1046
A N A L Y T I C A L CHEMISTRY Plutonium Project Report, Chapter on Spectrochemical Analvsis (not vet ~ublished). Fred, M., Nachke6, N. H.,’and Tomkins, F. S., J . Optical Soc. Am., 37,279 (1947). Gassman, A. G., and O’Neill, W. R., ANAL.CHEM.,21, 417 (1949).
Gerlach, Walther, and Schweitrer, Eugen, “Die chemische Emissionsspektralanalyse,” Pt. I, Leipaig, Leopold Voss. 1933.
Gramont, A. de, Compt. rend., 144, 1109; 145, 1170 (1907). Hartley, W.N., J . Chem. Soc., 41, 90 (1882). Jolibois, P.,Compt. rend., 202,400 (1936). Jolibois, P., and Bossuet, R., I b i d . , 204, 1189 (1937). Ibid.,209, 91 (1939). Kaiser, H.,and Honerjager-Sohm, M., Spectrochim. A c t a , 2, 1 (1941); 2, 396 (1944); 3, 159 (1948). Keirs, R.J., and Englis, D. J., IND. ENG.CHEM.,A k ~ . *ED., ~ . 12, 275 (1940). Lamb, F. W., Ibid., 13, 185 (1941). Lomakin, B. A., Z.Physik, 40, 548 (1927).
Lundeghrdh, H.,”Die quantitative Spektralanalyse der Elemente,” Pt. I, Jena, G. Fischer, 1929. Mann, K. E., Spectrochim. A c t a , 1 , 560 (1941). Nedler, V. V., and Efendiev, F. M.,Zauodskaya Lab., 10, 198 (1941).
Pavlovschi, G . , and Mavrodineanu, R., B141l. soc. roumaine phys., 42, 53 (1941).
Pierucci, M.,and Barbante-Silva, L., Suovo cimento, 17, 275 (1940).
Rivas, A . , Angew. Chem., 50,903 (1937). Rohner, F., Helu. C h i m . Acta, 20, 1054 (1937). Ibid., 21,23 (1938). Scheibe, G., and Rivas, A., Angew. Chem., 49, 443 (1936). Sloviter, H. A , and Sitkin, A,, J . Optical SOC.Am., 34, 400 (1944).
Sventitskii, N. S., J . Tech. P h y s . (U.S.S.R.), 14, 605 (1944). Twyman, F.,“Spectrochemical Analysis of Metals and Alloys,” Brooklyn, N. Y., Chemical Publishing Go., 1941. Twyman, F., and Hitchen, C. S.,Proc. Roy. SOC. ( L o n d o n ) , A133,72 (1931).
Uzumasa, Y., and Okuno, H.. J . Chem. S O C .J a v a n , 56. 1174 (1935).
Walti, R., dissertation, Eidgenossische Technische Hochschule, Zurich, 1943; Helu. C h i m . A c t a , 23, 1446 (1940). RECEIVED January 27, 1949. Presented in part before the E a s t Tennessee Section of the AxERICAN C H E Y I C A L SOCIETY, Oak Ridge, Tenn., June 5 , 1948, and the Optical Society of America, Detroit, hfich., October 22, 1948. Work performed under contract 7405 eng. 26 for the Atomic Energy Project.
Apparatus for Quantitative Separation of Butadiene from Its Dimer - -
JAMES L. JEZL’ AND CHARLES P. HABLITZEL Sun Oil Company, Toledo, Ohio
A method is described which permits quantitative removal of 4-vin~-l-l-cyclohexene from butadiene without changing the concentration of small amounts of Cs hydrocarbons in the butadiene fraction. In this procedure the sample is charged into a simple column and is distilled at a rapid rate with slight reflux until vapors no longer come over. The packing is dried by brief standing at room temperature, and the condensed overhead vapors are
I
N T H E analysis of butadiene, the dimer, Pvinyl-l-cyclo-
hexene, is an impurity whichnot only has been difficult to determine accurately, but also has been objectionable in various analyses in which high boiling impurities interfere. This interference is particularly pronounced in the determination of CS hydrocarbons by the Dorell weathering test apparatus (5); it causes high results even when present in comparatively low concentrations, The Dorell method, therefore, requires a sample free of dimer. Simple flash distillation methods fail to effert a good separation of dimer. Hobbs and Rector ( 2 ) present a method which is a marked improvement over unrefluxed distillstions. The apparatus described below was originally developed for quantitative separation of dimer prior to its analysis by chemical methods. It has, however, proved equally satisfactory for obtaining a dimer-free overhead sample in which the C, and Cb components are not altered in concentration. I n this way, the bottoms, such as dimer and nonvolatile residue, and overhead vapors may be separated by a single distillation in a manner satisfactory for subsequent analysis of each. The apparatus, moreover, has shown itself to be adaptable to many separations of a similar nature. 1 Present address, Developmpnt Laboratory, Sun Oil Company, Marcus Hook, Pa.
