ANALYTICAL CHEMISTRY
1330 The gravimetric aiid volumetric methods were compared on sninples of derris, cube root, resin, and dust extracted as described in the procedure of the Association of Official Agricultural Chemists ( 1 ) and also on samples of pure rotenone and pure rotenone-carlion tetrachloride solvate (Table 11).
advantage that insoluble niat,erial present with the rotenonecarbon tetrachloride solvate will not interfere in the deterniination. An attempt is being nisde to apply a modifirntion of this method to thc extracts directly.
DISCUSSION O F RESULTS
L I T E R i T U R E CITED
llercwic acetate can either add t o a double bond or act as an osidizing agent,. Under the coditions cniployed only addition t,akes place. Table I s h o w that the reaction can be carried out a t room temperature and is virtually complete after 15 minutes. Thrre is little further change in t.iter with time. Table I1 shon-s the volumet,ric method to give slightly higher results than the gravimetric method, but, as Jones ( 2 ) has shown, the latter method yields results generally about 1% loner t'haii the correct value. The volumetric method appears to hc :LS acncuriite as the graviniet,ric method. The n i e t h I ctesc,rilietl has the f'urther
(1) Assoc. Offic. .Igr. Chemists. "Official a n d T e n t a t i v e M e t h o d s of .Inalysis," Gth e d . , p. i4, 1948. (2) Jones. H. A , , IND.ENG.CHEY..ANAL.ED.,9, 2 0 6 1 0 (1937). (3) h l a r q u a r d t , 11. I'., and Luce, E. s.,~ A L CHE:Y.. . 20, 781-3 (1948). (4) Ibid., 21, 1194 (1949). (8) M a r t i n . R . W., Ibid., 21, 921 (1949). ( 6 ) Whitmore, F. C., "Organic C o m p o u n d s of M e r c u r y , " p. 31. S e w York, Chemical Catalog Co., 1921. RECEIVED Soveinhcr 30, 1950. Report of a study made under the IZe*enrch and Marketing Act, of 19-16. I r o i u a rhesis submitted in partial f u l f i l l ~ ~ ~ e n t of the requirements for the 11,s.degree a t the University of Marl-land.
Determination of Rotenone as an Impurity in Dihydrorotenone IRWIN HORNSTEIN Bureau of Entomology and Plant Quarantine, United States Department of Agriculture, Beltsville, Md.
HE catalytic hydrogenation of the isopropenyl side chain in Trotenone (I) with Raney nickel produces dihydrorotenone (11) in good yield (4-6). However, the hydrogenation of rotenone also proceeds with the opening of the oxygen link in ring E to give rotenonic acid (111). Cont,inucd hydrogenation of rotenonic acid producea dihydrorotenonic acid (I\-). Dihydrorotenol (V), formed by saturating the side-chain double bond and t.he opeiiing of ring C, may also occur ( 2 ) . Both dihydroroterioiiic acid and dihydrorotenol are formed by adding 2 moles of hydrogel1 for every mole of rotenone reacting in this manner. Thus, if a n appreciable amount of either or both of these products forins, mole-for-mole addition of hydrogen to rotenone will leave unreacted rotenone.
