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Author: Subject: Some questions on Lucas reaction + amine alkylation
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[*] posted on 1-6-2019 at 04:40
Some questions on Lucas reaction + amine alkylation


Well this forum has helped me a lot and this is my first post here so I want to make a few annoying questions :D.

1. What are the usual reaction conditions for Lucas reaction on a primary alcohol?
2. Can I use a heavy excess of alcohol to get volatile alkyl halides like chloroethane dissolved in it? I know they are very soluble in it. I could think of something to separate the water.
3. Can I use Lucas reaction to ciclize an hydroxyamine? Like, applying the reagent and heating then slowly neutralizing.
4. How much should I worry about side reactions? I know amines are much more nucleophilic than most other stuff, and I hope that if there is an excess of alkyl halide, it would slowly react with e.g. the less nucleophilic alcoholic solvent. But there are pretty electron-rich, heterocyclic aromatics too, and I'm worried that they might get an electrophilic aromatic substitution or something.
Thanks for any comment. If I'm breaking forum rules or something of the sort, I'm really sorrry :(.
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Boffis
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[*] posted on 1-6-2019 at 08:45


If you want a sensible answer you will need to supply a reference or an example. I have never heard of the Lucas Reaction only Lucas reagent which is a solution of zinc chloride in conc HCl that is used to distinguish between primary, secondary and tertiary alcohol but this is clearly not relevent here. Without a bit of background your questions don't make any sense. I could go off and do some research but if you can't be bothered to provide some background why should we spend our time researching the problem so we can answer it?
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[*] posted on 1-6-2019 at 15:25


Okay, what I call "Lucas reaction" is the nucleophilic substitution performed by the Lucas reagent on an alcohol. Like here but using ZnCl2, essentially the Lucas reagent. I seriously thought this was the name of the reaction... But hey, don't be angry; I mean, I've registered on this forum just to ask this, so this must've been my last resource in order to get this information, right?
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[*] posted on 1-6-2019 at 19:36


Quesion 1: Primary alcohols do not react appreciably with Lucas reagent at room temperature.
When it comes to primary alcohols especially, lucas reagent is usually just used as a test solution for analytical chemistry.
Ive never heard of anyone using zinc chloride and hydrogen chloride to substitute a primary alcohol, its probably not an easy thing to do and the yields will suck, just convert to the bromide instead.

Question 2: Maybe but it would be smarter to set up a distillation apparatus and attempt to condense and capture the more volatile product, considering chlorides are always more volatile that their alcoholic counterpart (due to lack of hydrogen bonding) this should be the case with all substitution reaction where a halide is the attacking neucleophile.

Question 3: ??? What the fuck are you on about here. You need to explain this alot more.

Question 4: Electrophilic substitution reaction on aromatics require an anhydrous lewis acid and a halogen, You have neither so that wont happen.
As for amines reacting with lucas reagent, all i know is ammonia forms complexes with zinc chloride, so i would say its likely that some other amines would react similarly.
Amines are basic and HCl and zinc chloride are acidic, they will neutralize one another under virtually all conditions.

No one is angry at you, this forum comprises mostly of old chemists whose interest lies solely in chemistry, most do not care at all about trying not to stand on your toes and will be very blunt.
Thats just the culture of the forum.




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[*] posted on 1-6-2019 at 20:41


I've heard of people using zinc chloride and hydrogen chloride to substitute a primary alcohol.
Took me about a minute to find it in prepchem for ethanol.
They said the yield is almost quantitative.

Bromide would be a lot better for alkylating ammonia though.
Easier to handle too with the higher boiling point.




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This sounds like the best idea since putting ortho tricresyl phosphate in Ginger Jake.
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[*] posted on 2-6-2019 at 07:54


Yes, ZnCl2/HCl will convert primary alcohols to alkyl chlorides. We did it in my undergrad o-chem lab.

Without knowing your substrate, I can't comment on possible side reactions.




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