77500-02-8Relevant academic research and scientific papers
Trapping of the Intermediate Formed in the E1cB Hydrolysis of Some Alkyl and Aryl N-(4-Nitrophenyl)carbamates in a Hydroxy Functionalized Micelle
Broxton, Trevor J.
, p. 77 - 83 (2007/10/02)
The basic hydrolyses of some alkyl and aryl N-(4-nitrophenyl)carbamates in the presence of micelles of cetyl(2-hydroxyethyl)dimethylammonium bromide (chedab) were studied.For compounds which react by the BAC2 mechanism, very similar results were obtained in cetyltrimethylammonium bromide (ctab) and in chedab micelles.However, for compounds which react by the E1cB mechanism, the intermediate p-nitrophenyl isocyanate was trapped by the hydroxy group of the functional micelle to form a new carbamate directly bound to the detergent molecules of the micelle.It was shownthat this new carbamate decomposed by a BAC2 mechanism. p-Nitrophenyl isocyanate added to an alkaline solution of chedab gave N-(4-nitrophenyl)carbamate ion.Thus, the isocyanate has to be generated within the micelle for trapping to occur.The rate of reaction of p-nitrophenyl isocyanate with OH-/H2O is faster than the rate of solubilization within the micelle.
Mechanism of Cleavage of Carbamate Anions
Ewing, Sheila P.,Lockshon, Daniel,Jencks, William P.
, p. 3072 - 3084 (2007/10/02)
Carbamates and monothiocarbamates of basic aliphatic amines undergo rate-determining C-N cleavage after a rapid equilibrium protonation step, as shown most directly by inverse solvent deuterium isotope effects of kD/kH = 3.6-4.8 for O,O- and O,S-N-n-butylcarbamates and by rapid acid-catalyzed exchange of the NH proton of n-BuNHCOS- with kexch = 5 107 M-1 s-1.The lifetimes of substituted N-protonated carbamates have been estimated to range down to -10 s.It is concluded that general acid catalysis of the cleavage of carbamates of weakly basic anilines (α = 0.84) occurs through an enforced preassociation mechanism with hydrogen bonding to the leaving protonated nitrogen atom and C-N cleavage in the rate-determining step.There is more proton transfer in the transition state (larger α) and a smaller β1g with more basic amines and upon substitution of sulfur for oxygen.The low pKa values of N-protonated carbamates and monothiocarbamates illustrate the strong electron-accepting ability of -COO- and -COS-.
