ANALYTICAL CHEMISTRY
1604
Table IV. Absorption Bands of Tetrazole Ring Compounds 5-Aminotetrazole 5-Hydraninotetranole Tetrazole 5-Bromotetraeole Anotetrazole Tetrazolyl azide Potassium 5-nitroaminotetrazole 5-Iodotetraaole Anilinium 5-nitroaminotetrazole Di-(diethylammonium)-5-nitroaminotetrazole
WAVE
Figure 41.
LENGTH
I N MICRONS
Infrared Absorption Spectra of Tetrazole Compounds
SAminotetrazole Tetrawlyl hydrazine Anilinium-5-nitroaminotetrazole Di-(diethylammonium)-5-nitroaminotetrazole Potassium 5-nitroamiuotetrazole F. Awtetrazole G . Tetrazole H . Tetrazolyl azide
LITERATURE CITED
(2j (3) (4) (5)
9.40 9.43 9.44 9.36 9.40 9.26 9.44 9.37 9.43 9.56
10.04 10.09 ,..
... ...
...
9.98
...
9.98
0.87
(6) Lieher, E . , and Levering, D. R., J . Am. Chem. SOC..73, 1313 (1951). and Cohen, J . , Ibid., (7) Lieher, E.. Sherman, E., Henry, R. 1., 73,2327 (1961). (8) Lieber, E., Sherman, E., and Patinkin. S., Ibid., 13, 2329 (1951). (9) McKay, 8. F., Ibid., 71, 1963 (1948). (10) Patinkin, S.,and Lieber, E., I b i d . , 72, 2778 (1950). (11) Pelliezari. G., and Gaiter, .4.. Gnzz. chini.ital.. 44, IIA, 72 (1914). (12) Phillips, R., and Williams, J. F., J . A n i . C h a . SOC.,50, 2465 (1928). (13) Randall, H. M., Fowler, R. C . , Fuson. S . , and Dangl, J. R., “Infrared Determination of Organic Structures,” New York, D. Van Noatrand Co., 1949. (14) Thiele, J., Ann., 270, 1 (1892). (15) I b i d . , 303,57 (1898). (16) Thiele, J., and Marias, J. T., Ibid., 273, 144 (1893). (17) Thiele, J., and Oshorne, W., Ibid., 305,64 (1899). (18) U. S. Naval Ordnance Test Station, China Lake, Calif., privata
A. B. C. D. E.
(1)
Wave Lengths. Microns
Colthum Tu’. B.. J . O ~ t i c a Soc. 2 Am.. 40.397 (1950). Davis,=T. L., “Organic Syntheses;” Coll. Vol. I, p. 392, New York. John Wiley & Sons, 1932. Hartmann, W. W., and Philips, R., Ore. Syntheses, 26, 9 (1946). Hofmann, K. A , and Roth, R., Ber., 43, 682 (1910). Ingersoll. A. W.. and Armendt. B. F., “Organic Syntheses.” Coll. Vol. I, p. 408, New York, John Wiley &Sons, 1932.
communication. RECEIVED August 31, 1950. Abstraated from a portion of the thesis submitted b y Dewey Robert Levering t o t h e Graduate School of Illinois Instit u t e of Technology in partial fulfilln~entof the requirements for the Ph.D. degree, August 1950.
Determination of Carbon-Hydrogen Groups in High Molecular Weight Hydrocarbons By Near-Inf rared Absorption ALBERT EVANS AND R. R . HIBBARD National Advisory Committee for Aeronautics, Lewis Flight Propulsion Laboratory, Cleveland, Ohio AND
A. S . POWELL, Case Institute of Technology, Cleveland, Ohio
A
METHOD for determining the numbers of CHa, CH2, and aromatic CH groups can provide information of interest in many fields of hydrocarbon chemistry. For example, the octane and cetane numbers of reciprocating engine fuels are strongly affected by the degree of branching in the fuel molecule and therefore by the ratio of CHs t o CH2 groups. A knowledge of the aumbers of C H S , CHZ, and aromatic CH groups in the hydrocarbons comprising lubricating oils would be helpful in determining the amount of ring substitution and degree of branching of paraffinic side chains. And, in the very high molecular weight range, the determination of the concentrations of the various C-H groups could be used to indicate the structure of some types of polymers-for example, the vinyl type. Recently, Saier and Coggeshall ( I S ) used absorption bands in the 3.2- t o 3.6-micron fundamental region, characteristic of various C-H and C=C vibrational modes, to analyze certain binary and ternary mixtures, and Francis ( S ) has established integrated intensities for -CH$, ‘CH,,
/
\ /
and -CH
groups at 2900, 1470, and
1360 cm.-l from spectra of twelve hydrocarbons, but no attempt has been made to determine these groups directly in multicomponent mistures. The 1.10- to 1.25-micron second overtone region appears to hold considerable promise for the direct determination of the concentrations of the various C-H groups in hydrocarbon systems containing a large number of components. Rose ( I f ) has shown that specific extinctions for the three types of carbonhydrogen groups are nearly constant in different hydrocarbons. This near-constancy permits quantitative as well as qualitative determination of these groups in a variety of hydrocarbon types after calibration with a few pure compounds. Rose used a spectrometer with t\vo glass prisms of 15-cm. base and 20-cm. high in a Littrow mounting which had a n effective slit width of 6. Hibbard and Cleaves (4)have shown t h a t the 1.10- t o 1.20-micron nearinfrared region is suitable for determining the concentrations of the various C-H groups in low and moderate molecular weight hydrocarbons. Although a commercial, small prism instrument with glass optics and an effective slit width of 22 cm.? was used,
V O L U M E 23, NO. 11, N O V E M B E R 1 9 5 1
A previous13 reported method of determining meth? I (CH3),methylene (CH,), and aromatic C€I groups in hydrocarbons by near-infrared absorption spectroscopy was limited to compounds containing 18 carbon atoms or less. The present investigation was undertaken to determine t h e feasibility of extending the anal) tical method to a higher molecular weight range. Sear-infrared spectra (1.10 to 1.25 microns) of 24 hydrocarbons containing 13 to 34 carbon atoms and representing tarious hydrocarbon types were obtained. Absorption per functional groiip was found to remain nearly constant for cornpounds of the same type, and unit absorp-
specific extinction6 for the functional C-H groups compared closely with those obtained by Rose, indicating that the small prism instrument \vas adequate for analytical measurements in this region. Accuracies of 0.15 C11, and CH, groups per molecule in paraffins and aromatics, and less t,han 0.4 of the same groups in naphthene or parafin-naphthene blends were reported. Large deviations in the determination of CHI and CH, groups in naphthenes were minimized by correcting the data for weight per cent riaphthene ring.
