Vinylacetylene synthesis with a low power submerged carbon arc in n-hexane

Abstract

A low power carbon arc (12–18 W) struck between two graphite electrodes submerged in n-hexane has produced selectively vinylacetylene as the main product. Vinylacetylene was identified through its electronic absorption spectrum, the HPLC-DAD analysis and its precipitation as silver vinylacetylide. The HPLC analysis has revealed that the main by-product accompanying vinylacetylene is 1,3-butadiene and small amounts of diacetylene and divinylacetylene. The formation of other important by-products detected using also GC-MS (e.g., indene, naphthalene and some others) were discussed also in an astrochemical perspective. In contrast, a higher power submerged carbon arc in n-hexane struck at 108–216 W, yields an abundant mixture of polyynes accompanied by PAHs by-products. In the two arc regimes two mechanism are effective in producing selectively different products. In the low power arc regime, vinylacetylene is formed by the pyrolysis of acetylene primarily produced from n-hexane cracking in the arc. Chemical thermodynamics arguments also explain the vinylacetylene formation in low power arc conditions and diacetylene (and higher polyynes) in a higher power arc conditions.

Keywords:

• Carbon arc
• vinylacetylene
• diacetylene
• polyynes
• chemical thermodynamics
• astrochemistry

Acknowledgements

We acknowledge support from the Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund (ERDF) under grant with reference PROID2020010051.

Additional information

Funding

Consejeria de Economia, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund.