particular advantage in mechanism studies. An application of this technique to the study of reaction mechanism is exemplified by a brief investigation we made to explain the inhibiting effect of MCP on the paraffin-acid reaction. Because N C P reacts with the acid manyfold faster than do the paraffins, it was postulated that one of its effects in the system is to shorten the life of the paraffin carbonium ion. This effect was demonstrated by a simple experiment involving the isomerization of 3-methylpentane to 2-methylpentane, a relatively rapid reaction. It was reasoned that, since the probability of
isomerization increases with increased time of ionic residence in the acid, a shortened ion life would result in a decrease in the ratio of isomerization to exchange (exchange being, by comparison, an essentially instantaneous reaction). A series of samples of 3methylpentane containing from 1 to 70% MCP was acid-treated in the usual manner, and analyzed. The results are shown in Figure 2, where the ratio of the radiopeak heights of isomer to parent is plotted against per cent hlCP. There is no doubt that MCP has a very pronounced effect in shortening ion life.
LITERATURE CITED
(1) Gordon, G. S., 111, Burwell, R. L.,
Jr., J . Am. Chem. SOC.71, 2355 (1949). (2) Ingold, C. K., Raisin, C. G., Wilson, C . L., J . Chem. Soc. 1936,1643. (3) Setkina, V. N., Plate, A. F., Sterlingov, 0. D., Kursanov, D. N., Doklady Akad. Nauk S.S.S.R. 99, 1007 (1954). (4) Stevenson, D. P., Wagner, C. D., Beeck, O., Otvos, J. W., J . Am. Chem. Soc. 7 4 , 3269 (1952). (5) Stewart, T. D., Harmon, D., Ibid., 68, 1135-6 (1946). (6) Wolfgang, R., Rowland, F. S., ANAL. CHEM.30,903 (1958). for review June 6, 1960. ACRECEIVED cepted September 12, 1960.
Liq uid- Liq uid Extract io n of Va na dium(V) with Tributyl Phosphate SANTOSH K. MAJUMDAR and ANlL K. DE Department o f Chemistry, Jadavpur University, Calcutta 32, India
b A fast and selective procedure is presented for the determination of vanadium(V) after extraction with tributylphosphate. Almost quantitative extraction of vanadium(V) can b e achieved from hydrochloric acid 3 5M b y a 5-minute equilibration with TBP (100%). The effects of TBP concentration, salting-out agent, and diverse ions have been investigated. Vanadium(V) can b e readily extracted in presence of copper(II), mercury(II), cobalt(ll), nickel(ll), barium(ll), bismuth (Ill), iron(lll), chromium(lll), thorium(lV), uranium(VI), molybdenum(Vl), phosphate, and EDTA. The extractable species is VOC13.2 TBP.
T
(TBP) has been used for the extraction of iron(II1) (6). From a hydrochloric acid medium, vanadium(V) is also found to give a yellow color in the TBP layer after a 5-minute extraction with TBP. This forms the basis of a fast extraction procedure, outlined in this paper, which has very few interferences. From the organic layer, vanadium(V) is backextracted by shaking with water and is determined volumetrically. The optimum conditions for extraction, separation, and measurement have been derived from critical investigations into the various factors involved. In the literature thus far no such n-ork has been reported. RIBUTYL PHOSPHATE
APPARATUS AND REAGENTS
Separatory funnels of 250-ml. volume were used for extraction. All the chemicals used, unless other-
wise mentioned, were chemically pure or reagent grade materials. A stock solution of vanadium(V) chloride mas prepared by dissolving about 5 grams of ammonium metavanadate (E. Merck) in 40 ml. of concentrated hydrochloric acid and diluting to 500 ml. with water. At first an orange precipitate of vanadium pentoxide appeared which immediately dissolved in the excess acid giving a clear lemon-yellow solution presumably due to Voc13 (7). Lingane (4) reports that the vanadium(V) species is VOz+ in acidic medium. The solution was found to be quite stable for over a month without the slighest indication of decomposition. The fact that the solution contained vanadium(V) only and not any of its lower oxidation state was confirmed by its failure to undergo oxidation with potassium permanganate. An aliquot of this solution was treated with a known volume of standard Mohr's salt solution, the excess of which was determined by back-titration with standard potassium dichromate solution (9). The solution, thus standardized, contained 5.081 mg. of vanadium per ml. Tributyl phosphate (Matheson, Coleman and Bell, Cincinnati, Ohio, U.S.A.), boiling point 143-145' C. a t 5-mm. pressure, was purified according to the procedure of Peppard et al. (6) and used as an extractant. GENERAL PROCEDURE
