V O L U M E 2 6 , NO. 4, A P R I L 1 9 5 4
759
molar quantity of methane (Table 11), the lithium aluminum hydride technique of Hochstein shows a maximum of 1 to 3% of enol present ( 3 ) . Presumably the methane arises through a direct reaction of the Grignard reagent with the active hydrogen atoms in the alpha position to the carbonyl group. A possible source of error in applying the method is the presence of traces of moisture (or other impurities containing active hydrogen) in the samples and solvents. I n certain cases the slowness or incompleteness of the reaction constitutes another source of error. Care must also be taken that all parts of the apparatus and accessories, especially the hypodermic syringes and needles, are thoroughly clean and dry. I t is desirable that these be kept in a desiccator over a suitablr drying agcnt when not in use. These precautions are necessary in all methods utilizing the Zerewitinoff analysis. In the authors' opinion, the present apparatus offers considerable advantages in simplicity over older, more complex assemblies (4, 5, 8, 10). The time required per analysis is small. I n spite of the simplicity in equipment and the saving in time, the accuracy and reproducibility of the measurements are satisfactory and compare very favorably Kith those realized by other methods (9). I t is apparent that the method can be applied to other reactions in which a gas is either evolved or absorbed. It had been hoped to utilize the procedure for analyses based on the reactions of lithium aluminum hydride and sodium borohydride. Unfortunately, time did not permit this study. The apparatus has been applied in the authors' laboratories for a study of the reac-
tion of hydrogen chloride with certain highly hindered tertiary alcohols (1). It proved entirely satisfactory in this application. ACKNOWLEDGMENT
This investigation was assisted by funds provided under a contract with the Office of Naval Research for the study of steric strains in chemical reactions. This assistance is gratefully acknowledged. LITERATURE CITED
Bonner, W. H., Ph.D. thesis, Purdue University, 1952. Brown, H. C., and Borkowski, XI.. J . Am. Chem. Soc., 74, 1894 (1952). Hochstein, F. A., Ibid., 71, 305 (1949). Kohler, E. P., and Richtmyer, iY.K., Ibid.,52, 3736 (1930). Kohler, E. P., Stone, J. F., Jr., and Fuson, R. C., Ibid., 49, 3781 (1927). Lehmann, R. z4., and Basch, II.,IND.ESG. CHEM., ASAL. ED., 17, 428 (1946). Luttgens, W., and h'egeleixi, E., Biochem. Z., 269, 177 (1934). Kiederl, J. R., and h'iederl, Y., "Micromethods of Quantitative Organic Analysis." 2nd ed., pp. 263-72, New York, John TWey 8r Sons, 1942. Ollefman, E. D.. A s a r . . C m x , 24, 1427 (1952). Sieeia. S.. 'Quantitative Oreanic Analvsis via Functional Groups," pp: 41-8, S e w York, John f i l e y & Sons, 1949. Tschugaeff. L., Ber., 35, 3912 (1902). Yillars, S. D., J . A m . Chem. SOC.,70, 3655 (1948). Zerewitinoff, T., Ber., 40, 2023 (1907). I _
R E C C I V Efor U rrricw October 23, 1933. Accepted January 7, 1964.
Precipitation of Barium Chromate from Homogeneous Solution LOUIS GORDON and F.
H.FIRSCHING
Department of Chemistry, Syracuse University, Syracuse 70, N. Y.
