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Video Solution: Ethanol is:  A. a catalyst B. a reactive intermediate...

Problem

Ethanol is: 

A. a catalyst

B. a reactive intermediate

C. a Brønsted acid

D. a Brønsted base 

Video Transcript

Hey everyone. So, this question it wants to know what is ethanol in our reaction, so it could be A, a catalyst, B a reactive intermediate, a bronsted acid or a bronsted base. Now, remember that our catalyst is going to be regenerated, it's going to help our reaction move forward. Now, do you think that ethanol is the intermediate, that's going to be reactive, we'll see, or bronsted acid lower base and what are the definitions of these again, do you remember? Well, for the acids is going to be a proton donor and for the next one is going to be a, what do you guys think? proton, what's the word I'm looking for starts with an A, acceptor, okay? So let's see, if we go to our reaction again, let's scroll up, this was for our first question, the answer was C and now let's take a look at our graph and our reaction. Now, where is ethanol? do you see it? right here, okay? It's an ethyl group, right? An ethyl alkyl group and then it has an alkyl, an alcohol, so what do you think? Well, it's not going to be a catalyst, right? It's not generated at the end of our reaction and what ethanol actually is it's one of the reagents that we use, okay? So it's not going to be an intermediate like our carbocation is. Now, what that does is it eliminates answer choice A, right? With it's not a catalyst because it's not regenerated, what we get is we get a species that's entirely different, okay? It's not an intermediate, right? Because you guys remember intermediate as your carbocations, your different transition states, right? So, ethanol is not reacting as that, so it must be either a bronsted acid, bronsted acid or a bronsted base, okay? So let's scroll down and cross down our first two answer choices. So, let's again review the definitions of bronsted acid and bronsted base, which you should definitely memorize, right? So, bronsted acid. Remember, is a proton donor, okay? So, be thinking it has acid in the name, right? We know that acids usually protonate, right? And then a bronsted base, okay? And you've encountered bases, right? And that's going to be a proton acceptor, so what it's going to do is deprotonate, so if we scroll up, what do you think ethanol is doing? I've drawn up a little bit of the mechanism, you see that the ethanol is going to come in and grab that H, okay? And notice that is our ethanol accepting a proton or is it donating one? Well, look it's protonated at the end, so what does that mean our answer is? it's a bronsted base, okay? Our final answer here is ,D you can go ahead, we can cross out C and highlight our answer here to be D, ethanol in our reaction is a bronsted base. Alright, so I hope that made sense and let me know if you have any questions.

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