Reaction of 2-Imidazolidinone and 2-Imidazolidinethione with Formaldehyde. Pyrolysis and Mass Spectra of Their Reaction Products

Abstract

Methylol compounds were prepared by the reaction of 2-imidazolidinone [1 a] and 2-imidazolidinethione[ b] with formaldehyde. In all these reactions, bis(hydroxymethyl) cornpounds were stable and can easily be isolated. Pyrolysis of [1 a], [1b], 1, 3-bis(hydroxymethyl)2-imidazolidinone [2 a] and 1, 3-bis(hydroxymethyl)-2-imidazolidinethione [2b] were investigated by the thermal analysis. The cleavage mechanism by electron impact for [2 a]and [2b] was investigated by mass spectra. The pyrolysis reaction of bis(hydroxymethyl)compounds was found to be thermal decomposition via the polycondensation reaction stage after the molten state (Fig.2). The polycondensation stage obeyed the first order kinetics which characterizes the ordinary thermal polymerization in the solid state (Fig.5). The kinetic data of the polycondensation reaction were evaluated by analysis of the dependences of the area of isothermal DSC curves upon the reaction time (Table 2, 3, 4). The DTA and DSC curves for [1 a] revealed a single reversible endothermic peak resulting from polymorphism at a temperature lower than its melting point (Fig.1). In the decomposition by electron impact of [2 a] and [2b], the cleavage of the fivemembered ring which corresponded to the molecular ion peaks for [1 a] and [1 b] was considered to take place after a successive cleavage of the two side chains. The main fragmentation mechanism for [1a]and C.. /1: 1 was found to consist of three cleavage modes (Scheme 2, 3, 4). Deuterium labeling has enabled mechanistic interpretations for the principal ion (m/e 30)being formed in the mass spectric fragmentation of [1 a]. High resolution mass spectrometry established the composition of many peaks in the low-resolution spectra of the compounds studied (Table 5).