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Natural Science Forum / Chemistry / Organic Synthesis / September 2003Carbon-13 enriched trifluoroacetic acid
Hi, Uranium is enriched as the more volatile UF6. Since 13C chemistry is so expensive we need to think through our options, carefully. We need trifluoroacetic acid enriched (at least) at the 2 position. Natural abundance TFA is cheap in quantity. The formula weight of TFA is 114 so isotopic enrichment of TFA should be a lot easier than isotopic enrichment of UF6. The use of fractional distillation (or possibly fractional crystallization) is worth considering. As far as I know the most number of theoretic plates per unit distance can be achieved using a high quality vacuum jacketed spin band distillation column refuxed at equilibrium for a long time. Comments? How could we estimate the b.p. increase of doubly enriched TFA with F.W. 116? What would be the required number of theoretical plates necessary to achieve a given % enrichment over a given period of time. Comments? Thanks. dgn  SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA > Hi, > Uranium is enriched as the more volatile UF6. Since 13C chemistry is > so expensive we need to think through our options, carefully. We need [quoted text clipped - 9 lines] > would be the required number of theoretical plates necessary to > achieve a given % enrichment over a given period of time. Comments? Ask ISOTEC. They isolate ~100 kg of highly enriched C-13 every year. I doubt you can see any TFA isotopic separation in 100 meters of open bore capillary GC much less spinning band distillation. SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) "Quis custodiet ipsos custodes?" The Net! -- Paul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA David Naugler wrote > Hi, > Uranium is enriched as the more volatile UF6. Since 13C chemistry is > so expensive we need to think through our options, carefully. We need [quoted text clipped - 9 lines] > would be the required number of theoretical plates necessary to > achieve a given % enrichment over a given period of time. Comments? Sorry for the error in logic. Doubly enriched 13C TFA would only have a relative abundance of 10^-4. We would be happy to achieve single enrichment TFA, F.W. 115. That would give 50% enrichment in the 2 position but a 50X improvement in signal intensity in carbon/fluorine HSQC. Any helpful comments and ideas would be greatly appreciated. dgn SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<bjibid$rho@panther.Gsu.EDU>... > David Naugler wrote: > > Hi, > > Uranium is enriched as the more volatile UF6. Since 13C chemistry is > > so expensive we need to think through our options, carefully. We need [quoted text clipped - 9 lines] > > would be the required number of theoretical plates necessary to > > achieve a given % enrichment over a given period of time. Comments? > Ask ISOTEC. They isolate ~100 kg of highly enriched C-13 every year. ISOTEC wants tens of thousands of dollars per gram, hence the question. > I doubt you can see any TFA isotopic separation in 100 meters of open > bore capillary GC much less spinning band distillation. Thanks for dissuading me from a bad idea. Remaining possibilities are related to laser enrichment from freons or oxidative fluorination of 13C enriched acetic acid, which is cheap. Most likely, I'll end up doing electrochemical oxidative fluorination. SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA > Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<bjibid$rho@panther.Gsu.EDU>... > > David Naugler wrote: [snip] > > Ask ISOTEC. They isolate ~100 kg of highly enriched C-13 every year. > [quoted text clipped - 8 lines] > 13C enriched acetic acid, which is cheap. Most likely, I'll end up > doing electrochemical oxidative fluorination. You could look to see if intuition obtains in fact. How thermally stable is TFA? I can't see any sort of throughput at usable enrichment, if any. I've done vacuum teflon spinning band distillations separating cis- from trans-farnesol. Even with a trivially easy GC separation I managed less than 0.5 ml/hr at 95% enrichment through a foot of spinning band after a day of equilibration. Vacuum is bad for theoretical plates. One starts thinking "MTBF" for the apparatus. I'd try turning vinegar into TFA. If that goes well, do it with C-13 acetic acid. All the kinetic enrichment schemes I've seen rely on exquisitely equilibrated perfect circumstances or a large number of almost perfect stages. It's OK if it is business over years, but kinda rough as a lab prep. There are plants that produce fluoroacetic acid [hence from (C-13)O2] as an anti-feedant, but not TFA to my knowledge. SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) "Quis custodiet ipsos custodes?" The Net! -- Paul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA |
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