Το νερό ως διαλύτης επιλογής στις αντιδράσεις 1,3-διπολικής κυκλοπροσθήκης νιτρονών:
Creators: name: Σαρρίδης, Πρόδρομος Αναστασίου
Publisher: name: Aristotle University of Thessaloniki
Year: 2008
Subjects: Νερό
1,3 -διπολική
Κυκλοπροσθήκη
Νιτρόνη
Υδατικά μέσα
Πράσινη Χημεία
Water
1,3-dipolar
Cycloaddition
Nitrone
Aqueous media
Green chemistry

description: Μελέτη της χρήσης του νερού ως διαλύτη στις αντιδράσεις 1,3-διπολικής κυκλοπροσθήκης νιτρονών. Οι αντιδράσεις έγιναν παράλληλα σε οργανικό διαλύτη και σε υδατικό αιώρημα "On water" συνθήκες. Ολες οι αντιδράσεις έγιναν στο νερό με ικανοποιητικές αποδόσεις και σε μικρότερους χρόνους από ότι σε οργανικούς διαλύτες. Επίσης σε ορισμένες περιπτώσεις παρατηρήθηκε και αλλαγή στην στερεοεκλεκτικότητα. Λόγω των παραπάνω πλεονεκτημάτων αλλά και από την σκοπιά της Πράσινης Χημείας το νερό μπορεί να είναι ο διαλύτης επιλογής για τις 1,3 διπολικές κυκλοπροσθήκες νιτρονών.
description: Even the chemistry of live organizations, which in the bigger part is organic chemistry, takes place in aqueous environment, for many years water is thought to be an incompatible solvent for the most reactions which are applied in organic synthesis. But after the significant work of Breslow and his coworkers, that noticed that Diels-Alder reactions accelerated substantially in aqueous medias, the prosecuting of many organic reactions in aqueous medias concentrate a big interest because of the economics and environmental advantages of the use of the water. In the view of the “Green Chemistry” water is the solvent of choice because is cheap and no toxic.Additionally because of its unique physical and chemical properties the use of the water as solvent in organic reactions affects in many cases substantial changes in the stereoselectivity of the reactions. The accelerations and the changes in the stereoselectivity are attributed mainly in the hydrophobic influences which are developed in aqueous solutions.Although the big synthetic interesting and the similitude with the Diels-Alder reactions, the use of the water as solvent in cycloadditions of nitrones had n’t studied as it should be. So inquire investigation of these reactions seems to be particularly interesting, because that could lead in improved conditions with many applications in synthesis of products with biologic activity.The reactions were performed parallel in organic solvents and aqueous suspension by stirring. In all cases the dipolophile was used in excess and the end of the reaction was checked by the disappearance of the spot of the nitrone in TLC.In summary from the results of the reactions were studied, all of the reactions performed on the water in well yields and significantly sooner rather than in organics solvents.All of the nitrones were used are expressed hydrophobic and insolubly in water, so the reactions can be thought that are performed “on water” conditions. The relatively reductions that observed on the times of the reactions with the methyl acrylate and the dodecyl acrylate are approximately the same, thus the use of a more hydrophobic ester doesn’t seem to favor additionally the reaction. The use of supersonic that tested in some cases, also doesn’t affect substantially the times of the reaction.Concern of the influence of the water on the stereoselectivity of the reactions wasn’t observed spectacularly changes. The small changes were noticed, are in all cases consentaneous with the idea that the stereoisomer products that come up from transition states with the smallest volume, are enforced. This attribute is agreed with the model of hydrophobic influences that is developed in aqueous media and favor the products that come from the most compressed transition states.Conclusively from the study of the above reactions, results that the water should be the solvent of choice for the 1,3-dipolar cycloadditions of nitrones because of environmental reasons, additionally shows advantages by the efficiently reduction of the time of the reactions. Also, in many cases it seems to show important influence in the yields. Further, there are indications that the water shortly affects the diastereoselectivity of the reactions, which possibly could be optimized by choosing suitable substrates.