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How to use the Norrisch reaction to create a huge breakthrough in chemical synthesis?
The Norrisch reaction, named after scientist Ronald George Veriford Norrisch, is a photochemical reaction that occurs on ketones and aldehydes.Such reactions can be subdivided into Norrisch type I reactions and Norrisch type II reactions, although their synthetic uses are limited, for light of polymers such as polyolefins, polyesters, certain polycarbonates and polyketones Oxidation is of great significance.
Norish Type I Reaction
The Norrisch type I reaction is a photochemical cleavage reaction of ketones and aldehydes, in which the ketone or aldehyde forms an intermediate of two free radicals (α-break) after being exposed to light.In this process, the carbon group absorbs photons and excites to the photochemical singlet state.By passing through the system, a triple state can be formed.When the rupture of the α-carbon bond occurs, two free radical fragments can be generated.
The size and properties of these fragments depend on the stability of the generated free radicals.
For example, cleavage of 2-butanone mainly produces ethyl radicals, and the possibility of unstable methyl radicals is less.Depending on the molecular structure, these fragments can undergo multiple secondary reactions.The fragments can be simply re-bound to form the primordial carbon-based compound and racemic in the place of α-carbon.When the acyl radical loses one molecule of carbon monoxide, a new carbon radical will be formed at the other α-carbon, and then a new carbon-carbon bond will be formed.
The product rate of this reaction is related to the bond dissociation energy of the alpha substituent of the ketone.Generally speaking, the more alpha substituted ketones, the greater the possibility of this reaction to obtain the product.Furthermore, extraction of alpha-protons from carbon-based fragments aims to form a ketone alkenes and an alkane, while extraction of beta-protons may form aldehydes and olefins.
This reaction is of great significance in the field of photopolymerization, especially in the development of photoinitiators required for two-photon polymerization.
The role of the Norrisch-type I reaction in the polymerization of two-photons is essential because it involves the breaking of carbon-carbon bonds in the photoinitiator molecule under the excitation of ultraviolet or visible light, resulting in two free radicals.These radicals are highly active and can effectively promote the polymerization of monomers in local regions required for application in high-resolution additive manufacturing.
Norish Type II Reaction
The Norrisch Type II reaction is a photochemical internal extraction of γ-hydrogen (hydrogen at three carbon positions from the carbonyl group) by excitation carbon-based compounds, producing 1,4-diradicals as preliminary photoproducts.The reaction was first reported in 1937.In this process, secondary reactions may occur, such as breaking (β-breaking) to form internal recombination of olefins with enols (quickly changing into carbonyls) or two radicals to form substituted cyclobutane (Norish-Yan) (Norish-Yan) reaction).
Range of reaction
Environmental chemistry studies of the Norrisch reaction show that it is of great significance in the photolysis reaction of aldehydes in the atmosphere, especially n-heptanaldehyde.Ni-heptanal photolysis under similar atmospheric conditions formed 62% of 1-pentene and aldehydes (aldehydes) and cyclic alcohols derived from Norrisch type II channels.There are also about 10% hexanal (the initially formed n-hexyl radical reacts with oxygen) that is generated from type I channels.
A study showed that photolysis of an amide derivative in water containing hydrogen tetrachloroaulic acid (HAuCl4) yielded nano-gold particles with a diameter of 10 nanometers due to the ketone hydrogen radical produced by Norish Restore Au3+ to Au0.
Leo Paquette synthesized dodecene in 1982, involving three independent Norris-type reactions, with the entire synthesis process about 29 steps.When Phil Baran and colleagues synthesize biologically active cardioside compounds, they found an early synthesis method that started with the Norrisch Type II reaction and optimized the reaction conditions to minimize side reactions, such as the competition type I channel. Side reactions.
The Norrisch reaction is not only important in basic scientific research, but also with the advancement of organic synthesis, what changes has it brought to the chemical synthesis process?
