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9.6.5 - Reaction with nitrous acid

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Reactions of Primary Aliphatic Amines

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Teacher
Teacher

Today, we're exploring how primary aliphatic amines react with nitrous acid. Do you remember what nitrous acid is made of?

Student 1
Student 1

It's made from a mineral acid and sodium nitrite, right?

Teacher
Teacher

Exactly! When primary aliphatic amines react with nitrous acid, they form what type of compound?

Student 2
Student 2

Aliphatic diazonium salts?

Teacher
Teacher

Right! And what happens to these diazonium salts?

Student 3
Student 3

They are unstable and release nitrogen gas and alcohols!

Teacher
Teacher

Good job! The release of nitrogen gas is helpful in estimating amino acids and proteins. Remember this with the mnemonic 'DAN' - Diazonium, Alcohol, Nitrogen.

Student 4
Student 4

DAN makes it easier to remember!

Teacher
Teacher

Let's summarize: primary aliphatic amines create unstable diazonium salts which break down to give nitrogen and alcohol. Great work, everyone!

Reactions of Aromatic Amines

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Teacher
Teacher

Next, let's talk about aromatic amines. How do they react with nitrous acid?

Student 1
Student 1

They react at low temperatures, between 273 K and 278 K, to form diazonium salts.

Teacher
Teacher

Excellent! Why are these diazonium salts important?

Student 2
Student 2

They are used for synthesizing various aromatic compounds!

Teacher
Teacher

That's correct! Remember, think of them as building blocks in organic synthesis. We can use the acronym 'DASH' - Diazonium, Aromatic, Synthesis, Hydrogen- bonded.

Student 3
Student 3

DASH helps link the uses together!

Teacher
Teacher

Great summary! To recap, aromatic amines react to form useful diazonium salts at specific temperatures, and they play a crucial role in organic synthesis.

Comparative Analysis of Amines with Nitrous Acid

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Teacher
Teacher

Now that we've covered the primary and aromatic amines, how do secondary and tertiary amines react differently with nitrous acid?

Student 1
Student 1

I think we didn't cover that in detail. What do we know?

Teacher
Teacher

Correct, we lack detailed information. They generally do not form diazonium salts. It’s essential to understand this difference.

Student 2
Student 2

Why is that?

Teacher
Teacher

Their structure prevents the formation of stable diazonium intermediates, making them behave uniquely compared to primary and aromatic amines.

Student 3
Student 3

So, it's about how their molecular structure affects their chemistry.

Teacher
Teacher

Exactly! To remember this, think of 'DYNAMO' - Diazonium, Not, Aliphatic or Aromatic. This helps us track what does not happen.

Student 4
Student 4

That's a handy way to remember!

Teacher
Teacher

Excellent! In summary, secondary and tertiary amines do not react with nitrous acid like primary and aromatic amines due to their structural differences. Well done!

Introduction & Overview

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Quick Overview

Amines react with nitrous acid in distinct ways, leading to the formation of diazonium salts, particularly in primary and aromatic amines.

Standard

This section discusses the reactions of amines with nitrous acid, describing how primary aliphatic, aromatic, as well as secondary and tertiary amines each react differently, with primary aliphatic amines forming unstable diazonium salts that release nitrogen gas, while aromatic amines form stable diazonium salts at low temperatures.

Detailed

Reaction with Nitrous Acid

Three classes of amines react differently with nitrous acid, which is generated on-site from a mineral acid and sodium nitrite.

Reactions Explained

  1. Primary Aliphatic Amines: When primary aliphatic amines react with nitrous acid, they yield aliphatic diazonium salts. These salts are unstable and decompose to release nitrogen gas (A1) and alcohols. The quantitative release of nitrogen is utilized in the estimation of amino acids and proteins.

Reaction: R-NH2 + HNO2 (NaNO2 + HCl) → R-N2+ + ROH + N2 + HCl

  1. Aromatic Amines: Aromatic amines, on the other hand, react with nitrous acid at low temperatures (between 273 K and 278 K) to form diazonium salts, which are key intermediates for synthesizing various aromatic compounds, as will be discussed in Section 9.7.

