Organocatalysts

Catalysts refer to a substance that changes the chemical reaction rate (increasing or decreasing) of a reactant in a chemical reaction without changing the chemical equilibrium, and whose mass and chemical properties are not changed before and after the chemical reaction. According to the International Union of Pure and Applied Chemistry (IUPAC), 1981, a catalyst is a substance that changes the rate of reaction but does not change the total standard Gibbs free energy. Organocatalysts are catalysts containing only carbon, hydrogen, sulfur, and other non-metallic elements.

Applications

Organocatalysts can catalyze a variety of reactions, which can be divided into activation reactions(enamine activation, SOMO activation, hydrogen bond activation, chiral phase-transfer activation and nitrogen heterocyclic carbene activation), oxidation reactions, condensation reactions, carbonyl reduction reactions and oxo synthesis reactions according to the catalytic mechanism.

• Enamine activation: The carbonyl compound is condensed with a secondary amine in the presence of an organocatalyst such as p-toluenesulfonic acid to form an enamine which is hydrocarbylated or acylated with a halogenated hydrocarbon or acid halide to form a substituted enamine which is then hydrolyzed to give an α-hydrocarbyl group or Alpha-acyl carbonyl compound.
• SOMO (singly occupied molecular orbital) activation: After the reaction of the aldehyde with the amine, the equilibrium of the enamine and the imine can be rapidly established, and the two reactive intermediates can be reacted separately with the electrophilic and nucleophilic reagents. If this balance is interrupted and new active intermediates are produced, a new catalytic pathway can be achieved.
• Hydrogen bonding activation: The diaryl prolamine derivative can catalyze the asymmetric alpha-the reaction of the β-ketoester.
• Chiral phase transfer catalyst activation: Chiral quaternary ammonium salts and chiral crown ethers as the organocatalysts can be used in various asymmetric catalytic reactions (including addition, substitution, oxidation, and reduction).
• Nitrogen heterocyclic carbene activation: As a unique organic catalyst, nitrogen heterocyclic carbene is widely used for the polarity reversal reaction of aldehyde compounds, but the reaction substrate of this mode is limited to aldehyde compounds.
• Condensation reaction: It is a reaction in which two or more organic molecules interact to form a macromolecule by covalent bonding, often accompanied by a loss of small molecules (such as water, hydrogen chloride, alcohol, etc.)
• Reduction reaction: Some scholars have used oxazol borane as a catalyst to prepare chiral alpha-hydroxy acids and chiral alpha-amino acids. Other researchers have used chiral borane to asymmetrically reduce ketones to produce chiral alcohols.
• Oxo synthesis reaction: Oxo-synthesis refers to the process of carbon monoxide and hydrogen and olefin forming a fatty aldehyde having one more carbon atom than the original olefin in the presence and absence of a catalyst, so it is also called "hydroformylation (reaction)" or "hydrogenation". The reaction of introducing an organic compound molecule into a carbonyl group in the presence of an excessive metal organic framework (MOF) catalyst is generally included in the range of the carbonylation reaction.

• Oxidation reaction: The action of introducing organic matter into oxygen or dehydrogenating during the reaction of organic matter is called oxidation. The essence of the oxidation reaction is that the substance loses electrons.

Production

Each method of making a catalyst is actually a combination of a series of operating units. Traditional methods include mechanical mixing, precipitation, spray evaporation, hot melt method, etc. And the new methods are chemical bonding, fiberization, etc.

Figure 1. Organic sulfur hydrolysis catalyst

References

1. Wang Jing, Zheng Changlong. ( 2012). "Ninth grade chemistry" Beijing: People's Education Press, volume 1: 392.
2. Huang Zhongtao. (2006). " Industrial Catalysis." Chemical Industry Press.