[Enthalpy]

Hello erudite people!

Do you believe that carbon monoxide could serve as a carbene? If yes, it could give cyclopropanone, which has a limited lifetime but would anyway serve for further steps. I naively imagine that the divalent oxygen is better than dichlorocyclopropane to make bridges or close cycles with amines, and this would then lead to spiro compounds as on the attached image - where the two last, if any possible, would supposedly use the amines as a ligand to a metal ion to favour the four-membered ring.

Comments please!
Marc Schaefer, aka Enthalpy

[yesway]

To my knowledge, CO is sufficiently stabilized only in transition metal complexes to confer typically migratory insertion reactions into metal-carbon bonds. Free CO is quite inert.

[Enthalpy]

Thank you!

CO has the basic advantage of stability, hence is easier to make than usual carbenes... So you feel it's too stable to react as a carbene and make cyclopropanes with alkenes?

[Enthalpy]

Nist gives the enthalpy of formation of dichlorocarbene and cyclopropanone, thanks a lot, so I could compare standard carbene and carbon monoxide: the cyclopropanation is exothermic with dichlorocarbene and would be endothermic with carbon monoxide, with figures clear enough.

Though, this one difficulty can be solved. Strong and efficient xenon excimer lamps emit at 172nm, the perfect wavelength to excite ethylene, and ArF at 193nm fits heavier alkenes. Even the excited state keeps a fraction of the 690kJ/mol photon, the hoped cyclopropanation is now exothermic.

Will this produce a cyclopropanone or something else? At least the trial and hypothetic production look simple: mix little ethylene (to limit cyclobutane formation) in carbon monoxide, illuminate with a xenon excimer lamp, check for cyclopropanone before it decomposes, or use it for further synthesis. Cold would condense cyclopropanone away from light as it forms.

What do you think?
Marc Schaefer, aka Enthalpy

[Enthalpy]

The absorption spectra and vapour pressures support the suggested reaction conditions, see the appended diagrams if you're logged in. Though, I took acetone data for want of cyclopropanone.

• Carbon monoxide absorbs UV below 95nm. Optical data stops at "less than 10^-18cm² "; I put an electron scattering curve too, but they use to be magnitudes above the photon curve. Expect CO to absorb >2 magnitudes less than alkenes at 172nm, so it can dilute the alkene >10 times.
  
• Ethylene has the nice peak at 172nm, fitting the efficient Xe exciplex lamps. Longer alkenes absorb 172nm well and can accept 193nm from ArF. 1mbar ethylene absorbs 172nm UV over 37mm.
• Acetone happens to show a dip at 172nm, nicely two magnitudes lower than ethylene. The cyclopropanone may absorb more, but the plan is to remove it from the reaction zone as it forms.

The vapour pressure curves show that cyclopropanone is easily condensed away, or if desired frozen, while leaving a wide choice of pressures for all species. The curves start at the melting points and finish, except for acetone, at the critical points; the acetone curve is less accurate below 260K. For instance at 195K provided by dry ice, 0.2mbar of acetone and 10mbar of monoxide would absorb far less UV than 1mbar of ethylene. A UV detector could measure the ethylene pressure for automation.

How easy is it to convert a (normal) ketone to an alcohol, a bromide or something similar? Cyclopropanone (if obtained!) has a limited lifetime, and reacting it only with amines would limit its usefulness.
Marc Schaefer, aka Enthalpy

[discodermolide]

I suppose you could imagine a radical process for the reaction of ethylene and CO to give cylcopropanone. I guess you would need a strong source of UV but the yields may be low and not useful.

[Enthalpy]

Everyone knew it but me... Common ketones reduce to alcohols with LiBH₄, or cheaper with H₂ over Raney nickel, none being really safe on a big scale.

I suppose you could imagine a radical process for the reaction of ethylene and CO to give cylcopropanone. I guess you would need a strong source of UV but the yields may be low and not useful.

If only I knew any yield! I've no idea what the excited ethylene will do with the monoxide, opinions welcome. At least, Xe excimer lamps can convert 40% of the electricity to 172nm light, and studies claim that close around 172nm, light absorption results from the pi to pi* transition only, so this step is efficient.

• One 900We*40% lamp produces in 8 hours 15 photon moles, so if the cyclopropanation is 1/3 efficient (Or 100%? Or 0%?) we get 200g of parent cyclopropane.
• 500 lamps working 16h*20day in a month produce 4t, enough for a rocket third stage.
• Over 3000h life, one lamp draws 2700kWh or 270€ electricity, may cost as much to buy (no data!), and produces 75kg of parent cyclopropane, so it would contribute 7€/kg to the product cost.