Iron oxinate

Discussion. Iron(III) (50-200 fig) can be extracted from aqueous solution with a 1 per cent solution of 8-hydroxyquinoline in chloroform by double extraction when the pH of the aqueous solution is between 2 and 10. At a pH of 2-2.5 nickel, cobalt, cerium(III), and aluminium do not interfere. Iron(III) oxinate is dark-coloured in chloroform and absorbs at 470 nm. 

Procedure. Weigh out 0.0226 g of hydrated ammonium iron(III) sulphate and dissolve it in 1 L of water in a graduated flask 50 mL of this solution contain 100 g of iron. Place 50.0 mL of the solution in a 100 mL separatory funnel, add 10 mL of a 1 per cent oxine (analytical grade) solution in chloroform and shake for 1 minute. Separate the chloroform layer. Transfer a portion of the latter to a 1.0 cm absorption cell. Determine the absorbance at 470 nm in a spectrophotometer, using the solvent as a blank or reference. Repeat the extraction with a further 10 mL of 1 per cent oxine solution in chloroform, and measure the absorbance to confirm that all the iron was extracted. 

Discussion. Various metals (e.g. aluminium, iron, copper, zinc, cadmium, nickel, cobalt, manganese, and magnesium) under specified conditions of pH yield well-defined crystalline precipitates with 8-hydroxyquinoline. These precipitates have the general formula M(C9H6ON) , where n is the charge on the metal M ion [see, however, Section 11.11(c)]. Upon treatment of the oxinates with dilute hydrochloric acid, the oxine is liberated. One molecule of oxine reacts with two molecules of bromine to give 5,7-dibromo-8-hydroxyquinoline ... 

Beryllium is sometimes precipitated together with aluminium hydroxide, which it resembles in many respects. Separation from aluminium (and also from iron) may be effected by means of oxine. An acetic (ethanoic) acid solution containing ammonium acetate is used the aluminium and iron are precipitated as oxinates, and the beryllium in the filtrate is then precipitated with ammonia solution. Phosphate must be absent in the initial precipitation of beryllium and aluminium hydroxides. 

Hydroxyqninoline (oxine). Iron (III) ca 30 mg in 25 mL of weakly acidic (HCl) solution). Add a solution of 3 g ammonium acetate in 125 mL water, followed by 12-15mL of reagent solution 2 per cent in 2M acetic (ethanoic) acid. Heat the solution at 80-90°C for 30 minutes, filter and wash the precipitate with 1 per cent acetic acid and with water. Dry at 130-140 °C and weigh as Fe(C9H6ON)3 (Section 11.28). 

Molybdenum(VI), vanadium(V), mercury, and iron interfere permanganates, if present, may be removed by boiling with a little ethanol. If the ratio of vanadium to chromium does not exceed 10 1, nearly correct results may be obtained by allowing the solution to stand for 10-15 minutes after the addition of the reagent, since the vanadium-diphenylcarbazide colour fades fairly rapidly. Vanadate can be separated from chromate by adding oxine to the solution and extracting at a pH of about 4 with chloroform chromate remains in the aqueous solution. Vanadium as well as iron can be precipitated in acid solution with cupferron and thus separated from chromium (III). 

Determination of Iron (III) as the 8-hydroy quinolate complex [Iron (III) oxinate]... 

DETERMINATION OF IRON (III) AS THE 8-HYDROXY QUINOLATE COMPLEX [IRON (III) OXINATE]... 

Materials Required Hydrated ammonium iron (III) sulphate 0.0266 g oxine solution ( AnalaR -Grade, 1% w/v in chloroform) 50 ml chloroform 100 ml ... 

Repeat the extraction with a further 10 ml quantity of 1% oxine solution, and measure the absorbance again so as to confirm whether all the iron was extracted or not. Usually three extractions suffice the complete extraction of Fe (III). 

The acid-catalyzed aquation of iron(III)-(substituted)oxinate complexes involves iron oxygen bond breaking and concomitant proton transfer in transition state formation. The latter aspect contrasts with the much slower acid-catalyzed aquation of hydroxamates, where proton transfer seems not to take place in the transition state. Reactivities, with and without proton assistance, for various stages in dissociation of a selection of bidentate and hexadentate hydroxamates, oxinates, and salicylates are compared and discussed—the overall theme is of dissociative activation. ... 

A multiple-path mechanism has been elaborated for dissociation of the mono- and binuclear tris(hydroxamato)-iron(III) complexes with dihydroxamate ligands in aqueous solution. " Iron removal by edta from mono-, bi-, and trinuclear complexes with model desferrioxamine-related siderophores containing one, two, or three tris-hydroxamate units generally follows first-order kinetics though biphasic kinetics were reported for iron removal from one of the binuclear complexes. The kinetic results were interpreted in terms of discrete intrastrand ferrioxamine-type structures for the di-iron and tri-iron complexes of (288). " Reactivities for dissociation, by dissociative activation mechanisms, of a selection of bidentate and hexadentate hydroxamates have been compared with those of oxinates and salicylates. ... 

