Synthesis Of Pyrophosphate And Phosphorus-nitrogen-based Flame Retardants

Pyrophosphate and dithiopyrophosphate are two kinds of classic flame retardants, which are widely used in viscose fibers with the method of add blending. In industrial production, they are synthesized by two steps. Neopentyl glycol as the starting material reacted with thiophosphoryl chloride or phosphorus oxychloride to get the intermediate, then the intermediate was reacted with water to prepare target products. However, the process requires tedious steps to separate and pure the intermediate, which largely increases the production cost. In this paper, the industrial synthetic route of this kind of flame retardant was improved, designing one-pot process without separation the intermediates. Meanwhile, the paper optimized the reaction conditions, such as solvent, catalyst, acid binding agent and chose toluene as solvent,4-dimethylaminopyridine as catalyst and triethylamine as acid binding agent and the overall yield was84.1%and83.2%respectively. We designed recovery distillation device and the recovery rate of toluene and triethylamine was80%, which significantly reduced the production cost.Organic phosphorus-nitrogen-based flame retardants containing both phosphorus and nitrogen elements have better effect than phosphorus compounds. The nitrogen element mainly comes from the reactants, such as amine and diamine. In this paper, pyrophosphate as raw material reacted with ethylenediamine,1,2-diaminopropane and1,3-diaminopropane respectively and prepared three phosphorus-nitrogen-based flame retardants with the yield of85.6%,81.7%and82.3%respectively.Pentaerylthritol diphosphonate dichloride containing symmetrical chloride group is bifunctional reactive flame retardant, and it can react with compounds containing amino, imino or hydroxyl to prepare more complex flame retardants. It is synthesizd in the paper by pentaerylthritol and phosphorus oxychloride with mole ratio of1:5, and the yield is80.6%. Besides, it reacted with aniline, p-toluidine and piperidine respectively to prepare three spiro phosphorus-nitrogen-based flame retardants with the yield of75.3%,71.6%and82.6%respectively.