Determination of Normal Alpha-Olefins by Hydrobromination JOSEPH C. SUATONI Gulf Research and Development Co., Pittsburgh, Pa.
b A method i s described for the determination of normal alpha-olefins in olefinic mixtures within the CI2-C18 range. Hydrobromination of the olefin sample in the presence of lauroyl peroxide is utilized to convert normal alpha-olefins to normal primary alkyl bromides which can be separated from other alkyl bromides b y 5-A Molecular Sieve pellets. The weight of nonadsorbed bromides i s a measure of the impurity in normal alpha-olefins. The method determines normal alphaolefins in the presence of betabranched alpha, non-beta-branched alpha, normal and branched internal, and cyclic olefins.
C
and expense have been expended by the petroleum industry t o produce high purity normal alpha-olefini. These olefins are particularly valuable in the manufaeture of biodegradable detergent-,. Therefore, the necessity accurate method for det purity of the normal alpha-olefin;. Terminal olefins may be analyzed by infrared techniques (8, 9 ) , but thi; spproach does not differentiate normal alpha-olefins from alpha-olefin. having branching other than on the beta-carbon atom. These non-beta-branched alpha-olefins (H2C=CHR, where R iq a branched group) could be present with normal alpha-olefins, especially if the alpha-olefins are produced by a n a v cracking process. Thus, a study was initiated to inveetigate hydrobromination as a tool for the quantitative determination of the nonbranched terminal olefin type. Kharasch (2-5) reported that alpha-olefins when reacted in the presence of hydrogen bromide and organic peroxide form only primary alkyl bromide-. He worked primarily with lower nioleculai weight olefins because of a lack of pure high molecular neight alpha-olefin. His limited work n i t h high niolecular weight olefins (6) resulted in good yield. of primary bromides. Therefore, if the reaction were quantitative, the primal jbromides resulting from normal alphaolefins might be separated from the primary bromides formed from branched alpha-olefins, and from the secondary bromides formed from the reaction of
normal internal olefin.; by adsorption on 5-h Molecular Sieve-.. h measure of the weight of the bromides which were not adsorbed by Molecular Sieves n ould then be a direct indication of the total impurity in the normal alphaolefin. 1 number of morkers (6, 7 , 10) have used llolecular Sieves (synthetic zeolites) for the separation of normal paraffins from branched paraffins. Barrer ( 1 ) found that natural zeolites could be used to separate secondary bromides from primary bromides. Korking nith chabazite, gnielinite, and analcite, he found that primary alkyl bromides are adsorbed by aieves s l o d y at room temperature, and that secondary alkyl bromides were excluded.
ONSIDERABLE EFFORT
2196
ANALYTICAL CHEMISTRY
EXPERIMENTAL
Reagents. All chemicals were reagent grade unless otherwise specified. The olefins were obtained from the Phillips Co., American Petroleum Institute, and the Chemical Procurement Laboratories. The anhydrous hydrogen bromide was purchased from the Matheson Co. The 5-4 Llolecular Sieves pellets, purchased from Linde Co., were dried prior t o use by heating for 6 hours a t 450" C. under 1 to 5 mm. of Hg prebsure, and then cooled under vacuum. The solvent, 2,2.-l-trimethylpentane, n-as obtained from the Phillips Petroleum Co. Prior t o use. all normal paraffins nere removed from the solvent by adsorption with Molecular Sieves. Apparatus. The hydrogen bromide reaction flask was a 150-ml. capacity two-necked, round-bottomed flask fitted with a medium porosity fritted tlisk, 11 mm. in diameter, for hydrogen bromide dispersion. The gas chromatographic apparatus employed for evamination of the olefins and alkyl liromides consisted of a n F and h l Model 300 programmed-temperature chromatograph equipped with a 6foot. 1/4-inch column packed with 26% SE-31 Silicone Gum on Gas (;h;."oni P. Procedure. T o approximately 0.70 gram of samule in t h e reaction flask, &Id 0.05 gram of lauroyl peroxide nhich has been dissolved in 40 ml. of 2.2,4-trimethylpentane. Immerse the flask in a carbon tetrachloride bath. .Idd d r y ice t o t h e b a t h until t h e car11011 tetrachloride solidifies, and pass
