Analysis of Commercial Allethrin Determination of Allethrin Content by Reaction w i t h Ethylenediamine J. S . EIOGSETT, 11. W. KACY,
AYL)
J . H . JOHNSOS
Carbide and Carbon Chemicals Go.. Division of L nion Carbide and Carbon Corp., Sozcth Charleston, IF'. I u. ,I lie large scale manufacture of allethrin, a synthetic insecticide, has necessitated the development of accurate and precise methods for evaluation of the conirnercial product. This paper describes a method for the determination of the allethrin Content by reaction w-ithethylenediamine to form an equivalent aniount of the amine salt of chrysanthenium monocarhx)lic acid, which is titrated with standard sodium methylate in pyridine solution. Chrysantherniini monocarboxylic acid, anhydride, or acid chloride, if present in the sample, is deterniined independently, and qitantitative corrections are applied to obtain the true allethrin content. For producers and consumers of allethrin and related compounds, the methods provide a specific and accurate means of evaluating these materials as produced. Preliniiriary investigations have indicated that the method niay also be useful for the deterinination of allethrin in insecticidal formulations. Of general interest to analytical chemists is the application of the ethylenediamine method to the deterniination of esters of beta-keto alcohols and a tie*- procedure for determination of acid anhydrides in the presence of the corresponding acids.
THE
structure and synthesis of allethrin have been tlescribed by Srhechter, Green, ~ n J,a d Forge ( 5 , 6). -4llethrin is an adopted rianie for the cliemical, dl-2-all~-l-4-hydrosy-3-methyl-2cyclopenten-l-one (allylmethylcyclopentenolone) esterified with a mixturc of ris- nntl tt.ans-dl-c,hrysitnttiemum monocarbosylic acids:
1 ire ~lJn~poUfld n l ~ oII:L+ 1)een called tlie ailj I homolog of cinerin I. By virtue of its special toxic action on insects and its low toxicity toward warm-blooded animals, allethrin has found wide application u an insecticide in aerosol and space s p r a y for both military and civilian uses, in dairy and livestock sprays, and i n the protection of stored grains. The recent commercial production of allethrin has required the development of accurate and reprotluc4)le methods for tlie determination of the purityof the product as well as its concentration in insecticide formulations. Existing analytical procedures for the analysis of pyrethrum flowers and extracts, which have been the subject of several publications ( 1 . 3 , 4, 9) containing many conflicting data, were entirely inadequate for the analysis of allethrin, the results being neither accurate nor reproducible. A11 attenipts in this laboratory to measure quantitatively the ester, carbonyl, and unsaturated groups by conventional functional group (teterniinntions or motlificatioris thereof were unsuccessful. , 7
In the search for reactions of technical allethrin which might be applicable to its analysis, a sample was made to react witli ethylenediamine. A titratable acid was formed which gave a calculated purity of approximately 80%. When it was discovered that a comparative estimate by extensive PeebGrady (biological activity) tests (IO)agreed favorably with this figure, an intensified investigation of the reaction was begun. Experience with nonaqueous titrations in other applications facilitated the development of a simple method of analysis based on these principles. In a pyridine medium ethylenediamine is neutral to thymolphthalein indicator, whereas most organic acids are distinctly acidic and can be quantitatively titrated with standard sodium methylate in pyridine. The allethrin sample reacts with ethylenediamine to form a quantity of chrysanthemum acid stoichiometrically equivalent to the allethrin present. The chrysanthemum monocarboxylic acid formed is determined by titration with standard sodium methylate i n pyridine solution. Chrysanthemum monocarboxylic acid, its anhydride, and acid rhloride also react quantitatively and must be determined iridependently and corrections applied to obtain the true allethrin content. The acid chloride is determined by reaction of the mmple with methanol and titration of the hydrogen chloride formed with methanolic potassium hydroxide, using dimethyl yellowmethylene blue indicator. hcid plus arid chloride is determined by titration with standard sodium hydrovide in an ethanolic medium using alphanaphtholbenzein indicator. The reaction in each case is equimolar. Acid chloride plus anhydride is determined by reaction with a measured ewess of morpholine in a methanolic medium, followed by titration of the excess morpholine with standard methanolic hydrochloric acid using dimethyl yellom-methylene blue indicator. In this determination the acid chloride, when present in dilute concentrations in allethrin, consumes morpholine mole for mole and also produces a mole of titratable acid (hydrochloric acid), so that its equivalent weight is one half the molecular weight. The anhydride consumes morpholine mole for mole and produces a mole of chrysanthemum monocarboxylic acid which is neutral under the conditions specified. From these four titrations the amounts of allethrin, chrysanthemum monocarboxylic acid, acid chloride, and anhydride are ralculated. REiGEhTS
