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Formimidoyl Group Transfer from Activated Amidines. Part 1. Hydrolysis of 1-(N-t-Butylformimidoyl)imidazole and Related Imidazole-containing Formamides

DOI: 10.1039/P29800001318

Source and publish data:

Journal of the Chemical Society. Perkin transactions II p. 1318 - 1325 (1980)

Update date:2022-08-04

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Authors:

Chandler, AnneChandler, Anne

Hegarty, Anthony F.Hegarty, Anthony F.

McCormack, Margaret T.McCormack, Margaret T.

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Article abstract of DOI:10.1039/P29800001318

The hydrolysis of 1-(N-t-butylformimidoyl)imidazole (7a) to t-butylformamide and imidazole has been examined in the absence of buffer species at 25 deg C in water.The rate of hydrolysis was pH-independent at pH 7-14 and reaction in this region is shown to occur via HO- attack on the protonated substrate (whose pKa is 5.0; protonation site, imidazole nitrogen).Alternative mechanisms such as H2O attack on the neutral substrate and reaction via the zwitterion (15) were eliminated using solvent isotope effect, deuterium labelling, and substituent effects.Below pH 6 acid catalysis of hydrolysis is observed due to H2O reaction with the protonated substrate (pH 4-6) and with the diprotonated substrate (pH 0-4); at pH 0, t1/2 for hydrolysis is <10-2s.The N-arylformamidines (7b) and (7c) react via similar acid catalysed pathways but a new reaction (identified as HO- attack on the amidine) occurs in base, in preference to the pH independent pathways. p-Nitrophenylformamide is itself hydrolysed in basic solution so that complex kinetics result.The C-substitued amidines (7e) and (7f) react 104-102-fold more slowly than the corresponding formamidines.Buffer catalysis of the hydrolysis of (7a) by phosphate and amines is complex, the slope of kobs. versus plots being greater at low than at high buffer concentrations.This is consistent with the formation of a tetrahedral intermediate in the reaction pathway whose formation and beakdown is subject to general acid-base catalysis.

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