Organic Chemistry Second Edition Chapter 23 David Klein Amines

Organic Chemistry Second Edition Chapter 23 David Klein Amines
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.1 Introduction to Amines
Amines are derivatives of ammonia Amines are designated as primary, secondary, or tertiary The terms, 1°, 2°,and 3° are used differently for amines than for alcohols. HOW? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The trigonal pyramidal nitrogen atom of an amine carries a partial negative charge on its lone pair HOW do you think the amine is likely to react? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Amines often react as a base or as a nucleophile What feature(s) of the amine do you think might determine whether it is more likely to act as a base or as a nucleophile? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.3 Properties of Amines The N atom in typical amines is sp3 hybridized The angles are 108 degrees. WHY? The C-N bond lengths are 147 pm, which is slightly shorter than C-C bonds. WHY? Under what circumstances would the nitrogen be sp2 hybridized? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.3 Properties of Amines N atoms with three different alkyl groups are chiral Chiral compounds are generally optically active. WHAT does that mean? Amine are generally not optically active. WHY? See next slide Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.3 Properties of Amines Klein, Organic Chemistry 2e

23.3 Properties of Amines Many small molar mass amines have unpleasant odors Practice with conceptual checkpoint 23.4 and 23.5 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.4 Preparation of Amines: A Review
Let’s review all of the methods we’ve learned in previous chapters to synthesize amines Carbon skeleton expanded by 1 carbon Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Let’s review all of the methods we’ve learned in previous chapters to synthesize amines Carbon skeleton is not changed Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Let’s review all of the methods we’ve learned in previous chapters to synthesize amines Reduction with a metal is a bit more mild than reduction with H2. WHY might mild conditions be preferred? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Let’s review all of the methods we’ve learned in previous chapters to synthesize amines Why is NaOH used in a final step? Practice with conceptual checkpoints 23.10 and 23.11 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e

23.5 Preparation of Amines via Substitution Reactions
Let’s learn some new amine syntheses Explain WHY the reaction will not stop at the primary amine but will continue to form a quaternary ammonium salt Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The Gabriel synthesis produces primary amines as well First, potassium phthalimide is formed Although the N1- is stabilized by resonance, it is still nucleophilic Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.6 Preparation of Amines via Reductive Amination
Recall the method for forming imines If a reducing agent is present, the imine can be reduced in situ to form an amine Reductive amination can be accomplished with a variety of reducing agents Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Sodium cyanoborohydride, which is similar to NaBH4, is commonly used The inductive effects of the –CN group make the cyanoborohydride reagent more selective HOW? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.7 Synthetic Strategies Let’s review reactions that form amines

23.7 Synthetic Strategies Let’s review reactions that form amines
Practice with SkillBuilder 23.4 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.8 Acylation of Amines Recall that amines can attack acyl chlorides
Two moles of the amine are used. WHY? Polysubstitution is not observed. WHY? An acyl group can act as a protecting group. HOW? An acyl group can help to limit the reactivity of amines in EAS reactions – see next slide Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.8 Acylation of Amines How might you perform the following synthesis? Adding bromine won’t work, because polysubstitution can not be avoided Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.8 Acylation of Amines How might you perform the following synthesis? The disadvantage of this synthesis is that amide hydrolysis requires harsh conditions Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.8 Acylation of Amines Aromatic amines also can not undergo Friedel Crafts directly How does the addition of the AlCl3 group deactivate the ring? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.8 Acylation of Amines To achieve ring alkylation, first the amine must be acylated Practice with conceptual checkpoints through 23.24 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.9 The Hofmann Elimination
Like alcohols, amines can be converted into leaving groups for elimination reactions Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Like alcohols, amines can be converted into leaving groups for elimination reactions Unexpectedly, the less substituted (less stable) product is observed – see next slide Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

23.11 Reactions of Aryldiazonium Ions
Alkyl diazonium salts are extremely reactive (potentially explosive) because of the excellent N2 leaving group Aryl diazonium salts are a bit more stable and synthetically versatile Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

There are many other diazonium salt substitutions Using this synthesis, amines can be used as a directing group and subsequently replaced with a –H atom Practice with conceptual checkpoint 23.30 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Diazonium salts can also be attacked by aromatic rings with an activating group – EAS mechanism Draw each resonance contributor of the sigma complex Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Azo coupling produces azo dyes WHY are azo compounds colored? Varying the substitution on the rings affects the specific dye color Practice with SkillBuilder 23.6 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Organic Chemistry Second Edition Chapter 23 David Klein Amines

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