with this reagent. ('orrecting for the difference in tlie color intensity of rot,enoiir- :is cvinipnred Kith that of dihydrorotenone and suhtracting this corrwted figure from the red-color dihydrorotenone v:iluc givv the :ic*tunl dihydi,orotenone content of the s:i mple. I'REP.iR&TION OF RO
NONE AND DIHYDROROTEYOSE
Rotenone was obtained by exhaustive chloroform extraction of dried Tephrosia virginiana roots. T h e solvent was removed, and an excess of ether precipitated t,he crude rotenone. Three recrystallizations froin carbon tetrachloride and recrystallization of the solvate from ethyl alcohol gave a pure product, melting point 163" C. in borosilicate glass, no melting point lowering of an authentic sample of rotenone; [a]:,"was -230" in benzene. Dihydrorot,enone \vas ol)tained by the method of Haller and Schaffer (.$-6), usiiig a 1I:inc.y nickel catalyst. Dihydrorotenone was separated froni the 1)henolic substances with alkali and purified by recrystallizing t'rom carbon tetrachloride and ethyl alcohol. The dihytlrorotenone was again subjected to hydrogenation, and the dihytlrorotenone obtained after alkali extraction was recrystallized froin carbon tetrachloride and from ethyl alcohol until no further test for unsaturation could be obtained h mercuric acetate. This product melted a t 216" i n boro.ate glass; [CY]:," ~ a -225" a in benzene. A K A LY SI s
Guodhue anti IIaller ( 2 ) found tlitlt dihydrrir(Jt~,noiie\vas t8hc only reduction product givillg :HI appreciablt. red-color test hy the Goodhue ( 1 ) modification of the C;loss-Sniith test (3). This color is similar to the color given 1)y rut.enone and some of the rotenoids. In their methiid (it' clratcrnlining dihydrorotenone any rotenone present would not I i c l tiktinguiahrd from dihydrorotenoiie. The physical properties in g(iIiera1 : i r ~similar for the two coinpounds . Hoxever, rotenone can bc qualltitativrly doterniinrd by measuring the unsaturation in tlie rotcfinone sidr chain, using the mercuric acetate met,hod ( 7 ) . I)ihydlorcitc,nt,nc d o w not react
The Goodhue modification of the Gross-Smith rrd-culor test is carried out, on separat,e samples of pure rotenone and dihydrorotenone, as descril-led k)y Gootihue and Haller ( 2 ) . Extinction curves are plotted by drawing a straight line from zero concent,ration and extiiict,ioii to tiit. point determined by the concent,ration and extinction of each of these tlvo st,andards. The color developed by both rotcxiione and dihydrorotenone follows Beer's law, and plotting est,inctioris against concentration gives a straight line. On the photometer used per cent transmitt,ance is read direct.ly. The per ccwt transmittance on valurR arc converted to extinction values liy nleiins of the formula 100 E = log ______
- =
yo transmittance
2
- log yotransmittancc
R h e n a niiyture of dihydrorotenone and rotenone IS :inalyzed, the transmittance for :in accurately weighed sample of approximately 20 mg. is determined and the extinction calculated for the mixture. The per ceiit rotenone is then determined by the mercuric acetate method ( 7 ) . This figure multiplied by the
V O L U M E 23, NO. 9, S E P T E M B E R 1 9 5 1
1331
Table 1. Dihydrorotenone in Mixtures with Rotenone Dihydrorotenone in Sample
%
MoC
100 95 90 80 70 60 50 0
Mixture Used in Red- Transmittance Color Test for Mixture
24 24 22 24 20 22 24 24
Rotenone b y DihydroMercuric rotenone Acetate Method Found
%
%
%
45.7 45.7 48.5 45.0 51.6 47.9 44.0 42.6
0.0 5.0 9.9 20.1 29.9 40.0 50.2
100 94.6 90.0 80.4 70.0 59.6 50.4 0
100
Table 11. Dihydrorotenone and Rotenone (Foiind;liy combined use of mercuric acetate and red-color methods in samples of dihydrorotenone) DihydroSn 111IJle Method of Preparation rotenone Rotenone I 2
3 4
5
G
Hydrogenation of rotenone (iresh catalyst) Ilsdrogenation of rotenone (re-used catalyat from sample 1) Hydrogenation of rotenone (fresh catalyst) IIydrogenation of rotenone (re-used catalyst from sample 3) Sample 4, recrystallized from carbon tetrachloride and irom ethyl alcohol 1)iliydrorotenone from a n outside source
%
70
93.0
7.0
90.2 96.1
8.9 4.2
94.0
5.8
94.7 97.5
6.2 2.5
If a sample is known to consist only of dihydrorotenone and rotenone, it should be possible to omit the red-color test and obtain the amount of dihydrorotenone by difference. Sample Calculation. For the mixture containing 80% of dihydrorotenone the observed per cent transmittance is 45.0. 100 The extinction of this mixture equals log or % transmittance’ 0.347. The rotenone found by the mercuric acetate method is 20.1’3&. Therefore, the rotenone in the 24-mg. sample analyzed colorimetrically is 4.8 mg. The extinction due t o this amount of rotenone, read from the standard rotenone curve, is 0.075. The extinction of the dihydrorotenone equals the extinction of the mixture minus the extinction due t o rotenone, or 0.272. From the standard dihydrorotenone curve this extinction value is equal to 19.3 mg. of dihydrorotenone. The dihydrorotenone found is therefore 80.4Tc of the mixture. Table I1 shows that nearly 10% of rotenone may be present in dihydrorotenone samples. Re-use of the Raney nickel catalyst in the preparation of dihydrorotenone by the addition of 1 mole of hydrogen per mole of rotmone appears to decrease the yield of dihydrorotenone slightly. Recrystallization does not materially increase the purity of dihydrorotenone. LITERATURE CITED
weight in milligrams of the sample used in the red-color test gives the weight of rotenone contributing to the color. The extinction due to that amount of rotenone is read directly from the rotenone curve. The extinction of the dihydrorotenone equals the extinction read for the niixture minus the extinction due to thp rotenone. From this extinction on the dihydrorotenone graph the weight of dih3 drorotenone present in the original sample can be read. Table I shows that the values obtained for dihydrorotenone :ire accur:ite to +0.5OjC and those for rotenone are better than that.
