# Can I use calcium chloride instead of sodium sulfate as drying agent?

In the synthesis of N-ethoxycarbonyl L-proline methyl ester from L-proline and ethyl chloroformate, I dry the organic phase over sodium sulfate. Can I use calcium chloride instead of sodium sulfate? I searched for information and I found that calcium chloride can contain basic impurities such as $$\ce{Ca(OH)2}$$ and $$\ce{CaCl(OH)}$$. Does someone know if it is actually the case? If it would be correct I think that it cannot be used because the impurities can hydrolyse the ester.

• Why you want to change the drying reagent? – Mathew Mahindaratne Aug 4 '20 at 15:58

Similar to @MathewMahindaratne's comment: if you know the drying agent suits your needs well enough, keep it. In particular here, sodium sulfate is a neuter one (as is calcium sulfate, too) is a safe option because while drying the organic layer, the agent will neither protonate, nor deprotonate your product. Thus, if the protocol states $$\ce{Na2SO4}$$, stick to it.
This is in contrast to calcium chloride which not only will contain traces of calcium hydroxyde when taken from the jar, but upon contact with additional water (a.k.a. while drying your organic solution) will create new $$\ce{Ca(OH)2}$$ and thus is considered a basic (and potentially deprotonating) drying agent. Note, $$\ce{MgSO4}$$ is considered as an acidic drying agent. Using the wrong salt solutions or drying agents during the workup actually may cleave off (e.g., protecting) groups and thus complicate the isolation and purification of your product.