L Le ev ve el l 2 2 – – C Ca as se e 2 23 3
H Hy yd dr ro ol ly ys si is s o of f 2 2- -A Am mi in no ob be en nz zo oa at te e E Es st te er rs s
K Ke ey y p po oi in nt t: : I In I In In In I I t tr t tr tr t tr t t a
ra r ra ra ra ra r ram mo ol le le l le le le l lec cu ul la la l la l la la l lar r g ge en ne er ra ra r ra ra ra ra r ral l b ba as se e c ca at ta ta t ta ta ta ta t tal ly l ly ys ys y ys ys ys ys y y i is is i is is is i i
NH 2
O
OR
H 2 O
O
OH
NH 2
ROH
R = C 6 H 5 , p-NO 2 C 6 H 4 , CH 2 CF 3
H Hy yd dr ro ol ly ys si is s o of f 2 2- -A Am mi in no ob be en nz zo oa at te e E Es st te er rs s
The hydrolysis of phenyl 2-aminobenzoate is pH dependent. The reaction follows
a pseudo-first order rate law and the plot of log k obs
k k versus pH shows OH
– cataly–
sis at pH > 9 and a large pH independent region between pH 4 and pH 8.5. The
plot bends downward near pH 4 to give a slope of 1.0. The downward bend corresponds with the pK a
K K of the amino group (Fig. 23.1).
2
4
6
8
1 0
-5. 0
-4.0
-3.0
-2.0
log k obs (s
s
- 1
)
pH
Figure 23.1
To determine the mechanism of the reaction in the pH-independent region, the
hydrolysis of phenyl, p-nitrophenyl and trifluoroethyl 2-aminobenzoates 1–3 has
been studied (Scheme 23.1). The three esters hydrolyze with similar rate constants