Double nitrates

Sulfates and nitrates are known and in all cases they decompose to the oxides on heating. Double sulfates of the type M (S04)3.3Na2S04.12H20 can be prepared, and La (unlike Sc and Y) forms a double nitrate, La(N03)3,2NH4N03.4H20, which is of the type once used extensively in fractional crystallization procedures for separating individual lanthanides. 

The classical methods used to separate the lanthanides from aqueous solutions depended on (i) differences in basicity, the less-basic hydroxides of the heavy lanthanides precipitating before those of the lighter ones on gradual addition of alkali (ii) differences in solubility of salts such as oxalates, double sulfates, and double nitrates and (iii) conversion, if possible, to an oxidation state other than -1-3, e g. Ce(IV), Eu(II). This latter process provided the cleanest method but was only occasionally applicable. Methods (i) and (ii) required much repetition to be effective, and fractional recrystallizations were sometimes repeated thousands of times. (In 1911 the American C. James performed 15 000 recrystallizations in order to obtain pure thulium bromate). 

However, solubility, depending as it does on the rather small difference between solvation energy and lattice energy (both large quantities which themselves increase as cation size decreases) and on entropy effects, cannot be simply related to cation radius. No consistent trends are apparent in aqueous, or for that matter nonaqueous, solutions but an empirical distinction can often be made between the lighter cerium lanthanides and the heavier yttrium lanthanides. Thus oxalates, double sulfates and double nitrates of the former are rather less soluble and basic nitrates more soluble than those of the latter. The differences are by no means sharp, but classical separation procedures depended on them. 

Several cubic double nitrates of the composition K3M2(N03)9 (M=Pr, Nd, Sm) have been prepared by Carnall et al. (228), to study the electronic and vibrational spectra of the complexes. During this study, they have also investigated the structure of the Pr(IH) analogue and found that each Pr(III) ion is surrounded by twelve oxygens, from six bidentate nitrate groups, in a distorted icosahedral... 

The nitrate, (Y(NO)3)3 ) exists as a number of hydrates. The hexahydrate formed by action of HNO3 upon the hydroxide, is dehydrated at 100°C to give the tnhydrate and the anhydrous salt. However, other hydrates are known, as well as double nitrates (especially with the lanthanide elements) and oxynitrates. of the general formula, XY2O3 3 05 -ZH2O. 

The anhydrous nitrates are addition products of nitrio anhydride and the metallio oxide, Cs20+N20B = 2CsNOa, e.g, the nitrates of the five alkali metals, silver, barium, strontium, magnesium, thallium, gallium, and lead and the double nitrates of gold or silver with the alkali metals e.g. KAu(N03)4,KAg(N03)2. 

A New Series of Anhydrous Double Nitrate Salts of the Lanthanides. Structural and Spectral Characterization, W.T. Camall, S. Siegel, J.R. Ferraro, B. Tani, and E. Gebert, Inorg. Chem. 12, 560-564 (1973). 

Nitrogen oxides and oxygen in combination with Beta zeolites give also high conversion but do not show a selectivity improvement with respect to the classical Kyodai nitration process. However, for the double nitration of toluene, Beta is very selective towards the 2,4-dinitro isomer. 

The double nitrates Mg3M2(N03)12, 24 H20 can be recrystallized in strong nitric acid and serve to separate the lighter lanthanides M = La, Pr, Nd and Sm (where Ce has been removed after oxidation to the quadrivalent state). Judd noted 109) that the fine-structure of the absorption band belonging to each /-level of M(III) was so peculiar that it looked as if the chromophore was icosahedral with N = 12 (which is almost unheard about, outside boron chemistry). The crystal structure 110) of the cubic crystals confirmed entirely Judd s proposal, it is indeed [Mg(OH2)6]3 ... 

So we need to make the required aromatic diamine. We might guess from what we did earlier in this chapter as well as from Chapter 22 that this is likely to be achieved by nitration and reduction so we should check that double nitration of our proposed starting material will occur in the right positions (regioselectivity). Remember that at this stage we are just making proposals—we can only predict whether the reactions will actually occur or not... 

Our earlier nitration system involving nitric acid and acetic anhydride in conjunction with zeolite HP has been adapted to include trifluoroacetic anhydride, which enhances the reactivity considerably and allows the nitration of deactivated aromatics. Optimisation of the process has enabled the most selective double nitration of toluene yet attained, giving 2,4-dinitrotoluene in high yield. 

Double Nitrates.—A double nitrate of nickel and bismuth, 3Ni(N03)2.2Bi(N03)3.24H20, has been prepared as green crystals, melting at 69° C. without decomposition.3 Other double nitrates are known,4 including double nitrates of certain rare earth metals,5 and several basic salts had been prepared.6... 