1605
tion coefficients calculated from the spectral data agreed closely with coefficients determined previously with entirely different groups of compounds. Agreement of absorption coefficients indicates that the average number of each of these three types of CH groups can be determined in samples containing any number of compounds of a single hydrocarbon type. Saturate fractions from five lubricating oils were analyzed to give reasonable results; the results from t h e analysis of paraffin wax and polystyrene agree with the generally accepted structures for these products. No other method is known which will yield similar analytical data.
fluoride, etc., conimonly employed for Jvorli in the fundamental region; glass-windowed absorption cells are more stable dimensionally, are not attacked by atmospheric moisture, and do not require frequent polishing. Higher photon energies make possible the use of a photoconductive cell instead of thermocouple and bolometer receivers, permitting a simplified amplifying system and elimination of mechanical vibration problems, although advantage was not taken of this possibility in the present investigation. INSTRUJIENT A l i D MATERIhLS
The inPtrument used was a modified Model 12-A Perkin-Elmer spectrometer. The amplifier, prism, and light source have been described ( 4 ) . The instrument was further modified by mounting the General Electric tungsten ribbon filament lamp in an inverted
I-CYCLOPENTYL-4(3-CYCLO PENTYLPROPYLIDODECANE
.40
’‘ *
XI-
I,
%
2
0
.02
0
.04
.06
.08
\
-
I, I DIPHENYLHEPTANE I-PHENYL-3-CYCLOPENTYL-
---
: --
PROPANE I-PHENYL-2-CYCLOHEXY LETHANE I-cYcLoHExYL-3(2-cYcLoHEXYLETHYL) HENMCANE
2 .IO
SLIT WIDTH, m m Figure 1. Resolution of 8860 Cm.-’ Mercury Line As function of epectrometer slit width
Previous work was limited t o hydrocarbons containing 18 carbon atoms or less and, therefore, application of the method t o hydrocarbons of higher molecular weight could not be established. T h e research reported herein represents a n attempt t o extend the application of the method of Hibbard and Cleaves t o higher molecular weight rmges. Twenty-four pure compounds ranging in molecular weight from 180 to 500 (Cia t o Cad) and representing normal, singly anti doubly branched paraffins, cyclohesanes, cyclopentanes, 1-, 2-, and 3-ring aromatics, and aromatic-cycloparaffins were studied. The method was applied t o five nonaromatic fractions obtained from aircraft lubricating oils, t o one petroleum wax, tcr styrene, and to polystyrene. While absorption in the 2- t o 15-micron infrared has provided the basis for many analytical methods, relatively few have used the 1- t o 2-micron region. Several advantages inherent in the near infrared might well be mentioned here. Glass is transparent in this region and g l a ~ soptics may be used; glass prisms are cheaper and more durable than those of sodium chloride, lithium
WAVE NUMBER, cm-1
Figure 2.
?x
io3
Typical Absorption Spectra
position 2 inches t o the left of (facing away from the monochromator housing) and slightly behind the spherical mirror so that the light path from source t o entrance slit was not changed in length. Light was reflected from the plane mirror onto the spherical mirror, which was adjusted t o bring an image of the lamp filament on the entrance slit. In this position a shadow of the plane mirror covered the entrance slit and excluded stray light. This arrangement of the source provided free access t o
.
