Hoechst Aktiengesellschaft

Albert Mainski

Klaus Gehrmann

Alexander Ohorodnik

Stefan Schafer

Pure methyldichlorophosphane is recovered from a mixture containing phosphorus trichloride and methyldichlorophosphane as its principal constituents by distillation in two stages. Phosphorus trichloride and other low-boiling material are distilled off overhead in the first stage and methyldichlorophosphane is distilled off from high-boiling material in the second stage, the latter being fed with base product coming from the first stage. More specifically, there is dissolved in the said mixture, prior to admitting it to the first distillation stage, 0.01 to 1 weight % of an organic barium compound or 0.1 to 10 weight % of a non-ionic surfactant, and the base product coming from the first distillation stage is admixed, prior to admitting it to the second distillation stage, with 1 to 10 weight % of phosphorus oxychloride.

Production of pure methyldichlorophosphane

Dilute sulfuric acid contaminated with acetic acid and hydrogen chloride is purified with the resultant formation of concentrated sulfuric acid and acetic acid. To this end, the contaminated sulfuric acid is heated in a first step to at most 60.degree. C under 25-30 mm Hg so as to expel all of the hydrogen chloride together with minor proportions of acetic acid and water. In a second step, the sulfuric acid is heated to at most 165.degree. C under 20-25 mm Hg so as to distil off the bulk of acetic acid together with water. In a third step, the sulfuric acid is cooled down to 60.degree.-90.degree. C, diluted with 10-30 wieght % of water with agitation and while cooling is continued. Following this, the sulfuric acid is heated to 160.degree.-165.degree. C under 20-25 mm Hg and thereby freed from the water and residual acetic acid.

Purification of sulfuric acid containing acetic acid

Crude hydrogen chloride gas obtained as a by-product in the production of chloroacetic acids by the catalytic chlorination of acetic acid with chlorine gas in contact with acetic anhydride and/or acetyl chloride, and contaminated with about 0.6 up to 3 % by volume of acetyl chloride is purified. To this end, crude hydrogen chloride gas is introduced into the base portion of a scrubbing zone and scrubbed countercurrently therein with 0.5 up to 20 liter, per normal cubic meter (S.T.P) of hydrogen chloride gas, of a cooled scrubbing liquid under circulation, consisting substantially of 20-80 weight % of concentrated H.sub.2 SO.sub.4, 15-60 weight % of acetic acid, and 5-50 weight % of water. The resulting purified moist hydrogen chloride gas issuing at the head of the scrubbing zone is introduced into the base portion of a drying zone and scrubbed countercurrently with precooled sulfuric acid under circulation.

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Rodenkirchen, Germany

Albert Mainski