DETAIL 'A'
Figure 1. Pneumatic shuttle-rabbit system for multiexposure activation analysis
might dislocate the rabbit. Exactly 30 seconds later the timer opens valves 3 and 4 and the reversed air current transfers the rabbit back to the counting position, '/* inch from the center of the face of the scintillation counter. A spring-arrestor, a part of the air lock, positions the rabbit for counting. When 1.5 seconds have elapsed for the transfer, the timer turns on either a multichannel analyzer or a scaler for a prrdetermined counting time. The cycle is repeated once a minute until enough counts have been accumulated. The basis of this fluorine analysis ib the production of the 7.4-second N16 by the reaction Flg (n, a ) "6, which is induced by the fast neutron component of the available flux. The Q value foi this reaction can be calculated from the isotopic masses as -1.5 m.e.v. [lT7apstra, A. H., Physica XXI, 367 (1955)l. TJse of the penetrating 6.1-m.e.v. y-ratliation of NIB for counting permits the determination of fluorinc in thr prepvnce of most other elements.
I I
2
3
4
I
6
7
E N E R G Y (M.E.V.)
Figure 2. Gamma spectrum of a fluorine-containing N a C l sample collected into 70 channels of a multichannel analyzer
Oxygen also gives risc t o X16 by the for which the reaction 0 ' 6 (n, p ) "6. Q value is calculated as -9.6 m.e.v. However, because of the high Q value of this reaction, no interference of the fluorine determination is experienced with the flux available at this installation. This is seen from a n attempt to induce the ieaction in purifird water as reported in Table I. The sensitivity of the method, employing 10-cycle runs and the maximum permissible deuteron cmrent (36 pa.) for the production of neutrons lies at approximately 0.1 mg. of fluorine or I00 p.p.m. for 1-gram samples.
Table I gives some representative fluorine analyses as well as the observed count rates. Only pulses equivalent to 4.5 m.e.v. or more were used for the counts. A 30-pa. deuteron beam was used for the activations. Figure 2 gives the y-spectrum obtained from a fluorine-containing NaCl sample as well as the spectrum of its fluorine content. No interference due to the matrix material is experienced in the range above 4.5 m.e.v. OSWALDU. ANDERS Radiochemistry Laboratory The Dow Chemical Ch. Midland. Mich.
Rapid Determination of 3-Chloropropene by Methoxymercuration Sin: The quantitative reaction of mcwuric acetate with certain ethylenic vompounds has been used for their detrrmination (1, 2, 6-7). Other ethylenic compounds react more slowly with mercuric acetate and their determinations are difficult. When mercuric acetate is added to unsaturated compounds such as methacrylic and acrylic esters in the presence of catalytic amounts of a strong acid such as perchloric, the reaction is greatly accelerated and these compounds can be determined by this procedure (3, 4) The chloropropenes react very dowly with mercuric acetate, but the author found that in the presence of small amounts of perchloric acid, the rate of reaction is greatly increased hfeth-
oxymercuration of 1-chloropropene, 3chloropropene, 2,3-dichloropropene, and 3-chloro-Zmethylpropene was studied in the presence of varying concentrations of perchloric acid in methanol medium under different conditions. Only 3-chloropropene3 which reacted quantitatively within 15 minutes a t room temperature, wva~ determined successfully. EXPERIMENTAL
Reagents. Mercuric acetate solution, approximately 0.1M in methanol containing ca. 0.005 t o 0.01M perchloric acid. Diphenylcarbaxone solution, in ethyl alcohol.
0.2%
Hydrochloric acid solution, 0.1N in butyl alcohol, standardized by the procedure (1) using thymol blue or diphenylcarbazone &s indicator. All reagents were analytical grade. Procedure. Standard solutions of the chloropropenes about 0.05 to 0.1M in methanol were accurately weighed into glass-stoppered bottles. Mercuric acetate solution was added t o the chloropropene solutions and allowed to stand a t room temperature for 15 minutes. After addition of 1 or 2 drops of diphenylcarbazone indicator to a reaction mixture, i t was titrated with standard hydrochloric acid in butyl alcohol. Reaction conditions were varied in all cases by increasing the concentraVOL 32, NO. 10, SEPTEMBER 1960
1369
tion of perchloric acid, reaction time. and reaction temperature. Only in the case of 3-chloropropene was the reaction quantitative. Typical data are shown in Table I. In methanol, mercuric acetate reacts with ethylenir compounds as follows: Hg(CH,COO),
>p-$
+ CH,OH + >c=Cy-$
titration with only does the react, but also product rc’acts
+ 2HC1+ HgCl?
