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For converting $\ce{OH}$ of methylated polyethylene glycol. The first step is converting hydroxyl group to imidazole carbamate as an active intermediate. But what about the next step?

If I will add primary amine containing group to form carbamate linkage, how can I convert it to a free amine?

Reference: Zhou, S.; Wang, J.; Wang, G.; Jiang, Z.; Ren, H. An approach to developing high dielectric constant nanocomposites based on polyrotaxane derivative. European Polymer Journal 2017, 90, 312-322. DOI: 10.1016/j.eurpolymj.2017.03.037.

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    $\begingroup$ I don't think it will convert to a free amine. If you add an amine, you will make a carbamate where PEG has acted as a carrier or intermediate. For what it's worth, if you want a hydroxyl to amine conversion, I would try diphenylphosphoryl azide. Then convert the azide to the amine by hydrogenation or triphenylphosphine. $\endgroup$
    – Beerhunter
    Apr 4, 2018 at 22:47

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Conversion of Hydroxyl group to free amine in polyethylene glycol: This is a case of converting a primary alcohol to a primary amine

$$\ce{R-CH2OH -> -> -> R-CH2NH2}$$

To my understanding, converting hydroxyl group to imidazole carbamate as an active intermediate is not the way to do this. First thing come to my mind was a named reaction called the Mitsunobu reaction. The Mitsunobu Reaction allows the conversion of primary and secondary alcohols to esters, phenyl ethers, thioethers and various other compounds including amines. The reaction uses triphenylphosphine ($\ce{Ph3P}$) and diethylazodicarboxylate ($\ce{DEAD}$) to activate hydroxyl group. Then, activated alcohol can undergo substitution reaction with a suitable nitrogen nucleophile (either phthalimide or hydrogen azide can be used) followed by reduction (in the case of azide formation) or acid or base hydrolysis (if phthalimide were used as nucleophile) to give primary amine groups.


Late edit:

Actually, to answer OP's curiosity, N,N'-Carbonyldiimidazole has been used to convert terminal hydroxyl group to amine group. For example, see Ref.1. However, the reference given by OP (Ref.2) has an error on the product structure, which probably made the OP confused about the reaction. Reference 2 has used diamine (1,2-ethylenediamine) as the sunstrate, but the product structure have missed one amine group, which is the one replaces terminal hydroxyl group:

Reference structure from Ref.2

Otherwise, this method (CDI) can be used to convert terminal $\ce{OH}$ group to terminal $\ce{NH2}$ group without using Mitsunobu reaction. Yet, I'd use one $\ce{NH2}$ protected diamine to avoid unnecessary byproducts.

References:

  1. Rajappa Vaidyanathan, Vikram G. Kalthod, Duc P. Ngo, Jerad M. Manley, and Sean P. Lapekas, "Amidations Using N,N'-Carbonyldiimidazole: Remarkable Rate Enhancement by Carbon Dioxide," J. Org. Chem. 2004, 69(7), 2565–2568 (ODI: https://doi.org/10.1021/jo049949k).
  2. Shuwei Zhou, Jingwen Wang, Gaoqiang Wang, Zhi Jiang, and Hua Ren, "An approach to developing high dielectric constant nanocomposites based on polyrotaxane derivative," European Polymer Journal 2017, 90, 312-322 (ODI: https://doi.org/10.1016/j.eurpolymj.2017.03.037).
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  • $\begingroup$ I actually know this method but i am asking about the other using CDI in the attached paper ? $\endgroup$
    – Hossam
    Mar 31, 2018 at 4:20

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