(Hive Bee)
09-21-03 08:48
No 460196
(Rated as: good read)
The trouble I've had trying to rearrange the glycol with 15% H2SO4!!! Yields range between 5 and 31%. Anyway, I'll talk about that in another post.
With Tosic acid, I've had yield between 55 and close to 90%. I've used 2 methods.
A) Tosic + Glycol __> P2P
B) Tosic + toluene + glycol __> P2P
A)
1) 53.3g Glycol and 0.7g of tosic acid monohydrate was added to a 250ml RBF in an oil bath and set up for fractionl vacuum distillation.
2) Vacuum and heat was applied, glycol started to turn brown/red with oil bath at 120°C. First sign of water creeping down the flask was seen at 130°C. At about 60mbar, with bath at 140°C came some water, propenylbenzene, then after that a bit of P2P, which then stopped.
3) Another 0.7g of tosic was added and a few more ml of P2P came over then stopped.
4) 1.4g tosic was added, this time P2P came over till the end. With bath between 128 - 162°C and pressure between 7.5 and 15mbar, P2P came over between 77.5 - 81°C. Collected 39.9g raw P2P.
5) I estimated that 53.3g glycol came from 42.2g propenylbenzene, which gives me a yield of about 83% before I redistill. About 5.5% w/w tosic was used.
Whatever water was in the receiver was carefully pipetted out so I could get a good idea of the yield. The only water that I saw being evolved was at the begining of the distillation, but as I have seen before, the vacuum gauge drops from 5 or 7 mbar to around 15 to 22mbar right at the end, and then recovers somewhat. Why does that happen? I didn't notice more water.
B)
1) 29.4g glycol, 90ml toluene and 0.3g tosic acid was placed in a 250ml RBF and set up for reflux with a dean stark trap.
2) With oil bath at 150°C, the system refluxed for 2 hours. Only a small amout of water was collected, so another 1.3g tosic acid was added. This refluxed for a further 1 3/4 hours. Approx 1.7ml water was collected.
3) Oil bath was removed and solution was orange/red and darker when cooled. This was transfered to a sep funnel and neutralised with 60ml 10% NaHCO3 then washed with 60ml brine and dried with MgSO4. Colour was bright yellow.
4) Toluene was removed with simple distillation under vacuum. Product was transfered to a 100ml RBF and set up for fractional vacuum distillation and collected 0.8g P2P, pressure 5.5mbar and bath up to 160°C. Didn't like that!!
5) Added a small amount of tosic 0.2 - 0.5g. A tiny amount of water came over first then nothing but the clearest P2P came over. Bath 160 - 164°C, pressure 12 - 8 mbar, (but once again, lost vacuum at the end of distillation but then recovered), temp 82 - 83°C.
6) Collected 24.4g P2P and 3.3g tar as residue. Yield before redistilling 92.3%
Why did I not get P2P straight from toluene reflux with more than 5% tosic w/w (based of weight of glycol)? Can one of you true chemistry dudes explain what happened?
First time I used this method I tried benzene, glycol and 5% tosic acid, refluxed 3 hours (Solution was still clear), forgot to neutralise and wash, went straight to distillation and got 79% P2P.
The glycol was gotten from performic with NaHCO3 and Na2CO3. Yield of glycol was;
With NaHCO3 62.7%,
With Na2CO3. 94%
Regards,
FF
Be joyful, though you've concided the facts!
(Hive Addict)
09-21-03 12:35
No 460218
and heat, ketone decomposes at 180 you washed with base (although a weak one), it has a tendancy to not as readily disslove upon washing (escpecially carbonates). even the weak carbonate can patially convert to the oxide under heat ( a stronger base) and cause polymerization (tar)
I hope that helps, and thanks for the notes on the tosic rearrangement it seems far supeiour to subjecting, glycol, glycol esters, and ketone to strong acid and heat.
B)
1) 29.4g glycol, 90ml toluene and 0.3g tosic acid was placed in a 250ml RBF and set up for reflux with a dean stark trap.
2) With oil bath at 150°C, the system refluxed for 2 hours. Only a small amout of water was collected, so another 1.3g tosic acid was added. This refluxed for a further 1 3/4 hours. Approx 1.7ml water was collected.
3) Oil bath was removed and solution was orange/red and darker when cooled. This was transfered to a sep funnel and neutralised with 60ml 10% NaHCO3 then washed with 60ml brine and dried with MgSO4. Colour was bright yellow.
4) Toluene was removed with simple distillation under vacuum. Product was transfered to a 100ml RBF and set up for fractional vacuum distillation and collected 0.8g P2P, pressure 5.5mbar and bath up to 160°C. Didn't like that!!
5) Added a small amount of tosic 0.2 - 0.5g. A tiny amount of water came over first then nothing but the clearest P2P came over. Bath 160 - 164°C, pressure 12 - 8 mbar, (but once again, lost vacuum at the end of distillation but then recovered), temp 82 - 83°C.
6) Collected 24.4g P2P and 3.3g tar as residue. Yield before redistilling 92.3%
Why did I not get P2P straight from toluene reflux with more than 5% tosic w/w (based of weight of glycol)? Can one of you true chemistry dudes explain what happened?
The second attempt can be explained by stoichiometry, and Lechattleir's principle.
you simply were'nt using a suffiecient amount of para-methyl-benzene,sulfonic acid to effect dehydration and rearrangment, which is discernable by the amount of water you collected in the dean stark.
Calculate the molar amount of the H20 and from that you can derive how much glycol was converted.