1606
ANALYTICAL CHEMISTRY
the cuvette holder. A cuvette holder, equipped with a shutter and a mechanism for sliding the cells into and out of the light beam, was attached to the monochromator housing in front of the entrance slit. Glass absorption cells with path lengths of 1.0 and 2.54 cm. were used. The procedures for wave-length calibration and testing the performance of the monochromator have been described ( 4 ) 5 ) . I n Figure 1 is plotted half-energy band width against d i t width, showing the prismatic resolution(at zero slit width)to be 28 cm. -l
All absorption measurements were made a t a slit width of 0.010 mm., equivalent to 34 cm.-l. As an additional check of instrument performance, absorption spectra of n-heptane and iso-octane (2,2,4-trimethylpentane) uere scanned between 8000 and 9000 a n - ' for comparison with Figure 2 in ( 4 ) . Location of absorption peaks compared within 20 cm.-l and values of molecular extinction within 5%. From this evidence, performance of the instrument was considered equivalent to that obtained previously. The twenty-four compounds examined were obtained from the School of Chemistry and Physics, Pennsylvania State College (synthesized by Research Project KO.42, ilmerican Petroleum Institute). Purity was 97% or better. All samples were liquid a t room temperature and m r e used without dilution. Carbon tetrachloride of technical grade was used in the reference cell and had no measurable absorption in the spectral region being studied. Three lubricating oils with high viscosity index and grades of SAE 10, 30, and 60 and two lubricating oils with low viscositv indev and grades of SAW10 and 30 were fractionated by the adsorption procedure of Lipkin and others (?') into aromatic a n i nonaromatic mixtures. The oils contained no additives. Values of some physical properties of the saturate fractions obtained are listed in Table I. Molecular weight determinations were made cryoscopically in benzene. Aromatic content was found t o be 1% or less, by the ultraviolet absorption method of Cleaves (2). Only saturate fractions were used for infrared study, as the recovered aromatic fractions were too small. Paraffin wax which melted a t 54' to 55' C. was obtained from the Standard Oil Co. of Ohio. Styrene of C.P. grade, stabilized with lert-butylcatechol, was obtained from the Eastman Kodak Co.
Table 1. Lube Oil NO.
3042 1065 1120 2110 2190
Physical Properties of Lubricating Oils and Saturate Fractions Tisco'sity Index
Viscobity
High High High Low
10 30 60 10 30
LO\V
SAE
Saturate F r a c t i o n Density .Lo \I.\V. ~~
0.8326 0 8632 0.8619 0.8.583 0.8922
1.46'33 1.4792 1.4796 1,469'3 1.4842
370 6 437.3 510.3 366.4 321 0
PROCEDURE
Absorption measurements of 24 pure hydrocarbons were made on undiluted samples in a 1.0-cm. cell using carbon tetrachloride in
(
the reference cell. Values of extinctions E = log
%transmittance used for calculations varied from 0.3 to 1.0 for the pure compounds. illthough some of the measured extinctions were greater than that desirable for maximum analytical accuracies, the improvement in accuracy that would be made possible by diluting the samples Rith solvent to yield extinctions near the optimum value could not be obtained because of the necessity of keeping the compounds in their original pure form. Nonaromatic fractions extracted from lubricating oils were diluted with carbon tetrachloride to yield extinctions near 0.4 in 1.00-cm. cells. Cells of 2.54-cm. path length were used for paraffin wax and polystyrene measurements. Absorption spectra were plotted as E against wave number. Extinctions a t preselected wave numbers were used to calculate molar extinctions by means of the exmession 100 log % transmittance where c is concentration of hydrocarbon in moles per liter and d is cell thickness. Readings of extinction, E, a t a given microdrive setting were not always reproducible, largely because of improper temperature compensation of the glass prism. A constant relationship
between microdrive setting and wave number was not maintained, and to compensate for this source of error, wave-length calibrations were made before and after each series of readings, using the 8860-cm.-' mercury line. A series of readings wa3 taken over a narrow spectral range and extinction values were plotted. Values of extinction a t the same wave number taken from the plots checked within 2% for repeat runs. Concentrations of the various C-H groups were calculated by means of the following simult'aneous equations:
+ ++
el = A (moles CH3/mole) B (moles CHz/mole) (1) € 2 = C (moles CHB/mole) I1 (moles CHz/mole) (2) €8 = F (moles CHs/mole) G (moles CH2/mole) H (moles aromatic CH/mole) (3) where e l , e > , and eg are molar extinctions a t the three analytical wave numbers vi, u p , u 3 ; d and B are coefficients equal to the average extinctions per mole of the respective functional groups a t u , , C and D are the same at v p , and F , G , and H are the same a t us. The aromatic CH group has negligible absorption a t v1 and v P , thereby eliminating the need for third terms in Equations 1 and 2. Values of d and B iri Equation 1 were determined by means of el measurements for a number of pure compounds and the known numbers of CH, and CHZ groups per molecule. The met'hod of least squares was applied to obtain the best average values. The remaining coefficie~itswere evaluated similarly. Concentrations of the various functional groups in moles per mole of hydrocarbon (or number of groups per molecule) were calculated by substituting molar extinctions for each compound in the proper equations. Values obtained were compared to the known values and deviations were calculated.
