Thioquinanthrene

Thioquinanthrene, also known as thiochinathren, is an aromatic organic chemical compound. It has the chemical formula C18H10N2S2 and reacts with alcoholates or alkoxides. One of the key uses is to act as a catalyst poison in the Rosenmund reduction. It has the IUPAC name of 2,13-dithia-10,21-diazapentacyclo[12.8.0.03,12.04,9.015,20]docosa-1(14),3(12),4,6,8,10,15,17,19,21-decaene.

Rosenmund catalyst poison
In the Rosenmeund reaction, an acid chloride is reduced to an aldehyde. Continuing the reduction produces an alcohol. This further reaction is undesirable as the alcohol will now react with the acyl chloride to produce the unwanted ester product. For this reaction (over reduction) to be prevented, the catalyst needs to be poisoned. Thioquinanthrene was used initially, although other materials have been used since.