ANALYTICAL EDITION
108
Vol. 3, No. 1
Problems in Estimation of Unsaturated Hydrocarbons in Gases 111-Some Factors in Bromination with Potassium Bromide-Bromate Mixture1I2 H. S. Davis,’ G. S. Grandall,‘ and W. E. Higbee, Jr.4 MASSACHUSETTS INSTITUTEOR TECHNOLOGY, CAMBRIDOE, MASS.
It has been shown that aluminum chloride and cerAlthough the bromideHE estimation of the tain other metallic salts prevent the quantitative bromate solution is stable in unsaturated content of titration of ethylene by the bromide-bromate method. neutral solution, j t &cornpetroleum fractions by I t has further been established that oxygen prevents poses when acidified, liberab halogenation m e t h o d s has the quantitative titration of acetylene by the bromideing bromine, An equivalent been found to be subject to bromate method. disconcerting v a r i a t i o n s quantity of acid is necessary A standard procedure is developed by which ethylene to liberate the bromine as is Further, the addition of the and acetylene and some of their higher homologs are shown by the following equahalogens to the acetylenes is titrated quantitatively by bromide-bromate solution. tion: incomplete. The causes for This procedure is applied to the analysis of synthetic these v,ariations have remixtures of gaseous olefins and acetylenes with enKBr03 5KBr f 3H*S04 = mained obscure. Two excel3Kzso4 3Brz 3Hz0 couraging results. lent reviews of this subject I t is suggested that oxygen may be one of the prinHence, by slow addition of the have recently been given (9, cipal causes of the irregularities found in halogen titraacid, the bromine is liberated 12), and the present paper tions of the acetylenes by other methods. slowly, and the rate can be so deals with an experimental Propine and butine-1 are prepared and their boilcontrolled that the bromine is investigation of the factors ing points determined in a vacuum-jacketed spiral taken up by the unsaturated affecting the completeness of column. comp6unds as fast as it is the titration of unsaturated generated. I n this manner, hydrocarbons by b r o m i n e , the concentration of the halogen-is kept low so that substitu: using the bromide-bromate method of Francis (11, I, 2)tion reactions are practically avoided. After the reaction is Experimental completed, saturated potassium iodide solution and considerable water are added. The vacuum is broken and the stopper Since this research dealt mainly with gaseous hydro- removed. Then the iodine formed is titrated with standard carbons, it was necessary to develop a special procedure for thiosulfate solution. The mols of bromine absorbed by one the titrations. The equipment required was a stout-walled mol of gas can easily be calculated. reaction bottle fitted with a stopcock, described below, a After a large number of preliminary tests had been made machine to shake the reaction bottles set in a vertical position on the olefins and acetylenes, the important fact was disat a rate of 250 strokes per minute with a 4.5-cm. stroke, covered that oxygen prevents the quantitative titration of gas burets, Hempel gas pipets, 2 Geissler burets, and 1 Mohr acetylenes and probably of some diolefins. Accordingly, buret fitted with a rubber tube 40 cm. long. The materials a procedure has been adopted which excludes oxygen as far used were potassium bromide-bromate solution (approxi- as possible from the reaction flask. mately 0.5 N ) , sodium thiosulfate solution (about 0.1 N ) , 10 per cent sulfuric acid, bromine in potassium bromide Standard Procedure solution, 33 per cent potassium hydroxide solution, potassium pyrogallate solution, and saturated potassium iodide solution. The bromide-bromate solution required for the experiment The reaction bottle is