Academic literature on the topic 'Consecutive photoreactions'

Facile large-scale synthesis of the benzyl-dibromo-phosphines RPBr2 (R = C6H5CH2, 3,5-Me2C6H3CH2, 2-BrC6H4CH2) is accomplished by the photochemical reaction of toluene, mesitylene, and 2-bromotoluene, respectively, with PBr3 in the absence of solvent. If the reactions are carried out up to 50% completion the amount of by-products formed is remark­ ably low, rarely exceeding 10% of the total amount of products formed. The selectivity of the photoreaction may be improved up to 98% if it is carried out in a modified Soxhlet apparatus which allows the predominant irradiation of only the starting materials. The appar­ ent limitations imposed by the low turnovers required to achieve good product selectivity are by far outweighed by the large amounts of desired products formed in a short period of time and by the easy recovery of unreacted starting material by distillation. Thus in the case of 2-BrC6H4CH2PBr2, in a typical run 94 g (261 mmol) of product may be isolated after 2.5 h of irradiation of 970 mmol of 2-BrC6H5CH3 and 1.39 mol of PBr3. In this case the turnover is 32%. the isolated yield 27%, and the by-product 2-methylphenyl-dibromo-phosphine only amounts to less than 2%. The benzyl-dibromo-phosphines are easily methylated with two equivalents of MeMgCl to give the respective benzyl-dimethyl-phosphines in 79-93% yield. Tertiary benzylphosphines MePRR′ (R = 2-BrC6H4CH2, R′ = Me3SiCH2; R = R′ = 2-BrC6H4CH2) are obtained in easy one-pot syntheses by consecutive reactions of 2-BrC6H4CH2PBr2 with Me3SiCH2MgCl and MeMgCl, and with 2-BrC6H4CH2MgBr and MeMgCl, respectively.

The kinetics of drugs photodegradation have traditionally been treated using thermal kinetic analysis methods consisting most commonly in zero and first order kinetics. These treatment strategies were shown to lack specificity and present a number of limitations when applied to photoreactions kinetics. Nevertheless, these methods have widely been used due to a lack of integrated rate-laws for the majority of photoreactions types, in turn, due to the presence of a variable time-dependent factor in most photoreactions rate-laws that prevents their mathematical integration. To address these limitations, a new methodology for the development and validation of semi-empirical integrated rate-laws that faithfully describe photoreactions kinetics and photoreactions simulated cases generated by numerical integration methods (NIMs), is hereby presented. Using this methodology, a new kinetic order was ascribed to photoreactions namely the Φ-order kinetics. Semi-empirical integrated rate-laws were, thus, developed for three photoreaction types namely, unimolecular, AB(1Φ), photoreversible ,AB(2Φ), and consecutive, AB4(4Φ), photoreactions. The proposed models were further tested experimentally on drugs following these photodegradation mechanisms using; nifedipine and nisoldipine for unimolecular photoreactions; montelukast and fluvoxamine for photoreversible reactions; and riboflavin for consecutive photoreactions. The developed models not only accurately described the photoreaction kinetics of these drugs but also allowed the determination of all the kinetic parameters that characterise them. Furthermore, the above studied drugs were shown to act as precise and simple actinometers when analytically treated with the Φ-order kinetic methods, hereby presented. A universal standard method for the precise and worldwide reproducible study of drugs stability and compounds photoreactions, based on monochromatic irradiation and Φ-kinetics data analysis, is also detailed and adopted throughout the thesis. Finally, two new kinetic parameters namely, the pseudo-rate-constant and pseudo-initial velocity have been identified and shown to be more reliable and accurate in the description and universal comparison of photoreactions kinetics.