398
Anal. Chem. 1983, 55. 398-400 1234
1. 2.
3. 4.
5.
6. 7. 8.
Flgure 1. Schematic diagram of attachlng fused slllca capillary tublng to a glass capillary column by heat shrinkable Teflon tubing. on-column injection (1-5) to such coiled columns, we have devised a simple procedure for attaching a linear inlet portion. This is an alternative to the method of Sandra et al. (6).
EXPERIMENTAL SECTION Procedure for Attaching a Linear Inlet Section. A 10-20 cm straight length of fused silica capillary tubing (coated or uncoated) is selected having an outer diameter just sufficient to permit it to be inserted into the glass capillary tubing. A section of heat shrinkable PTFE (Teflon) tubing of sufficient length to overlap the joint is slipped in place, and heat is applied to form a snug, fully sealed connection (Figure 1). Fused silica capillary sources utilized include J. and W. Scientific, Inc., Rancho Cordova, CA, Quadrex Corp., New Haven, CT, and Scientific Glass Engineering Ltd., North Melbourne, Australia. The 0.32 mm i.d. fmed silica tubing provides an excellent fit for the commonly used 0.020 in. i.d. glass capillary tubing. Heat shrinkable PTFE (Teflon) tubing was obtained through Chemplast Inc., Wayne, NJ. Complete thermal stability up to 205 “C is claimed by the manufacturer (7) and the supplier states that a heat shrinkable Teflon seal is stable and free of leaks under chromatographic conditions up to 225 “C (8). This is in accord with our own experience. Grob (9) has reported the successful use of PTFE seals of this kind up to 300 OC. Gas Chromatographic Procedure. A test of this technique was conducted in an HP 5830A gas chromatograph equipped with a flame ionization detector. A 30 m X 0.02 in. i.d. glass capillary column supplied by Schwartz (IO) was utilized with an attached inlet injection and outlet sections of fused silica capillary tubing (uncoated, 20 cm X 0.32 mm i.d., Quadrex Corp., New Haven, CT). A 1p L hexane solution contained about 1 part in 6000 of each of benzene, toluene, ethylbenzene, and xylenes (para, meta), and about 1 part in 25000 of each of n-nonane, n-decane, and n-undecane was injected with our on-column injector (11). The injection syringe was a IO-pL, 701 SN model having a 10 cm, 32 gauge needle (Hamilton Co., Reno, NV). RESULTS AND DISCUSSION Figure 2 shows the chromatogram obtained with on-column injection using the attached fused silica inlet injection section
BENZENE TOLUENE ETHYLBENZENE p-XYLENE m-XYLENE n-NONANE n-DECANE n-UNDECANE
Flgure 2. Chromatogram obtained In a glass capillary column with attached inlet Injection and outlet sectlons of fused silica capillary tublng: on-column injection used, with column initially at 60 O C for 2 min and then programmed at 2 ‘Clmln; solvent, 1 pL of hexane: carrier gas, helium; attenuation, 2’. and outlet section previously described. Chromatographic conditions are given in the figure caption. The resolution and peak shapes of the components are satisfactory and comparable to that obtained in our laboratory using on-column injection in bonded phase fused silica capillary columns (11). There was no evidence of any artifacts which might arise as a result of decomposition of the heat shrinkable Teflon joint. This technique for attaching a linear injection section to coiled glass capillary columns is a rapid, simple, and effective one for permitting the use of on-column injection. With only modest care, the Teflon joint results in a negligible dead volume to the system and prevents direct contact with samples. In the routine use of glass capillaries, breakage often occurs at either the inlet or the outlet due to its fragility, and this technique obviates such problems.
