Thermochemical kinetics of nitrogen compounds. V. The unimolecular thermal decomposition of diallylamine in the gas phase

Abstract

The kinetics of the thermal decomposition of diallylamine to propylene and prop-2-enaldimine have been studied in the gas phase in presence of an excess of methylamine over the temperature range of 532.7 to 615.6"K, using a static reaction system. Methylamine reacted with the unstable primary product prop-2-enaldimine, forming the thermally stable N-methyl prop-2-enaldimine.First-order rate constants, based on the internal standard technique, fit the Arrhenius relationship log kfs-1) = (1 1.04 f 0.13) -(37.1 1 f 0.33 kcal/mole)/2.303 RT. They were independent on the initial total pressure (46-340 torr), the initial pressure of diallylamine (9.2-65 torr), or methylamine as well as the conversion attained. Despite an apparent surface sensitivity, the reaction is essentially homogeneous in nature as demonstrated by experiments carried out in a packed reaction vessel. The observed activation parameters for the title reaction together with those observed earlier for triallylamine and allylcyclohexylamine are consistent with the proposed concerted reaction mechanism involving a cyclic 6-center transition state. The observed substituent effects suggest a nonsynchronous mode of bond breaking and bond formation. Jn troductionT h e thermal decomposition of diallylamine has been investigated as part of a series of studies on the thermochemical kinetics of N-substituted N-allylamines in a n attempt to obtain more information about the effect of substituents and heteroatoms on the concerted nature of the common reaction mechanism, involving a 6-center transition state complex as indicated in eq. Research, 5303 Wurenlingen, Switzerland. EGGER AND VITINSOf particular interest is the question of the extent of nonsynchronous bond breaking and bond formation, i.e., the amount of polar character in the ground and transition states.To this end we have so far reported measurements on N-allyl-N-cyclohexylamine [ 1 ] and triallylamine [2] and are presently investigating N-allyl-N-methylamine and N-allyl-N-methylaniline, as well as 1,6-hexadiene.Experimental Materials N-diallylamine (DAA) and toluene (T) (used as an internal standard) were obtained from Fluka Chemical Corporation, Buchs, Switzerland. After distillation, DAA was found by gas chromatography (GC) to be 99.0% pure, containing one major light impurity which proved to be thermally stable at the reaction conditions used and did not interfere in the analysis of the product mixture.Two starting mixtures (denoted by A and B ) with mole ratios DAA/T of 0.928 and 0.855, respectively, have been used. The mixtures were stored under nitrogen and gave GC analyses reproducible within =t0.6% over the period of several weeks.Methylamine, supplied by Fluka Chemical Corporation, was purified by distillation and stored as a gas in a 2-1. bulb. GC analyses showed it to be 98% pure. The observed impurities did not affect the analysis of the starting or product mixture. Apparatus and procedureThe static high vacuum system and general procedures used for the kinetic studies were essenti...

Rate of the retro‐Diels‐Alder dissociation of 1,2,3,6‐tetrahydropyridine over a wide temperature range

“…Using the careful experiments of Eggers and Vitin [9] for the allylethyl ether rate constants, we obtained log k z (s-') = 14.87 -53.06/8, which compares well with previous work. It is known that such heteroatom substitution leads to reduced rate parameters for the related retro-ene reactions.…”

“…It is known that such heteroatom substitution leads to increased rate constants and reduced activation energies for the related retro-ene reactions [9]. In this article we present a collaborative study of the retro-Diels-Alder dissociation of 1,2,3,6-tetrahydropyridine (THP) (1) -1,3-butadiene + CH,=NH This study combines three separate techniques in three laboratories, (i) laser-schlieren shock tube measurements (LS): (ii) single-pulse shock-tube measurements (SP); and (iii) comparative rate flow system measurements (FS), to cover 650-1450 K and more than 9 orders of magnitude in the rate constant.…”

Transition structure for the retroene-type elimination reaction of propene from allylamines

“…These studies have permitted also to make suggestions about the nature and the likely geometry of the transition state. The temperature dependence of the kinetic deuterium isotope effect and a lack of substituent effects on the reaction rate for allyl ethers [4][5][6] were used as evidence to propose a nonplanar transition state and a highly concerted mechanism. The allyl sulfides [7,8], on the other hand, showed a temperature-independent kinetic isotope effect [8] and an important substituent effect [7] on the rate of the pyrolysis, suggesting a polar transition state in which the higher reactivity was due to an enhanced acidic character of the ␣-H atom to be transferred in a nonlinear 1-5 shift path.…”

“…For the thermal generation of silenes from allylsilanes [3,13,14], a concerted retroene elimination of propene was proposed. Thermal decomposition of allylamines [9][10][11][12] has shown that the rate of pyrolysis is dependent on the substituent on the N atom and on the acidity of the H atom likely to be transferred, suggesting a polar transition state with a, perhaps, less concerted mechanism than for the allyl ethers.…”

“…generation of some carbon-heteroatom double bonds; among these can be cited C‫ס‬O [4][5][6], C‫ס‬S [7,8], C‫ס‬N [9][10][11][12], C‫ס‬Si [13,14], and recently, C‫ס‬P [15,16].…”