Making Benzene (C6H6)

[00:00:02][music] >> This their video is going to cover making benzene C6H6. Benzene was first isolated in 1825 by Michael Faraday and he used oil lamp residue. He collected this from multiple lamps and then distilled it. A six-membered ring was first hypothesized in 1865 so 40 years later by August Kekule. It had already been determined it had six carbons and six hydrogens sometime in the 1840s.

[00:00:37]August believed it had been given to him in a dream and he saw a snake biting its own tail and today that's called the ouroboros but he applied this then to the benzene C6H6 and came up that it must be a ring. This story is debated though. Benzene is typically distilled from crude oil or coal tar. As a ring it doesn't like additions or the additions would likely break the ring. Chemically speaking it does like subtractions though. It can deal with them. It's melting point is approximately 5.5°C.

[00:01:03]Its boiling point is approximately 80.1°C.

[00:01:06]And I drew this right here because the benzene ring is typically drawn like this but in all reality the electrons that surround it are delocalized so we will write it as a double bond or a single bond but in reality those electrons are uniformly dispersed both around the carbon ring and below the carbon ring. Early in the 1900s benzene was used in paints, rubber cement, printing inks, gasoline and believe it or not some aftershaves. Around 1920 to 1930 people have noticed an increase in bone marrow cancers in those who are chronically exposed to benzene meaning all the products that it contained.

[00:01:36]Sometime in 1960 to 1980 it was definitely a health hazard especially acute myelogenous leukemia and it was then taken out of most consumer products which is true today. In this experiment we're going to use a strong base and heat to decarboxylate the sodium benzoate which you can buy very easily which will of course yield benzene.

[00:01:52]Interestingly the sodium benzoate is made from benzene that's made from toluene that's derived from crude oil.

[00:01:58]So, you don't think crude oil plays a big part in our lives? Forget just the gasoline, it's involved in everything, including your Cheerios or your Rice Krispies that tend to have sodium benzoate as a preservative, which came from crude oil. Our materials we need sodium benzoate, as I mentioned, you can buy this almost anywhere, 100 g. You want this as fine as possible. I did find it uh sold as a cosmetic, which is like a powder practically, and you need sodium hydroxide, 60 g. The single reaction we'll go over is using the sodium benzoate, which looks like this with the double bonds to the carbon separated by single bonds. This is known as the Kekule form, going back to August Kekule, and you can see off the carbon here, we have another carbon that has a double bonded oxygen and a single bonded oxygen, and therefore this one's got a negative charge, which electrostatically attracts the sodium, making it sodium benzoate. But, you have an oxygen, an oxygen, and a carbon, which is CO2, and therefore decarboxylation means removing that CO2. When we add the sodium hydroxide and then heat, we're going to tear off that carbon dioxide there, and we're going to left with a pure benzene ring here, and then sodium carbonate as a residue. Benzene is known as an aromatic. It is organic, so this is actually organic chemistry, something I usually don't do. It's uh defined by a cyclic, flat molecule with a ring of overlapping electrons, much like this up here.

[00:03:12]And those electrons must be delocalized and highly stable. There are more rules to it that are more than I want to get in into in this video. If you want to look them up, you can. Our methods, we want to powder our sodium benzoate, SB, and our sodium hydroxide. So, they're as fine as possible because this is a dry experiment where both powders are used in their dry form. So, you want them as fine as possible, and then mix them well either in a container or in a plastic bag, that works well, too. Once you've powdered things well, we're going to do our first distillation, which includes a can and an adapter, and I have this adapter right here. This adapter is actually made for adapting two different size glasses, uh so to speak in chemistry. This is a 24/40, and it adapts to a 19/22, 19/22, which is the size just below it. But it this adapter, which isn't that much, actually works really well in this situation because you put that bottom part into a can, seal it well, and then the top part, which is right here, will fit any distillation setup that's a 24/40. So, you set up your can, you have your adapter right there, then just a typical distillation right here with the receiving round bottom flask over here.

[00:04:11]The mix is inside the can dry again. I'm going to use a camp stove because the interior has to reach 300 to 400° C, and I don't have any heating mantle or hot plate that will reach that. So, once you've got the can, the adapter, and then this setup, go ahead and run this whole thing until this stops dripping over. You want to monitor monitor the distilled liquid, not the temperature.

[00:04:31]This temperature doesn't mean a lot.

