The Beckmann Rearrangement
has been shown by rearrangement of benzophenone oxime to benzan-
ilideinH 218 0:
Ph Ph HO Ph O Ph
\ / \ / \ /
c -* c ^ c
II II I
.N .N HN
- \ * \ \
OH Ph Ph
Provided that neither the initial oxime nor the anilide produced
will exchange their oxygen for^18 0 when dissolved in H 218 0 (as has
been confirmed), a mere intramolecular exchange of Ph and OH
cannot result in the incorporation of any lsO in the rearranged pro
duct. In fact, however, the benzanilide is found to contain the same
proportion of mO as did the original water so that the rearrangement
must involve loss of the OH group and the subsequent replacement
of oxygen by reaction with water.
The rearrangement is believed to take place as follows:
R R
\ R COCI _\
C=N > C=N (XXX)
/ V
KS
£
a
/ \ «
R' OH e,c- R' OX • OX©
(T\ R
H,OL V ©J © /
>N-yC=*C > C=N
R
\
C=N
/ \m • / " /
R' OH R' R'
H (XXIX)
H
O HO R HO® R
|| \ / -H9 \ /
R'—C—NHR <— C=N <— C=N
/ /
R' R'
In fairly strong acid, the rearrangement proceeds by protonation
of the oxime, followed by loss of water to yield the species (XXIX)
having an electron-deficient nitrogen atom; while with acid chlor
ides, etc., the ester (XXX) is obtained which loses an anion, eOX, to
yield the same intermediate. Support for the latter interpretation is
provided by the fact that such O-esters may be prepared separately
and shown to undergo the subsequent rearrangement in neutral