Author Topic: aryl halides' sensitivity to metal hydrides...by Rev. Drone(2) -Teonanacatl  (Read 1513 times)

0 Members and 1 Guest are viewing this topic.

dormouse

  • Guest

   the Hive BB
  Serious Chemistry Forum
  aryl halides' sensitivity to metal hydrides...by Rev. Drone
  
profile | register | preferences | faq | search
 
 next newest topic | next oldest topic 
Author  Topic:   aryl halides' sensitivity to metal hydrides...by Rev. Drone 
Teonanacatl
Hive Bee   posted 12-15-1999 04:24 PM          
--------------------------------------------------------------------------------
Hi...I keep getting an error when I try to post on the other thread...maybe that list did throw things off ...anyways, I looked a couple of them up, read through a bit and then decided that I needed to find something more general, something which explains why all these reactions are occuring (or not)...so I did...here's a couple bits of info for you Drone...hopefully you can pull them together better than I could:
This one only kind of applies to the scenarios you're looking at, as it is specific to aromatic nitro derivatives, not aliphatics...basically, in with transition metal derivatives (they list SnCl2, Cu(acac)2, CuBr.SMe2, CuSO4, (Ph3P)Ni, NiCl2, Ni(OAc)2, CuCl2 and BiCl3), aromatic nitro groups can be reduced to amines in ether, dioxane or alcohols WITHOUT changing halogen (including aromatic halogens) or acid groups. Reductions of these aromatic nitro groups with KBH4-CuCl2 in MeOH does not affect bromide or esters, but it does reduce iodides....

they then explore the reduction of aliphatic nitro groups with NaBH4 in THF with palladium on charcoal...reduces the nitro to an amine without affecting esters, nitriles or chlorides, but it does reduce aryl bromides....

a different source stated that aromatic halides are extremely resistant to hydrogenolysis with LAH...LAH reduction of 1-chloro-2-iodobenzene at 65° for 30 min gave 40% chlorobenzene, with 37% of the dihalide recovered...this next one applies very well..."When 3,4-methylenedioxy-5-bromo-beta-nitrostyrene is refluxed for 2 hours with the theoretical amount of LAH the product is 3,4-methylenedioxy-5-bromo-beta-phenylethylamine. When 3,4-methylenedioxy-5-bromo-beta-nitrostyrene is refluxed with excess LAH for 10 hours the aromatic bromine is eliminated to yield 3,4-methylenedioxyphenylethylamine. By employing conditions between the two extremes of LAH concentration and reaction times, a mixture of [the two products] is obtained."...aluminum hydride is reported to reduce aromatic halides as well....

Finally, just a quick mention of catalytic hydrogenation procedures...(aromatic nitro groups again...they seem in general to be slightly easier to reduce than aliphatics with most of the procedures I've seen)...stated that hydrogenation of aromatic nitro groups over a nickel or palladium catalyst occurs in preference to most other functional groups (except double and triple bonds)...with a Pt. catalyst in a neutral solutions, nitro groups reduce preferentially to olefins, but all aromatic halides except flourides are reduced during this reaction....interestingly they mention that this cleavage can be inhibited slightly is the reaction is performed in 1N sulfuric acid over a Pt. catalyst...hydrogenation of nitrobenzenes over platinum oxide in anhydrous HF actually produces p-flouroaniline!

One last thing...does anyone here know much about lithium amino borohydrides? I ran across them and was interested since they can be handled in dry air and actually reduce compounds quite efficiently in dry air reactions...no requirement for N2 atmosphere, plus they're easier to store (last 6 months in dry air conditions...)...unfortunately there was no direct mention of whether they could reduce nitro groups, in the article I read they had only been tested on aliphatic and aromatic esters in dry air (reduction in 30 min. @ 30° C)...anyways, I think I've wasted enough of your time...


 
K.C. Nicolaou
Hive Bee   posted 12-15-1999 11:05 PM          
--------------------------------------------------------------------------------
The one about the bromo-methylenedioxynitrostyrene is pretty interesting and more or less confirms my thoughts about that rxn. As for the catalytic hydrogenation thing, I've got to laugh at the poor bastard who had to run that rxn in HF. Anhydrous HF is quite possibly one of the nastiest substances know to man. What the hell is a lithium amino borohydride?
 
