Submitted to: Acta Crystallographica Section E: Structure Reports Online
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/23/2013
Publication Date: 8/31/2013
Citation: Fontenot, K.R., Easson, M.W., Fronczek, F.R., Condon, B.D. 2013. 1,1',4,5-tetrahydrotrispiro[1,3,2-diazaphosphole-2,2'-[1,3,5,2,4,6]triazatriphosphinine-4',6''-dibenzo[d,f][1,3,2]dioxaphosphepine-6',6'''-dibenzo[d,f][1,3,2]dioxaphosphepine]. Acta Crystallographica Section E: Structure Reports Online. 69(9):o1491-o1492. Interpretive Summary: The unambiguous determination of the title compound’s structure is necessary to achieve a true understanding of its nature. Several alternative analytical methods can be employed to determine structure such as nuclear magnetic resonance spectroscopy or mass spectroscopy, but none is as definitive as X-ray crystallography at revealing atomic interconnectivity in three dimensions. Obtaining a suitable crystal for X-ray analysis is something of an art, and many crystal structures simply cannot be obtained due to characteristic hydrogen bonding, inherent molecular instability, or the inability to produce a pure crystalline form. Additionally, there is a pressing need in the commercial sector for safe, environmentally-friendly flame retardants for application to cotton textiles. Many of the existing flame retardants contain halogenated species, many of which have been shown to persist for long periods of time in the environment or to bio-accumulate in animal tissues. The manuscript presents the total synthesis and X-ray crystallographic structure of the title compound which is shown to be an effective, non-halogenated, organophosphorus flame retardant in preliminary testing on cotton fabrics. These achievements are further enhanced by the ease with which the title compound was synthesized in overall high yield. The synthetic procedure required no column chromatography for purification and is, therefore, ideally suited for larger scale-up by industrial stakeholders.
Technical Abstract: The title compound 1,1',4,5-tetrahydrotrispiro[1,3,2-diazaphosphole-2,2'-[1,3,5,2,4,6]triazatriphosphinine-4',6''-dibenzo[d,f][1,3,2]dioxaphosphepine-6',6'''-dibenzo[d,f][1,3,2]dioxaphosphepine], C26H22N5O4P3, at 100°K has monoclinic (P21/c) symmetry and is achieved in a two step synthesis that does not require chromatography. This molecule has a strained seven membered spirocyclic structure at the P1 and P2 position and a five membered ring containing new P—N bonds at the P3 position. Preliminary data of this novel compound has shown that it is a promising flame retardant.