Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Sonic Hedgehog on January 14, 2018, 07:12:29 AM
-
Hi all,
Does anyone have a simple procedure for the hydrolysis of an amide? Is it easier with acid or base? I wasn't able to find much online...
Or if not hydrolysis, are there any other reactions that amides can undergo at relatively mild conditions?
Thanks
SonicH
-
Did you look under peptide hydrolysis? The acidic conditions are pretty harsh, and I don't happen to recall much about basic conditions at the moment.
-
Basic conditions I used was to reflux with KOH. Probably could work under milder conditions if you tosylate the nitrogen (in case of primary amide)
-
I couldn't find much on peptide hydrolysis unfortunately.
I was going to try heating with NaOH without reflux, hopefully that works.
I don't need to isolate the product of this reaction, I'm just trying to chemically alter the amide in some way. Are there any other reactions that amides undergo at relatively mild conditions (maybe less than 75deg) using common laboratory reagents?
Thanks for your help :)
S
-
Peptide acid hydrolysis came up on this forum about a year ago, and I seem to recall discussing how to degas the constant boiling HCl.
http://www.chemicalforums.com/index.php?topic=89829.msg323413#msg323413
-
I couldn't find much on peptide hydrolysis unfortunately.
I was going to try heating with NaOH without reflux, hopefully that works.
I don't need to isolate the product of this reaction, I'm just trying to chemically alter the amide in some way. Are there any other reactions that amides undergo at relatively mild conditions (maybe less than 75deg) using common laboratory reagents?
Thanks for your help :)
S
They can be alkylated for example. They can be converted into amine using hoffman rearangement. Its realy hard to tell becuase I am not sure what exactly you want to do neither what is your substrate structure
-
They can be alkylated for example. They can be converted into amine using hoffman rearangement. Its realy hard to tell becuase I am not sure what exactly you want to do neither what is your substrate structure
The substrate is a bile acid called tauroursodeoxycholic acid, I'm trying to hydrolyse it, or modify it in some way to change it's mass (I want to change its mass to charge ratio on a mass spec).
Thanks for the Hoffman rearrangement idea, I saw an article using hypochlorite for this reaction but couldn't access the article :/.
The bile acid also has 2 hydroxyl groups which I thought about trying to modify, but I don't want to use dichromate to oxidise, and most other reactions that I know about occur at conditions which are more extreme than I would like...
-
Peptide acid hydrolysis came up on this forum about a year ago, and I seem to recall discussing how to degas the constant boiling HCl.
http://www.chemicalforums.com/index.php?topic=89829.msg323413#msg323413
Cheers, I'll give it a read 😊
-
By far the easiest way to functionalize this material for Mass spec in my mind is to TBDMS protect the alcohols. Such silyl ether protection is a very standard procedure for helping to volatilize compounds that don't want to fly. TBDMS protection is also dead easy using TBDMS-chloride and imidazole at room temp.
-
By far the easiest way to functionalize this material for Mass spec in my mind is to TBDMS protect the alcohols. Such silyl ether protection is a very standard procedure for helping to volatilize compounds that don't want to fly. TBDMS protection is also dead easy using TBDMS-chloride and imidazole at room temp.
That sounds ideal :), I'm using LCMS as opposed to GCMS, so the injection solvent is usually methanol/acetonitrile or water, do you think that reaction would be compatible with acetonitrile for example? A few of the methods I saw online use DMF...
-
Yes, I usually run it in dcm or acetonitrile
Here is a reddit post where I give out some detail on how I like to run such reactions
https://www.reddit.com/r/chemistry/comments/6g7lqk/what_is_your_favourite_chemical_reaction_and_why/
-
Thanks that's really useful :)
-
Be careful because it has two OH groups, you might get mixture of mono/bis silylated compounds. Also the sulfonyl OH might react as well. Silicon has very high affinity for oxygen so you might want to work realy careful to get reproducible synthtetic results
-
You can use a significant overequivalence to make sure there are no mono-substituted ones. For MS, some leftover silyl ether dimer won't matter. Or its easy enough to get off with a silica plug like I mention in the reddit post.
I've never heard of protecting sulfonates with TBDMS, but I feel like it would be very hydrolyzable and fall apart during aqueous workup or in the LC, unlike the protected alcohols. I also had this PM exchange with OP that I would like to post here because it contains important info
Hey mate, I just had a few more questions I was hoping you could help me with regarding the TBDMS reaction.
You mentioned that you need an aprotic solvent- my alcohol is actually in human plasma (which obviously contains water), do you think I would have to remove the water?
Sorry with all the questions, I'm not a chemist haha.
I appreciate your help :)
All the best,
S
Yeah, you definitely would need to totally dry it out. Freeze drying would probably work best.
So its just your molecule in a solution of various salts right? Few to no other organic molecules in it?