used for tests requiring a sample that is free from dimer. The residue may be further treated and analyzed chemically for dimer and other relatively nonvolatile materials. Data and graphs showing accuracy and reproducibility of the method are presented. The column is adaptable to other separations of similar nature in which small concentrations of relatively high boiling material are to be removed from volatile samples. 4PPARATUS
The complete apparatus is shown in Figure 1. A is a 125-ml. flat-bottomed flask with a 24/40 standard-taper joint, serving a s boiling kettle for the apparatus. The short vacuum-jacketed column, B , consists of a Figure 1. Comground-glass joint to fit plete Assembly flask A , a 125-mm. secfor tion of 0.3-cm. (0.125inch) glass helix packing which serves as the dimer-stripping section, and small dry ice reflux condenser, C. Vapor outlet D is connected to condensing trap F by means of vapor line E. The trap is maintained in a dry ice-acetone bath, G. All glass is Pyrex, and connections to vapor line are made with neoprene tubing. Water bath W is a 1000-ml. beaker. The column is shown in Figure 2 with complete dimensional data.
V O L U M E 2 1 , NO. 9, S E P T E M B E R 1 9 4 9
Figure 2.
1047
Column for Dimer Removal
The vacuum jacket surrounding the packed section is unsilvered. Columns without jackets have worked satisfactorily, although greater reproducibility is possible with a jacketed column. The packing in the column is retained by two whorls of Chrome1wire. The upper whorl is kept in place by glass crossbars sealed into the inner n d . The lower whorl is retained and held firmly against packing by means of a closely wound Chrome1wire spring which fits snugly to the wall of the column. A t a point within the ground-glass joint the end of the spring is enlarged to form an adjustable ring somewhat larger than the smallest inside diameter of the joint. In this way, the spring, upon insertion into position, seats itself against the wall of the joint and maintains firm, constant pressure against the packing.
Figure 4.
OPERATIOS
The columri is mounted on a ring stand, and the vapor line IS connected to the glass receiver, F, which is kept in a dry iceacetone bath (below -40" C.). About 1 inch (2.5 em.) of pulverized dry ice is placed in the column condenser, C. The chilled sample (50 or 100 ml.) is measured in a chilled graduate and introduced into flask A . The flask is connected to the coluinn (no stopcock grease is necessary). Approximately 500 ml. of warm water (45' * 5' C.) are added to the water bath and refluxing of sample is started a t a rate of about 2 drops a second by momentarily immersing the flask in the water bath a t required intervals. Initial vapors should be completely condensed. After 1minute on "total reflux," the reflux rate is cut down to 1 drop every 4 seconds and about 0.3 em. (0.125 inch) of the bottom of th.1 sample flask is submerged in the water bath. The transition from total reflux is readily achieved by agitating the dry ice in the condenser during the first minute and then permitting the ice to go undisturbed. If the reflux rate falls too low, slight agitation of the dry ice or constant pressure by a test tube or glass rod on the ice will bring up the rate. More dry ice is added when necessary. When the volume of the residual butadiene decreases to approximately 10 ml., the flask is submerged in the water bath to the neck and the distillation is permitted to con-
Dorell Curves for Isopentane-Vinyl Cyclohexene SIixtures
tinue to dryness. About 10 minutes are required for the distillation of a 50-ml. sample. After the flask reaches dryness, the residual dry ice in the condenser is removed and the assembly is permitted to stand for 5 to 10 minutes to ensure complete drying of packing. Liquid dimer may be visible in the flask or on the lower portion of the packing if appreciable quantities are present in the sample. The glass trap is disconnected from the flask, the condensate is thoroughly mixed, and the sample is used for the Dorell weathering test or for other tests requiring a dimer-free sample. The complete distillation operation should take less than 30 minutes. If a dimer analysis is desired on the residue remaining in the column, chloroform is introduced into the column through vapor outlet D , a steam-heated Ivater bath is substituted for It7, the last traces of butadiene are stripped from the column, and the cooled chloroforin residue is analyzed for dimer by the bromination method of Hablitzel and Jezl ( 1 ) . .hthe rccovcry 16 quantitativc, other trsts on the nonvolatile portion may also he made. RESULTS AXI) DISCUSSIO\
In urdei tu test the efficiency of the column for dimer reinoval, butadiene samples before and after distillation through the
1048
ANALYTICAL CHEMISTRY sists of a glass tube graduated from 0 to 40 ml., the first 10 nil of which are accurately calibrated and enclosed by a removable vacuum jacket. Heat is supplied by a pinpoint heater of copper fused into the bottom of the tube and in contact with a special cartridge heater. A Cottrell pump sprays the vapor-liquid equilibrium mixture formed at the pinpoint heater onto a thermometer having a range from -10" to + l o " C. and accurately graduated to 0.1" C.. A sample chilled to about -20" C. is charged to the tube to the 40-ml. mark, the thermometer is inserted into place, and the sample is "weathered away" to dryness. Temperature readings are taken a t 10.0,9.0,8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, 1.0, 0.8, 0.6, 0.4, 0.2, 0.1 ml., and a t the dry point. Special precautions are taken to keep the pump operating efficiently during the weathering of the last 10 ml.
