The Desulfurization of Polynuclear Aromatic Sulfur Compounds with a Raney Nickel

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Abstract
The mechanism of the desulfurization of the polynuclear thiophene compounds with a Raney nickel was studied in ethanol at atmospheric pressure and from 0 to 78.3 °C. The desulfurization rate was initially fast but reached zero in about 30 minutes. The major products were biphenyl in the desulfurization of dibenzothiophene (1), 1-phenylnaphthalene in the desulfurization of benzo[b]naphtho[1,2-d]thiophene (2), and 2-phenylnaphthalene in the reaction of benzo[b]naphtho[2,3-d]thiophene (3) and benzo[b]naphtho[2,1-d]thiophene (4). The desulfurization extent for the four compounds decreased in this sequence: 3>1>2>4. The extent of the desulfurization of the polynuclear thiophene compound was not related to the reaction indices, Fr(E), Fr(N), and Fr(R), of the sulfur atom of the compounds, which were calculated by using a simple Hückel theory; rather, it was related to both the free valence and the π-electron density. Therefore, the polynuclear thiophene compounds were considered to adsorb on a Raney nickel through the free-electron pair of the sulfur atom; consequently, the adsorption led to the C–S bond scission.