Ethynamine - Ketenimine - Acetonitrile - Rearrangements: A computational Study of Flash Vacuum Pyrolysis Processes

10.26434/chemrxiv.5373964.v1 ◽

2017 ◽

Cited By ~ 2

Author(s):

Curt Wentrup ◽

Didier Begue ◽

Regis Leung-Toung

Keyword(s):

Transition State ◽

Radical Pair ◽

Computational Study ◽

Physical Reality ◽

Second Step ◽

Flash Vacuum Pyrolysis ◽

Vacuum Pyrolysis ◽

Experimental Shock ◽

Very High ◽

Concerted Reaction

The rearrangements of ethynamine 3 (H-CºC-NH2) to ketenimine 4 (CH2=C=NH) and acetonitrile 5 (CH3CN) were investigated computationally up to the MP4(SDTQ)/6-31G*//MP2(FU)/6-31G* level. The calculated barrier for a concerted reaction 3 -> 4 is very high, 74 kcal/mol, the structure of the transition state very unusual, and this path is discredited. A lower barrier of about 60 kcal/mol via aminovinylidene 2 and imidoylcarbene 15 has been found. The calculated barrier for a concerted second step 4 -> 5 is 61 kcal/mol, and the transition state structure is again very unusual with a virtually linear CCN backbone, but this does not appear to correspond to physical reality. Instead, CASPT2 calculations predict reaction via vinylnitrene 9 and/or homolysis of 4 to the radical pair ·CH2CN + H· (11) with a barrier of 67-70 kcal/mol in agreement with experimental shock-tube data. Recombination (maybe via roaming) affords acetonitrile 5. There is strong experimental evidence for homolytic paths in pas-phase pyrolyses of ketenimines.

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On the Thermally Induced Rearrangement of 2-Alkoxypyridines to N-alkylpyridones

Australian Journal of Chemistry ◽

10.1071/ch03044 ◽

2003 ◽

Vol 56 (9) ◽

pp. 913 ◽

Cited By ~ 16

Author(s):

Troy Lister ◽

Rolf H. Prager ◽

Michael Tsaconas ◽

Kerry L. Wilkinson

Keyword(s):

Transition State ◽

Condensed Phase ◽

Vapour Phase ◽

Thermally Induced ◽

Flash Vacuum Pyrolysis ◽

Structural Assignment ◽

Vacuum Pyrolysis

Analogues of 2-methoxypyridine undergo rearrangement to N-methylpyridones under flash vacuum pyrolysis (FVP) conditions. Ethoxy derivatives undergo competitive ethyl migration and elimination of ethylene. Analogues of 4-methoxypyridine do not undergo rearrangement under FVP conditions, but demethylation on silica may occur. The ease of rearrangement follows the basicity of the alkoxyhetarene to some extent. The vapour-phase rearrangements have been contrasted to condensed-phase pyrolyses, and a four-centre transition state for the former is supported by computation. The rearrangement allows structural assignment to the two products from the reaction of 2,4-dichloroquinoline with pyrrolidine.

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Formation of a pre-reaction hydrogen-bonded complex and its significance in the potential energy surface of the OH + SO2→ HOSO2 reaction: A computational study

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633617500468 ◽

2017 ◽

Vol 16 (05) ◽

pp. 1750046 ◽

Cited By ~ 3

Author(s):

Vijay M. Miriyala ◽

Priya Bhasi ◽

Zanele P. Nhlabatsi ◽

Sanyasi Sitha

Keyword(s):

Potential Energy ◽

Transition State ◽

Potential Energy Surface ◽

Energy Surface ◽

Computational Study ◽

Stationary Points ◽

Second Step ◽

Computational Calculations ◽

Reaction Complex ◽

Hydrogen Bonded

Using computational calculations, we have revisited the potential energy surface (PES) of the reaction between OH and SO2, which is believed as the rate-limiting step in the atmospheric formation of H2SO4. In this work, we report for the first time the presence of a pre-reaction hydrogen-bonded complex between OH and SO2 in the reaction PES. Based on this finding, it has been shown that the reaction can be considered as a two-step process in which the first step is the formation of the pre-reaction complex and the second step is the transformation of this complex to the product. It was observed that due to the presence of this pre-reaction complex as a potential well in the reaction PES, the barrier height got increased by around two-fold for the second step. Based on this observation, it has been proposed that the kinetics of the reaction is going to be affected. Also based on the analysis of the geometries of this pre-reaction complex and the transition state, it has been argued that the step involving the transformation of this pre-reaction complex to the product via the transition state is going to be the slowest step as this transformation involves large structural changes of the stationary points involved.