LITERATURE CITED (1) Schomburg. G.; Behlau, H.; Dielmann, R.; Weeke, F.; Husmann, H. J . Chromatogr. 1977, 142, 87-102. (2) Grob, K.; Grob, K., Jr. J . Chromatogr. t978, 151, 311-320. (3) Grob, K . J . Hlgh Resolut. Chromatogr. Chromatogr. Commun 1978, 1 , 263-267. (4) Schomburg, G.; Husmann, H.; Rlttmann, R. J . Chromatogr. 1981, -2nd - . , 85-96 -- - -. (5) Verzele, M.; Redant, 0.; Qureshl, S.; Sandra, P. J . Chmmalogr. 1980, 199. 105-112. (6) SandralP.; Schelfaut, M.; Verzele, M. J . Hlgh Resolut. Chromatogr. Chromatogr. Commun. 1982, 5 , 50-51. (7) Du Pont, Technical Bulletin “Teflon-Safety in Handling and Use”, 1981. (8) Alltech Associates, Inc., Catalog No. 45, pp 90. (9) Grob, K . , jr. J . Chromatogr. 1982, 237, 15-23. (IO) Mathews, R. G.; Torres, J.; Schwartz, R. D. J . Chromatogr. 1979, 186, 183-188. (11) Wang, F A . ; Shanfleld, H.; Zlatkls, A. Anal. Chem. 1982, 5 4 , 1886-1 888.
.
RECEIVED for review September 2,1982.
Accepted September
23, 1982.
Determlnation of Double Bonds and Isomer Purity of Olefins Louis F. Heckelsberg Research and Development, Philllps Petroleum Company, Bartlesvllle, Oklahoma 74004
A novel method has been developed for the rapid and accurate determination of double bond locations and isomer purity in olefins by using the olefin methathesis (disproportionation) reaction. In particular, it is based on the “four-
center-mechanism” theory and on a metathesis catalyst that is catalytically active at conditions where double bond isomerization is negligible. The “four center mechanism” (FCM) or “quasi-cyclobutane
0003-2700/83/0355-0398$01.50/0 @ 1983 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
399
Table I. GLC Analyses of the 1-Octene Sample and Reaction Products (wt %) olefins Figure 1. Four-center meclhanism.
structure" was proposed by Bradshaw, et al. (1) in 1967 to explain the metathesis reaction, and, although superseded by other mechanisms, is still valid for predicting the products of a metathesis reaction. According to the FCM theory, two olefins, R1HC=CHR2 and R3HC=CHR4, react to yield two new olefins, R1HC=CHR3 and R2HC=CHR4. This may be diagramed as shown in Figure 1. For the metathesis catalyst, the heterogeneous rhenium oxide/alumina catalyst (2)has proven to be especially suitable as it is active enough to operate in the temperature range of room temperature to 80 "C with high conversions and selectivities and does not exhibit any double bond isomerization activity in this temperature range. The advantage of this method is the ability to perform these tests quicker and more accurately than present methods. This method is intended, therefore, primarily for the heavier or liquid olefins as the lighter olefins are readily analyzed by other methods such as GLC.
EXPERIMENTAL SECTION The catalyst can be prepared by impregnating an amorphous alumina having a surface area greater than 100 m2/g with a water solution of ammonium perrhenate. The finished catalyst should contain enough rhenium oxide to be equivalent to 8% rhenium heptaoxide based on total catalyst weight (9.65 g of ammonium perrhenate per 100.0 g of 10-20 mesh alumina). The impregnated catalyst is then pretreated with dry air at 400 "C for 3 h in a quartz tube mounted vertically in1 an electric tube furnace. After the pretreatment, the catalyst can be cooled in a stream of air and then used for an analysis OF stored. It is recommended that the catalyst receive such a pretreatment just before an analysis. At the end of the analysis, the catalyst can be recovered, washed if necessary, and dried before storage. The procedure for the analysis is very flexible hence the following procedure is only suggestive in nature. The analysis is usually carried out in a flarak that has been dried at 125 "C for 1 h. Enough of the olefin to be analyzed is added to fill about one-fourth of the volume of the flask. The catalyst is then added to the liquid directly from the cooled pretreatment tube. The weight ratio of the catalyst to the olefin is about 0.5. The flask is then capped with a rubber septum and a hypodermic needle is inserted thru the septum to vent any pressure formed during the metathesis reaction. The flask is then either allowed to sit at room temperature or heated slightly on a hot plate (50-70 "C). Reaction time should be held to a minimum because of the