The system in Figure 25-8 can be adapted to produce the strong acid eluent methanesulfonic acid

The system in Figure 25-8 can be adapted to produce the...

Key Concepts

Electrode Reaction Mechanisms and Polarity Reversal

Electrode reaction mechanisms refer to the chemical transformations that occur at the electrode surfaces during electrolysis. Reversing electrode polarity alters the direction in which ions migrate, thereby enabling the control of which ions accumulate in certain compartments of a system. This principle is crucial for designing systems that target specific ion production or removal, as it directly influences the electrochemical reactions occurring at each electrode.

Electrodialysis

Electrodialysis is a separation process that applies an electric potential to drive the movement of ions across ion?selective membranes. This process exploits the migration of charged particles toward oppositely charged electrodes, allowing for the selective concentration or removal of specific ions from a solution. It is widely used in water treatment and chemical separation processes and is fundamental to systems where control over ion distribution is critical.

Ion Exchange Membranes and Resins

Ion exchange membranes and resins are key tools used to control the passage and retention of ions based on their charge. These materials are designed to either allow or block the transport of particular ions. By loading exchange sites with a specific ion, the materials can be tailored to preferentially exchange that ion with others in solution. This selective ion exchange is essential for processes aimed at generating a pure ion stream or removing impurities.

Transcript

0:00 All right.

00:02 So on the left, we have phenol with a pca of about 10, right? it's kind of acidic for an organic molecule, very acidic for an alcohol.

00:13 And then you have nitrophinol, para nitrofenol, where the pca is about two and a half to three times smaller, lower.

00:26 It means the phenol is more acidic, right? so why? do you why can we why why is that right um we have to explain through resonance so um you may just be thinking hey matt i don't understand why this is a problem because um protons that are electrophilic are uh are more likely to be deprotonated right which means that electron like protons that lack electron density are better are better acids so therefore if you have a nitro group that's sucking electron density out of the oh -h, then your, your proton's going to be more acidic because it's more electrophilic.

01:06 It has less electron density.

01:07 So why do i have to, why is this the second to last problem in the chapter implying it's difficult? and then i would say, i don't know.

01:16 I think that this is an interesting example because you've, you're used to, well, first of all, you're used to pushing positive charge around the ring.

01:27 This example, shows you the difference in electron, an arrow pushing when you have to push a negative charge around a ring.

01:34 But also, there are different rules for what stabilizes carbon ions.

01:42 And through residence, that's going to be electron withdrawn groups.

01:46 So when you have the nitro group, that's ortho or para, to the phenol, or i guess by extension, and also an amino group would be okay if this was an anelin instead, you have a more stable.

02:01 Base through residence and i'll show you what we mean.

02:03 So i drew all the frames down here, right? so when you have regular phenoxide, your protons gone.

02:08 The electrons are now back on that oxygen.

02:11 I could take the lone pair.

02:12 I could push it down into the ring.

02:15 And then i'm going to pop one of the bonds out onto the carbon atom.

02:20 So when i do that, now i have a double bond.

02:23 So you have a carbonyl.

02:25 I put a loan pair on the carbon, and now you have a carbonyon.

02:27 Carbon has a formal charge of negative 1, five valence electrons, formally belonging to carbon, which makes the formal charge negative 1.

02:37 Right.

02:38 And then you can't just move the double bond around.

02:41 If i did this, that will be giving the carbon an extra electron, right? that's not how you push negative charge around a ring.

02:48 You have to reform the bonds with that loan pair and then push.

02:53 So now the dumb bond is going to be here, which means i have to push.

02:58 The electrons onto the paracarbon um so i'll do that again so it's more clear there we go paraposition so now you end up with this carbon ion and then finally i could push them like that so now they are on the ortho carbon again um i forgot my double bonds there we go so you notice that the phenol the phenoxide anion is stabilized through resonance in the benzene ring so that's fine um now, let's do it with the nitro.

03:33 So you might be able to see at what point we're going to be able to have the nitro group help us out a little bit.

03:45 Sorry.

03:46 And the nitro groups, the nitrogen is always positive.

03:51 One of the oxygen is negative.

03:52 So what we're going to do is we're going to take the lone pair, just like we did with phenol, the phenoxide.

03:57 We're going to push them down.

03:58 We'll pop out an ortho loan pair there.

04:01 There, boom.

04:03 So now we have this and that.

04:06 Now this is going to be the resident structure where we see some good stuff.

04:15 Right.

04:15 So now you have a negative charge that is, i'm forgetting about the nitro group...

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