Adams catalyst solubility

Ammonium chloroplatinate often can be used to advantage in place of chloroplatim c acid in the preparation of Adams catalyst. A mixture of 3 g. of ammonium chloroplatinate and 30 g. of sodium nitrate in a casserole or Pyrex beaker is heated gently at first until the rapid evolution of gas slackens and then more strongly until a temperature of 500° is reached. This operation requires about fifteen minutes and there is no spattering. The temperature is held at 500-520° for one-half hour and the mixture is then allowed to cool. The platinum oxide catalyst, collected in the usual way by extracting the soluble salts with water, weighs 1.5 g. and it is comparable in appearance and in activity to the material prepared from chloroplatinic acid. 

Reetz, M.T. and Koch, M., Water-soluble colloidal Adams catalyst preparation and use in catalysis,... 

Considerably easier is the preparation of aqueous colloidal forms of transition metal oxides, which was optimized with the emergence of a straightforward method. The first example pertains to a water-soluble colloidal form of Adams catalyst (Pt02) [52]. 

The practical difficulty with carrying out a crystalhzation DTR process is the need to operate under conditions that allow selective crystalhzation of the least soluble diastereomer while permitting the racemization to take place. Amine racemization catalysts, such as SCRAM , Shvo, Pd/C, and Adam s, are more active at higher temperatures, which runs counter to the conditions required for crystaUization. A solution to this problem is to separate the diastereomeric resolution and racemization steps but couple them with a flow engineering design. In this way each reaction can be operated under optimal conditions for example, temperature, concentration and solvent, via an intermediary solvent exchange unit Since the racemization catalyst itself may affect the crystalhzation (or indeed the crystalhzation may affect the catalyst), it is preferred to keep them separate. This can be achieved by having the catalyst or product either permanently or temporarily in a different phase by immobilization, extraction, precipitation, distil-... 

Using Mossbauer spectroscopy to monitor the formation of p-hematin under in vitro reaction conditions, Adams et al. have demonstrated that the reaction is a psuedo-zero-order process [109]. Such a process is consistent with a mechanism whereby a small concentration of heme is kept soluble via acetate, functioning as a phase-transfer catalyst, in a heme-saturated solution. In the rate limiting step, the soluble heme aggregates to P-hematin, which in turn grows until it precipitates from solution. There are clearly complicated heterogeneous reaction equilibria involved in the aqueous chemical formation of p-hematin. Consequently, it should be emphasized that the detailed mechanistic analysis of the complex solubilization of the species involved in the chemical synthesis... 

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