A
COMMONLY used method for the separation of barium from strontium is that of Skrabal and Neustadtl ( 2 ) which employs a double precipitation of barium chromate. Modifications of this procedure have been proposed by Beyer and Rieman (1) who added a buffer to an acid solution containing barium and dichromate to raise the pH to 4.6. The present paper describes a modification of these procedures in which the p H of the acid solution is slowly raised by the use of urea (3) thus effecting precipitation of barium chromate in the form of large, readily filtered and easily washed crystals which exhibit minimized coprecipitation.
throughout the solution. After 2.5 hours remove the beaker, cool, and determine the pH; a high temperature glass electrode may also be used with the hot solution. The final pH should be approximately 5.7. If the pH is below this value, reheat until pH 5.7 is reached-around p H 5.5 the pH will change about 0.1 p H unit €or each 4 minutes of heating. When the pH is a p proximately 5.7, filter the solution while hot, reheating if necessary, as there is some tendency toward erratic results if the solution is cooled and then filtered. Wash the precipitate thoroughly with a 0.5% potassium dichromate solution adjusted to pH 5.7. Finally, wash with three small portions of cool distilled water. Dry the precipitate of barium chromate a t 120' C. for 2 hours before weighing
PROCEDURE
Add 10 grams of urea and 6 grams of ammonium acetate to a solution containing 0.1 gram of barium in a 250-ml. beaker. Dilute to 150 ml. and adjust the pH of the solution to approximately 1.7 to 1.8 with hydrochloric acid or ammonia. Then add 20 ml. of a 10% solution of potassium dichromate. Place the beaker on a hot plate set to give a solution temperature of about 95" to 98" C. In about an hour dense crystals will begin to form
Table I.
Determination of Barium
(Barium taken, 0.0972 gram)
PH
Barium Found, Gram (Av.)
No. of Detns.
Standard Deviationa, Mg.
PRELIMINARY INVESTIGATIONS
Materials Used. Barium chloride, c.P., was recrystallized once from distilled water. Strontium chloride, c.P., was freed from barium by adding enough ammonium dichromate to precipitate all of the barium along with some strontium. The strontium in the filtrate was then precipitated with ammonium carbonate, filtered, washed thoroughly with distilled water, then dissolved with hydrochloric acid. The precipitation of strontium carbonate was repeated four times to effect the complete removal of chromium.
Effect of pH. The original solution must he below pH 2 hefore potassium dichromate is added, or some precipitate will form. As the urea hydrolyzes in the hot solution, there is a gradual increase in p H with the initial precipitate forming a t about pH 3.5. The final p H must be close to 5.7. If it is several tenths of a unit below this figure, some barium will remain in solution; if it is several tenths of a pH unit above, some additional strontium may precipitate. The pH values in this investigation were obtained after cooling the solution to room temperature. Except where noted, the precipitates were always filtered from hot solution.
760
ANALYTICAL CHEMISTRY
There is evidence in the literature that barium chromate is quantitatively precipitated a t pH 4.6 ( 1 ) . However, barium chromate is not quantitatively precipitated a t this pH under the conditions employed in the present separation. At p H 4.6 a sizable portion of barium remains in solution. Quantitative precipitation does not occur until the pH range 5.5 to 6.0 is reached.
Table 111. Determination of Barium in the Presence of Strontium PH
Barium Found, Gram
Barium Taken, 0.0972 Gram. 5.0 0.0971 5.3 0.0971
5.4
:.: 5.6 5.8 6 0
Table 11. Comparison of Volumetric and Gravimetric Results" (Barium taken. PH 5.1 5.4 5.4 5,s .5 , 7 6.4
0.0972 gram = 0.1792 grain of BaCrOi)
BaCrOh Found, Gram Gravimetric Volumetric 0.1760 0.1771 0.1781 0.1777 0.1778 0.1790
Ratio,
0.1757 0.1773 0.1776 0.1781 0.1784 0.1785
Barium Taken, 0.0972 Gram.
Strontium Taken, 0.097 Gram
c%?2L
-0.3 0 9 0.5 1.3 1.2 0.4 0.8 0.3 1.2
Vol.
1,002 0.999 1.003 0,998 0.996 1.003 .iv,
-0.1 -0.1 0.0 -0.3 0.1 0.4 0.3 0.2 0.1
0.0972 0.0969 0.0973 0.0976 0.0975 0.0974 0.0973
5.5
6 1
0 0984
1 000
Upon Reprecipitation
a Described procedure was followed, except t h a t solutions were cooled and allowed to stand several hours before filtering.
