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 S y n t h e t i c 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 (CHs)rC-CH
I
1
0-HC-C=O
I
iC="
JH /\
dH /\ Hac CHCHZCH-C-CHCHS
CH-C(CHs)z
Pyrethrin I
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
INDUSTRIAL AND i3NGINEERlNG CHEMIXTRY
January 15, 1931
duced by comparison with a standard dextrose solution has been described by Gnadinger and Corl (I). The acid method, originally published by Staudinger and Harder (3) , has been simplified by Tattersfield, Hobson, and Gimingham (6,6). Their short acid method for pyrethrin I is a determination which requires but a small sample and can be carried out in a short time. Briefly, 10 or 20 grams of flowers are extracted with petroleum ether in a Soxhlet extractor, the extract is hydrolyzed with alcoholic soda, is made acid and steam-distilled. The distillate is titrated with 0.02 N caustic soda. Pyrethrin I has been shown to be more toxic to insects than pyrethrin 11. Tattersfield, Hobson, and Gimingham found pyrethrin I1 to be but one-tenth the toxic strength of pyrethrin I, but in a more recent paper @), Gnadinger and Corl maintain it is about 80 per cent as toxic. Inasmuch as the ratio of pyrethrin I to pyrethrin I1 is fairly constant, a method for the determination of pyrethrin I in flowers or an extract gives a good index of its toxic strength, regardless of the relative toxicity of the two constituents. Sample 1, a sample of 1928 Dalmatian flowers, was run by both the short acid and the copper reduction methods with results that gave a good comparison between these two. The short acid method gave 0.31 per cent pyrethrin I, while the copper reduction method showed 0.75 per cent total pyrethrins. The short acid method has been applied to a group of Dalmatian and California flowers, with the results given in Table I. Table I-Analysis of Pyrethrum Flowers SAMPLE PYRETHRIN I DESCRIPTION
% 1 36 31 61 56 63
1928 Dalmatian, closed 1928 Dalmatian, closed 1928 Dalmatian, closed 1929 Dalmatian, closed 1929 California, open Stems fr2m sample 56
0.31 0.24 0.23 0.21 0.20 0 021
Experimental Work
Both these methods have been described only for samples of flower, stems, stalks, etc. A method for determining these constituents in a kerosene extract would be of value as a control test in the preparation of such extracts as are often used in commercial insect sprays. The short acid method was selected as the one best suited for developing into a control method. No sample of pure pyrethrins or of an extract contai'ning a known concentration of them was available to serve as a standard for experimental work, so a sample of concentrated kerosene extract was run several times by the method described for the flowers. A 5-cc. sample was used, along with 45 cc. of low boiling petroleum ether. A dilute extract was prepared by adding nineteen parts of kerosene to one part of concentrated extract, and this sample was run by the various methods described below. Table I1 shows the results on the original and dilute samples. For purposes of comparison, the results on the dilute sample have been calculated back t o the original sample. Table 11-Pyrethrin METHOD
I C o n t e n t of Concentrated Extract PYRETHRIN I Grams/liter
Original Dilute samples. Original Superheated steam Vacuum distillation Hydrolysis (2 extractions) Hydrolysis (3 extractions)
3 . 6 , 4 . 6 , 4 . 8 , 4 . 8 , 5 , 4 , 6 . 2 (av. 4 . 9 ) 1.8 4.7, 5 . 1 5.0,.5.1 4.6, 4.9 5.0
It will be noted that when the short acid method was applied directly to this dilute extract, using a 100-cc. sample, less than one-half the pyrethrin I is determined. This is probably due to the large volume of kerosene present in the
111
distillation flask since 100 cc. more distillate collected gave but a small additional titration. A small volume of kerosene does not seem to affect the distillation. The method which makes use of superheated steam is one in which 90 to 95 per cent of the kerosene is distilled, after hydrolysis of the pyrethrins, a t a temperature of about 200" C. in a current of superheated steam. The results obtained were in good agreement with results from other methods, but no further work has been done on this one because the hydrolysis method gave equally good results, and is simpler. In the vacuum distillation method, the same amount of kerosene was distilled at a pressure of from 2 to 3 mm. This method was not further developed on account of mechanical difficulties which render it unsatisfactory as a control method. The hydrolysis method is based on the saponification of pyrethrin I to form the sodium salt of chrysanthemum monocarboxylic acid. COONa AH /\ (CHa)iC-CH.CH-C(CHs)z
This removes the pyrethrin I from the kerosene layer, which may then be discarded. I n order to keep the volume low and avoid transferring to a separatory funnel, the kerosene solution is extracted with two successive portions of alcoholic soda, and these extracts, along with a few cubic centimeters of kerosene, are then combined. Two extractions were found sufficient for complete removal of the pyrethrin I. When acid is added, the sodium salt breaks up, and the monocarboxylic acid is steam-distilled and titrated in the manner described by Tattersfield and Hobson (6). Good checks were obtained using this method. Different operators running the same sample obtained results checking within 10 per cent of the total pyrethrin I, and an experienced operator can check himself within 5 per cent. Table I11 shows the results of a series of experiments in which ground Dalmatian flowers were steeped with kerosene at approximately 40" C. for 24 hours, after which the flowers were drained (but not dried), and analyses were run on both the wet flowers and the extract. The kerosene content of the wet flowers was about 30 per cent. Table 111-Comparison
SAMPLE
of S p e n t Flowers w i t h Extracts PYRETHRIN I Wet flowers Extract
%
a
37 0.067 40 0.040 0.018 42 44 0.015 46 0.008 ... 64a Sample 64 was a mix of equal parts of samples
% 0.064 0.041 0.024 0.012 0.009 0.030 40 and 42.
