Infrared- Mass Spectrometer Combination Method for light Hydrocarbon Analysis M. J. O'NEAL, JR., Houston Research Laboratory, Shell Oil Company, Houston, Tex. butenes) to be based upon masi spectrometer data and the butene iplit to be made by means of infrared data. The reeulting analysie takes advantage of the superior infrared accuracy for butenes and retains the accuracy and wide range of applicability of the mass spectrometer to other light hydrocarbons.
A method is presented for the complete analysis of C1 to C, paraffin-mono-olefin hydrocarbons (including differentiation of cis- and trans-%-butene)without the usual low temperature distillation or other separation methods. A simple total preseure computation allows all components (including total
T
must be made. Furthermore, the mass spectrometer analysis for these isomeric butenes is far less accurate than for the other hydrocarbon components, and is also inferior to that obtained by the usual distillation-infrarcd technique. The inaccuracies involved in the butene analysis by maas spectrometer range from 1.0 to 4.0 mole yo,depending upon the concentration ranges and extent of drifts in instrument calibrations. Milsom el al. ( 8 ) use infrared data to determine isobut,ane (2-methylpropane) and isobutene and mass spectrometer data for n-butane and 1-butenes. Starr and Lane have shown (7) the maw spectrometer to be equal or superior to the infrared for the analysis of all components in this range except the butene isomers. The total butene value was shown to be accurate by the mass spectrometer, whereas the infrared waa of considerably greater accuracy in the determination of the individual components. Thus it appeared that a logical technique would be to utilize the superior infrared butene accuracy and the extended range of the maw spectrometer in one method to arrive a t data comparable to those obtained by the more time-consuming method of low temperature distillation and subsequent infrared determination.
HE use of infrared spectrometry and mass spectrometry individually in the analysis of various hydrocarbon mixtures has been covered thoroughly in previous publications ( 1 4 , 6 , 8 ,&'). A method has been described ( 6 ) foi, the combination of data from both infrared and m w spectrometers in which only 1-butene and isobutene (2-methylpropene) splits are obtained; empirical pressure correction factors are introduced to compensate for instrument fluctuations to derive an absolute basis for the computation. The combination method of analysis employed in this laboratory differs from that described (6) in several significant respects: The present method employs a simple total pressure computation to derive an absolute basis for the combination calculation; the normalization procedure is different in that a simple correction on the butenes can be made once the mass spectrometer data have been made absolute; and the components determined by infrared are different. In order to obtain a complete isomeric analysis for butenes in C1 to C4 hydrocarbon mixtures, it is generally necessary to perform a low temperature distillation to Pegregate the butanes and butenes for subsequent infrared analysia (e). The resulting analysis yields values for all the butene isomers, including cis- and transd-butene. The mms spectrometer can be used to obtain a comparable analysis, except that the cis- and trans-2-butene bomera cannot be distinguished and thus a total 2-butene analysis
Table I. Wave Length,
e
Pressure M m . Hg
Methane
Ethene
Ethane
9.05 10.4 11.4 14.4
570 40 55 70
0.001 0.OOO 0.000
0.180 0.235 0.164 0.011
0.011 0.010 0.040 0.002
a
0.OOO
APPARATUS
The mass spectrometer used waa a Model 21-102 instrument manufactured by the Consolidated Engineering Corporation,
Infrared Calibration Coefficients" (Beckman IR-1) Propene Propane 0.094 0.286 0.228 0.015
0.030 0.004 0.016 0.011
Iao-
butane
Butane
n-
1Butene
cia-2butene
tranr-2butene
0.026 0.002 0.004 0.011
0.047 0.086 0.001 0.020
0.595 0.116 0.111 0.037
0.135 0.160 0.016 0.636
0.119 0,724 0.017 0.008
180-
Isopentane
n-Pentane
0,118
0.044 0.041 0.002 0.011
0.062 0.004 0.034 0.021
butene
0.006
0.662 0.014
Corrected absorbance a t unit mole fraction.
