Prepn. of anhydrous sodium dithionite - by reacting sulphur di:oxide with sodium formate and sodium hydroxide, in aq. organic medium with addn. of methyl formate

摘要

Anhydrous sodium dithionite is prepd. by the action of SO2 on NaOOCH in excess and NaOH in a reaction medium formed of H2O and an organic solvent. Methyl formate is also added to the reaction mixt. in a proportion which is =15 wt. % w.r.t. the organic solvent, and pref. when the reaction mixt. contains >=66% of the theoretical amt. of SO2 to be used. The molar proportions of NaOH and SO2 do not exceed the ratio 1:2. The process gives increased yields of a purer and more stable sodium dithionite, with a better granules size distribution. Pref. the initial reaction mixt. contains all the NaOH required in the form of an aq. soln., possibly contg. a part of the NaOOCH and/or the SO2. The remaining NaOOCH and SO2, as well as the cH3OOCH, are then added to this initial reaction mixt.