ORGLIST: Dimerisation condition of nitroso comp. in synthesis

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From: Andrea Giordano (angiord$##$hotmail.com)
Date: Thu Apr 20 2000 - 15:43:38 EDT

Dear readers of orglist,
I first apologise for the length of this mail, and i hope it may contribute
to useful discussion among the interested people.

1. A well documented property of nitroso compounds is possible dimerisation
of nitroso monomers via N=N bond. Recently, dimerisation of gem-chloro
nitroso comp. has been reported, with ritention of chlorine atoms in the
molecule ( I don't know the mechanism).

2. It is known that gem chloro-nitroso may be obtained via normal
chlorination procedure (gaseous Cl2) over the corresponding oxime R=NOH.

3. Nitroso comp. are usually colored (blue) while dimers appear colourless;
also gem chloro-nitroso cycloexane (from cycloexanone oxime and Cl2) has
been described as a blue liquid. I don't know about an eventual
chloro-nitroso dimer.

Here is the matter: I am supposed to have in hand a gem chloronitroso which
appears colourless. Being a substrate different from the usual ones
(presence of C=O groups in the molecule) i don't know wheter this lack of
colour is significant. To your knowledge, GS/MS and electrospray/MS analysis
failed to reveal the presence of chlorine atom, probably because of
deterioration of the sample in the first, and lack of protonation of the
substrate in the second. In my hands i have only C13-NMR spectrum, where are
evident the desappear of C=N signal of the starting oxime and a quaternary
carbon signal at upper field, say 60 ppm, which is not too much intense
respect to the others, considering that concentration of the sample is about
20mg/mL in CDCL3.

My problem, of course, is the correct identification of my sample...can you
help me?
Do you also know in which conditions dimerisation of nitroso compounds is
achieved in organic synthesis??

Thank you very much!
Andrea, CNR, Rome.

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