Competing Channels in the Thermal Decomposition of Azidoacetone Studied by Pyrolysis in Combination with Molecular Beam Mass Spectrometric Techniques (original) (raw)
Related papers
2004
The thermal decomposition of 2-azidoacetamide (N 3 CH 2 CONH 2 ) has been studied by matrix-isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. N 2 , CH 2 NH, HNCO, CO, NH 3 , and HCN are observed as high-temperature decomposition products, while at lower temperatures, the novel imine intermediate H 2 NCOCHdNH is observed in the matrix-isolation IR experiments. The identity of this intermediate is confirmed both by ab initio molecular orbital calculations of its IR spectrum and by the temperature dependence and distribution of products in the photoelectron spectroscopy (PES) and IR studies. Mechanisms are proposed for the formation and decomposition of the intermediate consistent both with the observed results and with estimated activation energies based on pathway calculations.
Another Look at the Decomposition of Methyl Azide and Methanimine: How Is HCN Formed?
The Journal of Physical Chemistry, 1996
Ab initio molecular orbital calculations have been used to study the decomposition of methyl azide (CH 3 N 3 ), methanimine, and its isomers (CH 3 N) in both lowest lying singlet and triplet states. Geometries were optimized using UMP2/6-31G(d,p) level of theory while energies of the stationary points on potential energy surfaces were obtained from QCISD(T) calculations with larger 6-311++G(d,p) and 6-311++G(3df,2p) basis sets and corrected for zero-point energies. The temperature dependence of the rate constants of various dissociative processes has also been calculated using the conventional transition-state theory. While the decomposition of methyl azide occurs, in the singlet state, through a concerted motion of N 2 elimination with hydrogen shift, giving methanimine, the triplet methyl azide does not exist as a discrete species but falls apart, giving triplet methylnitrene plus N 2 . Starting from singlet methanimine, 1,1-H 2 elimination giving HNC is found to be favored over 1,2-H 2 elimination giving HCN, a 1,2-H shift yielding aminocarbene, and N-H bond cleavage producing the H 2 CN radical. The hot HNC molecule is expected to rearrange rapidly to HCN. From singlet aminocarbene (HCNH 2 ), 1,2-H 2 loss giving HNC is also a less energy-demanding step than the 1,2-H 2 loss, generating HCN. Overall, it appears that, in the lowest singlet state, HCN is not directly formed upon fragmentation of methanimine but rather from rearrangement of HNC which is the primary product. In the triplet state, the HCN formation from either methylnitrene or methanimine passes through successive losses of H atoms. R 2 CH-N 3 f R 2 CdNH + N 2 (1)
Organic & Biomolecular Chemistry, 2012
Experimental section General aspects 1 H and 13 C NMR spectra were recorded on Bruker Avance II spectrometer in DMSO-d 6 (400 and 100 MHz, respectively) using Me 4 Si as an internal standard. The mass analyzer was a Bruker Daltonics MicrOTOF-Q II mass spectrometer with an electrospray ionization source (ESI-MS). The nominal resolution of the instrument was 17,500. The instrument was operated in positive ion mode with m/z range of 50-800. The capillary voltage was 4500 V, and the capillary exit was 166 V. The nebulizer gas pressure was 0.8 bars, and the drying gas flow was 4 L/min. The drying temperature was 250°C. The spectra average was set to 3, and the summation was 5,000, corresponding to 1 second sample time. The transfer time was 70 microseconds, and the hexapole RF was 100 Vpp. UV spectra were recorded with a Perkin Elmer Lambda 50 UV/VIS spectrometer. Microanalyses were performed on Carlo Erba 2700 II elemental analyzer. The progress of the reactions and the purity of the compounds were monitored by TLC on TLC Silica gel 60 F 245 Aliminium sheets (Merck KGaA) in EtOAc-hexanes (5:1 or 4:1) system. 5-Methyl-1,2,3-triazole-4-carboxylates 1a-d, 1 5-methyl-1,2,3-thiadiazole-4-carboxylate 7 2 and 1,2,3-triazole-4-carboxylate 3b 3 were prepared according to a literature procedures. X-Ray experiment. X-Ray structural experiment was performed in Center of Joint Usage "Spectroscopy and Analysis of Organic Compounds" IOS UB RAS at 295(2) K on a Xcalibur S automatic single-crystal diffractometer at the standard procedure (graphite-monochromated MoK α-radiation, ω-scanning technique with a step of 1º). Crystal data for 4a: chemical formula
Rediscovering the Wheel. Thermochemical Analysis of Energetics of the Aromatic Diazines
The Journal of Physical Chemistry Letters, 2012
Thermochemical properties of pyrimidine, pyrazine, and pyridazine have been measured and re-evaluated to provide benchmark quality results. A new internally consistent data set of Δ f H m°(g) has been obtained from combustion calorimetry and vapor pressure measurements. The gas and condensed phase enthalpies of formation of the parent diazines have been re-evaluated, and the results were compared to current theoretical calculations using the highly accurate first-principles methods: G3, G4, CBS-APNO, W1(RO). Simple "corrected atomization procedures" to derive theoretical Δ f H m°(g) directly from the enthalpies H 298 have been tested and recommended as an alternative to using the bond separation and isodesmic reaction models for organic cyclic and heterocyclic compounds containing one to three nitrogen atoms. SECTION: Molecular Structure, Quantum Chemistry, and General Theory D iazabenzenes are key building blocks used to develop compounds of biological, medicinal, and chemical interest. There are three isomeric diazabenzenes or diazines: the 1,2-, more commonly known as pyridazine; the 1,3-, more commonly known as pyrimidine, and the 1,4-, more commonly known as pyrazine (Figure 1).
The Journal of Physical Chemistry A, 2011
Motivated by the necessity to understand the pyrolysis of alkylated amines, unimolecular decomposition of acetamide is investigated herein as a model compound. Standard heats of formation, entropies, and heat capacities, are calculated for all products and transition structures using several accurate theoretical levels. The potential energy surface is mapped out for all possible channels encountered in the pyrolysis of acetamide. The formation of acetamedic acid and 1-aminoethenol and their subsequent decomposition pathways are found to afford the two most energetically favored pathways. However, RRKM analysis shows that the fate of acetamedic acid and 1-aminoethenol at all temperatures and pressures is to reisomerize to the parent acetamide. 1-Aminoethenol, in particular, is predicted to be a longlived species enabling its participation in bimolecular reactions that lead to the formation of the major experimental products. Results presented herein reflect the importance of bimolecular reactions involving acetamide and 1-aminoethenol in building a robust model for the pyrolysis of N-alkylated amides.