+ 2CH3COOH
+ HCl+
OCHa HgO CO CHI
>.-$
+ CHBCOOH
OCH, HgCl Instead of thymol blue, \\hich IS more generally used (3, 4 ) , diphenylcarbazone was used as indicator in the titration with hydrochloric acid. It gives a strong blue-violet color in the presence of mercuric acetate or mercury addition products in methanol and immediately turns colorless when the
hydrochloric acid reacts conipletely to give undissociated mercuric chloride and acetir acid. Diphenylcarbazone was as effective as thymol blue and had an added advantage in that its use eliminated the need for the addition of sodium chlonde to a mercuric awtate solution containing free acid (3, 4). Khen chloropropene solution is added to reaet with a known escess of niercuric acrtatt. in methanol, the amount of the compound c m be determined from the difference between thc two titers as follows: (a
- b)
x
1000
’\
=
moles of chloropropene
where acid titci i n milliliters for rragent solution b = acid titer for sample S = normality of acid a
=
ACKNOWLEDGMENT
The author expresses his grateful thanks to Philip W.West for laboratory facilities. LITERATURE CITED
( 1 ) Das, 31. S . , ANAL.CHEM. 26, 1086
(1954). (2) Johnson, J. B., Fletcher, J. K.. IDic1.. 31,1563 (1959). (3) Mallik, K. L., Das, M. N., ( ‘ h e m . CV Znd. ( L o n d o n ) 1959, 162. (4) Mallik, K. L., Dae, M. N., unpublishrcl work. ( 5 ) Marquardt, R. l’.. Luce, E; S . , AKAL.CHEM.20, 751 (19%). (6) Ibid., 21, 1194 (1949). ( 7 ) Martin, K.IT-.,I b z d , 21,921 (1949) KANAILAL11 II,I.Ih Coates Chemical Laboratories Louisiana State University Baton Rouge, La. Present address, Chemistry I k p a r t ment, University of Utah, Salt Lake City, Utah.
Determination of Ascaridol in Chenopodium Oil with Hydrogen Bromide in Acetic Acid SIR: The standard procedure (1) for determining ascaridol in chenopodium oil is based on the titration with sodium thiosulfate of the iodine liberated when the oil is treated with potassium iodide and hydrochloric acid. The conditions prescribed in the assay must be carefully controlled and, a t best, the procedure is an approximate one. Since the chemical reaction is not understood, the calculations involved are empirical. Other methods of analysis (5, 6) have been proposed but apparently offer no advantage. The procedure described here is a modification of a method proposed by Durbetaki ( 4 ) for the determination of osiraiie oxygen in eposy-type compounds
Analysis of Chenopodium Oil. . I sample of chenopodium oil, 150 t o 200 mg., is accurately weighed into a n iodine flask. Twenty milliliters of glacial acetic acid is added t o the flask, follotved by exactly 25 ml. of 0 , l Y hydrogen bromide solution. The flask is tightly stoppered, shaken briskly for 5 minutes, and permitted to stand a t room temperature for 21 hours, Excess hydrogen bromide is determined by titrating the solution potentiometrically nith a Fisher titrimeter equipped with a glass-calomel electrode system. A blank is run with a series of three analyses. A typical titration curve is shown in Figure 1. Results of analysis of chenopodium oil for ascaridol content are shon-n in Table I. Calculation. Per cent ascaridol is calculatcd from the expression :
Table I.
Analysis of Chenopodium Oil for Ascaridol Content
Recovery, h-ational formulary method
7c Proposed method
66.95 06 54 65 52 65.26 ti4.97 64.86 64 04
65.83 65.61 65.23 65.17 64.97 64.80 64.56
ti5 45
65.17
dev. 0.78
0.33
Av. AV.
EXPERIMENTAL
Reagents. Hydrogen biomide ill acetic acid, 0.1N ( 3 ) Sodium acetate, 0.1N (2).
1370
ANALYTICAL CHEMISTRY
Vol. 0.LV acetate ronsuined in blank - vol. 0.1W acetate consumed in run weight of sample, mg.
1
16.8
100 =
ascaridol