[00:04:32]It's interesting maybe to follow, but what's really important is watching the distillation dripping over here. Once it stops dripping, you know you are done.

[00:04:38]Next step is to take your crude benzene, put it into a separatory funnel, and wash it two times with 20 ml of water each time because benzene is lighter than water, it will be sitting on the top. The water will go to the bottom here, and of course you're drawing water out of the benzene because like absorbs like. So, you're going to drip the water out and then do it again with 20 ml water. When you're done with that, you're going to want to put your crude benzene into a flask with anhydrous calcium chloride. You can also use anhydrous magnesium sulfate for this, and you want to mix it around. You do want to cap it cuz benzene is an aromatic and it does actually want to evaporate pretty quickly. So, once you've done that for 1 to 2 hours, you've dried up most of the water in your benzene and you move on to the next step. And the next step is right here where you're setting up a final distillation. You're going to want to use an oil bath. You don't have to, but it does work well for these lower temperature boiling points. The temperature that benzene comes over is 80.1° C, but it will come over anywhere between 80 and 85° C.

[00:05:29]When it does come over, it will be clear and pure, and anything that made it orange or orange-red colored will stay behind over here. Again, you want to ice bath this to make sure the benzene stays where it's at as much as possible as you did over here. Once we get our pure benzene, we'll measure it. Our expected yield is 61 ml, so we'll compare whatever we get with that. But that's it. That should complete the entire experiment, and let's go ahead and make our benzene.

[00:06:01]100 g of finely powdered sodium benzoate pre-weighed as tiny particles are still floating around. 60 g of sodium hydroxide pre-weighed. As I mentioned, because the sodium hydroxide and the sodium benzoate is a dry reaction, the sodium hydroxide crystals are pretty big. So, I'm going to go ahead and grind these down until I can get it close to hopefully as fine as the sodium benzoate, although that might be difficult.

[00:06:21]It's a pretty fine powder, but it doesn't seem to be getting any better, so I'm going to call it quits right here. This is the can I'm going to use.

[00:06:25]It's a quart can. I just need to put a hole in the center here. Here's the obvious hole I drilled, and I used a 3/4 in bit to do that. I'm going to wrap the tape around there, and well, jam it into that hole.

[00:06:39]That's approximately 10 times wrapped, and see how it ends up fitting in here.

[00:06:46]Oh, yes, this is nice, actually. This is This is good. This is really snug.

[00:06:50]So, okay, terrific. [music] We've got it all set up. Now, we can go ahead and mix our powders and start the reaction. I'm ready to mix those powders. I'm going to use a plastic bag to do this, and you really want to add the sodium benzoate first because if you add the sodium hydroxide first, it tends to stick together, and then never really gets mixed well.

[00:07:05]All right, sodium benzoate's in, and sodium hydroxide goes next.

[00:07:10]This has been sitting here now for about 15 minutes. It should be calmed down quite a bit, but both of these are extremely fine [music] and will irritate your nasal passages something awful, especially the sodium hydroxide. So, I am wearing a mask, which is why my voice probably sounds a little different, but it's time to very carefully pour it in.

[00:07:29]All right, I just need to knock this down in there.

[00:07:31]So, of course, this can is our reaction vessel.

[00:07:35]I'm going to step away and let everything calm down. All right, that's a lot better. So, you can see this fills up about a third of the can. There's plenty of room to fit it, [music] and I'm going to now take this, put it here, which is where we'll start our distillation, of course, and hammer [music] this down good so it stays in place.

[00:07:48]Well, that will certainly keep it in place, but actually I didn't mention the most important part, and that is that the entire thing is sealed except for the opening at the top. Well, obviously I'm outside here, which is where this needs to be done, but there's a lot of extraneous noises from cars and trucks and other things, [music] so bear with me here. This is the reaction chamber we just mixed our dry ingredients in in this part. Well, of course, you saw me make that. The rest of this is just a simple distillation setup, and if I just look over on this end, right over there is, of course, my water pump [music] and just a tubing to connect it. I'll put ice in the aquarium there before we start so the water is really cold, and there is the [music] electronic or digital thermometer.

[00:08:21]All right, I'm going to turn the heat on.

[00:08:24]I'm going to put it at medium.

[00:08:29]It's been about 15 minutes, and there's a nice vapor forming, which is what we would hope to get.

