It is known that Dimethyl Sulfoxide (DMSO) is a highly polar solvent. It is easily miscible with fatty acid like Oleic acid . My question is that does varying pH affect on the miscibility of DMSO and Oleic acid ? I have observed an increasing turbidity of this solution with increasing pH. What could be the reasons. Is it forming any emulsion ?
Dear Koushik:
You add an aqueous alkali solution to increase the pH? Water and dimethyl sulfoxide are dissolved in each other in unlimited quantities. Therefore, no phase separation, and should not form an emulsion. Most likely in solution formed of micelles oleic soap. In aqueous solution of dimethyl sulfoxide also occur hydrophobic interactions. See:
J. Chem. Faraday Trans. 1979. N3. P. 636-645
It seems the alkali and maybe also the soap have limited solubility in DMSO. I found a value of 0.13 g/l NaOH/DMSO.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwiclOmNwsLLAhVL63IKHXf7DLUQFggpMAE&url=https%3A%2F%2Fwww.researchgate.net%2Ffile.PostFileLoader.html%3Fid%3D55d7c60a61432517e68b4575%26assetKey%3DAS%253A273836749066240%25401442299179275&usg=AFQjCNHXXmN-OlMVLw14osZua3bO0H224g&sig2=zM_qKJMp__VpW_tGRmtPiw&cad=rja
You have carried out well-known synthesis of sodium oleate with all that it implies.
Thank you Prof. Mirgorod and Prof. Sobisch for your answers. I added Tetramethylammonium hydroxide (25% in aqueous solution) to increase the pH. Is it like that at high pH, COOH groups of oleic aicd get deprotonated and due to the change in electrostatic interaction between these charged groups of oleic acid micelles have been formed. The role of hydrophobic interaction is surely affecting here as you mentioned.
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