Table 11. Mass Spectral Sensitivity Coefficients of c1-C~Hydrocarbons (Divisiorw'mioron pressure)
Nesi
n-C,Htr
i-CiHa
2
...
,..
CC'Hro 1.10
n-CdHio 0.75
i-C4HlO
I-CIHI
0.60
0.96
0.90
0.48
0.59
0.68
70.30 101.6 1.79 1.89
100.32 2.09
191.5 7.16
...
16
0.62
1.07
1.20
0.61
1.38
28 30
29.72 2.47
19.26 2.94
21.67 2.29
131.9 3.93
13.94 0.69
32
1.84
1.92
...
42 43 44
266.6 468.3 15.21
252.9 301.9 9.78
243.2 11.37
49.88 413.1 13.48
56 57 58
10.24 61.30 2.78
50.22 169.1 7.39
13.26 0.52
...
3.23 10.36 50.44
70 72
0.45 41.13
0.33 18.64
121.8 0.14
.. .. ..
...
1.42
... 154.7 480.4 15.61
l-c4H1 2 4 H 1 0.78
...
.,.
...
12.48 0.36
12.15 0.56 0.03
10.81 0.38 0.03
..,
1.81 156.2 138.7 164.4 14.58 7.63 6.98 6.94 12.19 0.22 0.14 0.17
... ...
...
...
... ...
.. .. ..
CaHb 0.92
0.98
CIHI 0.81 0.64 3.34 0.06
CIHI 0.86
0.47 246.3
19.50 77.54 93.35
169.5 5.61 0.12
...
... . ...
... ... ...
...
I..
.. .. ..
.... ..
... ..
... ...
NI
1.08
...
... ...
276.3
...
...
...
...
... ... ... ...
380.7 278.8 90.06 0.12
...
...
CH4
1.31
...
t .
CaH4
1.86
... ... ... ...
...
Or
H;
...
126,3
38.20
... . . I
220.9
,..
...
,..
,..
...
...
...
... ...
. I .
. I .
...
...
...
*. ... ... ...
... ... ...
ANALYTICAL CHEMISTRY
992
m
,
.
...
hh0
a
mwo m
5
::::::?S@Fj? '00-
0
0
I
1
Pasadena, Calif. The infrared spectrophotometer employed was a Beckman IR-1 instrument manufactured by National Technical Laboratories, Pasadena, Calif. An electrical computer, Model 30-102, manufactured by the Consolidated Engineering Corporation, was employed in the solution of all matrices. The general techniques of operation of these instrumelits have been previously described (1,4,8). PROCEDURE
m
. .
-J-
Sm
%"
+ +
Calibrations were obtained by standard techniques using the same pure hydrocarbons on both instruments. Four wave lengths in the infrared were used a t a given standard pressure for each wave length as shown in Table I. The principal absorbers were found to obey Beer's lamover the concentration range normally encountered (to about 50%). I t was unnecessary in subsequent calculations, therefore, to employ correction curves for deviations from Beer's law. Calibrations at each of the four wave lengths were calculated in the usual manner ( 8 ) from nulltype galvanometer measurements, and expressed as absorbance per unit mole fraction. A summary of mass spectrometer calibration data is shown in Table 11. The only precaution in handling of the sample was that a small sample was taken into a glass bulb for the mass spectrometer simultaneously with the filling of the infrared cell to ensure identical samples for both instruments. The mass spectra were recorded and the peak intensities at the selected mass numbers were read from the record. METHOD OF COMPUTATION
+ + ..
+ + h
.. ..
