Precipitation of copper salicylaldoximate from homogeneous solution

327

Short communications

heat-transfer data; furthermore, since only the rates of cooling before and after solidification are required for the evaluation of latent heats of fmion%complete cooling CXFWSneed not be recorded, The o&y requirementfor the app~~b~~ of Plato’s method is the availab%ty of a Comparisonsample of known latent heat of fusion and of melting point close to that of the unknown substance, so that similar experimenta conditions obtain for the measurementsinvolved.

R. F. KEMPA

E)epartmentof Chemistry

w. R, LEE

Battersea College of Technology Londbn, S. W.11, England

latent heat of fusion of ethylene carbonate, a useful cryoscopic solvent for many organic ~mpo~ds, has been determined(a) from a study of its cooling curve, and (b) from Cryoswpy. The results are shown to be in gnod agreement.

W-The

Zuwnmenfassuns_dithylencarbonat

ist ein gutes kryoskopisches LEisemittel fti viele organische Verbindungen. Seine latente Schmelzwkme wurde aus Abkiihlungskurven und kryoslcopischen Daten bestimmt. Die nach den beiden Methoden erhaltenen Werte stimmen gut iiberein. R&sum&--Lesauteurs ont d&ermin& la chaleur latente de fusion du carbonate Sbthylene, solvent cryoscopique usuel pour de nombreux compo&s organiques: af d’ap& une &de de sa caurbe de cong&ation--b) par cryoscopic. Les r&&tats obtenus par les deux m&odes sent en bon accord. REFERENCES 1 W. Plato, 2. phys. Chem., 1906,35,721. * W, F. Whiie, J. Phys, Chem., 1920,24,393. s I&. Crit. Tubles, 1929, 5, 133. 1 R. F. Kempa and W. H. Lee, J. Chem. Sot., 1958,1936. h S. K. Gross and C. Schuerch, Rnafyt. Chem., 1956,2X%227.

(Receiwd 18 September 1961. Accepted 15 &tuber

196i)

INTRODUCTION the use of salicylaldoxime as a reagent for the gravimetric determination of copper. An advantage of this organic reagent is its large solubility in the aqueous acidic solutions used for the precipitation of copper. Disadvantages are the tendency of the reagent to decompose and the fo~ation of a gelatinous precipitate which is diicult to filter. In the method to be described in this paper, a dense precipitate of copper s~~ylaidox~te is produced by reacting salicy~aldehyde and hydroxyl~~e hy~ochloride in the presence of copper” ions. EXPERIMENTAL IN 1930, Ephraim1~8proposed

Reagents

Unless otherwise specified, all chemicals were reagent grade, Copper so~at~on: C.P. copper metal, 99.9 “/, pure, J. T. Baker Chemical Co., P~ipsb~g, New Jersey, U.S.A., was dissolved in nitric and sulplmric acids. The solution was staadardised by electrolysis t43.01 mg of Cu/2.5 ml, standard deviation 0.09 mg (5 determinations)] and by precipitation with &hydroxyquinoline [43*19mg of Cu/25 ml, standard deviation @17 mg (5 determinations)] by the method of Berg.* 8-~ydraxy~ui~ol~e: ‘l%e Matheson Co,, Inc,, Norwood, Ohio, U.S.A. lrup ~h~or~~: Harshaw Scientific, Cleveland 6, Ohio, U.S.A. NkkeIn sufp-kate ~x~y~ate and hydroxylamine hy~ochlor~&: I. T. Baker Chemical Co., Ph~ipsb~g, New Jersey, U.S.A. Salicykddehyde: The Dow Chemical Co., Midland, Michigan, U.S.A. Salicylaldoxime: Eastman Organic Chemicals, Distillation Products Industries, Rochester 3, New York, U.S.A.

328

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Procedure Add a solution containing O-65 g of salicylald~hyde in 250 ml of distilled water to approximately 25 ml of a weakly acidic solution conta~n~g 10-50 mg of copper. Adjust the pH to 2.9 by the addition of filtered 6N ammonium hydroxide or sodium hydroxide solution and cool in an ice bath to approximately 5”. Dissolve O-33 g of hydroxylamine hydrochloride in 10 ml of distilled water and add 1 ml of this solution with stirring to the cold copper solution. When precipitation begins (approximately 15 min), add the remaining 9 ml of the hydroxylamine hydrochloride solution with stirring. Allow the mixture to stand overnight. Filter onto a glass fritted crucible, wash with cold distilled water, dry at 110” for 3 hr, and weigh as Cu(C,H609N)%; the conversion factor for Cu~~(C,H~O~~~ is O-1892. Precipitation conditions The concentration of the reagents, mode of addition, temperature of reaction, pH range for precipitation, etc., were evaluated in preliminary investigations for the purpose of establishing a gravimetric method. The reaction of salicylaldehyde and hydroxylamine proceeded so rapidly at room temperature that it was found necessary to cool the solution of copper to approximately 5” in order to obtain a precipitate with desirable physical characteristics. Further, for complete precipitation of 50 mg of copper, 3 x the stoichiometric amount of salicylaldehyde and hydroxylamine had to be used. The addition of buffer was not found necessary, although the addition of the hydroxylamine hydrochloride solution lowered the pH from 2.9 to 2.6, where precipitation is still quantitative.4 Precipitates of copper salicylaldoximate were found to come to constant weight after drying for 3 hr at 110”. In studies of the precipitation of copper in the presence of diverse ions, nickel” was added as sulphate and iron”’ was added as chloride. RESULTS