a modification of the type used is measured from the buret into the reaction bottle. The by Dobrjanski (7), and consists of a 300-cc. glass-stoppered volume used should be only about 2 cc. in excess of the equivabottle with a capillary stopcock sealed through the stopper. lent quantity, which must be determined by trial experiments A short connecting tube of larger bore is sealed to the stop- or from a priori information about the approximate comcock for attaching the apparatus to burets. position of the sample. The bottle is then evacuated by a The general procedure for the titration of gaseous olefins water pump until the solution boils. If the tap water is not is as follows : The bromide-bromate solution is measured considerably cooler than room temperature, it may be into the reaction bottle which is then stoppered and evacu- necessary to heat the bottle with warm water. The gas ated by a water pump. A measured volume of the gas is sample is measured in a buret, is washed twice with potassium drawn in without breaking the residual vacuum. Then pyrogallate solution in a Hempel pipet (shaking one-half dilute sulfuric acid is admitted slowly from the Mohr buret. minute each time), and is then drawn into the buret and measured. The connecting tube of the evacuated bottle is 1 Received September 4, 1930. This paper contains results obtained filled with water to prevent the addition of air. It is then in an investigation of the “Relative Rates of Reaction of the Olefins,” listed as Project No. 19 of American Petroleum Institute Research. Financonnected to the buret and the washed sample drawn into the cial assistance in this work has been received from a research fund of the bottle. The connecting tube is again filled with water and American Petroleum Institute donated by John D. Rockefeller. This fund attached to the Mohr buret containing 10 per cent sulfuric is being administered by the Institute with the cooperation of the Central acid. The rubber tube is about 40 em. long to permit vigorPetroleum Committee of the National Research Council. Contribution No. 65 from the Research Laboratory of Organic Chemisous shaking of the bottle while it is attached to the buret. try, Massachusetts Institute of Technology. One cubic centimeter of the acid is added every half minute, 8 Present address, Research Laboratories, Vacuum Oil Company, the bottle being shaken vigorously between the additions. A Paulsboro, N. J. volume of acid equal to the volume of bromide-bromate 4 Junior research fellows, Project No.19.
T
.
+
+
January 15, 1931
INDUSTRIAL AND ENGINEERING CHEMIXTRY
mixture taken is added, which is about a 200 per cent excess. When all the acid has been added, the buret is disconnected and the acid in the connecting tube is nearly all drawn in, care being taken that no air is admitted. The bottle is then shaken by the machine for 1 to 11/4 hours to complete the reaction. At the end of this time the bottle is removed and 3 to 5 cc. of saturated potassium iodide solution added; 20 cc. of water are also added before the vacuum is broken, the bottle is opened, and the solution diluted to from 100 to 150 cc. The iodine liberated is titrated to a colorless solution with standard thiosulfate solution. The total volume of unsaturated gas in a separate portion is determined by finding the fraction that is absorbed by bromine in potassium bromide solution. Only a slight modification of this method is necessary for the titration of liquid or solid samples. The sample is sealed in a thin-walled glass capsule (4), weighed, and placed in the reaction bottle. After evacuating, the capsule is broken by shaking the bottle, the sulfuric acid is added, and the remainder of the analysis carried out as above.