+
RESULTS
Typical spectra of the compounds studied are shown in Figure 2. Several general characteristics of spectra of the hydrocarbon types are noticeable. The n-heptadecane spectrum has a CI& peak a t 8235 em.-' and shows t h a t the 8360-cm.-' peak due to methyl groups, which is very pronounced in the n-heptane spechas been masked by increased absorption of methylene trum (4), groups. The etTect of naphthene rings depends upon the number of carbon atoms in t,he ring. The spectrum of l-cyclohexyl-3-(2cyclohexylethyl) hendecane shows a shift of the methylene peak to a slightly larger wave number and a general broadening of the band due to absorption of cyclohexyl groups in the 8360-cm.-' reg:on. Both effects are characteristic of cyclohexanes. Effect of the five-membered ring structure can be seen in the spectrum of 1cyclope1ityl-i(3-cyclopentylpropyl)dodecane. The methylene peak occurs again a t 8235 em.-' and a sharp peak exists a t 8370 cm.-l due to strong absorption of cyclopentyl groups in this region. The spectrum of 1,l-diphenylheptane is typical of those aromatics studied. The methylene peak occurs a t 8260 cm.-l, the aromatic C H peak is a t 8740 em.-', and a shoulder is a t 8400 em.-' due to methyl groups. Spectra of two aromatic-naphthenic type compounds illustrate the effects of cycloparaffin rings upon aromatic spectra. The shoulder a t 8400 em.-' in the 1-phenyl-2-cyclohexylethanespectrum must be attribut,ed to the cyclohexyl group, since this compound contains no methyl groups. Strong absorption of cyclopentyl groups accounts for the peak a t 8375 cm.-l in the 1phenyl-3-cyclopentylpropanespectrum. For all spectra obtained, absorption maxima for the paraffinic CH, group fell b e t w e n 8220 and 8255 cm.-l; for paraffinic CH3, between 8365 and 8375 cm.-l; and for aromatic CH, between 8670 and 8740 cm. -I. PARAFFINS
Molar extinctions of six paraffins were measured a t wave numbers of maximum absorption, or a t 8360 cm.+ if no peak was resolved for the CH3 group a t this position, and the coefficients A , B , C, and D were evaluated. Using these coefficients, the numbers of CH3 and CH2 groups per molecule were calculated for the six compounds and are given in Table 11. Average deviation of 0.26 CH3 group is somewhat larger than the deviation of 0.10 CHI group reported in ( 4 ) for a group of twelve normal and
V O L U M E \ 2 3 , NO. 11, N O V E M B E R 1 9 5 1 branched paraffins and in (11) for nine normal paraffins alone, but it is smaller t'han the deviation of 0.3 reported in ( 1 1 ) for a group of eighteen branched paraffins a t the same wave numbers. hverage deviation of 0.36 CH, group also falls between the values of 0.23 and 0.5 reported in (11 ) for normal and branched paraffins. Percentagewise the present' determinations Of CH2 groups are than those of ( 4 ) or (fl), because of the larger numbers of C ~ I groups Y present' in the compounds of higher molecular weight. For the studied, an average
1607
Table V. CH, and CHQGroups in Naphthenes Corrected for Per Cent Naphthene Ring wTeight No. of CHa Groups KO.of CH%Groups haphper M o l e c u l e per Molecule thene DifferDifferXaphthene Ring, % Found T r u e ence Found True ence 7-Cre10hexyltridecane 34.0 1.22 2 -0.78 15.81 15 0.81 l-Cyclohexyl-3(2-cyclohexylethyl)-hendecane 4 3 . 7 -0.79 1 - 1.79 22.13 21 1.13 l-Cyclopentyl-4(3-cyclopentylpropy~)dodecane 40.2 2.95 1 1 . 9 5 19.09 21 -1.91
~
,
~
~
~
i
~
~
~
pentane 1,7-Dicyclopentyl-4(2-cyclohexylethyl)heptane 11-Cyclopentylheneicosane ~ - ~ - ( ~ i ~ 3-Bicyclo-octy1)-nlethylhepta-0.3. decane ll~Cyclohexylmeth~l~h~n~icosane 11-(2,5-Dimethylcyclohexyl)-heneicosane 11-a-Decahydronaphthaleneheneirosane Arerare error
~
~
~
~
56.5
~
h
-0.17
0
-0.17
~
64.6 21.1
-0.93 2.58
0 2
38.2 20.8 21.2 37.1
2.11 1.04 3.00 -0.29
2 2 2 2
~
3
(
3
-
20.67
21
-0.33
0.93 0.58
19.08 20.85
21 22
-1.92 -1.15
0.11 -0.96 1.00 2 29 1.06
19.83 24.97 22.75 26 55
20 24 21 25
-0.17 0.97 1.75 1.55 1.17
~
position of CH2 absorption maxima was -~ ~ - . - .._~~________ ____ found t o be 8235 cm.-l, and, while a CH3 peak was not resolved for these compounds, a shoulder appeared near 8360 cni.-'. These wave NAPHTHENES numbers are also the averages of absorption maxima reported Because naphthenes often occur with paraffins in petroleum fractions and are not easily separated therefrom, it is desirable to and used for determining these groups in paraffins. Therein (4) determine them using the same wave numbers and the same cofore, A , B , C, and 11 viere again evaluated from molecular exefficients evaluated from paraffin data. Accordingly, extinctions tinctions a t 8235 and 8360 ern.-', the numbers of CHI and CH, groups per molecule were calculated, and the results a t 8235 and 8360 cm.