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Author: Subject: what form of formaldehyde is used in grignards?
draculic acid69
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[*] posted on 22-11-2018 at 21:51
what form of formaldehyde is used in grignards?


Having read that primary alcohols are formed when grignard reagents are reacted with formaldehyde it doesn't say anything about what form the formaldehyde is in for example is solid paraformaldehyde used or is it decomposed by heating into a gas and bubbled in or ( I doubt this one ) an aqueous 37%solution used? I know grignard s are incompatible with water so don't bother pointing this out any help will be appreciated.
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DavidJR
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[*] posted on 23-11-2018 at 03:51


I haven't done this but I would try generating formaldehyde gas by heating dry paraformaldehyde, and then bubbling that into the grignard reagent.
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UC235
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[*] posted on 23-11-2018 at 06:27


I'm pretty sure that reacting grignards with formaldehyde is something that every textbook teaches and which can be made to work, but is rarely done. Here is an example. The paraformaldehyde has to be decomposed to formaldehyde gas and lead into the reaction mixture: http://www.orgsyn.org/Content/pdfs/procedures/cv1p0188.pdf

The notes indicate to use a wide bore glass tube and considerable excess of paraformaldehyde since it repolymerizes all over the walls. Magpie details his problems with this in this thread: http://www.sciencemadness.org/talk/viewthread.php?tid=18110&...

Note 5 on the orgsyn prep indicates that paraformaldehyde can be added directly, but the yield is substantially lower. Keep in mind that this is paraformaldehyde that was dried for 48h over P2O5 in a vacuum dessicator. Yield would be lower still if not dried.

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draculic acid69
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[*] posted on 26-11-2018 at 18:36


So does anyone have experience with depolymerizing paraformaldehyde into formaldehyde gas and dissolving in ether or thf? Or tips about drying paraformaldehyde?
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clearly_not_atara
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[*] posted on 26-11-2018 at 20:03


The solution is not stable. It must be consumed as it is generated. As the report notes, it repolymerizes onto the glass.

It may adhere less to some plastics. Silica is usually hydroxyl-terminated which may allow it to react with formaldehyde to form acetals.




[Edited on 04-20-1969 by clearly_not_atara]
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Melgar
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[*] posted on 26-11-2018 at 22:00


I wonder if 1,3,5 trioxane could work here? It would definitely interact with Grignard reagents, and it seem like it'd be too reactive to stabilize it as a ligand.



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[*] posted on 27-11-2018 at 07:05


Yeah, 1,3,5-trioxane and paraformaldehyde can be used in Grignard reactions. I have looked into this previously.

Here is a small example of such a reaction in this patent.
https://patents.google.com/patent/US8115028B2/en

[Edited on 27-11-2018 by Loptr]




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