Classical methods of separation [7] are (1) fractional crystallization, (2) precipitation and (3) thermal reactions. Fractional crystallization is an effective method for lanthanides at the lower end of the series, which differ in cation radius to a large extent. The separation of lanthanum as a double nitrate, La(N03)3-2NH4N03-4H20, from praseodymium and other trivalent lanthanide with prior removal of cerium as Ce4+ is quite a rapid process and is of commercial significance. Other examples are separation of yttrium earths as bromates, RE(Br03>9H20 and use of simple nitrates, sulfates and double sulfate and alkali metal rare earth ethylenediamine tetraacetate complex salts in fractional crystallization separation. 

These exhibit high coordination numbers. Double nitrates Mg3Ln2(N03)i2.24H20, which contain [Ln(N03)6] ions, are important historically as they were once used for the separation of the lanthanides by fractional crystallization. Use of counter-ions like Ph4P+ and Me4N+ allow isolation of the 10-coordinate [Ln(N03)5] ions. 

Nitrate complexes are of historical importance for their role in separation of the early lanthanides by fractional crystallization, when magnesium double nitrates, Mg3Ln2(N03)i2 -24H20, were used. These complexes contain 12-coordinate [Ln(N03)6] groups, also found in some crown ether complexes. Other nitrate complexes characterized include 10-coordinate [Ln(N03)5] , as salts with counterions... 

Although it might be assumed quite reasonably that the coordination chemistry of the some 15 elements known during Werner s lifetime would have developed significantly during that period, the literature contains only a few accounts of synthesis and characterization. Indeed, the 1920 edition of Werner s classic monograph (50) records essentially the same information as the 1908 edition, namely the compositions of a limited number of double nitrates, sulfates, and oxalates. Both Spencer ( 5) and Little in their comprehensive compilations of data at about the same time, describe only certain lanthanide double salts and adducts, but not within the framework of complex compounds or coordination chemistry. 

The nitrates are very soluble indeed and form double nitrates with magnesium, 3Mg(N0g)2.2Ln(N03)3.24H20 these were formerly used for separations within this series of elements. Their solubilities increase with molecular weight. 

Praseodymium is difficult to obtain in pure compounds buffi because of its scarcity and close resemblance to other elements. The best methods of separation are as follows (1) Hot. out from a double magnesium nitrate scries such fractions us contain only lanthanum and praseodymium continue the fractionation of the same salt or of double ammonium nitrate, Praseodymium appears at the soluble end, but usually neodymium appears there also, even if its presence is unsuNficctcd at first. (2) Remove from the magnesium double nitrate series the fractions which contain only praseodymium and neodymium and continue the fractionation as the manganese double nitrate, when praseodymium separates in the least soluble portions, Other methods used are Crystallization of the oxalates from nitric add of the double ammonium nitrate or double carbonate. 

Double nitrates of the cerium group are easily crystallized. Th stability decreases gradually with rise of atomic weight of the metal, a in the yttrium group crystalline double nitrates do not form. Cfc sequently, the use of the double nitrates in fractionation is limited to I cerium group. 

The nitrate, TKNCDs, is prepared by dissolving TI2O3 in nitric acid. It forms deliquescent crystals, Tl(NOs)3 -3 H20, is easily hydrolyzed and decomposed, and forms double nitrates. 

Ceric nitrate, Ce(N03) 4, is not known as a simple salt, but double nitrates of the type Ce(N03)4 2 M N03 are formed with the alkali metals and ammonium. In aqueous solutions these salts are readily hydrolyzed, but they are the most stable ceric salts. The ammonium ceric nitrate is important in the purification of cerium. A series of double nitrates, M (N03)2 Ce(N03)4 8 H2O, is also formed, but they are less stable than the alkali double salts. When ceric hydroxide is evaporated with nitric acid, crystals of the basic salt 2 Ce0H(N03)2 9 H2O are obtained. 

Compounds. — In its chemical relations thorium resembles both zirconium and quadrivalent cerium. It is somewhat more markedly electropositive than either of these elements, acidic properties being entirely absent. Its neutral salts are hydrolyzed somewhat in solution, and consequently are acid to indicators. They are however sufficiently stable to permit recrystallization from water solution. In basicity thorium approaches the elements of the yttrium group. Double salts are less common than with cerium and zirconium, but characteristic double nitrates, R2 Th(N03) 6, crystallize well and are iso-morphous with the analogous ceric double nitrates. Thorium resembles cerium in forming a double potassium sulfate which is insoluble in potassium sulfate solution, hut differs from it in... 

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