Sciencemadness Discussion Board - Bromoacetone from Copper (II) Bromide

Bromoacetone from Copper (II) Bromide

TheMrbunGee - 14-12-2016 at 00:56

So I was just experimenting with Copper bromide, reacted HBr with CuO, got green solution, I evaporated off the water and it became violet, dried it more and It became grey!

That is all fine, strange was that I tried to purify it by dissolving it (purple stuff) in acetone, so again - In lower concentrations solution was dark green and higher concentration solutions was dark violet! It was really nice looking color change, so I took some of solution and put in small vial (air tight, ember glass, in a dark place)

Two days later - something that really bring tears in my eyes had happened! Literally! Solution (which was really dark green) has turned pale green, and I now have tear gas in the vial!

Okay, I understand, that bromoacetone has formed, but the real question is - where did the copper go? There is no precipitate, and the color is nearly gone! What colorless copper compound has formed?

woelen - 14-12-2016 at 02:49

The copper is reduced to copper(I) and this apparently forms a complex with acetone.

I think that a redox reaction occurred, something like

2 CuBr2 + CH3COCH3 ----> 2 CuBr + HBr + CH2BrCOCH3

The CuBr most likely formed a soluble complex, either with acetone or with the bromoacetone. CuBr is colorless, the acetone-adduct apparently also is colorless.

Try adding a few drops of the liquid to cold water. I expect formation of a white precipitate, which in contact with air quickly turns dirty brown/green, due to oxidation by oxygen from air.

JJay - 14-12-2016 at 09:22

Very interesting. I wonder if CuBr in acetone will react with aluminum. CuCl2 in acetone does not, or if it does, the reaction is not very vigorous at room temperature. I played around with it a while back to see if I could find a quick and easy means to form aluminum chloride but set it aside when I learned that aluminum chloride is difficult to remove from acetone.

I'm not sure if CuCl2 will produce chloroacetone with acetone at room temperature with no catalyst, but at no point did I notice any lachrymatory fumes.

Of course, CuCl2 in water cuts through aluminum like a hot bandsaw through Crisco. I assume that CuBr2 will do the same.

[Edited on 14-12-2016 by JJay]

AvBaeyer - 14-12-2016 at 19:48

The reaction of copper(II) halides with ketones to give monohaloketones is a well recognized reaction. One of the first people to study this was J Kochi who had several JACS papers on this. If you use Google scholar and search for Kochi's papers then look at the citations you will find plenty of information. As it turns out, ketone halogenation with Cu(II) halides is a very useful synthetic reaction.

AvB

TheMrbunGee - 14-12-2016 at 22:56

Quote:

I wonder if CuBr in acetone will react with aluminum

It does not!

Quote:

Of course, CuCl2 in water cuts through aluminum like a hot bandsaw through Crisco. I assume that CuBr2 will do the same.

It does react, but not as vigorous!

Quote:

Try adding a few drops of the liquid to cold water. I expect formation of a white precipitate, which in contact with air quickly turns dirty brown/green, due to oxidation by oxygen from air.

It did formed white precipitate, I just did the experiment, It has not turned green/brown yet!

Thanks for the answers, guys!

As always - very helpful!

JJay - 14-12-2016 at 22:58

This paper (one of Kochi's early ones) says that rate of the reaction is dependent on halide ion concentration, in particular, chloride....

TheMrbunGee, is it possible that there was some water present in your acetone or copper (ii) bromide?

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TheMrbunGee - 14-12-2016 at 23:12

Quote: Originally posted by JJay

This paper (one of Kochi's early ones) says that rate of the reaction is dependent on halide ion concentration, in particular, chloride....

TheMrbunGee, is it possible that there was some water present in your acetone or copper (ii) bromide?

Yes, it had, I evaporated the water @ 40°C, and because the bromide is hydroscopic - some water was present! And the concentration was high, I dissolved about 10g of bromide in about 40ml of acetone.

JJay - 14-12-2016 at 23:51

I wonder if the reaction would still take place if you used really dry acetone and dehydrated your CuBr2 at 300 C for several hours.

It does look as though the method you used is one of the safest ones for preparing a haloketone.

