Stannous chloride catalyst activator

Catalysis is done by an acidic solution of the stabilized reaction product of stannous chloride and palladium chloride. Catalyst absorption is typically 1—5 p-g Pd per square centimeter. Other precious metals can be used, but they are not as cost-effective. The exact chemical identity of this catalyst has been a matter of considerable scientific interest (19—21,23). It seems to be a stabilized coUoid, co-deposited on the plastic with excess tin. The industry trends have been to use higher activity catalysts at lower concentrations and higher temperatures. Typical usage is 40—150 ppm of palladium at 60°C maximum, and a 30—60-fold or more excess of stannous chloride. Catalyst variations occasionally used include alkaline and non-noble metal catalysts. 

Nitriles may be converted to their imino chloride salts by the action of dry hydrogen chloride in ether. These intermediates ate reduced by anhydrous stannous chloride to stannic aldimonium chlorides, which on hydrolysis yield aldehydes. Chloroform may be added to facilitate the solution of the nitrile. The quality of the stannous chloride catalyst is important the preparation of an active and dependable form has been described. The yields are usually high for many aromatic nitriles, as in the preparation of /3-naphthaldehyde (95%). The reaction has also been employed in the heterocyclic series, as in the synthesis of 4-methyl-thiazole-5-aldehyde (40%). The reduction of the cyano group in the... 

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

The success of this type of reaction depends on the quality of the catalyst. The most active and dependable form of anhydrous stannous chloride 1 is prepared as follows In a 600-cc. beaker is placed 204 g. (189 cc., 2 moles) of acetic anhydride (99-100 per cent) and, while the liquid is stirred by hand, 226 g. (1 mole) of commercial c.p. crystalline stannous chloride dihydrate is added. This operation should be performed in a hood, for the heat of the reaction is sufficient to cause the acetic anhydride to boil. After about one and a half hours, the anhydrous stannous chloride is filtered on a large Buchner funnel, rinsed with two 50-cc. portions of dry ether, and dried overnight in a vacuum desiccator. The yield is quantitative (189 g.). The product may be kept in a tightly closed bottle until it is wanted. The product secured by dehydrating crystalline stannous chloride in an oil bath at 195-200° is satisfactory in many instances but is not dependable. 

Catalysts for didectric surfaces are more complex than the simple salts used on metals. The original catalysts were separate solutions of acidic stannous chloride [7772-99-8], used to wet the surface and deposit an adherent reducing agent, and acidic palladium chloride [7647-10-1], which was reduced to metallic palladium by the tin. This two-step catalyst system is now essentially obsolete. One-step catalysts consist of a stabilized, pre-reacted solution of the palladium and stannous chlorides. The one-step catalyst is more stable, more active, and more economical than the two-step catalyst (21,23). A separate accderation or activation solution removes loose palladium and excess tin before the catalyzed part is placed in the electroless bath, prolonging bath life and stability. 

Monomethylation of cis-glycols by diazomethane. Stannous chloride dihydrate is a particularly active catalyst for the methylation of adenosine (1) by... 

Several polymerization methods, including melt, solution and emulsion have been applied to lactone monomers to form high molecular weight polymers. Typically, a catalyst such as a metal oxide or metal salt, stannous 2-ethylhexanoate or stannous chloride, is used along with a free hydroxy containing initiator such as water, an alcohol, hydroxy acid or ester to activate the lactone ring to initiate polymerization. 

---