Preparation of P2P via PhI and AcetylacetoneIntroduction:In post:
Post 470750 (missing)
(Rhodium: "Cognate Preparation", Methods Discourse) and
Post 464635 (missing)
(Lego: "P2P from bromobenzene/CuI/Acetylacetone", Methods Discourse), a seemingly easy preparation of P2P's is described. This has been tried on the methylenedioxy substituted version without much luck. This time the substrate was iodobenzene, which is supposed to work like a charm. Obviosly this has to be tested
, so here goes:
Preparation of Sodium acetylacetonate:1 mole (39.99 g) NaOH was mixed with 250 mL denaturated EtOH
and stirred heavily. 1 mole (100.05 g) 2,4-pentanedione dissolved in 100 mL den. EtOH was added while cooling and stirring during ten minutes. The reaction was quite exothermic. When all the acetylacetone was added, the whole thing was a big white slurry. The EtOH and formed water was removed under vacuum on a warm water bath. The precipitate (sodium acetylacetonate) was scraped out and saved.
The main reaction:Reactants:200 mmole iodobenzene (MW = 203.94 g/mole) = 40.79 g (actual = 40.80) g
500 mmole Sodium AcetylAcetonate (MW = 122.03) = 61.02 g (actual = 70.15 g)
20 mmole CuI (MW = 189.83) = 3.8 g (actual = 3.81 g)
500 mL DMSO
Main Reaction:The iodobenzene was dissolved in 500 mL DMSO and lowered into an oilbath which had a temperature of 130
oC, while stirring heavily. The CuI was added in one portion, causing the reaction mixture to go more brownish. The sodium acetylacetonate was added in on portion, causing an immediate colour shift to a light green and within minutes to a very dark green. The mixture was stirred for 5 hours at 115
oC (internal temperature).
After this period 1.5L dilute hydrochloric acid was added (containing 250 mL 30% HCl), and stirring was continued for another 30 mins. This was extracted with 3*180 mL diethylether. The water / DMSO phase was discarded, and the ether stripped. The residue was stirred with 200 mL aq. NaOH, which caused a heavy gas evolution (probably acetone). The basic sludge was stirred for one hour, and then extracted with 3*150 mL ether (reused from the prior extractions). The ether was washed twice with brine and dried over epsom salt.
Workup:The ether was stripped, leaving a browning looking residue. This was distilled at aspirator vacuum at 95
oC-110
oC, to yield a perfectly clear oil. The yield was 20.45 g's and the density 1.39 g/mL (indicating that it was NOT pure P2P).
Conclusion:Later GC-MS results, performed by Prometheuz, showed that the distillate only contained 30% P2P, with the remains being unreacted iodobenzene.The only thing i can think of that could cause this miserable yield is the amount of acetylacetonate used. The original article posted by Lego, suggests the use of 5-10 molar eq. of the acetylacetonate. The later post by Rhodium only suggests a double molar amount.
Perhaps a 5-10 molar excess will boost the yield? Don't know if ill bother with this procedure anymore. It's REALLY messy, uses a shitload of solvents etc.
If anyone has some brigth ideas on how to boost the yields, please post away... I'm not touching this crappy reaction untill i get a "aha moment"
Enjoy folks!
Regards
Bandil
