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Offline donaxad704

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Question about recrystallisation
« on: June 21, 2021, 03:51:13 PM »
Hi,
so I am quite new into organic recrystallisation and want to try out recrystallisation with 2,4-Disulfophenyl-N-tert-butylnitrone. I found a tutorial recommending to use for 9g of this about 100ml acetone and 100ml of ethanol for the crystallisation. I know it has a theoretical solvability in water of about 79mg/ml at room temperature and is hardly soluble in ethanol (2mg/ml if I recall correctly). Can somebody maybe explain me how the crystallisation process in this case would work. In my idea one could either dissolve the 2,4-Disulfophenyl-N-tert-butylnitrone first in this solution and then slowly evaporate the acetone in the hope that by this the solvability decreases slowly. Alternatively I thought about slowly adding more ethanol to decrease solvability. Finally another option might be to just heat up this mixture to roughly 55 degree Celsius, add up as much 2,4-Disulfophenyl-N-tert-butylnitrone until one has reached the saturation point and then just cools it down to room temp and then even to 0 degrees and lower. Which of these options is in your opinion the best way to go.

I also thought of trying out this experiment with Disodium 4-formyl-1,3-benzenedisulfonate but did not find any detailed info about the solubility of this compound for ethanol, acetone, methanol or water. I believe that it might dissolve easier in water and a little bit less in ethanol, but this is just my guess. Does anybody have a more sophisticated guess.

Looking forward for answers

Cheers!

For this I would use a 1:1 mixture of 100ml acetone and 100ml for roughly 9g of 2,4-Disulfophenyl-N-tert-butylnitrone. The question is whether I can 'train' for this crystallisation by using instead Disodium 4-formyl-1,3-benzenedisulfonate? It would be especially interesting to know which one of these dissolves easier in ethanol, methanol and water. For 2,4-Disulfophenyl-N-tert-butylnitrone I already know that it does not dissolve very well in ethanol at room temperature but

Offline jeffmoonchop

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Re: Question about recrystallisation
« Reply #1 on: June 21, 2021, 04:42:45 PM »
Whats the solubility in acetone?

In general, the slower the evaporation or cooling, the fewer the nucleation sites and larger the crystals. Evaporation is often much slower than cooling unless you have a controlled cooling machine.

If you solution is too clean there will be nothing for critical sized nuclei to continue growing on, so its less likely it will grow, even though the solution is supersaturated. If the supersaturation continues to rise in this state, its more likely you will achieve primary nucleation, but then the crystallization will proceed rapidly, as supersaturation drives crystallization.

If a single nuclei starts to grow in a highly supersaturated solution, it will act as a seed for other nuclei to attach onto, if this process is too rapid, you'll get many nuclei, which will end of smaller.

So its best to hold at low supersauration until nucleation, which is an unpredicatble event. As low supersaturation, you can try scratching the solution to give the solute something to grab onto.

Offline donaxad704

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Re: Question about recrystallisation
« Reply #2 on: June 29, 2021, 02:49:55 PM »
Thank you for your reply and sorry for the late response. Unfortunately I do know almost nothing about 2,4-Disulfophenyl-N-tert-butylnitrone in terms of solvability. I only now the solvability in ethanol and water and for these two even only at room temperature. That was why I hoped that maybe 4-formyl-1,3-benzenedisulfonate might have similar properties as 2,4-Disulfophenyl-N-tert-butylnitrone such that one could do solvability experiments on 4-formyl-1,3-benzenedisulfonate and find the solvability of this substance in ethanol, water, methanol and acetone at various temperatures and then transfer these values (albeit with some error) for 2,4-Disulfophenyl-N-tert-butylnitrone.


Do I understand you correctly, that you correctly, that without a proper nucleus to start crystallisation the crystallisation will not happen for a long time until it suddenly happens very rapidly. So in order to compensate it one should already provide a nucleus (for example a hair in the solution) such that the crystallisation happens immediately at the saturation point?

May I also ask how you would proceed for this crystallisation if you knew that ethanol is the solvent in which  2,4-Disulfophenyl-N-tert-butylnitrone does not dissolve very well and acetone the one in which supposedly it solves very well?

Offline jeffmoonchop

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Re: Question about recrystallisation
« Reply #3 on: June 30, 2021, 10:46:56 PM »
If you want nice crystals, prepare your saturated solution in the solvent that dissolves more compound. Its often the case that the metastable band width will be wider, so you can bring the solution to a point of low supersaturation, without it crashing out.

To ensure a saturated solution, add your compound until it doesn't dissolve anymore. Filter the solution and you'll be left with a saturated solution. Bring it to low supersaturation by cooling slightly or allowing to evaporate. It may take a long time for crystals to appear, so scratching with a needle may help. If its still taking too long, raise the supersaturation again until you get something.

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