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Precipitation from homogeneous solutions of mixed solvents
Talanta, 1961, Vol. 8. pp. 445 to 449. Pergamon Press Ltd. Printed in Notthem Ireland
SHORT COMMUNICATIONS
~~ipi~ti~n
from ho~ogen~~
solutions of mixed sdvd~
(Received 16 January 1961; Accepted 21 February 1961) THE literature pertaining to methods of achieving precipitation from homogeneous solution has been carefully reviewed by Gordon, Salutsky and Willard. 1 A study of this compilation reveals that past procedures may be broadly classified into one of two groups. One of these involves the direct in situ generation of the precipitating ion by a controlled reaction, usually hydrolysis; and the other is an indirect method which utilises a gradual change of pH to decrease the solubility of the desired compound slowly. Although the precipitant may be a general reagent capable of the precipitation of several ions, serious limitations exist in the application of either of these methods. In the first case the generation reaction usually has a high pH dependence and thus the acidity of the solution must be within a specific range in order to achieve the required rate of precipitation. In the second case the use of a pH change to effect the p~ipitation results in the pr~ipitation of all salts insoluble over the pH range employed. In neither case is one permitted a free choice of the pH required for selective precipitation. This project represents an attempt to arrive at a method whereby a general precipitating agent may be used to effect precipitation from an initially homogeneous solution of any desired PH. The general principle of the procedure involves the use of an organic precipitant which is added to a mixture of the solution containing the ion to be precipitated and a water-miscible organic solvent. Then, after the addition of the buffer, the organic solvent is removed by a slow vola~i~tion and precipitation of the desired compound at a pre-selected pH is permitted. That such a process should yield the desired increase in crystallinity, with its associated increase in ability to separate similiar species, is borne out by recently reported work of Firsching* and by an earlier paper by Wilson and Wilson.* The present authors have shown that this method may be successfully employed for precipitating aluminiumlrl I-quinolinate from a homogeneous acetone-water mixture to which all the requisite components, including buffering reagents, have been added. The procedure employed was to mix in a 250-ml beaker exactiy 10 ml of an al~nium*x* solution and 50 ml of distilled water. To this mixture were then added 60 ml of acetone, 4 ml of 5 ok I-hydroxyquinoline in 2N acetic acid, and 40 ml of 2N ammonium acetate. The reaction mixture was placed on a water bath at 70”-75” and left uncovered for 3 hr. Visible precipitation began after about 15 min. At the end of the evaporation period the beakers were removed from the bath, allowed to cool, and filtered through medium-porosity sinteredglass crucibles. The precipitates were washed three times with distilled water and dried for 3 hr at 135”-140”. The product was weighed as anhydrous Al(C,H,ON),. The ~urniniurn*II solution was prepared from KAlSOI.12He0 so that 10 ml contained 10.06 f 0.03 mg of AlI*’ as shown by the analysis of ten samples by the method of Olson, Koch and Pimentel.4 When the above procedure was followed, the Al”1 recovered from ten samples of 10 ml each was 10.04 i 0.04 mg. The precipitates obtained were highly crystalline and were very easily filtered and washed. Using a similar procedure, samples containing 1Omg of Mglr have been analysed with good precision and accuracy, but with little improvement over conventional methods in the crystallinity of the precipitates formed or in the ease of filtering and washing. Precipitates obtained by both the evaporation method and the usual method of direct addition are grainy and easily handled. In the case of zinc” even large amounts of acetone fail to retard precipitation longer than about 1 min after the addition of the buffer solution. A co-precipitation study of magnesiumI 8-quinolinate on zincI &quiuolinate was made, and the results obtained were essentially identical to those of Moyer and Remington.6 445
446
Short communications
In addition to these studies, research on other solvent systems, cations, interfering ions and organic precipitating agents is in progress. Qualitative precipitations of aluminiumrrr 8-quinolinate from eth~ol-water mixtures have been a~omplish~ although the use of such mixtures entails evaporation times longer than those required when acetone is the organic component. Acknowledgement-The Corporation.
authors gratefully acknowledge the financial support provided by the Research LESTERC. JERRY L.
Department of Chemistry ~~~versi~y of Arkansas Fayett~ilie, Ark., U.S.A.
HOWICK@
JONES
Summary-It has been shown that precipitation from homogeneous solutions of mixed solvents may be effected by the preferential volatilisation of one of the solvent components. The precipitation of aluminiumlrr I-quinolinate from an acetone-water system yields quantitative results and a highly crystalline precipitate.
Zusammeafassung-Es wird gezeigt, dass Fallung aus homogener L&sung erzielt werden kams, indem man eine der Losungsmittelkomponenten biniirer Solventien bevorzugt verdampfen liisst. Die Fallung von Aluminiumoxinat ergibt quantitative Fallung aus Azeton-Wassermischung und ein schbn kristalliner Niederschlag wird erzielt.