+ c
In a combination of mass spectrometer and infrared data, both must be expressed in the same t e r m and a method devised for adjusting each set of data to an absolute basis. The difficulties involved in combination of two sets of unnormalized data can be illustrated by an example in which one half of the sample composition is determined by each-Le., 60% by mass spectrometer and 50% by infrared. If, say, the mass spectrometer components computed to be 45% and the infrared to 55%, the apparent total would be 100% although the actual values were low and high, respectively, by 5%. It will thus be apparent that a t least one set of the data must be computed on an absolute basis, so that iinal normalization can be correctly applied to only the unnormaliaed data. The general expression for mass spectrometric computations is as follows :
+ AiaPa.. . .AiJ'n = Mi +++ AizPz AzzPz + AmPa . . .AznP, = M z A,zPz + A n p a . . . A3nPn = M 3 + An2Pz + ASaP3. . . . AnnPn = M ,
AiiPi AziPi A321 AniPiJ
where A , , is the calibration coefficient at mass i of component i; P , is the concentration of component j; and M , is the ion intensity a t mass i. The solution of this general matrix result6 in the inverse or reciprocal matrix which may be expressed as follows:
+ +
+ + .-c
This inverse expression gives the concentrations, P, of components 1 through n as a linear relation of the ion intensities, M , by means of the inverse coefficients, I . When Mi is expressed as peak height (divisions) and Ai! as sensitivity (divisions per micron pressure), P, is given as partial pressure; when both Mi and A , , are expressed aa sensitivities, Pj results in mole per cent. Although relative sensitivities, M i , may be determined by use of the experimentally measured pressure, such sensitivity values are often in error becltuse of instrumental fluctuations, etc. Milsom et al. (6) more nearly approximate absolute sensitivity expressions by applying an empirical correction factor determined from n-butane sensitivity ratios. However, this method represents only an approximation of the actual pressure, because complete stability of the mass spectrometer unit is assumed for the time elapsed between the butane sensitivity determination and the unknown determination The point of emphasis here is that the mass spectrometer data can be expressed on an absolute basis by a simple computation. Referring to the in-
V O L U M E 22, NO. 8, A U G U S T 1 9 5 0 Table IV. Equa$ion 1 2 3 4 5
6 7
8 9
10 11 12
Infrared and Mass Spectral Calibration for Mass Spectrometer-Infrared Combined Matrix
1 Maas or Wave Length, p n-CrHlr 72 41.13 57 61.30 2.78 58 43 468.3 0.062 9.05 0.021 14.4 0.004 10.4 0.034 11.4 44 15.21 42 266.6 2.47 30 29,72 28
2
3
i-CaHi: 18.54 169.1 7.39 301 .9 0.044 0.011 0.041 0.002 9.78 252.9 2.94 19.25
2 30
Wave Length, p $4,063 - 18.973 1 CrHk 2 CsHa 63 +10,745 129 - 497 3 CiHe 4 CaHs ... 5 ~-CIH, 1,090 +i,iOl 1,392 6 trana-2-CkHs +5,585 - 68 7 ci8-2-Cdb 12 925 +3,788 8 1-CIHs 29 +112 9 S-CIHIO -2 ... 10 n-CIHia 170 644 11 i-CaHa +288 12 WC6Hlr 76 I: mole +1,466 +4,050 Ii All coefficients multiplied by 10-8.
0.086
--+ -
-2,707 -2,420 59 -390 141 19 +299 135 f2.206
+ iMp ;I,2
+
$5
-
+
+Ma
6:94 0.17 0.38 0.135 0,636 0.150 0.016 0.03 10,81 2.09 100.3
5
4 44
11.4 -406,408 -34,520 7 1,174
- 7,906
e:04 0.17 0.38 0.119 0,008 0.724 0.017 0.03 10.81 2.09 100.3
~-CIHI 7.63 0.22 0.38 0'. 118 0.014 0,005 0.562 12.48 1.79 70.30
-
7
6
10.4 -492,265 -33,149 -49,171
900 +315 10,995 +1,536 +1,974,021 +144;199 +198,221 +1,591,436 +2,200 163 19,929 1,934 +1,155 288,612 187.293 -2,224 +19,217 +14,088 +525 +829 -41 io4,ezs 79,006 +47,331 +35,359 15 +5,433 +1,308,897 +941,160
+
-
-
-
+
. ..M,
&in
This total pressure equation may be computed without going through the complete inverse solution with subsequent summation of terms. In the normal inverse solution, employing an electrical computer, each column of the matrix is solved separately by successive substitution of unity in each M position with zero in the remainder of the M's (4).The explicit form of the summation equation can be obtained by simultaneous substitution of unity or a smaller number suitable for the computer in each of the M positions and solving. The resultant equation is the n
10
11
12
CaHa
CsH6
CsH6
CrHi
... ...
