As a kid I used to play guitar and I can remember the distinct smell that the strings had and that they would transfer it to my fingers. It was the same smell that I got when I handled coins and I can remember smelling it on other metallic things like nails, chains on park swings, and railings. So, from a young age the smell was really locked into my head as being metallic. But, the weird thing is that you cant smell metal and the reason you can't is because metal completely fails the two major requirements for smell. The first major requirement is that it needs to be volatile meaning that it lets off a vapor. This is because when we smell something we aren't detecting it directly What we're picking up is the gas that its releasing which can then travel through the air and get to our noses. Almost everything, both liquids and solids, passively release vapor to a certain extent. However the rate that this occurs at is highly variable and it really depends on the substances unique properties. In particular, it depends on the strength of the interactions between its molecules. Liquids generally have weaker interactions than solids and they tend to let off more vapor which is why we usually find them easier to detect. As we move to the solid phase, the interactions get stronger, but some of them do still let off a decent amount of vapor. These more volatile solids are usually organic compounds because their interactions are still relatively weak. However, as we move on to inorganic solids like salts metals and minerals, the story changes. The interactions in these are significantly stronger and all the molecules hold onto each other really tightly. The likelihood of any of these molecules getting enough energy to spontaneously jump to the gas phase and escape is extremely small. And for many inorganic solids its low enough that we consider them to be giving off no vapor at all. The one major exception to this tho, in terms of metals, is mercury. At room temperature its a liquid -- Which tells us that even though its a metal it has relatively weak inter-molecular bonds. And because of this like many other liquids, its actually able to evaporate and let off vapour. This vapour is one of the biggest dangers when working with liquid mercury and unfortunately, not only is it invisible, it also has no odor. This is because metals also fail the second major requirement to smell something which is sensitivity. So not only do pretty much all metals not even release vapour, even if they did it wouldn't really matter. The question now though is, then what are we smelling? Because as I mentioned before metals do clearly have a distinct odor. Well as it turns out, we're actually just smelling ourselves. Our hands are covered in oils and sweat and when we touch certain metals, like iron copper or zinc they catalyze some reactions. In particular they catalyze the oxidation of various skin oils and they convert them to new ones with different odors. All of these new molecules help create an overall musty odor. But the major one that's responsible for that metal smell is called 1-octen-3-one. This is why these metals only smell after they've been touched. If you want to test this out for yourself, you can try washing some coins or something else metallic, and then smelling it without ever touching it. If you did a proper job washing it you shouldn't smell anything except maybe the faint smell of soap. Then if you pick it up and play around with it a bit in your hand It should start to stink again. When I first found out about this, I thought it was honestly kind of hard to believe because of how strongly I had associated this scent to metal. So what I wanted to do was to make pure 1-octen-3-one myself and to try putting it on some non metal things. I thought that if I made some metal smelling glass or plastic it could be really weird and maybe mess with my brain. When it comes to synthesizing molecules its possible to do it all the way from the ground up, but that usually isn't the most efficient way. Generally you want to start with the cheapest and most available precursor that's closest to the final product. In this case I think the best thing to start with is 1-octen-3-ol which is extremely close. To convert it all I need to do is something called an oxidation reaction where this alcohol group is converted to a ketone. Now to acually get the 1-octen-3-ol, its pretty easy because its often sold as a perfume additive. Oddly enough, it's a natural and major component of mushroom odor, and it has a fungal and kind of earthy smell to it. I ended up picking it up online from a website called The Perfumer's Apprentice and I got 80ml of it for 20 dollars US. Now at first this reaction might seem a bit simple because we're only changing a very small thing but its actually a bit tricky. There are many ways to do oxidation's in general but in this case we have this reactive double bond here. A lot of the common methods might attack it and potentially mess it up. To prevent this, I need to be careful with both the conditions, and the chemicals that I use and it doesn't leave me with many options. I was able to find a paper though, that outlined a method that supposedly worked. So I decided to try it out and these were