-l were measured for ten naphthenes and concentrations of CH3 and CH, groups were calculated using the are given in Table 111. -4s expected, the deviations are larger coefficients that had been used for paraffins a t these wave numthan those obtained a t absorption maxima. -4verage deviations of 0.31 CH, group and 0.40 CH, group are larger than those rebers. Results are shown in Table IV. Average deviations of 2.93 CHI groups and 2.48 CH, groups are large enough t o prevent ported in (4)(0.24 CH3group and 0.28 CH, group), but again the useful analysis by this method. Deviations in CH3 groups are all deviation in CH, group8 is smaller, percentagewise. high by 0.9 to 5.5 groups, while CH, values are, with one exception, low by as much as 5.6 groups. Plotting absolute deviations as a function of weight per cent Table 11. CH3 and C K Groups in Paraffins Determined naphthene ring ( 4 , 8) and assuming straight-line correlations for Of from Extinctions 3'easured at Wave the various hydrocarbon types, correction lines resuked whose Absorption slopes were five t'o six times greater than those reported in ( 4 ) . S o . of C H I Groups S o . of CHz Groups However, when deviations in terms of per cent of total carbon per I\Iolecu$per I\Iolecule DifferDifferatoms present in the molecule were plotted as a function of weight Paraffin Found True ence Found True ence per cent naphthene ring, again assuming straight-line correla-0.49 11.56 11 0.56 1.61 2 n-Tridecane -0.38 15.07 15 0.07 tions, correctionlines\vereobtained~~ithequalslopesforbothsets 1.62 2 n-Heptadecane of data. Naphthene data obtained formerly are included in ,j,14-Dibutyloctadecane 9-Octylheptadecane 11-Neooentylheneicosane 5 . 1 3 5 0 13 18.48 19 -0.52 Figures 3 and 4 for comparison. As shown in Figure 3, the 11-Decyltetracosane 3.07 3 0.07 29.78 30 -0.22 greatest per cent deviations in CH3 groups occur in cyclopentanes, o , 36 .iverage error 0.26 while cyclohexanes follow a line with about one half the slope of ____~~~___ the cyclopentane line. Points for the present group of compounds are concentrated in~ the 20 to 60% Table 111. CH, and CH, G~~~~~ in paraffins ~ ~ ~ ~ ring range, ~ while points i for the ~ previous group of compounds are all above 60% ring. A4greement from Extinctions Measured at 8235 and 8360 Cm.-' for the two sets of compounds is good considering the wide range No. of CHs Groups T o . of C H ? Groups per Rlolecule per Molecule in amount of alkyl side chain substitution. D a t a for CH, groups, DifferDifferParaffin Found True ence Found True ence shown in Figure 4, have approximately the same characteristics n-Tridecane 1.53 2 -0.47 11.53 11 0.53 but withoppositesign. 15.04 15 0.04 n-Heptadecane 1.58 2 -0.42 Because no means of differentiating between these classes of 21 -0 42 3.74 3 0.74 20.58 9 - 0 c t lheptadecane 5,14-l;ibutyloctadecane 4.14 4 0.14 20.66 20 0.66 naphthenes is available, lines representing average deviations 19 -0.55 11-Neopentylheneicosane 4 . 9 7 5 -0.03 18.45 l l-Decyltetracosane 2.95 3 -0.05 29.82 30 -0.18 have been drawn on both plots to provide corrections for the calAverage error 0.31 0.40 culated numbers of CH3 and CH, groups per molecule as a function of weight per cent naphthene ring. These corrections Table IV. Uncorrected Determination of CHI and CH, Groups in were applied t o yield the data in Table Naphthenes V. Average deviations of 1.06 CH, Ko. of CHa Groups S o . of CHz Groups group and 1 . l i CH, group are not large per hlolecule_ per Molecule considering the compromise nature of DifferDifferNaphthene Found True ence Found True ence the correction factors. Improved results 7-Cyclohexyltridecane 3.32 2 1.32 14.08 15 -0.92 could be obtained if the type of naphl-Cyclohexyl-3(2-cyclohexylethyl)-hendecane 2.76 1 1.76 19.20 21 - 1.80 thene or relative amounts of different 1-Cyclopentyl-4(3-cyclopentylpropyl)-dodecane 6.23 1 5.23 ' 16.36 21 - 4 64 1,5-Dicyclohexyl-3(3-cyclopentylpropyl)-pentane 4 . 4 6 0 4 46 16.87 21 -4.13 types present in a mixture were known. 1,7-Dicyclopentyl-4(2-cyclohexylethyl)-heptane 5.42 0 5.42 15.40 21 -5.60 11-Cyclopentylheneicosane 4.37 2 2 37 19.39 22 - 2 61 For the compounds listed in Table V, the 9-n-(cis-0.3.3-Bicyclo-octyl~niethylheptadecane 5 . 3 6 2 3.36 17.20 20 - 2 80 average deviations would be reduced to 11-Cyclohexyltnethylheneicosane 2.92 2 0.92 23.40 24 -0 60 11-(2,5-Dirnethylcyclohexyl)-heneicoaane 5.00 2 3.00 21.10 21 -0 10 0.76 CH3 group and 0.59 CII, group if 11-a-Decahydronaphthalenc.hrneicosane 3.46 2 1 46 23.45 25 -1.55 the proper correction line for each type Average e r r o r . 2.93 2 48 had been used. ~ - ~ _ _ _ _
~
~
~~~
:$:
~
2
:$: i:,::
,!g,
~
ANALYTICAL CHEMISTRY
1608 Table VI.
per Molecule DifferAromatics Found True ence i-Phenyltridecane 2.53 2 0.53 1 0.60 1,l-Diphenylheptane 1.60 9-(2-Phenylethyl)-heptadccane 2.59 2 0.59 8-w-Tolvlnonadecane 4.03 3 1.03 l,j-Dipbenyl-4(3-phenylpropyl)-heptane 1.44 'I 1.44 Average error 0.81
Table VII.