.. ...
...
...
0:oll 0,002 0.010 0.040
0:ie.o
, I .
5.98 0.14 0.56 0,595 0,037 0.116 0.111 0.03 12.15 1.89 101.5
verse expression above, it is apparent that the total pressure may be computed by summation of the individual pressures. An expression may be obtained for the total pressure by summation of the columnar inverse c0efficient.sof common M terms:
$Pi = M I
9
8
:
77 57 0.030 0.011 0.004 0.015 93 I35 19.50 7.16
191.5
5.61 0,094 0.015 0,235 0.228 0.12 169.5 0.06 3.34
...
... ...
...
.
...
.
I
0.011 0.235 0.154
... ...
0.12 278.8
9b:66
380.7
Final Inverse' for Mass Spectrometer-Infrared Matrix
3 42
-
7 trana-2CiHs
cia-2CiHa
...
14:5s 12.19 480.4 0.026 0.011 0,002 0.004 15.61 154,7 0.69 13.94
0.001 13.48 49.88 3.93 131.9
+1,504 107 +6,185
-
6
5
L-CIH~O 1-C4Ha
10:36 50.49 413.11 0.047 0.020
++
+-
4
n-CIHla
Table V. 1 28
Maas
993
n
general solution for ZPi, and the ZZI, values obtained are used in all subsequent analyses. From this expreaion the total pressure may then be computed for any mixture simply aa the sum of multiplicative terms involving the mixture peak height and the n
corresponding ZIr term. In the caae of CIto C I hydrocarbon mixtures a satisfactory total pressure matrix includes the components hydrogen, methane, ethane, ethene, propane, propene, n-butane, isobutane, total butenes, isopentane (&methylbutane), n-pentane, and total pentenes. This lsequation matrix containa all possible components with the exception of air, hydrogen sulfide, carbon monoxide, and carbon dioxide. The latter two ordinarily may be ignored, ae their presence usually is made improbable by the source of such mixtures. Diolefins and acetylenes were not considered, because they were not expected to be present in significant quantities. Air and hydrogen sulfide may be computed separately, if present, from their unicomponent maases (32 and 34). A total butene value is used because of the similarity of spectra. I t haa been found that no significant error is introduced in the total pressure calculation even when the butene concentration is above 50%. The total pentene value is included to make the method applicable t o samplea containing small amounts of pentenes (less than 3%)
-
-
-
9 43
8
14.4 9.05 -437,421 546,891 -29,245 -30,252 -44,025 -72,269 -314 -336 +139,937 197,311 +135,220 +84,034 -I-1,591,509 -96,134 -220,755 -.1,934.454 I +11,635 C9.748 +943 +1,681 -71,069 -63,193 +32,075 +28,908 +839,937 +884,034
-
-
75 +7 -2,162 -358 +a57
-
+SO8
2;
+2,770 635 -324 146 +1,028
-
+
10
11 57
58
-7,637
- 772 + 12,375 - 12
-2,753 -4,492 - 567 +887 21,767 +24,985 788 345 +701
-
+-
12 72
-
649 183 -4,947 +2;296 +1,473 +69
fll6 -657 705 +6,971 -3.148 +649
-
-5,281 - 690 -8,913 10 +3,501 i-4.327 326 - 83 -27,377 +6,278 -8,549 +28,178
-
-
-8.967
but is not intended for samples containing a large concentration of these components, The total pressure matrix is shown in Table I11 aa prepared from the maas spectral calibrations in Table 11. The factored and transposed coefficients are shown with the factor value for each row and the M value. This matrix is set up in the computer and a solution is made according to the usual technique (4). The solution is shown aa read from the computer as well as the final
Table VI.