Acetic acid - 8-hydroxyquinoline reagent - dissolve 10 g 8-hydroxy-quinoline in a solution of 2.5 % (v/v) acetic acid and make up to 1 I. (The 8-hydroxyquinoline blocks the readsorption or precipitation of phosphate by active iron and aluminium during acetic acid extraction. Synonyms hydroxybenzopyridine oxine phenopyridine 8-quinolinol. Not carcinogenic, but may be harmful if swallowed, and causes irritation to eyes, respiratory tract and skin safety data sheet at http //www. jtbaker.com/msds/q7250. htm.)... 

An interesting property of resins impregnated with oximes or oxines is that the selectivity of, for example, copper over iron(III), approaches that of a pure solvent-extraction process only when an inert solvent is present in the pores of the resin.396 Thus, in a /S-hydroxyoxime SIR, the selectivity for copper over iron(III) improved by a factor of 20 when the solvent perchloroethylene was introduced into the SIR, and by a factor of 700 in a similar resin impregnated with 8-hydroxy-quinoline.396 This is believed to be due to kinetic and thermodynamic restrictions in the extraction of iron(III), but not of copper, at an aqueous—organic boundary.396 397... 

The more modern style of Skraup synthesis is used to make 8-quinolinol or oxine . ortho-Amino-phenol has only one free position ortho to the amino group and is very nucleophilic, so acrolein can be used in weak acid with only a trace of strong acid. Iron(III) is the oxidant with a bit of boric acid for luck, and the yield is excellent. 

The diphenylcarbazide method is almost specific for chromium(Vl). Interferences result only from Fe, V, Mo, Cu, and Hg(II) present at much higher concentrations than the chromium. Iron(lll) can be masked by phosphoric acid or EDTA. Iron(III) can also be separated as Fe(OH>3, after chromium has been oxidized to Cr(VI), or by extraction. Vanadium can be separated from Cr(VI) by extraction as its oxinate at pH -4. Molybdenum is masked with oxalic acid, and Hg(II) is converted into the chloride complex. 

From weakly acid solutions, Fe(III) is extractable with acetylacetone [5], hexafluoroacetylacetone [6], and HTTA [7]. Iron(III) can be extracted with oxine in chloroform [8,9], HDEHP [10], dithiocarbamates [11,12], and Adogene 464 (in toluene) [13,14]. 

Traces of iron can be separated from Al, Ti, V, U, and phosphate, by precipitation as the sulphide from tartrate medium. Cadmium, lead, or any other metal which gives a sparingly soluble sulphide can be used as collector. Oxine is also useful as a precipitant for the separation of iron [8]. 

Another way to slow substitution is to covalently bond a ligand to silica— compare bonding ligands to monoclonal antibodies above. Oxine bound to silica reacts much more slowly with Al, for example, than when it is in solution. Another example of slow substitution at Al is related to the indium chemistry mentioned above, involving its slow transfer from its transferrin complex by reaction with iron(III)-citrate to form the much more stable combination of iron-transferrin and aluminum-citrate complexes. Further examples of slow substitution kinetics involving ferritin will be found in the iron(III) section (Section 8.3.4). 

The question was then posed does oxine act on bacteria by removing metals essential to bacterial welfare, or does it cause traces of metal ions to become more toxic to the bacteria The latter proved to be the case. When we incubated Staphylococcus aureus in distilled water, with oxine, with iron, and then with both chemicals together, subsequent plating out on nutritive medium showed that only bacteria that had been exposed to both oxine and iron were killed (see Table 2.3) (Albert, Gibson and Rubbo, 1953). In further work, it was found that iron is a necessary co-toxicant for all kinds of bacteria, whereas copper takes over this function for fungi. 

Cobalt is well known for its ability to break an oxidatively destructive chain reaction catalysed by another metal (cf. Baur and Preis, 1936). This suggested to the Dutch workers that the iron and copper complexes of oxine, pyrithione, and dimethyldithiocarbamic acid were oxidatively destroying thioctic acid (dihydrolipoic acid) (2.28) which is the essential coenzyme for the oxidative decarboxylation of pyruvic acid. This was confirmed when they found pyruvic acid accumulating in the medium (Sijpesteijn and Janssen, 1959 also personal communications from these authors). The receptor in all three examples is the small molecule (2.28) although, at the time, it caused surprise to find one of such low molecular weight. 

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