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This question is inspired from the following questions:

  1. Reaction of citric acid and calcium chloride
  2. Precipitation of citric acid by CaCl2 and Ca(OH)2?

The answer to the 1st question says that calcium citrate is highly unlikely to form from calcium chloride and citric acid because of its inability to be present in deprotonated form and will not precipitate in acidic medium. 2nd question also addresses a similar kind of problem. But what about calcium benzoate?

Which calcium salt can succesfully precipitate calcium benzoate from benzoic acid? Would calcium hydroxide work for that? I am pretty sure calcium chloride won't work because it is a good dehydrating agent and would rip off water molecules to form something else. Calcium benzoate is also somewhat more soluble in water than calcium citrate. So, what should be the necessary measure to successfully precipitate calcium benzoate?

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  • $\begingroup$ I think calcium hydroxide would be sufficient to form calcium benzoate solution, but the solution must be heated to increase the solubility of calcium hydroxide and benzoic acid. Another method is to dissolve benzoic acid in NaOH solution(in equimolar amounts) and then react Ca(NO3)2 with it. $\endgroup$ – Shoubhik Raj Maiti Mar 1 '18 at 8:27
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Thanks to @Shoubhik who pointed out that calcium hydroxide is good enough to make calcium benzoate. To support this claim, I found a patent which indeed describes that calcium hydroxide was used to make calcium benzoate (See comments). Here is the summary of the patent:

The invention relates to a processing method for synthesizing calcium benzoate at low temperature. The method comprises the following steps: heating and stirring 65-85kg of industrial-grade benzoic acid, 28-32kg of calcium hydroxide, 1-3kg of catalysts comprising triethanol distearate, ethylene distearamide and ethylene bislauramide and 300-500kg of clear water in a reaction kettle at 333-363 K to react for 2-4 hours; and then adding 5-15kg of separant, stirring for half an hour, filtering and drying. The method provided by the invention can be used for directly synthesizing calcium benzoate, thereby lowering the equipment investment, reducing the working procedures, lowering the labor intensity of workers, increasing the output, enhancing the quality, lowering the cost and preventing the environmental pollution.

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