Trimethylglycine - no heating over 40C?

Read here that TMG is not to be heated over 40C https://flowertalescosmetics.com/en/catalogue/product/trimethylglycine

Any validity to tihs?
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Comments

  • PharmaPharma Member, Pharmacist
    Betaine aka trimethylglycine is very stable and you can cook, even bake, betaine or preparations thereof without any degradation ;) . The only thing happening upon heating pure betaine hydrate is that it looses crystal water turning into anhydrous betaine at one point. It will only degrade if brought close to melting temperature of 300°C.
  • lmoscalmosca Member
    @Pharma and @Zink,
    this paper's abstract:
    https://link.springer.com/article/10.1023/A:1019931016615
    seems to say that both the anhydrous and hydrate form are quite stable. 

    Even I cannot access the full text, but if interested, I can try request it through interlibrary exchange. 
  • PharmaPharma Member, Pharmacist
    @lmosca I don't see much usefulness coming from this paper for us... pyrolysis above something around 280°C. Who heats his cosmetics up that much? The one thing is that below this temp., they did not detect any degradation neither in an oxygen nor nitrogen atmosphere.
  • lmoscalmosca Member
    @Pharma agreed, that is not the case, however some of the keywords for the paper refer to Hoffman elimination. Trimethylglycine would be a powerful substrate for a unimolecular elimination, assisted by the enolization of the alpha carbon. If so a pH shift toward a near-neutral to mildly basic, and a 10-15 degrees increase in temperature can accelerate this reaction in a non-negligible way (temperature alone would double the reaction rate every 10 degrees). Unfortunately solid state reactions are far more different than in solution.
    I believe the precaution to be only that, and nothing more, but I would be careful if I were nearby pH of 7. Should you smell fishy, that is the sign that trimethylglycine is getting degraded.
  • PharmaPharma Member, Pharmacist
    @lmosca Nice to have someone here to discuss some organic chemistry :) .
    I can't agree on the Hofmann elimination. Elimination of trimethylamine (the fishy smell) can't happen by traditional Hofmann elimination, because betaine is lacking a vicinal proton but has a carbonyl instead (being nitpicking here, I know). They also observed intramolecular methyl transfer (= dimethylglycine methyl ester) I find highly interesting and obviously standard decarboxylation.
    What makes you think that a pH of 7 is the weakest spot?

    I have to concur that solid state reactions are different to what we usually observe in our 'chemical' everyday life.
    What I frequently observed (my wife isn't too happy about my kitchen chemistry, you can believe me) when heating solutions or water-free melts of betaine or choline salts with compounds like sugars, carboxylic acids, or polyols on a water bath is that distinctive fishy smell which forms already after maybe 20 minutes at temperatures as low as 80°C. Also, replacing the quaternary ammonium compounds with amino acids results in an array of unfortunately too often not very pleasant scents due to Maillard type reactions (for non-chemists: that's the reaction between amino acids and sugars which happens during cooking/baking and gives for example bread crust, grilled meat, or roasted coffee their typical flavours).
    Although all my mixtures should have been stable under my kitchen conditions, they were not. This is likely due to the presence of moisture, air instead of inert nitrogen, and impurities as much as the fault of our nose which is fairly sensitive to certain compounds like said fishy smell.


  • ZinkZink Member
    Thanks a lot, seems like I'll be fine heating it to 40C in water to help dissolve salicylic acid, then adding it to a cooling emulsion at 70C or so..
  • lmoscalmosca Member
    @Pharma, likewise!

    That's what surprised me as well, I've ordered the paper, just to satisfy my curiosity. 

    My idea of elimination would be enolization-like. Whereas enolization is very fast in a system like that, and even more so in a protic solvent, thanks to the protons available to be exchanged, it does not rule out the possibility of trimethylamine (fishy smell) as a mediocre leaving group. 

    pH= 7 was only a guess, I've actually checked the pKa of TMG and it is 1.8-1.9. The enolization would happen on the carboxylic acid, and, only with more difficulty on the carboxylate. 

    Ah, mix some sugar in, some people might like a lotion with "pot roast" scent! :smiley:
    Pharma said:
    Also, replacing the quaternary ammonium compounds with amino acids results in an array of unfortunately too often not very pleasant scents due to Maillard type reactions (for non-chemists: that's the reaction between amino acids and sugars which happens during cooking/baking and gives for example bread crust, grilled meat, or roasted coffee their typical flavours).
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