Abstract: A process for the preparation of phosphonic acid dihalides of the formula ##EQU1## IN WHICH R is .alpha., .beta.-unsaturated alkyl, .alpha., .beta.-unsaturated alkyl, phenyl or benzyl and may be further substituted, which comprises reacting corresponding phosphonic or pyrophosphonic acids or their functional derivatives with acid halides of the formula (CO).sub.n Hal.sub.2 where n is 1 or 2.

Abstract: Flame-repellant linear polyesters are obtained by incorporating by condensation phosphorus-compounds having the formula ##EQU1## wherein R and R.sub.1 are organic radicals which may also contain hereto atoms into the linear polyesters, preferably those from terephthalic acid and ethylene glycol. These polyesters are materials of which flame-repellent filaments, fibers, sheets, press-moulded and injection-moulded articles may be made. Products of the invention can be used whereever especially acute risks of ignition and fire exist.

Abstract: Production of halogen-containing tertiary phosphine oxides of the general formula I ##EQU1## in which the substituents R.sub.1, R.sub.2 and R.sub.3, being identical or different, stand for an alkyl, alkenyl, aryl or aralkyl radical, at least one of those radicals containing at least one aliphatically combined halogen atom. The compounds are made by reacting one or more compounds of the general formula II ##EQU2## in which R.sub.4, R.sub.5 and R.sub.6, being identical or different, stand for an alkyl, alkenyl, aryl or aralkyl radical, at least one of those R.sub.4, R.sub.5 and R.sub.6 radicals containing an aliphatically combined hydroxyl group, with at least equivalent proportions, based on the number of hydroxyl groups, of gaseous hydrogen halide with agitation, if desired, at temperatures within the range about 100.degree. and 300.degree.