Cerium nitrites

F. T. Freriehs and E. F. Smith obtained didymium nitrite in aq. soln. as a dark brown viscid liquid. G. Kriiss and A. Loose attempted to prepare yttrium and cerium nitrites and to use the result as a means of separation of the earths. 

Discussion. Satisfactory results are obtained by adding the nitrite solution to excess of standard 0.1 M cerium(IV) sulphate, and determining the excess of cerium(IV) sulphate with a standard iron(II) solution (compare Section 10.96). 

Procedure. Weigh out accurately about 1.5 g of sodium nitrite and dissolve it in 500 mL of boiled-out water in a graduated flask. Shake thoroughly. Place 50 mL of standard 0.1 M cerium(IV) sulphate in a conical flask, and add 10 mL of 2M sulphuric acid. Transfer 25 mL of the nitrite solution to this flask by means of a pipette, and keep the tip of the pipette below the surface of the liquid during the addition. Allow to stand for 5 minutes, and titrate the excess of cerium(IV) sulphate with standard 0.1 M ammonium iron(II) sulphate, using... 

Determine the volume of the standard cerium(IV) sulphate solution which has reacted with the nitrite solution, and therefrom calculate the purity of the sodium nitrite employed. 

No satisfactory direct gravimetric procedure is available but nitrite can be oxidised to nitrate by permanganate or cerium(IV) and then determined in that form. The determination of total nitrate + nitrite is an important analysis, e.g. for soil samples. Nitrite may be destroyed using urea, sulphamic acid or hydrazine sulphate the reaction with the former is ... 

Nitrobenzaldehyde has been prepared from />-nitrotoluene by treatment with isoamyl nitrite in the presence of sodium methylate,1 by oxidation with chromyl chloride,2 cerium dioxide,3 or chromium trioxide in the presence of acetic anhydride.4 It can also be prepared by the oxidation of -nitrobenzyl chloride,5 7>-nitrobenzyl alcohol,6 or the esters of -nitrocinnamic acid.7... 

Nitration of naphthalene by use of cerium(IV) ammonium nitrate suspended on silica gel, or in homogeneous solution, in the presence of alcohols, sodium or tetrabutylammonium nitrite and acid gives mainly l-alkoxy-4-nitronaphthalenes together with some of the 2-nitro isomers.34 The results are consistent with initial attack by N02- alone or complexed with cerium(IV) ion at the 1- and 2-positions in a ratio of 5 1. 

Lee and Field [318] have discussed a technique of post-column fluorescence detection of nitrite, nitrate, thiosulphate and iodide anions by high performance liquid chromatography. These anions react with cerium(IV) to produce fluorescent species in a post-column packed bed reactor. 

Recent work has been reported on the nitro complexes [Os(N02)(terpy)(bipy)]+, made from [Os(terpy)(bipy)Cl]+ and nitrite ion in ethylene glycol, and on 0s(N02)bipy2Cl, prepared from [Os(NO)bipy2Cl]2+ and sodium hydroxide. Oxidation of [Os(N02)(terpy)(bipy)]+ with cerium(IV) to give [0s(N02)(terpy)(bipy)]2+ is followed by its disproportionation (equation 8). 

A further derivatization technique for forming fluorophors has been described by Lee and Fields [37]. They reacted oxidizable inorganic anions such as nitrite, thiosulfate, and iodide with cerium(IV), thereby forming fluorescing cerium(III) according to Eqs. (190), (191), and (192)... 

For the reaction of the column effluent with the cerium(IV) reagent, instead of a simple injection loop, Fields et al. used a solid-bed reactor with a volume of 2.8 mL. This relatively large volume is necessary to allow the required reaction time of at least two minutes for the oxidation of nitrite ions with cerium(IV). While the reaction of nitrite ions with cerium(IV) is comparatively slow, the maximum fluorescence yield with iodide is obtained in less than ten seconds. On the other hand, the reaction kinetics with thiosulfate appears to be completely different. As seen in the respective diagram in Fig. 6-21, this reaction is characterized by a fast rise of the fluorescence yield within a short time, which increases as the reaction product from Eq. (191), tetrathionate, also reacts slowly with cerium(IV). 

Fig. 6-21. Time dependence of the fluorescence yield for the reaction of nitrite, thiosulfate, and iodide with cerium(lV) (taken from [37]).

Fig. 6-22. Analysis of nitrite, thiosulfate, and iodide upon application of fluorescence detection after derivatization with cerium(IV). — Separator column Vydac 302 IC eluent 0.001 mol/L KHP + 0.01 mol/L Na2S04 pH 5.5 with Na2B407 flow rate 1 mL/min detection fluorescence after reaction with cerium(IV) injection volume 100 pL solute concentrations 0.5 ppm nitrite, 1.1 ppm thiosulfate, and 1.5 ppm iodide (taken from [37]).

