reaction 1 and no interference of reaction 2 could be stated either at room temperature or at elevated temperatures. EXPERIMENTAL
Reagents. Commercially available 6 N butyllithiurn in hexane and sodium o-hydroxymercuribenzoate (HMB) 0.01R’are used. Dissolve 3.2 grams of o-hydroxymercuribenzoic anhydride in 20 ml. of I N sodium hydroxide and dilute t o 1000 ml. with 50% aqueous ethanol. T h e normality is calculated from t h e weight of the anhydride. Indicator. A solution of thiofluorescein in 0.5N ammonia in 50y0 aqueous ethanol is prepared. The blank value of the indicator should be not more than 0.05 ml. of 0.01N H M B per 1 ml. of the indicator solution. Procedure. A sample of organic disulfide is dissolved in 10 ml. of dry benzene and treated with 0.5 ml. of 6.V butyllithium, the time and temperature being chosen according to the di-
sulfide in question (see Table I). Then 15 ml. of ethanol cooled in ice are added and the solution is titrated with 0.01N H M B in the presence of thiofluorescein (1 ml.) indicator until the blue color disappears. The results are summarized in Table
co-oxidation of thiols. I n as short time as one minute the oxidation is negligible a t room temperature as well as at elevated temperature.
I.
(1) Sshworth, I!. R. F., “Titrimetric Organic Analysis,” part 11, pp. 669-81, DISCUSSION
Three possible sources of error must be taken into account, viz.: the incomplete reaction with butyllithium, the oxidation of thiols by oxygen, and the decomposition of thioethers. At room temperature the conversion of such disulfides as butyl disulfide could not be carried out with higher recovery than 9770, because the increase of the time of reaction increases the oxidation. I n spite of the fact that the disulfide produced by oxidation will react with butyllithium again the thiol content will decrease. Possibly butyllithium, being readily oxidized itself, causes the
LITERATURE CITED
Interscience, New York-London-Sydney, 1965. (2) Porter. hf.. Saville. B.. Watson. A. A,.
‘ J . Chem: Soc: 1963, I;.346. (3) Stahl, C. R., Siggia, S., ANAL.CHEM. 29,154 (1957). (4) Wrbnski, M., Wiadomosci Chem. 17, l(1963). STIGVEIBEL LIIECZYSLAW WR6NSK11 Department of Organic Chemistry
Technical University Copenhagen, Denmark M.W. is indebted to the Danish Ministry of Education for financial support during this work. 1 Permanent address: Department of Chemical Technology, University of Lbdi, Poland.
Spectrophotometric Determination of Copper in Lead, Tin, Aluminum, Zinc, and Their Alloys with Biscyclohexanone Oxalyldihydrazone SIR: The amount of copper contamination in lead-base and tin-base alloys is of considerable metallurgical interest, particularly in type metals in which only small amounts of copper, not more than 0.13Oj,, can be tolerated because of its effect in forming crystals enriched with copper during the pouring of the types. The production of copper-free leade.g., for the manufacture of sheet, pipes, and shot-necessitates close control of the decopperization process. Furthermore, the alloying amounts of copper in bearing metals, tin and its alloys, aluminium and its alloys, and zinc and its alloys meet narrow specification ranges which call for a reliable and sufficiently fast method for the determination of copper in the wide range of 0.05 to 10%. Neocuproine (2,Q-dimethyl-1 ,lophenanthroline) (2) and sodium diethyldithiocarbamate (6) have been recommended for the absorptiometric determination of copper in a variety of materials, but both involve extraction of the copper-organ0 complex. The recommended method of the American Society for Testing Materials ( I ) involves the use of hydrogen bromide while photometric measurement is taken; i t is generally conqidered as being tedious. Publications describing the use of biscyclohexanone oxalyldihydrazone in the determination of copper, first suggested by Nilsson (4) and later applied to the examination of plant material ( 8 ) ,paper (7), steel (S), and titanium and zirco-