Reaction: C6H5NH2 + NaNO2 + 2HCl → C6H5N2Cl + NaCl + 2H2O (273-278 K)

  1. Secondary and Tertiary Amines: Both secondary and tertiary amines behave differently upon reaction with nitrous acid, but their specific reactions are not elaborated in this section.

Understanding these reactions is crucial as they highlight the distinct properties and reactivity of different amine types with nitrous acid.

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Audio Book

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Reactions of Primary Amines

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Primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts which being unstable, liberate nitrogen gas quantitatively and alcohols. Quantitative evolution of nitrogen is used in estimation of amino acids and proteins.

Detailed Explanation

When primary aliphatic amines come into contact with nitrous acid, they transform into diazonium salts. However, these salts are known to be unstable. As they break down, they release nitrogen gas and form alcohols. The amount of nitrogen gas released during this reaction can be measured, which is a method used in laboratories to determine the concentration of amino acids and proteins in biological samples.

Examples & Analogies

Imagine a soda can that, when shaken, builds up gas pressure. When you open it, the gas escapes quickly. Similarly, when the diazonium salts form and become unstable, they quickly release nitrogen gas, which is a useful indicator in scientific experiments.

Reactions of Aromatic Amines

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Aromatic amines react with nitrous acid at low temperatures (273-278 K) to form diazonium salts, a very important class of compounds used for synthesis of a variety of aromatic compounds discussed in Section 9.7.

Detailed Explanation

Aromatic amines undergo a reaction with nitrous acid at specific low temperatures, resulting in the formation of diazonium salts. These diazonium salts are crucial intermediates in many synthetic processes, allowing chemists to create various aromatic compounds. This reaction demonstrates the different behavior of aromatic vs. aliphatic amines with nitrous acid.

Examples & Analogies

Think of making ice cream. If you pour cream into a machine that churns it at the right temperature, it turns into ice cream. In this case, the right temperature is essential for aromatic amines to react successfully with nitrous acid to form diazonium salts.

Reactions of Secondary and Tertiary Amines

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Secondary and tertiary amines react with nitrous acid in a different manner.

Detailed Explanation

Unlike primary amines, secondary and tertiary amines do not form diazonium salts when they react with nitrous acid. Instead, their reactions can lead to different products, which are not as well defined as those from primary amines. The distinction is important for understanding the chemical behavior of different types of amines.

Examples & Analogies

Consider how different types of fruit react to being smashed. Berries may turn into a puree, while bananas can become mushy but look different when smashed. Similarly, secondary and tertiary amines react differently than primary amines with nitrous acid.

Definitions & Key Concepts

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Key Concepts

  • Amines react differently: Primary aliphatic amines form diazonium salts that release nitrogen gas, while aromatic amines form stable diazonium salts.

  • Temperature matters in aromatic reactions: Aromatic amines react at low temperatures for optimal diazonium salt formation.

  • Secondary and tertiary amines differ: They do not form diazonium salts through their reaction with nitrous acid.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example of primary aliphatic amine reaction: CH3NH2 + HNO2 → CH3N2+ + H2O + N2

  • Example of aromatic amine reaction: C6H5NH2 + NaNO2 + 2HCl → C6H5N2Cl + NaCl + 2H2O

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Nitrous acid's in heat; aliphatic amines, it can't be beat.

📖 Fascinating Stories

  • Imagine a primary amine chasing after a gas balloon. The balloon pops as nitrogen escapes, making room for alcohols to join the party!

🧠 Other Memory Gems

  • DAN - Diazonium, Alcohol, Nitrogen helps recall products from primary amine reactions.

🎯 Super Acronyms

DASH - Diazonium, Aromatic, Synthesis, Hydrogen-bonded to remember important aspects of aromatic amine reactivity.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Aromatic Amines

    Definition:

    Compounds containing an amine group attached to an aromatic ring.

  • Term: Diazonium Salts

    Definition:

    Salts containing a positively charged diazonium group, which are important intermediates in organic synthesis.

  • Term: Nitrous Acid

    Definition:

    A weak acid (HNO2) formed in situ from sodium nitrite and an acid, significant in the reaction with amines.

  • Term: Aliphatic Amines

    Definition:

    Amines where the nitrogen atom is attached to an aliphatic carbon group.