McLeod—The Walden Inversion—A Critical Review. 509 
agent. That an inversion should not take place with esters 
much more reactive than brompropionic, is not at all inconceiv¬ 
able if it really does take place with the free acid; this, however, 
would supply a serious objection to Fisher’s proof of which re¬ 
agent causes inversion. Later on, 10 Fisher demonstrated that a 
(3 halogen substituted fatty acid did not give an inversion with 
silver oxide and that the action of nitrosyl bromide on the cor¬ 
responding amino acid was undoubtedly normal in this case also. 
By moving the halogen one C atom back from the COOH group, 
the compound ordinarily becomes far less reactive. As a simple 
ilustration of this, we may compare the action of « chlor and P 
chlorpropionic acid with silver oxide. 11 By checking the speed 
of the action, we should expect to get a normal replacement of 
halogen by hydroxyl, using silver oxide as agent, just as Fisher 
has determined experimentally with ft chlorbutyric acid. Mc¬ 
Kenzie very recently 12 confirms this observation by proving that 
phenyl P brompropionic acid does not give an inversion with 
silver oxide. There is no reason, however, a priori, for not get¬ 
ting an inversion with very reactive ft halogen or amino substi¬ 
tuted acids as well as «. 
The phenomena, giving rise to the ‘Walden inversion’ (real 
or apparent), take place, as far as I have been able to judge, as 
the result of a very rapid action. The replacement of halogen 
by hydroxyl in a perfectly normal manner takes place when the 
reaction proceeds more slowly. 
We must bear in mind the fact that « brompropionic acid 
forms sodium and potassium salts which have a fair degree of 
stability towards water and dilute alkali. I have succeeded in 
recovering sodium brompropionate almost quantitatively from 
a water solution of the free acid neutralized with sodium hydrox¬ 
ide and subsequently distiled off at reduced pressure (20 mm) 
heating finally to 60°C; while, contrary to the statement of Beck- 
urts and Otto, 13 by no conceivable method could I get a trace of 
ioBer. [May, 1909], 1219. 
ii Wichelhaus: Ann. 143, 1. Moldenhauer, Ann. 131, 323. 
is J. L. Ch. Soc. March, 1910', p. 121. 
is Beckurts & Otto: Ber. 18, 223; Ber. 16, 576. W. H. Perkin; J. L. 
Ch. Soc. Vol. 11, p. 25; Yol. 32, p. 90. 
