Sciencemadness Discussion Board - Metacresol purple: Pan Galactic Gargle Blaster

Metacresol purple: Pan Galactic Gargle Blaster

wg48temp9 - 15-2-2022 at 21:23

According to wiki metacresol purple can be used as capnographic indicator for detecting carbon dioxide in exhaled breath. Many years ago I attended a theater version of the Hitchhiker's Guide to the Galaxy. In the foyer of the theater they sold a cocktail that was claimed to be a Pan Galactic Gargle Blaster. The cocktail appeared to be a colored carbonated drink containing a sugar cube and a cocktail onion. There was a plume of bubbles emanating from the cube with the plume differently colored from the rest of the liquid. I assumed there was a ph indicator in the liquid and the outgassing of carbon dioxide caused by the sugar cube had increased the ph sufficiently to change the indicator color in the plume.

Perhaps metacresol purple would be a suitable ph indicator to produce the color change in plume. Irritatingly I don't have any metacresol I think will be difficult to make it. I do have toluene so all I need is a way of chlorinating/bromating the ring with preferably a significant amount of meta product.

Can anyone suggest a method ? I am thinking of bromine and FeBr3 but the meta yield will be low and the work up difficult.

Texium - 15-2-2022 at 21:56

Unfortunately m-cresol is something that isn’t very practical to make. The most reliable way to get to m-bromotoluene would be to brominate benzaldehyde followed a Wolff-Kischner or Clemmensen reduction to reduce the carbonyl to a methyl group. But then you still have to deal with converting the aryl bromide to a phenol, which isn’t trivial either. You could try and brute force that by roasting it in a sealed vessel with NaOH, or you could make the grignard, react that with trimethyl borate to make the boronic acid, and then oxidize to the phenol with hydrogen peroxide. Either way it’s steppy and would be quite the expensive and arduous ordeal if you don’t already have most of the necessary reagents.

mayko - 16-2-2022 at 07:40

If the solution is out-gassing, wouldn't the neighborhood of the bubbles be depleted of carbonic acid and less acidic?

That's a really cool-sounding trick! Worthy of the Special Effects Cookbook for sure. Maybe there was dye in the sugar cube?

wg48temp9 - 17-2-2022 at 03:04

Quote: Originally posted by Texium

Unfortunately m-cresol is something that isn’t very practical to make. The most reliable way to get to m-bromotoluene would be to brominate benzaldehyde followed a Wolff-Kischner or Clemmensen reduction to reduce the carbonyl to a methyl group. But then you still have to deal with converting the aryl bromide to a phenol, which isn’t trivial either. You could try and brute force that by roasting it in a sealed vessel with NaOH, or you could make the grignard, react that with trimethyl borate to make the boronic acid, and then oxidize to the phenol with hydrogen peroxide. Either way it’s steppy and would be quite the expensive and arduous ordeal if you don’t already have most of the necessary reagents.

Thanks for that. I will probably use use the zinc reduction method using gallium. I do have several old big bulb mercury thermometers as a source of mercury but I prefer to avoid mercury use if I can.

The other key reagent is o-Sulfobenzoic acid anhydride. Apparently that can be synthesised from saccharin which I do have, but I have not found a procedure yet.

I have found procedure for the m-cresol purple. The yield is low at 19% but I only need a fraction of a gram

Here is the procedure: The brackets were added by me as the procedure does not give the temperature units.

Condensation of m-cresol with o-sulfobenzoic acid anhydride.-The
process must be carried out at a temperature below 1100 if m-cresol-
sulfonephthalein is to be obtained. This has been confirmed by
Orndorff and Purdy, who find that higher temperatures favor the
formation of dimethylsulfonfluoran, the anhydride of the di-ortho
compound. No particular advantage was noted in the employment
of condensing agent like zinc chloride so far as improvement in
the yield is concerned. The yield is low, between 15 and 20 per cent
a.t the best, and is probably due to a retardation effect exerted by
the meta-methyl group.
Crystalline o-sulfobenzoic acid anhydride, 30.8 gm., was added to
36.2 gni. of dry, redistilled m-cresol which had been warmed to 110 (C/F) ?.
The mixture was stirred and held for six hours in a bath kept at a
temperature of 106(C/F ?). The compound formation was followed by
observing the amount of color produced bv a test drop in 10 per cent
sodium carbonate solution and in dilute acid. The fusion was
terminated when the color reached a maximum. The mixture was then
steam distilled to remove m-cresol. Solid sodium carbonate was
then added carefully to the hot solution until the color became
deep purple. The solution was allowed to stand overnight to cool
and settle out. It was filtered, the precipitate was discarded, and
to the filtrate was slowly added concentrated hydrochloric acid
until a deep red color developed. This solution was evaporated on
the water bath under reduced pressure. Uniform, small green
crystals of the sulfonephthalein separated as evaporation progressed.
The crystalline product may be washed with cold water to remove
adherent acid and salt, and is sufficiently pure (over 95 per cent) for
ordinary indicator purposes. The yield up to this point was 12 gm.,
or about 19 per cent.

From Attachment: m-cresol-purple-4578119.pdf (2.3MB)
This file has been downloaded 346 times

[Edited on 2/17/2022 by wg48temp9]

wg48temp9 - 17-2-2022 at 03:21

Quote: Originally posted by mayko

If the solution is out-gassing, wouldn't the neighborhood of the bubbles be depleted of carbonic acid and less acidic?

