Photochemical multi-phase

Multiphase copolymers, Ziegler-Natta catalysts for, 26 535, 537-540 Multiphase laminar flow patterning, in microfluidics, 26 961 Multiphase reactions, in microbial transformations, 16 412-414 Multi-phase reactors, 21 333-335 Multiphoton effects, in photochemical technology, 19 109... 

Flow systems also allow the use a two phase liquid-gas flow. This form of multi-phase flow increases the surface area between the gas and liquid phases, allowing for more effective mass transfer between the two phases and an increase in reaction efficiency. Such liquid-gas slug flows have been applied to a variety of photochemical transformations wherein the gas is a reagent for the reaction. " An excellent example by Kakiuchi and co-workers is a diastereoselective [2 -I- 2] cycloaddition of ethylene. ... 

Multi-phase photochemical reactions take place across phase boundaries. In most cases, substrate molecules are either dissolved in different liquid phases or one reactant is in the gas phase and interacts with the liquid phase. For this reaction category, phase transfer kinetics, in addition to the actual photochemical reaction, have to be taken into account, assuming microreactors to be ideal reaction engineering tools due to their low mass transfer limitations. 

An early example of a multi-phase microreaction was reported by Wootton et al., who demonstrated the continuous photochemical production of singlet oxygen and its use in organic synthesis for the cydooxidation of a-terpinene to ascaridol (Scheme 16.5) [10]. 

Multi-phase Photochemical Reactions 449 1 -Chlon)melhyl-2,4 dii ocyanatobenzene (1 -CI-TDI)... 

Multi-phase photochemical processes in the marine boundary layer convert a portion of the particulate chlorine to volatile products. This process is the major global source of gaseous chlorine in the troposphere. In [305] the planetary chlorine reservoirs (atmosphere, pedosphere and hydrosphere) and the processes transferring chlorine among these reservoirs are discussed in detail. 

Until recently organic photochemistry has only partially focused on stereoselective synthesis, one of the major challenges and research areas in modern organic synthesis. This situation has dramatically changed in the last decade and highly chemo-, regio-, diastereo- as well as enantioselective reactions have been developed. Chemists all over the world became aware of the fascinating synthetic opportunities of electronically excited molecules and definitely this will lead to a new period of prosperity. Photochemical reactions can be performed at low temperatures, in the solid or liquid state or under gas-phase conditions, with spin-selective direct excitation or sensitization, and even multi-photon processes start to enter the synthetic scenery. 

Abstract Key features of tropospheric photochemistry are highlighted including both homogeneous gas-phase and heterogeneous reactions that are important in clouds and haze aerosol. Fundamental aspects of photochemical kinetics are reviewed and then extended to the major chromophores present in the multi-phasic, tropospheric atmosphere. Tables of up-to-date absorption cross sections and quantum yields as a function of wavelength range are presented. Primary emphasis is placed on reactions occurring within the troposphere and within clouds. 

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