Comparison of Mass Spectrometer-Infrared Inverse and Graphical Solution
Component Propene Propane n-Butane lsobutane cia-%butene trana-2-butene Isobutene 1-Butene n-Pentane Isopentane Pentenes
Concentration, Mole ?& Graphical solution inverse M.S.-I.R. solution 6.3 10.5 30.2 14.7 3.6 1.9
Difference
6.5 10.4 30.0 14.6 3.6 2.0
8.5 6.0 8.5
0.2 0.1 0.2 0.1 0.0 0.1 0.0 0.2 0.0
8.5
6.2 8.5
-
9.6
ni
9.5
0.2 100.0
0.2 100.0
Av.
0.0 0.09
Table VII. Infrared, Mass Spectrometer, and Mass Spectrometer-Infrared Comparison Analyses on C, Fraction0 Component
n-CkHla t-CiH10 1-CIHa cra-2-C1Ha trana-2-C4Ha i-C4Ha
Composition, Mole % Mas8 Infrared spectrometer Sample 1 5.4 5.8 4.0 5.0 33.9 30.7 7.5 10.4 0.6 48.2 48.5 Sample 2 32.1 31.2 48.2 48.0 0.3 3.9 3.0 5.9 0.0 10.4 11.2
1
M.8.-I.R. 5.4 5.0 33.8 6.7 0.6 48.5 31.2 48.0 6.6 3.0 0.0
11.0
ANALYTICAL CHEMISTRY
994
total pressure equation corrected for row factors and M conversion to unity. This equation may be used for any mixture of the listed Components except those involving large pentene concentrations. Thus, an equation haa been derived for a relatively simple method of computing a "spectral" total pressure for use in determining absolute sensitivities. Thia spectral pressure is equal to the same value obtained by making a complete analysis of the maas spectrometer data and computing the theoretical pressure from the analysis. Because the use of theoretical pressure eliminates the need for subsequent normalization of the maea spectrometer components, a satisfactory closure of the data can be made by normalization of the butenes. The total pressure aa calculated above can now be used to compute mixture sensitivities which can be directly substituted in a combined matrix with corrected infrared absorbances in a straight-forward technique. 'Phis matrix is shown in Table IV. Equations 1 through 4 and 9 through 12 represent mass spectral sensitivity coefficients at the 72, 57, 58, 43,44, 42, 30,and 28 masses for the components shown. Equations 5 through 8 represent infrared calibration coefficients (absorbance per unit mole fraction) at 9.05, 14.4,10.4,and 11.4 mitrona for the same components. Table V shows the inverse for this combined array aa solved by the electrical computer. Methane, hydrogen, and air are not included in the matrix. These components can be computed from the mass spectrum aa residuals or by isotope correction, for their parent maases are essentially unicomponent and exhibit no absorption at the infrared wave lengths. Pentenes may be calculated by correcting mass 70 for pentanes. However, samples containing over 2 to 3% pentenes should be avoided in this method because of the large absorption by pentenes at the infrared wave lengths. The resulting computation by use of the inverse should total a mole fraction of 1. However, if normalization is necessary, corrections should be made only on infrared components, inasmuch aa the maas spectra components have been normalized by use of theoretical pressure as calculated from the SP,equation. The butene correction factor for normalization is calculated as follows : :C4- (corrected) = 1.00
-
'
[Z N
- ZC4- (uncorrected)]
'TI' (corrected)-
= ZC4' (uncorrected)
where 2C4' = total C4olefins, by infrared 2 N = total mole fraction by maea s ctrometer and infrared calculations
F
= correction factor for individuaPebutenes
The resulting values represent the final analysis of the data, with each component expreseed in mole fraction. ACCURACY
