50888-73-8Relevant academic research and scientific papers
Retro-Ene Reactions in Acylallene Derivatives
Bibas, Herve,Koch, Rainer,Wentrup, Curt
, p. 2619 - 2626 (2007/10/03)
Allenic esters and amides 4 undergo a retro-ene reaction to vinylketene (6) and an aldehyde or imine (5) under the conditions of flash vacuum thermolysis (FVT). The same products are obtained by FVT of cyclobutenones 7 via electrocyclic ring opening to alkoxy- or aminovinylketenes 3 and 1,3-rearrangement of ketenes 3 to allenes 4. All the intermediates and products were characterized by matrix isolation IR spectroscopy, and in the case of 4c the reaction was also monitored by online mass spectrometry. A lower temperature for the retro-ene reaction of 4c, eliminating an imine, than for 4a, eliminating formaldehyde, is in agreement with a lower calculated activation barrier (167 and 181 kJ mol-1, respectively, at the G2(MP2,SVP) level of theory). The allenic amide 11 undergoes an analogous retro-ene reaction to the (unobserved) vinylketene 13, the latter isomerizing to cyclohexenylacrolein 16 in a 1,5-H shift (calculated barrier 125 kJ mol-1; G2 (MP2, SVP)).
Gasphasen-Reaktionen, 22. Thermische Erzeugung von C4H4O: Vinylketen und Ethylidenketen
Mohmand, Shamsher,Hirabayashi, Takakuni,Bock, Hans
, p. 2609 - 2621 (2007/10/02)
Thermal HX elimination from unsatured carboxylic acid derivatives CH3-RC=CH-COX represents another method to generate the short-lived isomers C4H3RO with R = H, CH3 in the gas phase.The temperature-dependent changes of amounts of products in the heated flow system are analyzed by photoelectron spectra: based on MNDO calculations and in accordance with literature data, the vinylketene structure CH2=CR-HC=C=O is assigned to the thermolysis product.The isomeric alkylideneketenes H3C-RC=C=C=O with R = H, CH3 are produced in the 760 K short-path pyrolysis of alkylidenemalonates and rearrange on prolonged residence time in the heating zone into the thermodynamically more stable vinylketene derivatives.
Gasphasen-Reaktionen, 21. Thermische Erzeugung von Alkyl- und Halogenketenen
Bock, Hans,Hirabayashi, Takakuni,Mohmand, Shamsher
, p. 2595 - 2608 (2007/10/02)
Thermal gas phase reactions for the generation of ketenes can be optimized PE-spectroscopically.To eliminate HX from acetyl derivatives R2CH-COX increasing temperatures are required in the sequence HO2CCH3 ca.HCl HBr H2O ca.ROH CH4.By adding NH3, HCl can be removed from the gaseous mixture and thus the PE spectra of pure alkyl ketenes R2C=C=O (R e.g.H, CH3, C2H5) may be recorded. "Fulvene ketene" (4) is obtained from cyclopentadienecarbonyl chloride (this from the dimer) and ethyleneketene (7) by pyrolysis of cyclopropyl spirosubstituted Meldrum's acid (6).Chloro- and bromoketenes are generated as follows: ClHC=C=O from ClH2C-COCl, Cl2C=C=O from Cl3C-COBr with Zn, BrHC=C=O from 2-bromocyclobutanone and NC-HC=C=O from NC-HC=C=O from NC-H2C-COCl.The PE spectra are assigned by radical cation state comparison based on MNDO calculations.
