluding cyclobutane, were prepared by Stein in this laboratory by methods reported in the literature. The three phenylcyclobutane derivatives were prepared by Kluge (16).
218
3083 3060 3038
2990 2982
but the value of this assignment in qualitative ivork. These authors point out that it would be unrealistic to expect both bands in compounds containing only CHR or CR2. They also point out that Tallent and Siewers, as well as Henbest et al. (fl), show that there is close correspondence between C-H absorptions in a three-membered carbocyclic ring and those in an epoxy system. For example, Tallent and Siewers report bands for epichlorohydrin a t 3003 and 3058 cm.-l. One of these bands occurs in the cyclopropyl range, but the other does not. Henbest et al. in a study of epoxides showed a band in the range of either 2990 to 3004 cm.-l or 3029 to 3050 cm.-l, but only one out of a dozen compounds showed both bands. In the case of the epoxide ring in a polycyclic system such as a steroid molecule, the epoxide band is swamped by the main CH absorptions. It would be logical to expect that the CH2 groups in a four-membered ring would have bands intermediate between the three- and five-membered ring systems. Cyclobutane has bands a t 2990 and 2900 cm.-l, which lie between those given for cyclopropyl and cyclopentyl derivatives. To establish this point more firmly, Stein (24) studied the spectra of 10 cyclobutyl derivatives. The data he obtained are tabulated in Table I. Stein suggests the bands a t approximately 2985 and 2907 cm.-l as characteristic of the cyclobutyl ring system. The band in the range of 2855 to 2874, which occurs in all the compounds except cyclobutane, may be the CH where the substitution occurs. I n the case of the compounds with methyl and ethyl groups it could be explained as the sym-
metric CII, stretch, but this would iiot be the case for the other compounds listed in Table I. I n any event, more data are needed on four-membered ring compounds.
AROMATIC COMPOUNDS
It was pointed out by Bonino (4) in 1929 that the characteristic C-H bands of aromatic compounds occur a t a higher frequency than they do for
aliphatic compounds. Fox and Martin (6-7) examined the following aromatic compounds: benzyl alcohol, diphenylmethane, bibenzyl, fluorene, acenaphthene, naphthalene, I- and 2-methyl-
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VOL. 32, NO. 2, FEBRUARY 1960
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219
stretching vibrations to estimate various aromatic components combined with aliphatic materials. Josien and Lebas (14) have studied in some detail 19 monosubstituted derivatives of benzene. Most of these corn-
naphthalene, quinoline, and isoquinoline. They found that C-H aromatic stretching vibrations produce generally three bands close to 3038 cm.-l in carbon tetrachloride solution. Saier and Coggeshall(23) used these aromatic
pounds contain a band a t approximately 2934 cm.-l and from two to five bands in the region from 3000 to 3100 em.-'. All but one of the bands can be assigned to combinations of bands in the 1400to 1610-cm.-' region. They assign the
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ANALYTICAL CHEMISTRY
remaining band, which is usually the strongest in the 3000-am.-’ region, to a fundamental vibration characteristic of monosubstituted benzenes. The frequency of this band does not correlate too well with molecular environment. These same authors (16) have discussed the spectra of p-substituted benzenes between 3000 and 3200 cm.-l. I n this laboratory hlontgomery (18) has obtained the spectra of some 60 aromatic compounds using a lithium fluoride prism. The liquids were measured in a 0.027-mm. sealed cell or in thinner films to resolve the bands. The solids were measured in potassium bromide at a concentration of 1%. To check the purity of the compounds the spectra were also obtained in the usual rock salt region and compared with the American Petroleum Institute Catalog of Infrared Spectra where possible. These spectra are shown in Figures 2 and 3. As is evident, all of these compounds shorn a distinctive structure and the patterns are different for the ortho-, meta-, and para-substituted derivatives. I n general it is difficult to establish distinct correlations for these iaomeric compounds. The aromatic C-H ranges in Figure 1 are based on these 60 compounds only nnd are shon-n to indicate where the bands usually occur. The range for all aromatic compounds probably is from 3000 to 3100 em.-’, inclusive. Of the BO aromatic compounds studied, all have at least one band in the region of 3000 to 3100 em.-’. However. 2301, have only one band, while 77y0 have tn-o or more bands and 4570 have three or more bands. If there is a halogen atom present in the aromatic compound, there is always a band in the region
from 3048 to 3096 em.-’, usually centered a t approximately 3066 cm.-l. hlonosubstituted aromatic compounds usually have more bands than the di- or trisubstituted compounds. The ranges for 25 monosubstituted aromatics are : All but thrcc have a band from 3027 to 3039. All but one h a w n band from 3053 to 3075. Fiftem linw a band from 3054 to 3096. Thus, they closely resemble benzene, which has bands a t 3033, 3071, and 3091 cm.+. I n the case of disubstituted derivatires of benzene of which a total of 42 was studied, the numbers of compounds having one, two, and three bands above 3000 em.-’ are 12, 14, and 16, respectively. There is no definite pattern by which ortho-, meta-, and para-compounds can be readily identified as such. Only three trisubstituted derivatives of benzene were studied. Mesitylene and 2,4-dimethylphenol have only a single band at 3019 cm.-I, while 1,2,4trichlorobenzene has two bands, one a t 3009 and the other a t 3089 em.-’. Thus, as would be expected, as the number of substituents on the ring increase, the number of bands observed decrease. LITERATURE CITED
(1) Allen, C. F. H., Davis, T. J., Humph-
lett, W. J., Stewart, D. TV., J . Org. Chem. 22, 1291 (1957). ( 2 ) Bellamy, L. J., “Infrared Spectra of Complex RIolecules,” 2nd ed., Wiley, New York, 1958. (3) Bennett, J. G., Jr., Ph.D. thesis, Rensselaer Polytechnic Institute, 1959.