The general extraction and measurement procedures were as follows: An aliquot (5 ml.) of vanadium(V) chloride solution containing 5.081 mg. of vanadium(V) per ml. was mixed with the requisite volume of hydrochloric acid of known strength to give the desired
acid concentration ( 6 X ) , diluted to 25 ml. with water, and introduced into a separatory funnel (250 ml.). In the runs involving salting-out agents and diverse ions, the appropriate salting and foreign ion, respectively, were added Drior to the dilution step. The resultant aqueous solution was- extracted for 5 minutes with 10 ml. of 100% TBP. Where the effect of TBP concentration was studied, chloroform was the diluent and 10 ml. of the chloroform solution was employed. At the end of extraction, the layers were allowed to separate and the aqueous layer was removed. Vanadium(V) was back-extracted from the T B P phase by shaking for 10 minutes with two 20-ml. portions of water, and was directly estimated in these aqueous extracts in the same way as in the standardization step. RESULTS AND DISCUSSION
Effect of Acidity. The solvent extraction behavior of vanadium(V) with respect to T B P was investigated a t varying concentrations of hydrochloric acid from 1.0 to 9.8M. The partition coefficient, D, was computed from the ratio of the concentrations in the organic and aqueous phases (Table I, Figure 1). The vanadium (V) content in the organic phase was obtained by titration according to the general procedure, and that in the aqueous layer, by difference from the total amount of vanadium(V) originally taken. Table I shows that the extraction with 1 0 0 ~ oT B P starts from about 2 M hydrochloric acid and becomes almost quantitative (-98%) from 5M acid onwards. In Figure 1, a steep rise in VOL. 33, NO. 2, FEBRUARY 1961
297
Table I.
Partition Coefficient as Function of Acidity
[Vanadium(V), 25.4 mg.] Partition TBP HCI, M Coefficient, D 1 100% 2 0.085 3
4 5
6 7 75%, 2.75M
3
4
2.47
7
65 0.45 1.49 6.04 8.8 9.9"
6 7 8 9 9.8 6
3070, 1.10-44
0.03 0.46
5
6
50%, 1.83M
1.51
9.0 49 99 99
7 8
8.5
_I
-2
Figure 1. Extraction of vanadium(V) with TBP as function of hydrochloric acid concentration in aqueous phase
0.19 1.17
5
Table 11. Effects of Ammonium and Magnesium Chlorides as Salting-out Agents
[Vanadium(V), 25.4 mg.; TBP, 10070] Par tition Salting-out HC1, Coefficient] M D Agent NHdC1, M 2.24 1 0.13 2 1.02 3 5.29 4 49 0.5 0.11 4.03 1 0.13 2 2.37 3 49 4 99 MgCln.6Hz0, M 0.5 0.04 1.0 1 0.16 2 1.22 3 6.58 4 8.8 2.0 0.5 0.28 1 1.49 2 6.71 3 13.29
TBP Concentration. The concentration of T B P was varied from 30% (1.10M) t o 100% (3.66M), with chloroform as diluent. The effect on extraction was noted at different acid concentrations (Table I). Dilution of T B P lowers the extraction (Figure(Figure 1). A 2)plotreveals of log the D us.comlog CTBP position of the extractable species. The best lines through the points at 6 and 7M hydrochloric acid indicate slopes of 2.4 and 2.1, respectively, showing that the extractable species is v o c b . 2 TBP. This is analogous to other dissolvate species-ea., H IFeCL. (TBP)2] (b), ZrCli.2 TBP, or Th(NO3)?, 2 TBP (1, 3)-at high acidity. Emdently the extraction system conforms to the limiting square law in the case of vanadium(V). The optimum reagent concentration is 100% (3.66M). Salting-out Agent. The presence of ammonium or magnesium chloride in the aqueous phase serves t o exert a salting-out effect leading to increased
Table 111.
