I would like to scan NMR for a compound name : 4,4'-dibromo-2,2'-diaminobiphenyl.
According to some papers, the NMR solvents used are either CDCl3 or DMSO-d6.
However, when I try to dissolve my sample in a vail, they are clear at first. When I shake it to mix them well, it turned into white suspension.
Am I dissolved it in a wrong way or shall I use another NMR solvent, like acetonitrile?
It is possible that there is trace DCl in the CDCl3 (a common impurity in deuterochloroform), which reacts with the analyte to form a salt which precipitates. You can neutralize the CDCl3 using basic alumina immediately prior to dissolving the sample (filter carefully to avoid getting alumina in the NMR tube).
I don't know of too many molecular compounds that are insoluble in dmso. You might try just making samples of smaller concentrations (you don't need that much for a good proton spectrum). Or it could be that there is a significant amount of pi-pi interactions that the dmso can't break up. It's rather expensive and smelly, but pyridine-d5 might be a good solvent for diaminobiphenyls.
It is possible that there is trace DCl in the CDCl3 (a common impurity in deuterochloroform), which reacts with the analyte to form a salt which precipitates. You can neutralize the CDCl3 using basic alumina immediately prior to dissolving the sample (filter carefully to avoid getting alumina in the NMR tube).
I don't know of too many molecular compounds that are insoluble in dmso. You might try just making samples of smaller concentrations (you don't need that much for a good proton spectrum). Or it could be that there is a significant amount of pi-pi interactions that the dmso can't break up. It's rather expensive and smelly, but pyridine-d5 might be a good solvent for diaminobiphenyls.
Have you tried C6D6 or read the MSDS to see it's physical properties? Also just to clarify, are you saying the sample initially dissolves when you add CDCl3 or DMSO-d6 and precipitates out of solution? Or the white powder is never dissolved? Gently heating might dissolve the biphenyl compound, but use caution when heating.
hi,
first solution: you coul do as usual and than filtered the suspension into the NMR tube. With some luck you have enough dissolved compound in the filtrat.
second solution: are you sure of the purity of the 4,4'-dibromo-2,2'-diaminobiphenyl? I don't believe that the salt of it in DMSO insoluble. Check the purity! you may have some inorganic compound coming from the work-up.
Rather than using straight CDCl3 or DMSO-d6, it is often useful to add just a small amount of DMSO-d6 to the CDCl3. That mixture often dissolves things that do not dissolve well in either separately. In addition, as suggested above, I would filter CDCl3 through basic alumina to remove DCl, and be sure the DMSO is dry. (It is quite hygroscopic.)
You can use deuterated aromatic solvents, methanol, the mixtures of methanol/CDCl3, methanol/water or CF3COOD.
Your description of the sample dissolving at first and then precipitating sounds like it is reacting with dissolved CO2 to form a carbamate which precipitates. You may need to bubble N2 through the solution to avoid this.
Dear Shu,
to check for presence of DCl in CDCl3 a simple trick is to extract one 1ml of CDCl3 with 1ml of water by shaking. If the pH (measured prior and after this extraction) of the aqueous phase changes substantially (>0.5 units) you have acidic DCCl3.
Have you taken a NMR spectrum of your milky suspension (which should work)? To see what you find.
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