0.0971 0.0968 0.0970 a , b,
ilttempts to obtain bettrr buffering action with reagents other than acetate were limited by the strong oxidizing properties of the chromate ion as vel1 as by the complexing and precipitating properties of the possible buffers. Quantities ot Reagents Selected. , The various amounts of reagents were chosen because they produced the largest crystals, gave a reasonable time for hydrolysis, and gave the most reproducible results. DISCUSSION OF RESULTS
Determination of Barium. The results obtained isith the recommended procedure are given in Table I. Low results were obtained where the final p H was too lo^. The higher the p H the more quantitative the precipitation of barium, but unfortunately the tendency for strontium to coprecipitate also increases. -1pH of about 5.7 is most suitable. At this recommended pH, about 0.1 to 0.2 mg. of barium appears to remain in solution. An attempt mas made t o determine the composition of the precipitate, since slight fluctuations in the weight of the precipitate were obtained. Barium chromate precipitates obtained in different experiments from the same quantity of barium chloride stock solution were dissolved and the resulting solutions \$ere heated to boiling with ammonium pereulfate and titrated potentiometrically with standard ferrous ammonium sulfate. The results given in Table I1 indicate that the barium found gravimetrically is equal to the chromium found volumetrically. P Determination of Barium in Presence of Strontium. T ~ data
Difference, hlg.
Strontium Taken, 0.039 Gram
-0 1 -0.4 -0.2
Samples reprecipitated.
obtained using the recommended procedure are shoFT n in Table 111. Approximately 100 mg. of barium can be separated in a *ingle precipitation from about 40 mg. of strontium; 100 mg. of Strontium require a double precipitation. Determination of Barium in Presence of Calcium. .1 good separation of barium and calcium is indicated by the results given in Table IV. The pH does not have to be controlled as closely as is the case hen strontium is present. A complrte separation can be obtained n ith a single precipitation.
Table IV.
Determination of Barium in Presence of Calcium
(Bariuin taken, 0.0972 gram. Calcium taken, 0.1 gram) Barinin Found, Grain Difference, AIg. 5.6 0.0972 0.0 pH
6.6 7.0
0.0972 0.0974
0 0 0.2
LITERATURE CITED
(1) Beyer, G. L., and Rieman, W.. A S ~ LCHEY., . 19, 35 (194T). (2) Skrabal, A., and Seustadtl, L., 2 . anal. C h e m . , 44, 742 (1905) (3) Willard, H. H., . ~ K . % L ,C H E x , 22, 1 3 i 2 (1950). RECEIVED for review October 10, 1953.
.Iccepted January 2 5 , 1954.
Chromatographic Separation of Acid Obtained from Oxidation of Alpha-Pinene DORIS E. BALDWIN, VIRGINIA M. LOEBLICH, and RAY V. LAWRENCE N a v a l Stores Research Division, N a v a l Stores Station, Olustee, F / a ,
I
S CONSECTIOS with the oxidation of a-pinene, a constituent of turpentine, to pinonic and pinic acids (1, 4 ) , a satis-
factory method of qualitative and quantitative analysis was needed. The crude oxidation products obtained contain a number of mono- and dicarboxylic acids. Most of the acids involved are cyclic compounds, including cyclobutane and cyclopentane derivatives as well as acids containing ylactone structures. Some of these acids are produced as by-products and some are formed from impurities present in commercial a-pinene.
Marvel and Rands ($I, Ranisey and Patterson (5, 6 ) , Higuchi, Hill, and Corcoran (Z), and others have reported simultaneous qualitative and quantitative analysis of certain straight-chain acids by partition chromatograph>-. The insolubility of the acids under consideration in aliphatic hydrocarbons prevented use of the procedure presented by Ramsey and Patterson (6) for acids of comparable molecular vieight. Data from chronlatograms employing the method presented by Marvel and Rands (3) are reported as well as the results of a
