Along with having bodily fluids based on copper chloride, the Sarrians from Hal Clement's Iceworld are described as breathing gaseous sulfur. Even ignoring the copper chloride, the need to have sulfur in gaseous form puts their minimum operating temperature at around 445C--because that's the temperature at which sulfur boils!
Whether complex chemistry capable of supporting life can even exist at that temperature at all is itself a thorny question... but sulfur melts at a mere 113C, which is much more accommodating.
So, assuming that some kind of life can exist at temperatures in which sulfur is fluid, can it ever make sense to actually "breathe" sulfur as a metabolic oxidizing agent in place of oxygen?
The primary problem I see is that carbon disulfide has a positive heat of formation... which means you actually get more energy by just producing elemental carbon and sulfur than by trying to react them together. Forming silicon disulfide, on the other hand, is exothermic, so maybe that would work for some kind of high-temperature siloxane-based life... but silicon disulfide is a polymer with a melting point over a thousand degrees, so either we really stretch the limits of where we think life can exist far beyond what even Clement was willing to do, or we're probably stuck with a microbial world.
But, on the other hand, the thermodynamic information I have access to is only for STP conditions--maybe CS2 is a more favorable product at higher temperatures. Or maybe there's some other favorable reaction path--like, just reacting sulfur with hydrogen, and doing something else to handle the carbon wastes from metabolizing fats and carbohydrates. I dunno! Hence, well... I'm asking.
(Note that this is not a question about Iceworld, merely inspired by. Answers need not address potential Sarrian biology at all, and positive answers need not be compatible with how Sar and Sarrians are depicted. If they are, that's just a bonus.)