Amines

Unit 9: Amines & Diazonium Salts - 250+ Q&A

I. Fundamentals of Amines

Q: What is the fundamental structural unit from which amines are derived?
A: Ammonia (NH₃)
Q: How are amines structurally different from ammonia?
A: One or more hydrogen atoms of ammonia are replaced by alkyl or aryl groups.
Q: In what type of natural compounds can amines be found?
A: Proteins, vitamins, alkaloids, and hormones.
Q: Give examples of synthetic products where amines are present.
A: Polymers, dye stuffs, and drugs.
Q: Name two biologically active compounds containing secondary amino groups.
A: Adrenaline and ephedrine.
Q: What is the use of Novocain in dentistry?
A: It is used as an anaesthetic.
Q: What is the function of Benadryl?
A: It is an antihistaminic drug.
Q: What type of compound are used as surfactants?
A: Quaternary ammonium salts
Q: What is the role of diazonium salts in the synthesis of various compounds?
A: They are used as intermediates in the preparation of a variety of aromatic compounds, including dyes.
Q: What structural feature of amines is responsible for their basic properties?
A: The unshared pair of electrons on the nitrogen atom.
Q: What type of hybridization does the nitrogen atom in amines possess?
A: sp³ hybridization.
Q: Describe the geometry of amines.
A: Pyramidal.
Q: Why is the bond angle in amines slightly less than 109.5°?
A: Due to the presence of the unshared pair of electrons, which exerts repulsion on the bonded pairs.
Q: What is the bond angle in trimethylamine?
A: Approximately 108°.
Q: How are amines classified based on the number of alkyl or aryl groups attached to the nitrogen atom?
A: Primary (1°), Secondary (2°), and Tertiary (3°).
Q: Define a primary amine with a general formula.
A: R-NH₂ or Ar-NH₂
Q: What is a secondary amine and what is its general formula?
A: An amine with two alkyl or aryl groups attached to the nitrogen atom; R-NH-R' or Ar-NH-R.
Q: What is a tertiary amine, provide a general formula?
A: An amine with three alkyl or aryl groups attached to the nitrogen atom; R-N-R'-R" or R-N-R'-Ar
Q: What is meant by a "simple" amine?
A: An amine where all the alkyl or aryl groups attached to nitrogen are the same.
Q: How does a "mixed" amine differ from a "simple" amine?
A: A "mixed" amine has different alkyl or aryl groups attached to the nitrogen atom.
Q: What is the common name of CH₃NH₂?
A: Methylamine.
Q: How do you name an aliphatic amine in the common system?
A: By prefixing the name of the alkyl group to the word "amine."
Q: How are secondary and tertiary amines with two or more identical groups named in the common system?
A: With the prefixes "di-" or "tri-" before the name of the alkyl group.
Q: How are primary amines named in the IUPAC system?
A: As alkanamines.
Q: What is the IUPAC name of CH₃CH₂NH₂?
A: Ethanamine.
Q: How are amines with multiple amino groups named in the IUPAC system?
A: By using prefixes like di-, tri- and indicating the position of -NH₂ on the parent chain.
Q: What is the IUPAC name of H₂N-CH₂-CH₂-NH₂?
A: Ethane-1,2-diamine.
Q: How do you indicate substituents on the nitrogen atom in secondary and tertiary amines in the IUPAC system?
A: By using the locant "N".
Q: What is the IUPAC name of CH₃NHCH₂CH₃?
A: N-methylethanamine
Q: What is the common name of C₆H₅NH₂?
A: Aniline
Q: How are arylamines named in the IUPAC system?
A: Replace the 'e' of arene by "amine"
Q: What is the IUPAC name of C₆H₅NH₂?
A: Benzenamine
Q: What is the common name of 2-methylaniline?
A: o-toluidine
Q: What is the IUPAC name of p-bromoaniline?
A: 4-bromobenzenamine or 4-bromoaniline