AND

DISCUSSION

The results obtained by precipitation from homogeneous solution (PFHS) and conventional precipitation are shown in Table I. The values agree closely with those obtained by electrolysis, but not with precipitation with 8-hydroxyquinoline. TILED.-DE~R~ATIONOF~OPPER

Method of precipitation

ALONE

Conventional

Copper taken, mg a

PFHS

43.01 -0.32, iO.00 -0.16, -0.25 +0,04, +o*OO

Copper found, rng dijkrence Standard deviation

ho.20

860

43.01 SO.11, +0.06 +0+6, to.06 -0.23, $0.09

I j

I I

10.01 10.07

1 I

ho.13

5 Electrolysis value

Method of precipitation

Conventional

Diverse element

Ni*+, 100 mg

PFHS

Conventional

PFHS

Ni2+, 100 mg / FeJ+, 50 mg

Fe%+, 100 mg -!

Copper taken,

mg Copper found, mg di$rence

43.01

-0.08,

10.06

1

43.01

43-01

+0.15, +O*ll j +0.13, +0.04

j

43.01

Fesf, 50 mg

I I

43-01

$0.43, +0.49 , $0.15, +0.27

Short commumcations The determination of copper in the presence of diverse ions ventional and the PFHS method gave satisfactory results with 100 mg of iron III by PFHS was not satisfactory, but with 50 mg with both methods. However, filtration is easily accomplished PFHS; furthermore, reagent decomposition is avoided.

329 is shown in Table II. Both the con100 mg of nickel**. Separation from of ironIn, good results were obtained when precipitation is carried out by

Acknowledgements-The authors acknowledge the partial assistance of the United States Atomic Energy Commission in supporting the investigation described herein under Contract AT(ll-l)-582 and the help of Fred Kohl who performed some of the early exploratory work. Sunnna~-Salicylaldoxime can be synthesised in aqueous medium by the reaction of salicylaldehyde and hydroxylamine hydrochloride in order to precipitate copper in a readily filterable form. Copper can be easily separated from nickel’1 and ironnr. Zusammenfassung-Salizylaldoxim kann in wassriger Losung synthetisiert werden durch Reaktion von Salizylaldehyd und Hydroxylaminhydrochloride urn Kupfer in leicht filtrierbarer Form abzuscheiden. Kupfer kann derart leicht von Nickel und Eisen(II) getrennt werden. R&sum&La salicylaldoxime peut &tre prepat& synthetiquement en milieu aqueux par reaction de salicylaldehyde et de chlorhydrate d’hydroxylamine afin de precipiter le cuivre sous forme facilement filtrable. Le cuivre peut &tre aisement &pare du nickel(I1) et du fer(II1). RICHARD F. PIETRZAK* Department of Chemistry LOUIS GORDON@ Case Institute of Technology Cleveland 6, Ohio, U.S.A. REFERENCES 1 F. Ephraim, Ber., 1930,63,1928. a Idem., ibid., 1931,64, 1215. a R. Berg, 2. analyt. Chem., 1927,70,341. 4 L. P. Biefeld and D. E. Howe, Znd. Eng. Chem., Analyt., 1939, 11 251.

An investigation by electron-spin resonance of the redox indicator Variamine Blue (Received 7 December 1961. Accepted 16 December 1961) VANAMINEBlue [N-(p-methoxyphenyl)-p-phenylenediamine hydrochloride] is a redox indicator with many applications in analytical chemis?ry .r The redox potential at the colour change E,, in the pH range 1.5-63, with reference to the standard hydrogen electrode, is given by the expression E, = $0.712 - 0.059 pH volt In this pH range the colourless Variamine Blue undergoes two-electron oxidation by strong oxidising agents (bromine, chlorine, etc.) to a violet-red iminoquinone.+4 The colourless reduced form of Variamine Blue (R) combines reversibly with the violet-red iminoquinone (Q) to yield an intensely coloured blue quinhydrone (D).

R+Q+D Polarographic investigation of Variamine Blue and its derivatives, and analysis of the potentiometric titration curves, have indicateda- that the blue quinhydrone (D) may dissociate partially, in many cases, into a semiquinone-type ion (S) which has a free radical structure. D + 2s’ Although the intense blue colour which appears during the colour change of Variamine Blue suggests that a dissociation of this type occurs, the potentiometric data cannot be taken in all cases as conclusive proof of such a dissociation. For example, Holden, Yager and Merritr failed to detect paramagnetic resonance absorption in the closely related dyestuff, Bindschedler’s Green, which on * Present address: Department of Chemistry, Miami University, Oxford, Ohio, U.S.A.