volume dissolved quickly in bromine water, and the remainder slowly; b. p. -28" to -27' C. (compare the value -34.4" C. given in the International Critical Tables, 15). The values obtained in various experiments are collected in Table I. T a b l e I-Results
of Experiments w i t h Various S u b s t a n c e s
Hours PARAFFINS"
Methane Ethane Butane Isobutane
21/n I'/a
Standard Standard Standard Standard
ll/r ll/r
*
1 1 1 1
0.01 0.00 0.02 0.07
In this series the gases were not shaken with pyrogallate solution, but were washed with bromine in potassium bromide solution t o remove any unsaturated compounds t h a t were present. 5
PROCEDURE
SUBSTANCE
OLEFINS
Ethylene
Substances
PARAFFINS-Samples of gases compressed into small steel bottles were purchased. The degree of purity claimed for them was: methane, 92 per cent; ethane, 99 per cent; isobutane, 99 per cent; and normal butane, 99 per cent (10). OLEFINS-The methods by which the olefins were prepared have already been described (S,5). DIoLEFINs-Propadiene (allene), b. p. -32.8"to -31.3"C., was prepared by slowly dropping 2, 3-dibromopropene (Eastman Kodak Company) into boiling alcohol and zinc dust (IS). 1,%Butadiene (erythrem),b. p. -2" to -1 " C., was prepared by reducing erythrene tetrabromide with zinc dust in boiling alcohol solution. As Thiele has pointed out (19), it is necessary to add the tetrabromide slowly to the alcohol in order to obtain good yields. This requirement was met by placing the crystals in a test tube under the drip from a reflux condenser fitted to the flask, and under these conditions the yield of butadiene was 80 per cent of the theoretical. The erythrene tetrabromide, which had been prepared from cracked gases and recrystallized, was obtained through the kindness of V. Schneider. ACETYLENES-ordinary acetylene from a tank of the compressed gas was washed with water, with concentrated potassium hydroxide, with concentrated sulfuric acid, and was then stored over water. The sample gradually became contaminated with air. Methylacetylene, b. p. -20" to -18" C. (compare -27.5" C., International Critical Tables, 1.4, was prepared by slowly adding methyl iodide to sodium acetylide in liquid ammonia (IS). The liquefied product was fractionated through a vacuum-jacketed spiral column. Ethylacetylene was prepared in a similar manner, using ethyl iodide in place of methyl iodide, b. p. 6.8" to 8.5" C., (compare Picon's figure, 8" C., 18). The value 18.5" C. given in the International Critical Tables (17) seems to be too high. Samples of 1-heptine, 1-octine, Zoctine, and 4-nonine1were kindly supplied by R. L. Wakeman, who will describe their preparation elsewhere. CYCLICHYDROCARBONtiCyClOpTOpane (trimethylene) was prepared by dropping trimethylene bromide (Kahlbaum) into boiling isoamyl alcohol and zinc dust (20). The evolved gas was bubbled through 10 per cent potassium permanganate to remove olefins, liquefied, and fractionated. However, the product was not pure, probably because the permanganate treatment was not thorough enough. About 20 per cent by
109
Propene 1-Butene 2-Butene Isobutene IsoDrouylel:hene
Standard With 7 X With 5 X With 5 X With 5 X With 5 X With 5 X With 5 X Standard With 5 X Standard With 6 X With 5 X Standard Standard
10-3 10-8 10-8 10-8 10-8 10-8 10-8
niols Oa mols AlC18 mols Ala S04)8 mols Alz!CIHlOs)s mols NiCla mols NiSOi mols HCI
10-8 mols Ah(SO4)a 10-8 mols AlCb
10-8 mols Alt(S0i)a
No' 4 2 1 2 1 1 2 1 1 1 1 1 1 1 1
MOLSBra
OF
PER 1 MOL SUBSTANCE
1.01 0.96 0.16 0.46 0.47 0.16 0.46
1.02 1.01 1.00 1.07 1.04 0.98 1.01 1.06
DIOLEFINS
Propadiene (allene) Standard 1,a-Butadiene (erythrenei Standard
1
1.94
1
2.00
Standard
1
1.89
Standard (except not washed by pyrogallate)
1
1.47
1.36 X 10-8 mols On added
1
1.64
3.23 X 10-8 mols Oa added Standard Standard Standard Standard Standard Standard
1 2 2 1 2 1 1
1.49 1.97 2.02 2.01 1.74 2.05 1.76
AClTYLENESb
Acetylene j25.6% mixture in air) Acetylene mixture in (25.6% air) Acetylene (1.48 X 1 0 - 8 mold Acetylene (1.42 X 10-8 mols) Methyl acetylene Ethyl acetylene 1-Heptine 1-Octine 2-Octine 4-Nonine
b Numerous oreliminarv exoeriments carried out before the role of oxygen wss recog'nized indicatbd that aluminum, nickel, and mercuric salts aided the quantitative titration of acetylene, but since these same salts prevent the quantitative titration of ethylene they were not further investigated. CYCLIC IIYDROCARBONS~
Cyclopropane (trimethylene)
Standard With air present
1 1
0.17 0.16
C About 20 per cent of this sample dissolved rapidly in a solution of bromine and potassium bromide, the remainder very slowly, hence it must have contained some olefin (see preparation above).
