I am looking for confirmation of how I understand the selective synthesis of mono-BOC-cystamine.
I have already successfully synthesized the product, however, am lacking a few of the details to completely understand the reaction.
A referral of the mechanism: https://www.jkchemical.com/post/556
1. 1 mol. eq. of cystamine dihydrochloride in MeOH was brought to 0.5 celsius (what is the purpose of this solution being so cold?
2. Taken off the ice, 3 mol. eq. of triethylamine (TEA) was stirred in the cold solution for 30 min. allowing it to come to room temperature (are 2 mol. eq. of the TEA used up here to deprotonate the primary amine salt?
O was added dropwise over 3 hours. To describe the mechanism, is this a nucleophilic attack
of the amine nitrogen to the carbonyl carbon?
4. Following the amine attack of Boc2
O, an electron transfer occurred from the nitrogen to carbonyl oxygen. Can you say that this formed a carbamate intermediate
or a tetrahedral intermediate
? The extra electron pair then transfers to the sp3 hybridized C-O bond and further to the next internal C-O bond, cleaving tert-butyl carbonate.
5. The result of the cleavage leaves a protonates mono-BOC-amine, where the last molar equivalent of TEA deprotonates this.
6. If the above use of TEA as a base is correct, then I don't understand why the protocol I followed uses 1 M of NaOH for the extraction with DCM. Originally, I thought that the NaOH was basifying (or free-basing) any salt form of amine left (or maybe this is still true)?