Chemical Reactions of Amines

5 Key excerpts on "Chemical Reactions of Amines"

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  eBook - ePub

  Principles of Organic Chemistry

  • Robert J. Ouellette, J. David Rawn(Authors)
  • 2015(Publication Date)
  • Elsevier

    (Publisher)

  We described some reactions of amines in earlier chapters. These reactions occur because the nonbonding electron pair of the nitrogen atom makes amines nucleophilic. We will review each type of reaction in this section.

  Reactions of Amines with Carbonyl Compounds

  In Chapter 10 , we described the addition-elimination reaction of amines with carbonyl compounds. An amine adds to the carbonyl carbon atom to give a tetrahedral intermediate. This product is unstable, and it loses water to form an imine. In general, imines are less stable than carbonyl compounds. Thus, the reaction is favorable only if water is removed from the reaction mixture. Most imines are not stable; they rapidly hydrolyze in aqueous solution to give carbonyl compounds.

  Reactions of Amines with Acyl Halides

  In Chapter 11 , we noted that an amide can be made by treating an amine with an acid halide. We recall that acid halides are very reactive acyl derivatives of acids; amides are very stable.

  Only ammonia and primary or secondary amines form amides. That is why pyridine, which cannot form an amide, is often used as a base to react with the HCl formed in the reaction.

  Reactions of Amines with Alkyl Halides

  We described nucleophilic substitution reactions of alkyl halides in Chapter 7 . Primary and secondary alkyl halides react with nucleophiles by an SN 2 mechanism. Amines are nucleophiles that can displace a halide ion from a primary or secondary alkyl halide to form an ammonium halide salt that is subsequently neutralized.

  The initial product of the nucleophilic substitution reaction is a secondary ammonium ion. It can lose a proton in an equilibrium reaction with the reactant primary amine. The secondary amine then can continue to react with the alkyl halide to give a tertiary amine and eventually a quaternary ammonium ion.

  Quaternary ammonium salts are ammonium salts that have four alkyl or aryl groups bonded to a nitrogen atom. Some quaternary ammonium salts containing a long carbon chain are invert soaps.

  Invert soaps differ from soaps and detergents because the polar end of the ion in the micelle is positive rather than negative. Like soaps, the long hydrocarbon tail associates with nonpolar substances, and the polar head dissolves in water. Invert soaps are widely used in hospitals. They are active against bacteria, fungi, and protozoa, but they are not effective against spore-forming microorganisms. Benzalkonium chlorides are one type of invert soap. The alkyl groups of these compounds contain from 8 to 16 carbon atoms.

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  Science of Synthesis: Knowledge Updates 2020/2

  • M. Christmann, Z. Huang, J. A. Joule, M. Christmann, Z. Huang, J. A. Joule(Authors)
  • 2020(Publication Date)
  • Thieme

    (Publisher)

  315 40.1. 1.4.3 Synthesis of Amines by Rearrangement (Update 2020) C. I. Ochoa and U. K. Tambar General Introduction The synthesis of amines is one of the most important areas of research in organic chemis-try due to the prevalence of nitrogen atoms in many functional molecules, including nat-ural products, pharmaceutical drugs, and agrochemicals. The synthesis of amines through rearrangement reactions has been heavily researched and discussed over the past few decades. One of the most comprehensive reviews of this topic was included in Science of Synthesis (Section 40.1.1.4). The chapter was arranged in two sections: rearrange-ments from carbon to nitrogen, and rearrangements from nitrogen to carbon. In this ex-tension of the original chapter, the same organization is preserved for consistency and ease of cross-referencing between the two chapters. The purpose of this chapter is to pro-vide an up-to-date account of new methods and synthetic developments in amine re-arrangement reactions within the last decade. Over this period of time, new chemistry has been developed which was not discussed in any particular section in the original ac-count on this topic. Thus, this chapter will not only serve as a supplementary document to the previous volume. It will also be a source of new synthetic strategies not discussed previously. It should be noted that although this section of Science of Synthesis is focused on the formation of alkyl-and cycloalkylamines, some examples shown in this chapter give products that are not part of these two categories; examples that give products such as anilines, amides, and ureas, have also been included to highlight both the broad scope and the power of the rearrangement reactions discussed. Every effort has been made to make this an in-depth review; however, there may be publications that have been inten-tionally or unintentionally omitted. 40.1. 1.4.3.1 Rearrangements from Nitrogen to Carbon 40.1.

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  Pyrolysis of Organic Molecules

  Applications to Health and Environmental Issues

  • Serban C. Moldoveanu(Author)
  • 2009(Publication Date)
  • Elsevier Science

    (Publisher)

  hapter 13 Pyrolysis of Amines and Imines

  S.C. Moldoveanu

  13.1. Primary amines

  General aspects

  Primary amines can be considered as compounds derived from ammonia by the substitution of a hydrogen atom with an organic radical alkyl or aryl, or as compounds resulting from the substitution of a hydrogen atom from an organic molecule with the group NH2 . The general formula of primary amines is R–NH2 (for aromatic primary amines the formula Ar–NH2 is sometimes used). Continuing the substitution of hydrogens from ammonia with alkyl or aryl organic radicals, secondary amines (R2 NH) and tertiary amines (R3 N) are generated. The formation of quaternary ammonium cations ( ) is also possible, these compounds being the equivalent of ion having the hydrogen substituted with organic radicals. The amines are named either using the name of the organic radical with the suffix amine (e.g., methylamine for CH3 –NH2 ) or using the prefix amino followed by the name of the hydrocarbon (e.g., aminomethane for CH3 –NH2 ). The substitution of a hydrogen from ammonia with an acyl radical (R–C(O)–) leads to the formation of amides. Amides can be considered derivatives of acids, and their pyrolysis is discussed in Chapter 20. Amine oxides can also be considered compounds different from amines and are discussed in Section 14.4.

