Thioquinanthrene, also known as thiochinathren, is an aromatic organic chemical compound.

[1] One of the key uses is to act as a catalyst poison in the Rosenmund reduction.

[4] In the Rosenmeund reaction, an acid chloride is reduced to an aldehyde.

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.