Calcium carbonate as support for palladium catalyst

Calcium carbonate as support for palladium catalyst, 46, 90 Calcium hydride, 46, 58 D,L-Camphor, sulfonation to d,l-10-camphorsulfonic acid, 46,12 10-Camphorchlorosulfoxide, 46, 56 d,l-10-Camphorsulfonic acid, 46,12 conversion to acid chloride, 45,14 10-Camphorsulfonyl chloride, 45, 56 d,l-10-Camphorsulfonyl chloride,... 

Calcium carbonate as support for palladium catalyst, 46, 90 Calcium hydride, 46, 68 D,L-Camphor, sulfonation to d,l-10-camphorsulfonic acid, 46,12... 

This pure Z-alkene was needed for studies on the mechanism of a rearrangement reaction. In Chapter 24 you met catalytic hydrogenation as a means of reducing alkenes to alkanes, and we introduced Lindlar s catalyst (palladium and lead acetate on a support of calcium carbonate) as a means of controlling chemoselectivity so that alkynes could be reduced to alkenes. What we did not empha-... 

The most common catalyst for low- and medium-pressure hydrogenation is platinum. Platinum oxide is available from a number of suppliers and is converted to colloidal platinum in situ by hydrogenation. Palladium is another commonly used catalyst and is usually prepared on some inert support such as charcoal, barium sulfate, or calcium carbonate. The procedure for the preparation of these catalysts is given in Organic Syntheses. - A rhodium catalyst appears to be particularly effective in reducing aromatic compounds at low pressure and is available on an alumina support. ... 

Lindlar catalyst (Section 9 9) A catalyst for the hydrogenation of alkynes to as alkenes It is composed of palladium which has been poisoned with lead(II) acetate and quino line supported on calcium carbonate... 

Many workers (5,6,7,87) have compared various metals for the selective hydrogenation of lower acetylenes to olefins, and it was always found that palladium was by far the most selective. This conclusion concurs with the usual synthetic experience, but under special circumstances other metals, such as platinum, may prove more useful (35,63). The catalyst support may also have an influence (21,65). Carbon, calcium carbonate, and barium sulfate are frequently used supports. Examples of some differences are noted later,... 

Platinum in a finely divided form is obtained by the in situ reduction of hydrated platinum dioxide (Adams catalyst) finely divided platinum may also be used supported on an inert carrier such as decolourising carbon. Finely divided palladium prepared by reduction of the chloride is usually referred to as palladium black. More active catalysts are obtained however when the palladium is deposited on decolourising carbon, barium or calcium carbonate, or barium sulphate. Finely divided ruthenium and rhodium, usually supported on decolourising carbon or alumina, may with advantage be used in place of platinum or palladium for some hydrogenation reactions. 

The reaction we propose to study is the hydrogenation of 2-methyl-2-nitropropane into /-butylamine through the nitroso and the hydroxylamine intermediates (scheme 1). This sequence is called "the main reaction". A preliminary study, encompassing temperature, catalyst mass, hydrogen pressure, initial reactant concentration, metal and support effects has already been carried out [5], For this nitroaliphatic compound, palladium appears to be more active than platinum, and less active than rhodium. On the other hand, carbon seems to be more appropriate as support than alumina or calcium carbonate. 

The design of highly selective catalysts for the hydrogenation of dienes and alkynes is an important problem. Among the transition metals palladium is well known as being the most selective of all for the production of mono-olefins. This selectivity can even be improved when doped, as in the so-called commercial Lindlar catalyst which is composed of palladium and lead supported on calcium carbonate. There is still a need for stable and highly selective catalysts, especially at high conversion. 

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