Organic Compounds containing Nitrogen

The One Thing

The behaviour of amines is governed mainly by the availability of the nitrogen lone pair, which is affected by alkyl groups, resonance, electron-withdrawing groups, solvation, and steric hindrance. Diazonium salts are valuable aromatic intermediates because their diazonium group can be replaced by several other groups, often with the elimination of stable nitrogen gas.

Reactions, Processes and Experiments

Key Terms

• Amine: An organic compound derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups.
• Primary amine: An amine with one organic group attached to nitrogen; general formula RNH2.
• Secondary amine: An amine with two organic groups attached to nitrogen; general formula R2NH.
• Tertiary amine: An amine with three organic groups attached to nitrogen; general formula R3N.
• Quaternary ammonium salt: A positively charged nitrogen compound containing four organic groups; general formula R4N+X−.
• Aliphatic amine: An amine in which nitrogen is attached to alkyl groups, such as methylamine or ethylamine.
• Aromatic amine: An amine in which nitrogen is directly attached to an aromatic ring, such as aniline, C6H5NH2.
• Aniline: The simplest aromatic primary amine, with formula C6H5NH2; it is less basic than ammonia because the nitrogen lone pair is delocalised into the benzene ring.
• Basicity of amines: The ability of an amine to accept a proton using the lone pair of electrons on nitrogen.
• Carbylamine reaction: A test for primary amines in which a primary amine reacts with chloroform and alcoholic potassium hydroxide to form a foul-smelling isocyanide.
• Hinsberg test: A method for distinguishing primary, secondary, and tertiary amines using benzenesulphonyl chloride in the presence of alkali.
• Diazotisation: The conversion of a primary aromatic amine into a diazonium salt using nitrous acid at low temperature.
• Diazonium salt: An aromatic compound containing the diazonium group, Ar−N2+, usually present as Ar−N2+X−.
• Benzenediazonium chloride: A commonly studied diazonium salt with formula C6H5N2+Cl−, prepared from aniline using sodium nitrite and hydrochloric acid at 273–278 K.
• Sandmeyer reaction: Replacement of the diazonium group by Cl, Br, or CN using copper(I) salts such as CuCl, CuBr, or CuCN.
• Gattermann reaction: Replacement of the diazonium group by chlorine or bromine using copper powder and the corresponding hydrogen halide.
• Azo coupling: A reaction of a diazonium salt with an activated aromatic compound, such as phenol or aniline, to form a coloured azo compound.
• Azo compound: An organic compound containing the azo linkage −N=N−, often strongly coloured and used as a dye.
• Hofmann bromamide degradation: Conversion of a primary amide into a primary amine containing one fewer carbon atom using bromine and aqueous alkali.
• Gabriel phthalimide synthesis: A method for preparing primary aliphatic amines by reacting potassium phthalimide with an alkyl halide followed by hydrolysis.
• Amide: A nitrogen-containing derivative of a carboxylic acid with the functional group −CONH2, −CONHR, or −CONR2.
• Nitro compound: An organic compound containing the nitro group −NO2, such as nitrobenzene.

Easily Confused

• Primary, secondary, and tertiary amines: Classification depends on the number of organic groups attached to nitrogen, not on the number of carbon atoms in the molecule.
• Aliphatic and aromatic amines: Aliphatic amines have nitrogen attached to alkyl groups, whereas aromatic amines have nitrogen directly attached to an aromatic ring.
• Amines and amides: Amines are more basic because the nitrogen lone pair is available; amides are much less basic because the lone pair is delocalised toward the carbonyl group.
• Aniline and ammonia: Aniline is less basic than ammonia because its nitrogen lone pair is delocalised into the benzene ring.
• Sandmeyer and Gattermann reactions: Sandmeyer reactions use copper(I) salts such as CuCl, CuBr, or CuCN, whereas Gattermann reactions use copper powder and the corresponding hydrogen halide.
• Carbylamine reaction and Hinsberg test: The carbylamine reaction is given only by primary amines and produces a foul-smelling isocyanide; the Hinsberg test distinguishes all three amine classes through their sulphonamide reactions.
• Diazotisation and azo coupling: Diazotisation forms a diazonium salt from a primary aromatic amine at low temperature; azo coupling uses the diazonium salt to form a coloured azo compound with phenol or aniline.
• Gas-phase and aqueous basicity: In the gas phase, electron-releasing alkyl groups generally determine the basicity order; in aqueous solution, solvation and steric effects also influence the order.

What Gets Asked

• Writing amine classifications and general formulas: Questions may require the formulas RNH2, R2NH, R3N, and R4N+X−. Marks are lost by classifying an amine according to its number of carbon atoms rather than the number of organic groups attached to nitrogen.
• Explaining relative basicity: A question may ask why aniline is less basic than ammonia or how electron-releasing and electron-withdrawing groups affect aromatic amine basicity. The key omission is failing to refer to delocalisation or the availability of the nitrogen lone pair.
• Identifying amines using the carbylamine reaction and Hinsberg test: The relevant observations must be distinguished: a foul-smelling isocyanide indicates a primary amine, while Hinsberg results differ for primary, secondary, and tertiary amines.
• Writing preparation reactions: Questions may examine reduction of nitro compounds, ammonolysis of alkyl halides, Gabriel phthalimide synthesis, or Hofmann bromamide degradation. In Hofmann bromamide degradation, the product has one fewer carbon atom than the starting amide.
• Completing diazotisation and diazonium substitution equations: Required conditions include 273–278 K for formation of benzenediazonium chloride, and the correct reagent must be matched to the substitution product, such as CuCl for chlorine, CuBr for bromine, CuCN for a nitrile, potassium iodide for iodine, water for hydroxyl, and hypophosphorous acid for hydrogen.
• Describing azo coupling and aniline substitution: Questions may require the medium for coupling with phenol or aniline, the formation of a coloured azo compound, or the ortho/para direction of substitution in aniline. Direct nitration may cause oxidation and side reactions unless the amino group is protected as an amide.