product can be obtained in an economic manner the flame retardant cellulose can be present in the form of e g a fibre or a film depending on the shaping procedure regenerated flame retardant celluloses in accordance with the invention contain the compound s of formula i in quantities of 5 35 weight percentage preferably 10 25 weight percentage and in particular 25 weight percentage related to 100 weight percentage of pure regenerated cellulose corresponding amounts of the compound s of formula i are added to the cellulose solution before shaping in the case of the lyocell process however the compounds of formula i can also be added to an aqueous suspension of cellulose in tertiary amine oxides which is used for making the solution the manufacture of dispersions in accordance with the invention is performed in well known manner e g by grinding a concentrated mixture comprising a dispersion agent a dispersion medium and compound s of formula i e g in a ball sand glass bead or quarzite mill until the size of the undissolved particles lies in the average of 0 5 5 u03bcm preferably 1 u03bcm and if necessary by the adjustment of the desired concentration as a result of.