So after a false start (accidentally bought sodium BISULFITE vice sodium BISULFATE), I acquired some 93% bisulfate ph decreaser. I tried to dehydrate it in a ceramic evaporation dish using a propane torch, but the torch ended up spraying the bisulfate powder everywhere.

Lacking another suitable container, I resigned myself to using a stainless steel crucible instead, heedless of the warnings about impurities mentioned in this very thread. It took about 5 minutes of exposing the bisulfate powder to the torch's flame before the crystals began to melt into what looked like water, collecting into a liquid pool. The molten bisulfate pool went from transparent to thick and brownish-yellow. I kept exposing this to the flame and the pool of liquid bubbled slightly but otherwise didn't do anything.

I waited and waited, hoping it would finally boil down into the solid mass described by others. Even after 20 minutes, the liquid bisulfate didn't really do anything except gradually turn yellow. The yellowing was clearly the beginning of nickel salt impurities, but at this point I didn't care.

20 minutes of running the torch was clearly too long, so I gave up and was about to call the whole thing a failure before the idea struck to use a stovetop instead. On the stove, the liquid came to a slow boil, began to reduce in volume slightly, and grew into a deeper shade of yellow.
After a while, there was a steady evolution of colorless white smoke. Okay, I thought, now we're getting somewhere.  But what started off as a bit of smoke soon became a worrisome fucking lot, so bad I had to keep stopping the heat and air out my workspace. This stubborn fucking yellow liquid shit pile wouldn't do anything but smoke smoke smoke.

At this point, I was fed up. The reaction mix was also turning light green at this point, so I threw my hands up in defeat and left the shit to cool so I could throw it away. Well much to my surprise, after it cooled, it became a solid, rock-hard mass.

I thought that maybe my bisulfate to pyrosulfate run hadn't been a complete loss, and that in the unlikely event that it was actually pyrosulfate, that if I could distill propionic anhydride from it, the nickel salt impurities wouldn't carry over anyway.

So. I crushed up about 20 grams of my now green pyrosulfate and added an equal amount of calcium propionate. Heated up for an hour in a steam bath and the powder mass condensed into a solid clump. Started an oil bath with the clumpy mass, temp raised to about 180c and vapors began to form in the reaction vessel. Ran the vapor through a condenser as I pondered the still lingering clouds of mystery smoke (water vapor? no, too smoky. SO3? No smell. What the hello is it?), I noticed a vinegar stench.

Great, now the mystery melt is composing into fuck knows what...Wait a minute...VINEGAR SMELL?!??! I looked into the distillation head and there it was, a clear liquid reeking of vinegar. It worked!

All told, I ended up with only 1 millimeter of what must be propionic anhydride. Not quite sure what sort of yield I should have expected, but considering the thoroughly ghetto nature of the whole endeavor, I can't complain.

Only question now is: what the hell was going wrong with the thermal decomposition of the sodium bisulfate? At no point under heat did the bisulfate stop smoking and turn solid. It was only after I turned the heat off that I got anywhere with it. I was so sure in fact that I had the pyrosulfate once it had cooled that O reheated some of it with the torch for a while. Like the pyrosulfate described by others, it didn't melt, give off smoke or in any other way react to the heat at that point, but while it was under continuous heat, all it did was bubble and smoke. What gives?

frronkis, your yield kill was because of the intense amount of heat you used. the pyrosulfate is decomposing at those temps. better heat control is needed. the fumes are, as vesp already stated, SO3 reacting with H2O vapors to form H2SO4 as evidenced by PH paper on previous trials. when the fumes start to pick up intensely back off the heat and cool. then distill and workup per usual...had a similar run long ago and this ammended it.

I might add that a vinegar smell is not evidence of success. You will get that smell even if there is no pyrosulphate at all in your bisulphate. Bisulphate combines with propionate to form propionic acid, which smells similar if not identical to propionic anhydride.

A simple test you can do is to put some cold water in a test tube and a few drops of the supposed propionic anhydride. Propionic acid will dissolve in the water, but the anhydride will not dissolve for at least several minutes and will sink to the bottom as oily droplets because it is denser than water.

thanks for that contribution everlasting riegn
just wanted to say that hydrate or no that sodium pyrosulfate will eat up any water never had any propioni acid distill over it might lower yeilds though.

Probably your "anhydrous" sodium acetate/propionate was not really anhydrous. All carboxylate salts should be meticulously dried beforehand, especially sodium salts.

K i dehydrated my bisulfate with a vision ware amber pot on an electric stovetop.  This was put in a beer bottle with an equal volume of calcium propionate.  I heated the beer bottle on medium heat on the stove top. I distilled the gas being generated into another beer bottle connected by vinyl hosing and medical tape. The resulting liquid smelled of vinegar and sulfur, it was clear. In the reaction bottle the mixed solids turned yellow/ off white and the very bottom of the mixture was black.

My question, does propionic anhydride smell like vinegar and slight sulfur?

So true.

I stop raising the heat on the molten solution when it starts smoking.  I remove from heat when bubbles stop forming. It only hardens upon cooling. I am doing this in a porcelain pan on medium heat (electric stovetop element). Is this sufficient dehydration of the sodium bisulfate to turn it to pyrosulfate.

Weigh it before and after. It should have lost at least 7.5% weight (starting from anhydrous).