Abstract
In this article, we report the synthesis of 2,4,6-substituted s-triazine-based organophosphorus compounds via a two-step process, which enables their production in high yields, and with a high purity as solids. In the first step, a Michaelis–Arbuzov rearrangement of cyanuric chloride with triethyl phosphite afforded 2,4,6-trisdiethoxyphosphinyl-1,3,5-triazine (HEPT). Subsequently, the nucleophilic substitution reaction on the triazine carbon was achieved, owing to the electron-withdrawing ability of the phosphonate groups. This characteristic of HEPT facilitated its derivatization with bi-functional amines, producing novel P–C containing bridged triazine organophosphorus compounds. The molecular structures of all of the compounds were confirmed by NMR spectroscopy, CHN elemental analysis, and single crystal X-ray analysis. In the thermogravimetric analysis in an N2 environment, >33% char formation was observed for the bridged compounds. The chemical composition analysis of the char obtained under the oxidative thermal decomposition of the bridged compounds confirmed the presence of phosphorus- and nitrogen-enriched species, which indicate their function in the condensed phase. Comparatively, the detection of HPO and H–C≡P in the gas phase during the pyrolysis of the bridged compounds can act as a source for PO•, which is known for its gas phase flame inhibition reactions. The synergy of significant char formation and the generation of intermediates leading to PO• during pyrolysis makes these molecules promising flame-retardant additives.
Highlights
Nitrogen-containing heterocycles are common organic compounds that play a crucial role in different applications
Cyanuric chloride was used as a starting material to synthesize bridged triazine-based organophosphorus compounds
The Michaelis–Arbuzov rearrangement of triethyl phosphite with cyanuric chloride afforded intermediate HEPT, which was used for the further substitution reactions
Summary
Nitrogen-containing heterocycles (azaheterocycles) are common organic compounds that play a crucial role in different applications. The symmetric 1,3,5-triazine, which is referred to as s-triazine, is considered monotonous [1], new synthetic approaches were investigated to produce new substituted 1,3,5-triazine derivatives [2]. The most common chemical reaction hereof is the substitution of the chlorine atom of the commercially available 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride) with nucleophiles [3]. Cyanuric chloride has been known since the early 1800, and has a similar reaction. Molecules 2019, 24, 2672 profile to acyl chlorides, rather than alkyl chlorides; since it has received great attention as a chemical reagent for different chemical reactions, as shown in Scheme 1 [4,5]. General schematic example for using cyanuric chloride as a chemical reagent
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