NileRed - 2016-02-19
I made some fast edits. Hopefully it's okay now. ------------------------------------------- In this video, we whip up some benzyl chloride. It is a pretty useful chemical and I plan to use it to make denatonium benzoate. Nile talks about lab safety: https://youtu.be/ftACSEJ6DZA ------------------------------------------- • NileRed Store: https://nilered.tv/store • Patreon: https://www.patreon.com/nilered • NileRed Newsletter: https://nile.red/home#newsletter ------------------------------------------- • Discord: https://nilered.tv/discord • Facebook: https://www.facebook.com/NileRed2 • Instagram: https://www.instagram.com/nile.red • Snapchat: https://nilered.tv/snapchat • TikTok: https://www.tiktok.com/@nilered • Twitter: https://twitter.com/NileRed2 -------------------------------------------
For all the people saying that this reaction will be overwhelmingly SN1 in terms of mechanism due to resonance stabilization, you would be right EXCEPT:
Expect experimentally, the sn1 and sn2 mechanisms for specifically benzyl halides are almost 50/50 favored. The reason for this is due to kinetics. Although the carbocation has exceptional stability and would be expected to be the major product, it relies on the relatively slow step of the water spontaneously leaving. The SN2 reaction proceeds via an attack by the relatively weak chloride nucleophile but this process can happen much faster. Therefore the reaction mechanism is almost an even split. Sn1 is greater favored due to stability but hindered by a slow leaving step. The sn2 is fast with the attack by the chloride, but does not have the benefit of the stability of resonance.
This illustrates the importance of kinetics for determining the experimental outcome of a reaction beyond theoretical expectations
This is much more Sn1 than Sn2 because the positive charge is extremely stable, having 4 resonance structures total
You would think so, but the ratios of which mechanism prevails is actually pretty close to 50/50. It all comes down to kinetics. Although the resonance stabilized carbocation is definitely very stable, the rate determining step is how quickly the H2O group spontaneously leaves. For SN2 reactions all it takes is the chloride coming in and attacking which happens much faster than the H2O leaving. So it’s almost a 50/50 mix. This illustrates the interplay between how kinetics, and resonance/sterics comes into play. From ones understanding of resonance, sn1 should be greatly favored and be the major product, but it’s fighting against the relatively slow process of the water molecule leaving. Whereas the sn2 attack by the chloride happens much faster before the resonance structure can be established.
@spiderdude2099 correct me if my intuition is off here, but..
From what I understand, SN1 shouldn’t really happen here, since it‘s a terminal carbon atom, and even if you have a nice protic solvent the terminal carbocation should be waaaay too unstable. I don’t know to what degree the resonance structures would help, but in general terminal groups should always undergo SN2 reactions.
Edit: just looked it up. Substitutions in the benzyl position will prefer SN1 if the benzyl group has electron-donating groups attached.
As it is, the unsubstituted benzyl like seen here should prefer SN2.
@もろぴぃ the issue with that is that the stabilization given by resonance even by an unsubstitued benzyl ring is absolutely HUGE. Draw the resonance structures for the primary carbocation and you’ll see this. The charge is able to move to other carbons such that it leads to several resonance structures where the charge is on a secondary carbon. This greatly stabilizes it, and leads to SN1 occurring to a much greater degree than it should for being a primary carbon. The experimental results of performing SN1 vs SN2 reactions on benzyl halides comes out to around 50/50 because this effect is so strong. The effect of resonance can’t be overstated because, yes, you’re right as a primary carbon this should be much more dominated by SN2, but it’s not, they’re almost equal. It also has to do with kinetics. The resonance stabilized carbocation should actually make this reaction more SN1 than SN2, but the formation of the cation relies on the very slow kinetic step of water leaving and creating a charged carbon. Whereas SN2 doesn’t have this problem. It relies on nucleophilic attack which is a much faster kinetic step. This further leads to an equal split of the two mechanisms
Jesus, Bob.