A comparison can be made of results calculated from the data (as described above) with results obtained by a graphical approximation of the data. This approximation waa carried out by the usual analysis of the mass spectrometer data, solving for total butenes and subsequent approximations and corrections of the infrared absorbances by use of a graphical plot of the minor absorbers at the various wave lengths. Such a comparison is shown for a C& mixture in Table VI. The largest deviation is 0.2% with an average value of 0.09%. A comparison of the maas spectrometer-infrared method on CCfractions can be made with both the maea spectrometer method and the infrared aa shown in Table VII. The infrared method is generally accepted aa more accurate than the maaa spectrometer on such mixtures and it ia apparent that the m m spectrometer-infrared method is in good agreement with the infrared method where mass spectrometer and infrared are not in close agreement. An indication of the absolute accuracy of the method can be obtained through the analysis of synthetic mixtures. Table VI11 shows three synthetic mixtures of different relative compositions and the analysis of each by the mass spectrometer method alone and the maea spectrometer-infrared method. In the case of the first two synthetics, the butene analysis by the mass spectrometerinfrared method is considerably better than that by the maea spectrometer alone. Synthetic mixture 3 is analyzed with approximately the same degree of accuracy by both methods. The average error for butenes by the maw spectrometer-infrared method ranges from 0.5 to 0.870 as compared with 0.7 to 3.170 by the maea spectrometer. The other components vary from 0.2 to 0.5% and 0.1 to 0.3%, respectively, giving an overall average error for all Components of 0.3 to 0.6% for the m w spectrometer-
V O L U M E 22, NO. 8, A U G U S T 1950
99s
Table IX. Repeatability of Analysis Hydrogen Methane Ethene Ethane Propene Propane Ieobutene trona-2-butene cia-2-butene 1-Butene Isobutane n-Butane Isopentane n-Pentane
Mass Spectrometer-Infrared 1 2 3 Spread 0.1 4.5 4.6 4.5 0.2 5.3 5.3 5.5 4.4 4.7 4.7 0.3 0.4 4.6 5.0 4.7 7.8 7.8 7.5 0.3 0.1 10.1 10.0 1 0 . 0 21.5 21.2 21.5 0.3 5.5 5.3 5.5 4.3 4.2 4.3 0.2 9.3 9.1 9.2 0.0 9.8 9.8 9.8 0.2 6.3 6.4 6.2 0.1 4.7 4.7 4.6 1.9 2.0 0.1 2.0 Av. = 0 . 1 8
Maas Spectrometer 1 2 3 Spread 4.5 4.7 4.4 0.3 5.0 5.3 5.0 0.3 5 . 5 5.5 5.2 0.3 4.4 4.6 4.5 0.2 8 . 2 8.0 7.9 0.3 10.3 10.3 10.4 0.1 20.4 19.5 20.3 0.9 10.1 9 . 0 9.7 1.1 8 . 6 10.3 9 , 5 1.7 9.7 9.9 9.7 0.2 6 . 6 6 . 4 6.1, 0.2 4.9 4.8 4.9 0.1 1 . 8 1 . 8 1.8 0.0 0.44
::?I
found to be fully adequate for all studies of this type encountered to date where the pentene and CS concentration is less than 3%. This method easily may be applied to higher hydrocarbons of the gasoline range where the maiw spectra of any two or more components may be similar. If these components exhibit sufficient difference in the infrared absorption spectrum, an accurate analysis by the combination method can be made. Because the baeis of the method depends upon the distinguishing infrared spectra (or other properties) for those components of similar mase spectra in the particular type of mixture under examination, it may well fit into a number of schemes of analysis for “closed” system of a finite number of components. ACKNOWLEDGMENT
