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Details van artikel 103 van 124 gevonden artikelen
| Titel: |
Storage Stability of Polyynes and Cyanopolyynes in Solution and the Effect of Ammonia or Hydrochloric Acid |
| Auteur: |
Cataldo, Franco |
| Verschenen in: |
Fullerenes, nanotubes & carbon nanostructures |
| Paginering: | Jaargang 15 (2007) nr. 3 pagina's 155-166 |
| Jaar: |
2007-05 |
| Inhoud: |
The storage stability of an acetonitrile solution of polyynes and monocyanopolyynes was studied by liquid chromatographic analysis for about 50 days at room temperature in a closed Pyrex flask. Monocyanopolyynes decomposition starts immediately after their synthesis; the decomposition can be approximated by a pseudo-first-order kinetic law and the rate constant is dependent from the length of the monocyanopolyyne chains, being faster for longer chains. For instance, for HC7N the decomposition rate is k=-3.4×10-7 s-1 but becomes -7.0×10-5 s-1 for HC13N decay, 204 times faster than the decay of the former compound. Polyynes mixed with monocyanopolyynes in the same CH3CN show an induction time before starting to decompose. The induction time appears linked to the decomposition of monocyanopolyynes, which seems to protect the polyynes from the decomposition. Once the monocyanopolyynes are vanished also the decomposition of polyynes starts with a slower kinetics than monocyanopolyynes and following the rule that longer chains disappear at higher speed than shorter chains. For example, the pseudo-first-order rate constant for C8H2 is k=-1.31×10-8 s-1. Ammonia exerts a deleterious effect on monocyanopolyynes. In fact, ammonia addition to an acetonitrile solution of monocyanopolyynes causes their immediate decomposition due to a nucleophilic addition of ammonia to the polyyne chains. Instead, hydrogen-teminated polyynes are much more resistant toward the nucleophilic addition of ammonia. Hydrochloric acid does not influence the stability of polyynes and monocyanopolyynes. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 103 van 124 gevonden artikelen
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