nium alloys (9) suggested, because of a large number of noninterfering elements, a possible application to the determination of copper in lead-base alloys and nonferrous alloys generally. To provide a suitable method for a wide variety of nonferrous metals and their alloys, the biscyclohexanone oxalyldihydrazone procedure has been investigated. EXPERIMENTAL
Reagents. Hydrogen bromide-bromine mixture. T o 180 ml. of hydrogen bromide, add 20 ml. of bromine. Perchloric acid, 70-72% .w./w. Sulfuric acid, 5 N . Ammonium citrate solution, 20%. Neutral red indicator solution, 0.05%. Sodium hydroxide solution, 10%. Sodium borate buffer solution. Dissolve 15.45 grams of boric acid in 400 ml. of water and dilute to 500 ml. (solution A). Dissolve 2.0 grams of sodium hydroxide in 90 ml. of water and dilute to 100 ml. (solution B). T o 400 ml. of solution A, add 60 ml. of solution B and mix. Biscyclohexanone oxalyldihydrazone solution, 0.5%. Dissolve 0.5 gram of the reagent in 100 ml. of ethanol-water mixture (4:3). Procedure. I n general, t h e procedure as given under Calibration Graph for preparation of the sample solution can be followed. Calibration graphs covering the ranges 0.003 to 2.0% using appropriate aliquots of a standard copper nitrate
solution were identical with those in the presence of the major alloying metals of lead-base, tin-base, aluminum-base, and zinc-base alloys. Tests have shown that the method can be successfully extended to the determination of up to 10% of copper by using a smaller sample weight. The addition of reagents, noting subsequent color development, and measurement of absorbance have been followed in all cases exactly as given under Absorption. A 5.0-ml. aliquot of the filtered sample solution has been used throughout the investigation. .~BSORPTION. High purity copper (0.25 gram) was dissolved in 20 ml. of diluted nitric acid ( 1 : l ) and the solution boiled for 3 minutes to expel nitrous fumes. It was then cooled, transferred to a 1-liter volumetric flask, and diluted to the mark with distilled water. A 20ml. aliquot of this solution was then diluted to 500 ml., so that 1 ml. contained 0.01 mg. of copper. Diluted copper solution (1.5- and 15ml. portions) was added to two 50-ml. volumetric flasks; 10 ml. of distilled water were added to a separate 50-ml. volumetric flask to serve as a reference solution (blank). T o each flask were added 10 ml. of 20yG ammonium citrate solution and 2 to 4 drops of 0.05yGneutral red indicator solution. A 10% sodium hydroxide solution was then added from a buret until the color of the solution changed from red to yellow; then 1 ml. was added in excess. A 50ml. capacity semiautomatic buret with plastic reservoir and spring-loaded rubVOL. 38, NO. 7, JUNE 1966
* 91 1
ber valve (Dr. Schillings-Burette, Jena GMBH, hlainz, TVest Germany) was found to be most satisfactory for adding the sodium hydroxide solution. -45-ml. portion of a sodium borate buffer and 2 ml. of 0.5% biscyclohesanone osalyldihydrazone in ethanol-water (4: 3) were added. After 3 minutes, a suitat le portion of the reference solution was transferred to an absorption cell, the spectrophotometer (Unicam SP 600)
Table 1.
adjusted, and the absorbance measured in 4-cm. and 1-cm. cells, respectively. Measurements, made at wavelengths between 560 and 640 mp, confirmed (7’) that the masimum absorbance is a t 595 mk. CALIBRATION GRAPH. Three calibration curves were prepared by transferring appropriate portions of the standard copper nitrate solution into 50-ml. volumetric flasks and reagents
Determination of Copper . . in Standard Samples and Synthetic Compositions
B.C.S. No. 17711
B.C.S. No. 17711
Certified value for Copper Copper by proposed method, yo copper, % added, % Pb, 84.5%; Sb, 10.47,; Sn, 0.007 ... 0.006,0.0065,0.006 5.09%; Fe, 0.004%; Bi, 0 002yc; As,