>
298
ANALYTICAL CHEMISTRY
;ir w
u
LL LL
U w
z 0
0
t
+ [r 2
-
u _J
1.0
1.5
L O G 'I B P C O N C N .
2.0
(%I
Figure 2. Partition coefficient as function of TBP concentration A.
Aqueous phase, 7M HCl
B. Aqueous phase, 6M HCI
Effects of Diverse Ions
[Vanadium(V), 25.4 mg.] Amount Vanadium( V) Ion Added, Mg. Source Material Extracted, 98.8b c u +2 100 97.8 Hg +2 102 97.gb c o +z 100 Ni 1 2 99.8 100 96.8 Ba +2 105 95. 6b UOI +2 UOzCl2 25 97.2 Bi +3 100 BiOCl 98.0 FeC13.6H20 Fe+3 102 95.5 Cr(S04)3.18Hz0 Cr +3 110 94.6b Th +( ThCla 25 95.Zb Mo+6 ("4)6MO&.4HzO 95 98.1 Pop-3 NazHP04.12HzO 95 99.0 (EDTA)- 4 100 Disodium salt (EDT 53.0 Citric acid Citrate-3 100 41.3 Tartaric acid Tartrate-3 100 No interference noted with any forei n ions except citrate and tartrate. * Coextraction but no interference w i t , analysis of vanadium(V). Foreign
extraction is observed at low acidities, followed by a plateau region at higher acidities. The former is probably due to the salting-out from the aqueous phase by the chloride ion, whereas the latter effect may be attributed to hydrochloric acid competition for the available T B P which has a tendency to level off the extraction. For quantitative extraction, the optimum acid concentration is from 5M onwards. The maximum partition coefficient value was 99 corresponding to an acid concentration 6M.
0
H Y D R O C H L O R I C A C I D (M) IN T H E AOUEOUS PHASE
0.02
9 2.31 9.8 5,58" Incomplete back-extraction a t this acidity; TBP layer retains slight yellow color even after back-extraction.
4
0
0
extraction of vanadium(V) (Table 11, Figure 1). The partition co0.5 efficients a t lower acidity-e.g., to 2M-are found to increase by several orders of magnitude. Under this condition T B P is less combined with the acid and so is more available for extraction. This occurs in conjunction with the salting-out function of the chloride ion from the salt added. The extractant used was 100% TBP. Diverse Ions. The aqueous phase Ivas adjusted to 6 M in hydrochloric acid and the following ions were tested for interference (Table 111) : C U + ~Hg+2, , C O + ~Xif2, , U02+2,Ba+S, Bi+3, Fe+3, Cr+3, Th+4, iVIoi-6, PodT3, citrate, tartrate, and EDTA. It is interesting to note that none of these ions interfere, except citrate and tartrate. Both citrate and tartrate appear to be oxidized by vanadium(V) since the aqueous phases are blue at the end of extraction, indicating formation of vanadium(1V). Thrre is coextraction, of course, with copper (11), cobalt(II1, uranium(VI), iron(III), tho-
rium(IV), and molybdenum(V1), but these ions do not interfere in the subsequent analysis of vanadium(V). Addition of ferrous sulfate in the analysis step does not alter the oxidation states of these coextracted ions. Extraction of vanadium(V) in the presence of uranium(V1) and iron (111)is important since these are commonly associated in minerals. Furthermore, the very fact that none of the common ions tested above interferes proves that the extraction procedure is highly selective for vanadium(V). From ten runs using the recommended procedure (vanadium = 25.04 mg.), and average recovery of 96.5 =k 1.91 was obtained so that the standard deviation was It 2.0%. The total operations in each run require 25 to 30 minutes only. The suggested method possesses the advantages of simple and rapid operations with good selectivity and reproducibility. ACKNOWLEDGMENT
The authors thank the Council of
Scientific and Industrial Research, India, for sponsoring the project and awarding a fellowship to one of them (S. K. M.). They also thank A. K. hlajumdar for laboratory facilities. LITERATURE CITED
(1) Alcock, K., Bedford, F. C., Hardwick, W. H., McKay, H. ,4.C., J . Inorg. &
Nuclear Chem. 4, 100 (1957). (2) Charlot, G., Bezjer, D., “Quantitative Inorganic Analysis,” p. 623, Wiley, New I’ork, 1957. (3) Hesford, E., IllcKay, H. A. C., Scargill, D., J . Inory. & Xuclear Chem. 4,321 (1957). (4) Lingane, J. J., “Electroanalytical Chemistry,” p. 122, Intcrscience, New York. 19.53. (5) Majumdar, S. K., De, A. K., unpublished data. (6) .Peppard, D. F., Driscoll, W. J., Sironen, R. J., McCarty, S., J . Inorg. dl. Nuclear Chem. 4,326 (1957). (7) Sidgnick, N. V., “The Che,mical Elements and Their Compounds, Vol. 1, p. 816, Clarendon Press, Oxford, 1950. RECEIVEDfor review April 6, 1960. Accepted October 17, 1960.
