P1P to B-Methylstryene. Yield 85.6%
P1P to B-methylstyrene.
354.3g P1P
880g MeOH
29.9g NaBH4
528g dH2O
319ml 2M HCl
7.9g KHSO4
DCM
MgSO4
dH2O
NaHCO3
NaCl
354.3g tech grade P1P and 880ml methanol was placed in a 3L erlnmyer flask with thermometer and stir bar, sitting in an ice tray. 14.9g NaBH4 and
264g dH2O @ 1 deg C was mixed and poured in a 250 ml sep funnel and placed on top of the 3L flask. Ice only was loaded into the tray and addition
started. Ambient temperature of mixture was 16 deg C. Whem temp hit 25 deg, water was added into the ice tray. Max temp was 28 deg. Another 15g NaBH4
and 264g dH2O was mixed and loaded into the sep funnel after the first lot was dropped in. Temp range was 22 - 26 deg with this second lot. Addition
took 26 min.
Ice bath was removed when temp fell to 24 deg, then rose slowly to 26.6 then fell after 1hr. Left stirring for a few hours. Next day, cooled 315 ml
2M HCl to 2 deg and dropped it in the mixture over 20 min till pH 7. Temp rose from 14 - 16 deg. Approx 5 ml HCl remained. Solution slowly separated
into to layers. On another run the layers separated spontaineously but the temp was higher. Transfered to a 2L sep funnel.
Tapped the aqueous layer back into the 3L flask, and the organic layer into a 500 ml sep funnel. Aqueous layer was put back into the 2L sep and
extracted 2 X 350ml DCM and 1 X 170 ml DCM, tapped that into a 2L beaker, dumped the aqueous and put the DCM back in the 2L sep, along with the
organic layer. The beaker and small sep was washed with 170 ml DCM and added with the rest. This was washed with 2 X 600 ml dH2O, tapped into a the 3L
flask with a table spoon of MgSO4, filtered into a 2L RBF and simple distilled, in a water bath.
When most of the DCM was removed, the liquid was transfered to a 500 ml RBF and again set up for simple distillation with a recovery tube (with copper
wire wrapped around it) instead of a distillation head, and sitting in an oil bath. 7.9g KHSO4 was ground to a powder and added to the flask. A 500 ml
RBF was used as the receiver.
When the oil bath reached 135 deg, water was seen forming on the recovery tube. At 145 deg a heat gun was aimed at the tube to make sure no water
dropped back in. This was continued untill water stopped coming over and propenyl benzene started distilling, about 197 deg. At 202 degC the propenyl
distills very well, at 206 about 2 drops/sec. When distillation slowed right down, temp was allowed to climb to 215 deg, then heat removed. 20 ml was
left as a light orange residue, which propably contains unreacted P1P. This was neutralised with NaHCO3, washed and dried.
The distillate which was light grey/green, was mixed with 1L DCM and washed with 450 ml 10% NaHCO3, Probably way too much, then 2 X 600 ml dH2O.
Second wash should have been brine. All washed were back washed with some DCM, combined, dried with a spoon of MgSO4 and filtered into a 2L RBF and
set up for fractional distillation with a packed 400 mm tube.
Most DCM was removed with a water bath up to boiling. The propenyl was then transfered to a 500 ml RBF and now vacuum was applied to remove the rest
of the DCM and water which again caused problems. Obviously the MgSO4 is not good enough. Product came over between 42.5 and 44 deg at 5.25mbar.
246.2g distillate was collected with the residue being light/yellow (not weighed).
The column was washed down with some dcm and combined with all residues in a 250 ml RBF and vacuum fractionally distilled this time with a much
smaller column collecting a further 20.7g that came over at 44.5 to 45 deg at 5.5 to 5.75 mbar. Leaving a light orange residue of about 50 ml that has
a definate mix of P1P and propenylenzene.
Total yield. 266.9g B-Methylstyrene. 85.6%
What do you think.? Not enough borohydride? Should the NaBH4 be stabilised with NaOH? Not enough MeOH? Swim feels sure the yield could easily go over
90% How can this be improved, especially the work up. What needs to be there, what doesn't. Comments please.
Regards
FF.
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