Author Topic: Synthesis of methylene bromide  (Read 1469 times)

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Antoncho

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Synthesis of methylene bromide
« on: October 17, 2001, 10:19:00 AM »
Guys i can't believe it but since this obviously isn't on Rhodium's site as well as non-TFSEable i assume it hasn't been covered.
Ah, this lovely TFSE - it brings about such a wonderful wealth of info as well as ever-present fear of being ridiculed :) ...

I just followed the ref that Cherrie Baby posted, the US patent #2553518.

The authors state this as a general procedure for convertion of any mono- or poly- chlorinated alkane or cycloalkane to the respective bromides. This is achieved through bubbling HBr into chloroalkane and some AlBr3 or AlCl3 at RT , although higher temps are also of use. The Al bromide can bee made in situ from Al powder (for those fond of Friedel-Crafts: this looks like an easy way to make anh. AlCl3 8) )

This is sort of a digest procedure from examples 3 and 6 (that's 'cause #6's only purpose is to show that AlBr3 can bee generated in situ and in the rest they use ready AlCl3/AlBr3)



Gaseous HBr is bubbled through a suspension of 2,7 g of Al powder in 239 g CHCl3 until the weight of HBr passed in is 289 g. Al promptly dissolves in the beginning of the addition. The rxn is then washed w/water, dryed and analyzed. It was found to consist of 2% unreacted chloroform, 15% CHBrCl2, 40,9% CHBr2Cl and 41,2 CHBr3.




Antoncho

Rhodium

  • Guest
Re: Synthesis of methylene bromide
« Reply #1 on: October 17, 2001, 11:09:00 AM »
And you suggest that this procedure should be applied on dichloromethane to give dibromomethane/bromochloromethane? Sounds okay.

catastrophe

  • Guest
Re: Synthesis of methylene bromide
« Reply #2 on: October 17, 2001, 12:12:00 PM »
Nice find Antoncho! Just wanted to clarify, but did you notice they were making bromoform and not DBM? However after reading this...


The authors state this as a general procedure for convertion of any mono- or poly- chlorinated alkane or cycloalkane to the respective bromides. This is achieved through bubbling HBr into chloroalkane and some AlBr3 or AlCl3 at RT , although higher temps are also of use.




...it seems it would work just fine. Nice!
Do you think it would be possible to replace NaI with NaBr in the diiodomethane synth on Rhodium's to give DBM?

https://www.thevespiary.org/rhodium/Rhodium/chemistry/ch2i2.html




catastrophe

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Re: Synthesis of methylene bromide
« Reply #3 on: October 17, 2001, 12:18:00 PM »
Oh BTW... really like your work on the Mn(C2H302)3 and also the AA via S2Cl2. Very good research, bravo.

Rhodium

  • Guest
Re: Synthesis of methylene bromide
« Reply #4 on: October 17, 2001, 01:09:00 PM »
Catastrophe: No, that procedure only works with NaI.

Aurelius

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Re: Synthesis of methylene bromide
« Reply #5 on: October 17, 2001, 03:11:00 PM »
catastrophe, that rxn is something like "finkelstein" rxn.  not exactly sure the exact spelling.

catastrophe

  • Guest
Re: Synthesis of methylene bromide
« Reply #6 on: October 17, 2001, 03:59:00 PM »
Hey Rhodium, NICE PAGE! You've really tightened everything up, noticed it when getting the CH2I2 link...
Anyways thanks for the responses you two. Will definitely look up "finkelstein" rxn.
If one were to make some CH2Br2, are the methylenation type reactions similar to CH2I2? Swic was thinking a route to MMDA via hydroxyvanillin in an aprotic solvent like acetone(no DMF :( ), some CH2Br2, and K2CO3 as the base, followed by a 4 day reflux. Would this be viable, or is the iodide required? Thank you.

PolytheneSam

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Re: Synthesis of methylene bromide
« Reply #7 on: October 17, 2001, 04:46:00 PM »
I saw that in the Merck Index before (under methylene bromide).  The references (last of page of patent) are pretty good, too (US patents 1891415, 2120675 and 2347000) Also, US patent 3923914 which gives US 2553518 as a reference is good, too.  3923914 involves the use of an alkali metal bromide.

http://www.geocities.com/dritte123/PSPF.html

Antoncho

  • Guest
Re: Synthesis of methylene bromide
« Reply #8 on: October 17, 2001, 10:06:00 PM »
Thanks, Sam, these patents are also good. i strolled thru them and now i'm 100% positive the same method will work for specifically for DBrM (instead of 97,5% positive as before :) ) as they make it specifically with essentially the same rxn.
(Actually, i posted this to bee a CH2Br2 method since Cherry Baby said it was the reference in Merck for preparation of it, although it's not mentioned in the patent.)

It also should bee noted that elemental bromine is just as suitable for this rxn, although technically of course more difficult.

Antoncho