Ethyl propanethioate. So here we have our thioester, and it's reacting with aqueous hydroxide ion. Right. So this is a basic solution. Now, in step 1, we're going to have the hydroxide ion attack the carbonyl carbon forming an alkoxide.

So here, the oxygen with its lone pair comes in, hits the carbonyl carbon breaking the bond, and kicking it up here. What we're going to make now is a negatively charged oxygen since it's making one bond and has 3 lone pairs. And here goes the hydroxide we just added. This is an alkoxide ion because we have a negative oxygen connected to this carbon chain. Now, in step 2, we're going to say the alkoxide ion pushes its electrons to kick out the thiol as a thiolate anion.

Alright. So this is going to come down to make a double bond, and it's going to kick this out. So what we're going to make is a carboxylic acid plus this thiolate anion. But here's the thing, we're not allowed to have this type of environment. Steps 3 a and 3 b are connected to one another.

They're both part of proton transfer. Here in step 3 a, we're going to say the thiolate anion deprotonates the carboxylic acid forming a carboxylate anion. Carboxylic acid is very acidic, so it's naturally going to become deprotonated by the thiolate anion. So here, we're going to say it comes in, removes this H⁺, oxygen holds on to the electrons. As a result of this, we make our carboxylate anion, and we have a thiol.

And then for step 3 b, we're going to say a thiol, it has a pK_a of roughly around 10, and is sufficiently acidic to remain deprotonated in a solution of hydroxide ion, which typically has a pK_a of around 15.7. So what's going to happen here is this O_H is strong enough that it's going to deprotonate this. The thiol here gives up its hydrogen, the electrons go to the sulfur. So here we have R, negatively charged sulfur plus water.

So these were the steps, all the steps when it comes to the basic hydrolysis of a thioester. Right? So just keep in mind, we're including a basic environment, so it's hard for these various acidic groups to stay in their protonated form. It's very easy for them to become deprotonated.