Osman M. E. El-Dusouqui

Chemistry of 2-arylhydrazonals: utility of substituted 2-arylhydrazono-3-oxoalkanals as precursors for 3-oxoalkanonitriles, 3-aminoisoxazole and 1,2,3- and 1,2,4-triazoles

Efficient routes to 2-arylhydrazono-3-oxoalkanonitriles, 1,2,3- and 1,2,4-triazoles, and 3-aminoisoxazole utilising the oximes of the title hydrazones are reported. The behaviour of the oximes on pyrolysis in the gas phase and by flash vacuum is analysed. X-ray crystallography were used to confirm the structure of the triazole 10b and the 3-oxoalkanonitrile 12f.

Kinetics and mechanism of thermal gas-phase elimination of ?-substituted carboxylic acids: role of relative basicity of ?-substituents and acidity of incipient proton

2-Phenoxypropanoic acid together with five of its aryl derivatives, its phenylthio and its N-phenylamino analogues were pyrolyzed at 494–566 K. The reactions were homogeneous, polar and free from catalytic and radical pathways, and obeyed a first-order rate equation. The limits of the Arrhenius log A (s−1) and E (kJ mol−1) values obtained for these reactions averaged 11.98 ± 1.71 and 158.1 ± 17.4, respectively. Analysis of the pyrolysates showed the elimination products to be carbon monoxide, acetaldehyde and the corresponding phenol, thiophenol or aniline compounds. The pyrolysis of 2-phenoxy- and 2-(N-phenylamino)-1-propanol was also investigated over the temperature range 638–792 K. The kinetic results and products analysis lend support to a reaction pathway involving a five-membered cyclic polar transition state. Copyright

Kinetics and mechanism of pyrolysis of sulphonyl hydrazones and oximes. Part 2—Structural effects and molecular reactivity

The kinetics and products of the pyrolytic reaction of six tosyl arenecarboxaldoximes were studied over the temperature range ca 334 – 401 K to yield the following Arrhenius log A/s−1 and Ea / kJ mol−1, respectively: 10.92 and 98.25 for tosyl benzaldoxime and 10.83 and 100.4 for m-nitro-, 10.66 and 97.53 for p-chloro-, 11.80 and 107.8 for m-chloro-, 11.60 and 101.5 for p-methyl- and 10.84 and 97.75 for p-methoxybenzaldehyde O-[(4-methylphenyl)sulphonyl]oxime. At 500 K, the oxime compounds were found to be 9.4 × 103 – 2.7 × 104-fold more reactive than their hydrazone analogues. Copyright

Gas-phase pyrolytic reactions of N-ethyl, N-isopropyl, and N-t-butyl substituted 2-aminopyrazine and 2-aminopyrimidine

The rates of gas-phase elimination of N-ethyl (1), N-isopropyl (2), N-t-butyl (3) substituted 2-aminopyrazine and N-ethyl (4), N-isopropyl (5), and N-t-butyl (6) substituted 2-aminopyrimidine have been measured. The compounds undergo unimolecular first-order pyrolytic reactions. The relative rates of the primary:secondary;tertiary alkyl homologues at 600 K are 1:14.4:38.0 for the pyrazines and 1:20.8:162.5 for the pyrimidines, respectively. The reactivities of these compounds have been compared with those of the alkoxy analogues and with each other. Product analyses, together with the kinetic data, were used to outline a feasible pathway for the elimination reaction of the compounds under study.

Gas-phase pyrolytic reactions. Rate data for pyrolysis of N-t-butylthioacetamide and N-acetylthioacetamide: role of polarity of transition state and γ-carbonyl group protophilicity

In the gas phase, both N-t-butylthioacetamide and N-acetylthioacetamide undergo unimolecular first-order elimination reactions for which log A= 11.58 s–1 and 10.64 s–1, and Ea= 16.45 kJ mol–1 and,117.15 kJ mol–1, respectively. The results are in accord with a reaction pathway involving a cyclic six-membered transition state, and show each compound to be more reactive than its oxygencontaining analogue. At 600 K, the statistically corrected reactivity ratios: t-butyl thioacetate (1)/ t-butyl acetate (2); N-acetylthioacetamide (3)/diacetamide (4); and N-t-butylthioacetamide (5)/N-t-butylacetamide (6) are 83, 173, and 1 404, respectively. The above rate factors are consistent with the tenet that as Cα–X bond fission becomes less rate-contributing in these electrocyclic reactions, so attack by the CY bond upon the β-hydrogen atoms becomes more important. Thus, whereas t-butyl acetate at 600 K is some 68 700 times more reactive than N-t-butylacetamide, t-butyl thioacetate is only 4 060 times more reactive than N-t-butylthioacetamide.