II. Preparation of Amines

Q: What is the reducing agent used in the reduction of nitro compounds to amines, using metals in acidic media?
A: Sn+HCl or Fe+HCl.
Q: In the reduction of nitro compounds, why is iron scrap preferred over other metals?
A: FeCl₂ formed is hydrolyzed to release HCl, so only small amount is needed to initiate.
Q: What is the process by which alkyl halides react with ammonia to form amines called?
A: Ammonolysis.
Q: What kind of substitution reaction takes place during ammonolysis of alkyl halides?
A: Nucleophilic substitution reaction.
Q: What byproducts are formed during ammonolysis of alkyl halides?
A: Mixtures of primary, secondary, tertiary amines, and quaternary ammonium salts.
Q: How can a primary amine be obtained as the major product in the ammonolysis of alkyl halides?
A: By taking a large excess of ammonia.
Q: Which alkyl halide reacts faster in ammonolysis: RI, RBr, or RCl?
A: RI (R-I)
Q: What reducing agent can be used for the reduction of nitriles to amines?
A: LiAlH₄.
Q: How is a primary amine prepared by using nitriles?
A: By reducing a nitrile using LiAlH₄ or catalytic hydrogenation.
Q: In the reduction of nitriles, what happens to the carbon chain?
A: The carbon chain is increased by one.
Q: What reducing agent is used for the reduction of amides to amines?
A: LiAlH₄
Q: What product is formed from the reduction of amides using LiAlH₄?
A: An amine
Q: What is Gabriel Phthalimide synthesis used for?
A: Preparing primary amines.
Q: Why can’t aromatic primary amines be prepared using the Gabriel phthalimide synthesis?
A: Because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide
Q: What is the key step in the Gabriel Phthalimide synthesis for preparing primary amines?
A: The reaction with the alkyl halide and alkaline hydrolysis.
Q: What reaction is used for the synthesis of a primary amine containing one carbon less than the starting amide?
A: Hofmann Bromamide Degradation Reaction.
Q: What are the reagents used in the Hofmann Bromamide degradation reaction?
A: Br₂ with aqueous or ethanolic NaOH.
Q: What is the byproduct in Hoffmann Bromamide Degradation Reaction?
A: Carbonate, Sodium bromide, water

III. Physical Properties of Amines

Q: What is the characteristic odor of lower aliphatic amines?
A: Fishy odor
Q: How does the physical state of amines change with increasing molar mass?
A: Gases to liquids to solids
Q: What is the typical appearance of aniline and other arylamines?
A: Colorless when pure but become colored on storage
Q: Why are lower aliphatic amines soluble in water?
A: They can form hydrogen bonds with water molecules
Q: How does the solubility of amines change with an increase in molar mass?
A: Solubility decreases due to increase in the size of the hydrophobic alkyl chain.
Q: Which is more soluble in water, butan-1-ol or butan-1-amine, and why?
A: Butan-1-ol because it is more polar and forms stronger intermolecular hydrogen bonds than amines.
Q: In what type of solvents are amines typically soluble?
A: Organic solvents like alcohol, ether, and benzene.
Q: How does intermolecular association due to hydrogen bonding vary among primary, secondary, and tertiary amines?
A: Primary amines have more hydrogen bonding than secondary, while tertiary amines have no intermolecular hydrogen bonding between the molecules
Q: Which type of isomeric amine has the highest boiling point: primary, secondary, or tertiary?
A: Primary amines.
Q: What is the reason for the boiling point difference between isomeric amines?
A: The extent of intermolecular hydrogen bonding.

