Reduction of 4-methoxydiazosulfonate to 4-methoxyphenylhydrazinesulfonate
The reduction of a diazosulfonate to a phenylhydrazine salt.
REACTION
The reduction is effected by sodium bisulfite as follows:
However, the resulting bisulfate can affect the yield of the reaction, and so base is added to neutralize it as it forms:
NaHSO4 + NaOH -> Na2SO4 + H2O
PROCEDURE
In 40ml of water, dissolve 4.855g (20mmol) of the diazosulfonate (prepared in a similar fashion to that described in my 4-hydroxydiazosulfonate
procedure).
Add 2.08g (20mmol) NaHSO3.
Add 4ml 5M NaOH solution (this can probably be a bit weaker or stronger as long as molar amount is conserved. I just had this concentration on hand.
Having said that, minimizing the amount of water is useful).
Heat this solution with stirring to 50 - 60C for 0.5 hr.
On removal from heat and cooling to room temperature, a mass of shiny yellow crystals precipitates. The crystal are filtered and pressed dried, then
heated at 50C for a few hours to dry completely.
3.29g collected after drying = 13.8mmol = 69% yield.
The most noticeable difference I have seen between the diazosulfonates and the phenylhydrazinesulfonates is the much more "crystalline" nature of the
result.
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