Show the products of the reactions of these carboxylic acids with PBr 3 /Br 2 before and after hydrolysis. (a) pentanoic acid (b) phenylacetic acid (c) succinic acid (d) oxalic acid

Hello everyone. Today, you're the falling problem. Draw the structures of the major products expected from the reactions given below. So these reactions show a special type of reactions known as rumination and rumination uses browning, of course, along with phosphorous tri bromide followed by water. And what this does, it essentially replaces an alpha hydrogen of the carb oxalic acid with a browning atom. And so if we were to look at these early starting materials, we wouldn't have to identify the alpha hydrogen first. So for reaction, a, we always look for the ketone, which is this double bonded structure here. This is our ketone and the alpha hydrogen is going to be the hydrogen that is attached to the carbon next to our ketone. So for a, that would be the alpha hydrogen. For B, this would be the alpha hydrogen first. See this will be the alpha hydrogen since this is our car box like acid here. And lastly, for d this would be our alpha hydrogen. So if we start with a domination of this, we're going to retain our original carbon structure and even that key tone there. But where that alpha hydrogen was we're going to replace it with a bromine atom. We're gonna do the same thing. We're gonna retain our original carbon structure, including our car buck silic acid. And then we're simply going to place a blooming where that alpha hydrogen was for c yet again, we are retaining our original carbon structure with our car box full of gas it there. And then we are placing a bro man where that alpha hydrogen was. And then lastly, we are going to maintain that original carbon structure, even our to carve oxalic acids. And since the alpha hydrogen was here, that will be where our browning goes. And with that, we have solved the problem overall, I hope this helped. And until next time.

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24. Enolate Chemistry: Reactions at the Alpha-Carbon

Hell-Volhard-Zelinski Reaction

Organic Chemistry

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Hell-Volhard-Zelinski Reaction

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Problem 17

Textbook Question

Show the products of the reactions of these carboxylic acids with PBr₃/Br₂ before and after hydrolysis.
(a) pentanoic acid
(b) phenylacetic acid
(c) succinic acid
(d) oxalic acid

Verified step by step guidance

Step 1: Understand the reaction mechanism. The reaction involves the conversion of carboxylic acids into α-bromo acids using PBr3 and Br2, followed by hydrolysis. PBr3 activates the carboxylic acid, forming an acyl bromide intermediate, which reacts with Br2 to introduce a bromine atom at the α-carbon.

Step 2: Analyze the structure of each carboxylic acid. For (a) pentanoic acid, the α-carbon is adjacent to the carboxylic group. For (b) phenylacetic acid, the α-carbon is next to the benzyl group. For (c) succinic acid, there are two α-carbons due to the dicarboxylic nature. For (d) oxalic acid, there are no α-hydrogens, so bromination does not occur.

Step 3: Predict the intermediate products after the reaction with PBr3/Br2. For (a), the α-carbon of pentanoic acid will be brominated, forming α-bromopentanoic acid. For (b), phenylacetic acid will form α-bromophenylacetic acid. For (c), succinic acid will form α,α'-dibromosuccinic acid. For (d), oxalic acid will remain unchanged as it lacks α-hydrogens.

Step 4: Consider the hydrolysis step. Hydrolysis converts the acyl bromide intermediate back into the carboxylic acid, retaining the bromine substitution at the α-carbon. For (a), (b), and (c), the brominated carboxylic acids remain intact. For (d), no change occurs.

Step 5: Summarize the products. (a) α-bromopentanoic acid, (b) α-bromophenylacetic acid, (c) α,α'-dibromosuccinic acid, and (d) oxalic acid (unchanged).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Carboxylic Acid Reactivity

Carboxylic acids are organic compounds characterized by the presence of a carboxyl group (-COOH). They are reactive due to the polar nature of the carbonyl and hydroxyl groups, allowing them to undergo various reactions, including halogenation and esterification. Understanding their reactivity is crucial for predicting the products formed when they react with reagents like PBr3 and Br2.

PBr3 and Halogenation

Phosphorus tribromide (PBr3) is a reagent commonly used to convert alcohols and carboxylic acids into their corresponding bromides. In the presence of Br2, PBr3 facilitates the halogenation of the carboxylic acid, leading to the formation of acyl bromides. This step is essential for understanding the initial products before hydrolysis occurs.

Hydrolysis of Acyl Bromides

Hydrolysis is the reaction of a compound with water, leading to the breakdown of that compound. In the context of acyl bromides formed from carboxylic acids, hydrolysis results in the regeneration of the carboxylic acid and the release of bromide ions. This step is critical for determining the final products of the reaction sequence involving PBr3 and Br2.

Show the products of the reactions of these carboxylic acids with PBr3/Br2 before and after hydrolysis. (a) pentanoic acid (b) phenylacetic acid (c) succinic acid (d) oxalic acid

Key Concepts

Carboxylic Acid Reactivity

PBr3 and Halogenation

Hydrolysis of Acyl Bromides

Show the products of the reactions of these carboxylic acids with PBr₃/Br₂ before and after hydrolysis.
(a) pentanoic acid
(b) phenylacetic acid
(c) succinic acid
(d) oxalic acid