Liquid ammonia ammoniation reactions

Ammoniates of boranes. The ammonia addition compound of B2H6 has a molecular weight in liquid ammonia corresponding to the formula B2H6. 2 NH3. An ionic structure NH4 [BH3. NH2- BH3] has been suggested, but the formulation as a borohydride, [H2B(NH3)2] (BH4) , is now preferred. This would appear to be consistent with its reaction with NH4CI ... 

The decay of Bn h the pulse radiolysis of liquid ammonia is second order with a rate coefficient [96] of (1.1 0.2) x 10 ° Imole sec". By contrast, the disappearance of Bn h 3 in alkali metal-ammonia solutions at concentrations <10 is first order and very slow. The ammoniated electron formed in the radiolysis probably reacts with other intermediates produced, e.g. -NHj or NH4, and does not decay via the reaction... 

If this view is correct, the ammoniate should behave as an acid in liquid ammonia (13), that is, the solution should conduct and the hydrogen should be replaced by metal in a neutralization reaction. Actually the conductivity of liquid ammonia is increased considerably when S4N4 dissolves in it and the solution is warmed to —47° (17). Thus with a S2N2 NH3 molarity of 1.67 X 10-4 mole/liter, the specific conductivity is 0.104 X 10—3 at 21.01 X 10 4 mole/liter it is 0.62 X 10 3 and at 13.24 X 10 3 mole/liter, 2.84 X 10-3 ohm-1 cm-1. 

In a salt-like description of these compounds, AE, the alkali metal A transfers its valence electron to the tetrel , and - in agreement with the Zintl-Klemm-Busmann concept [9] - the tetrel elements form P4-analogous tetrahedral clusters [ 4] . These highly charged clusters [ 4] are retained in a liquid ammonia solution of RbPb, as shown by Korber et al. via the crystallization of the ammoniate Rb4Pb4(NH3)2 [10]. The isotypic compounds A4Sii4(N 143)2 were obtained for A = Rb and Cs from reactions of the element Sn, as well as from Cs with Sn(C6Hs)4 in liquid ammonia [10]. 

The cyclic trimer, (PNCl2)3 (7.319a) will react with liquid ammonia in a sealed tube to give the fully ammoniated derivative PN(NH2) 3. The action of heat on this latter compound first produces a form of phospham in which the trimeric rings probably remain intact (7.28), but this eventually loses more ammonia and decomposes along the route (7.27). The normal form of phospham, made from PCI5 and NH3 probably has a random network structure (7.30), like the product from reaction (7.29). 

Several reports on reactions in liquid ammonia have been published, including the proceedings of the Fifth International Conference on excess electrons and metal-ammonia solutions,proton exchange at cobalt(III) ammine complexes, and the reaction of the ammoniated electron with thiosulfate... 

Europium and ytterbium metal dissolve in liquid ammonia to give blue solutions containing the ammoniated electron. They are the only lanthanide metals to do so samarium does not undergo this reaction (Thompson et al, 1966 Warf, 1970). 

As was mentioned in section 2.3.3, ytterbium metal dissolves in liquid ammonia to yield ammoniated electrons and Yb " ions. This solution was used by White et al. (1978) to perform reductions of various aromatic systems, similar to the Birch reactions which use lithium or sodium as the metal. The addition of benzoic acid or anisole dissolved in a 10 1 mixture of THF-tert-butyl alcohol, to an ytterbium-ammonia solution gives 1,4-dihydrobenzoic acid (56% yield). Triple bonds are cleanly reduced to trans olefins (i.e. PhC CPh traK5-PhCH=CHPh 75%). The C=C double bonds of conjugated ketones are also reduced by this system. Since the reaction medium initially contains both solvated electrons and Yb + ions it is likely that the above reactions are not directly connected with the presence of divalent ytterbium species. 

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