Teonanacatl
Hive Bee   posted 12-15-1999 11:47 PM          
--------------------------------------------------------------------------------
Well...it appears I'm the only one who can't post on that thread anymore...eliminated from the discussion by default ...anyways, I only took a brief glance at the sodium aminoborohydride article, so I can't tell you exactly what they are, but I remember them saying that they could be produced from any amino acid...if it's useful for these procedures, I'm thinking possible OTC source for one of the reagents in forming a nice reducing agent that can be used in reactive (non N2/Argon) environments...know anything about this Drone?...think I should take a closer look?
 
Teonanacatl
Hive Bee   posted 12-18-1999 01:35 AM          
--------------------------------------------------------------------------------
Damn! I'm still stuck with this thread...oh well I'm used to talking to myself...anyways, I took a closer look at lithium aminoborohydrides...they're produced by the reaction of n-BuLi with amine-boranes...but I haven't seen any reference to their ability to reduce conjugated nitroalkenes...it seems doubtful, that and they have been shown to reduce halides...I also discovered that Red-Al easily reduces halides even if acetylinic, so it's probably not to useful for this procedure...I recommend a book called "Reductions by the Alumino- and Borohydrides in Organic Syntheses"..(Jacqueline Seydon-Penne)...it's full of references to a multitude of reductions with over twenty types of reducing agents...also very recent (1997)...K.C., do you know if the Rev. has noticed this offshoot thread to his? Since I can't post on the other thread any more, I can't tell if he's getting this info...
------------------
Danger...ethnic digestion tabernacles on now; privacy robotic doubles, rolling rehab threat machines, reformulators, heightened insensitivity vehicles, erotic invisible empires on now...


rev drone
Hive Bee   posted 12-18-1999 07:16 AM          
--------------------------------------------------------------------------------
Teo,
Under what conditions does Red-Al reduce aryl halides? I'll definatly take a look at that book this week.

My suspicion is that the halide was reduced under reflux conditions (or at least considerably elevated temperatures), since LAH seems impervious to reducing aryl halides until such conditions are met. Am I right?


rev drone
Hive Bee   posted 12-18-1999 07:16 AM          
--------------------------------------------------------------------------------
Teo,
Under what conditions does Red-Al reduce aryl halides? I'll definatly take a look at that book this week.

My suspicion is that the halide was reduced under reflux conditions (or at least considerably elevated temperatures), since LAH seems impervious to reducing aryl halides until such conditions are met. Am I right?

------------------
-the good reverend drone


 
Teonanacatl
Hive Bee   posted 12-18-1999 08:08 AM          
--------------------------------------------------------------------------------
It definately reduced them under reflux conditions...but it also appears that Red-Al is specific to reducing halides, moreso than LAH...here's some info from that book I mentioned:
"The features of Red-Al are the following: It easily reduces halogenated derivatives, even if acetylinic..."
and:
"The alkoxyaluminohydrides reduce aliphatic and alicyclic iodides and bromides but not the corresponding chlorides. An exception is Red-Al in benzene, which reduces all halides , as well as the cyclopropyl and aromatic derivatives. The reduction of 1-bromoalkynes by the latter reagent cleanly gives the debrominated alkyne, unlike other aluminohydrides that give a mixture. Difluoroalkenes, meanwhile, are converted to the monoflouro derivatives.":
RCCBr --(red-al/benzene)--> RCCH
PhCH=CF2 --(red-al/benzene 0°C)-->PhCH=CHF (91%)
PhCH=CF2 --(red-al/benzene reflux)->PhCH=CH2 (86%)

I was curious whether you've looked at NaBH4-CuSO4 in alcoholic medium, which the same book has stated can be used to reduce aliphatic and aromatic nitro groups without affecting halogen or acid groups...(S. Yoo ans S. Lee, Synlett, 419 (1990).
I've also become quite curious about something called the borohydride exchange resin (BER)-Ni(OAc)2 which supposedly reduces aliphatic nitro groups at r.t. in MeOH (no mention of it's affect on halides, although NaBH4/Ni(OAc)2 (which only reduces aromatic nitro groups) does not affect halides...sooo...maybe a reducing agent that reduces aliphatic nitro groups in an easy to use medium at r.t. and may not affect halides? hmmm...sounds to good to be true!

------------------
Danger...ethnic digestion tabernacles on now; privacy robotic doubles, rolling rehab threat machines, reformulators, heightened insensitivity vehicles, erotic invisible empires on now...


Teonanacatl
Hive Bee   posted 12-18-1999 08:10 AM          
--------------------------------------------------------------------------------
Whoops, forgot the ref on that last one (it's from that book too, but here's the primary ref, which I haven't seen yet ) :
N.M. Yoon and J. Choi, Synlett, 135 (1993).
 
