Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of N-Alkylated Piperidines

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The standard molar enthalpies of formation ΔfH°m(l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization ΔlgH°m of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase ΔfH°m(g) were derived for: A −(61.39 ± 0.88); B −(88.1 ± 1.3); C −(105.81 ± 0.66); D −(126.2 ± 1.3); E (−88.21 ± 0.75); F −(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol−1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.

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