| Pages:
1
2 |
Crowfjord
Hazard to Others
Posts: 390
Registered: 20-1-2013
Location: Pacific Northwest
Member Is Offline
Mood: Ever so slowly crystallizing...
|
|
When performing an alkylation of a phenol in acetone, one needs to add a base in order to make the phenol reactive toward the alkylation agent. Since
the phenol is more acidic than acetone, it reacts more quickly, i.e., the base prefers to remove a proton from the phenol than the acetone. Of course,
acetone may be deprotonated a bit as well, but the weaker acid gives a stronger conjugate base which is this case would be the acetone enolate. Any
acetone enolate that forms would go on to deprotonate the phenol present, forming a phenolate which is not strong enough to deprotonate acetone.
Aldol reaction may occur in these reactions to some extent, but not in any significant enough amount as to interfere with the intended process; the
intended reaction (phenolate formation) just happens much more quickly.
|
|
|
CuReUS
National Hazard
Posts: 928
Registered: 9-9-2014
Member Is Offline
Mood: No Mood
|
|
yes now i understand
also in many reactions a base is added to phenol to make it more reactive
for example ,phenol is treated with base to form sodium phenolate through which carbon dioxide is passed under high pressure to form the
corresponding sodium phenol carbonate which rearranges to give salicylic acid upon acidification
also sodium phenolate instead of phenol to prepare para nitrosophenol
but at that time i thought that it was done to prevent phenol from solidifying or
getting oxidised by the sulphuric acid,as ionisation prevents oxidation
[Edited on 13-10-2014 by CuReUS]
|
|
|
Avapple
Harmless
Posts: 1
Registered: 18-3-2017
Member Is Offline
Mood: No Mood
|
|
I opted to follow Klute’s method (http://www.sciencemadness.org/talk/viewthread.php?tid=9921) to prepare this aldehyde.
8.30g vanillin was added to a 50mL round bottom flask with a stir bar, and dissolved in 10mL DMF. I did not dry the DMF at all; indeed, it was from a
half-emptied solvent bottle a couple years old, as I didn’t think to check my storage for fresh DMF. It wouldn’t be hard to get a new bottle and
dry the contents over sieves, if need be for future work.
3.3g coarsely crushed KOH was added to a 100mL 3-neck RBF with a stir bar, and suspended in 30mL DMF. The RBF’s center neck was fitted with a
septum-capped, needle-vented, water-cooled condenser, and the other two necks were capped with septa.
Cannulae were threaded through the flasks and connected to an argon supply.
After a 20min purge, the vanillin solution was cannula transferred into the KOH suspension by argon pressure. The mixture slowly turned green-orange
over 10 min, and most of the KOH gradually dissolved, but some stubbornly remained. To speed up the process, the mixture was heated on an oil bath to
50°C for an additional 20 minutes. Most of the remaining KOH dissolved, and the mixture turned a stronger orange, but no phenolate precipitated.
At this point the heat was shut off, and 9.3g EtBr slowly injected into the reaction flask, wearing a gas mask as a precaution. The solution slowly
turned cloudy with precipitated KBr, and was left to stir for 1h30 min.
At this point the temperature had dropped to 35°C, and the mixture had gone completely white. The oil bath was set to 60°C for 12 hours and the
reaction left to run overnight. At a final check 1 hour later, the mixture had acquired a faint reddish-pink tint.
The next day, the mixture was at room temp, and filled with a white suspension. Stirring was shut off and the setup disassembled. The precipitate
settled to the bottom, leaving a colorless solution.
The solution was decanted into a flask with 50mL water, leaving the precipitate behind for now. A new white precipitate formed in the decanted
solution and quickly redissolved with stirring. Adding another 50mL water did not restore it, but a few small crystals were noticed floating in the
solution.
Prepared 21mL 10% NaOH and slowly added it to the solution. Spectacular fluffy white material precipitated, and the solution turned yellow-green. NaOH
solution was added until as much fluff was precipitated as possible. A nasty smell of dimethylamine became evident, despite working in a hood, so a
gas mask was put on again. The solution was added to a sep. funnel with 25mL DCM and shaken.
Both layers turned cloudy white/green. The bottom organic layer was acidified with 25mL 10% H2SO4, then washed with a bit of water and 20mL 5% NaOH.
The organic layer was now nicely clear.
The organic layer, largely DCM, was transferred to a 50mL RBF and the solvent removed under reduced pressure; although some DMF/water remained,
beautiful white/translucent cubic crystals formed in it. After decanting the remaining solvent and rinsing with water, the crystals were scraped from
the flask as best as possible into a beaker and left to dry in air.
The aqueous layer was extracted again with 25mL DCM and discarded. The slightly cloudy organic layer was transferred to the 50mL RBF, but no crystals
precipitated in the remaining solvent once the DCM was pulled off. A drop of water was added to check for dissolved material and a white powder
precipitated, so the flask was placed in the freezer. The familiar cubic crystals formed within a few hours. The DMF was decanted and the crystals
rinsed with water before allowing them to dry.
The residual white material in the original reaction flask was mixed with 25mL water and 25mL 10% NaOH, which induced more precipitation. It was
extracted with 25mL DCM as usual. As with the second extract of the first aqueous layer, no crystals precipitated once the DCM was pulled off. The
remaining DMF was transferred to a vial and placed in the freezer.
The dried, crystalline product has a vanillin-like smell, but with a distinct, but faint “woody” note. It is mostly white/translucent, but some
crystals have a very slight green tinge.
After collecting and drying most of my material (there are a few hundred milligrams of precipitate in the vial I’ve yet to collect), I recovered
5.72g total for a crude yield of about 58%. It melts at 57-58°C; Alfa lists a melting range of 59-63°C.
1H NMR (CDCl3): δ 9.81 (s, 1H), 7.44-7.39 (dd, 2H), 6.93 (d, 1H), 4.16 (q, 2H), 3.91 (s, 3H), 1.48 (t, 3H).
I can post images of the product and spectrum on request.
|
|
|
| Pages:
1
2 |
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
