Benzene at 200

There's a two step-process to stochiometry.

The first step, as people have elaborated below, is combust the compound and measure the weights of various oxides, which (after the atomic masses of the relevant elements were settled around the 1820s) lets you work out the empirical formula of an unknown molecule. For benzene, this would tell you that there is 1 C : 1 H, but this doesn't tell you if it's C₄H₄ or C₆H₆ or C₁₁₁H₁₁₁.

The second step is to determine the molar mass of your compound, which requires finding something that depends on the amount of substance but not the mass directly. (In modern times, this is primarily mass spec). Back in the 19th century, this is probably abusing the ideal gas law, which lets you compute the number of moles in a gas given the pressure, temperature, and volume of a vessel. Combine this with the mass of that container, and you know how much a mole weighs. If you get out, say, 77g/mol, and you know that the ratio is 1 C : 1 H, well, the only formula that makes sense is C₆H₆ (which should ideally have 78g/mol, but you might not get the right answer for various experimental reasons).

What these early chemists accomplished with, to our eyes, extremely crude methods is astounding. Physical methods like weighing, burning and collecting residue; describing crystallization and precipitation behavior, even smelling (and sometimes tasting) was at one point a routine thing to do.

I think you're right,

https://en.wikipedia.org/wiki/Kaliapparat

Yes.

It's kind of hard to explain how widespread a usage like "solvent" is. A huge amount of chemical reactions are most convenient to do in a liquid, a liquid that can dissolve the materials you're working with. That's a solvent. Benzene can dissolve a lot of things, including some that are really hard to dissolve otherwise. So it can be used for a huge variety of reactions, but as the sort background player that you might not pay attention to unless you can't have it.

It's a little like asking "what are the uses of water in chemistry", where you're tempted to answer, "um, everything?" Not quite, but not that far off either. (And with more cancer of course.)

Edit: disclaimer, I'm not a chemist, just an interested layman.

https://en.wikipedia.org/wiki/Benzene#Uses

Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene (and other alkylbenzenes), cumene, cyclohexane, and nitrobenzene. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes around 10% of the world's benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides.

It's an important feedstock in the chemical industry but it is no longer used directly in household products. It used to be common in solvent/glue/grease remover formulations before the health hazard was widely appreciated.

Benzene was what made decaf coffee possible in 1905 (if can you consider this a productive use).

The beans were soaked in warm water then rinsed (several times?) with benzene, which was able to extract the majority of caffeine, and presumably not much else affecting the flavour.

It would have the benefit of evaporating with no residue given enough time, but due to the possibility of residue and the difficulty of working with it safely, decaffeination processes have since moved on.

Benzene is really bad for you

One of my elderly colleagues once told me that at the end of each day, they'd put all the lab coats in a big vat of benzene to clean them. The next day, they took them out, let them dry for a short while and then just put them on again. I think it was in the early 80s? He did develop cancer later.

This was the traditional solvent for cleaning up and removing excess ink in print shops all over the place.

Often still known by its archaic name Benzol when I was growing up. In high school, walking by the student print shop you could smell it way down the hall at all times. The chem labs were not nearly as bad because they had better ventilation to begin with.

Plus before my time benzene had also been prized as high-octane motor fuel for early cars back when it was obtained for sale naturally by removal from aromatic crude oils in some refineries. This was not such pure benzene however the significant percentage of impurities at the dispenser acted with an "antifreeze" effect and it handled no differently than regular gasoline below 32 degrees F.

Pure benzene freezes at about 40 degrees F, and that pure of a hydrocarbon ended up being too expensive to burn anyway.

IIRC it can really make a lawn mower cut taller grass than premium gasoline, and scientifically it does have about 100 antiknock rating so it's no surprise.

> does anyone know what useful stuff has come out of those yet?

Quip: Every chemical researcher's #1 need is for research funding, no?

Agree: https://en.wikipedia.org/wiki/August_Kekulé#Kekulé's_dream

(I had the impression from somewhere else that his "reverie or day-dream" might have instead been a pipe dream — as in the literal pipe dream (opium?). But I can now find nothing to substantiate this at all so, maybe just ignore.)

EDIT: perhaps I was reading too much into this page from the Golden Book of Chemistry: https://www.slideshare.net/slideshow/the-golden-book-of-chem...

Was going to make the same comment.

https://i.imgur.com/EGyYmkX.jpg

https://www.nytimes.com/1988/08/16/science/the-benzene-ring-...

For a tangent on Kekule, I really enjoyed Cormac McCarthy's essay The Kekule Problem - published in 2017 and apparently his first published work of non-fiction.

Omitting such an important story from the article feels sloppy.

For me, no other story from Chemistry is as fascinating as Kekule dreaming up Benzene’s molecular structure. An important reminder to me about the power of narrative and storytelling.

Yeah, and it's especially sad because they specifically mention that the structure was worked out later in the 19th century. Why not include a fun little detail like that?

The answer is probably because the author hasn't taken organic chem and so never heard the story.

This does seem like an important omission.

I immediately "Ctrl+F" for "Kekule" and saw nothing on the page. Disappointing.

When I read a "History of Organic Chemistry" textbook, Kekule and Benzene were essentially the springboard.