Question

Alkenes combine with carbon monoxide and hydrogen in presence of octacarbonyldicobalt as catalyst under high temperature and pressure to form (a) aldehydes which can be further reduced to alcohols by hydrogen (b) alkanes which are formed by addition of hydrogen

Short answer

Alkenes will initially form aldehydes through hydroformylation in the presence of octacarbonyldicobalt, which can subsequently be reduced to alcohols by additional hydrogenation.

Step-by-step solution

Identify the Chemical Reaction

The chemical reaction described is the hydroformylation (oxo synthesis) of alkenes, where an alkene reacts with carbon monoxide (CO) and hydrogen (H2) in the presence of a catalyst - here, octacarbonyldicobalt - to form an aldehyde. Hydroformylation is typically carried out under high temperature and pressure.

Determine the Product of Hydroformylation

The initial product of the hydroformylation is an aldehyde. This product can be identified after the alkene has reacted with CO and H2 in the presence of the octacarbonyldicobalt catalyst.

Identify the Additional Reduction Step

The aldehyde formed from hydroformylation can then undergo a further reduction process. When hydrogen is added to the aldehyde in the presence of a suitable catalyst (such as palladium on carbon or nickel), it is reduced to an alcohol.

Key concepts

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, represented chemically as C=C. This double bond is a region of high electron density, making alkenes reactive towards certain types of chemical agents. For example, during hydroformylation, alkenes react with carbon monoxide and hydrogen in the presence of a specific catalyst.

Due to the nature of the C=C bond, alkenes exhibit geometric isomerism, meaning that there can be different physical arrangements of the atoms that result in distinct molecules. Additionally, the C=C bond can undergo addition reactions, where the double bond opens up to allow new atoms or groups to attach to the carbon atoms. This is essential in converting alkenes into more complex molecules like aldehydes and alcohols through processes like hydroformylation and further reduction.

Octacarbonyldicobalt Catalyst

The octacarbonyldicobalt catalyst, consisting of cobalt and carbon monoxide, is a metallic complex that plays a pivotal role in the hydroformylation process. Specifically, it facilitates the addition of a formyl group (CHO) and a hydrogen atom across the double bond of alkenes to form aldehydes.

The effectiveness of octacarbonyldicobalt as a catalyst lies in its ability to provide a unique environment for the reactants. It transiently binds to the alkene and carbon monoxide, effectively bringing them close together in a controlled manner to encourage them to react. Catalysts are not consumed in the reaction, and a small amount can facilitate the conversion of a large quantity of reactants to products. Without this catalyst, the hydroformylation reaction would require much harsher conditions, be less efficient, or not proceed at all.

Aldehyde Synthesis

During aldehyde synthesis via hydroformylation, an alkene is converted into an aldehyde by introducing a formyl group (CHO) to one of the carbon atoms of the C=C double bond, while the other carbon atom bonds with a hydrogen atom.

The reaction is typically conducted under high pressure and temperature to promote the efficiency of the catalyst and the formation of the aldehyde product. The process involves a complex series of steps, where the octacarbonyldicobalt catalyst forms an intermediate complex with the alkene and the carbon monoxide. Subsequently, hydrogen is inserted into this complex to form the aldehyde. Ensuring the right conditions and the presence of a suitable catalyst like octacarbonyldicobalt is essential for the successful synthesis of aldehydes from alkenes.

Reduction to Alcohols

Aldehydes produced from hydroformylation can be further processed to form alcohols. This is achieved through a reduction reaction, where hydrogen (H2) is added to the aldehyde, converting the carbonyl group (C=O) into a hydroxyl group (-OH).

This reduction typically requires a separate catalyst, such as palladium on carbon or nickel, and may occur under different conditions than the initial hydroformylation reaction. The choice of reduction conditions and catalyst can influence the selectivity and yield of the desired alcohol. Reduction of aldehydes to alcohols is not only an important step in synthetic organic chemistry but also in industrial applications where alcohols are used as solvents, fuels, and precursors to various chemicals.