[amg]

Hi! So I'm new to an organic chemistry lab, and one of the first reactions I had to set up and run was a BOC protection. I'm trying to understand the mechanism of the reaction.

I used:
N-benzylglycine hydrochloride (being protected)
Triethylamine
Di-tert-Butylcarbonate (BOC group)
Water
HCl

After stirring the first four ingredients for a few hours, an aqueous HCl solution was added until the pH was 2. Why would I need to add the HCl? And in the deprotection, we also add HCl...why does it work in the protecting and deprotecting?? Any help at all will be greatly appreciated!

[PhDoc]

amg,

It's important that you demonstrate reasonable effort in showing that you've attempted to understand your experiment. For your own convenience in being guided to that understanding, please make two lists. First, the list of all reagents and quantities (mmol) used for the BOC protection, and second a comparable list for the deprotection. How do these two lists differ?

Also, it's very important that you are cognizant of the Lewis structure of each and every reagent used in the experiment.

[amg]

For protection:
N-Benzylglycine hydrochloride: 24.7954 mM
Triethylamine:54.5499 mM
Di-tert-butylcarbonate:29.7545 mM
Water:250 mL

I never performed a deprotection, I simply had it explained to me - probably part of why I'm so confused. I only know that HCl is involved.

I know the Lewis structure of the N-benzylglicine hydrochloride and the Di-tert-butylcarbonate, as well as the product, but my background in chemistry isn't huge (I'm a high school senior, and this is an internship, just for the summer), and I'm having trouble understanding how the whole thing functions, mostly how the HCl plays a role in both adding the BOC group and removing the BOC group. Even just a hint down the right path would helpful to my understanding. I've tried researching it, but I haven't been able to find much in the way of explanation.

Also, I like your icon!

[discodermolide]

HCl is not involved in the synthesis of the Boc protected amine. The amino acid comes as its hydrochloride salt, the triethylamine is there to remove that HCl salt and generate the free amine.
To remove the Boc you can use aqueous HCl, which will hydrolyse the compound back to the original starting material.

[amg]

HCl is not involved in the synthesis of the Boc protected amine.

The procedure I was given by my supervisor uses HCl though.

[discodermolide]

Perhaps in the work-up of the reaction?
Boc protection of amines does not use HCl.

[AlphaScent]

I would listen to disco and lennox.  They are both great for this forum.  But I am surprised you didnt simply google this.  Boc is a very common protecting group.  One would not have to versed in organic chemistry to simply google something. 

Acid is not used until the deprotection.  Did this in my lab not too long ago and it worked great.

Here is a start, you can deal with the mechanism.

http://en.wikipedia.org/wiki/Di-tert-butyl_dicarbonate

[TwistedConf]

After stirring the first four ingredients for a few hours, an aqueous HCl solution was added until the pH was 2. Why would I need to add the HCl? And in the deprotection, we also add HCl...why does it work in the protecting and deprotecting?? Any help at all will be greatly appreciated!

You probably acidified to make sure that you isolated 100% of the neutral product rather than some carboxylate salt.

The Boc group is fairly stable under this (brief) procedure.

Anyway- most people don't remove a Boc group with HCl, they use TFA- which is one of the big advantages of a Boc group in the first place.

[amg]

But I am surprised you didnt simply google this.  Boc is a very common protecting group.  One would not have to versed in organic chemistry to simply google something. 

Acid is not used until the deprotection.  Did this in my lab not too long ago and it worked great.

I did google it, and I understand how the reaction works when there's not an acid involved, but for some reason, my lab uses acid in the procedure to protect. I know for a fact we used acid in the protection, I've done it twice. That's why I'm so confused.

You probably acidified to make sure that you isolated 100% of the neutral product rather than some carboxylate salt.

The Boc group is fairly stable under this (brief) procedure.

Thank you, that's the only thing that makes a little bit of sense to me. I realize that my lab's procedure isn't normal, I'm just trying to understand why they do it this way

[discodermolide]

Your lab's procedure is OK. The HCl is not involved in the protection reaction, as Twisted said it is added to ensure that all the product is present as the carboxylic acid and as I said to remove any excess triethylamine.