Photochemical continuous flow process

This method tends to be relatively inefficient compared to a continuous-flow process. Photochemical reactions operated in continuous-flow have been investigated and have proven to be far more effective at large-scale photochemical synthesis than the corresponding batch approach [129]. However, batch reactions continue to be the most common approach to photochemistry. 

Naphthalenequinone methides (382) and (384) were photochemically synthesized from 1- and 2-adamantylnaphthol derivatives (381) and (383), respectively (Scheme 82). Photorearrangement of allqrl-aryl nitrones (385) via oxaziridines (386) afforded amide derivatives (387) as peptide fragments via continuous flow process (Scheme 83). ... 

Optical methods have been used to monitor chemical processes for a long time. In a photochemical reaction, a continuous flow of light is used to drive the reaction. In rare cases, light may be produced by a chemical reaction (chemiluminescence). A photochemical reaction may be initiated on the molecular level by a short pulse. By studying the absorption characteristics shortly after absorption, details on what happens on the molecular level can be obtained. We will first go through photokinetics, which is different from ordinary kinetics only in the appearance of radiation as a reactant. 

Pericyclic reactions involve the continuous flow of electrons in cyclic transition states (TS) by breaking and making of bonds in a concerted process, without formation of an intermediate. Hence, these reactions are known as concerted reactions [1]. These reactions are insensitive to solvent polarity and free radical initiators or inhibitors. These reactions are activated by heat (thermal) or light (photochemical). Detailed study of the mechanisms of these reactions by Woodward and Hoffmann [2] predicted that these reactions occur by the maintenance of symmetry properties of the orbitals of reactant(s) and product(s). The Diels-Alder reaction is a typical example. 

In this chapter we report and analyze examples of asymmetric organocatalytic reactions under non-classical conditions high pressure, microwave heating, ultrasound irradiation, and ball milling. Organocatalytic processes based on photochemical or electrochemical activation as well as applying continuous-flow reactors are not included. 

The [2 + 2] qrcloaddition reaction of maleimide and 1-hexyne in a photochemical microflow reactor has also been reported. The development of flow reactors for continuous processes can allow large-scale reactions [18]. This reaction can be achieved with 83% conversion on a large scale (0.7 kg) (Scheme 5.8). 

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