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How would one prepare magnesium citrate from magnesium chloride and citric acid? Will it work if I just heat a mixture of magnesium chloride and citric acid in water? I'd expect HCl to vaporize off.

Does anyone have experience with this reaction? Yield, purity, concentrations, byproducts, ... So if I just try to make magnesium citrate directly by mixing the chloride and citric acid, will that work – or is the citrate going to degrade/decompose into organic byproducts?

Background

I have a large amount of high purity magnesium chloride on hand which is slowly deliquescing anyway. I'd like to convert it into magnesium citrate (molar ratio of magnesium to citrate isn't hugely important, aim between 1 and 1.5) which is easier to store – and I need it anyways (need magnesium solution chelated with citrate and bitartrate).

I figure I could buy citric acid food grade, which is cheap enough, to make magnesium citrate. Objective is to have a high yield, low energy usage if possible (not having to boil off loads and loads of water, not having many steps), and no byproducts / few and easy purification steps necessary (a high grade end result consisting of only citrate and magnesium).

Economic feasibility (answer)

Magnesium chloride hexahydrate costs about 2.5 €/mol and sodium carbonate 1.1 €/mol. The product, magnesium carbonate is worth about 2.6 €/mol. So converting to carbonate results in a loss.
Citric acid monohydrate costs about 2.6 €/mol. The product, magnesium citrate is worth about 12.3 €/mol. So this step is profitable (gain 12.3 at a cost of 2.6+2.6).
Converting magnesium chloride into its citrate directly (if it were at all possible) would be profitable (gain 12.3 at a cost of 2.6+2.5).

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Eventual direct mixing of $\ce{MgCl2}$ and $\ce{H3Citr}$ to get $\ce{MgH-Citr}$ and $\ce{HCl}$ and eventual precipitation of the citrate would hit the stumble stone of acidification of solution, suppresion of dissociation of citric acid and stalled precipitation. You will probably end up wasting all.

You can mix solutions of magnesium chloride and sodium carbonate, filter out precipitated magnesium carbonate and dissolve it in citric acid solution to get magnesium citrate.

$$\begin{array}{|l|c|C} \hline \text{Compound} & \text{Molar mass }\pu{[g mol-1]}(*) & \text{Solubility }(**) \\ \hline \ce{MgCl2 . 6 H2O} & 203.31 \\ \ce{MgCl2} & 95.21 & \text{54.3 g/(100 mL) (20 °C)(anh)} \\ \hline \ce{Na2CO3.10 H2O} & 286.14\\ \ce{Na2CO3} & 105.99 &\text{ 16.4 (15 °C) / 34.07 (27.8 °C)(anh)}\\ \hline \ce{MgCO3} & 84.31\\ \hline \ce{C6H8O7. H2O} & 210.14 & \text{59.2% w/w (20 °C)}\\ \ce{C6H8O7} & 182.12\\ \hline \ce{C6H6MgO7} & 214.41 & \text{20 g/100ml} \\ \hline \end{array}$$

(*) (Rounded) molar masses have been taken from respective compound Wikipedia pages. (**) Solubility data have been taken from respective compound Wikipedia pages.

Compounds react with each other in 1 : 1 molar ratio, so the respective masses from the table are to be taken.

E.g. $\ce{\pu{203.31 g} MgCl2 . 6 H2O \text{and} \pu{286.14 g} Na2CO3.10 H2O}$
leads to $\ce{\pu{84.31 g} MgCO3}$.

Adding $\ce{\pu{210.14 g} C6H8O7. H2O}$
leads to $\pu{214.41 g}$ of magnesium citrate.

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  • $\begingroup$ It is always advantageous to provide the purpose and context of questions, leading to better answers and avoiding negative side effects, if responders know circumstances. If they know, they can for some scenarios say *Do not do this" or "Do rather that". $\endgroup$
    – Poutnik
    May 26 at 10:37
  • $\begingroup$ But at any rate, your solution using carbonate first seems easy and cheap enough. $\endgroup$
    – Mister Sir
    May 26 at 11:33
  • $\begingroup$ Oops I hadn't yet calculated the amount of sodium carbonate required. That is a lot of sodium carbonate I'm going to waste; I wonder if the step can be skipped. $\endgroup$
    – Mister Sir
    May 26 at 11:50
  • $\begingroup$ So I did some economic calculations. Converting MgCl hexahydrate into the carbonate makes a huge loss. So I can better try to sell my stock. Making Mg citrate is profitable. (see what I appended to my question) $\endgroup$
    – Mister Sir
    May 27 at 9:27
  • $\begingroup$ Say, what if I attempted to mix MgCl2 with citric acid directly, but added NaOH to overcome the acidification tumble stone? $\endgroup$
    – Mister Sir
    May 27 at 10:52

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