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Author: Subject: Catalytic or non-catalytic arylalkyne explosive trimerization?
Ritter
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[*] posted on 30-8-2008 at 08:06
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



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]

Alkyne trimerization.jpg - 47kB




Ritter
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\"The production of too many useful things results in too many useless people.\"

Karl Marx
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Ritter
National Hazard
****




Posts: 370
Registered: 20-6-2008
Location: Earth
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Mood: Curious

[*] posted on 30-8-2008 at 08:22


Here is the flow sheet for the synthesis of phenylacetylenes starting from Meldrum's Acid (a simple malonate) & simple benzaldehydes.

Here are details on setting up a lab scale flash vacuum pyrolysis (FVP) apparatus: http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=v82...



[Edited on 30-8-2008 by Ritter]

Arylacetylenes.gif - 20kB




Ritter
=============================
\"The production of too many useful things results in too many useless people.\"

Karl Marx
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