Mixtures
A synthetic mixture (Experiment 3, Table 11) containing 18.4 per cent of acetylene and 19.6 per cent of ethylene in
air was titrated by the standard procedure (fir& washing with pyrogallate solution to remove oxygen). A 98.0-cc. sample (3.88 X loL3mols) containing 38 per cent (1.47 X mols) of unsaturated gases, as shown by absorption in bromine water, reacted with 2.15 X mols of bromine. From these figures the composition of the gas is easily calculated:
% acetylene
= (2'15
-
X 100 = 17.6% (compare 18.4%
3.88
actual)
% ethylene
=
1'47)
-
3.88
2'151 X 100 = 20.4% (compare
19.6% actual)
These results are in fair agreement with the actual composition of the sample. As pointed out below, the pyrogallate solu-
ANALYTICAL EDITION
110
Vol. 3, No. 1
tion absorbs some of the unsaturated gases and more of the acetylenes than of the olefins. The collected results of the tests on synthetic mixtures are shown in Table 11.
periments cited above, the rates of bromine, addition were different. The products from the bromination of the acetylenes in the absence of oxygen were heavy colorless liquids which Table 11-Analysis of Synthetic Mixtures by Standard Procedure I OLEFIN 1 ACETYLENE sometimes crystallized. If, as seems probable, they are the MIXTURE corresponding tetrabromides, a way is open for the prepaMENT 1 Found Actual I Found Actual ration of numerous tetrabromides which formerly have been difficult to synthesize. l M o l % Mol% Mol% Mol% 1 Ethylene, acetylene 26.7 28.1 The influence of oxygen in titrations by the Hanus and 2 Ethylene, acetylene %:: %:: 27.1 28.1 other methods will bear investigation. Thus Faragher, 3 Ethylene. acetylene 20.4 19.6 17.6 18.4 4 Ethylene, acetylene 21.4 19.4 16.2 17.0 Gruse, and Garner (8) found that 1-heptine adds, from the 5 2-Butene. methvl acetvlene 33.2 37.1 66.8 62 9 Hanus reagent, only halogen corresponding to one double Dobrjanski ( 7 ) ha% used a similar method with success bond, whereas in our experiments both bonds were apparently for the determination of erythrene in its mixtures with saturated (see Table I). Now that the disturbing influence of oxygen in theee butenes, but his procedure is considerably more complicated. titrations has been made clear, the use of the bromide-broSince acetylene is known to be more soluble in water than some of the gaseous olefins, being 8.6 times as soluble as mate method for estimating unsaturated hydrocarbons can ethylene at 25" to 30" C. ( l 7 ) ,several semi-quantitative tests probably be considerably extended. The error caused by the solubility of acetylene in aqueous were carried out on the relative solubilities in pyrogallate solutions is serious. When in Experiment 1 of the acetylene reagent. Ethylene, propene, and 1-butene were absorbed a t a rate of approximately 0.1 cc. per minute of contact when section of Table I a correction is made for the solubility of 100 cc. of gas were shaken well in a Hempel pipet filled with the acetylene in the pyrogallate solution, the value 1.98 mols 'the reagent which was comparatively free from the olefins. of bromine per mol of acetylene actually admitted to the On the other hand, acetylene was absorbed a t a rate of 0.8 to reaction flask is obtained. Thus, it is obvious that for more accurate determinations of the unsaturated hydrocarbons in 0.9 cc. per minute of contact under similar conditions. mixtures, it will be necessary either to use some other method Discussion for removing the oxygen, or to determine experimentally