How to synthesize sodium metabisulfite?

Question

I am looking for ways to produce sodium bisulfite from $\ce{SO2}$ and $\ce{NaOH}$, but sources talking about $\ce{Na2S2O5}$ is quite scarce.

Do you have any recommendations of articles, books or any other type of source?

Answer 1

Wikipedia is a good start.

When you treat a solution of suitable base, say sodium hydroxide or sodium bicarbonate with sulfur dioxide, you get sodium bisulfite.

$$\ce{SO2 + NaOH → NaHSO3}$$ $$\ce{SO2 + NaHCO3 → NaHSO3 + CO2}$$

Now the same reaction can also lead to sodium metabisulfite. When the reaction is conducted in warm water, $\ce{Na2SO3}$ initially precipitates as a yellow solid but when you apply more $\ce{SO2}$, the solid dissolves and on cooling, it crystallizes to sodium metabisulfite.

$$\ce{SO2 + 2 NaOH → Na2SO3 + H2O}$$ $$\ce{SO2 + Na2SO3 → Na2S2O5}$$

Alternatively, if you have heaps of sodium bisulfite, you can simply heat it to get sodium metabisulfite.

You may refer to this book: Johnstone, H. F. (1946). "Sulfites and Pyrosulfites of the Alkali Metals". Inorganic Syntheses pt .2 pp. 162–167. doi:10.1002/9780470132333.ch49