Halogénation | EPFL Graph Search

L'halogénation est une réaction chimique qui permet d'introduire un ou plusieurs atomes d'halogène dans une réaction. En fonction de l'élément impliqué, on parle de fluoration, chloration, bromation ou d'iodation. Les halogènes ayant des propriétés similaires, ces réactions sont assez semblables. Il existe plusieurs réactions d'halogénation différentes :

l'addition radicalaire ;
la substitution radicalaire ;
l'halogénation des cétones ;
l'addition électrophile des halogènes sur les alcènes ou alcynes (dihalogénation et hydrohalogénation) ;
la substitution électrophile aromatique sur les noyaux aromatiques.

Addition électrophile trans Dihalogénation Il s'agit de l'addition d'un dihalogène sur l'alcène. Exemple de la dibromation : le mécanisme de bromation des alcènes peut se décrire comme suit. Les électrons π de la double liaison attaquent un brome rendu électrophile lors de l'approche des réactifs entre eux (le brome étant assez volumineux, il est d'

Determination of variables influencing the effectiveness of disinfection of surface water used for human consumption in Costa Rica

Clara Barret

Disinfection of water for human consumption is a challenge to ensure that water is free of pathogens and pollutants while avoiding the formation of potentially harmful undesirable products. The establishment of disinfection facilities must take into account the local context as well as technical and economic feasibility to ensure their sustainability. Chlorination is a disinfection technique that is widely used throughout the world and can take several forms. However, this technique can lead to the formation of disinfection by-products, some of which are harmful to human health and are a source of growing concern. This present report focuses on chlorination using tablets that release chlorine when eroded by contact with water. This study aimed at improving the understanding of the effect of various parameters on the efficiency of water chlorination in the Cartago region (Costa Rica). First a chlorination facility located in a village near Cartago was studied. The purpose of this assessment was to diagnose the current situation, determine the changes needed to improve it and implement them. It was showed that the chlorine concentration delivered by this facility was too low and variable. A new chlorinator and a tank allowing a better mixing of the chlorinated solution have been installed. These modifications have resulted in a higher and more homogeneous chlorine concentration in the storage tanks and an improvement in some water quality parameters. On the basis of the results, recommendations were made to ensure the proper functioning of the facility and the continuation of measurements during future campaigns. It should be noted that this was a short-term study, measurements over a longer period would allow more precise conclusions to be drawn. The second part of the project concerned 10 chlorination facilities in the Cartago region. The purpose was to compare the results of various parameters of surface and groundwater samples collected in the rainy/transition season in 2018 with those of the 2019 dry season. For the moment there were thus only two series of data but this has nevertheless allowed us to observe an improvement in certain parameters during the dry season. Future measurements campaigns will consolidate these results.

2019

Synthesis of Trifluoromethyl-Substituted Cyclopropanes via Sequential Kharasch–Dehalogenation Reactions

Yanouk Cudré, Julie Risse, Kay Severin

A two-step process for the synthesis of trifluoromethyl-substituted cyclopropanes is described. Halothane, an anesthetic agent, is added to olefins in a ruthenium-catalyzed Kharasch reaction. The resulting 1,3-dihalides are converted into cyclopropanes by dehalogenation with magnesium. This procedure represents an alternative to metal-catalyzed cyclopropanations involving trifluoromethyl diazomethane.

American Chemical Society2012

Fluorinated β-Diketones for the Extraction of Lanthanide Ions: Photophysical Properties and Hydration Numbers of Their EuIII Complexes

Jean-Claude Bünzli, Anne-Sophie Chauvin, Frédéric Gumy

Tris(β-diketonato)europium(III) with a series of variably fluorinated ligands derived from 3,5-heptanedione were synthesised with the aim of determining their hydration state under extraction conditions. The number of coordinated water molecules was determined by measuring the lifetime of the Eu(5D0) excited level in water and deuterated water. The hydration gain (Δq = q – q0) after shaking chloroform solutions during 10 min with 0.1 M NaClO4 aqueous solutions depends on the fluorination extent of the diketonates: fluorination of one methyl group leads to a decrease in Δq of ca. 0.5 unit, while fluorination of one ethyl group results in a decrease of ca. 1.3 units. Highly fluorinated complexes (i.e with hexafluoroacetylacetonate and related ligands) display a hydration number close to one while poorly fluorinated compounds (or nonfluorinated ones, such as the acetylacetonate complex) have a hydration state close to two. Photophysical properties of the EuIII β-diketonates are also described and the synthesis of the fluorinated β-diketones is re-investigated and discussed in details.

2006

Determination of variables influencing the effectiveness of disinfection of surface water used for human consumption in Costa Rica

Clara Barret

2019