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Author: Subject: Acetic anhydride preparation
National Hazard

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Registered: 3-11-2013
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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.

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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