anhydrous hydrogen bromide through the solution a t a rate of approximately 25 cc. per minute for 1.25 hours. At t h a t time, remove t h e b a t h and continue the hydrogen bromide addition for 0.5 hour. Disconnect t h e hydrogen bromide source, remove t h e flask from the reaction assembly, and add 0.5 gram of anhydrous sodium sulfate to remove traces of water if present. Place the flask in a water bath maintained a t 10" z 5' C. Purge the solution nith prepurified nitrogen for 25 minute- a t a rate of 25 cc. per minute. Decant the contents of the reaction flask into a 250-ml. Erlenmeyer flask fitted nith a 24/40 ground glass joint. Rinse the reaction flask n i t h four 7-ml. portion-. of solvent and add the washing* to the Erlenmeyer flask. -4dd 5 grams of dried 5-A 1\Iolecular Sieve pellets to the Erlenmeyer flask. Stopper the flask, snirl, and allow to stand a t room temperature for 25 minutei. Then add an additional 25 grams of sieve3 and reflux the mixture for 5.5 hour?. If the sample contains C18olefin. a reflux time of 6.5 houis is necessary. By means of a fine-fritted Buchner funnel filter the contents of the Erlenmeyer flask under 100 to 200 inin. of Hg pretsure. Rinse the flask and the Huchner funnel with five 20-ml portions of i-opentane and collect in the filteiing flask. Quantitatively transfer the contents, u-ing isopentane, to a previously 11eighed 250-ml. Erlenmewr flask. Place the flask in a n-ater bath, at room temperature, and evaporate the solvent by bloning air over the surface. If the olefin sample is C16 or CIS. the F'T apcxation time can be shortened bv maintaining the water bath a t 55' = 5' C. Obtain the neight of solvent-free re?idue and calculate the normal n!phaolefin content of the sample. RESULTS A N D DISCUSSION
General Discussion. This method is applicable to olefin fractions within the Clz to CI8 range. The method can be extended to higher molecular neight olefins by extending the reflux time for adsorption of the normal bromides. If the olefin sample contains normal paraffins, they will be adsorbed by the sieves and be calculated as normal alpha-olefinq. Branched saturates are not adsorbed and thus are calculated as impurity. The data in Tables I, 11, and 111, indicate the normal nlpha-
ISOOCTANE
Table I.
Reaction Yields of Higher Molecular Weight Olefins with Hydrogen Bromide
Sample size, gram 0 7136 0 6735 0 8737 0 8890 0.8935 1I-Tricosene 0.05 Gram added for lauroyl peroxide.
Olefin I-Hexadecene I-Tetradecene 1-Eicosene I
I
12
io
216
190
I
" 6
164
6 136
I
! 4
2
I12
86
0 TIME-MIN 6 0 T E M P 'C
Figure 1. Programmed chromatogram of product of 1-octene and HBr in isooctane
olefin content of an oldin fraction may be det,ermined with a relative error of ~t1.370. Hydrobromination of Olefins. T o determine the completeness of t h e reaction of hydroger. bromide 11-ith olefins, and if primar:: bromides only are formed from alpha-olefins, the reaction products were esamined by gas chromatography. 1-Octene was treated with hydrogeii bromide under t h e reaction condition,j specified above a n d a quantitative yield of l-bromooctane vas obtained. Figure 1 is a chromatogram of the reaction product of l-oct,ene with hydrogen bromide in isooctane. T h e presence of a n y nonreacted 1-octene rvould have been indicated by a peak a t 4.5 minutes. The retentmionh i e of 1-broniooctane was verified esperimentallp. The reaction of hydrogen broI nide and 2-oct'ene resulted (Figure 2 ) iii a quant,it'ative yield of 2-bromooctar.e and 3-bromooctane. Sonreacted 2-octene would have been indicated k~ya peak at 3.5 minutes. L-sing the iieight of t'he reaction product a.5 a nieisure of the conipleteness of the reaction n-it'll higher molecular weight. olefin., quantit,ative yield3 ivere also obtaiiied with l-tetradecene, 1-hesadeceiie, l-eico,kene! and 11-tricosene. The results are sunimarized in Table I. I n addition, these react'ion products of 1-tetradecene, 1-hesadecene, and 1l-i,ricoeene were refluxed with lloleculnr Sieves a t 99' C. The react'ion products of 1-tetradecene and 1-hesadecene were tot'ally adsorbed indicating the forniation of only primary bromides. The 11-t,ricosene reaction product rva. ,lot adsorbed, indicating secondary alkyl bromide.. Molecular Sieve Absorption Studies. T h e adsorption 3f n-bromohexadecanc (Table IV) bj. B--X Molecular Sieves n.as studied c.t a ratio of 25 grams of sieves to 1 gram of nbromohexadecane. The results of this study indicated t h a t at the reflux temperature of isocct'ane, 99' C., the time necessary f 3r complete adsorption of n-bromohesadecane was 5.5 hours. The reflux time may be decreased by increasing the ratio of sieves t o bromide. Fw example, at, a