IV. Chemical Reactions of Amines

Q: Why are amines considered as Lewis bases?
A: They possess an unshared electron pair on the nitrogen atom.
Q: What products are formed when amines react with acids?
A: Amine salts
Q: How are parent amines regenerated from their salts?
A: By treatment with a base like NaOH.
Q: Why are amine salts soluble in water but insoluble in organic solvents?
A: They are ionic compounds.
Q: What are pKь and Kь values for amines useful for?
A: To understand the basic character of amines.
Q: How does the +I effect of alkyl groups influence the basicity of amines?
A: Alkyl groups increase electron density on the nitrogen atom, making amines more basic than ammonia.
Q: Are aliphatic amines or aromatic amines stronger bases than ammonia?
A: Aliphatic amines are stronger bases, while aromatic amines are weaker.
Q: Why is aniline a weaker base than aliphatic amines?
A: The unshared pair of electrons on the nitrogen is delocalized into the benzene ring.
Q: How do electron releasing groups influence the basic character of aromatic amines?
A: They increase the basic character of the amine.
Q: How do electron withdrawing groups influence the basic character of aromatic amines?
A: They decrease the basic character of the amine.
Q: What is the effect of steric hindrance on the basicity of amines?
A: Steric hindrance decreases basicity.
Q: How does solvation influence the basicity of amines?
A: Smaller the ion, more is the solvation and more is its stabilization.
Q: What is the general reaction for the alkylation of amines?
A: R-NH₂ + R'-X → R-NH-R' + HX (followed by subsequent alkylation)
Q: What type of reaction is acylation of amines?
A: Nucleophilic substitution reaction.
Q: What are the products of acylation of amines?
A: Amides
Q: What reagents are used for acylation of amines?
A: Acid chlorides, anhydrides, esters
Q: What type of base is required for acylation reactions of amines and why?
A: A stronger base than the amine (e.g., pyridine) to remove the HCl formed and shift the equilibrium.
Q: What is the carbylamine reaction also known as?
A: Isocyanide test.
Q: What type of amines respond to the carbylamine reaction?
A: Primary amines (both aliphatic and aromatic)
Q: What are the products of carbylamine reaction?
A: Isocyanides or carbylamines which are foul smelling substances.
Q: What are the products formed when primary aliphatic amines react with nitrous acid?
A: Unstable diazonium salt, which further decomposes to give alcohol and nitrogen gas.
Q: What type of amines form stable diazonium salts when they react with nitrous acid?
A: Primary aromatic amines.
Q: What is the use of quantitative evolution of nitrogen when amines react with nitrous acid?
A: For the estimation of amino acids and proteins.
Q: How does the reaction with nitrous acid differ between primary, secondary, and tertiary amines?
A: Primary amines form diazonium salts, which may decompose, while secondary and tertiary amines form other different products.
Q: What reagent is used for testing primary, secondary, and tertiary amines?
A: Benzenesulphonyl chloride (Hinsberg's reagent)
Q: What is Hinsberg’s reagent and its structure?
A: Benzenesulphonyl chloride (C₆H₅SO₂Cl)
Q: What type of compound is formed when a primary amine reacts with Hinsberg's reagent?
A: N-alkylbenzenesulphonamide
Q: What property of N-alkylbenzenesulphonamides makes them soluble in alkali?
A: The hydrogen attached to nitrogen is strongly acidic.
Q: What type of compound is formed when a secondary amine reacts with Hinsberg's reagent?
A: N,N-dialkylbenzenesulphonamide
Q: Why do tertiary amines not react with benzenesulphonyl chloride?
A: Because they do not have hydrogen attached to the nitrogen atom.
Q: What is the nature of the amino group in aromatic electrophilic substitution reactions?
A: Ortho- and para-directing, powerful activating group
Q: What product is formed when aniline reacts with bromine water at room temperature?
A: 2,4,6-tribromoaniline
Q: What is the main issue encountered during electrophilic substitution reactions of aromatic amines?
A: Their very high reactivity.
Q: How is the activating effect of the –NH₂ group in aniline controlled during monosubstitution reactions?
A: By protecting it by acetylation with acetic anhydride.
Q: What is formed when aniline is acetylated with acetic anhydride?
A: N-phenylethanamide (acetanilide)
Q: Why does direct nitration of aniline lead to a mixture of products?
A: Because it gets protonated in acidic medium, forming meta directing anilinium ion.
Q: How is nitration controlled to obtain the p-nitro derivative of aniline as the major product?
A: By using the protecting group in aniline (acetylation followed by nitration)
Q: Why does aniline not undergo Friedel-Crafts reaction?
A: Because it forms a salt with the Lewis acid catalyst.
Q: What type of charge does the nitrogen of aniline acquire during salt formation with Lewis acid?
A: A positive charge.