Following these measurements, an attempt was made t o determine the presence of normal paraffins in the fractions by employing the urea-adduct formation method described by Zimmerschied, Higley, and Lien (Id). Only trace amounts of material were removed and, upon re-examination, no significant changes were noticeable in any of the spectra; this indicated the absence of normal paraffins.
CHa, CH2, and Aromatic CH Groups in Aromatics S o . of CHI Groups KO.of CH2 Groups No. of Aromatic
CH per Jlolecule Groups per Molecule DifferDifferFound True ence Found True ence 9.85 -0.15 5.43 5 0.43 4.68 -0.32 9.59 -0.41 14.28 16 -1.72 4.96 -0.04 -0 07 3.21 4 -0 79 15.93 16
'8
6.96
9
's
-2.04 0.86
14.63
15
-0.37 0 41
CHs, C€L, and Iromatic CH Groups i n Aromatic-Naphthenes S o . of CHa Groups S o . of C l I z Groups No. of Aromatic CH Per L I o ' e c u l e per Jlolecule ~ ~ _ _ _Groups _ per Molecule DifferDifferDifferFound True ence Fuiind T r u e ence Found True enre
l-I'lien~l-2-cycloh~ylethane 1.29 l-I'lienyl-3-cyclopentylpro~~~ne2 . 7 1 l.~-L)iuhenvl-3(3-cvclur,entvl- 3 . 2 8 prrrpyi)-pentane Average error
0 0 0
1.29 2 il 3 28
5.8i i.21 1.10
1 ,
11
2 43
- 1.13 -2.79 -3.90
2 61
AROMATICS
Large shifts occur in the position of the aromatic CH absorption maximum, making impossible a completely satisfactory choice of wave nuniber suitable for analysis for this group in all aromatic compounds. Inspection of the spectra of five aromatic compounds indicated that 8710 cm.-1 was a better average of the absorption maxima for these compounds than 8755 em-'. as used in (4). Too few compounds were available to establish coefficients separately for one-, two-, and three-ring aromatics. Coefficients a t 8710 cm.-' were evaluated from the data on five aromatics and used with the coefficients for 8235 and 8360 cm.-' evaluated from paraffin data, assuming zero absorption for aromatic C-H a t 8235 and 8360cm.-l. The numbersof CHI, CH2, and aromatic CH groups were determined and average deviations are shown in Table VI to be 0.84 CHI group, 0.86 CH2 group, and 0.41 aromatic CH group per molecule. AROMATIC-NAPHTHENES
Three conipounds of the mixed aromatic-naphthene type were studied. Extinctions were measured a t the three analytical wave numbers and the numbers of the various C-H groups calculated using the coefficients established above for aromatics. Results are shown in Table VII. Average deviations are 2.43 CHS groups, 2.61 CH2 groups, and 0.23 aromatic CH group. Determinations a r e high for CHa groups and low by approximately the same amount for CHZ groups, similar t o results obtained for alkylnaphthenes and probably due to the same causes. Average deviations of 0.64 CH1 and 0.95 CH2 groups are obtained when the corrections of Figuree 3 a n d 4 are used with the known weight per cent naphthene ring. However, corrections of this type cannot be made in practice, as no method is known for the determination of the per cent naphthene ring in aromatic-containing samples. The presence of the naphthene ring had no noticeable effect on the determination of aromatic CH groups.
The spectrum of a petroleum wax in carbon tetrachloride solution (0.124 gram,per ml.) was obtained between 8000 and 9000 cm.-l in a 2.54-cm. cell. The 0.23 wax had an average molecular weight of 388 as estimated from the molecular weight-refractive index a t 80" C. correlation of Mills and others (10). Values of CHa and CH, groups calculated from molar extinctions s t 8235 and 8360 cm.-' were 2.21 and 25.01, respectively.
4.68 4.84 9.80
-0 32 -0.16 -0.20
3 5 10
POLYSTYRENE
In Figure 6 are plotted spectra of styrene, and of polystyrene measured after polymerizing 13 days a t 100" C. Stabilizer was removed by caustic washing and no catalyst was added prior to polymerization. Absorption measurements were made on undiluted samples in 2.54-cm. cells. The thicker cells were used to show more clearly the effects due to CHJ and CH, groups and the per cent transmittance a t the aromatic CH absorption band near 8700 cm.-1 became so low as to be unreliable. Molar extinctiona were calculated using the density and molecular weight of monomeric styrene and the numbers of methyl and methylene groups
cn
$
0 0
40
20
CYCLOPENTANES CYCLOHEXANES AVERAGE
e /
-
10-
10 NAPHTHENE RING, PERCENT BY WEIGHT
Figure 3. Per Cent Deviations in Numbers of CH3 Groups
NONAROMATIC LUBRICATING OIL FRACTIONS
Nonaromatic fractions extracted from five typical aircraft lubricating oils were scanned in the 8000- to 9000-crn.-l region. Typical spectra are shown in Figure 5. Molar extinction is shown t o increase with increasing molecular weight. A definite peak in the 8360 crn.-l region was obtained in all cases. Concentrations of CHa and CH, groups were calculated using the coefficients established for paraffins, the extinctions measured a t 8235 and 8360 cm.-l, and the average corrections from Figures 3 and 4. Corrected results are shown in Table VI11 together with the values of weight per cent ring and total carbon atoms used in making the corrections.