Ethl1 alcoliol, :tnhydrou*, S.D.2-€3. Phenolphthalein indicator, 1.Oq solution in methanol. Standard 0.02 .V sodium hydroxide. hlet hanol, anhydrous commercial grade. Standard 0.1 .V sodium hydroxide. Hydrochloric acid, 0.1 S alcoholic solution. Transfer IT nil. of 6 S hydrochloric acid to a 1000-ml. volumetric flask and dilute to the mark with methanol. Standardize by titrating exactly 40 ml. of the acid with standard 0.1 S sodium hydroxide using phenolphthalein indiratoi. For the change of normality with temperature use A \ - / ' C'. = -0.0001. hlorpholine solution. Tranafer 8 . i ml. of redistilled morpholine to a 1-liter reagent bottle and dilute to 1 liter with methanol. Fit the bottle with a two-hole rubber stopper and through one hole insert a 20-ml. pipet so that the tip extends through the iuiface of the liquid: through the other hole insert a short piece of glnqs tubing to which i q attached a rubber atomizer liull) 1207
ANALYTICAL CHEMISTRY
1208 Dimethyl yellow-methylene blue mixed indicator. Dissolve 1.0 gram of dimethyl yellow (p-dimethylaminoazobenzene)and 0.1 gram of methylene blue in 125 ml. of methanol. Pyridine, redistilled. Thymolphthalein indicator, 1.OYOsolution in pyridine. Ethylenediamine (ED,4), redistilled; water content, 3y0, maximum. Caution. Ethylenediamine vapor is injurious to skin and attacks rubber. Sodium methylate-0.1 S p)-ridine solution. Transfer 25 ml. of 4 S sodium methylate to a 1-liter reagent bottle containing 75 ml. of methanol and dilute to 1 liter with redistilled pyridine. Standardize this solution against Bureau of Standards benzoic acid, using pyridine as a solvent and thymolphthalein indicator. For the change of normality with temperature use A N / ' C. = -0.0001. The reagent readily absorbs carbon dioxide from the air. and is best oreserved and used in a 50-ml. automatic buret. Ali vents open t'o the air must have protective Ascarite tubes. Alpha-naphtholbenzein indicator, 1.0% solution in ethyl alcohol. Standard 0.02 X methanolic potassium hydroxide. PROCEDURE
Determination of Allethrin. Introduce an amount of sample calculated t o contain 0.8 to 1.1 grams of allethrin into each of two 250-ml. glass-stoppered flasks. Reserve two additional flasks as blanks and t o each of the samples and blanks introduce 25 ml. of redistilled ethylenediamine, using a suitable dispensing buret protected from the atmosphere by Ascarite tubes. Swirl the samples to effect solution. Allow the samples and blanks to stand together a t 25' to 30" C. for 2 hours. (With most samples of commercial allethrin the determination may be hastened by conducting the reaction in heat-resistant pressure bottles for 0.5 hour a t 98' f 2' C. However, a few samples apparently contain impurities which react a t the higher temperature, giving erroneous results.) Unstopper the flasks and wash down the sides of each with 50 ml.of redistilled pyridine. To each flask add 6 to 10 drops of the thymolphthalein indicator and titrate with standard 0.1 N sodium methylate in pyridine to the first permanent blue end point, (Some samples of commercial allethrin are sufficiently brown in color to change the normal color of the thymolphthalein end point from blue to blue-green. However, the authors' experience has been that this change in color does not shift the end point of the titration nor decrease the reproducibility of the determination.)
B = acid chloride, meq. per gram B X 18.67 = chrysanthemum monocarboxylic acid chloride,
TaamilieX N grams of sample
ml. of N normal sodium sample T b l a n k = average ml. of A' normal for the blank A = apparent allethrin, meq. (A 2B - C - D ) X 30.24 =
Tsnmple =
+
methylate required for the sodium methylate required per gram allethrin,
TaamDle = ml. of N normal sodium hydroxide required for the sample C = acid acid chloride, meq. per gram (C - B ) X 16.82 = chrysanthemum monocarboxylic acid, % bv weight Determination of Chry&nthemum Monocarboxylic Anhydride. Carefully pipet 20 ml. of the morpholine solution into each of four 250-ml. flasks. Fill the pipet by exerting pressure in the reagent bottle with the atomizer bulb. Reserve two of the flasks for blanks and introduce 1.5 to 2.5 grams of sample into each of the remaining flasks. Swirl the flasks and allow the samples to stand together with the blanks a t 25" to 30' C. for 5 minutes. Add 4 or 5 drops of dimethyl yellow-methylene blue indicator to each of the flasks and titrate with standard 0.1 N alcoholic hydrochloric acid until the color changes from green to a faint red when viewed by transmitted light.