I left my chemistry cursus for about 10 years now (wow how times fly) and I completely forgot about Sn1 and Sn2. That brings back some old memories. Funny thing is that I always struggled with organic chemistry, but it seems all so logical now, even if I never used it in my working years.
I love in depth chemistry. More of that if you have time for it. :)
More theory definitely!
The benzylic carbocation is very stable and can be expected to contribute overwhelmingly to the reaction mechanism.
Exactly right. The reaction conditions (polar protic solvent) in combination with the benzylic position bascially are screaming SN1.
Expect experimentally, the sn1 and sn2 mechanisms are almost 50/50 favored. The reason for this is due to kinetics. Although the carbocation has exceptional stability and would be expected to be the major product, it relies on the relatively slow step of the water spontaneously leaving. The SN2 reaction proceeds via an attack by the chloride which can happen much faster. Therefore the reaction mechanism is almost an even split. Sn1 is greater favored due to stability but hindered by a slow leaving step. The sn2 is fast with the attack by the chloride, but does not have the benefit of the stability of resonance.
This illustrates the importance of kinetics for determining the experimental outcome of a reaction beyond theoretical expectations
Sn2 gets a stabilized transition state, don't forget that...
I love all the mechanistic stuff. I'd love to see more in the future
Nilered: does extremely difficult math to determine how to perform careful experiments
Also Nilered: "SUBSTITION"
I believe this will be almost all Sn1. Chloride is a weak nucleophile, benzyl carbocation is almost as stable as a tertiary if not more, water is a great leaving group.
@Brian Ta Dude I'm nowhere near an expert but I'm well beyond that part of OChem, so yes I think that I understand it quite well. You have to think about it from a kinetics perspective. Reaction rate is inversely proportional to activation energy, and a carbocation mechanism (even if stabilized by resonance or hyperconjugation) will almost always require much more energy than a SN2 mechanism on an accessible carbon. If a reaction doesn't have to go through a higher energy activation step it doesn't. Then again, a chloride is a weak nucleophile, so that probably slows down the SN2 mechanism to such an extent that the carbocation formation (which is the determining step for speed in SN1) becomes faster.
But what I was trying to say is that benzylic carbon doesn't automatically equal SN1. If it was, for example, methoxide + benzyl chloride the mechanism would 100% be SN2.
@Andrei Gheorghe
No they aren't
https://www.quora.com/Which-carbocation-is-more-stable-Benzyl-or-Tertiary
https://www.quora.com/Which-is-more-stable-carbocation-tert-butyl-carbocation-or-allylic-carbocation
At least not definitely, as stability is relative to the condition and depends on solvent, temperature and a bunch of other factors. But measured in standard conditions (I don't know which ones specifically) tertiary is more stable than benzylic and always more stable than allylic.
@Peter Pepper
Yes but you still have to specify if the carbon is primary, secondary or tertiary. You can have both primary benzylic carbons and tertiary benzylic carbon. Those informations are equally as relevant to chemical reactivity, and they're not mutually exclusive.
@Pietro Tettamanti Which is why I said that primary benzylic would have been the best way to formulate this.
Apparently water leaves it slowly enough and the chloride attacks it fast enough that it's an even split here.
I would love to see more "theoretical chemistry" in your videos (which I already find very interesting)
Damn, you didn't mess around with this one lol. Your passion for chemistry really shines through with your thoroughness - really separates the amateurs from the real chemists! I was getting exhausted just from watching all the product purification steps you took lol. Good work!
I'm a big fan of you going over the reaction mechanism. My work mostly revolves around surface chemistry and watching vids like this keep the parts of my brain that learned organic chemistry alive.
Man I'm not a chemist or studying chemistry, but this channel is so interesting
Me too
As someone who works in an organic laboratory, it is very intriguing for me to see your videos! I say that because there are reactions that I simply never conducted in my career but have been taught in textbooks. It is very educating for me. Keep up the excellent content!
I know this is an old video but I really appreciated the explanation of SN1 and SN2 mechanism.
I'm a chemistry student and before I was introduced to organic chem I was wondering what was happening in the reaction.