column were analyzed in a Dorell weathering test apparatus in the specified manner. The Dorell apparatus is a modification of the Cottrell boiling point apparatus, especially adaptcd to volatile liquids. I t con-
Table 1.
Analysis of Synthetic Samples Distilled through Dimer-Removing Column Weight "c Isopentane Theoretical Dorell Actual analysis" analysis
hIixture Composition 0.00 0.02 0.20% dimer (b.p. 129' C.i 0.00 0.03 0.50% dimer 0.00 0.02 1.00% dimer 0.24 0.24 0.24% isopentane (b.p. 27.9' C . ) 0.22 0.00% dimer 0.25 0.24 0.24% isopentane 0.22 0.20% dimer 0.20 0.20 0 . 2 0 % isopentane 0.20 0.20% dimer 0.50 0.50 0 6 0 7 isopentane 0.50 0 : 20% dimer 1.0 1.0 1.00% isopentane 1.0 0.20% dimer 0.50 0.50 0.20% n-pentane (h.p. 36.0' C.1 0.48 0.00% dimer 0.50 0.50 0.20% n-pentane 0.48 0.20% dimer 0.65 0.65 0 . 2 0 7 dimethylacetylene (b.p. 27.1' C . ) 0.20% dimer 1.2 1.2 O.4OY0 dimethylacetylene 0.20% dimer 1 . 5 1 .? 0.50% dimethylacetylene 0.20% dimer 0.23 0.20 0 , 0 6 7 isoprene (b.p. 34.1' C . ) 0 . OOJ dimer 0.23 0.25 0.0f370 isoprene 0.22 0.20% dimer 0.65 0.63 0.20% isoprene 0.62 0.20% dimer 0.80 0.83 0.207& &-trans-piperylene (h.p. 42.3O C . ) 0.80 0.00% dimer 0.83 0.80 0.20% cis-trans-piperylene 0.86 0.20% dimer 0.22 0.18 O.O5T0 1.3-cyclopentadiene (h.p. 41 .Oo C.) 0.20 0.00% dimer 0.22 0.20 0.05% 1.3-cyclopentadiene 0.20 0 . 2 0 % dimer a Values obtained by comparing D o d l weathering curve8 of undistilled samples containing stated concentrations of Gr h y d m r b o n e (without dimer) with standard isopentane Dorell curves (Figure 6).
.
Because of submersion of the thermometer bulb in the someyhat superheated sample, readings a t 10 and 9 ml. were generally high and were disregarded. If no constant boiling temperature was apparent, the 8-ml. value was taken as the constant boiling temperature from which temperature elevations were calculated. The operation of the Dorell apparatus has been described fully ( 2 , 3 ) . Figure 3 shows the effect of various concentrations of dimer (4-vingl-l-cyclohe\ene) on the Dorell weathering test. Only the last 10 ml. are plotted. Temperature elevations mere obtained by algebraically subtracting the constant boiling temperature from the observed temperature for a particular volume reading. A curve for 0.20% isopentane (2-methylbutane) is included for comparison. From these curves it is apparent that the effect of dimer on Dorell weathering is many times that of isopentane. Figure 4 shows the effect of distillation through the column on samples with varying concentrations of dimer and isopentane. So-called "pure" butadiene, which Fas used in preparing all mixtures, was butadiene of high purity which, when analyzed by a Dorell apparatus, shos-ed an elevation of no moIe than 0.1 O C from the constant boiling temperature to the dry point. Curves D and E coincide with B, indicating that the columrl neither removed measurable isopentane from the overhead sample nor permitted dimer to escape into the condensing trap. The completeness of dimer removal is further indicated by curve F , which nearly coincides Tvith curve G for pure butadiene. Figure 5 shows the effect of distillation on samples containing n-pentane instead of isopentane. Here, curves C and D coincide with B, indicating again a quantitative removal of dimer vithout loss of the C j hydrocarbon. Table I summarizes data obtained in this laboratory on most of the C6 compounds normall>- present in butadiene. Dimethylacetylene is included because its effect on Dorell Feathering is oomparable with a CI compound. Column 1 gives the composition of the mixture before dimer removal; column 2 shows the Dorell analysis obtained by analyzing the sample before dimer addition and determining the equivalent amount of Ci calculated as isopentane, by use of the curves in Figure 6; and column 3 shows the analysis after dimer removal, again by use of the curves in Figure 6. The values in columns 2 and 3 should be identical, within limits of the accuracy of the Dorell weathering test apparatus, if the column is giving quantitative separations. This laboratory has found that the Dorell apparatus can repeat to approximately 0.03% of the true value a t about 0.2% isopentane. At higher concentrations the inaccuracy increases until a t 1.0% isopentane the discrepancy approximates 0.1%. A 10 to 15% relative error should therefore be allowed on either side of the expected value for the Dorell apparatus. Considering this