PS This sort of discussion is still well suited for doing on your post. We want information disseminated as widely as possible.
-wildfyr
-
@kriggy I found this (http://onlinelibrary.wiley.com/doi/10.1002/047084289X.rb381.pub2/abstract)
tert-Butyldimethylsilyl Trifluoromethanesulfonate
"(highly reactive silylating agent and Lewis acid capable of converting primary, secondary, and tertiary alcohols1b to the corresponding TBDMS ethers, and converting ketones2 and lactones2a,3 into their enol silyl ethers;...
Handling, Storage, and Precautions: the material should be stored under argon at 0 °C. The compound has an unpleasant odor and reacts rapidly with water and other protic solvents.
-
Looks scary :D
im not saying the silylation at the sulphonate will happen but I like to consider all possibilities.
-
@kriggy I found this (http://onlinelibrary.wiley.com/doi/10.1002/047084289X.rb381.pub2/abstract)
tert-Butyldimethylsilyl Trifluoromethanesulfonate
...
Handling, Storage, and Precautions: the material should be stored under argon at 0 °C. The compound has an unpleasant odor and reacts rapidly with water and other protic solvents.
Would it be completely necessary to store under an inert gas?
https://www.cerilliant.com/shoponline/Item_Details.aspx?itemno=c3130131-d64a-4844-b8cd-ed1bacaeaa2f&item=M-108
This reagent^ is surprisingly cheap, has anyone used it before? Does it work as well as TBDMS-Cl?
-
No, I have used it, you dont need inert gas for storage although it keeps fresch longer.
Its similar to TBDMS-Cl, just more reactive.
-
No, I have used it, you dont need inert gas for storage although it keeps fresch longer.
Its similar to TBDMS-Cl, just more reactive.
I hoped that was the case haha
After the derivatization I plan on adding an equal volume of water to the derivatization mix (50:50 water/organic mix)- that wouldn't cause an issue would it? I've read the TBDMS ethers are >100 times more stable to hydrolysis compared to TMS ethers, so hopefully it's ok.
-
"A silylation derivatisaion using N-methyl-N-t-butyldimethylsilyltrifluoroacetamide (MTBSTFA) replaces the active hydrogen with tert-Butyldimethylsilyl (t-BDMS) group. The tert-Butyldimethylsilyl derivatives which are more resistant to hydrolysis and can be up to 10,000 times more stable than TMS derivatives. N-methyl-N-t- butyldimethylsilyltrifluoroacetamide will target sulfonic and phosphoric groups if present"
I just found this- it looks like this reagent will react with sulfonic acid groups, which I really want to avoid :(. TBDMS-Cl might be the better option...
-
MTBSTFA is probably more selektive for sulphonat and phosphate then hydroxyl-groups, I beleive this silylation is catalyzed by acid when it attacks these groups. TBDMS-groups ar stable to water under neutral conditions so your work-up should be OK. If you get silylation on the suphonat this will be more sensitive to hydrolysis and maby can be cleaved during work-up.
-
Sorry, didn't mean to sidetrack this discussion. You should use tbdms-Cl. my post about the trifluoromethane sulfonate was just sharing some info with kriggy since the topic came up.
MTBATFA is an interesting piece of Chemistry to find (thanks! It's new to me) but I don't think you want to deal with it in this case. The simple way is best. If you want a literature procedure I'll be happy to direct you to one (probably plug one of my papers haha).
-
Sorry, didn't mean to sidetrack this discussion. You should use tbdms-Cl. my post about the trifluoromethane sulfonate was just sharing some info with kriggy since the topic came up.
MTBATFA is an interesting piece of Chemistry to find (thanks! It's new to me) but I don't think you want to deal with it in this case. The simple way is best. If you want a literature procedure I'll be happy to direct you to one (probably plug one of my papers haha).
Yeah if you have a few references to methods I'd really appreciate it :)
-
Its in the supporting info of this paper (http://onlinelibrary.wiley.com/doi/10.1002/anie.201506253/abstract) or the main body of this one (http://pubs.acs.org/doi/full/10.1021/acs.macromol.7b02372). Mine are in DCM or DMF, but any moderately polar aprotic solvent has worked fine in my hands as long as its dry. Looking back, I should have added that I dried the organic layer with MgSO4 in my first reference.
You mentioned you're not a chemist, so I would think about going to one of the organic labs at your university and asking an experienced grad student there to run it for you in exchange for an authorship credit or mention in the acknowledgements. It should be a pretty trivial reaction taking only one or two attempts and an afternoon's work. I did add some nitty gritty details in that reddit post you should show them.
Doing this with no synthesis bench experience is not the end of the world, but you're not likely to have good success right away or the right materials/glassware/setup like an organic lab would. And you never know when some technical issues could crop up. For instance, since you will have a charged species (sulfonate salt) it may be necessary to force the product into the organic layer with brine.