[Edited on 15-12-2016 by JJay]

TheMrbunGee - 15-12-2016 at 00:23

Quote: Originally posted by JJay

I wonder if the reaction would still take place if you used really dry acetone and dehydrated your CuBr2 at 300 C for several hours.

It does look as though the method you used is one of the safest ones for preparing a haloketone.

[Edited on 15-12-2016 by JJay]

I would try it, but I ran out of acetone!

Not sure, when I am going to get some more! :?

About that - yes, and I think there is a pretty decent yield!

Haven't tried to purify it, I really suck it the field of equipment!

JJay - 15-12-2016 at 01:59

I'm thinking about giving it a try on an extremely small scale....

AvBaeyer - 15-12-2016 at 14:48

Here are some papers from my files which point to the broad utility of Cu(II) halides as halogenation reagents. A wide variety of solvents can be used for the reaction. I have used ethyl acetate and chloroform as solvents with excellent results. Cupric chloride is easily available but seems to require lithium chloride as an activator for good results. Cupric bromide is much more reactive but is difficult to find and often quite expensive. Interestingly, cupric bromide is reactive enough that it can used catalytically in conjunction with eg potassium bromide for bromination reactions.

Have a look at these papers. The cupric halides are interesting reagents for examination in the home lab.

AvB

Attachment: Cupric Chloride halogenation JOCv28p630 .pdf (561kB)
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Attachment: Cupric Halide Halogenations Castro paper.pdf (704kB)
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Attachment: Reactions of Some Organic Compounds with Cupric Bromide fort1961.pdf (336kB)
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Attachment: Reduction of Cupric Chloride by Carbonyl Compounds Kochi.pdf (617kB)
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mayko - 15-12-2016 at 17:39

Quote:

I wonder if the reaction would still take place if you used really dry acetone and dehydrated your CuBr2 at 300 C for several hours.

Heads up: cupric bromide is not very heat-stable. At high temperature, it will decompose to cuprous bromide and elemental bromine:

2CuBr2 -> 2CuBr + Br2

This happens at fairly low temperatures, so I'm not sure where the literature melting point comes from. Brauer says the decomposition occurs on "dry heating", but I don't know how 500C could be called a wet heat. Brauer also says that solutions of cupric bromide decompose at the boiling point, but I did not observe this. This is probably why the preferred drying method is in vacuum over a desiccant. I had good results by heating an aqueous solution in a water bath most of the way, then adding portions of anhydrous ethanol to evaporate off the water azeotrope, then heating the rest of the alcohol off below the bp of water. But, good luck getting it bottled before it absorbs ambient moisture!

I mention this both because it sounds like the decomp is being described here:

Quote:

I evaporated off the water and it became violet, dried it more and It became grey!

and as a safety consideration, so no one is caught unawares by bromine fumes

Solid copper bromide is a purple-black crystalline solid, looking very much like elemental iodine. (I'd hesitate to call it violet, though the cobalt salt is a spectacular lavender) It's far and away the most deliquescent substance I've ever seen:

Cuprous bromide and lingering bromine, after heating the cupric salt:

Cuprous bromide after washing:

JJay - 15-12-2016 at 19:21

Quote: Originally posted by mayko

Quote:

I wonder if the reaction would still take place if you used really dry acetone and dehydrated your CuBr2 at 300 C for several hours.

Heads up: cupric bromide is not very heat-stable. At high temperature, it will decompose to cuprous bromide and elemental bromine:

2CuBr2 -> 2CuBr + Br2

Interesting. Apparently, this decomposition can be detected at temperatures as low as 50 C, and it continues to completion above 280 C... so drying at 300 C is definitely not a good idea. Wikipedia says to dry CuBr2 over phosphorus pentoxide.

It looks to me as though the kinetics for the ketone halogenation reactions of different copper halides would be very different.

I'm burning with curiousity about what would happen if you refluxed aluminum turnings with toluene, acetone, and CuBr2.

[Edited on 16-12-2016 by JJay]

Metacelsus - 15-12-2016 at 20:07

I've seen papers using Li₂CuBr₄ and Li₂CuCl₄ as mild halogenating agents, but in general the system has to be highly activated towards halogenation.