the main chemicals that I needed to do it. I was able to find most of them online from places like Ebay, but this one called triphenylphosphine dichloride, I couldn't find anywhere. I generally try to avoid it, but in this case I ended up having to order it from Sigma. But anyway with all that being said its finally time to get started. To a large flask I added all of the triphenylphosphine dichloride that I had which was 25 grams. And then on top of this I poured in 300ml of DCM solvent and I turned on the stirring. About a minute later all of the powder had dissolved and it was now time to set up to cool part of this reaction. The reaction needed to be carried out below around -60c and the best way to do this is by using a dry ice bath. So to a bowl I added a bunch of dry ice and then I poured in some acetone. The acetone immediately started to cool down and the dry ice let off a lot of CO2 gas. I waited about a minute and then I lowered in the flask from before and turned on the stirring. I let it sit there for about 15 minutes and I occasionally replenished the bowl with more dry ice. I didn't test the temperature because I didn't, well, have anything to do it with but at this point it was definitely at least around -70C. So I started adding the next ingredient, which was DMSO. I didn't just dump it all in though, and I did it slowly and drop-wise, to make sure the whole thing stayed cold. As far as I know the reaction that going on here hasn't exactly been proven but the authors of the papers I was following are pretty sure they know what was going on. As the DMSO was added it slowly reacted with the triphenylphosphine dichloride to make this intermediate molecule. This intermediate isn't super soluble in cold DCM though so as the reaction proceeded and more of it was made it started precipitating out. This caused the solution to turn white and opaque but the contrast in the flask here isn't the best so its kind of hard to tell. This now had to be stirred like this for the next hour so I covered the top with plastic to prevent any moisture from getting into the flask. And In the mean time I prepared the alcohol solution that I would need for the next step. So I went and got a beaker and I added 6.4 grams of the 1-octen-3-ol. I then attempted to wash the vial with a small amount of DCM but, there ended up being an error. I honestly have no idea how this happened though because I've never done anything that clumsy before. I was so shocked by it that instead of trying to recover things by washing off the vial, I just decided to restart. So I re-weighed out the 6.4 grams and carefully washed the vial this time. Then it was all diluted with more DCM up to around 100ml. I turned on the stirring to mix it all together and it was pretty much good to go. About an hour later I came back to the main reaction and I started adding the alcohol. To try and keep things as cold as possible though the alcohol solution was prechilled using a smaller dry ice bath. When it was eventually all added I covered the top again and I waited 15 minutes. The reaction here again isn't known for certain, but its believed that the oxygen in the alcohol attacks the sulphur in the intermediate and it kicks off the other oxygen. This forms the second intermediate molecule which is kind of a combination between the 1-octen-3-ol and the DMSO. At this point it had been about 15 minutes and the next thing I had to do was add some nice and stinky triethylamine. I started out by doing it dropwise, but when there was only about half of it left, I ended up just dumping it in. What's happening here is an acid-base reaction where the basic triethylamine is pulling off an acidic hydrogen. This generates a negative charge which then attacks the hydrogen in the alcohol. This triggers a whole shift of electrons where the electrons in the hydrogen bond move to form a double bond with the oxygen and the sulphur is kicked off. This whole reaction mechanism is very similar to a popular one called the Swern oxidation. In that one, though, instead of using the phospherous compound It using something called oxalyl chloride. I almost definitely could have done the Swern here instead, but I chose to do this one because I thought it might have been better. Oxalyl chloride is quite hard to get and make and it's also a lot more dangerous. I figured that if this end up working, it could be a safer and more accessible alternative. But anyway, assuming that it did work the final result of this reaction was supposed to be a new carbon-oxygen double bond and my beautiful 1-octen-3-one. However, it also made some side products like triphenylphosphine oxide and dimethyl sulfide that I needed to separate out. Before I could process any of it though, I had to let the reaction go to completion by just letting it warm up to room temperature. So I took away the dry ice bath and I let it sit there for about two hours. During this time, a bunch of white stuff settled out and I think this was mostly triphenylphosphine oxide, and maybe a bit of triethylamine hydrochloride, but I'm not 100% sure. The next step was to get rid of as much of the DCM and dimethyl sulfide as possible. The authors in the paper probably did it with a fancy thing called a Rotovap but I