How to synthesize sodium metabisulfite?

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?




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.](https://chemistry.stackexchange.com/a/17324/17368)


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](https://onlinelibrary.wiley.com/doi/10.1002/9780470132333.ch49)


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