Charcoal-supported reagents

Arene thiocyanation. Thiocyanation of arenes with metal thiocyanates usu-illy results in both arenethiocyanates and the more stable areneisothiocyanates. The reaction can be effected with CuSCN supported on charcoal. Thus iodo- and romoarenes react with this supported reagent (excess) in f-butylbenzene at 150° v give the corresponding thiocyanates in 70-80% yield. 

The actual chemical nature of the support material may be and often is of direct importance to its usefulness as a support material.15 Silicas can react with small nucleophiles such as F-, OH- and CN. Thus, silica-supported fluorides are inactive, both as nucleophilic fluorinating agents and as bases. Similarly, silicas are not effective support materials for cyanides due to the formation of strong Si-CN bonds. For different reasons, an acidic clay would not be a suitable support for cyanides, due to the possible formation of toxic HCN. Charcoal is the most effective support material for stabilising Cu(I), probably due to its aromatic character.16 For many chemisorbed supported reagent catalysts, silicas are preferred since they give relatively strong surface bonds. However, Si-O-C bonds are hydrolytically vunerable and direct Si-C bonds are preferred.17... 

Platinum and palladium are the most common catalysts for alkene hydrogenations. Palladium is normally used as a very fine powder supported" on an inert material such as charcoal (Pd/C) to maximize surface area. Platinum is normally used as PtC, a reagent called Adams catalyst after its discoverer, Roger Adams. 

An interesting activation of Cul by alumina and by charcoal has been reported106. These reagents are applied for the iodination of aryl chlorides and bromides to the corresponding iodides via a halogen exchange process. The presence of the support is found to be essential and no reaction is detected in its absence. 

You have met the first two of these features, but the last two may be new to you. An aromatic nitro group is easy to turn into an amino group—a number of reagents will do this, but the most common are tin in dilute HCl or hydrogenation with a palladium catalyst supported on charcoal (written as Pd/C). 

A more radical approach is to use unwanted stocks of CFCs to prepare useful reagents and an example of this is provided by the catalytic synthesis of HCN from CCI2F2 (CFC-12) and NH3. Nickel titanate, Ni, Fe or Co metals, platinum metals or gold supported on LaFa, AIF3 or activated charcoal, are all possible catalysts, conversion and selectivity for HCN depending on the catalyst used [84]. Reactions occur in the temperature range 600-800 K. 

Lipshutz showed that nickel on charcoal ( Ni/C ) was found to be an efficient heterogeneous catalyst for mediating carbon-carbon bond constructions involving chloroarenes 28 and functionalized organozinc reagents to give 29 Importantly retention of nickel on the solid support offers control over such critical parameters as waste disposal and toxicity. 

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