Pyrolysis of ?-hydroxyketones and ?-ketoesters: Gas-phase elimination kinetics of 3-hydroxy-3-methyl-2-butanone and methyl benzoylformate

The rates of gas-phase elimination reactions of methyl benzoylformate (1) and 3-hydroxy-3-methyl-2-butanone (2) were obtained at T = 600 K. The two substrates undergo unimolecular first-order elimination for which the Arrhenius equations are, respectively, log k = 13.2 − 53270/(4.574 × 600) for (1) and log k = 12.4 − 53060/(4.574 × 600) for (2). The products of pyrolysis of (1) are benzaldehyde, formaldehyde and CO, while those of (2) are acetaldehyde and acetone. The kinetics of the elimination reactions show benzoylformic acid to be 106-fold more reactive than (1), and pyruvic acid ca. 105-fold more reactive relative to (2); an indication of the rate-controlling part played by the acidity of the hydrogen atom involved in the elimination process of the present compounds in this particular type of reaction.

Gas-phase kinetics of elimination reactions of pentane-2,4-dione derivatives. Part ii [1]. Thermolysis of derivatives and analogues of 3-phenylhydrazonopentane-2,4-dione

Six analogues and derivatives (1–6) of 3-phenylhydrazonopentane-2,4-dione (7) were subjected to gas-phase thermolysis. The Arrhenius log A (s−1) and Ea (kJ mol−1) of the analogues (1–5) are, respectively: 10.42 and 140.8 for 1-cyano-1-phenyl-hydrazonopropanone (1), 11.19 and 135.4 for 1-cyano-1-(-nitrophenylhydrazono)-propanone (2) , 10.68 and 144.9 for 1-cyano-1-(-methoxyphenylhydrazono)propanone (3), 11.76 and 137.8 for 1-cyano-3-phenyl-1-phenylhydrazonopropanone (4), and 11.29 and 145.9 for 1-cyano-1-phenylhydrazonobutanone (5). The corresponding values for ethyl 3-oxo-2-phenylhydrazonobutanoate (6) are 11.90 s−1 and 143.3 kJ mol−1. The rates of reaction at 600 K are compared with those of the title diketone (7) and of pentane-2,4-dione (8) and rationalized in terms of a plausible elimination pathway involving a semiconcerted six-membered transition state.

Kinetics and mechanism of pyrolysis of sulphonyl hydrazones and oximes. Part 1. Contribution to reactivity from hydrazone HNN and oxime ON bond polarity

Abstract Rates were obtained for the pyrolysis of tosyl arenecarboxaldehyde hydrazones (1–5), and mesyl benzaldoxime (6). The substituted tosyl sulphonamides (TsHNN=CHAr: 1–5) and the mesylate (6) gave in a novel pyrolytic reaction the following Arrhenius log A/s−1 and Ea/kJ mol−1 values, respectively: 12.70 and 157.7 (1, ArC6H5), 12.29 and 152.6 (2, p -NO2C6H4), 11.85 and 148.2 (3, m -NO2C6H4), 12.17 and 152.0 (4, p -ClC6H4), 11.01 and 140.8 (5, p -CH3OC6H4), and 12.96 and 109.9 for (6). Tosyl benzaldoxime (7) was also studied. The reactions yielded cyanoarenes together with sulphonic acids from 6 and 7, and p -methylbenzenesulphonamide from compounds 1–5.

Gas-phase replacement σ0 substituent constants of heteroaryl groups1

Abstract Hammett replacement σ 0 substituent constants of pyridyl, thienyl, and furyl groups are reported for the first time from gas-phase eliminations of their t -butyl and isopropyl heteroarylcarboxylate esters.

Gas-phase pyrolytic reactions. part 3. Hammett ϱ constants of gas-phase eliminations of alkyl arylcarboxylate and ethanoate esters and their correlation with substrate molecular framework☆

Abstract The kinetics of the gas-phase thermal elimination of seven tert-butyl (hetero)arylcarboxylate esters (GCO2But) were measured over a temperature range = 50 K; the groups were the phenyl, 3— and 4—pyridyl, 2— and 3-fnryl, and 2— and 3—thienyl moieties. The reactions were homogeneous and unimolecular with log A /s-1scaling 12.45 ±0.44, and with an entropy of activation uniformly negative and small. The kinetics obeyed a first-order rate equation, and at 600 K the rate coefficients (l03k/s-1) of the esters, in the order given above, were: 54.1, 85.3, 120.5, 76.9, 43.2, 86.3 and 46.1, respectively. Hammett correlation of the present kinetic data with the literature σ0 values of the given substituents gave a reaction ϱ constant compatible with the ethanoate molecular frame rather than with the carboxylate structure. The physical constants of five new t-butyl heteroarylcarboxylate esters are also described.