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Author: Subject: Acetic anhydride preparation
clearly_not_atara
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[*] posted on 14-5-2016 at 17:39


byko3y: Noted. Although I continue to insist that the differences in reactivity between SCl2 and S2Cl2 can be considered analogous to C2H4Cl2 vs CH2Cl2. SCl2 has a much smaller dipole moment because the two S-Cl bonds are in opposing directions. Likewise SOCl2 and COCl2 have large dipole moments because the C=O and S=O bonds are highly polarized.

It seems like the intent was to make anhydrous zirconium (IV) sulfate, Zr(SO4)2, which is both a dehydrating agent and a Lewis acid. Zirconium (IV) and titanium (IV) both like to form covalent-ish bonds with chlorine, nitrogen and oxygen, and TiCl4 is volatile. However, note that while it is a metal salt, it's not exactly easy:

". Excess water was evaporated on a water-bath and the resulting sample was oven-dried at 120 °C for 12 h and calcined at 500 °C for 4 h in air atmosphere and stored in vacuum desiccator."

I doubt that anhydrous zirconium sulfate can be made by an "easy" method. It's likely that simply adding zirconium to anhydrous sulfuric acid will result in passivation. In this case the half-reaction comprises 3 moles of Zr(SO4)2 reacting with 5 moles (acid / 2) of water.

http://www.sciencedirect.com/science/article/pii/00406031938...

Notably, the method as reported is consistent with this analysis of the thermodynamics of zirconium sulfate, since Zr(SO4)2 begins to decompose just above 500 C at 540 C. The half-reactions are Zr(SO4)2 + H2O >> Zr(SO4)2*H2O, Zr(SO4)2*H2O + H2O >> Zr(SO4)2*2H2O, and the one where I know the energetics, 2 AcOH + ~90 kJ/mol >> Ac2O + H2O. So the heat of hydration of Zr(SO4)2 would have to be at least 90 kJ/[mol H2O], probably higher as entropy decreases.

[Edited on 15-5-2016 by clearly_not_atara]
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[*] posted on 26-1-2017 at 15:17


What about decomposition of an acetate using dry chlorine, related to the production of nitrogen pentoxide:
2AgNO3+Cl2->2AgCl+ N2O5+O2
Enthalpy of formation:
Acetic Anhydride:-625 kJ/mol
Sodium Chloride:-411 kJ/mol
Sodium Acetate:-709 kJ/mol

Assuming we use sodium acetate, the reaction is not favored, but there may be a way to drive the reaction in favor, perhaps by using a silver salt and then recovering the silver.
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[*] posted on 7-2-2017 at 17:09


Chlorine will probably attack acetic anhydride, since the alpha-protons on anhydrides act similar to ketones, i.e. enolizability and stuff. Silver acetate can already be used to prepare acetic anhydride by simple heating as long as it's done under the right conditions. Apparently the AgOAc and surrounding atmosphere has to be completely dry to produce Ac2O because otherwise it undergoes water-catalyzed decomposition to CO2 and acetone.

There's also a method with zinc acetate that sadly has 25% theoretical yield and a possibility of using copper acetate as well although I've never seen literature on Cu(OAc)2 decomposition specifically. I'm guessing all of the dry distillation methods require exquisitely anhydrous conditions.

Another possibility if it works might be to react methylene halides with silver acetate to get the acylal (AcO)2CH2 which decomposes to Ac2O in the presence of catalytic acid. According to this page the bp of methylene diacetate is 164 C:

http://www.apolloscientific.co.uk/display_item.php?id=41521

CH2Cl2 seems much nicer to work with than Cl2, assuming it's actually reactive enough (or you'd have to use the iodide or bromide instead).
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[*] posted on 8-2-2017 at 07:53


Quote: Originally posted by clearly_not_atara  

Another possibility if it works might be to react methylene halides with silver acetate to get the acylal (AcO)2CH2 which decomposes to Ac2O in the presence of catalytic acid. According to this page the bp of methylene diacetate is 164 C:

http://www.apolloscientific.co.uk/display_item.php?id=41521

CH2Cl2 seems much nicer to work with than Cl2, assuming it's actually reactive enough (or you'd have to use the iodide or bromide instead).



All possible way for synthesis of methylene diacetate by reaxys

(item 4/36 and 19/36 and is interesting):

Quote:

Methylene Diacetate Stock Solution:
Bu4NOAc (11.4 g, 37.8 mmol) and anhyd benzene (60 mL) wereplaced in a round-bottomed flask equipped with a Dean–Stark apparatus. This solution was refluxed under an argon atmosphere with continuous removal of the azeotrope over a period of 1 h. Then the flask was connected to a vacuum line to remove the rest of the benzene. Finally, anhyd CH2Cl2 (37 mL) was added to the flask containing Bu4NOAc (11.2 g, 37.1 mmol) under an argon atmosphere.
This stock solution was allowed to stand at r.t. for 3 d before use and then kept at 4 °C
Boron Trifluoride Mediated Prins Reaction of Methylene Diacetate with Styrenes. One-Pot Synthesis of 3-Chloro-3-arylpropanolsAlper Isleyen, Özdemir Dogan*Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
item 19/36




Attachment: Methylene Diacetate.pdf (309kB)
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[Edited on 8-2-2017 by Waffles SS]
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[*] posted on 8-2-2017 at 10:02


Well now I'm not sure if silver acetate would work or not. Apparently acetate ion will eventually react with CH2Cl2, so the counterion shouldn't matter *too* much, right?

Tetrabutylammonium acetate would of course be preferable. I wonder if you can get away with tetraethylammonium acetate? But take precautions in handling tetraethylammonium (full body covering) as its salts are highly neurotoxic and you don't want it on you
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