PARAFFIN WAX
As function of weight 96 naphthene riw
Table VIII.
3042 1065 1120 2110 2190
.
CHI and CH2 Groups in Nonaromatic Lubricating Oil Fractions (Corrected for weight 70 naphthene ring) Weight Total S o . of CHI Carbon Groups per % Aton1s hlolecule Ring 33.0 27.2 3.14 32.7 32.i 3.50 30.3 36.5 4.36 38.4 26.3 2.96 57.3 23.1 1.98
N o of CH3 Groups per Molecule 18.49 22.06 23.90 17.49 14.82
1609
V O L U M E 23, NO. 11, N O V E M B E R 1 9 5 1
Ll
0
IO
I
I
I
A s function of weight
70
I
I
naphthene ring
are based on the monomer unit. The maximum a t 8250 to 8260 cm.-' results from CH2 groups being formed during the polymerization reaction. Some gas bubbles, which were formed and trapped during the polymerization, gave rise t o a background absorption. A correction for this background was made based on the increase in absorption a t 8000 cm.-l over t h a t expected for the polymer and this correction was applied to the values observed a t 8235 and 8360 em.-'. The corrected values of CH3 and CH2 groups were 0.08 and 1.00group per monomer unit.
ently with two groups of compounds in both molecular weight ranges. Coefficients A , B , C, and D, evaluated from extinction measurements at wave numbers of maximum absorption and again a t preselected wave numbers, are presented in Table IX. Included are values reported for low molecular weight hydrocarbons in ( 4 ) and those reported in (11) for measurements a t 8254 and 8400 cm.-'. The molar extinction per functional group is shown to remain constant in paraffins of both low and high molecular weight by constancy of major coefficients B and C. Agreement is very good among the values determined a t wave numbers of maximum absorption. For values determined a t preselecte&wave numbers, B and D agree very well. Less agreement among the values for A and C i s not surprising, as they refer to the methyl group and relatively few were present in the compounds used. It should be possible then, to determine the three C-H groups in paraffinic hydrocarbons containing up to 35 carbon atoms by evaluating the necessary coefficients with readily available compounds of low molecular weight. Agreement with similar coefficients reported in (11) for measurements a t slightly different wave numbers is good, considering the differences in instrument, compounds, and wave numbers used. Although only a few compounds of intermediate molecular weight (Clb t o C20) were used in the evaluation of these coefficients, it is probable that no significant changes in numerical values would have resulted i more compounds in this range had been included.
STYRENE POLYSTYRENE 1 I
V
DISCUSSION
I 1 I
' z 080
Extension of the infrared method of analysis to hydrocarbons of high molecular weight requires that molar extinctions of methyl, methylene, and aromatic C H groups remain constant. The extent to which this is true can be determined by eomparing values of the coefficients in Equations 1, 2, and 3 evaluated independ-
I-
t W
,
I
1
. ---- I065 I 120 ---
0
3042
80 Figure 6.
8.2
A B C
D
F G H
6.0
I 6.4 0.6 6.6 WAVE NUMBER, cm-1
6.2
t
~103
Figure 5. Typical Spectra of Nonaromatic Fractions Obtained from Lubricating Oils
Comparative Values
A t Wave Number ,of Maximum Absorption This Table X I V work (4)
0.0050 0.0195 0.0274 0.0091
9OX
Styrene and Polystyrene Spectra
Table IX.
