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Author: Subject: Interesting hydrodechlorination of PCE to (edit) dichloroethylene
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[*] posted on 20-6-2021 at 04:30
Interesting hydrodechlorination of PCE to (edit) dichloroethylene

Hello all, on my search for a neat chloral procedure for its use in preparing trichloroacetic acid I stumbled upon an interesting paper that discusses a method of preparing dichloroethane (FIX: dichloroethylene) from perchloroethane that proceeds via a perchloroethylene intermediate. For a while I’ve been looking for a simple method of preparing dichloroethane (FIX: dichloroethylene) and spent quite a while looking for a preferable method of obtaining DCE from the rather easily, and cheaply, obtained perchloroethylene. Perchloroethylene (PCE) is used in the dry cleaning industry to get all of your nasty ketchup stains off your cheap $100 suits. All jokes aside, the method enclosed in the paper I will link doesn’t seem half bad. Iron metal is deposited with silver metal via iron reduction of silver nitrate onto its surface. Perchloroethane, or in our case tetrachloroethylene, is reacted in an aqueous solution to hydrodehalogenate our chlorinated solvent. The authors of the paper even were nice enough to provide reaction rates of each product within the paper. I was thinking a modification of conducting the hydrodehalogenation at 90C would help us distill our intended product out of the solution as it is formed. This will also give us the added benefit of speeding up the reaction.

Curious as to what you all think.

BIG EDIT: I have mistaken dichloroethylene for dichloroethane. When I read the paper, their mention of “DCE” was received as dichloroethane and not dichloroethylene

Attachment: wu2014.pdf (790kB)
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[Edited on 20-6-2021 by Opylation]
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[*] posted on 20-6-2021 at 12:58

That is an interesting paper Opylation. I have a synthesis in mind that requires dichloroethylene and it would be very handy if it could be prepared from Perk which is still fairly easily available.
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[*] posted on 21-6-2021 at 07:35

The reaction rates in the abstract are 0.0073 L.m−2.h−1 for Fe, 0.0136 L.m−2.h−1 for Fe/Cu, 0.0189 L.m−2.h−1 for Fe/Ag, and 0.0084 L.m−2.h−1 for Fe/Pd. I don't understand what "L" refers to - liters of hexachloroethane (would be nice) or liters of treated water (would be a joke). But my point is that the reaction rates only vary by a factor of two, so why not use plain iron and skip the bother of plating it? But this seems contradictory to Figure 2 which shows more like a four-fold increase in reaction rate for the plated metals.

I think the problem with applying this to macro scale reduction is that the paper uses a huge excess of iron - 50 grams to reduce 100 mL of a 1000 mL aqueous stock solution containing 20uL of 3M methanolic hexachloroethane (HCA? where does this acronym come from? Hexachloroacetylene?). So the proportion of reactant to iron in the paper is infinitesimal. The yield may not be as good at a preparative proportion.

In the paper, which uses too many acronyms, DCE refers to 1,2-dichloroethylene. Figure 5 shows that the product from dechlorination of hexachloroethane, by way of TCE (1,1,2-trichloroethylene) according to Figure 7, is a mixture of what looks from the graph to be 52% cis-1,2-dichloroethylene and 24% trans-1,2-dichloroethylene. Hopefully your intended use for the 1,2-dichloroethylene works with a mixture of isomers.

Edit: This post kept failing to post because I tried to use a mu character instead of a "u" for microliters. Does anyone have a suggestion?

[Edited on 21-6-2021 by Jenks]
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