Analysis of Commercial Phenothiazine Used as an Insecticide J
L. E. SRIITH. Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, \t-ashington. D. C.
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X THE search for synthetic organic compounds that might replace the arsenicals now comnionly used as stomach poisons for the control of various insects of economic importance, a great number of organic compounds have been prepared and tested. One compound, phenothiazine, has been found especially toxic to newly hatched codling moth larvae under laboratory conditions. I t has also given a high degree of control of this insect in field tests in the Xorthwest, but because of certain practical difficulties it is not yet in commercial use. The method for the preparation of phenothiazine on a commercial basis consists in heating 1 mole of diphenylamine with 2 atoms of sulfur a t about 180" C., using iodine as a catalyst The reaction is practically quantitative, and for use as an insecticide no purification of the product is necessary. However, a dark green compound, which is insoluble in anhydrous ethyl ether, is formed in varying quantities When tested against certain species of insects, this compound has been found to be relatively nontoxic.' Its chemical nature has not been fully determined, but it appears to be isomeric with, or a polymer of, phenothiazine.
weighed amount of the compound is placed in a tared Soxhlet thimble and extracted with ether in the usual manner. The residue, Tvhich consists of the green material, is then determined from the increase in weight of the dried thimble. Little or no unchanged diphenylamine has been found in samples of commercial phenothiazine. Diphenylamine is precipitated almost quantitatively, however, from an anhydrous ethyl ether solution by means of dry hydrogen chloride. This precipitate can be filtered on a tared Gooch crucible, washed with anhydrous ethyl ether, dried, and weighed. By this procedure, 97.2 per cent recovery, as the hydrochloride, was obtained from an ether solution containing a known quantity of diphenylamine. Six samples of phenothiazine that were used in various field tests the past season were submitted to the Division of Insecticide Investigations for analysis. All material was purchased from the same manufacturer. The results are ac follolvs : Insoluble in Ethera
1
1.14 1.43 1.21
Sample NO.
Insoluble in Ether"
4
1.34
%
Calculated for ClLHsNS:C, 72 36; H, 4 52 Found: C, 71.41; H, 4.31
2 3
The insolubility of this green material in anhydrous ethyl ether is utilized in analyzing commercial phenothiazine. A 1
Sample No.
The analyses were carried out Insecticide Investigations. a
% 5
6
1.09 1.23
Miss Ruth Capen oi the Division of
These results rrill appear as a scientific note in the Journal of Ecoiiomir RECEWED December 2, 1937
Entomology
Determination of Iron with o-Phenanthroline 1
A Spectrophotometric Study W.B. FORTUNE WITH SI. G. 3IELLON, Purdue University, Lafayette, Ind. cision and accuracy than is possihle with visual methods. A General Electric recording instrument was used in all transmittancy measurements in this work. The cells were 1.00 cm. thick, the "blank" in the reference beam of light being Nled with a solution containing the same amount of hydroxylamine hydrochloride and o-phenanthroline as was used with the iron in the other cell. All pH measurements were made with a "universal" potentiometer and glass electrode, as described by Mellon ( 2 ) . The standard solution of iron was prepared by dissolving electrolytic iron wire in dilute hydrochloric, nit,ric, or perchloric acid. The solutions were then diluted to volumes such that 1.00 ml. contained 0.100 mg. of iron. A 0.10 per cent solution of o-phenanthroline was prepared by dissolving the monohydrate in doubly distilled, iron-free water. Say\Tell and Cunningham uJed an ethanol solution but the authors found that the reagent dissolved readily in water heated to about 80" c . It is important that, the o-phenanthroline monohydrate be free from impurities. Certain contamination, at least, is evidenced by a pink coloration of the crystalline material, and a lowering of the melting point, stated by Smith (6) to be 99' to 100" C. A 10 per cent solution of hydroxylamine hydrochloride, used as a reducing agent for the iron, was prepared by dissolving the c . P. reagent in doubly distilled water. Solutions used in the determination of interfering cations were prepared from the chloride or nitrate salts of the metals; the anion solutions were prepared from the sodium or potassium salts. In making up all colorimetric solutions used in this study, the following procedure was adopted: The required amount of the standard iron solution was measured out; 1.0 ml. of the
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T WAS shown by Kalden, Hammett, and Chapman in 1931 that the complex ion formed with ferrous iron and
o-phenanthroline has a high oxidation potential and may be used as an internal indicator in certain oxidimetric analytical procedures ( 7 ) . Previously Blau had given an extensive descript,ion of the properties of o-phenanthroline, along with the method of preparation (1). Saywell and Cunningham reported recently that one can make a quantitative determination of iron in small concentrations in various fruit juices and other products by comparing the color of the o-phenanthroline complex with that of a series of standards ( 5 ) . Hummel and Willard (IA) have applied the method to biological materials. The purpose of the present paper is to present a critical study of various factors which may affect' the formation of the colored complex, including a st,udy of the effect of varying concentrations of fifty-five ions liable to be encountered in routine analysis.
Apparatus and Methods In the determination of iron in fruit products, as carried out by Saywell and Cunningham ( 5 ) , the color comparisons were made in graduated test tubes and in a colorimeter. The development of the photoelectric spectrophotometer, described by Michaelson and Liebhafsky ( d ) , has provided a means of detecting very small color changes with a much higher degree of pre60