Yield, grams Found Theory" 1 00s 1 021 0 998 I nni 1 167 I lT1 I 225 1 196 1 137 1 167
ratio of 50: 1, the time for complete adsorption of n-bromohexadecane a t 99' C., was trate, n-bromohexadecane was refluxed for 5.5 hours with sieves in the presence of isooctane saturated with hydrogen bromide. The amount of n-bromohesadecane adsorbed was 14% compared to 100% in the absence of hydrogen bromide. TKO techniques were evaluated to study the removal of hydrogen bromide from the reaction mixture. Initially the reaction mixture was evaporated on a steam bath t o a volume of 15 ml. This approach was not suitable for the complete removal of hydrogen bromide. Finally the hydrogen bromide was successfully removed by purging the reaction solution with nitrogen followed by the addition ISOOCTANE
Mole co reacted
9s Y
09 1 $19 5 100 2 'Ji i
of 5 grams of sieves. Some primary alkyl bromide may be adsorbed a t this st'age, but this causes no error since the nest step involves t'he removal of primary bromide by the addition of 25 grams of sieves. The nonadsorption of normal secondary alkyl bromides by 5-.\ Molecular Sieves was established by esperinient.ation with 2-bromobut.ane. -hi isopentane solution containing 2-bromobutane and naphthalene as she internal .standard \I-as allo\\-ed to stand for 48 hours at room ternperahre with JIolecular Sieves. The isopent,ane solution u-as examined chromatographically prior to the addition of sieves and aft'er t.he
Table II.
Examination of Synthetic Olefin Blends
Mole cC. normal alpha-olefin Theory Found
Compound I-Tetradecene 99s 1l)O.l) I-Tetradecene C14impurity" 95 0 9.5 6 1-Tetradecene C14 impurity" 51 0 0" 0 a 8'3% R,C=CH, and 115 RaC=CHR.
+ +
Table 111. Hydrobromination and Infrared Analysis of Normal AlphaOlefins
Carbon range CL2
Mole normal alpha-olefin Hydrohromination Infrared 96 1 'JLI .n 95 T
93 6
Cl4
03 3
93 1 I
I
I
I
I
12
IO
190
8 164
6 138
4
216
'
112
2 86
I 0 TIME-MIN. 6 0 T E M P 'C
Figure 2. Programmed chromatogram of product of 2-octene and HBr in
94.5
isooctane
Table IV.
Compound n-Bromohexadecane %-Bromohexadecane n-Bromohexadecane n-Bromohexadecane Lauroyl peroxide
Molecular Sieve Adsorption Studies
Temp., "C. 26 26
Time, hours
99 99
5112 5112
21/4
4'14 6
26
VOL. 35,
Weight 5-h adsorbed 77.0 86 2 S8 6 100 0 100 .0
NO. 13, DECEMBER 1963
2197
addition of sieves. These data are shown in Figure 3. It is evident that 2-bromobutane was not adsorbed by 5-A sieves. The nonadsorption of secondary alkyl bromides was further confirmed by the exclusion of the reaction product of 11-tricosene with hydrogen bromide. Examination of Synthetic Blends. Because of the lack of pure olefins in the C M range, the impurities used to blend with 1-tetradecene were isolated from a commercial C14 alpha-olefin. The impurities were separated by contacting the alpha-olefin with 5-A Molecular Sieves for 18 hours a t the reflux temperature of 2,3-dimethylbutane. After removal of the solvent, the impurities were blended into API I-tetradecene. It can be seen from Table I1 t h a t there is good agreement between the actual normal alphaolefin content of the sample and the normal alpha-olefin determined by this method. Hydrobromination Analysis of Alpha-Olefin Samples. Table I11 is a comparison of the analysis of alphaolefin samples by the hydrobromination and infrared techniques (8). The samples that were analyzed were formed by an ethylene polymerization process. Since the olefins contain little if any
2-8ROMOBUTPNE
1
lSoPENTANE
ORE S I E V E S )
ACKNOWLEDGMENT
lLENE
2;.
employed; whereas, the infrared technique wiIl be in error to the e,utent of non-beta-branched alpha-olefin.
