Sciencemadness Discussion Board

Possible Hydrodehalogenation?

wakatutu - 7-12-2018 at 00:11

2Cu2O + 2HCl + CH2Cl2 ---->

2CuO + 2CuCl + H2 + CH2Cl2 ---->

2Cu2O + HCl + CH3Cl + Cl2

What I'm describing here is the reaction of Cuprous Oxide with Hydrogen Chloride to produce Cuprous Chloride, Cupric Oxide and Hydrogen. The Hydrogen reacts with Dichloromethane to produce Chloromethane and Hydrogen Chloride while the Cuprous Chloride and Cupric Oxide react to form Cuprous Oxide and Chlorine.

It may be that this same balancing act takes place in which the copper forms an intermediate compound with dichloromethane directly, which would be a different equation altogether.

I'm posing this as a question - does this seem feasible? If not, why not?

EDIT: I remembered to put chlorine in the written description but forgot to write it in the equation. Thanks metacelsus

[Edited on 7-12-2018 by wakatutu]

[Edited on 7-12-2018 by wakatutu]

Metacelsus - 7-12-2018 at 11:27

Take another look at your equations. I don't think they're balanced (specifically, the second reaction).

Also, Cu2O isn't a strong enough reducing agent to produce H2 from HCl.

However, copper(I) salts are effective for some dehalogenations, so you might not be completely wrong. See for example:

[Edited on 2018-12-7 by Metacelsus]

AJKOER - 9-12-2018 at 12:04

My suspicions on how the RT reaction is proceeding are as follows:

The first reaction resembles a cuprous / H+ / O2 electrochemical reaction (a battery cell) resulting in a cupric and the release of an electron. The electron can further react with H+ to form a hydrogen atom radical (e- + H+ --> .H), some of which can self react forming hydrogen (.H + .H = H2). The latter radical is then the operative reducing agent (being created in the first reaction courtesy of cuprous) that results in the removal of a chlorine atom creating HCl. Hence the term hydrodehalogenation.

Note, the reference supplied by Metacelsus cites other reactions that normally operate at high temperatures, where H2 is converted into the hydrogen atom radical (also referred to as just the hydrogen atom).

[Edited on 9-12-2018 by AJKOER]

wakatutu - 9-12-2018 at 21:20

Thanks, AJKOER.

It makes sense that there would be an essentially electrochemical mechanism at work here.

I put together the equations based on the starting materials and the ending materials. Around 15 months ago, I was extracting 5-OH-Vanillin from an acidified and mostly dehydrated reaction mixture containing copper salts (Cu2O, CuCl), sodium chloride, sodium bromide, and hydrogen chloride using DCM at reflux temperature (which is 34C in my locale). This process took exceedingly long (30 hours, maybe more, can't remember exactly and don't feel like grabbing my notes).

As a result, during the evaporation process I developed profoundly disturbing neurological symptoms, and painful pulmonary symptoms. Extensive research indicated that my symptoms were extremely similar to case reports of MeCl, MeBr, and MeI poisonings. And washing up with acetone produced lachrymatory symptoms consistent with haloacetone case reports (which were difficult to find btw).

So about 6 months ago I got down to trying my hand at balancing equations to figure out what exactly DID happen. I realized that the end result of this mystery reaction had to be a halogen (or interhalogen) and a methyl halide. It seemed unlikely that the amount of bromine in the reaction would be sufficient to produce enough methyl bromide to cause the problems, and no clear path to that compound appeared likely to have occurred.

For what it's worth, I made a complete recovery. The first several weeks I had daily recurrence of the neurological symptoms, slowly progressing toward milder symptoms, and at some point the episodes began to take place less regularly. My last episode took place about 2 weeks after the previous one, in January of this year.