(4) Bonino, G. B., Trans. Faraday SOC. 25 , 8T6 (1929). (5) ~, Fox. J. J.. hlartin, A. E.. J . Chein. Soc. 1939.’318. ’ (6) Foi, J. J., hfartin, A. E., Proc. Roy. Soc. A167, 257 (1938). (7) Ibid., A175, 208 (1940). (8) Gore, R. C., Waight, E. S.,“Determination of Organic Structures by Physical hfethods,” Chap. 5, p. 219, Academic Press, Kew York, 1955. (9) Guertin, D. L., Wiberley, S. E., Bauer, IT. H., J . Am. Oil Chemists’ SOC.33, No. 4, 172 (1956). ( 10)T,Hastings, S. H., Watson, A. T., R illiams, R. B., Anderson, J. A., h A L . CHEM. 24,612 (1952). (11) Henbest, H. B., Meakins, G. D., Kicholls, B., Taylor, K. J., J . Chena. SOC.1957, 1459. (12) Ibid., p. 1462. (13) Hill, R. D., hfeakins, G. D., Ibid., 1958, 760. (14) Josien, &I. L., Lebas, J. XI., Bull. SOC. chim. France 1956, 53, 57, 62. (15) Kluge, H. D., Ph.D. thesis, Rensselaer Polytechnic Institute, 1941. (16) Lebas, J. XI., Carrigou-Lagrange, C., Josien, h1. L., Speckochim. Acta 1959, 225. (17) hIarcelli, J. F., Ph.D. thesis, Rensselaer Polytechnic Institute, 1958. (18) Montgomery, D. C., B. S. thesis, Rensselaer Polytechnic Institute, 1958. (19) Pinchas, S., ANAL. CHEM, 27, 2 (1955). (20) Plyler, E. K., Acquista, K., J . Research Katl. Bur. Standards 43, 37 (1949). (21) Potter, G. H., Ph.D. thesis, Rensselaer Polytechnic Institute, 1958. (22) Pozefsky, A., Coggeshall, N. D., AXAL.CHEX 23, 1611 (1951). (23) Saier, E. L., Coggeshall, K. D., Ibid., 20, 812 (1948). (24) Stein, R. P., B. S.thesis, Rensselaer Polytechnic Institute, 1958. (25) Tallent, W.H., Siewers, I. J., 4 x . 4 ~ . CHEM.28, 953 (1956). 126) Wiberlev. S. E.. Bunce, S.C., Ibid., 24, 623 (19”g2). ‘ I
RECEIVEDfor review June 4, 1959. Accepted October 5, 1959. Pittsburgh Conference on Analytical Chemistry and ’4pplied Spectroscopy, March 1959.
Determination of Traces of Vanadium, Iron, and Nickel in Petroleum Oils by X-Ray Emission Spectrography CHIA-CHEN CHU KANG, EDWIN
W. KEEL, and ERNEST SOLOMON M . W. Kellogg Co., Jersey City, N. J.
Reseurch and Development laboratories, The
b The trend toward processing of residual petroleum stocks has made i t increasingly desirable that rapid analytical methods b e devised for the determination o f trace quantities of metals in these stocks. X-ray emission spectrography has been employed in the determination of vanadium, iron, and nickel. The method i s r a p i d and direct, 40 minutes sufficing for the determination of all three elements in a 4-ml. sample. Correction i s made for sulfur absorption; interferences due to
other elements are negligible. The l p.p.m., estimated accuracy i s to i or of the amount, whichever i s greater.
is70
T
HE evident, trend toward processing of residual petroleum stocks has made increasingly desirable rapid analytical methods for the determination of the trace quantities of metals associated with such stocks. Residua, defined as the bottoms from atmospheric
or vacuum distillations, have in general more than 1 p.p.ni. each of iron, nickel, and vanadium. X-ray emission spectrography is applicable in this range without preliminary concentration of the metals by ashing. Metals in petroleum oils have customarily been determined by either colorimetry or emission spectrography. Birks et al. ( 1 ) used x-ray spectrography to determine tetraethyllead in gasoline, and Davis and Van Xordstrand (4) used it to determine barium, calcium, VOL. 32, NO. 2, FEBRUARY 1960
221