That's a really cool-sounding trick! Worthy of the Special Effects Cookbook for sure. Maybe there was dye in the sugar cube?

Yes the outgassing reduces the acidity ie increases the ph.

Yes the the sugar cube may have been doped with some thing but I suspect not. I removed the cocktail onion as I thought its acidity may have been part of the effect and it made the drink taste terrible to my pallet. Removal of the onion did not change the effect.

PS: your link points to a book selling site.

[Edited on 2/17/2022 by wg48temp9]

unionised - 17-2-2022 at 05:07

Bromocresol purple isn't the most toxic stuff in the world but...

https://en.wikipedia.org/wiki/Anthocyanin
looks like a better bet.
On a related note
https://www.masterofmalt.com/gin/sharish-gin/sharish-blue-ma...

wg48temp9 - 18-2-2022 at 11:14

Quote: Originally posted by unionised

Bromocresol purple isn't the most toxic stuff in the world but...

https://en.wikipedia.org/wiki/Anthocyanin
looks like a better bet.
On a related note
https://www.masterofmalt.com/gin/sharish-gin/sharish-blue-ma...

Yes the potential toxicity of metacresol purple (or bromocresol purple) could be an issue if anyone was planning to drink it. As this particular Gargle Blaster was sold way back when they still used arsenic to stop childrens wooden play furniture from rotting and organic chemistry labs stank of benzene, so the toxicity of the blaster's ingredients may not have been much of a concern.

The anthocyanin of the purple cauliflower look intense so perhaps not much would be need and probably its not very expensive. However, apparently the reason they use of metacresol purple for CO2 detection is the sharpness
of the colour change but I don't how important/significant that is.

I guess it would be possible to estimate the change in ph due to say the outgassing of 10ml of CO2 in say 50ml of water but I do not see the sharpness of the color change of ph indicators given very often.

Boffis - 21-2-2022 at 12:23

wg48temp9; If you are interested I have some spare m-cresol certainly 40-50ml and I may even have some bromocresol purple. U2U me if you are interested.

wg48temp9 - 1-5-2022 at 10:15

I ordered some M-Nitrobenzaldehyde to convert it to m-cresol but the supplier made an error and did not have any. Fortunately Boffis has kindle supplied me with some m-cresol. Thanks Boffis.

Now all I need is o-Sulfobenzoic anhydride. It can be synthesized from Saccharin via acid ammonium o-sulfobenzoate see the Org.Synth below.

Unfortunately the anhydride synthesis require thionyl chloride.. I suspect and hope there is an alternative synthesis that does not require thionyl chloride.

From: Attachment: o-SULFOBENZOIC-ANHYDRIDE-CV1P0495.pdf (315kB)
This file has been downloaded 180 times

The section 3 of the above document gives alternative methods:

SWIM - 2-5-2022 at 09:48

Quote: Originally posted by unionised

My first thought was red cabbage when OP mentioned the taste.
It sounds like a probable kitchen as opposed to lab solution.

Edit: was the drink reddish by any chance?

[Edited on 2-5-2022 by SWIM]

wg48temp9 - 9-5-2022 at 01:57

Quote: Originally posted by SWIM

Quote: Originally posted by unionised

My first thought was red cabbage when OP mentioned the taste.
It sounds like a probable kitchen as opposed to lab solution.

Edit: was the drink reddish by any chance?

[Edited on 2-5-2022 by SWIM]

It was a long time ago so my memory is vague, probably most of the drink was blue or purple with the plume of CO2 bubbles and liquid above the sugar cube straw coloured.

wg48temp9 - 9-5-2022 at 02:14

I have discovered that sulphuric acid can be used to convert the saccharin to o-Sulfobenzoic anhydride and then couple that to the m-cresol in a one pot synthesis. The yield is not great at about 20% to 30%. If I achieve 10% I will be happy.

See these two notes:
Attachment: Synthesis-of-43-SYNCOM-SULFONEPHTHALEIN1 (3).pdf (340kB)
This file has been downloaded 190 times
Attachment: Solvent-Free-Synthesis-Sulfonephthalein-scccc.pdf (91kB)
This file has been downloaded 181 times

Tsjerk - 9-5-2022 at 03:29

I just ran the reaction between o-Sulfobenzoic anhydride and thymol as described here this weekend and the colors were very promising, so very red when acidic and very purple when basic. But the yield was an abomination. I might have been a bit impatient though. Next time I will let the reaction run overnight.

wg48temp9 - 9-5-2022 at 07:04

Quote: Originally posted by Tsjerk

I just ran the reaction between o-Sulfobenzoic anhydride and thymol as described here this weekend and the colors were very promising, so very red when acidic and very purple when basic. But the yield was an abomination. I might have been a bit impatient though. Next time I will let the reaction run overnight.

As thymol is readily available on ebay I thought I would try the sulphuric acid method on thymol first as practice and to see how it goes. I still don't have details of the work up.

Tsjerk - 9-5-2022 at 13:20

I think the workup is quite simpel. I got it from the paper mentioned in the topic I linked to.

You neutralize the acidic reaction mixture, dissolve the solids in sodium bicarbonate, filter off the remaining solids and precipitate the product with acid again. I skipped the following column chromatography.

[Edited on 10-5-2022 by Tsjerk]