22396-07-2Relevant academic research and scientific papers
Laboratory-Scale Membrane Reactor for the Generation of Anhydrous Diazomethane
Dallinger, Doris,Pinho, Vagner D.,Gutmann, Bernhard,Kappe, C. Oliver
, p. 5814 - 5823 (2016/07/26)
A configurationally simple and robust semibatch apparatus for the in situ on-demand generation of anhydrous solutions of diazomethane (CH2N2) avoiding distillation methods is presented. Diazomethane is produced by base-mediated decomposition of commercially available Diazald within a semipermeable Teflon AF-2400 tubing and subsequently selectively separated from the tubing into a solvent- and substrate-filled flask (tube-in-flask reactor). Reactions with CH2N2 can therefore be performed directly in the flask without dangerous and labor-intensive purification operations or exposure of the operator to CH2N2. The reactor has been employed for the methylation of carboxylic acids, the synthesis of α-chloro ketones and pyrazoles, and palladium-catalyzed cyclopropanation reactions on laboratory scale. The implementation of in-line FTIR technology allowed monitoring of the CH2N2 generation and its consumption. In addition, larger scales (1.8 g diazomethane per hour) could be obtained via parallelization (numbering up) by simply wrapping several membrane tubings into the flask.
Iron-catalyzed cyclopropanation in 6 M KOH with in situ generation of diazomethane
Morandi, Bill,Carreira, Erick M.
scheme or table, p. 1471 - 1474 (2012/07/13)
Diazomethane is a common and versatile reagent in organic synthesis whose broader use is generally impeded by its explosiveness and toxicity. Here we report that a simple iron porphyrin complex catalyzes the cyclopropanation of styrenes, enynes, and dienes under the demanding conditions [aqueous 6 molar potassium hydroxide (KOH) solution, open to air] necessary for the in situ generation of diazomethane from a water-soluble diazald derivative. A biphasic reaction medium arising from the immiscibility of the olefin substrates with water appears essential to the overall efficiency of the process. The work we describe highlights an approach to catalysis with untoward reactive intermediates, in which the conditions for their generation under operationally safe regimes dictate catalyst selection.
Electrophilic Aromatic Nitration in the Gas Phase
Attina, Marina,Cacace, Fulvio,Yanez, Manuel
, p. 5092 - 5097 (2007/10/02)
Aromatic nitration by MeO+(H)NO2, in essence nitronium ion solvated by one methanol molecule, has been studied in the gas phase by using an integrated approach, based on the coordinate application of ICR, Cl, and CID mass spetrometric methods with a highly complementary radiolytic technique.The latter can be used in gases at atmospheric pressure and allows direct evaluation of key mechanistic features, in particular of substrate and positional selectivity.The results resolve early discrepancies between gas-phase and liquid-phase studies, characterizing the reaction as a typical, well-behaved electrophilic substitution of moderate selectivity.The date from the gas-phase nitration of ten monosubstituted benzenes fit a Hammett's type linear plot, characterized by a ρ value of -3.87.The correlation does not extend to highly activated substrates, such as anisole and mesitylene, since the nitration rate tends to a limiting value that cannot be increased by further enhancing the activation of the substrate, exactly as in "encounter-rate" nitrations occurring in solution.The mechanism and the energetics of the gas-phase nitration have been investigated, and the relative stability of the charged intermediates involved, in particular of the isomeric protonated nitrobenzenes, has been estimated by theoretical approaches at two different levels, using STO-3G minimal basis and 4-31G split-valence basis sets.