(Chief Bee)
09-22-03 02:31
No 460297
Spisshak: That post of yours was very unclear, on the verge of being incomprensible. Also, you write:
"the lower yeilds can be a result of residual base and heat, ketone decomposes at 180"
This is totally incorrect. FriendlyFinger is talking about P2P, not MDP2P, and the former definitely doesn't decompose at 180°C, its boiling point is 214-216°C at 760mmHg (atmospheric pressure) and this value is even quoted in the Merck Index.
Also, I have a hard time believing that any residual sodium carbonate would stay in the washed glycol, and then being "converted to the oxide" (I assume you mean sodium hydroxide here), and even if there would be any such traces left, it would be immediately neutralized by the tosic acid and turn into harmless sodium tosylate.
FriendlyFinger: Good job!
To me it seems like the pinacol rearrangement of the glycol only is efficient when the solution is really hot, as when you are distilling. I am baffled by the fact that a long reflux in toluene failed to produce any water or P2P.
Have you tried to use any larger amounts of tosic acid from the start using the azeotropic distillation setup? It would be so much better if one could just mix the glycol and a large enough amount of tosic acid in toluene, distill with azeotropic water removal for 1-3 hours, and then either distill directly, or wash with base and then distill.
(Hive Bee)
09-22-03 10:54
No 460365
I will use a larger amount of tosic soon. I would love to get a good result with toluene, and I feel sure I will.
But in in the mean time, I'm not sure how to work out exactly how much water I should get in the dean stark trap concidering that Dal Carson said:
"The mass spectrum of the major oxidation component indicates that it is phenyl-1-hydroxyl-2-formyl-propane. Its isomer, phenyl-1-formyl-2-hydroxy-propane, is also formed. The diformyl glycol and the free glycol, phenyl-1,2-dihydroxypropane is also found in smaller amounts"
I know he is refering to the performic with acetone so is what he said relevent to the buffered performic?
Thanks,
FF
Be joyful, though you've concided the facts!
(Hive Addict)
09-22-03 11:09
No 460367
I am very interested in this route also FF
Ritter mentions that yioeld can be increased by adding a "Higher Boiling tertiary amine" to quickly neutralise the acid.
Post 333006 (Ritter: "tosic acid pinnacol rearrangement", Methods Discourse)
Read and learn: http://www.polyarchy.org/
(Chief Bee)
09-22-03 22:40
No 460442
FF: You said you worked with the glycol (I thought you had the actual glycol in hand), as you didn't mention that you actually used the crude product from a buffered performic oxidation, in which case you most likely have a mixture of the glycol formyl esters, as well as some epoxide and free diol.
The formic acid liberated from the reaction of the formyl ester with tosic acid will probably not end up in the dean-stark. Did you use commercial tosic acid, or did you synthesize it yourself?
abolt: I don't think that P2P is nearly as acid-sensitive as the MDP2P Ritter was working with, so the addition of that amine may be unnecessary in this case. Let's first concentrate on optimizing the tosic acid rearrangement before adding any other variables. The main problem we seem to have at the moment is that the rearrangement reaction itself is sluggish until large amounts of tosic acid is added.
(Master Whacker)
09-24-03 21:25
No 460783
Don't forget that the mono-formyl ester hydrolyzes into a molecule of formic acid in addition to the expected water. Both the formic acid and water will azeotrope over into the Dean-Stark trap.
(Hive Bee)
09-26-03 11:09
No 461169
Yes, After the 24hr performic the formyl esters and whatnot was distilled and that was what I worked with. Also I used commercial Tosic monohydrate. I redistilled the crude P2P and this was the result;
B) Tosic + toluene + (glycol + esters etc) __> P2P was 93.6%.
This was then fractionally distilled at 5-5.75 mbar collecting between 71-74°C with a final overall yield of 86%. When I can get the rearrangement happening in toluene I'm sure the yield will be higher.
A) Tosic + (glycol + esters etc) __> P2P. Yield was 83.3%.
This 39.9g P2P was acid to litmus so was mixed with 90ml DCM and washed with 2 x 80ml 10% NaHCO3 dried with MgSO4 and DCM distilled with bath at 55°C.
Transfered to a smaller RBF, then evaporated the rest of the DCM with vacuum, and with bath up to 80°C. Collected 31.5g P2P with 1.6g left as residue. Final overall yield 65.7%.
Around 6g was lost somewhere, even if I account for holdup in the glassware. Where did it go? Did I loose it while evaporating DCM with vacuum and high heat?
Be joyful, though you've concided the facts!
(Hive Addict)
09-26-03 11:22
No 461172
why would H2SO4 hydrolysis fail for unsubstituted P2P?
is this a known issue?
n'importe quoi
(Hive Bee)
09-27-03 08:04
No 461302
I just read this in an answer to one of my old posts Post 232908 (abc123: "Re: Why vacuum distill DCM", Newbee Forum);
"(in the performic dcm can distill over up to twice its boiling point because it gets azeotropically bound with something)."
Does that actually you can loose product (eg, P2P) if combined with medium vacuum?
Thanks.
FF.
Be joyful, though you've concided the facts!
(Chief Bee)
09-27-03 16:38
No 461340
Lose it through the vacuum pump? No, not if you have a decent condenser.
Lose it by it co-distilling with a solvent? Unlikely, as long as you don't try to separate it from something as high-boiling as xylene without using a column. Toluene should be all right as long as you distill slowly and/or use a fractionating column.