Your videos are great, I suggest you to put more explanations but also a time skip for those who are here for the calming and quality video.
That's some great yield for a fractional atmospheric distillation. I personally prefer to dry the final product with anhydrous potassium carbonate. It will both dry it and help remove any HCl dissolved during the distillation (I could see yours fuming as you poured it).
Sn1/sn2 explanation was very informative and helpful. I appreciated it greatly as I only did an A level in chemistry and don't have a degree. I would have loved to have seen even more on the topic you mentioned of 'resonance'
I'm currently studying Chemistry in my first year at university and I was wondering when you were talking about the mechanism of reaction here whether SN1 would be more prevalent due to the solvent being water. My thinking is that water is obviously protic and so can solvate the carbocation intermediate formed in by SN1 better than the transition state from SN2. Would you agree with this? I just want to make sure I have my understandings of how the mechanisms are affected correct. Also great job on the videos, really enjoy it when you synthesise multiple compounds and then use them to achieve the formation of a final product. I'm hoping to become a synthetic organic chemist so it's really interesting to me :)
I really am enjoying the explanations and in depth discussions you are providing in these videos! Thank you. :)
I learn more from watching this 16 minute video than sitting in my 2 hour O Chem lecture
Hey, Nile!
Good on you for getting so many videos out in such little time. Cool information!
Question: Would you say this Benzyl Chloride here burned your eyes as much or less than the chloroacetone?
Yeah the benzyl chloride was a bit less painful than
getting soap in my eyes for a few hours.
+Nile Red ouch.
+Nile Red I stored like 75ml of this in a Pyrex reagent bottle, and opened it after a few days and as soon as I opened the cap it sprayed a mist out and freaked me out. I liked for the decomposition facts on it but couldn't find much. and it turned a muddy brownish red color. it was over molecular sieves also. any ideas on why? did it decompose? it was out of light but in a hot garage seeing how I really don't want it in my house. how long is the shelf life? I've tried finding lit on it but come up empty handed.
@shanehuse can you describe how you synthetized it?
Very nice, Nile. Both your lab technique and your explanation of SN rxns were lovely. I only worried about the lack of a fume hood.
Nice explanation of the SN1 and SN2 reactions. I noticed that the quality of the equations is often lower than the resolution of the video. Do you use Chemdraw? In this case I might have a hint :)
+Random Experiments International I do use it. What is your tip? :)
+Nile Red First you draw everything as usual. Then you increase the size of the document. (File -> Document settings -> Layout -> Poster) I usually change it to 100 cm x 100 cm. Then I mark everything and make it as large as possible. I know it sounds a bit stupid, but when you save this document as a picture, the resolution is much higher :)
Cool, i never even thought of increasing the document size.
It would also favor some Sn1 because the reaction is performed in a polar protic solvent (water).
I'm just now realizing what the sn1 and sn2 substitution after being in IB chemistry HL and you explained it really good
I did enjoy the organic chemistry lecture; reminded me a little of OChem 2 with Dr. EJ McWhorter!
Also, I think it would be fun to see some polymer chemistry on this channel.
For the record, I'm REALLY grooving on the extra explanation. It helps answer a lot of questions I've had (f'rinstance: If you mix KCl and NaOH, are you going to get NaCl and KOH? When doesn't this happen?
etc.
Between y'all and chemplayer, I'm actually lerning this stuff....
That's actually a good question. Basically, assuming by mix you mean dissolve both in water, the ions dissociate completely because the Ksp is high enough for KCl, KOH, NaCl, and NaOH. (If you haven't learned about equilibrium constants such as Ksp it might be good to look it up now.) So you just end up with a soup of K+, Na+, Cl-, and OH-. Usually when you have a reaction in the form of AB + CD > AD + CB it means one of the products is insoluble so it drops out of solution as a precipitate. For more information on that, look up double displacement reactions.
