Catalytic or non-catalytic arylalkyne explosive trimerization?
While the standard wisdom states that arylalkynes undergo a cyclic [2+2+2] trimerization to form substituted benzenes in the presence of a transition
metal catalyst such as Co or Ni, I am aware of a serious explosion that took place in a commercial 'kilo lab' involving an attempt to vacuum distil
500 grams of a phenylacetylene containing an electron-donating functional group para to the alkyne function. As far as I am aware, no catalyst was
present, though there is the possibility that traces of the Pd catalyst used in the Heck reaction synthesis of this compound might have been present.
(I'm making the assumption that trimerization & release of a lot of energy in the process were the cause of the explosion).
I found this reference where the compound in question was formed under conditions that were likely much more thermally extreme than existed during
that failed distillation attempt:
| Quote: | Methyleneketenes and methylenecarbenes. III. Pyrolytic synthesis of arylacetylenes and their thermal rearrangements involving arylrnethylenecarbenes
RFC Brown, FW Eastwood, KJ Harrington and GL McMullen
Abstract
Flash vacuum pyrolysis (550-600°) of 5-benzylidene derivatives of 2,2- dimethyl-1,3-dioxan-4,6-dione(isopropylidene malonate) gives
phenylacetylenes bearing m-or p-substituents (H, Me, MeO, Cl, CN)in 64-98% yield.
Australian Journal of Chemistry 27(11) 2391 - 2402
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I haven't found much literature on the explosive nature of this class of compound but they should be of interest to anyone interested in exploring
novel energetic materials, especially those not containing the nitrogen compounds that modern explosives detection sensors are designed to detect. It
is apparent that a great deal of energy is contained in that acetylene group & that it can be released under the right conditions.
[Edited on 30-8-2008 by Ritter]
Ritter
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\"The production of too many useful things results in too many useless people.\"
Karl Marx
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