[00:08:33]It's been about 20 minutes, and you can start seeing our benzene dripping very nicely.

[00:08:39]Interestingly, the temperature has bounced all over the place. Uh it's going up and down. Uh recently it had gone down to 83° C, but it's on its way back up now.

[00:08:50]So, it stopped. It's been just over an hour. I've been watching this for about 10 minutes, and nothing's happening. Our temperature has dropped really low, 41.8° C, and you can see our vapor has dropped a lot. It's just not even making up high enough there. So, I'm going to call it quits here. I'm going to take this apart, and we'll see how much we got.

[00:09:08]Well, here's our benzene. You can clearly see it inside of here.

[00:09:12]It's crude, of course. It needs to be cleaned up. Just a quick look [music] at the sodium carbonate that's left behind, and I'll probably toss in this, all of it, and the makeshift adapter we made, which actually did a pretty well. But, we talked about our crude benzene here.

[00:09:24]I want to talk about those temperature fluctuations, and I believe it is probably because we mixed two dry powders, and although I did my best at mixing it in the bag, they probably weren't perfectly mixed. So, when it got heated, we had uneven heating, and probably allowed for some hot spots, and when those hot spots occur we get superheated vapor and that superheated vapor was sending the temperature up to 120 130 degrees Celsius at one point but then it would always drop back down to around 100 to 105 and then it dropped to 95. So [music] we were measuring the temperature of the vapors not the exact temperature in that can. Looking at our crude benzene it's definitely orange this is super common when you do this reaction here and that's partly because it has organic impurities you can get by phenols and turpenols coming over both of which contain benzene rings but I think the most likely reason this happens is because when we open that can you could see the sodium carbonate in there but it was all charred very badly including the inside of the can which was flaking a little bit and I think it's really when we heat it and we get the charring >> [music] >> that some of those vapors come over and discolor it. In addition if you look at this really closely here you can see a bubble bottom there of water and that water comes over pretty much every time also. We're going to get rid of it through a separatory funnel. One last thing with the lights out here mostly at least it's it's darker.

[00:10:33]Those organic impurities are actually fluorescent so I have a small fluorescent light here and you can see how brightly that lights up.

[00:10:41]Unfortunately I only have a 1 L separatory funnel and we have maybe 50 ml we're working with which is about 5% of the total volume. Because of that I am not going to undo this separatory funnel every time I'm just going to shake the sand and the entire thing.

[00:10:54]Just adding our crude benzene.

[00:10:58]You can see that little bit of water at the bottom there when I add the 20 ml of water for the first mix of course we do this twice. I already mentioned this but just as a reminder.

[00:11:07]And shaking.

[00:11:10]Releasing the water layer.

[00:11:13]The second 20 ml of water.

[00:11:22]Next we're going to add some calcium chloride just to remove any water that I just might have missed. 4 g of anhydrous calcium chloride pre-weighed. Adding the calcium chloride. Flakes would be better or pellets [music] but uh all I have is uh pretty much powdered.

[00:11:35]Just because it's easier to remove it later, but I plan on putting all of this into the last distillation.

[00:11:42]So, if I put it all into the distillation, obviously the calcium chloride will stay behind.

[00:11:49]We're on to the very last step here before we get our purified benzene, the final [music] destination. I mean, the final distillation. I'm ready for the distillation. I'm going to be adding the benzene to >> [music] >> the heating flask here.

[00:12:01]Most of it stayed behind naturally.

[00:12:03]Almost ready to go. So, I'm going to go ahead and turn on the heat [music] here.

[00:12:06]We'll monitor that temperature.

[00:12:10]Well, I missed the first drop, but the benzene's starting to come over.

[00:12:20]As we near the end here, the leftovers are just simmering away there, but we can see the temperature is definitely starting to drop here, so we're very close to being done.

[00:12:29]Over the last 10 minutes, this has stopped dripping, and our temperature is at 71° and dropping. So, I'm going to take this apart and we'll see what our yield is. It hasn't quite cooled down yet, but you can see how concentrated that orange color becomes. It almost has a red hue to it now. Final purified benzene, crystal clear, of course. Let's see how much we made.

[00:12:51]That reads [music] 44 ml, and our expected yield was 61 ml. So, let's figure that out real quick.

[00:12:59]Essentially, 72%, which isn't bad at all. I'll definitely take it. And just to prove it's benzene and not water, >> Hey.