Chemistry Reference
In-Depth Information
The carbocation reacts with water, which is a nucleophile and is present in large
excess:
H
H
+
-
H
C
OCH
3
C
OCH
3
+
+
O
H
H
H
2
O
H
C
OCH
3
OH
The sequence is then repeated, beginning with protonation of the methoxy oxygen of
the hemiacetal:
H
H
H
H
+
-
CH
3
OH
+
C
OCH
3
C
OCH
3
OH
OH
H
C
OH
+
H
H
+
-
CO
H
COH
+
The whole process is driven forward because water is present in excess.
9.13
In the first step, one bromine is replaced by a hydroxyl group:
Br
OH
+HO
-
Br
-
H
3
C
C
CH
3
H
3
C
C
Br
CH
3
+
Br
Loss of HBr gives acetone:
O
H
O
-
OH
-
H
3
C
C
CH
3
C
+O
H
2
+B
H
3
C
CH
3
Br
Even if both bromines were replaced by hydroxyl groups, the resulting diol (acetone
hydrate) would lose water since acetone does not form a stable hydrate.
O
H
O
H
3
C
C
CH
3
C
+O
H
2
H
3
C
CH
3
O
H