Aci d- Cata I yze d Ace ty Ia ti o n Determination of Ketoximes and vic-Dioximes GEORGE H. SCHENK Chemistry Department, Wayne State University, Detroit 2, Mich.
b Perchloric acid-catalyzed acetylation is used to determine 0.5 meq. of carbonyl derivatives such as ketoximes and benzophenone hydrazone in 5 to 10 minutes reaction time at room temperature. A special hydrolysis procedure is used to determine most aryl aldoximes and vic-dioximes to retard possible hydrolysis during the titrimetric finish. A brief study is made of the role of pyridine in the mechanism of the acetylation. Such procedures ought to b e useful for finding the equivalent weights of unknown ketones or aromatic aldehydes by conversion to an oxime followed b y acetylation.
0
NE LOGICAL functional group method
for carbonyl derivatives such as oximes and hydrazones is the acetylation of the hydroxyl and amino groups of the C=iYOH and and C=TU”H2 functions. Although no analytical acetylation in refluxing pyridine of either function appears to have been reported, the acid-catalyzed acetylation of or-benzoin oxime has been reported by Fritz and Schenk ( 5 ) . Other approaches include the potentiometric titration of weakly basic acetoxime in glacial acetic acid by
Hall and Werner (7) and the titration of dialkyl ketoximes in acetic acid by Higuchi and Barnstein (8). Hall’s (6) data suggest that both diacetylmonoxime and dimethylglyoxime can be titrated as strong bases in acetic acid. The hydrolysis of cyclohexanone osime and subsequent reduction with Ti(II1) by Prochazka, Czerepko, and Jansa (10) exemplifies redox methods reported for oximes. Diaper and Richardson (2) determined cyclohexanone oxime and other oximes by a colorimetric Ce(1V) oxidation method. Banks and Richard (1) have reviewed other methods for and have developed an elegant iodometric method for the assay of most vie-dioximes. Sensbaugh, Cundiff, and Markunas (12) have characterized carbonyl compounds by nonaqueous titration of their 2,4-dinitrophenylhydrazones as weak acids. The methods below are valid for the determination of ketoximes, some aldosimes, and hydrazones based on acidcatalyzed acetylation a t room temperature in pyridine. The acetic anhydride in the blank and after reaction with the sample is determined by hydrolysis
to acetic acid and titration with alcoholic base. The amount of oxime or hydrazone is calculated from the difference of these two titrations. CHOICE
OF
ACETYLATION CONDITIONS
Acetylation of the oxime hydroxyl group in refluxing pyridine (4) poses too many difficulties to be satisfactory. Aldoximes may dehydrate to nitriles in the presence of reflusing acetic anhydride. Oaime acetates may hydrolyze in the hot mater used to hydrolyze the anhydride, regenerating acetic acid. In addition, Milone (9) has reported that hydrolysis of diacetates of cicdioximes takes place a t room temperatures in carbonate-bicarbonate mixtures, which probably have a pH close to the pH of 10 a t the end point in titrimetric finish below. Acetylation of cyclohexanone oxime in refluxing pyridine is accompanied by a dark bronn color which obscures the end point. Acetylation of cyclohesatnone oxime a t room temperature in ethyl acetate gives high results although Schenk and Fritz (11) found that holding the reaction time t o 5 minutes with the 0.25121 VOL. 33, NO. 2, FEBRUARY 1961
299