opted for just a classic distillation. They also did it under vacuum but I didn't think it was really necessary here. I also didn't really want to use one either because if I didn't condense things well enough, it would start throwing a lot of stinky methyl sulfide into the air. It all started boiling relatively quickly because both DCM and dimethyl sulfide have boiling points below 40°C. I then insulated the flask with a bunch of aluminum foil and I waited for the vapor to make it over. It eventually made it to my cold condenser where it was recondensed back into being a liquid. This was all slowly collected in my receiving flask, and at first, it was a mixture of the dimethyl sulfide and DCM. However, as I got closer to the end of the distillation, it was probably mostly just DCM. It's kind of hard to see here, but eventually, in the flask, it looked like there was a lot of solid stuff and very little DCM. In the paper, it said to get rid of most of the DCM and I figured this was good enough. So, I took it off the heating and I cooled it down with some ice water. When I got it back to around room temperature, I added a 50/50 mixture of hexanes and diethyl ether. The purpose of this was to dissolve the 1-octen-3-one, but to kick out all of the triphenylphosphine oxide, which is insoluble in these solvents. The moment it was added, it started to precipitate as a bunch of white powder. To get out as much as possible, it was important to mix it really well, so I just shook it around for a couple minutes. Then, to separate it off, I just did a vacuum filtration. I turned on my pump and started pouring everything in and after just a couple minutes, I was left with this nice, white powder. I then washed the flask and all the powder a few more times with more of that 50/50 solution. When I was done, all the triphenylphosphine oxide here was relatively clean, it just had a bunch of solvent mixed with it, still. So, I just dumped it somewhere to dry for a bit and then I transferred it to a bottle. Even though it's a biproduct in this reaction, triphenylphosphine oxide can be useful in other ones, so I think it's worth keeping. But in any case, getting back to things, this was everything that filtered through. Now, just like before, to get rid of all the solvent, I had to do another distillation. What was nice, though, was that the glassware was already set up from the last one, so I just had to reattach this flask. I turned on the heating mantle, and over the course of a few hours, I slowly distilled over everything. I was eventually left with this oily stuff at the bottom which I was initially happy with. However, I was also kind of skeptical because there was just way too much stuff here. Based on the amount of 1-octen-3-ol that I used, my maximum yield should only be several milliliters, but this looked like it was something around 40. To cool it down faster, I used ice water again and I started poking at it. This caused it to start crystallizing, and I was eventually left with a semi-solid paste. Pure 1-octen-3-one is an oil, though, so there was clearly a lot of impurity here. But, unfortunately, I didn't really know exactly what it was. In the paper, they did it on a really low scale, and because of this, they were able to purify this stuff by column chromatography. However, I scaled things up by about a factor of 50 and it's just way too much to do it with. So now, I had to deviate from the procedure and come up with my own purification method. Just as a disclaimer, though, this is by no means at all the best method, and it was just what I ended up coming up with. The first thing I did was add about 100mLs of distilled water and I mixed it around. Then I put it on a heating mantle, cranked up the temperature, and turned on the stirring. As it warmed up, all the solid stuff slowly melted, and it went back to being an oil. The major purpose of this step was to get rid of any excess triethelamene that still remained as well as its salted reactive form. I let it mix around for a couple minutes, and then I took away the heating mantle. To help it cool I used an ice bath, and I was really hoping it would stay as an oil. However, it very quickly solidified, just like before. This told me that there was still a bunch of junk there, but it wasn't water soluble stuff. This nasty water did reek of methyl-sulfate and triethylamine though, so I quickly got rid of it.
I don't think so. I work in a steel mill where we melt down and pour liquid steel into billets. No one touches these, they smell like metal. Furthermore I work in the machine shop and I can tell you for certian a untouched bar of brass smells a heck of a lot different then a untouched bar of 4140. I could be wrong though...should be fun for my co workers tomorrow as I walk around smelling metals
Why does blood smell like metal?
NileRed (the channel that made this video) is AMAZING. Even if you don’t necessarily enjoy chemistry or science in general, you’ll likely enjoy his videos.
What about taste? Pennies taste awful.
Interesting!
But my signature scent is Canadian Penny.
As someone who works with metal daily.... I'm gonna call bullshit on that.
Sometimes the smell is from ass pennies, TYL
Is it possible for something to have no smell at all ?