Sciencemadness Discussion Board

Calcium formate synth question

angelhair - 27-1-2011 at 20:42

I was looking at US Patent 5248818 "Process for the production of calcium formate"

Abstract;

"Calcium formate is produced in aqueous phase by reaction of calcium hydroxide with formaldehyde in the presence of hydrogen peroxide or by reaction of calcium peroxide with formaldehyde. The molar ratio of CaO or Ca(OH)2 to H2CO to H2O2 is 1 to 2 to 1-1.2 and the molar ratio of CaO2 to H2CO is 1 to 2. Calcium formate is obtained in an almost substantially quantitative yield and in highly pure form. The process avoids the disadvantages of prior processes for the production of calcium formate from calcium hydroxide and formaldehyde."

They also use an inhibitor to limit formation of formoses. In one example;

76.4 g calcium hydroxide (97% by weight; 1 mol), 600 ml water, 0.5 g NaBO2.4 H2O (0.0036 mol) and 162.5 g formaldehyde (37% by weight; 2 mol) are introduced into a reactor equipped with a stirrer and gas outlet pipe at a temperature of around 40.degree. to 50.degrees C. 120g H2O2 (30% by weight; 1.05 mol) is added dropwise over a period of 15 minutes with intensive cooling at a maximum temperature of up to 60.degrees C., followed by stirring for 30 minutes. The insoluble lime constituents (gangue) are filtered off. 950 ml of a colorless solution having a pH value of 7.2 and a residual formaldehyde content of 0.06% are obtained. Yield of calcium formate: 124.0 g = 95.3% of the theoretical."

What concerns me is the point where you evaporate to dryness. Suppose your formaldehyde is old and less than 37% and suppose you use more exess of H2O2 and evaporate in a water bath or whatever. I know heat and alkaline conditions can deteriorate the peroxide, but surely some H2O2 might remain and be concentrated. Am I right in thinking there may be some potential dangers here?










ScienceSquirrel - 28-1-2011 at 03:24

I would not worry about a slight excess of hydrogen peroxide, it will decompose during the concentration stage.
If you live in the UK you could start from this stuff and calcium hydroxide, it would be easier and probably cheaper;

http://www.boots.com/en/Ataka-Bath-Stain-Remover-Kettle-Desc...

not_important - 28-1-2011 at 11:06

Yup - boiling the solution will slowly decompose the H2O2 and/or carry it off in the water-steam.

If you're really worried you could always make chloroform from calcium hypochlorite and ethanol, evaporate the aqueous portion to recover calcium format mixed with CaCl2, Ca(OH)2, and CaCO3. Treatment with concentrated hydrochloric acid gives a mix of water, formic acid, and CaCl2, distill ff the formic acid mixed with water.

bbartlog - 28-1-2011 at 16:50

Quote:
Treatment with concentrated hydrochloric acid gives a mix of water, formic acid, and CaCl2, distill ff the formic acid mixed with water.


Any suggestion on how to separate the HCl and formic acid in this workup, though? I mean if you really know exactly how much of of each constituent you have, you can of course add an exact stoichiometric amount of HCl and do just as you propose. And I guess you could also lowball the amount of HCl and sacrifice a little yield to avoid the problem. But if you do end up with HCl in solution with formic acid, how do you get just the formic acid? I'm actually curious because I have a solution of mostly-HCl with some formic acid (est. 20% HCl, 10% formic acid, in water), and can't figure out a particularly convenient way to separate them.
For additional formate you could also hydrolyze the chloroform that was produced, but I don't know that this can be done in a reasonable amount of time with Ca(OH)2.... might have to use KOH and then somehow switch out the potassium for calcium.

not_important - 28-1-2011 at 19:33

Just use slightly too little HCl, so there's excess format salt; say just above pH 4 or so. Bothersome to separate the mixed acids, I'd just sacrifice the HCl by adding sufficient Ca(OH)2 or CaCO3 to get get back to pH 3.3 to 3.5, then distill to pull off water and formic acid. Or take it all the way alkaline, dry it out, then add just enough HCl to from the formic.

Yeah, I've messed about with the hydrolysis of the chloroform in the mix, as opposed to just separating it. You could add NaOH or KOH sufficient to hydrolyse most of the CHCl3, boil off any of that remaining, and acidify the aqueous stuff to get mixed Ca+Na chlorides. As the intent is distill the formic acid away to NaCl or KCl aren't going to do harm, and as they are neutral pH they'll not affect the end point for acidification to speak of.

angelhair - 30-1-2011 at 19:07

Thanks for that. I think I'll try it anyway and then latter on give the chloroform method a go.

I'm aiming to get formic as dry as possible, I don't need it dry, I just want to do it so when I get the dry Calcium formate I'm going to put some in a wash bottle and gas it with HCL.

I believe this will probably take a long time as I don't have any formic to use as a solvent, but I think it will work.

ScienceSquirrel - 31-1-2011 at 04:56

Quote: Originally posted by angelhair  
Thanks for that. I think I'll try it anyway and then latter on give the chloroform method a go.

I'm aiming to get formic as dry as possible, I don't need it dry, I just want to do it so when I get the dry Calcium formate I'm going to put some in a wash bottle and gas it with HCL.

I believe this will probably take a long time as I don't have any formic to use as a solvent, but I think it will work.


Why?

Think about what you are trying to do.

Working it out on paper, doing thought experiments is always a good start and cheaper than the real thing.

not_important - 31-1-2011 at 15:55

Note that highly concentrate formic acid is prone to slow decomposition, forming carbon monoxide and water. It thus both dilutes itself, and builds up pressure inside sealed bottles; concentrations above 95% (or maybe lower) are stored in bottles with self-venting caps and generally plastic bottles are used.

So it can be easier to just go for 85 to 90 percent formic acid, unless you really need a higher concentration for some specific purpose. If so it's better to make it soon before using it.