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Natural Science Forum / Chemistry / Organic Synthesis / September 2003acids for catalytic hydrogenation
Hello everyone, I'm want to conduct a catalytic hydrogenation under acidic conditions. The reference uses traces (0.5 mL per 20 mL solvent hexanes) perchloric acid (HClO4), which for safety reasons and the lack of a washdown fumehood, I cannot and don't want to use. I quick scan through Catalytic Hydrogenation by P. Rylander only mentions acid conditions using typical acids (sulfuric and hydrochloric) and acetic acid as solvent. I was thinking of using a trace amounts of trifluoroacetic acid in place of perchloric. Thoughts? Suggestions for another type of acid? Thanks for any input. Yonek  SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA > Hello everyone, > I'm want to conduct a catalytic > hydrogenation under acidic conditions. The reference uses traces (0.5 mL [quoted text clipped - 3 lines] > conditions using typical acids (sulfuric and hydrochloric) and acetic acid > as solvent. > I was thinking of using a trace amounts of trifluoroacetic acid in place > of perchloric. Thoughts? Suggestions for another type of acid? TFA or triflic acid ought to do it. What is your bomb made of? 316 SS is not happy with acids and it gets eaten by halide. Do you use a glass or teflon liner? 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 > I'm want to conduct a catalytic >hydrogenation under acidic conditions. The reference uses traces (0.5 mL [quoted text clipped - 6 lines] > I was thinking of using a trace amounts of trifluoroacetic acid in place >of perchloric. Thoughts? Suggestions for another type of acid? What you suggest makes good sense. The choice of acid might depend on the product (e.g., salt form) that you'd like to isolate. Another common combination is HCl in methanol or ethanol. This can be made by adding an appropriate volume of conc. aq. HCl to the alcohol, or, if anhydrous solvent is needed, the calculated amount of acetyl chloride to the alcohol. Very polar / acidic conditions increase catalyst activity and hydrogenation rate. Steve Turner Real address contains worldnet instead of spamnet SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA TFA is perfectly fine for the purpose. (HClO4: looks like this is a pretty old procedure, perchloric acid is not used much now.) Also, AcOH (neat) is not too bad. Neat acetic acid is somewhat unpleasant to evaporate, but AcOH is an excellent solvent for hydrogenations. > Hello everyone, > I'm want to conduct a catalytic > hydrogenation under acidic conditions. The reference uses traces (0.5 mL [quoted text clipped - 3 lines] > conditions using typical acids (sulfuric and hydrochloric) and acetic acid > as solvent. > I was thinking of using a trace amounts of trifluoroacetic acid in place > of perchloric. Thoughts? Suggestions for another type of acid? > Thanks for any input. > Yonek SignaturePaul 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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