possibility of further metathesis reactions between the initial products. The reaction is not sensitive to air, and no rigorous precautions are necessary to exclude air. RESULTS AND DISCUSSION T o demonstrate this method of analysis, we will describe four examples of actual ainalyses: (1)The first example will describe an analysis to determine the isomer purity of a sample of 1-octene (previously considered 99% pure). If the sample was 100% 1-octene, the products predicted by FCM would be only ethylene and the C14 olefin, 7-tetradecene. The analysis was conducted by reacting 20 g of the sample over 10 g of the rhenium oxide catalyst. GLC analyses of the reactants after a 15-min reaction time are given in Table I along with the analysis of the 1octene sample. The major metathesis reaction in this analysis is the reaction of 1-C8 with itself, and to a much lesser extent, the reactions of 2-C8 and 3-C8, the most probable impurities, with the
c2 c3 c4 c5 C7 C8 c9 c10 c12 C13 C14 C15
starting material 1-octene
gas
products liquid
97.8 2.2 trace 99.7 0.3 0.3 0.7 99.0
Table 11. Possible Metathesis Reactions and Illustration of the Method of Calculating the Analytical Results of Example 1 calculation, Fr, reaction 1428 2-C8 3-C8 total 1-C8 - 1428 + i-Cl-l 1-C8 - 2-C8 + 6C13 1-C8 - 3-C8 5 C 1 2
.- C2 T
T
C3 C4
final calculated results final results reported
99.0 0.4
0
0
0.3
0.2
0
0 0.1
99.6 99
0.3 1
0.1 trace
99.0 0. i
0.3 100.0
Table 111. Compositions of the 4-Nonene Sample and of the Liquid from the Metathesis Reaction of the Konene olefin c7 C8 c9 c10
c11
starting material 4-nonene
liquid from metathesis reaction 20.8 wt %
1OOwt%
52.1 27.1
23 mol % 53 24
predominating 1-C8. These reactions and an illustration of the method of calculating the analytical results are given in Table 11. The most probable impurity in this sample would be 2octene which would react with the predominating 1-octene to yield, according to FCM, propylene and a C13 olefin. These two hydrocarbons appear in the products as shown in Table I to the extent that indicates less than 1% 2-octene in the 1-octene sample. There are traces of other hydrocarbons as evidenced by the C9 in the 1-octene analysis and the C12 in the liquid product. These data indicate with a conservative bias that the sample olefin is a mixture of 99% 1-octene, 170 2-octene, and traces of other hydrocarbons. For this type of analysis of an olefin where gaseous products are possible, the following recommendations are made: (1) gaseous sample to be collected in a long needle syringe, (2) gaseous sample to be collected early in the run, and (3) the reaction be run vigorously enough to give a copious volume of gas to prevent stratification of the various gaseous products in the flask. Experience has shown that while the analysis of the gaseous product is quicker, the analysis of the liquid will give more accurate results. (2) The second example describes the determination of the isomer purity of a sample of a nonsymmetrical olefin, 4nonene, which will not give a gaseous product. If the sample consisted only 4-nonene, the FCM would predict the products to be a C8 olefin (4-octene) and a C10 olefin (5-decene). In this test 10 mL of the 4-nonene was metathesized over 2 g of
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Anal. Chem. 1983, 55,400-403
Table IV. Analyses of Olefin Blend before and after One Hour of Reaction ( w t %) olefin C6 c7 C8 c9 c10
c11
c12 C13 C14
Table V. GLC Analysis of the Liquid from the Self-Metathesis Reaction of lJ3-Tetradecadiene
before reaction after reaction
olefin
16.3
amt, wt %
48.0
13.9 1.0
Composition of Gas Phase c2 91 c3 9 c4
52.0
30.5 0.9 29.7 0.3 7.4
Composition of Liquid Phase C24 c25 6.7 C26 91.6 C27 1.7