Teonanacatl
Hive Bee   posted 12-18-1999 08:13 AM          
--------------------------------------------------------------------------------
Ahhh! One more post...I think I just realized that the borohydride exchange resin (BER) IS NaBH4/Ni(OAc)2! So we do have something here...I think...Drone, what about you?
 
Strontium
Hive Bee   posted 12-18-1999 12:23 PM          
--------------------------------------------------------------------------------
Red-Al will reduce arylhalides under quite harsh conditions. Temps around 90-130 deg C are usually required. And yields are actually piss-poor, 25-55%. So the halides should stay just were they are with milder conditions.
Strontium


Teonanacatl
Hive Bee   posted 12-18-1999 02:19 PM          
--------------------------------------------------------------------------------
Where did you get this from Strontium? I think the main point though is that more caution should be used in reducing aryl halides with Red-al than LAH, since it is actually used in preference for reduction of most halides and has been shown to reduce aromatic halides under some conditions (I have to look up the primary reference to this one to find out exactly what they were and the yield obtained...)
 
rev drone
Hive Bee   posted 12-19-1999 08:45 AM          
--------------------------------------------------------------------------------
I'm a little hesitant about Ni2B- promoted catalytic reductions via NaBH4, since preliminary tests have had such mixed results. If this could be made to owrk as solidly and consistantly as in the literature, this would be a great procedure.
------------------
-the good reverend drone


 
Teonanacatl
Hive Bee   posted 12-19-1999 12:40 PM          
--------------------------------------------------------------------------------
Are these your preliminary tests your talking about? What was the problem?...was it that it reduced halide bonds, or simply didn't reduce nitro styrenes at all...(I'm assuming this may have been the test material  )...
 
Strontium
Hive Bee   posted 12-19-1999 02:38 PM          
--------------------------------------------------------------------------------
Teo:
I´ll give you some refs for Red-Al and arylhalides...
Strontium


alpha
NewBee   posted 12-20-1999 12:40 AM          
--------------------------------------------------------------------------------
A careful re-reading of Shulgin uncovered the synthesis of what he calls ORTHO-DOB which is 2-bromo-4,5-dimethoxyamphetamine. He notes:
"Reduction to the amphetamine had to be conducted at a low temperature and using only an equimolar amount of lithium aluminum
hydride, to minimize reductive removal of the bromo group."

No further details, unfortunately.

The remark about low temperature is kind of interesting in light of the report about 3,4-MD-5-bromo-nitrostyrene being resistant to debromination after 2h in refluxing LAH. Some sort of directing effect, presumably?

For what it's worth, he also reports that the bromination of 3,4-MD-amphetamine proceeded in very low yield.

That's about all that's there, but if you're interested, this is under the META-DOB entry.


chemstu
unregistered   posted 12-27-1999 10:28 PM           
--------------------------------------------------------------------------------
gggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg  ggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg
 
Strontium
Hive Bee   posted 01-15-2000 08:40 AM          
--------------------------------------------------------------------------------
Teo
Here are some examples of reductions of alkyl- and arylhalides with Red-Al.


Compound Temp Product Yield
-------- ---- ------- -----
Fluorobenzene 110 Benzene traces
Chlorobenzene 110 Benzene 2%
Bromobenzene 135 Benzene 53%
Iodobenzene 110 Benzene 45%
Benzylchloride 78 Toluene 55%

1-Chloroheptane 78 Heptane 40%
1-Bromoheptane* 78 Heptane 96%*
2-Bromoheptane 78 Heptane 64%
1,2-Dibromo -''- 115 Heptane 3%
1-Heptene 74%
2-Bromoheptane 16%
(c)Hexylbromide 115 Cyclohexane 14%
Cyclohexene 6%
1,2-dibromo-
cyclohexane 115 Cyclohexene 42%
Cyclohexylbromide 2%


Reaction time was 1 hour.
Reaction time for * was 4 hours

Sorry it took so long time to get this written down.

Strontium


Strontium
Hive Bee   posted 01-15-2000 08:42 AM          
--------------------------------------------------------------------------------
FUCK!!!
It didn´t look like this when I wrote it down. Fuck this software all the way down to the DEA-sulfur pit......

Strontium


Teonanacatl
Hive Bee   posted 01-15-2000 01:42 PM          
--------------------------------------------------------------------------------
Thanks Strontium...don't worry about the formatting, it passes along the info anyways, even if it ain't pretty