Sciencemadness Discussion Board
Not logged in [Login - Register]
Go To Bottom

Printable Version  
Author: Subject: Adding organics, CHCl3, and concentrated H2SO4?
querjek
Hazard to Self
**




Posts: 76
Registered: 26-8-2008
Member Is Offline


[*] posted on 1-1-2011 at 11:07
Adding organics, CHCl3, and concentrated H2SO4?


Hello,

I am attempting to perform a Schmidt reaction (RCOOH ----NaN3/H2SO4----> RNH2) for a project at school. All of the literature I've found on this reaction suggests to dissolve the substrate in chloroform, add concentrated H2SO4, and then add the NaN3 slowly and later.

The problem is, every time I add the H2SO4, my CHCl3 solution starts to darken and a tar begins to form immediately. I've tried cooling the H2SO4 and CHCl3, as well as making the addition extremely slow. I've also tried extensive drying of the chloroform before use.

Any suggestions to make this run smoothly?

Thanks!




it's all about chemistry.
View user's profile View All Posts By User
mario840
Hazard to Others
***




Posts: 225
Registered: 20-1-2010
Member Is Offline


[*] posted on 1-1-2011 at 11:23


chloroform and H2SO4 is a method of purifying of CHCl3, just use ether or dichloromethane
View user's profile View All Posts By User
querjek
Hazard to Self
**




Posts: 76
Registered: 26-8-2008
Member Is Offline


[*] posted on 1-1-2011 at 11:28


Tried it in DCM and got the same tarry results. Also, lots of literature has said not to use DCM because of its explosion risk with the HN3 formed in situ. Ether I'm not entirely sure about, but I haven't seen that used a solvent in my research, and given its latent explosion risk, adding HN3 doesn't sound like a good idea to me...

[Edited on 1-1-2011 by querjek]




it's all about chemistry.
View user's profile View All Posts By User
rrkss
Hazard to Others
***




Posts: 193
Registered: 18-12-2009
Member Is Offline


[*] posted on 1-1-2011 at 11:31


Distill the the darkened CHCl3 and try again with the more pure distilled product. Usually H2SO4 is added to CHCl3 to destroy organics.
View user's profile View All Posts By User
mario840
Hazard to Others
***




Posts: 225
Registered: 20-1-2010
Member Is Offline


[*] posted on 1-1-2011 at 11:32


why not ?? just generate it from NaN3 and H2SO4 etc. and condensate or not and introduce into solution with rubber hose this is so simple , calculate how many grams do you need and make it from x g of NaN3 , maybe your chemical are bad quality
View user's profile View All Posts By User
rrkss
Hazard to Others
***




Posts: 193
Registered: 18-12-2009
Member Is Offline


[*] posted on 1-1-2011 at 11:37


Quote: Originally posted by mario840  
why not ?? just generate it from NaN3 and H2SO4 etc. and condensate or not and introduce into solution with rubber hose this is so simple , calculate how many grams do you need and make it from x g of NaN3 , maybe your chemical are bad quality


Look up HN3, not a good idea what you are proposing, highly toxic and explosive.
View user's profile View All Posts By User
smuv
International Hazard
*****




Posts: 842
Registered: 2-5-2007
Member Is Offline

Mood: Jingoistic

[*] posted on 1-1-2011 at 11:50


I used to have a reference that pretty meticulously described how to preform the schmidt reaction and prepare the hydrazoic acid solution...unfortunately I cannot find it. I believe this is the citation: Wolff, H. Org. React. 1946, 3.

While hydrazoic acid solutions are dangerous, they may be prepared in a safe manner if proper protocols are followed.

Edit: I found the reference, I can't upload it though because I only have the raw scanned pages, I don't have time to convert to pdf. It sounds like you are doing everything right, although you are generating the HN3 in situ. Maybe you should try an ex situ preparation of an HN3 solution and then add this to your substrate. Ref attached. You could also use benzene as a solvent.

There is a good possibility the compound you are doing the reaction on is not very acid stable causing the strongly acidic reaction conditions to destroy it. I can provide more help if you tell me specifically what compound you are performing the schmidt on.

img021.jpg - 309kB

[Edited on 1-1-2011 by smuv]
View user's profile View All Posts By User
mario840
Hazard to Others
***




Posts: 225
Registered: 20-1-2010
Member Is Offline


[*] posted on 1-1-2011 at 12:22


when you working with HN3 soon or later you will be exposed to this chemical beacuse of low boiling point , withouth experience and most important PROPER LAB GLASS , you will fail , like myfan64 who died probably from phosgene, for me easiest way is bubbling HN3 through ChCl3 or beznzene or ether (of course with a little phenidone), everything is toxic try some 250 g NaCl and good luck to your kidneys
View user's profile View All Posts By User
querjek
Hazard to Self
**




Posts: 76
Registered: 26-8-2008
Member Is Offline


[*] posted on 1-1-2011 at 12:26


Thanks for that reference! I've give it a shot later. Any ideas whether toluene would function as a solvent?

The substrate is methylenedioxyphenylpentanoic acid--I gather that the methylenedioxy bridge isn't too acid-stable?




it's all about chemistry.
View user's profile View All Posts By User
smuv
International Hazard
*****




Posts: 842
Registered: 2-5-2007
Member Is Offline

Mood: Jingoistic

[*] posted on 1-1-2011 at 12:48


Yeah, definitely prepare the Hydrazoic acid first, it is a way weaker acid than sulfuric. If that doesn't work you can do the hoffmann reaction and avoid acidic conditions, use dioxan as a co solvent (might be able to get away with methanol).

OK must stop procrastinating...I will post that full ref later. My gut about toluene is it won't be a good solvent but I can't really think of any reasonable reaction it would undergo with HN3 that benzene wouldn't, but I really haven't given it much thought.
View user's profile View All Posts By User
The WiZard is In
International Hazard
*****




Posts: 1617
Registered: 3-4-2010
Member Is Offline


[*] posted on 1-1-2011 at 14:50


Quote: Originally posted by smuv  
I used to have a reference that pretty meticulously described how to preform the schmidt reaction and prepare the hydrazoic acid solution...unfortunately I cannot find it. I believe this is the citation: Wolff, H. Org. React. 1946, 3.



Me the analogue guy again. The ever useful Merck Index has
a chapter on Named Reactions — Under Schmidt they list your
Wolff ref. and among others -

Review. T.Shioiri, Comp. Org. Syn. 6, 817-821 (1991).

By da the original ref dobe Ber. 57, 704 (1924)


Try this &c., from Google.com/books

Named organic reactions - Page 251

Thomas Laue, Andreas Plagens - 2005 - 310 pages - Preview
Schmidt Reaction Reaction of carboxylic acids, aldehydes or ketones with hydrazoic acid ORC + HN3 ... aldehydes or ketones with hydrazoic acid in the presence of a strong acid is known as the Schmidt reaction.1,2 A common application is ...
View user's profile View All Posts By User
Ozone
International Hazard
*****




Posts: 1170
Registered: 28-7-2005
Location: Good Olde USA
Member Is Offline

Mood: Integrated

[*] posted on 1-1-2011 at 22:31


There must be crap in your chloroform. Concentrated sulfuric acid is routinely used as a clean-up method for halogenated organics--frequently yielding red-tar-stuff.

Acid chould be OK.

Do *not*, however, mix with a strong alkali such as NaOH--You will make carbene and the risks of explosion, etc. increase rapidly.

cheers,

O3




-Anyone who never made a mistake never tried anything new.
--Albert Einstein
View user's profile View All Posts By User

  Go To Top