The most important facts which have been made clear corrections for the solubilities of the gases present in the by these experiments are that oxygen prevents-the titration of mixture. acetylenes and that the titrations are largely quantitative in Literature Cited its absence. What may be a similar effect has been observed (1) Bacon, IND. ENG.CHEM.,20, 970 (1928). by Verhoogen (&) in brominations of the stereoisomers of (2) Cortese, Rec. trao. chim , 48, 564 (1929). (3) Davis, IND.ENG.CHBM., Anal. Ed., 1, 61 (1929). n,b-dichlorethylene. She found that the fraction of the (4) Davis and Davis, IND. ENG.CHBM.,16, 1057 (1923). bromine disappearing after 23 hours varied with the gas (6) Davis and Schuler, J . Am. Chem. Soc , 62, 721 (1930). in contact as follows: air, 0.14; nitrogen, 0.99; carbon (6) Demole, Ber., 11, 316 (1878). dioxide, 0.998; and oxygen, 0.03. (7) Dobrjanski, Neftyanoe Khoeyaislvo, 9, 574-7 (1925). Translated by Paul N. Rogerman. It is possible that the explanation of these phenomena is that (8) Faragher, Gruse, and Garner, J. IND. END.CHBY.,18, 1044 (1921). the intermediate dibromoethylenes absorb oxygen to give, after (9) Faragher, Morrell, and Levine, I b i d . , Anal. Ed., 2, 18 (1930). intramolecular rearrangement, bromacetyl bromides. Demole (10) Fischer Scientific Co., Pittsburgh, Pa., "Laboratory," 2, No. 3, 39. (6) showed that 1,l-dibromoethylene absorbs oxygen and Ver- (11) Francis, IND. ENG.CHEM.,18, 821 (1926). hoogen (91) showed that the trans-form of a,b-dirhlorethylene (12) Howes, J. Inst. Petroleum Tech., 16, 64-88 (1930). was greatly changed on standing 23 hours with oxygen. The (13) Hurd, Meinert, and Spence, J . A m . Chem. S O L ,52, 1138 (1930). (14) International Critical Tables, Vol. I , p. 181 (1926). resulting liquid fumed strongly in air, liberating hydrogen (15) I b i d . , Vol. I , p. 182 (1926). chloride and ketones. If this explanation is correct, it (16) I b i d . , Vol. I, p. 185 (1926). should be possible by careful measurements to detect the (17) Ibid., Vol. 111, p. 260 (1928). Picon, Comfit. rend., 158, 1185 (1914). actual absorption of oxygen, and also to identify the prod- (18) (19) Thiele, Ann., 308, 339 (1899). ucts. On the other hand we may be dealing here with (20) Traust and Winkler, J . firakl. Chem., (2) 104, 37-43 (1922). negative catalysis. Verhoogen concluded that in her ex- (21) Verhoogen, Bull. soc. chim. Belg., 84, 434-56 (1925).
1I
I
1
I
Quantitative Determination of Pyrethrin I' Ralph C. Vollmar CHEMICAL LABORATORY, STANDARD OIL COMPANY OF CALIFORNIA. RICHMOND, CALIF.
HE classical researches of Staudinger and Rudcka (4) established the constitution of the toxic principles present in pyrethrum flowers. They gave to the two active constituents the names pyrethrin I and pyrethrin 11, and assigned to them the formulas given herewith. Two methods for the quantitative determination of these constituents have been investigated by the author. It is the purpose of this paper to discuss the results which were obtained, and to report a series of experiments relating to the determination of these constituents in kerosene extract of pyrethrum flowers.
CHI
T
1
Received October 6, 1930.
CHa
dH /\ HzC CH.CHvCH=C-CH-CHs
I
0-HC-C-0
I
I
c-0 JH /\
(CHs)rC-CH CH-C(CHs)z Pyrethrin I
dH /\ Hac CHCHZCH-C-CHCHS
I
1
0-HC-C=O
I
iC="
CH COOCHa /\ / (CHs)rC-CH. CH-C 'CH* Pyrethrin I1
A method based on the ability of the pyrethrins to reduce alkaline copper solution and to measure the amount r e
