70 
For here we can verify the boric acid method by the classic one, 
as only the trans diol is not identical with its mirror image and 
consequently resolvable into optical antipodes. 
We shall not enter here into details about the preparation of these 
diols; suffice it to state, that the one diol was prepared by hydrating 
cyclopentene oxide, while the other was obtained from cyclopentene 
by oxydation with KMnQ,. 
The properties of the diols are as follows: 
m. p. of the | m. p. of the 
mp. bp. diphenyl di-p. nitro- 
urethane benzoate. 
C;H,(OH), from C5Hg andKMnO,| 29°—-30°.| 123.9°/29 205° 117°—118° 
C;H,(OH), from C;HgO and H20 54°.5—55° | 136°/21.5 P54 a 145° 
| 
In order to establish with certainty which of these two glycols 
was the cis and which the trans diol, they were treated with /-menthyl- 
isocyanate, in doing which the first one produced one single di-l- 
menthyl-urethane, while the highmelting diol yielded a mixture of 
di-l-menthylurethanes differing very much as regards rotatory power. 
Without isolating and saponifying these urethanes, we can draw the 
conclusion that here the urethanes of the trans diol were formed viz 
d-trans-cyclopentane-diol-di-l-menthyl-urethane and Ltrans-cyclopentane- 
diol-l-menthyl-urethane. 
From this however one must not conclude without further conside- 
ration that the diol with the higher melting point was in fact the 
trans diol. During the reaction of l-menthylisocyanate a sort of Walden 
inversion might have taken place 
However acloser inspection renders this improbable in a high degree. 
As we set forth in our last communication such an inversion is 
only to be expected when the reaction takes place at the atom which 
governs the configuration. 
This is not the case here: 
= C—O—H + RNCO = C—O —CO 
rs * 
RNH 
as the reaction takes place by detaching the O—H-linkage and so 
the typical C-atom is left alone’). 
1) It is for this reason that we have not applied other methods for the resolution 
into optical antipodes (c.q. esterification with active acids), because then the entire 
OH-group may be eliminated, in which case the C-atom determining the asymmetry 
is attached. 
—_—— pen 