infrared method and 0.4 to 1.1% by mass spectrometer alone. The slight increase in average error of the components exclusive of butenes is not believed to be significant. All three synthetic mixtures show a positive error of approximately 1% on isobutene by the combination method. This is not believed to be characteristic of the method because, as shown in Table VII, values obtained on C, fractions check with those from infrared analysis even when the total butene concentration is as high as 90%. The repeatability of the present method is shown in Table IX compared to that obtained with the msss spectrometer. The maximum spread is 0.4% by the mass spectrometer-infrared method as compared to 1.7% by the mass spectrometer alone. The average repeatability of all components is 0.18 and 0.44%, respectively. CONCLUSION
The combination method may be applied to any mixture of light hydrocarbons where there is required a more accurate butene analysis than can be obtained by m w spectrometer alone. In proceas research and some refinery practice it is often necessary to obtain the best possible accuracy for these components. Previously it haa been necessary to make low temperature distillations with a subsequent infrared analysis to obtain these data. The combined mms spectrometer-infrared method has been
The author wishes to express his appreciation for the interest and cooperation of R. Y. Seaber, C. K. Hines, H. J. Cannon, and other members of the Spectroscopic Section of the Houston Research Laboratory and also to members of the Physical Chemistry Section of the Houston Refinery Control Laboratory, especially Noel Lane, all of whom contributed in obtaining the measurements reported. LITERATURE ClTED
Brattain, R. R., and Beeck, Otto, J. Applied Phga., 14, 418 (1943).
Brattain, R. R., Raamuasen, R. S., and Cravath, A. M., Ibid.. 13,899 (1942).
Brewer, A. K., and Dibeler, V. H., J. Research Natl. Bur. Standards, 35, 125 (1945). Consolidated Engineering Corp., “Operation Manual for Twelve Equation Computer, C.E.C.,” October 1940. Mileom, Daniel, Petroleum Refining, 26, 719 (1947). Mileom, Daniel, Jacoby, W. R., and Reacorla, A. R., ANAL. CREM., 21, 547 (1949). Starr, C. E., Jr., and Lane, Trent, Ibid., 21,572 (1949). Waehburn, H. W., Wiley, H. F., and Rock, 8. M., IND. ENQ. CREM.,ANAL.ED., 15, 541 (1943). Washburn, H. W., Wiley, H. F., Rock, S. M., and Berry, C. E.. Zbid., 17, 74 (1945). RECEXVBD March 3, 1949,
Determination of Unsaturation of Butyl Rubbers and Certain Branched Olefins Iodine Monochloride Method T. S. LEE’, I. M. KOLTHOFF, AND E T H E L JOHNSON University of M i n n e s o t a , Minneapolis, M i n n .
A
RELIABLE and convenient method for the determination of unsaturation of hydrocarbon polymers and of olefins can generally be baaed on the addition of iodine monochloride to the carbon-to-carbon double bond. The reaction is represented as follows:
I c1
\c=d + IC1 +‘b-L’ / \ / * Present addresa, University
(1)
\
of Chicago, Chicago, Ill.
The procedure usually consists in adding an exceaa of iodine monochloride to the solution of unsaturated compound and, after a suitable reaction period, determining by titration the amount of iodine monochloride remaining. Although the iodine monochloride method yields accurate results for most olefins and polymers, it yields high results for certain olefins and polymers that are branched in the neighborhood of the double bond. A number of such compounds have been cited in the literature: &thy]Zpentene (18); trimethylethylene and limonene (11); isobutylene dimers, trimers, and tetramers (3); pinene, dipentene, and a-terpineol ( 4 ) ; dihydromyrcene and squalene ( 1 ) ; othei branched olefina (8); and Butyl rubbers (4, 18, IS). Other examplee are given herewith.
