Chloroplatinic add

When a very dilute cold aqueous solution of the 1 1-dichloride is treated with chloroplatinic acid, the chloroplatinate separates as a pale yellow microcrystalline powder, sintering at 190° C. and decomposing at 216° C. It is almost insoluble in water, but dissolves in chloroform or benzene. If the chloroplatinic add be added to a hot, moderately concentrated solution of the 1 1-dichloride, sparingly soluble orange bis-1 -chlorocycloselenipentane 1-chloroplatinate is precipitated. This decomposes at 160° C., is insoluble in organic solvents with the exception of alcohol, and has the constitution... 

The addition of hydridosilanes across the triple bond of alkynes can be accomplished using a variety of catalysts, the best being chloroplatinic add. cis-Addition, with terminal regioselectivity, is normally observed, with lower temperatures favouring a greater proportion of the terminal isomer (see also Chapter 17). 

The procedure for the preparation of the platinum compounds is an extension of the method described by Kharasch and Ashford. A glacial acetic add solution of chloroplatinic add is mixed with the appropriate olefin, and in the ensuing reaction the platinum is reduced from the 4 -h oxidation state to the 2 + state. The overall stoichiometry of these reactions is not known however, the reduction of the platinum is accompanied by the partial oxidation of the olefin. 

In a 125-mL Erlenmeyer flask 5.0 g (8.41 mmol) of hydrated chloroplatinic add is dissolved in IS mL of gladal acetic acid and the solution heated to 75°. 

A study has been reported by Glaunsinger and coworkers [39] on the reduction of chloroplatinic add by a variety of redudng agents inducting sodium borohy-dride, hydroxylamine hydrochloride, dimethylamine borane, sodium dtrate, hydrazine monohydrate, sodium formate, trimethylamine borane, sodium trime-thoxyborohydride, and formaldehyde. By careful variation of reaction temperature, protective polymer (PVP was found to be the most effective), time, pH, and reagent concentration, as well as the use of both direct and reverse addition of the reagents, it was shown that colloidal platinum could be produced as spheres, strands, or mosaic composites of platinum microcrystals. 

The reduction of metal salts with borohydride or trialkylborohydride is a widely used colloid synthesis method. The preparation of platinum microcrystals having a mean diameter of 28 A by the reduction of chloroplatinic add with sodium borohydride has been reported as a reprodudble standardized preparation. [52] PVP stabilized copper sols have been prepared by borohydride reduction of copper salts. [53, 54] In some cases, however, the formation of metal... 

The photolysis of metal complexes and salts is also an effective and dean method for the generation of collcndal metals, and it is amenable to all of the experimental protocols used for the stabilization of the resulting partides. Examples of this include the UV-visible irradiation of gold, silver, or platinum salts in microemulsions, surfactant solutions, or polymer solutions. [105-110] It was found from a comparative study of hydrogen reduction vs. photoreduction of chloroplatinic add in the presence of surfactants that the photoreduction produced smaller platinum partides with a narrower size distribution. [105]... 

In the present experiment the metal catalyst, platinum, is generated in situ by the reaction of chloroplatinic add with sodium borohydride. The reduced platinum metal is formed in a coUoidal suspension, which provides an enormous surface area, and therefore excellent conditions, for heterogeneous catalysis. The molecular hydrogen necessary for the reduction can also be conveniently generated in situ by the reaction of sodium borohydride with hydrochloric add ... 

ROP of 1,3-silacyclobutanes may be initiated thermally or catalytically. Most effective transition metal catalysts are hexa-chloroplatinic add, H2PtCl6, platinum metal, and platinum and rhodium complexes (eqn [43]). Polymerization of silacy-dobutanes is accompanied by dimerization, which is the dominant process in the presence of phosphine-platinum complexes. ... 

Formation and reduction of a hydrous oxide film on platinum resulted in an increase in the charge for monolayer oxide reduction in subsequent experiments. " Obviously the metal surface was roughened as a result of formation and subsequent reduction of the phas, pxide. However, the roughness developed with this technique teMed to decay under open-circuit conditions (a process that was accelerated by occasional potential sweeps for monitoring purposes). Such decay was more rapid than with platinum black deposits prepared from conventional chloroplatinic add baths— evidence perhaps that in the former case the active metallic layer is of a more highly strained, finely divided character. ... 

Method 2. From chloroplatinic acid. Dissolve 3 - 5 g. of the purest commercial chloroplatinic acid (3) in 10 ml. of water contained in a 250 ml. P3rrex beaker or porcelain casserole, and add 35 g. of A.R. sodium nitrate (1), Evaporate the mixture to dryness by heating gently over a Bunsen flame whilst stirring with a glass rod. Then raise the temperature... 

Acetylcholine chloride [60-31-1] M 181.7, m 148-150 , 151". It is very sol in H2O (> 10%), and is very hygroscopic. If pasty, dry in a vacuum desiccator over H2SO4 undl a solid residue is obtained. Dissolve in abs EtOH, filter and add dry Et20 and the hydrochloride separates. Collect by filtration and store under very dry conditions. [J Am Chem Soc 52 310 1930.] The chloroplatinate crystallises from hot H2O in yellow needles and can be recrystd from 50% EtOH, m 242-244° [Biochem J 23 1069 7929], other m given is 256-257°. The perchlorate crystallises from EtOH as prisms m 116-117°. [J Am Pharm Assocn 36 272 1947.]... 

Dissolve about i gram of an organic base (brucine, strychnine, quinine, c.) in 10 c.c. of a mixture of equal volumes of concentrated hydrochloric acid and water. To the clear hot solution add excess of platinic chloride and let it cool. Yellow microscopic crystals of the chloroplatinate of the base separate. (If the chloroplatinate of the base is very soluble in water, such as aniline, it must be washed with strong hydrochloiic acid, pressed on a porous plate and dried in a vacuum-desiccator over solid caustic potash.)... 

Color. Standards Stock standard. Dissolve 1.245g of potassium chloroplatinate (K2PtCl6) and l.OOOg of cobaltous chloride (C0CI26H2O) in water. Add 100ml of coned HQ, and dilute the soln to 1000.0ml with water. (This soln has a color of 500 on the APHA and ASTM platinum-cobalt scales)... 

Remove the flask B (500 ml capacity) from the apparatus assembly and add 100 ml of absolute ethanol, 5.0 ml of 0.2 m ethanolic chloroplatinic acid and 5g of decolourising charcoal insert a 38 mm Teflon-covered follower bar. 

Instead of adding two hydrogen atoms to an alkynyl silane we could add H and SiMe3 to a simple alkyne by hydrosilylation (addition of hydrogen and silicon). This is a cis addition process catalysed by transition metals and leads to a tram (E-) vinyl silane. One of the best catalysts is chloroplatinic acid (H2PtCl6) as in this formation of the E-vinyl silane from phenylacetylene. In this case photochemical isomerization to the Z-isomer makes both available. Other than the need for catalysis, this reaction should remind you of the hydroboration reactions earlier in the chapter. The silicon atom is the electrophilic end of the Si-H bond and is transferred to the less substituted end of the alkyne. 

This competitive adsorption drives the platinum deeper into the extrudates, and when sufficient HC1 is added, the PtCl 2 ) adsorption reaction is moderated to such an extent that a reasonably homogeneous distribution is obtained. One can also add acids that adsorb even more strongly than chloroplatinic acid, e.g. oxalic or citric acid, with which Pt profiles such as shown in Fig. 9.6 can be prepared. Profile (b) can be useful when a strongly adsorbing poison is present in the stream... 

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