+
- Tsnmple) x grams of sample
(Tblank
Table I.
= acid chloride, meq. per gram C = acid acid chloride, meq. per gram D = acid chloride anhydride, meq. per gram
+
+
Determination of Chrysanthemum Monocarboxylic Acid Chloride. .4dd 8 t o 10 drops of dimethyl yellow-methylene blue indicator to approximately 150 ml. of methanol in a suitable container, then add 0.1 'V methanolic hydrochloric acid dropwise, until the solution appears reddish brown by transmitted light. .kdd 0.02 methanolic potassium hydroxide dropwise until the appearance of the first green color: Transfer 25 ml. of this solution to each of three 125-ml. glassstoppered flasks. Reserve one of the flasks as a reference color for the end-point determination. Into each of the other flasks introduce 1.5 to 2.5 grams of sample. Swirl the flasks during the addition of the sample. Titrate each sample with 0.02 S methanolic potassium hydroxide to the first green end point, using the blank as a reference color. Perform the titration within 5 minutes of the addition of the sample to the methanolic solution.
T..%,,I, x -v = B grams of sample where Taampls =
AB8 Ka Blend 25 5-1052
*v = D
Reaction Rate of Allethrin with Ethylenediamine Allethrin, % b y Weighta 30 60 90 120 180 min. min. min. min. min. Experiments a t 98' C. . . . 96 0 95.7 95.8 95.8 90.6 91.0 90.8 90 8 . . . 90.6 74 7 74.7 74.5 , , 74.8 ... 71.8 71.9 72.0 , , , 72.0 ..,
15 min.
210 min.
...
. .. ~5 2 (2.0
Experiments a t Room Temperature 180 24.0 120 min. min. min. min. 95.6 95.9 ... ... ABa . . 89.7 90.8 90.5 90.7 Ks Ks (1 week later) 90.0 90.7 90.5 ... 73.4 74.5 74.6 74.6 Blend 25 70.5 71.7 71.7 71.7 5-1052 Allethrin percentages shown in this and subsequent tables have been corrected for chrysanthemum acid a n d chrysanthemum anhydride unless otherwise indicated. Samples contained no chrysanthemum acid chloride.
eo
% by weight
where
B
=c
where
Sample Designation
where
70
by weight Determination of Chrysanthemum Monocarboxylic Acid. Transfer 25 ml. of anhydrous ethyl alcohol to each of two 125ml. glass-stoppered flasks. Bdd 8 or 9 drops of alpha-naphtholbenzein indicator and cool the flasks and contents to approximately 0" C. in an ice bath. Neutralize the ethyl alcohol in each flask by the dropwise addition of 0.02 A' sodium hydroxide to a brilliant green end point. Introduce 1.5 to 2.5 grams of sample into each flask, and immediately titrate with standard 0.02 N sodium hydroxide to the same brilliant green end point.
ml. of iV normal potassium hydroxide required for the sample
Table 11. Sample Weight Variation and Reproducibility Sample Designation ABs
K8 5-1052
(At 98" C., 0 . 5 hour) Weight of Sample, Grams 1.1638 1.3132 1.1491
96 1
96 2
0 5160
90.4 90.8 90.6
1,0720 0.6203 1.5107 1 948.5 ...~ 0.5008
71.7 72.3 71.5 71.6 72.4
0.5766 0,6873 1.0575 1.1896 2.1874
74.9 74.7 75.3 74.7 74.8
0.9946 1,3014
~
Blend 25
Allethrin, b y Wt. 95 9
1209
V O L U M E 25, NO. 8, A U G U S T 1 9 5 3 Table 111. Effect of Variation in Amount of Ethylenediamine and Water Content Sample Designation
ED.%. All
KI
10 25 50
.A
Table IT'.
Kater Content oi ED.1. % b y \Tt.
Allethrin, b y Wt.
1. 5 1. 3
25
1.5 15.0
90.5 91.3 91.2 90.8
25 25
1.5 0.2
80.1 79.8
Effect of idded Chrysanthemum Monocarboxylic .4cid
Chrg santhemum hIonocarboxylio Acid, Sairiple % by Wt. Designation Found Calcd. I