1049
V O L U M E 21, NO. 9, S E P T E M B E R 1 9 4 9
of dimer, and the preparation of samples prior to determination of conjugated diene content. Private communications indicate that results are very gratifying. By a slight modification of conditions, such as reflux rate and temperature of the water bath, dimer in concentrations greater than stated above may be removed. Styrene may likewise be separated from butadiene, as has been demonstrated in this and other laboratories. Other separations of similar nature readilv suggest themselves. ACKNOWLLWGMENT
The authors wish to express their appreciation to L. R. Kumnick and to R. G. Bowers, chief chemist, for their suggestions and encouragement in this work. Figure 6.
Standard Dorell Curves for Isopentane
inaccuracy of measurement, the results in Table I for the wide range of C i s are satisfactory. A 4 1 t h ~ ~the g h foregoing data concern only butadielle and its dimer. other C, and Cg compounds have been satisfactorily wparated‘ The method has been adopted by both proOf butadiene for separations in ducers and tion with the Dorell test for C ~ ’ Sthe , chemical determination
LITERATURE CITED
(1) Hablitzel, C . P., and Jezl, J. L., -&SAL. CHEM..21. 1049 (1949). (2) Hobbs, A. P., and Rector, M. R., ISD.ENG.CHEM.,A X I L .ED., 18, 140 (1946). (3) Podbielniak, Ino., 8312 South Chicago Ave., Chicago 17, Ill., Circ. 28, “Dorell Weathering Test Apparatus.” RECEIVEDNovember 5 , 1948. Investigation carried out under sponsorship of the Office of Rubber Reserve, Reconstruction Finance Corporation, in oonnection with the government synthetic rubber program.
Determination of Butadiene Dimer (4-Vinyl1-cyclohexene) in 1,3=Butadiene Bromination Method CHARLES P. HABLITZEL AND JAMES L. JEZL’ Sun Oil Company, Toledo, Ohio
Ar
h ACCURATE determination of dimer (4-vinyl-1-cyclo-
hexene) in 1,gbutadiene is required not only for determining the purity of the butadiene but also for controlling an impurity which is considered detrimental to polymerization grade butadiene. All previous methods used for dimer determination have been mainly physical in nature, making use of the dimer’s relative nonvolatility (8). Such methods either have been time-consuming or have lacked accuracy and precision. The procedure described in this article overcomes these objections by using the fractionating column of Jezl and Hablitzel (3) for removing the butadiene quantitatively and determining the dimer present in the residue chemically by bromination. The investigations in this laboratory centered around chemical methods for determining dimer in 1,3-butadiene in order to avoid repeated weighings and to decrease the over-all time required by physical methods. The requirements for such a method included 1
Present address. Development Laboratory, Sun Oil Company, Marcus
Kook, Pa.
a means for the removal of the butadiene without lw of dimer, and a quantitative chemical determination not affected by the presence of p-tert butylcatechol (an antioxidant) and other nonvolatile residues usually present in polymerization grade butadiene. Subsequent to the work described herein several chemical methods for determining dimer or pure Pvinyl-l-cyclohexene in products other than butadiene were described. Laitinen, O’Brien, and Kawzonek ( 5 ) in determining 4-vinyl-l-cyclohexene in recycle styrene found iodine chloride addition satisfactory in a dioxane medium; the reaction was 93 to 97% complete, depending upon the purity of the material. These investigators found iodine bromide and bromine in glacial acetic acid w t i s f a c t o r y . Warshowsky and Elving ( 9 ) described the determination of butadiene dimer in tetrahydrophthalic anhydride using a cyclohexane extraction with the unsaturation determined by the bromidebromate titration method of Mulliken and Wakeman (6). Johnson and Clark ( 4 ) reported satisfactory bromination of 4vinyl-1-cyclohexene, purified by fractionation, with a bromine
