The work detailed in this thesis is mainly concerned with the carbonylation of fatty acid derivatives, using carbon monoxide atmospheres in the presence of a transition metal. The two systems under study were the conversion of oleonitrile to a cyano-ester using a cobalt catalyst, and formation of isocyanates from amines in the presence of a palladium salt. The objectives of each study were: (i) to assess the influence of physical conditions on the reaction (i.e. pressure, time and temperature);(ii) to examine the effect of various additives on the system (i.e. phosphines, iodides and bases); and (iii) to identify any catalytic species observed under reaction conditions.Three major techniques were employed in each study: autoclave reactions, high pressure infra-red studies and atmospheric pressure nitrogen-line chemistry. The proposed underlying reaction mechanism was examined critically for each system, comparisons being drawn between the postulated catalytic species and those actually observed by high pressure infra-red spectroscopy. The chemical properties of the proposed catalytic intermediates are discussed in relation to the effect of co-reactants on the system. In the case of the carbonylation of oleonitrile the high pressure infra-red studies are consistent with the proposed reaction mechanism based upon the acyl complex RCOCo(CO)(_4). Although the infra-red study on the carbonylation of amines did not reveal any definite information, the results of other experiments were found to be consistent with a system based upon a carboxamido species L(_2)Pd(Cl)(CONRR').