Calcium carbonate, catalyst support

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... 

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... 

Alkali moderation of supported precious metal catalysts reduces secondary amine formation and generation of ammonia (18). Ammonia in the reaction medium inhibits Rh, but not Ru precious metal catalyst. More secondary amine results from use of more polar protic solvents, CH OH > C2H5OH > Lithium hydroxide is the most effective alkah promoter (19), reducing secondary amine formation and hydrogenolysis. The general order of catalyst procUvity toward secondary amine formation is Pt > Pd Ru > Rh (20). Rhodium s catalyst support contribution to secondary amine formation decreases ia the order carbon > alumina > barium carbonate > barium sulfate > calcium carbonate. 

A great many materials have been used as catalyst supports in hydrogena-tion, but most of these catalyst have been in a quest for an improved system. The majority of catalyst supports are some form of carbon, alumina, or silica-alumina. Supports such as calcium carbonate or barium sulfate may give better yields of B in reactions of the type A- B- C, exemplified by acetylenes- cjs-olefins, apparently owing to a weaker adsorption of the intermediate B. Large-pore supports that allow ready escape of B may give better selectivities than smaller-pore supports, but other factors may influence selectivity as well. 

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,... 

Support has been shown to influence selectivity and some workers have obtained higher yields of cis isomer over palladium-on-calcium carbonate or palladium-on-barium sulfate 21), whereas others find carbon satisfactory. In general, carbon support makes the more active catalyst and it is, therefore, more prone to become hydrogen poor. 

Complete reduction to the alkane occurs when palladium on carbon (Pd/C) is used as catalyst, but hydrogenation can be stopped at the alkene if the less active Lindlar catalyst is used. The Lindlar catalyst is a finely divided palladium metal that has been precipitated onto a calcium carbonate support and then deactivated by treatment with lead acetate and quinoline, an aromatic amine. The hydrogenation occurs with syn stereochemistry (Section 7.5), giving a cis alkene product. 

Changing catalyst support from carbon to calcium carbonate leads to dramatic improvement of the cis/tran ratio from 6 1 to 18 1, that is the cis selectivity increases from 85.7% to 94.7%. The reason for better selectivity on CaC03 supported catalyst is attributed to its lower surface area leading to lower hydrogenation activity, but more selective to the desired product. The successful commercialization of the new route for sertraline synthesis demonstrates that for a stereoselective hydrogenation reaction, improve product selectivity can be achieved by proper selection of catalyst support. 

In order to increase the contact of a catalyst with hydrogen and the compounds to be hydrogenated platinum (or other metals) is (are) precipitated on materials having large surface areas such as activated charcoal, silica gel, alumina, calcium carbonate, barium sulfate and others. Such supported catalysts are prepared by hydrogenation of solutions of the metal salts, e.g. chloroplatinic acid, in aqueous suspensions of activated charcoal or other solid substrates [28. Supported catalysts which usually contain 5, 10 or 30 weight percent of platinum are very active, and frequently pyrophoric. 

Palladium catalysts resemble closely the platinum catalysts. Palladium oxide (PdO) is prepared from palladium chloride and sodium nitrate by fusion at 575-600° [29,30]. Elemental palladium is obtained by reduction of palladium chloride with sodium borohydride [27, 31], Supported palladium catalysts are prepared with the contents of 5% or 10% of palladium on charcoal, calcium carbonate and barium sulfate [32], Sometimes a special support can increase the selectivity of palladium. Palladium on strontium carbonate (2%) was successfully used for reduction of just y, (5-double bond in a system of oc, / , y, (5-unsaturated ketone [ii]. 

These reactions are unlike any we have encountered so far. They are heterogeneous reactions, which means that the reacting system consists of two or more phases. Usually, the metal catalyst is present as a finely divided solid suspension in the liquid or solution to be reduced. Alternatively, the metal is deposited on an inert solid support such as carbon, barium sulfate, alumina (A1203), or calcium carbonate. Then the mixture of the liquid substrate and solid catalyst is shaken or stirred in a hydrogen atmosphere. However, the actual reaction takes place at the surface of the metal catalyst and is an example of heterogeneous or surface catalysis. 

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. 

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-... 

However, by partially poisoning the palladium catalyst supported on calcium carbonate with lead acetate and quinoline (the Lindlar catalyst ) it is possible to reduce alkynes to... 

The various support materials have different effects on potential carbon formation. This seems to go in parallel with the Lewis/Bronsted acidity. The main commercially used catalyst supports can be ranked as follows in decreasing order of carbon forming tendency (and thus in decreasing order of the important minimum practical steam/ carbon ratio) a-alumina > magnesium aluminate (spinel) > calcium aluminate > alkalized calcium aluminate [419],... 

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. ... 

ARCO patents describe various approaches for the development of catalysts able to selectively epoxidize olefins other than ethene with oxygen. In all the catalyst formulations claimed, the main active component is supported silver, doped with various components [31a,b]. In the earlier patents, the best results reported were propene conversion 4.5%, selectivity for PO 59-61%, with a catalyst composition of 54% Ag, 2% K, 0.5% Mo, supported over calcium carbonate. Molybdenum was used to increase the selectivity (but the addition of Mo also caused a decrease in propene conversion). 

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. 

US patent 5,763,630 claims silver catalysts supported on other alkaline earth metal compounds than carbonates, such as calcium titanate, tribasic calcium phosphate, calcium molybdate, or calcium fluoride, as well as the magnesium and strontium analogues. Such supports provide significantly higher selectivity to the desired epoxide than would be expected from the performance of related materials. Selectivities are lower than those reported in the original Union Carbide patent. 

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