V. Diazonium Salts

Q: What is the general formula of diazonium salts?
A: R-N₂⁺X⁻ (where R is an aryl group and X⁻ is a counter anion).
Q: How are diazonium salts named?
A: By suffixing diazonium to the name of the parent hydrocarbon and then adding the anion name.
Q: Give an example of a diazonium salt?
A: Benzenediazonium chloride (C₆H₅N₂Cl).
Q: What is the name given to the N₂⁺ group in diazonium salts?
A: Diazonium group.
Q: How stable are aliphatic diazonium salts?
A: Highly unstable
Q: How stable are aromatic diazonium salts?
A: Stable for a short time in solution at low temperature.
Q: What is the reaction of converting primary aromatic amines to diazonium salts called?
A: Diazotization.
Q: What are the reagents used in the diazotization reaction?
A: Sodium nitrite and a mineral acid (HCl).
Q: What are the ideal temperature conditions to prepare diazonium salts?
A: Low temperatures (273-278 K).
Q: Why is the diazonium salt used immediately after preparation?
A: Due to its instability.
Q: What reaction is involved in the preparation of benzenediazonium chloride?
A: Reaction of aniline with nitrous acid.
Q: What are the products of the reaction between aniline and nitrous acid?
A: Benzenediazonium chloride.

VI. Reactions of Diazonium Salts

Q: What is the main feature of diazonium salts that makes them reactive?
A: The diazonium group (N₂⁺) is a very good leaving group.
Q: What is the general type of reaction that diazonium salts undergo?
A: Substitution reactions in which nitrogen group is replaced by other group and N₂ gas is liberated.
Q: What type of reaction is Sandmeyer reaction?
A: Reaction to introduce halide or cyanide ion into the benzene ring with Cu(I) ion as catalyst
Q: What are the reagents used in Sandmeyer reaction for introducing Cl, Br, or CN groups in the benzene ring?
A: Cu₂Cl₂/HCl, Cu₂Br₂/HBr and CuCN/KCN respectively.
Q: How is Gatterman reaction different from Sandmeyer reaction?
A: Gatterman uses copper powder instead of copper(I) salt, but produces the same products.
Q: How is the iodide ion introduced into the benzene ring using diazonium salts?
A: By treating the diazonium salt with potassium iodide (KI).
Q: How is the fluoride ion introduced into the benzene ring using diazonium salts?
A: By treating the diazonium salt with fluoroboric acid (HBF₄) followed by heating.
Q: Name the reagents that reduce diazonium salts to arenes.
A: Hypophosphorous acid (phosphinic acid) or ethanol.
Q: What product is formed when diazonium salts undergo hydrolysis?
A: Phenols.
Q: How is nitro group introduced using diazonium salts?
A: By treating diazonium fluoroborate with aqueous sodium nitrite in presence of copper.
Q: What type of reactions are coupling reactions of diazonium salts?
A: Electrophilic substitution reactions.
Q: What is the general product formed when diazonium salts react with phenols?
A: p-hydroxyazobenzene.
Q: What color are azo products typically?
A: Colored.
Q: How are azo dyes formed?
A: By coupling reactions of diazonium salts with phenols or arylamines.
Q: Name the product when benzenediazonium chloride reacts with aniline?
A: p-aminoazobenzene.

VII. Importance of Diazonium Salts

Q: Why are diazonium salts important in the synthesis of aromatic compounds?
A: They are useful intermediates for the introduction of various groups (-F, -Cl, -Br, -I, -CN, -OH, -NO₂) into the aromatic ring.
Q: Can aryl fluorides and iodides be prepared directly by halogenation?
A: No, they cannot.
Q: How are aryl cyanides prepared using diazonium salts?
A: By replacement of the diazo group using CuCN/KCN.
Q: What types of aromatic compounds are difficult to prepare without using diazonium salts?
A: Aryl fluorides, aryl iodides, aryl cyanides, phenols.