Edit: Fixed typo

[Edited on 12-16-2016 by Metacelsus]

JJay - 16-12-2016 at 02:29

I do wonder what exactly is going on here... it seems likely that aluminum is initially unreactive towards CuBr₂ in acetone because of the protective oxide layer... I suspect it would react pretty readily with an amalgam, but finding out by experiment requires being set up to deal with mercury waste.

[Edited on 16-12-2016 by JJay]

careysub - 16-12-2016 at 09:42

Quote: Originally posted by AvBaeyer

Here are some papers from my files which point to the broad utility of Cu(II) halides as halogenation reagents.

Any thoughts or insights how it might compare to making/using NBS for bromination (in either case I would need to prepare the bromination agent)?

DraconicAcid - 16-12-2016 at 09:57

Quote: Originally posted by Metacelsus

I've seen papers using LiCuBr₄ and LiCuCl₄ as mild halogenating agents, but in general the system has to be highly activated towards halogenation.

LiCuBr4 would contain Cu(III) and wouldn't be mild anything. Li2CuBr4?

Metacelsus - 16-12-2016 at 10:32

Yep, typo.

AvBaeyer - 16-12-2016 at 16:58

careysub:

In response to "Any thoughts or insights how it might compare to making/using NBS for bromination (in either case I would need to prepare the bromination agent)?"

I would generally favor NBS or 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) which is easily and very cheaply available relative to NBS. With a catalytic amount of p-TosOH, DBDMH easily and mildly brominates, for example, acetophenone and ethyl acetoacetate. I can post a tested procedure for this if you would like as well as some supporting references.

The only time I have found cupric bromide singularly advantageous was in the bromination of acetylpyridines. The reaction is run in ethyl acetate/chloroform and the product is the hydrobromide salt of the brominated ketone (soluble in the reaction solvent) thereby providing protection from self reaction.

(Un)forunately, not too long ago I got nearly a half-kilo of cupric bromide so now I will have to find something useful to do with it.

AvB

careysub - 16-12-2016 at 17:11

Quote: Originally posted by AvBaeyer

I would generally favor NBS or 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) which is easily and very cheaply available relative to NBS.

I have succinic acid and so could *make* NBS from bromine.

I have not found DBDMH to be easily available on a recent search, only BCDMH (1-Bromo-3-chloro-5,5-dimethylhydantoin).

Products that are listed in recent MSDS's (even ones dated as revised this year), and on-line, as being DBDMH were, on actual inspection of the shipping product to be BCDMH, which may serve, but with chlorine contamination.

Does anyone know of a product currently available consisting of DBDMH?

JJay - 16-12-2016 at 17:50

I've seen TBCA sold locally at department stores as a brominating agent for spas, but it doesn't seem to be very popular among amateur chemists.

I imagine it's a little more unwieldy to use than NBS.

[Edited on 17-12-2016 by JJay]

150px-Tribromoisocyanuric_acid.svg.png - 3kB

150px-Tribromoisocyanuric_acid.svg.png - 3kB

careysub - 17-12-2016 at 10:21

I followed up on a few leads sent to me, and did a bit more investigation and have confirmed that DBDMH is entirely gone from the market.

I have even gotten responses from two major "bromo tab" vendors (as well as two major distributors) and they have all confirmed that no DBDMH exists in any of the products they make/carry (but, see, this is an *improvement* I am assured).

Curious that this seems to have happened to the entire market within the last couple of years.

All products that formerly had it (even if the manufacturer and seller still claims that it is all bromine) now have the bromo-chloro version.

If anyone can actually find some (possibly old stock) please let me know.

Currently the only source seems to be ordering from China.\
[Edited on 17-12-2016 by careysub]

[Edited on 18-12-2016 by careysub]

careysub - 18-12-2016 at 14:30

The DBDMH saga continues (maybe this should be its own thread).

I have just been alerted by a vendor that Brilliance For Spas Sanitizer (NOT Bromo Tabs) still contains DBDMH.

I am ordering some to see if this is really true.

I have been burned before by advertised products showing DBDMH on the label (and on the website advertising, and on the MSDS) but not having it when I received it, but this vendor is telling me that they have this in stock.

[Edited on 18-12-2016 by careysub]