the rhenium oxide catalyst. Analysis of the liquid after 1 hour of reaction gave the results shown in Table 111. Also included are the results of the GLC analysis of the 4-nonene sample. For pure 4-nonene, the mole ratio of CS/ClO should be 1.00 and the value from the data in Table I11 is 0.95. These results indicate this sample to be at least 95% 4-nonene. (3) The third example describes the determination of the isomer purity of the symmetrical olefin 5-decene. Because of the symmetry of the 5-decene, the FCM predicts only one product, 5-decene. As a tool for analysis of symmetrical molecules such as 5-decene, an equal mole amount of a nonsymmetrical olefin is mixed with the symmetrical compound to be analyzed. I t has been found advantageous to use 1octene which, on metathesizing with the 5-decene, will yield according to the FCM four olefins, a C2, C6, C12, and C14 olefin. One possible impurity in 5-decene is 4-decene which on metathesizing with the 5-decene/l-octene mixture will yield, according to FCM, five additional olefins, a C5, C7, C9, C11, and C13 olefin. Hence a comparison of the amount of even-carbon-number olefins with the amount of odd-carbonnumber olefins in the product will indicate the isomer purity of 5-decene providing the major impurity is 4-decene. Forty grams of the blended olefins were metathesized over 20 g of the rhenium oxide catalyst. Analyses of the blended olefins before the run and after 1h of reaction time are given in Table IV. These results indicate the isomer purity of the 5-decene to be about 95% with about 5% 4-decene. The results of this analysis are also useful in emphasizing the necessity of keeping the reaction time to a minimum. There are at least six different olefins resulting from the initial reactions all capable of undergoing further metathesis reactions yielding still more different olefins. (4) The fourth example describes the analysis of the isomer purity of a sample of 1,13-tetradecadiene. FCM predicts for this analysis that the products should be ethylene and 1,13,25-hexacosatriene,a 26 carbon triene. On metathesization of 35 g of the tetradecadiene over 20 g of the rhenium oxide catalyst for 1h, the results given in Table V were obtained.
These data indicate the isomer purity of the 1,13-tetradecadiene to be approximately 95%, The major impurity was probably 1,12-tetradecadiene. The accuracy of the data given in the preceding four examples is believed to be about 1to 2% which is about the same accuracy of most of the GLC results. Since the metathesis reaction is stoichiometric, the accuracy can be improved if more care is taken in the GLC analyses and by using higher purity olefin samples.
CONCLUSIONS The preceding four examples demonstrate the flexibility and versatility of a method based on the metathesis reaction for the determination of the location of olefinic bonds in and the isomer purity of olefins. The method is simple, using only readily available equipment, and rapid. Only about 1h of total time was required for each of the four analyses described in this report. In conclusion it is worthwhile to point out that while the four examples in this report. were selected to illustrate different applications, they were also selected because they are examples of practical applications of this method. The purpose of each example was as follows: (1)check isomer purity of 1-octene feed to a metathesis reactor unit, (2) determine isomer purity of a 4-nonene sample for a potential customer, (3) check isomer purity of 5-decene, typical of a number of analyses of symmetrical olefins which are produced by the metathesis reaction of commercially available a olefins, and (4) test a hypothesis that the two olefinic bonds in the tetradecadiene were conjugated. Registry No. 1-Octene, 111-66-0; 4-nonene, 2198-23-4; 5decene, 19689-19-1;1,13-tetradecadiene, 21964-49-8. LITERATURE CITED (1) Bradshaw, C. P. C.; Howman, E. J.; Turner, L. J . Catal. 1967,7,269. (2) Heckelsberg, L. F. U.S. Patent 3676520,July 11, 1972.
RECEIVED for review June 25, 1982. Accepted November 8, 1982.
Industrial Hygiene Personal Sampling of 2-Ethylhexanol and Determination by Flame Ionization Gas Chromatography Joseph Russo' and Shane S. Que Hee" Department of Environmental Health, University of Cincinnati Medical Center, 3223 Eden Avenue, Cincinnati, Ohio 45267
2-Ethylhexanol (2-EH) is the most important and widely used synthetically produced higher aliphatic alcohol (1). It is used principally as an intermediate in the manufacture of 'Presently at Badische Corp., Kearny, N J 07032.
plasticizers, the major one being bis(2-ethylhexyl) phthalate, commonly called dioctyl phthalate (DOP) (2). It is also used in the manufacture of wetting agents, synthetic lubricants, and 2-ethylhexyl acetate, as well as a solvent of nitrocellulose, urea resins, enamels, alkyd varnishes, and lacquers ( 1 , 2).
0 1983 American Chemical Society 0003-2700/83/0355-0400$01.50/0