VIII. Rephrased Questions (Mixed)

Q: If an amine has the structure R₂NH, is it primary, secondary, or tertiary?
A: Secondary.
Q: How would you classify an amine with three different alkyl groups bonded to the nitrogen?
A: As a mixed tertiary amine.
Q: If a compound is named N,N-dimethylethanamine, what type of amine is it?
A: Tertiary.
Q: Instead of reacting an alkyl halide with ammonia, how can you make a primary amine with a shorter carbon chain from the corresponding amide?
A: By Hofmann bromamide degradation.
Q: What type of amine can be synthesized using the Gabriel phthalimide reaction?
A: Primary amines.
Q: What is an important limitation in using Gabriel phthalimide method?
A: Aromatic amines cannot be synthesized
Q: If an amine is a liquid at room temperature with fishy odor, what range of carbon atoms is expected in the alkyl chain?
A: Between 3 and more
Q: Why might the boiling point of an amine be surprisingly lower than a comparable alcohol?
A: Due to weaker intermolecular hydrogen bonding in amines
Q: How can you separate an amine from a non-basic organic compound?
A: By dissolving it in acid, forming a salt, and extracting, then regenerating amine by addition of base.
Q: Which part of the amine molecule is responsible for its Lewis base characteristics?
A: The unshared electron pair on the nitrogen atom.
Q: Why do some alkylamines deviate from the expected +I effect-based basicity trend in aqueous solutions?
A: Because of the subtle interplay of inductive effect, solvation, and steric hinderance
Q: If an aniline molecule has a -CH₃ group attached to its para position, would it be more or less basic than aniline itself?
A: More basic, because it's an electron-releasing group.
Q: Which is more reactive toward acids, an alkyl amine or an aryl amine?
A: Alkyl amines
Q: How can you convert primary amine to secondary amine via alkyl halide reaction?
A: Using alkyl halide and secondary amine is prepared when one hydrogen in primary amine is substituted with alkyl group, and this process can be repeated with the same or different alkyl halide.
Q: When a primary amine is treated with acid chloride, what does it generate?
A: Amide
Q: What reaction is used to distinguish between primary, secondary, and tertiary amines using chemical reactions?
A: Hinsberg's test (reaction with benzenesulphonyl chloride)
Q: What type of aromatic amines react with Hinsberg's reagent?
A: Primary and secondary aromatic amines
Q: During the nitration of aniline, what is the function of acetylation?
A: To control the reaction and obtain para substituted product
Q: What is formed when aniline is treated with bromine water?
A: 2,4,6-tribromoaniline
Q: How is the instability of diazonium salts beneficial in synthesis?
A: It allows the diazonium group to be easily replaced by other substituents.
Q: What is the chemical nature of diazonium salts?
A: They are ionic compounds.
Q: How can you convert a diazonium salt into an arene?
A: By reduction with hypophosphorous acid or ethanol.
Q: What is the importance of the Sandmeyer reaction in organic synthesis?
A: It allows introduction of Cl, Br, CN in the benzene ring, which is not possible by direct substitution.
Q: How are azo dyes prepared?
A: By coupling of diazonium salt with phenol or amines
Q: If you want to convert aniline to chlorobenzene, what reaction sequence would you use?
A: Diazotization followed by Sandmeyer reaction (CuCl/HCl).
Q: If you need a reagent to convert an arene diazonium salt to corresponding arene with H, what would be your choice?
A: Hypophosphorous acid or Ethanol.
Q: What does coupling reaction of diazonium salts with aromatic compounds involve?
A: Electrophilic substitution reaction.
Q: Which property of diazonium salts makes them good intermediates for synthesizing aromatic compounds?
A: The diazonium group is a good leaving group.