The method which has been used to determine pyrethrin I in kerosene extracts follows. The presence of any ester of the type which is often used for an odorant will cause high results, hence this method is applicable only to extracts which are known to contain no foreign material. For the same reason it is not suitable for use in the qualitative determination of pyrethrins in an unknown extract. Method
SOLUTIONREQuIRED-Sodium hydroxide in methanol, approximately 1 N . Fiftieth normal sodium hydroxide, 0.02 N . The strength of this solution should be checked occasionally. Sulfuric acid, 1 N . Petroleum ether, maximum boiling point 60" C. APPARATUS-For refluxing the sample and subsequent distillation, use a long-necked flask of 100 cc. capacity. The author used an ordinary distillation flask on which the side arm had been sealed.
112
ANALYTICAL EDITION
PROCEDURE-Measure 100 cc. of extract into a long-necked flask of the type described above. (A smaller sample may be used if more than 0.05 per cent pyrethrin I is known to be present.) Add 5 cc. alcoholic soda solution and reflux for 11/, to 2 hours, the bulb of the flask being immersed in a beaker of hot water. Shake occasionally. Remove from the beaker and pour off as much kerosene as can be decanted without disturbing the alcohol layer into another similar flask which contains a second 5 cc. portion of alcoholic soda. Reflux as before, and when completed, pour off the kerosene layer, rejecting it. A few cubic centimeters of kerosene will remain in each flask. Add to the second flask 11 cc. 1N sulfuric acid, shake, and transfer to the first flask. Rinse the second flask with two 25-cc. portions of petroleum ether, and after transferring these washings to the first flask, confirm its acidity with phenolphthalein. Distil in a current of steam, using a long condenser cooled with ice water. Do not apply a flame to the distillation flask until all the petroleum ether has been distilled. Collect the petroleum ether and 50 cc. of water in a separatory funnel, then continue the distillation until an additional 50 cc. of distillate has been collected. Keep the volume low in the distillation flask, but do not allow it to go dry. The titration is carried out in an Erlenmeyer flask to which has been added about 20 cc. carbon dioxidefree water, a few cubic centimeters of ethyl alcohol, and 1 cc. of phenolphthalein indicator. Add to this enough 0.02 N sodium hydroxide to give a definite pink color, usually one to two drops will be sufficient. Shake the contents of the separatory funnel vigorously and add the water layer to the second 50 cc. of distillate. Wash the petroleum ether layer
Vol. 3, No. 1
with about 20 cc. of water, then add it to the titration flask. Titrate to a definite pink, shaking well and allowing the layers to separate after each addition. Extract the combined distillates with a second 50-cc. portion of petroleum ether, and add this to the titration flask. Continue the addition of caustic until the pink color is the same as it was originally. A blank determination should be run, using 100 cc. of kerosene, and the proper deduction should be made from each determination. This will usually be about 0.3 cc. CALCULATIONS-From the molecular weight of 330, we get the relation, 1cc. 0.02 N caustic = 0.0066 gram pyrethrinI. Summary
The copper reduction and the short acid methods for determining active constituents in pyrethrum flowers are compared, and several samples of Dalmatian and California flowers run by the short acid method. A series of experiments on the adaptation of the short acid method to a kerosene extract of pyrethrum are discussed. A method for the quantitative estimation of pyrethrin I in a kerosene extract is described, along with a table showing pyrethrin I content of spent flowers and the extracts from these flowers. Literature Cited J . Am. C h e w Soc., 51, 3054 (1929); 62, 680, 684 (1930). (2) Gnadinger and Corl, Ibid., 62, 3300 (1930). (3) Staudinger and Harder, Ann. acad. sci. Fennicae, [ A ] 29, No. 18 (1927). (4) Staudinger and Ruzicka, Helu. Chim. Acto, 7,177,450 (1924). (5) Tattersfield and Hobson, J . AEr. Sci., 19, 433 (1929). (6) Tattersfield, Hobson, and Gimingham, Ibid., 19, 266 (1929).
(1) Gnadinger and Corl,
A Modified Balance for Approximate and Quick Weighing’ E. Karrer B. F. GOODRXCA Co., AKRON,OHIO
M
ANY cases arise when the time required to make a weighing must be kept at a minimum either because the weighings are approximate and large expenditure of time is unwarranted or because many things of the same kind are to be weighed. The economics of mass production demand that as little time as possible be spent upon each weighing. There is a very simple and inexpensive method for accomplishing this by modifying an ordinary beam balance as shown in Figure l. A spring, S,is mounted directly under the beam, H, in which two adjustable studs, A , are inserted. These studs barely make contact with the spring, X, in the balanced condition. For example, the distance between the hardened ends of the studs and the spring may be 0.01 inch (0.25 mm.). The index, B, is lengthened and its position read by a scale, C. I n making a weighing the scale pan, G, is depressed to the stop, E, and then is released quickly and carefully. If the weights on the two scale pans are equal the index will be deflected on its first swing to a point that may be marked zero on the scale, but if the weight on the scale pan, F , is slightly more than that on G, the index will not travel to that point. The distance traveled depends upon the difference in the weights on the pans. The modification described is best suited for comparing one article 1 Received September 20, 1930. Presented before the Division of Rubber Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12,1930.
with another which is intended to be of the same weight and which is to be trimmed or adjusted to a given weight within certain tolerances. I n such a case the standard article (“weigh-by”) may be placed upon the pan F, and others, placed on pan G, be compared with this.
Figure 1-Balance Modi5ed for Indicating Offweight on First Deflection
The scale C may be put in units of weight, of length, or of volume. For example, for comparison and control of pieces cut from ribbon or tubed stock, the wale C may be graduated in centimeters, indicating the length which must be cut from, or added to the piece in order to make its weight within tolerance limits equal to the weight of the standard. For