TTalues for G(Cem) of 3.28 in 0AM sulfuric acid and 8.32 in 1.0M nitric acid were reported by Challenger and Masters (7) for the radiolysis of cerium (IV) solutions with 50 kvp. x-rays. They presented evidence that the larger G(Cem) might be caused by reactions of OH radical with the nitrate ion. We presented definitive evidence (15, 23) that the larger G(Cem) in 1.0M nitric acid could not be attributed to reaction of OH radical with nitrate ion and proposed an alternative mechanism the effect of nitrate ion was attributed to excitation of nitrate ion with resultant decomposition to yield nitrite ion which reduces... 

Thermal Study Procedures. The reduction of cerium (IV) by nitrous acid was investigated in air-saturated sulfuric acid solutions. About 0.05 ml. of a 0.01 N NaOH stock solution containing 0.01 M sodium nitrite was added by means of a micropipette to about 4 ml. of a cerium (IV) solution in a 1 cm. square spectrophotometer cell and the chart drive of the spectrophotometer was turned on simultaneously. The square cell was then capped, shaken by hand, and placed in the spectrophotometer. The absorbance of cerium (IV) at either 320 or 340 m/x was then recorded as a function of time after mixing. 

Reduction of Cerium(IV) by Nitrous Acid Reaction Kinetics. Since the effect of nitrate ion on G(Cem) was previously attributed (23) to intermediate formation of nitrite ion, the thermal reduction of cerium (IV) by nitrous acid was investigated with reactant concentrations comparable with those encountered in the post-irradiation reaction. We discovered that the reduction of cerium (IV) by nitrous acid was slow, with reaction rates comparable with those rates observed in post-irradiation reactions. Typical experimental data are shown in Figure 3. About 5 seconds were required to prepare the mixture before the optical density could be recorded as a function of time after mixing. 

The simultaneous formation of nitrites and hyponitrites can be imderstood on the basis of the redox properties of Ce ions. Thus nitrites may form when NO is adsorbed on Ce " " ions with anion vacancies in their coordination spheres, leading to reduction of the cerium cation ... 

Silva et al.[44] developed an indirect Fl-AAS method for the determination of nitrate and nitrite in meats and vegetables following liquid-liquid extraction. Nitrate forms an ion pair with bis(2,9- dimethyl-l,10-phenanthrolinato)copper(l) which is extracted into IBMK. Copper is then determined in the separated mganic phase. When the nitrite is oxidized by cerium(VI) into nitrate before the extractirm, total nitrate is determined. When nitrite is ccmverted to nitrogen with sulfamic acid, only the origina] nitrate is determined. 

Handling, Storage, and Precautions while relatively insensitive to impact, the solid can decompose explosively above its melting point. It forms highly explosive azides with metals such as Cu, Pb, Hg, Ag, Au, their alloys and compounds, and reacts with acids to form hydrazoic acid (HN3) which is a toxic, spontaneously explosive gas. Explosive gem-diazides can be formed in CH2CI2 or other chlorinated solvents and shock or heat sensitive metal azidothioformates in CS2. All work with NaNs and other azides should be conducted on a very small scale behind a shield, in a fume hood. Excess NaNs on flasks, paper, etc. can be destroyed in a fume hood by soaking with acidifled Sodium Nitrite or by oxidation with Cerium(IV) Ammonium Nitrated... 

Miura, Y. Hatakeyama, M. Hosino, T. Haddad, P.R. Rapid ion chromatography of L-ascorbic acid, nitrite, sulfite, oxalate, iodide and thiosulfate by isocratic elution utilizing a postcolunm reaction with cerium(IV) and fluorescence detection. J. Chromatogr. A, 2002, 956,11-8A. 

When thorium is present with rare earth elements after the breakdown of monazite by sulphuric acid, the solution may be partially neutralized, to pH2, and absorption can take place onto the anion-exchange resin Amber-lite IRA-400. 8 Cerium is the only rare earth element which might absorb appreciably, but this can be prevented by reduction to the cerous state with sodium nitrite first. The thorium is eluted with 2N hydrochloric acid. 

An alternative American process uses a feed produced by oxalate precipitation of thorium and rare earths. This precipitate is calcined to the oxides and dissolved in nitric acid for extraction with undiluted TBP. After stripping with 8N nitric acid, a high proportion of cerium extracts with the thorium, but the other rare earths are eliminated. The cerium is then back-washed in a separate extractor by means of 0 1 N sodium nitrite solution, which reduces it to the solvent-insoluble cerous condition. Thorium is then backwashed in the last extractor with either water or 2 per cent sulphuric acid. In order to make this process economic it was necessary to devise an efficient system of oxalic acid recovery. This was based upon treatment of the thorium and rare earth oxalates with sodium hydroxide and recycling the resulting sodium oxalate to the precipitation stage. 

Figure 8.59 Time dependences of the fluorescence yield for the reactions of nitrite, thiosuifate, and iodide with cerium(IV) (reproduced with permission from Ref. [88]. Copyright 1984, American Chemical Society).

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