(1) Goodhue, L.D.,J . Assoc. Ofic.Agr. Chemists, 19, 118 (1936). (2) Goodhue, L. D., and Haller, H. L., IXD. ENQ.CHEM.,ANAL.ED., 12,652 (1940). (3) Gross, C.R.,and Smith, C. M., J . Assoc. Ojjic. Agr. Chemists, 17, 336-9 (1934). (4) Haller, H.L.,and Schaffer, P. S., Ind. Eng. Chem., 25,983 (1933). (5) Haller, H. L., and Schaffer, P. S., J . Am. Chem. Soc., 55, 3494 (1933). (6) Haller, H. L., and Schaffer, P. S., E. S. Patent 1,945,312(1934). (7) Hornstein, I.,ANAL. CHEM.,23, 1329 (1951). RECEIVED November 30, 1950. Report of a study made under the Kesearch and Marketing Act of 1946. From a thesis submitted in partial fulfillment of the rsqriirrnients for the M.S. degree a t the University of Maryland.
Determination of Chloride in Presence of Iodate LYMAN S. STANTOIV’ C‘nirersity of Wushington, Seattle, Wush.
K THE course of other work the writer found that in aqueous 1-solution the determination of chloride by the Volhard method is unsatisfactory in the presence of iodate, apparently because of the progress of a slow side reaction between iodic acid and sodium thiocyanate. -4s a literature search failed to disclose an entirely satisfactory procedure, an experimental study was carried out n-hich phowed that accurate results Kere obtained by the Volhard method if iodate was previously removed by use of barium nit rate. PROCEDURE
The solution (50 to 100 ml.) to be analyzed is acidified with nitric acid and then concentrated ammonium hydroxide is added, drop by drop, until the solut’ion is basic to phenolphthalein. Saturated barium nitrate solution (10 nil.) is added and, if precipitation is not immediate, a trace of precipitated barium iodate is introduced. The solution is stirred until crystals form and then is allowed to stand overnight. The barium iodate is then filtered off and washed thoroughly with hot dist.illed water. The filtrate is then analyzed for chloride by the Volhard method.
added and then chloride v a s determined by the above procedure. The effectiveness of the method is shotvn by the agreement found between the number of milliliters of standardized sodium thiocyanate solution required for titration of the samples to which potassium iodate had been added and the number of milliliters required for the samples to which no potassium iodate had been added-i.e., 20.46,20.43, and 20.46 versuq 20.47,20.42, and 20.47, respectively. Barium iodate is free filtering, but carbonates and sulfates will decrease the filtration rate. More rapid filtrations are obtained if carbonates are destroyed by acidification prior to barium iodate precipitation and if the presence of sulfates can be avoided. Kolthoff states that chloride ran be determined mercurimetrically in the presence of iodtite, but the method requires carefully standardized empirical correction8 ( 2 ) . Andrews gives an accurate but tedious method for eliminating iodate ( 1 ) . It is felt that the barium precipitation requires less laboratory time than these methods, especially if the amount of iodate is unknown and if only a small number of determinations are to be run.
DISCUSSION
To test the method, six samples of hydrochloric acid solution were pipetted out using the same pipet. Chloride was determined by the Volhard method on t,hree of these samples. T o each of the three remaining samples, 0.1 gram of potassium iodate was 1
Present address, California Research Corp., Richmond, Calif.
LITERATURE CITED
(1) Andrews, L. W., J . Am. Chem. Soc., 29,277-81 (1907). (2) Kolthoff, I. hl., and Stenger, V. A., “Volumetric Analysis,” T’ol. 11, 2nd ed., pp. 264, 331-3, New York, Interscience Publishers, 1947. RECEIVBD November 6, 1950.
