Abstract:

9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO), a versatile heterocyclic organophosphorus compound, is widely used for halogen-free fire retarding. In order to improve the synthesis process of DOPO, much effort has been devoted to analyzing these four reactions:esterification, acylation, hydrolysis and cyclization. However, due to the absence of suitable methods or instruments for analysis, it only led to some ambiguous results. In this paper, ³¹P nuclear magnetic resonance(³¹P NMR) and measuring the temperature of alkali solutions for HCl absorption were adopted to characterize the reactions to obtain precise optimized conditions for esterification and acylation. By ³¹P NMR, the effect of esterification temperature, the ratio of o-phenylphenol(OPP) to PCl₃ and the addition order of reactants on the component content of products from esterification was discussed, and conditions for the highest content of o-phenyl ester phenoxy phosphorus dichloride(CC) were revealed as 80 ℃, a feeding order of adding OPP into PCl₃ with 25%~50% extra PCl₃. The dependence of the content of 6-chloro-dibenzo[c.e][1,2]-oxaphosphorine(CDOP) in products from acylation on the component content of products from esterification was also established. The acylation was investigated by measuring temperature change of aqueous NaOH when it absorbed HCl released from the reaction to give desirable reaction temperature and dosage of catalysis. In the present work, when 0.2 g catalyst is used, acylation of 0.2 mol esterified products does not proceed at 150 ℃, but has increased rate at higher temperatures and can finish in 4 h at 180 ℃ and 1.5 h at 190 ℃; a catalyst dosage of 1~1.5 g catalyst per mol OPP is practicable for acylation at 180 ℃ which can complete in 3~4 h.

Key words: flame retardant, dihydro-oxa-phosphaphen-anthrene-oxide(DOPO), esterification, acylation