Sciencemadness Discussion Board

Synthesis of Mesitylene

semiconductive - 27-3-2024 at 08:13

I'm interested in synthesizing Mesitylene, experimentally, using the historical method with sulfuric acid.

A typical formula says, 25g of acetone, 56g of conc. H2SO4 + 15g of water.
After distillation, it is expected to produce 30% of theoretical yield.

Put 40 grams of quartz sand / glass into a flask.
Put 25 grams of acetone into sand.
??? how water is added is not mentioned ???
But: Slow drip acid into sand over several hours, keeping flask chilled.
So, this is a labor intensive process for most amateurs....

All I'm certain of is that the purpose of the H2SO4 is both to start the conversion from ketone to enol form, trigger condensation, and to remove water.

https://en.wikipedia.org/wiki/Aldol_condensation

So, it seems to me like the addition of water in the recipe would be counter-productive unless it's to stop excessive heat/reaction speed.

I am wondering: Is the purpose of the water to reduce heating of the acetone and acetone gas escaping before the reaction occurs ?

eg: The first step of the reaction with concentrated H2SO4 will produce mesityl oxide; I think.

The recipe does say to chill the flask as acid is added to acetone/sand. And if that's to slow evaporation ... then might the synthesis be more easily carried out in a salt mixture instead of pure acid ? It would be slower, but perhaps easier (since it could be automatic rather than manual) over a period of days?


For example, MgSO4 salt with some molar percentage of H2SO4, eg: 25%-50%, could be cooked almost to dryness and made into a Magnesium hydrogen sulfate sand. This could be allowed to cool, and put into a drying tube.

I think this new 'acid sand' would have a slower and cooler (but more water absorbing) effect; eg: MgSO4 can absorb 6 x it's water, and the remaining H2SO4 acts more as a catalyst.

Is this likely to work / or am I overlooking something?

eg: Is chilling of acetone to 0C merely to slow down the evaporation of acetone; or does chilling have some known effect on the selection of the aromatic ring structure?

Because if chilling does not affect the selectivity of aromatic rings, but is only intended to slow down evaporation of acetone; it seems to me that simply placing the sand in a drying tube *over* an empty flask followed by a bubble trap filled with acetone and a glass plug; I could force the acetone gas to slowly mix with the sand (backward), over a period of days. Any remaining acetone, or water, being polar would want to stick to the sand.


But, the desired product, being non-polar, would not stick to the sand but instead (high boiling point) condense into liquid and drip into the empty flask.

Thoughts?


What condition(s) are known to encourage formation of the cyclic aromatic ring over straight chain polymers?



[Edited on 27-3-2024 by semiconductive]

fx-991ex - 27-3-2024 at 09:37

In this video they cool the acetone in a flask, slowly add the H2SO4 then heat it, then they add water using a pressure equalizing funnel to steam distill.
https://www.youtube.com/watch?v=tGWzpt3X9kk

bnull - 27-3-2024 at 09:43

Hold on. Where did you find this "typical formula"? Do you have a paper or link or something similar to share?

The historical method is exemplified here: "Mesitylene". Org. Synth. 1922, 2, 41. It's about the same that Bob Kane (the Irish chemist) used in the 1830s.

The use of silica gel is presented here: J. A. Mitchell, E. E. Reid, "The Decomposition of Ketones in the Presence of Silica Gel". It seems that quartz sand was included (in the process you cited) to speed the process. Maybe if you cut the sulfuric acid by half and use silica gel you may get the same result.

[Edited on 27-3-2024 by bnull]

semiconductive - 27-3-2024 at 12:03

Systematic organic chemistry, by W. M. Cumming, 57, 1937.
Scaled down by a factor of 10.

There is a site, Prep-Chem, behind a captcha that hosts the excerpt. It does not indicate the purpose of the sand.

https://www.prepchem.com/synthesis-of-mesitylene/

The notes of your link are far more detailed. But it doesn't really describe why 10C is important.

The link by E.E. Reid, seems to indicate that the reaction proceeds hot.

I'm thinking:
Silica Gel and Magnesium Sulfate (anhydrous) are both desiccants. So the process might adapt to MgSO4 acidified sand; and if glass is important, to mixtures of MgSO4 sand + silicate. I'll get some silica gel along with quartz sand to try.

clearly_not_atara - 27-3-2024 at 12:08

The major side-reaction of interest is the formation of isophorone, not linear polymerization. So the normal intuition does not apply. Normally, rings are favored over polymers by increasing temperature.

