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I am interested in nitrating an aromatic ester in a solution of dichloromethane. I found the following paper that describes creating a nitric acid solution in dichloromethane using KNO3 and sulfuric acid:

Strazzolini P, et al. "Nitric Acid in Dichloromethane Solution. Facile Preparation from Potassium Nitrate and Sulfuric Acid." Tetrahedron Letters 42 (2001) 1387 - 1389.

This paper describes both the nitration of Benzyl Methyl Ester and the nitrolysis of Benzyl Tertbutyl Ester and Phenyl Tertbutyl Ester using their nitric acid in dichloromethane method.

But I am having trouble understanding how they controlled the reactions to get nitration of one ester and nitrolysis of another ester. The reaction conditions seem similar, but the concentration of nitric acid in the nitrolysis reactions is about twice as high as in the nitration reaction. Could the difference be in the tertbutyl group vs the methyl group on the ester?

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Tert-butyl esters are routinely cleaved by anhydrous acid conditions by loss of the tBu+ cation. TFA in DCM is a common system for this. Neat formic acid, HBr/AcOH and PTSA in refluxing benzene or toluene are also used (see Greene - Protective Groups in Organic Synthesis (2nd ed) p246).

Methyl esters usually need aq. acid for cleavage.

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  • $\begingroup$ Good to know, the compound I want to nitrate is usually dissolved in a TFA/DCM mixture, so if it can survive that, it can probably survive with the addition of nitric acid. $\endgroup$
    – user137
    Commented Nov 2, 2020 at 12:58
  • $\begingroup$ If you are happy with the answer please check the accept box. A quick google search for nitration of methyl benzoate produces a good number of hits with lab procedures, including one done in neat sulfuric acid. The only concern would be your workup if you quench into water. $\endgroup$
    – Waylander
    Commented Nov 2, 2020 at 13:54

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