awlb2 - 22-11-2016 at 10:28
Hello, I need some help on self-aldol condesation conditions. I am attempting to self-aldol react acetone. Does anyone know what pKa is needed to
enolate the ketone- does the pKa simply have to be lower than that of acetone? I would like to know if sodium carbonate is a suitable base to use-
note, I am not concerned about polymerisation (i.e. full enolisation) etc. I just want to attempt the reaction. Also what temperature is optimal.
Thank you in advance if you are able to help me.
DraconicAcid - 22-11-2016 at 11:03
To do this reaction, you would have to deprotonate the acetone. Carbonate isn't going to do this. Hydroxide might.
ETA: Hydroxide will work. http://d.web.umkc.edu/drewa/Chem322L/Handouts/EXP%209%20aldo...
[Edited on 22-11-2016 by DraconicAcid]
Marvin - 22-11-2016 at 11:23
Sodium carbonate will do this, acid works well, probably a better plan. Hydroxide is very strong and tends to resin. Another question is do you want
the alcohol products or the dehydration products (which tend to be easier to isolate - say by dumping into water).
UC235 - 22-11-2016 at 12:16
If you want to prepare diacetone alcohol or mesityl oxide, the prescribed procedures can be found in orgsyn:
Diacetone Alcohol from Acetone: http://orgsyn.org/Content/pdfs/procedures/cv1p0199.pdf
Mesityl Oxide from Diacetone Alcohol: http://www.orgsyn.org/Content/pdfs/procedures/cv1p0345.pdf
The products are prone to polymerization and self-condensation and simply adding a base to acetone in a flask will make a mess. The specialized
apparatus described for diacetone alcohol is deliberately meant to minimize this.
If you're merely interested in the reaction from an academic standpoint, I highly recommend preparing vanillideneacetone (dehydrozingerone) whose
preparation can be found elsewhere on this forum as the first step in preparing zingerone (or alongside the closely related rheosmin). It requires no
specialized apparatus or rigorously dry conditions and the product is an easily-crystallizable, attractive yellow solid obtained in high yield.
awlb2 - 22-11-2016 at 12:41
Thank you everyone for answering my questions, I appreciate the help. I will perhaps try UC235's idea of making vanillindeneacetone which sounds
rather interesting.