@Alex I Dissolving in water was what I was initially picturing, yes, but only as a speculative starting point. I've heard of equilibrium constants, but I haven't delved into it all that deeply, and I think that might be a gap I'd wish to fill. Thanks!
this is pretty informative pls do more when you have time. thank you
I don't understand how significant it is that the Sn1 process takes place. The Sn2 should be pretty much instantaneous, but if it's competing with the Sn1 mechanism to a small extent, wouldn't the act of creating that benzylic carbocation slow down the reaction time?
You, chemplayer, and nurdrage all uploading several videos all within hours of each other. It's been pretty entertaining.
The reaction conditions (polar protic solvent) in combination with the benzylic position bascially are screaming SN1. SN2 plays a very minor role, if any at all.
would it be inadvisable to use a higher concentration HCL to achieve an excess of HCL with less liquid volume, or would the exothermicity of the reaction actually cause issues with the chemistry being favored toward an undesirable combination.
I've just learned and remembered something else for my tomorrow's mechanism reaction exam!
I love you 💖
hello, im a chemist, good video. I think this helps students and amature chemist in understanding sn2 vs sn1. Maybe you can make a vid on solvent effects and sterochemistry of sn1 vs sn2. I should also mention that benzylchloride is on list II of DEA compounds.
So is everything else on the planet
wow what a chemistry day great job nile love your vids.
I would like to see the benzoic acid and benzaldehyde videos next. And I think the methyl iodide and methylamine hcl videos would be nice to see in the future.
I believe the SN1 pathway to be correct in this case due to the weak nucleophilicity of the chloride ion paired with toluene's ability to easily stabilize carbocations, carbanions, and even radicals through resonance.
I wonder if NileRed used a respirator and a fume hood with it. I read on wiki that this is a hell of a toxic compund. Wouldn't want to harm myself worse than I did from ammonia synthesis (took a whiff out of curiosity and felt some of the symptoms). Yet, who knows. Safrole isn't nearly as dangerous as it has been made out to look by the DEA, maybe same stuff could apply for BzCl.
The detailed tangent was interesting, thanks for doing that!
Dumb question but could you use molecular sivs to dry the water from hcl therefore concentrating it?
hey, what do you think of radical chlorination of toulene with chlorine under uv light in a refllux setup at 111°C?
could be nice to try out. When all toluene is chllorinated the boiling point should climb more towards 180°C where it should be kept until all Benzylchloride is chlorinated to Benzalchloride to prevent the forming of Benzyltrichloride
It would be pretty neat if you could do some teaching videos like Kahn academy to go over organic mechanisms like you did here describing Sn1 and Sn2
Its not just resonance! it is hyperconjugation of the sp2 carbon atoms with a movile charge! So yes, its fucking awesome chemistry.
Lovely and beautiful synthesis :)
Your tangents are what answer alot of random question's I would either have to dig threw a book or annoy my collage professor to answer. Keep it up !
Can you use CaCl2 for the last drying steps as well?
Dude I have a test about this exact topic today, thanks for the explanations.
"I don't want to fill my garage w/ hydrochloric acid vapor for obvious reasons"
Another on the list of reasons I don't do this at home and just watch these videos :D
Great vid but i really wanna see someone do it with N-bromosuccinamide or N-chlorosuccinamide and toluene.
Have you ever tried this?
I did. Symclosen (swimming pool), toluene and some radical starter for the polymerisation of styrene. Heating and reaction started. Use symclosen in some batches and every time new radical starter.
chaemelion - 2016-02-19
Another excellent video as usual. The SN1/SN2 explanation and mechanisms were much appreciated. I don't know about your other viewers, but I wouldn't mind seeing more technical information in the future.
Aeon Z1 - 2019-03-24
I agree, this gave me a better understanding of the difference between the Sn reaction types.
TheRainbowWillow - 2020-05-06
chaemelion I agree. I’m a chemistry 1 high school student, so I don’t understand all of it, but it’s good info to have!
ChemoMania - 2021-11-09
@TheRainbowWillow i am chemical engineering major currently...and i have leanrded a lot from nile ratjer from my proffessors