Coe5cient
84 86 88 WAVE NUMBER, crn-1
0,0070 0.0195 0.0270 0.0102
At 8235,8360,and
8710 Cm.-' This Table X I V
Table V
work
(4)
(11)
0,0039 0.0196 0.0231 0.0096 0,0033 0.0009 0.0110
0.0066
0,00629 0,01989 0,02705 0,00735 0.00327 0.00126 0.01121
0.0194 0.0260 0.0098
For the determination of aromatics, too few compounds were examined to establish coefficients F , G, and H of Equation 3 for single and multi-ring aromatic compounds separately. Values determined from €3 measurements a t 8710 cm.-' are given in Table IX and show good agreement with similar coefficients reported in (11). Pure compounds in this molecular weight range were not available for making the blends required to prove the accuracy of this near-infrared analysis on multicomponent systems. And, be-
1610
ANALYTICAL CHEMISTRY
SUMMARY cause no other method is known for the determination of the various types of C H groups, the infrared results on commercial Determination of methyl (CH,), methylene (CH,), and aroproducts cannot be checked by independent analysis. For the matic CH groups by near infrared absorption spectroscopy is apsaturate fractions extracted from lubricating oils, it is possible to plicable t o hydrocarbons of high molecular weight. Molar say only t h a t mixtures of paraffins and naphthenes can be postuabsorption coefficients for the functional groups remain sublated which will match all the experimentally observed data. stantially constant in the C13 t o Cpa molecular weight range. For example, a mixture of 0.2 mole of 6,10-dipentyl-8-cyclohexyl- Average errors of 0.40 group or less were obtained for pure pentadecane, 0.3 mole of 4,6-dimethyl-3,T-diethyl-4,6-dicyclo-paraffins, 1.20 groups or less for naphthenes, and 0.9 group or hexylnonane, and 0.5 mole of 6,ll-dicyclopentylhexadecane less for aromatics. The method gives reasonable results a hen would satisfy the values for molecular weight, total carbon atoms, applied to commercial products such as lubricating oils, paraffin weight per cent naphthene ring, and CH, and CH2 groups found way, and polystyrene. for the nonaromatic fraction from SAE 10 lubricating oil (3042). The compounds postulated contain monosubstituted cycloACKNOWLEDGMEKT paraffin rings, but it is impossible, from the data presented, to differentiate between this type and polysubstituted rings. ObThe authors wish t o express their thanks t o Robert W. Schiesviously these oils are very much more complex than the blend sugder, director of A.P.I. Research Project 42 a t Pennsylvania gested above and the example is given only to show t,hat rational State College, for providing samples of pure hydrocarbons necesresults can be obtained. sary for this investigation. Qualitatively, t,here is a strong indication that the saturate fractions of the lubricating oils contain a generous amount of LITERATURE CITED cyclopentane ring. It will be noted t h a t the spectrum of 1Burk, R. E., Thompson, H . E.. Weight, A. J., and Williams, I., cyclopentyl-4(3-cyclopentylpropyl)-dodecane (Figure 2 ) is re"Polymerization and Its Applications in the Fields of Rubber. markably similar to that, of lubricating oil fraction 3042 (Figure Synthetic Resins, and Petroleum," pp. 188-9, ACS Mono5 ) , both in position and height of the 8350-cm.-l peak. Densities graph Series, Kew York, Reinhold Publishing Corp., 1937. Cleaves, A. P., "Ultraviolet Spectrochemical Analysis for h o and molecular weights are nearly the same. The spectra of 1matics in Aircraft Fuels," NACh Wartime Report ARR cyclopentyl-4(3-cyclopentyl propyl)-dodecane and of %,-(cisE5B14 (1945). 0.3.3-bicyclo-octyl) methylheptadecane, containing 40 and 31% Francis, S. A , , J . Chem. Phys.. 18,861-5 (1950). cyclopentyl carbon atoms, show well defined minima between Hibbard, R. R., and Cleaves, A. P., ANAL.CHEM.,21, 486 (1949). 8200 and 8400 cm.-'. S o similar minimum is found even in the Hogness, T. R., Zscheile, F. P., and Sidwell, A. E., J . Phys. most highly branched paraffin examined ( 1l-neopentylheneicoChem., 41,379(1937). sane) nor in the compounds containing the cyclohexane ring. Kropa, E. L., and Barnes, R. B., paper presented a t lOlst MeetCHEMICAL SOCIETY, St. Louis, Mo., April ing of AMERICAN Therefore, the presence of minima in the saturate fractions of the 1941. lubricating oils indicates the presence of the cyclopentane ring. Lipkin, bI. R., Hoffecker, IT. A., Martin, C. C., and Ledley, R. For the wax and for polystyrene it is possible t o compare the E., ANAL.CHEM.,20,1 3 0 4 (1948). structures indicated by the near-infrared results with those that Linkin. M. R.. Martin. C. C.. and Kurta. S. S.. Jr.. IND.ENG. CHEM.,ANAL.ED.,18,376 (1946). other considerations indicate t o be present. Sachanen ( 1 2 ) has Marvel, C. S., "Frontiers in Chemistry, The Chemistry of Large concluded that commercial paraffin waxes are mixtures mostly of Molecules," by Burk and Grummitt, p. 219, New York, Internormal paraffins from C22H46t o CBOHU?.If this conclusion is asscience Publishers, 1943. sumed to be correct, the experimental values of 2.21 CH, and Mills, I. W., HirechIer, A. E., and Kurta, 8. S., Jr., I n d . Eng. Chem., 38,449 (1946). 25.01 CH, groups per molecule are reasonable for a was melting Rose, F. W., J . Research S a t l . Bur. Standards, 20,129 (1938). a t 55" C. Sachanen, A. N., "Chemical Constituents of Petroleum," p. 289, The infrared method cannot differentiate b e t w e n the two proNew York, Reinhold Publishing Corp., 1945. *posedstructures for polystyrene ( I ) , but when the single repeated Saier, E. L., and Coggeshall, N. D., ANAL.CHEM.,20,812 (1948). Zimmerschied, W.J., Higley, W.S.,and Lien, A. P., Symposium unit is considered alone, the values of 0.08 CH, and 1.00 CH, on Analytical Research, 16th hlid-Year Meeting of American group are very good. The same relative values will result if any Petroleum Institute Division of Refining, May 1, 1950. other finit.e chain length is chosen. Although some evidence has been presented for the formation of methyl groups during the RECEIVED February 7, 1951. Presented before the Division of Analytical polymerization of styrene ( 6 ) ; Marvel ( 9 ) has concluded that Chemistry at the 119th Meeting of the AMERICAXCHEMICALSOCIETY, their concentration must be very small. Cleveland. Ohio. ~
. .
