What are hydroformylation and the oxo process? Know more

What are hydroformylation and the oxo process? The oxo process, also known as the oxo reaction or the Kolbe-Schiemann reaction, is an industrial chemical process for making formaldehyde. This important raw material produces resins, fibers, and plastics. The hydroformylation reaction is related to this one; both are catalyzed by platinum. It was developed by Fritz Klatte after World War II and popularized in commercial use by Karl Ziegler. Hydroformylation is still the primary method of production of butyraldehyde, an important fragrance chemical.

The hydroformylation and the oxo process are related to each other. They both use the same platinum catalyst under the same reaction conditions. One is the synthesis or oxidation of an internal olefin with carbon monoxide and hydrogen. The C-C bond is formed between one of the two carbons on the olefin and one of the two hydrogens on carbon monoxide, while the other hydrogen and carbon monoxide combine to give water. In essence, it is a methanolysis and hydroformylation in one step.

Hydroformylation process

The hydroformylation reaction is a standard method for transforming alkenes into aldehydes, ketones, and carboxylic acids. The reaction involves the oxidative addition of formaldehyde to an alkene. Water can be present in the starting material, solvent, or catalyst. The principle and details of the reaction are similar to those of the Friedel-Crafts acylation reaction.

Alkenes react with formaldehyde to give a protonated double bond, which undergoes imine addition at the carbon adjacent to that double bond. The resulting imine undergoes an intramolecular Mannich reaction to form the aldehyde product.

Application of hydroformylation process

1. Decarboxylation of cyclic compounds

The hydroformylation process is used in the production of cyclohexanone. Cyclohexanol produced by the hydroformylation process can be oxidized to cyclohexanone. Cyclohexene and cyclooctene are also converted into cyclohexanone via hydroformylation and dehydrocyclization reactions.

2. Production of aldehyde

The reaction of formaldehyde with alkenes creates aldehydes, which are popular as fragrances and flavors. This process is called hydroformylation, and it produces such volatile compounds as acetals, aryl malonates, maleic malonates, and succinic malonates. Acetals are aldehydes that contain two alkyl groups attached to the aryl ring. To develop high-volume production of aldehyde, the catalysts must be stable at high temperatures. The hydrogenolysis reaction and dehydration condensation reactions are used in production of acetals, which are intermediates in perfume and flavors applications.

3. Synthesis of alkaloids

The hydroformylation reaction produces the corresponding saturated ring alkaloids, including substance P and calcein. Substances P, a non-protein basic glycoprotein, is found in the mammalian nervous system and consists of two disulfide-linked subunits (called tropomyosin) that are present in muscle spindles of neuromuscular junctions. Calcein is a red fluorescent dye that exists mainly as a mixture with acetals, which may be separated from this mixture by distillation or extraction.

Oxo process

The oxo process is a method of producing formaldehyde. This industrial scale reaction takes place under equilibrium between the liquid and gas phases. The oxo process begins with the introduction of hydrogen peroxide into a reactor vessel containing an aqueous solution of formaldehyde, followed by the introduction of air into the liquid phase to cause a homogeneous gas-liquid phase reaction. The resulting mixture of liquid and gaseous products is filtered to remove solid waste and discharged gases, and then condensed in another reactor vessel to produce the final product, which can be further purified by distillation.

Application of oxo process

1. Production of formaldehyde

Formaldehyde is very useful chemical and has a wide range of applications in addition to industrial production. It is used as building blocks in the production of pharmaceuticals, resins, plastics, elastomers and other materials. Formaldehyde is also used to make urea-formaldehyde resins (e.g., used in particle board) and melamine formaldehyde resin (used in countertops and plywood). It is also employed as embalming fluid and disinfectant. Formalin consists of 37% formaldehyde in water solution.

2. Production of methyoxymethane

Methyoxymethane is a reactive intermediate used to synthesize many organic compounds. It can be produced through the oxo process from formaldehyde and carbon monoxide or dimethyl ether, carbon monoxide, and water. The resulting product may also be used for producing 2-methyoxypropene by hydroformylation.

3. Production of phenol

Phenol is a biological and chemical raw material that is used in the production of plastics, dyes, herbicides, fluorescent dyes and pigments. It will react with oxygen to produce diphenyl oxide, a precursor in organic synthesis. The reaction occurs at room temperature.

Conclusion

Hydroformylation and the oxo process have a lot in common. The oxo process is an industrial method for the production of formaldehyde, which is an important chemical and can be used in many products.