Reduction of CO with Hydrogen

Using deuterium in place of hydre en, CD4 is produced. Tliis liydrc cnaiion has features in common with the stoichiometric work by Bercaw using zirconium complexes (17)- The driving force for these deoxygenation reactions may be the formation of metal oxides. 

The addition of a Lewis acid, thus creating an M - CO and l.ewis acid interaction, also aids in the reduction of CO by hydrogen. Mueuerties describes i1k catalytic hydrogenation of CO in a NaCl/AlClj melt using lr4(CO) [76]. Products were Ci-Cs linear and branched hydrocarbons. Turnover rates were very low. 

The same approach was also used foi OsafCOn in a BBrj solvent 77]. Besides linear and branched hydrocarbons, alkylbromides were also formed. Using BCU ouly hydrocarbons were produced. The mechanism is undemonstrated. Chain elongation could occur by insertion into a M R bond and Lewis acid interaction of the type (30). 

Somehow related to Uris Lewis acid assisied reduction of CO is the work by Olive, who describes the reaction of CO.II3 in the presence of benzene with W(CO) /AlCl3 (78). The gas phase contains small amounts of Ci and Cj hydrocarbons. As main products, alkylated benzenes are obtained w hich follow a Schulz—Flory distribution. By using CO. Vollhardi could demonstrate that the alkyl groups of the alkylated benzenes do not originate from CO/H2 but stem from the benzene used [79]. 

The use of AIR3 is also reported by Blanchard, who describes the formation of hydrocarbons with a Schulz Hoiy distribution vvhen reacting CO/II3 with a catalyst obtained by reducing cobalt(ll acety)aceionarc with Alt i3 ) 0J. It can be assumed that this system is heierr neous. 

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Reduciion ofCO with reducing agents other than molecular hydrogen, direct reduction of CO with hydrogen... 

The syntheses of some C-labelled key intermediates from CO are illustrated in Scheme 1.1. These compounds are prepared on a relatively large-scale by manufacturers. Yields are high as the methods are frequently scaled-down versions of industrial processes or utilise specialised equipment, they are not always suitable for use in the majority of chemical laboratories. For example, [ C]methanol is prepared by catalytic reduction of CO with hydrogen under pressure [59]. The method can be automated and used for the continuous preparation of large batches. In the majority of cases, the user may well find that he is unable to prepare intermediates of this type as cheaply as they can be purchased. Scheme 2.2 illustrates the preparation of widely used N-labelled compounds. More detailed reviews of the basic synthetic processes have been published [15, 26,60—63] and many of the preparations have been described in individual publications. Some more specialised labelled compounds such as amino acids, fatty acids, organic heterocycles, and sugars are also available commercially. 

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