I am optimizing the method of developing natural deep eutectic solvent by using different methods, molar ratio and water content. For heating and stirring method, I used 1:1 Choline chloride:1,2 propanediol. The combination does not form liquid either direct heating or in water bath up-to 2 hours. The temperature is below 100 degree C. I tried to add minimal amount of water (less than 50%). However, the combination does not form homogeneous solution. It only form clear homogeneous solution when I put more water (160%) and its stable at room temperature. My concern is some journals mention the excessive water content may disturb the hydrogen bonds between Choline chloride and 1,2 propanediol. I tried to rotavap to remove water content and it starts recrystallising again. I repeated the experiment by using total dried Choline chloride (freeze dried) after reading some suggestions from previous researchers that had similar issue that caused by wet Choline chloride. However, I obtained similar results 😢. May I have some other suggestions or opinions that may solve the problem? Thanks in advance
Why are you using a 1:1ratio of Choline chloride and propanediol? The literature that I have seen suggests a 1:2 or 1:3 ratio of choline chloride: propanediol.
Joe Olechno, I started off with 1:1 choline chloride: propanediol then I increased the molar ratio 1:2, 1:3, 1:4 and 1:5. I notice as I increased the amount of propanediol. the water required less in term of molarity but still more than 50%. I want to determine at which molar ratio is the best for the extraction of flavonoid from my plant extract.
For those arriving at this question: to properly answer this question you have to measure the solid-liquid phase diagram. It will tell you the maximum solubility of choline chloride in 1,2-propanediol at a certain temperature (e.g. 30 ºC). Probably a choline chloride mole fraction of 0.5 (1:1) is higher than the maximum solubility at the temperatures you work, resulting in the precipitation of (what is probably) pure choline chloride.
Adding water increases the solubility (lowers the melting point) and can be a solution. Of course also within the thermodynamic limits.
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