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I will have some samples of azobisisobutyronitrile and I want to perform Barton-McCombie reaction. The problem is that the reagent is quite old and I need to know whether it has not decomposed.

Do you know any kind of test that I could perform? I was thinking if benzophenone in THF would not become blue after addition of fresh AIBN which would indicate the presence of the radicals. But I am not sure if such a test would be a good idea.

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If azobisisobutyronitrile (AIBN) underwent homolytic cleavage over time, do you expect the resulting cyanoprop-2-yl radicals would survive as free radicals for a long period of time? If not, what would be the decomposed products?

Alkali metals reduce benzophenone in THF to form blue diphenylketyl radical anions. I'm not sure azobisisobutyronitrile (AIBN) or cyanoprop-2-yl radical can do that.

  1. Maybe you can test the structural integrity of AIBN by 1H-NMR, IR or Raman spectroscopy? The -N=N- stretching vibration of a symmetrical trans-azo compound like AIBN is "IR-forbidden" but absorbs in 1576cm-1 region of the Raman spectrum (1). If it decomposes, perhaps you can see the decomposed products in the mass spectrum.

  2. Maybe you can try to activate the subject AIBN as a radical initiator?

    a. Perhaps one can observe a minute amount of nitrogen gas upon homolytic cleavage?

    b. AIBN can be used as radical initiator in radical polymerization. Once activated as cyanoprop-2-yl radical, it readily attacks olefinic double bond of vinyl monomers. Perhaps you can test such reaction and see if some polymerization occurs using mass spectroscopy?

Reference:

  1. R.M. Silverstein and F.X. Webster: Spectrometric Identification of Organic Compounds (6th ed.)
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You'd think that the main decomposition product is tetramethylsuccinyl dinitrile (and perhaps also some peroxidic species.

In 13C NMR the quaternary carbons of both products should have distinct chemical shifts, and assuming relaxation times are similar (they should be) this should give a rough idea about the purity of the product.

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I don't think that reaction with benzophenone is good idea - as Wikipedia article about benzophenon says it turns blue when reacted with alkali metals - becoming ketyl anion. Those anions can trap other radicals but are too aggressive to discern whether your is AIBN good. You could maybe use DPPH - heat it in solution with AIBN and look if it reacts. Or maybe try if it can initialize another, simpler reaction like polimerisation, or maybe analyse it chromatographically - there are lots of options.

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