Ammine complexes formation from ammonia

The reactions of chlorobenzene and benzaldehyde with ammonia over metal Y zeolites have been studied by a pulse technique. For aniline formation from the reaction of chlorobenzene and ammonia, the transition metal forms of Y zeolites show good activity, but alkali and alkaline earth metal forms do not. For CuY, the main products are aniline and benzene. The order of catalytic activity of the metal ions isCu> Ni > Zn> Cr> Co > Cd > Mn > Mg, Ca, Na 0. This order has no relation to the order of electrostatic potential or ionic radius, but is closely related to the order of electronegativity or ammine complex formation constant of metal cations. For benzonitrile formation from benzaldehyde and ammonia, every cation form of Y zeolite shows high activity. 

With this situation in mind, the formation constant (ft) of the first ammonia molecule making the coordination bond with metal cations was taken as the measure of the ease of ammonia adsorption on metals. The values of (ft) were taken from Ringbom s table (H). The plot of the catalytic activity against formation constants of ammine complexes is shown in Figure 2. The correlation is good except for CdY. Again, the metals with lower formation constant (Na+, Ca+, Mg2+) have no activity for chlorobenzene reaction. 

The hydroxide Ni(OH)2 may be precipitated from aqueous solutions of Ni11 salts on addition of alkali metal hydroxides, forming a voluminous green gel that crystallizes [Mg(OH)2 structure] on prolonged storage. It is readily soluble in acid and also in aqueous ammonia owing to the formation of ammine complexes. Ni(OH)2 is not amphoteric. 

In this experiment you will start with an aqueous solution of cobalt(II) chloride, C0CI2. Ammonium chloride, NH4CI, will be added to provide a source of additional Cl", and aqueous ammonia, NH3, will be added to provide potential NH3 ligands. Finallly, hydrogen peroxide, H2O2, will be added to oxidize Co(II) to Co(III). After the reaction is complete, you will filter crystals of your cobalt-ammine complex. It is not uncommon in chemical syntheses that several products can be formed from the seuae set of reactants. In this experiment you should consider [Co(NH3)6]Cl3, [Co(NH3)5Cl]Cl2, and [Co(NH3)4Cl2]Cl as possible products (See PRELABORATORY QUESTION 1). Formation of one of the products can often be favored by subtle changes in the mole ratios of the reactants, the particular catalyst used, or conditions such as temperature. After purification of the primary product, its identity can be determined by analyses or by instrumental techniques. In this experiment, you will use two independent analyses for this purpose. 

To the supernatant liquid from the previous paragraph, add concentrated (15 M) aqueous ammonia, NH3, solution dropwise until the solution is basic to litmus paper then add 5 more drops of 15 M NH3, and stir for 2 minutes. Cu2+ and Cd2+ may initially form insoluble hydroxides, Cu(0H)2 and Cd(0H)2/ which slowly dissolve to form ammine complexes. If the solution turns deep blue from the formation of [Cu(NH3)4]2+, Cu2+ is present. Cd2+ forms a colorless ammine complex that is masked by the deep blue [Cu(NH3)4]2+. Place the test tube in a water bath at about 60.for 1 minute. The formation of a white precipitate of Bi(0H)3 indicates that Bi2+ is present. Nevertheless, both Cu2+ and Bi2+ should be confirmed by the following procedures. 

Since it is known that OH does not in fact attack co-ordinated ammonia, a rapid dissociation of the Co ammine complex followed by attack by this radical on the ammonia released would then account for the formation of NHa radicals. The reaction products are NH4+, Ng, N2O, and a relatively small amount of Oj. The yields of N2 and NjO are close to those expected if NH2OH were the intermediate giving rise to these gases. An interesting overlap on these studies is provided by data on the rate of detachment of NH3 from cobaIt(in) complexes reduced by pulse radiolysis. The rate constant Atq = 8 x lO 1 moI s for the process... 

Ni + yields a green precipitate of hydroxide Ni(OH)2 once pH > 7.2, insoluble in excess of the reagent but soluble in ammonia through the formation of blue nickel ammine complexes, in particular of hexamminenickel(II) [Ni(NH3)6] " ". Nickel hydroxide can again be separated from this solution with an excess of sodium or potassium hydroxide. 

In the other study [155], ammonia-complexed Hg(N03)2 was mixed with the selenosulphate solution. As for the corresponding HgS deposition, a white precipitate formed on addition of ammonia to the HgCNOs) [Eq. (4.9)]. This precipitate dissolved partly in the excess ammonia used, due to formation of various am-mine complexes, and completely when the selenosulphate solution was added, due to additional formation of selenosulphate (and maybe sulphite from the excess sulphite in the selenosulphite solution) complexes. It is likely that mixed ammine-selenosulphate/sulphite complexes were formed. The deposition was carried out on polyester substrates (the transparencies used in overhead projectors) at 10°C. Deposition occurred over several hours to a terminal thickness of ca. 250 nm. Bulk precipitation occurred in parallel with the deposition, suggesting that the cluster mechanism was dominant. 

Another example is found in the various platinum (II) ammines which contain acetonitrile. One such is formed by reaction of [Pt(CH3CN)2Cl2] with ammonia. This gives a product with a formal composition corresponding to [Pt(CH3CN)2(Cl)2(NH3)2]. For many years this was considered to be an unusual complex in which platinum (II) was 6-coordinated. There are very few instances (if any) in which platinum (II) exhibits a coordination number other than 4. It has been shown by x-ray studies (67) that the product of this reaction is [Pt(acetamidine)2Cl2] and that the reaction may be written as shown at the top of the next page. Here, the coordination act accentuates the electron drift from the nitrile carbon atom and makes it more susceptible to attack by nucleophiles—in this case, ammonia. This kind of process had been essentially substantiated by chemical studies carried out previously, and the formation of... 

The nickel complex, Ni ( 5115)2, has been made by the action of the Grignard reagent on nickel (II) acetylacetonate (217) or from potassium cyclopentadienyl and the ammine [Ni(NHs)el (S N)2 in liquid ammonia (58). It forms dark emerald-green crystals which sublime at 80-90° and which, when heated in nitrogen, melt, with decomposition and the formation of a nickel mirror, at 173-174°. It is only slowly oxidized in air, and cold water neither attacks nor dissolves it it is, however, readily soluble in organic liquids. Oxidation of the compound yields an orange-yellow solution containing the ion [Ni( 5H5)2]+, which is stable for a short period in weakly acidic media, and which may be precipitated as the reineckate or tetraphenylborate. 

In the presence of the ammonium cation, zinc hydroxide cannot precipitate either with alkaline hydroxides or with ammonia because of the formation of soluble ammine zinc complexes such as the tetraamminezinc(II) cation [Zn(NH3)4] ". However, Zn + can be precipitated from these complexes by alkaline sulfides ... 

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