[27.1] amines Flashcards

1
Q

what are amines?

A

organic compounds derived from ammonia, NH₃, where one or more H atoms in ammonia have been replaced by a carbon chain or ring

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2
Q

describe the 2 types of amines

A
  • aliphatic - N atom is attached to at least one alkyl group (R) eg. CH₃NH₂
  • aromatic - N atom is attached to an aromatic ring eg. C₆H₅NH₂
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3
Q

describe ammonia and the 3 classifications of amines

A
  • ammonia - N surrounded by 3 Hs and 1 lone pair
  • 1ʸ amine - N surrounded by 2 Hs, 1 R group and 1 lone pair
  • 2ʸ amine - N surrounded by 1 H, 2 R groups and 1 lone pair
  • 3ʸ amine - N surrounded by 3 R groups and 1 lone pair
  • 4ʸ ammonium salts - NOT AMINES - N⁺ surrounded by 4 R groups and a negative ion
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4
Q

how do you name primary amines?

A

add suffix ‘amine’ to name alkyl chain

eg. ethylamine, phenylamine

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5
Q

how do you name primary amines containing an amine group on another C?

A

use prefix ‘amino’ with a number to indicate position

eg. 2-aminobutane

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6
Q

how do you name secondary or tertiary amines containing the same alkyl group?

A

use prefix di- / tri-

eg. (CH₃)₂NH = dimethylamine, (CH₃)₃N = trimethylamine

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7
Q

how do you name secondary or tertiary amines where 2+ groups are attached to the N?

A
  • as an N-substituted derivative of the larger group
  • name: CH₃NHCH₂CH₂CH₃, CH₃N(CH₂CH₃)CH₂CH₂CH₂CH₃

N-methylpropyl amine, N-ethyl-N-methylpropylamine

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8
Q

do amines dissolve in water?

A

amines which dissolve in water produce weak alkaline solution

CH₃NH₂ (g) + H₂O(l) ⇌ CH₃NH₃⁺ (aq) + OH⁻ (aq)

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9
Q

how does solubility of amines change with carbon chain length and amine type?

A
  • small amines are very soluble in water due to hydrogen bonds forming with water
  • after about 6 carbons, solubility decreases as carbon chain length increases
  • tertiary amines don’t have H bonding, so are less soluble than primary amines
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10
Q

how do amines behave as bases in their chemical reactions?

A

lone pair of electrons on N atom can accept a proton

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11
Q

when an amine accepts a proton, what bond is formed?

A

dative covalent bond is formed between the pair of electrons on the N atom and the proton

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12
Q

draw the equation for a reaction of an amine as a base

A

slide 16 of C27.1 amines ppt

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13
Q

what properties does the N lone pair determine?

A
  • base strength depends on how well the N lone pair can accept a H+
  • the higher the electron densitiy of the N lone pair, the stronger the base
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14
Q

what is the order of base strength of the different types of amines?

A

tertiary > secondary > primary > ammonia > aromatic

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15
Q

reactions of amines with acids

A
  • produce salts
  • make sure to balance eg. ammonium sulfate salts

  • CH₃CH₂NH₂ + HCl -> CH₃CH₂NH₃⁺Cl⁻
  • 2CH₃CH₂NH₂ + H₂SO₄ -> (CH₃CH₂NH₃⁺)₂SO₄²⁻
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16
Q

what happens when you add aqueous sodium hydroxide to an ammonium salt?

A

free base is liberated from its salt

CH₃CH₂NH₃⁺Cl⁻ (aq) + NaOH (aq) -> CH₃CH₂NH₂ (l) + NaCl (aq) + H₂O (l)

17
Q

name process rather than description of method

how do you make aromatic amines?

A

reduction of nitrobenzene

18
Q

name process rather than description of method

how do you make aliphatic amines?

A
  • nucleophilic substitution with haloalkane
  • reduction of nitrile
19
Q

describe how to make aromatic amines

A
  • nitrobenzene is heated under reflux with Sn / conc HCl to form the ammonium salt, phenylammonium chloride
  • this is reacted with excess NaOH to produce the aromatic amine, phenylamine
  • tin and HCl act as a reducing agent

nitrobenzene + 6[H] -> phenylamine + 2H₂O

20
Q

reagent, conditions, product, nucleophile

making aliphatic primary amines: reaction of NH₃ with haloalkanes

A
  • reagent - excess, alcoholic ammoina
  • conditions - reflux in excess, alcoholic solution under pressure
  • product - amine or its salt due to reaction with acid
  • nucleophile - ammonia (NH₃)
21
Q

describe the role of ammonia in the production of amines

A
  • ammonia attacks haloalkanes as it has a lone pair and is a nucleophile
  • the amine produced also has a lone pair so can also attack a haloalkane
  • this leads to the formation of substituted (secondary and tertiary) amines
22
Q

why is excess ammonia used when making primary aliphatic amines?

A

ensures that all the haloalkane molecules with the ammonia before being able to react with any amines produced

23
Q

how do you liberate the free base from its salt when making primary aliphatic amines?

A

add aqueous sodium hydroxide

C₂H₅NH₃⁺Br⁻ (aq) + NaOH (aq) -> C₂H₅NH₂ (aq) + NaBr (aq) + H₂O (l)

24
Q

describe how to make aliphatic primary amines from reduction of nitrile compounds

A
  1. react haloalkane with KCN (nucleophilic substitution)
  2. reduce the nitrile form an aliphatic amine
25
Q

what are the 2 ways a nitrile can be reduced to form an aliphatic amine?

A
  • R–C≡N + 4[H] —> (LiAlH₄) R–CH₂–NH₂
  • R–C≡N + 2H₂ —> (Ni) R–CH₂–NH₂
26
Q

how are 2’ and 3’ amines formed?

A
  • 1’ amines still contain a lone pair of electrons on the N atom that can react further with excess haloalkane to form a 2’ amine
  • 3’ amines can be formed by further reaction of the 2’ amine