2-BROMOBUTANE
1
ISOPENTPNE
The author grat.efully acknowledges Robert E. Snyder for technical advice, Paul M. Brown for providing the gas chromatographic analysis, and Eleanor L. Saier for providing the infrared data. LITERATURE CITED
NAPHTHALENE
10 190
8
6
164
138
4 I12
2 86
0 TIME-MIN 60 T E M P - * C
Figure 3. Programmed chromatograms of 2-bromobutane and naphthalene in isopentane
non-beta-branched alpha-olefins, there is good agreement between the methods of analysis. I n the future, when normal alpha-olefins are prepared by other processed especially wax cracking, and nonbeta-branched alpha-olefins are present, the hydrobromination technique may be
(1) Barrer, R. M., J . Chem. SOC. Ann. Rept. X I Z , 44, (1944). (2) Kharasch, M. S., Hinckleng, J. A . , Jr. , J . Am. Chem. SOC. 56, 1212 (1934). (3) Kharasch, M. S., Mayo, F. R., Ibid., 55,2468 (1933). (4) Kharasch, M. S., McNab, M. C., Mayo, F. R., Ibid., p. 2531. (5) Kharasch, M. S., Potts, W. M., J . Org. Chem. 2, 195 (1937-8). (6) Nelson. K. H., Grimes, M. D., Heinrich, B. J'.,ANAL.CREM.29,1026 (1957). (7) O'Connor, J. G., Norris, M. S., Ibid., 32, 701 (1960). (8) Saier, E. L., Cousins, L. R., Basila, M. R., Zbid., 35, 2219 (1963). (9) Saier, E. L., Pozefky, A., Coggehall, N. D., Ibid., 26, 1258 (1954). (101 Schwartz. R. D.. Brasseaux. D. J.. Ibid., 29,1022 (i957j. RECEIVEDfor review July 19, 1963. Accepted August 26, 1963. Division of Petroleum Chemistry, 145 Meeting, ACS, Kew York, K. Y., September 1963.
Reflectance Fluorescence Spectra of Aromatic Compounds in Potassium Bromide Pellets B. L. VAN DUUREN and C. E. BARD1 Institute of Industrial Medicine, New York University Medical Center, New York, N. Y.
b The reflectance fluorescence excitation and emission spectra of solid aromatic compounds were measured in potassium bromide pellets in the concentration ranges 0.00002 to 0.2 mmole of compound per gram of potassium bromide. In some instances the fluorescence spectra were identical with those of solution spectra, whereas in others the maxima were shifted to longer wavelengths. For some hydrocarbons the appearance of the spectra was concentration-dependent. The fluorescence excitation and emission maxima of solid charge transfer complexes were also measured in potassium bromide pellets.
T
fluorescence spectra of dilute solutions of aromatic hydrocarbons have in recent years been investigated extensively (17') and are often used in analytical work (18). However, comparatively few studies have been carried out on the fluorefcence characteristics ocaromatic hydrocarbons in solid form. HE
2198
ANALYTICAL CHEMISTRY
The fluorescence of solids has been studied using powdered crystalline materials (13, 1 4 ,single crystals (18, 16), microcrystalline suspensions (6), and microcrystalline deposits on glass plates (2). In the present work the fluorescence of solid aromatic hydrocarbons was investigated in potassium bromide pellets. The pellet technique was first developed for infrared absorption spectrometry and it is noF widely used for this purpose. More recently pellets were also used for ultraviolet and visible absorption spectrometry (IO,19). The reflectance fluorescence method was developed for the examination of weak charge transfer complexes of biological interest. Such application will be described elsewhere. In the course of this work a number of observations were made on the fluorescence of solids and these are examined in this report. The method also offers the obvious advantage that absorption, fluorescence, and infrared spectra can be measured on the same sample.
EXPERIMENTAL
Purification of Aromatic Compounds. All compounds used in this
work were purified by one or more of the following procedures: column chromatography, crystallization, and vacuum sublimation. Purity was established by melting points, ultraviolet absorption spectra, and the absence of other fluorescent compounds as shown by thin-layer chromatography on silica gel plates ( 1 ) (solvent: cyclohexane-benzene, 1:1). Preparation of Periflanthene [Diindeno (1,2,3-cd:1',2 ',3'-1m) p e r y l e n e ] . This hydrocarbon was prepared by selfcondensation of fluoranthene with sodium amide in xylene ( 7 ) . The compound was purified by vacuum sublimation t o give red crystals (m. p. > 360" C.). Anal. Calcd. for CSHM: C, 95.97; H, 4.03. Found: C, 96.08; H, 4.03. 1,3,5-Trinitrobenzene. Commercial grade material (K & K Laboratories, Jamaica, N. Y.) was purified by repeated crystallization from 957, ethyl alcohol (m.p. 123-5" C.).