R6%ua&--Lesauteurs montrent que la precipitation
homog&ne a partir de solvants mixtes peut &re effect&e par la volatili~tion pr~f~rentie~e de Pun des ~nstit~nts du solvant. La p~ipi~tion du 8-quinolate d’aluminium dans le systeme eau-acetone donne des resultats quantitatifs et un pr&ipite fortement cristallin. REFERENCES r L. Gordon, M. L. Salt&sky and H. H. Willard, Precipitationfrom Homogeneous Solution. John Wiley Sons, Inc., New York, 1959. 2 F. II. Firsching, AmzZyt. Chem., 1960,32, 1876. s D. W. Wilson and C. L, Wilson, J. Chem. Sot,, 1939, 1956. 4 A. R. Olson, C. W. Koch, and G. C. Pimental, Introductory Quantitative Chemistry. W. H. Freeman and Company, San Francisco, 1956. 6 H. V. Moyer and W. J. Remington, Znd. Eng. Chem., Analyt., 1938, 10,212.
XXIX. Mittcbng
iiber quantitative
organische
Analysel
Eme automat&&eM&ode zu1 Mikrobestimmuagvon Kohlenstoff, Wasserstoff uad Stick&off ia orgaukben substaazea (Received 21 December 1960. Accepted 19 January 1961) WIR haben gefunden, dass sich Mikroeinwaagen organischer Substanzen blitzartig verbrennen lassen, wenn man sie auf dem Schiffchen mit aktiven, durch thermischen Zerfall von Kobaltoxalat erhaltenem CooOI mischt. Die Verbrenmmg kann man in einigen Sekunden ohne Explosionsgefahr durchfiihren, wobei die O~dation quantitativ verlauft, falls man die Prod&e tiber eine Schichte von i&O, auf einem geeigneten Katalysatortrager2 sowohl in Sauerstoff- als in Stickstoff- wie such in Kohlendioxyd-Atmosph&re fuhrt. Damit wurden einerseits die Methoden zur gravimetrischen Restimmung von Kohlenstoff und Wasserstoff sowie zur gasvolumetrischen Restimmung von Stickstoff extrem vereinfacht und wesentlich beschleunigt,5 anderseits konnten wir zur direkten Bestimmung der Verbrennungsprodukte
SHORT COMMUNICATIONS
~~ipi~ti~n
from ho~ogen~~
solutions of mixed sdvd~
(Received 16 January 1961; Accepted 21 February 1961) THE literature pertaining to methods of achieving precipitation from homogeneous solution has been carefully reviewed by Gordon, Salutsky and Willard. 1 A study of this compilation reveals that past procedures may be broadly classified into one of two groups. One of these involves the direct in situ generation of the precipitating ion by a controlled reaction, usually hydrolysis; and the other is an indirect method which utilises a gradual change of pH to decrease the solubility of the desired compound slowly. Although the precipitant may be a general reagent capable of the precipitation of several ions, serious limitations exist in the application of either of these methods. In the first case the generation reaction usually has a high pH dependence and thus the acidity of the solution must be within a specific range in order to achieve the required rate of precipitation. In the second case the use of a pH change to effect the p~ipitation results in the pr~ipitation of all salts insoluble over the pH range employed. In neither case is one permitted a free choice of the pH required for selective precipitation. This project represents an attempt to arrive at a method whereby a general precipitating agent may be used to effect precipitation from an initially homogeneous solution of any desired PH. The general principle of the procedure involves the use of an organic precipitant which is added to a mixture of the solution containing the ion to be precipitated and a water-miscible organic solvent. Then, after the addition of the buffer, the organic solvent is removed by a slow vola~i~tion and precipitation of the desired compound at a pre-selected pH is permitted. That such a process should yield the desired increase in crystallinity, with its associated increase in ability to separate similiar species, is borne out by recently reported work of Firsching* and by an earlier paper by Wilson and Wilson.