It also seems like oxidation is an important side-reaction since Orgsyn notes that sulfur dioxide is produced. So perhaps metaphosphoric acid could be a good catalyst since it is non-oxidizing. Finding a vessel in which to produce metaphosphoric acid is usually the hard part.

semiconductive - 27-3-2024 at 12:21

Quote: Originally posted by fx-991ex  
In this video they cool the acetone in a flask, slowly add the H2SO4 then heat it, then they add water using a pressure equalizing funnel to steam distill.
https://www.youtube.com/watch?v=tGWzpt3X9kk


Yes, that makes a lot of sense.
Hmmm: A yield of 25-30% seems a bit optimistic based on the volumes seen in the video and all the possible side reactions. But even if I get 20% yield, I will be very happy.

DraconicAcid - 27-3-2024 at 13:11

http://article.sapub.org/10.5923.j.ijmc.20120204.02.html

I tried this reaction recently, but using xylenes instead of toluene (as I didn't have six hours for the reflux). Unsurprisingly, it didn't work.

palico - 27-3-2024 at 14:56

I would like to perform that reaction. Technically is a cyclodehydration, so other dehydrating agent should be effective.

clearly_not_atara - 28-3-2024 at 07:21

Quote: Originally posted by DraconicAcid  
http://article.sapub.org/10.5923.j.ijmc.20120204.02.html

I tried this reaction recently, but using xylenes instead of toluene (as I didn't have six hours for the reflux). Unsurprisingly, it didn't work.


What? The paper says it prepares triarylbenzenes.

Why not just the usual AlCl3/xylene? These other methods are mechanistically interesting, but the old standard seems much easier.

DraconicAcid - 28-3-2024 at 10:31

Quote: Originally posted by clearly_not_atara  
Quote: Originally posted by DraconicAcid  
http://article.sapub.org/10.5923.j.ijmc.20120204.02.html

I tried this reaction recently, but using xylenes instead of toluene (as I didn't have six hours for the reflux). Unsurprisingly, it didn't work.


What? The paper says it prepares triarylbenzenes.


No kidding, Sherlock. It is, however, the same 3 RC(O)CH3 --> C6H3R3 condensation, and the same author has used similar methods (same catalyst) for a number of different ketones condensing to arenes.

clearly_not_atara - 28-3-2024 at 10:49

It appears that a great many catalysts are applicable for the preparation of s-triphenylbenzene from acetophenone:
https://pubs.acs.org/doi/pdf/10.1021/ja01119a053

However, BF3 gives instead the triphenylpyrylium fluoroborate.

In the case of acetophenone, the side-reaction that produces isophorone is forbidden.

semiconductive - 29-3-2024 at 14:33

Quote: Originally posted by clearly_not_atara  
The major side-reaction of interest is the formation of isophorone, not linear polymerization. So the normal intuition does not apply. Normally, rings are favored over polymers by increasing temperature.

It also seems like oxidation is an important side-reaction since Orgsyn notes that sulfur dioxide is produced. So perhaps metaphosphoric acid could be a good catalyst since it is non-oxidizing. Finding a vessel in which to produce metaphosphoric acid is usually the hard part.


Hmm..
My heating mantle tops at 400C, to prevent glass meltdown. But ... it's just hot enough to fuse PTFE dust into a solid.

I also have a potassium/phosphorous/titanium salt that I made (purple in color). I was trying to find a salt that could take kiln heat (900-1000C), and still dissolve in water afterward. This salt worked! (Table salt doesn't, nor does MgSO4 -- which becomes a rock!) I don't know the exact stoichiometry of my salt but I still have a sample of it. It will take yellow to white heat from Oxy-Acetalyne (or mapp gas) and not melt. Afterward, it dissolves in water again just fine. Perfect mold making material for kilns instead of sand.

But, the toughness of the salt makes me wonder what kinds of temperature are needed to make metaphosporic acid? If I lined a mold with PTFE dust (or perhaps PTFE + graphite), and sintered it, it should be able to handle around 350C all day long, afterward.
But that's a lot of work... if it's not hot enough.

I found a thread, attempting to make meta-P in a copper crucible; and that works, although the result is contaminated.

But, if deoxygenation of SO4 into SO2 is the main issue; wouldn't some acids with SO3 bonded to the hydrogen be a bit less likely to de-oxygenate? eg: something like, metabisulfite, sulfite, or sulfonic/sulfamic acids?

The synthesis reaction doesn't seem to require all that hot of a temperature. It just requires good desiccating properties and an acid to trigger the enol tranformation of acetone.

Magnesium sulfite (anhydrous) is as dessicating as Magnesium sulfate. I imagine magnesium sulfonate might also be a dessicant; though I'm not sure.

I don't need a fast process; so long as it's one that can be automated to run by itself for several days. I imagine the first product boils at a much higher temperature than acetone does! So, perhaps, after the initial reaction; refluxing the composite liquid just above 100C to drive off water might work?

I'm open to variations to experiment with. I don't mind trying four or five different experiments.


[Edited on 29-3-2024 by semiconductive]