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Sulfonyl isocyanides RSO2NC

10.26434/chemrxiv.5722528.v1 ◽

2017 ◽

Author(s):

Curt Wentrup ◽

Horst Briehl

Keyword(s):

Ir Spectrum ◽

Reaction Conditions ◽

Flash Vacuum Pyrolysis ◽

Vacuum Pyrolysis

Flash vacuum pyrolysis (FVP) of 5-azido-1-aryltetrazoles results in triple N2 elimination and formation of aryl isocyanides RNC, which rearrange in part to aroylnitriles RCN under the reaction conditions. Similar FVP of 5-azido-1-arenesulfonyltetrazoles generates a compound absorbing in the IR spectrum (77 K) at 2090 cm-1 and assigned the structure of arenesulfonyl isocyanide, ArSO2NC 11. FVP at temperatures above 600 oC results in progressively more nitrile ArSO2CN 12. Compound 11 also disappears on warming above -80 oC

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Sulfonyl isocyanides RSO2NC

10.26434/chemrxiv.5722528 ◽

2017 ◽

Author(s):

Curt Wentrup ◽

Horst Briehl

Keyword(s):

Ir Spectrum ◽

Reaction Conditions ◽

Flash Vacuum Pyrolysis ◽

Vacuum Pyrolysis

Flash vacuum pyrolysis (FVP) of 5-azido-1-aryltetrazoles results in triple N2 elimination and formation of aryl isocyanides RNC, which rearrange in part to aroylnitriles RCN under the reaction conditions. Similar FVP of 5-azido-1-arenesulfonyltetrazoles generates a compound absorbing in the IR spectrum (77 K) at 2090 cm-1 and assigned the structure of arenesulfonyl isocyanide, ArSO2NC 11. FVP at temperatures above 600 oC results in progressively more nitrile ArSO2CN 12. Compound 11 also disappears on warming above -80 oC

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Flash Vacuum Pyrolysis of Isoxazoles, Pyrazoles and Related Compounds

Current Organic Chemistry ◽

10.2174/1385272043370113 ◽

2004 ◽

Vol 8 (12) ◽

pp. 1071-1088 ◽

Cited By ~ 16

Author(s):

G. Yranzo ◽

E. Moyano

Keyword(s):

Flash Vacuum Pyrolysis ◽

Vacuum Pyrolysis ◽

Related Compounds

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Preparation of furanoradialene by the flash vacuum pyrolysis of diesters of 3,4-bis(hydroxymethyl)-2,5-dimethylfuran

Journal of the American Chemical Society ◽

10.1021/ja00338a032 ◽

1984 ◽

Vol 106 (26) ◽

pp. 8197-8201 ◽

Cited By ~ 9

Author(s):

Walter S. Trahanovsky ◽

Timothy J. Cassady

Keyword(s):

Flash Vacuum Pyrolysis ◽

Vacuum Pyrolysis

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The Pyrolytic Rearrangement of 1-Alkynoyl-3-methylpyrazoles: Synthesis of Pyrazolo[1,5-a]pyridin-5-ols and Related Compounds

Australian Journal of Chemistry ◽

10.1071/ch9940991 ◽

1994 ◽

Vol 47 (6) ◽

pp. 991 ◽

Cited By ~ 16

Author(s):

RFC Brown ◽

FW Eastwood ◽

GD Fallon ◽

SC Lee ◽

RP Mcgeary

Keyword(s):

Carbon Chain ◽

Ring Structure ◽

High Yield ◽

Methyl Group ◽

X Ray ◽

X Ray Crystallography ◽

Flash Vacuum Pyrolysis ◽

Vacuum Pyrolysis ◽

Fused Ring ◽

Related Compounds

Flash vacuum pyrolysis of 1-(alkyn-2′-oyl)-3-methylpyrazoles at 650°/0.03 mm forms pyrazolo[1,5-a]pyridin-5-ols, often in high yield, which may bear substituents at C2, C3 or C7. In the absence of a 3-methyl group in the precursor, N-ethynylpyrazoles are formed in low yield. The formation of both types of product is interpreted as involving 3-(N-pyrazolyl)propadienones formed by N1 → N2 migration of the N-alkynoyl group with inversion of the three-carbon chain. The fused-ring structure of 2-methylpyrazolo[1,5-a]pyridin-5-ol (25) was established by X-ray crystallography of the O-benzoyl derivative (27).

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