V O L U M E 27, NO. 11, N O V E M B E R 1 9 5 5 The method is satisfactory for preparations containing no significant amounts of impurities. Occasional lots have been encountered containing entrained ethylating agents or other substances which invalidate the method. Preliminary investigation has shown that in thcse cases the diethyl ethylmalonate and diethyl diethylmalonatc rontent mal- be estimated by resort to the base line method ( 1 , 3, ij), using the bands a t 11.18 and 13.51 microns, respectively. This method is less sensitive to impurities than the three-component spot method, but is not satisfactory for eqtimating dieth5-l malonate 4CK\OW LEDGMENT
T h e authors are indebted to James A. Gordon and Solomon Disman for the preparation and purification of the pure malonate
1813 esters, and t o Jerome Merkel and Frederick Scheske for technical assistance. LITERATURE CITED
(1) Barnes, R. B., Gore, R . C., Williams, E. F., Linsley, S. G., and Petersen, E. AI., ASAL. C H E Y . , 19, 620 (1947). (2) Carol, J., llolitor, J. C., and Haenni, E. O., J . A m . Pharm. Assoc., Sci. Ed., 37, 173 (1948). (3) Friedel. R. A . , and Pierce, L., . I N ~CL HE . M . 22, , 418 (1950). (4) Gamas, A . S.,Zaoodskaya Lab., 10, 155 (1941). (5) Heigl, J. J., Bell, 31. F., and White. J. U., ANAL.C H E M . ,19, 293 (1947).
RECEIVED for review March 2 , 1955. Accepted June 22, 1955.
Beta-Mercaptopropionic Acid as Colorimetric Reagent for the Determination of Cobalt EDWARD LYONS’ University o f Florida, Gainesville, Fla.
p-Mercaptopropionic acid is a useful reagent for the colorimetric determination of cobalt in dilute solution. The presence of nickel or copper in the same order of concentration i s not detrimental, as an excess of ammonium hydroxide which does not affect the cobalt test, will discharge an? color due to these metals.
T
HIOGLTCOLIC acid ( 2 ) was found t,o be a very useful reagent for bhe colo~~imetricdetermination of iron. phlercaptopropionic acid (B. F. Goodrich Co., Cleveland. Ohio), although of no partirular valuc. in the test for iron, was found to give excellent results with cobalt. Its use in the determination of nickel has been studied hy Uhlig and Freiser ( 3 ) and Lear with Mellon ( 1 j .
cobalt test and vice versa, However, in dilute solution (concentration as given for cobalt), the red color due to nickel is readily discharged by an excess of ammonium hydroxide. Consequently, in carrying out the test on nickel one must add only enough hydroxide just to neutralize the solution. Prepared unknoa ns n-ere thus readily compared with all dilutions of known concentrations, so that here too the proposed method may be used for a quantitative determination of nickel. I n testing for cobalt in the presence of nickel in equal concentration, the addition of 4 or 5 drops of ammonium hydroxide per drop of mercaptoacid will cause the color due to the nickel to be discharged, T h e green color due to the cobalt is not affected by the excess hydroxide used. On the other hand, cobalt may seriously interfere with the test for nickel. COLOR REACTION WITH PALLADIUM
COLOR REACTION WITH COBALT
FVhen a drop of mc,rcapt,opropioiiic acid is added to a concentrated solution of a cobaltous salt and the resulting mixture is made alkaline wit,h ammonium hydroxide, a deep green solut,ion is obtained. T h e dept,h of color depends on the concent’ration of cobalt and fails to appear when t,he concentration of cobalt is less t.han about, 2.5 p.p.m. Prepared “unknowns” in concenhatmionof 2.5 to 20 1i.p.m. lend themselves readily to matching with known standa.rd9. so that t,he method may be used for quantitative detmrrmin:tt8ioii. T h e green color, pirticdnrly in the more concentrated solutions, soon begin? to tun1 dark and ultimately the color becomes brown. It was found that oxidizing agents speed u p this change. I n the absence of rnetul ion? such as mercury (11)or gold (111) (which ma)- reduce t o the mPtalj, a “pinch” of sodium hyposulfite (Sa2S204.2H,O! added to the mixture prior to the addition of the ammonium h>-dro\-ide,retards the oxidat,ion. T h e resulting brilliant bluish green t’iiit makes the matching of color easier and it, is st:ihle over inany hours. COLOR REACTION WITH NICKEL
Because nickel is frequently associated with cobalt, the effect of its presence was studied. K i t h nickel the color obtained (when the test is carried out as previously described for cobalt) is deep red. Obviously, it was found to interfere with the 1
Present address, Pan-Orniond Corp., Ormond Beach, Fla.
A4cid palladium salts in concent,ration greater than 1000 p,p.m, impart a yellow color to the solution. Solutions of lesser concentration arc colorless. If to such colorless solution containing not less than about 40 p.p.ni. of palladium is added a drop of mercaptopropionic acid and the resulting mixture is made alkaline with ammonium hydroxide, the yellow color is again brought out. METAL IONS WHICH DO NOT GIVE COLORED SOLUTIONS WITH 8-4lERCAM’OPROPIONIC ACID
The following metal ions in solut,ion do not give charact’eristic color reactions with t,he reagent: silver, gold(II1 j , bismuth(II1 j ) calcium, chromium(III), copper( 11), mercury(II), magnesium, mnnganese(II), lead(II), platinum(IV), rhodiuni(III), tin(IT), thorium(IV), tit,anium(III),and zirconium(I1). Copper(I1) gives a yellow colored precipitate with thioglycolic acid and p-mercaptopropionic acid, which dissolves in ammonium hydroxide or sodium hydroxide with formation of a colorless solution. Therefore, copper should not interfere with the test for iron or cobalt when these mercapto acids are used. LITERATURE CITED
(1) Lear, J. B., with 31. G. lIellon, ANAL.C H E J ? .25, . 1411 (1953). ( 3 ) Lyons, E., J . A m . Cheni. Soc., 49, 1916 (1927). (3) Uhlig. L. J., and Freiser. H., . i h - a ~ .C H E M .23, . 1014 (1951). RELEIVED for r e n e w .January 13, 195%
Accepted J u n e 29. 1955