  Aliphatic primary amines

  Aliphatic primary amines have a carbon with sp3 hybridization and two hydrogen atoms connected to the nitrogen atom. Pyrolysis of these compounds can take place with the involvement of the NH2 group. In this case, there are two common paths, one with ammonia elimination and formation of an unsaturated hydrocarbon (similar to water elimination in alcohols) and the other with hydrogen elimination and formation of a nitrile. These two types of reactions are shown below:

  (13.1.1)

  (13.1.2)

  Other reactions involving the amino group were also noticed during pyrolysis of some amines, such as generation of HCN, N2

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  Organic Chemistry

  • David R. Klein(Author)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  1066 CHAPTER 22 Amines 22.5 Preparation of Amines via Substitution Reactions Alkylation of Ammonia Ammonia is a very good nucleophile and will readily undergo alkylation when treated with an alkyl halide. Ammonia A primary amine H 3 C H N H H CH 3 H N H H H N CH 3 H H N H H + - This reaction proceeds via an S N 2 process followed by deprotonation to give a primary amine. As the primary amine is formed, it can undergo further alkylation to produce a secondary amine, which undergoes further alkylation to produce a tertiary amine. Finally, the tertiary amine undergoes alkylation one more time to produce a quaternary ammonium salt. A primary amine H N H A secondary amine N H A tertiary amine N A quaternary ammonium salt N H 3 C N H H N H CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 H 3 C H 3 C CH 3 CH 3 CH 3 CH 3 H 3 C H 3 C H N H H H N H H + - + - + - If the quaternary ammonium salt is the desired product, then an excess of the alkyl halide is used, and ammonia is said to undergo exhaustive alkylation. However, monoalkylation is difficult to For example, a nitro group can be reduced selectively in the presence of a carbonyl group: H O O 2 N H 2 N O H 1) SnCl 2 , H 3 O + 2) NaOH When reducing a nitro group in acidic conditions, the reaction must be followed up with a base, such as sodium hydroxide, because the resulting amino group will be protonated under acidic con- ditions (as we saw in Section 22.3). CONCEPTUAL CHECKPOINT 22.10 Each of the following amines can be prepared from either an alkyl halide or a carboxylic acid. For each amine, draw the struc- tures of both possible starting materials. (a) NH 2 (b) NH 2 (c) NH 2 22.11 The following compound cannot be prepared from an alkyl halide or a carboxylic acid using the methods described in this sec- tion. Explain why each synthesis cannot be performed. NH 2 22.5 Preparation of Amines via Substitution Reactions 1067 achieve because each successive alkylation renders the nitrogen atom more nucleophilic.

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  Concerning Amines

  Their Properties, Preparation and Reactions

  • David Ginsburg, Robert Robinson(Authors)
  • 2016(Publication Date)
  • Pergamon

    (Publisher)

  62 CONCERNING AMINES REACTIONS OF AMINES BASICITY The presence of the lone pair on the nitrogen atom in amines confers the property of basicity on these compounds. Aqueous solutions of water soluble amines are blue to litmus, giving a visual indication of their basicity. The base strength of a given amine may, of course, be determined by titration. These methods do not exhaust the Hst of those available for preparing amines. There are methods for preparing tertiary amines, for example, by alkylation of primary amines or secondary amines using reagents different from those discussed heretofore. The Eschweiler reaction is a case in point. Here, one heats a primary amine or a secondary amine in the presence of formal-dehyde and formic acid, C H 2 O R N H 2 > RN(CH3)2 H C O 2 H C H 2 O RR'NH > RR'NCHa H C O 2 H The Mannich reaction is a method for preparing tertiary amines having a carbonyl group in another part of the molecule. Dimethylamine is usually the secondary amine starting material in this reaction. RCOCH3 +CH2O+HNCH3 RCOCH2CH2N(CH3)2 Mannich bases of the general formula RCOCH2CH2N(CH3 )2 are very useful synthetic intermediates. We shall deal with these special preparative methods in our discussion of reactions of amines. This is more logical from the didactic point of view although, granted, the classification imder preparative methods and certain reactions of amines, is an arbitrary one. PROPERTIES, PREPARATION AND REACTIONS 63 [RCO2H] T ABLE 2 BAsicrrv C ONSTANTS OF V ARIOUS A LIPHATO A MINES Amine Kb Methylamine 4-4x10-'^ Dimethylamine 5 1 x 1 0 -* Trimethylamine 6 0 x 1 0 -^ Ethylamine 4-7x10-* Diethylamine 9-5x10-* Triethylamine 5-5x10-* n-Propylamine 3-8x10-* Di-n-propylamine 8-1x10-* Tri-n-propylamine 4-5x10-* The equilibrium constant for the ionization of amines in water is called the basicity constant, (cf. page 4).

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