598-61-8Relevant articles and documents
Mechanisms of Methylenecyclobutane Hydrogenation over Supported Metal Catalysts Studied by Parahydrogen-Induced Polarization Technique
Salnikov, Oleg G.,Burueva, Dudari B.,Kovtunova, Larisa M.,Bukhtiyarov, Valerii I.,Kovtunov, Kirill V.,Koptyug, Igor V.
, (2022/03/15)
In this work the mechanism of methylenecyclobutane hydrogenation over titania-supported Rh, Pt and Pd catalysts was investigated using parahydrogen-induced polarization (PHIP) technique. It was found that methylenecyclobutane hydrogenation leads to formation of a mixture of reaction products including cyclic (1-methylcyclobutene, methylcyclobutane), linear (1-pentene, cis-2-pentene, trans-2-pentene, pentane) and branched (isoprene, 2-methyl-1-butene, 2-methyl-2-butene, isopentane) compounds. Generally, at lower temperatures (150–350 °C) the major reaction product was methylcyclobutane while higher temperature of 450 °C favors the formation of branched products isoprene, 2-methyl-1-butene and 2-methyl-2-butene. PHIP effects were detected for all reaction products except methylenecyclobutane isomers 1-methylcyclobutene and isoprene implying that the corresponding compounds can incorporate two atoms from the same parahydrogen molecule in a pairwise manner in the course of the reaction in particular positions. The mechanisms were proposed for the formation of these products based on PHIP results.
Synthese von Cyclobutan durch Dehalogenierung von 1,4-Dihalogenbutanen mit Alkalimetalldaempfen. Zur Relation von radikalischen und metallorganischen Reaktionskanaelen
Volnina, S. A.,Avakjan, V. G.,Guselnikov, L. E.,Yaya, A. Al
, p. 1061 - 1072 (2007/10/02)
Gasphase dehalogenation of 1,4-dichloro-, 1-chloro-4-bromo-, 1,4-dibromobutanes and 1,4-dibromopentane by Na/K vapors produces cyclobutane resp. methylcyclobutane with selectivities of 55.5, 46.7, 32.0 and 17 moles/100 moles resp..Side products of the reaction are ethylene and hydrogen, yields of which increase with increasing temperature and rising degree of substitution of chlorine by bromine.A mechanism is discussed in which the initiation step is the generation of halobutyl radicals of the type H2C*-(CH2)2-CH2X (X = Cl, Br) which are reacting further in two ways - by formation of tetramethylenediradical, splitting off the second halogen atom, or by the formation of the metallorganic compound 1-potassium-4-halogenobutane, which further cyclisizes to cyclobutane splitting off KX.Using some methods of theoretical chemistry such as quantumchemical calculations based on ab initio (STO-3G) and semiempirical (AM1) structures, on the relative energies of conformers of halogenobutylradicals and on models of the metallorganic intermediates, but also by conformation calculations of the content of rotation isomers of the intermediate formed, the correlation between the two reaction channels depending on the type of halogen was estimated.The calculations showed that only about 20 percent of cyclobutane are generated by the radical pathway.The high predominance of the metallorganic channel in the case of 1,4-dichlorobutane is caused by the high lifetime of chlorobutyl radicals in comparison with its bromoanalogues.
