The thermochemical kinetics of the retro-‘ene’ reactions of molecules with the general structure (allyl)XYH in the gas phase. Part IX. Unimolecular thermal decompostion of allylmethylamine

Abstract

The gas-phase unimolecular thermal decomposition of N-allyl-N-methylamine (AMA) w a s investigated in the temperature range 602-694 K. The principal products are propene and methylenearnine. First-order rate constants, calculated using the internal standard method, fit the Arrhenius relationship (i). The reaction appears log ( k J s -l ) = (1 1.37 f 0.56) -(43.38 f 1.62 kcal rn01-~)/2.3R7 5 0) to be homogeneous as a 15-fold change in surface :volume ratio of the reaction vessel yields no significant change in the rate constants. The decomposition of AMA follows a retro-' ene ' mechanism via a 6-centre transition state.The Arrhenius parameters for A M A decomposition are compared with those observed for other alkylallylamines.The significance of these observations in an evaluation of the extent of charge separation, i.e. non-synchronism, in the transition state is discussed.EARLIER studies of the thermal decomposition of Nsubstituted allylamines 1-3 have shown that reaction proceeds via a retro-' ene ' type mechanism analogous to the reactions of butenols,4y5 butenoic acid^,^^^ and certain olefins such as hepta-l,&diene,* involving a sis-centre transition state (Scheme 1

The Thermochemical Kinetics of Retro “‐Ene” Reactions of Molecules with the General Structure (Allyl)XYH in the Gas Phase. 8.. The Thermal Decomposition of Methylallylaniline in the Gas Phase

“…with the activation energies observed for N-methyl-N-allyl-amine (43.5 kcal mol-l) [13] and N-cyclohexyl-N-allyl-amine (42.2) [3], this implies that the phenyl group bonded to the nitrogen atom has no measurable effect on the 6-center transition state structure involved in these reactions, and shown in equation (1). This is a most remarkable finding which ties in with the large effect observed for vinyl subtituents in R1 or R2 position [l] [2] in view of the suggested non-synchroneiety, i.6.…”

Targeting the Rich Conformational Landscape of N‐Allylmethylamine Using Rotational Spectroscopy and Quantum Mechanical Calculations

“…Previous gas phase pyrolysis reports using allyl containing precursors, such as N-allylmethylamine (AMA, H 2 C=CHÀ -CH 2 À NHÀ CH 3 ) and its oxygen and sulfur counterparts, [8,9] have shown that the thermal decomposition of this class of compounds led to the formation of species of astrochemical and atmospheric interest. In the case of AMA, [8] the main kinetically favored products at temperatures of 602-694 K are propylene (CH 2 CHCH 3 ) [10] and methanimine (CH 2 NH) [11] which are known prebiotic molecules found in the TMC-1 and Sagittarius B2 molecular clouds, respectively. [2,8] This suggests that AMA is a good candidate to form novel molecular species which can then be characterized by rotational spectroscopy under laboratory conditions.…”

“…In the case of AMA, [8] the main kinetically favored products at temperatures of 602-694 K are propylene (CH 2 CHCH 3 ) [10] and methanimine (CH 2 NH) [11] which are known prebiotic molecules found in the TMC-1 and Sagittarius B2 molecular clouds, respectively. [2,8] This suggests that AMA is a good candidate to form novel molecular species which can then be characterized by rotational spectroscopy under laboratory conditions. Before understanding the products and processes in which AMA participates, a complete characterization of its conformational landscape, spectroscopic fingerprints and internal motions is compulsory.…”

Desulfinylation of Prop-2-enesulfinic Acid: Experimental Results and Mechanistic Theoretical Analysis

“…An analogous reaction is the thermolysis of homoallylic alcohol which fragmentates into propene and formaldehyde above 300 °C (Δ H ‡ ≅ 40 kcal/mol, Δ S ‡ = −8.8 e.u. , see also the retro-ene reaction of propargyl alcohols) follow a similar concerted mechanism. Thermolysis (287−375 °C) of allyl ethyl ether giving CH 3 CHO + propene might also follow a similar concerted retro-ene mechanism, , as well as thermolysis of allyl methyl amine giving propene + CH 2 NH (330−420 °C) (Scheme A). Retro-ene elimination of thioaldehydes or thioketones from β,γ-unsaturated thiols is not described, but examples of ene-reaction of thiocarbonyl compounds are known. , …”

“…78,79 see also the retro-ene reaction of propargyl alcohols 80 ) follow a similar concerted mechanism. Thermolysis (287-375 °C) of allyl ethyl ether giving CH 3 CHO + propene might also follow a similar concerted retro-ene mechanism, 81,82 as well as thermolysis of allyl methyl amine giving propene + CH 2 dNH (330-420 °C) 83 described, but examples of ene-reaction of thiocarbonyl compounds are known. 84,85 As stated above, β,γ-unsaturated sulfinic acids are unstable at room temperature.…”