A Level Chemistry AQA 3.3.11 Amines PDF

A LEVEL CHEMISTRY 3.3.11 AMINES AMINES OVERVIEW DESCRIPTION General CnH2n+1NH2 Formula The amine group (-NH2) h...

A LEVEL CHEMISTRY 3.3.11 AMINES AMINES OVERVIEW DESCRIPTION General CnH2n+1NH2 Formula The amine group (-NH2) has a trigonal planar shape. The lone pair on the nitrogen atom means that the group is: 1. a nucleophile 2. a weak base 1o amine 2o amine 3o amine 4o salt Description R H H R R N R N R N R N+ R H R R R The classification of amine relates to the number of R groups bonded 1o and 2o amines contain highly polar N—H bonds Polarity Which give Hydrogen bonding IMF’s. - Nucleophilic Substitution (with haloalkanes) Reactions - Nucleophilic Addition-Elimination (acylation) 1o and 2o amines are soluble. Since hydrogen is directly bonded to a highly electronegative element (nitrogen), it Solubility in can hydrogen bond with water molecules. Water Solubility decreases with increased carbon chain length (i.e. a longer non-polar section of the molecule) 4o amine salts are also highly soluble as they are ionic. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.11 AMINES PREPARATION OF AMINES Aliphatic amines can be prepared by nucleophilic substitution reaction with haloalkanes (e.g. a chloroalkane). 1o Amine Production excess haloalkane + ammonia 1o amine + ammonium chloride H H H NH3 H H δ+ δ- R C Cl R C N+ H R C N H H H H H H N H Cl- + NH4+ H + NH4Cl 2o Amine Production excess haloalkane + 1o amine 2o amine + 1o amine salt H H R RNH2 H H δ+ δ- R C Cl R C N+ H R C N R H H H H H N H Cl- + RNH3+ R + RNH3Cl AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.11 AMINES 3o Amine Production excess haloalkane + 2o amine 3o amine + 2o amine salt H H R NH3 H R δ+ δ- R C Cl R C N+ H R C N R H H R H R N H Cl- + R2NH3+ R + NH4Cl 2o Amine Production haloalkane + 3o amine 4o amine salt H H R δ+ δ- R C Cl R C N+ R Cl- H H R R N R R Quaternary (4o) amine salts are used as cationic surfactants. They form a How To Tackle Nucleophilic coating on wet surfaces and prevent Substitution Questions the build up of static. They are the active ingredient in conditioners for clothes and hair. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.11 AMINES 1o amines can also be prepared by the reduction of nitriles. Reagent: LiAlH4 (ether) or H2(g) + Ni/Pt catalyst H H R C N + 4[H] R C N H H AROMATIC AMINES Phenylamine is produced by the reduction of nitrobenzene as detailed in the Aromatic Chemistry section. NO2 NH2 conc.HCl + 6[H] + 2H2O Sn AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.11 AMINES BASE PROPERTIES The lone pair on the nitrogen atom in ammonia allows it to accept a H+ ion for forming a coordinate / dative covalent bond with it. e.g. H R N H + H+ R N+ H H H Ammonia and amines are weak bases. This means that they exist on equilibrium with the “protonated” version. However, the relative strength of the weak base depends on the availability of the lone pair in the nitrogen to make this coordinate bond with a H+. The more available the lone pair is, the stronger the weak base. The availability of the lone pair depends on the structure of the molecule. Strongest Base Weakest Base 1o Amine Ammonia Phenylamine R N H H N H H N H H H 1o amines are the strongest bases in this comparison. Phenylamine is the weakest base in Nitrogen is highly electronegative, this comparison. so it able to draw electrons towards it from the alkyl (R) group. The p orbital that holds the lone pair in the N atom overlaps with This increases the electron density the p orbitals of the benzene ring. around the N atom, making the lone pair more available to act as a This means that the lone pair is proton acceptor. drawn into the delocalised system making them less available to act This is known as the inductive as a proton acceptor. effect. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.11 AMINES AMINES AS NUCLEOPHILES The lone pair on the N atom in ammonia and amines makes them a nucleophile. There are three examples of nucleophilic reactions that they undergo….. and they have already been covered! 1. Nucleophilic Substitution with haloalkanes This mechanism was covered in detail earlier in this section. 2. Nucleophilic Addition-Elimination with Acyl Chlorides This mechanism was covered in detail earlier in Section 3.3.9 Carboxylic Acids & Derivatives. You need to know the reaction mechanism for ammonia + acyl chloride and for 1o amines + acyl chlorides. 3. Nucleophilic Addition-Elimination with Acid Anhydrides These reactions were covered in detail earlier in Section 3.3.9 Carboxylic Acids & Derivatives. You need to know the equations for ammonia + acid anhydrides and for 1o amines + acid anhydrides (no mechanism). AQA www.chemistrycoach.co.uk © scidekick ltd 2024