Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

22. Carboxylic Acid Derivatives: NAS

Nucleophilic Acyl Substitution

Organic Chemistry

22. Carboxylic Acid Derivatives: NAS

Nucleophilic Acyl Substitution

Previous problemNext problem

6:16 minutes

Problem 56

Textbook Question

One mole of acetyl chloride is added to a liter of triethylamine, resulting in a vigorous exothermic reaction. Once the reaction mixture has cooled, 1 mole of ethanol is added. Another vigorous exothermic reaction results. The mixture is analyzed and found to contain triethylamine, ethyl acetate, and triethylammonium chloride. Propose mechanisms for the two exothermic reactions.

Verified step by step guidance

Step 1: Understand the first reaction. Acetyl chloride (CH3COCl) reacts with triethylamine ((C2H5)3N). Triethylamine acts as a base and abstracts the proton from the HCl byproduct of the reaction, forming triethylammonium chloride ((C2H5)3NH+Cl−). The acetyl chloride undergoes nucleophilic acyl substitution, where the chloride ion (Cl−) is displaced. This reaction is highly exothermic due to the formation of strong ionic bonds in triethylammonium chloride.

Step 2: Write the mechanism for the first reaction. The carbonyl carbon of acetyl chloride is electrophilic due to the electron-withdrawing effect of the chlorine atom. Triethylamine does not directly attack the carbonyl carbon but instead neutralizes the HCl formed during the reaction. The mechanism involves the nucleophilic attack of a base (possibly trace water or another nucleophile) on the carbonyl carbon, followed by the elimination of Cl−.

Step 3: Understand the second reaction. Ethanol (CH3CH2OH) is added to the reaction mixture. Ethanol reacts with the acetyl chloride (if any remains) or with the acyl intermediate to form ethyl acetate (CH3COOCH2CH3) via a nucleophilic acyl substitution mechanism. This reaction is also exothermic due to the formation of a stable ester bond and the release of HCl.

Step 4: Write the mechanism for the second reaction. Ethanol acts as a nucleophile and attacks the electrophilic carbonyl carbon of acetyl chloride. This forms a tetrahedral intermediate, which then collapses to expel the chloride ion (Cl−) and form ethyl acetate. The HCl produced in this reaction is neutralized by triethylamine, forming triethylammonium chloride.

Step 5: Summarize the products. After both reactions, the mixture contains triethylamine (if in excess), ethyl acetate (the ester product), and triethylammonium chloride (formed from the neutralization of HCl by triethylamine). The exothermic nature of both reactions is due to the formation of strong ionic bonds and stable covalent bonds in the products.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophilic carbonyl carbon, leading to the substitution of a leaving group. In the case of acetyl chloride, triethylamine acts as a nucleophile, attacking the carbonyl carbon and resulting in the formation of ethyl acetate and triethylammonium chloride.

Exothermic Reactions

Exothermic reactions are chemical processes that release energy, usually in the form of heat, to the surroundings. The vigorous nature of the reactions described indicates that the formation of products from reactants is energetically favorable, often due to the stability of the products compared to the reactants, as seen in the reactions involving acetyl chloride and ethanol.

Role of Triethylamine

Triethylamine is a strong base and a nucleophile that plays a crucial role in the reactions described. It not only facilitates the nucleophilic attack on acetyl chloride but also helps in the deprotonation of the resulting triethylammonium ion, thus driving the reaction forward and stabilizing the products formed during the exothermic processes.

Watch next

Master NAS - The Three Rules with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

1. Propose a mechanism for the acid-catalyzed reaction of salicylic acid with acetic anhydride.

2. Explain why a single drop of sulfuric acid dramatically increases the reaction rate.

Textbook Question

Show how you would use anhydrides to synthesize the following compounds. In each case, explain why an anhydride might be preferable to an acid chloride.

(d) succinic acid monomethyl ester

Textbook Question

Predict the major products formed when benzoyl chloride (PhCOCl) reacts with the following reagents.

(d) anisole and aluminum chloride

(e) excess phenylmagnesium bromide, then dilute acid

(f) LiAlH(O-t-Bu)₃

Textbook Question

Predict the products of the following reactions.

(e)

(f)

Textbook Question

Phosgene is the acid chloride of carbonic acid. Although phosgene was used as a war gas in World War I, it is now used as a reagent for the synthesis of many useful products. Phosgene reacts like other acid chlorides, but it can react twice.

(a) Predict the products formed when phosgene reacts with excess propan-2-ol.

Textbook Question

In each part, rank the compounds in order of increasing rate of nucleophilic attack at C=O by a strong nucleophile like methoxide.

(b)

Textbook Question

Suggest the most appropriate reagent for each synthesis, and explain your choice.

(a)

Textbook Question

There are many methods for activating a carboxylic acid in preparation for coupling with an amine. The following method converts the acid to an N-hydroxysuccinimide (NHS) ester.

(a) Explain why an NHS ester is much more reactive than a simple alkyl ester.

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap