22. Carboxylic Acid Derivatives: NAS
Carboxylic Acid to Acid Chloride
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According to my three rules, would it be favorable to turn a carboxylic acid into an amide? Does that go in the right direction in terms of favorability? Remember that carboxylic acid was in the middle of the page. Direction in terms of favorability? Remember that carboxylic acid was in the middle of the page and amide was all the way on the left side. Yes, it would be because carboxylic acid is more reactive than an amide. That's exactly what we see. When you react to carboxylic acid with ammonia, you are going to get some amide. But there is a problem. It turns out that the energy difference between these two acyl compounds isn't high enough to give us good yields of amides. Actually, what winds up forming predominantly is an ammonium salt. The way around that is to use a lot of heat when you're doing this reaction. If you use a lot of heat, you can dehydrate the salt back to an amide. This reaction actually does follow the 3 rules. You're thinking, Why are you teaching me this if we already learned it on the three rules? Because it turns out that your yield is just a little bit too low to make it a great way to synthesize an amide. You have to use heat in order to force it to make the amide. It turns out in order to avoid those harsh heat conditions, chemists have found another molecule that's a dehydration agent. This is a dehydration agent. And this molecule is called DCC. Here I've shown you what the structure is. You might not need to know what the structure is. But you should know that DCC and this are the same thing. DCC when coupled with NH3, dehydrates the amide by itself. We don't need heat. It greatly increases our yield. Instead of having to use a lot of heat to get amide, we can combine NH3 with DCC and we're going to get a huge yield of our amide. Many times, you're going to see this agent, DCC, used to boost these reactions that are already favorable but to make them happen at higher yields. The whole point of this area is that you'll understand what the role of DCC is. Let's move on to the next one.
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