* The present authors have shown that this method may be successfully employed for precipitating aluminiumlrl I-quinolinate from a homogeneous acetone-water mixture to which all the requisite components, including buffering reagents, have been added. The procedure employed was to mix in a 250-ml beaker exactiy 10 ml of an al~nium*x* solution and 50 ml of distilled water. To this mixture were then added 60 ml of acetone, 4 ml of 5 ok I-hydroxyquinoline in 2N acetic acid, and 40 ml of 2N ammonium acetate. The reaction mixture was placed on a water bath at 70”-75” and left uncovered for 3 hr. Visible precipitation began after about 15 min. At the end of the evaporation period the beakers were removed from the bath, allowed to cool, and filtered through medium-porosity sinteredglass crucibles. The precipitates were washed three times with distilled water and dried for 3 hr at 135”-140”. The product was weighed as anhydrous Al(C,H,ON),. The ~urniniurn*II solution was prepared from KAlSOI.12He0 so that 10 ml contained 10.06 f 0.03 mg of AlI*’ as shown by the analysis of ten samples by the method of Olson, Koch and Pimentel.4 When the above procedure was followed, the Al”1 recovered from ten samples of 10 ml each was 10.04 i 0.04 mg. The precipitates obtained were highly crystalline and were very easily filtered and washed. Using a similar procedure, samples containing 1Omg of Mglr have been analysed with good precision and accuracy, but with little improvement over conventional methods in the crystallinity of the precipitates formed or in the ease of filtering and washing. Precipitates obtained by both the evaporation method and the usual method of direct addition are grainy and easily handled. In the case of zinc” even large amounts of acetone fail to retard precipitation longer than about 1 min after the addition of the buffer solution. A co-precipitation study of magnesiumI 8-quinolinate on zincI &quiuolinate was made, and the results obtained were essentially identical to those of Moyer and Remington.6 445
446
Short communications
In addition to these studies, research on other solvent systems, cations, interfering ions and organic precipitating agents is in progress. Qualitative precipitations of aluminiumrrr 8-quinolinate from eth~ol-water mixtures have been a~omplish~ although the use of such mixtures entails evaporation times longer than those required when acetone is the organic component. Acknowledgement-The Corporation.
authors gratefully acknowledge the financial support provided by the Research LESTERC. JERRY L.
Department of Chemistry ~~~versi~y of Arkansas Fayett~ilie, Ark., U.S.A.
HOWICK@
JONES
Summary-It has been shown that precipitation from homogeneous solutions of mixed solvents may be effected by the preferential volatilisation of one of the solvent components. The precipitation of aluminiumlrr I-quinolinate from an acetone-water system yields quantitative results and a highly crystalline precipitate.
Zusammeafassung-Es wird gezeigt, dass Fallung aus homogener L&sung erzielt werden kams, indem man eine der Losungsmittelkomponenten biniirer Solventien bevorzugt verdampfen liisst. Die Fallung von Aluminiumoxinat ergibt quantitative Fallung aus Azeton-Wassermischung und ein schbn kristalliner Niederschlag wird erzielt.
R6%ua&--Lesauteurs montrent que la precipitation
homog&ne a partir de solvants mixtes peut &re effect&e par la volatili~tion pr~f~rentie~e de Pun des ~nstit~nts du solvant. La p~ipi~tion du 8-quinolate d’aluminium dans le systeme eau-acetone donne des resultats quantitatifs et un pr&ipite fortement cristallin. REFERENCES r L. Gordon, M. L. Salt&sky and H. H. Willard, Precipitationfrom Homogeneous Solution. John Wiley Sons, Inc., New York, 1959. 2 F. II. Firsching, AmzZyt. Chem., 1960,32, 1876. s D. W. Wilson and C. L, Wilson, J. Chem. Sot,, 1939, 1956. 4 A. R. Olson, C. W. Koch, and G. C. Pimental, Introductory Quantitative Chemistry. W. H. Freeman and Company, San Francisco, 1956. 6 H. V. Moyer and W. J. Remington, Znd. Eng. Chem., Analyt., 1938, 10,212.
XXIX. Mittcbng
iiber quantitative
organische
Analysel
Eme automat&&eM&ode zu1 Mikrobestimmuagvon Kohlenstoff, Wasserstoff uad Stick&off ia orgaukben substaazea (Received 21 December 1960. Accepted 19 January 1961) WIR haben gefunden, dass sich Mikroeinwaagen organischer Substanzen blitzartig verbrennen lassen, wenn man sie auf dem Schiffchen mit aktiven, durch thermischen Zerfall von Kobaltoxalat erhaltenem CooOI mischt. Die Verbrenmmg kann man in einigen Sekunden ohne Explosionsgefahr durchfiihren, wobei die O~dation quantitativ verlauft, falls man die Prod&e tiber eine Schichte von i&O, auf einem geeigneten Katalysatortrager2 sowohl in Sauerstoff- als in Stickstoff- wie such in Kohlendioxyd-Atmosph&re fuhrt. Damit wurden einerseits die Methoden zur gravimetrischen Restimmung von Kohlenstoff und Wasserstoff sowie zur gasvolumetrischen Restimmung von Stickstoff extrem vereinfacht und wesentlich beschleunigt,5 anderseits konnten wir zur direkten Bestimmung der Verbrennungsprodukte