Skip to main content
UploadLanguage (EN)Support
BusinessMobileSocial MediaMarketingTechnologyArt & PhotosCareerDesignEducationPresentations & Public SpeakingGovernment & NonprofitHealthcareInternetLawLeadership & ManagementAutomotiveEngineeringSoftwareRecruiting & HRRetailSalesServicesScienceSmall Business & EntrepreneurshipFoodEnvironmentEconomy & FinanceData & AnalyticsInvestor RelationsSportsSpiritualNews & PoliticsTravelSelf ImprovementReal EstateEntertainment & HumorHealth & MedicineDevices & HardwareLifestyle
Shilpa Harak, profile picture
Uploaded byShilpa Harak
14,300 views

Amines

This document discusses the properties and reactions of amines. It defines amines as organic derivatives of ammonia with one or more alkyl or aryl groups bonded to the nitrogen atom. Amines are classified as primary, secondary, or tertiary depending on the number of alkyl or aryl groups attached to the nitrogen. The document discusses nomenclature, physical properties, basicity, reactions including salt formation and reactions with acids, and uses of amines such as in the synthesis of nylon and azo dyes.

Health & Medicine◦
Dr. S. S. Harak Asst. Prof. Pharm. Chem. Gokhale Education Society’s Sir Dr. M. S. Gosavi College of Pharmaceutical Education and Research, Nashik-5 AMINES ORGANIC CHEMISTRY
• Amines: - organic derivatives of ammonia with one or more alkyl or aryl groups bonded to the nitrogen atom. • Functional group: • Classification of amines: Primary amine Secondary amine Tertiary amine
• Primary (1o) amine: one alkyl or aryl group attached to the nitrogen atom. • Secondary (2o) amine: two alkyl or aryl group attached to the nitrogen atom. • Tertiary (3o) amine: three alkyl or aryl group attached to the nitrogen atom. • Quaternary (4o) amine: an ion in which nitrogen is bonded to four alkyl or aryl groups and bears a positive charge CH3 H3C N CH3 CH3
• Common names: -formed from the names of the alkyl groups bonded to nitrogen, followed by the suffix –amine. -the prefixes di-, tri-, and tetra- are used to decribe two, three or four identical substituents. 2CH3 CH2 NH ethylamine CH3 CH3 CH2 N CH3 ethyldimethylamine (CH3CH2CH2CH2)4N+ - CI tetrabutylammonium chloride CH3 N CH3 cyclohexyldimethylamine NAMING AMINES
• IUPAC names: - similar to that alcohols. -the longest continuous chain of carbon atoms determine the root name. -the –e in alkane name is changed to –amine, and a number shows the position of the amino group along the chain. -other substituents on the carbon chain are given numbers, and the prefix N- is used for each substituent on nitrogen. CH3 CH2 CH CH3 NH2 CH3 CH3 CH CH2CH2 NH2 CH3 CH2 CH CH3 NHCH3 CH3 CH3 CH3 CH2 CH CH CH CH3 N CH3 CH3 2,4, N, N-tetramethyl-3-hexanamine 2-butanamine 23 14 1234 3-methyl-1-butanamine 1234 N-methyl-2-butanamine
• The prefix ‘amino’ is used to indicate the presence of an –NH2 group in a molecule containing than one functional group. NH2CH2COOH aminoethanoic acid OH NH2 NH2 2,4-diaminophenol H2NCH2CH2OH 2-aminoethanol COH NH2 3-aminobenzaldehyde • For example,
• • • Aromatic amines have an amine group (-NH2) attached directly to the aromatic ring. Aromatic amines known as arylamines. Examples, NH2 CH3 NH2 NH2 NO2 4-nitrophenylamine (4-nitroaniline) phenylamine (aniline) 2-methylphenylamine (2-methylaniline) 2 3 4 5 1 6 1 2 3 4 6 5 NAMING AROMATIC PRIMARY AMINES
H2N (CH2)6 NH2 hexane-1,6-diamine (1,6-hexanediamine) H2N NH2 benzene-1,4-diamine (1,4-benzenediamine) • Compounds with two –NH2 groups are named by adding the suffix ‘diamine’ to the name of the corresponding alkane or aromatic compounds.
PHYSICAL PROPERTIES OF AMINES i) Boiling points: -the boiling points of amines is increase with increasing relative molecular mass. - the lower aliphatic amines are gases or low-boiling liquids. -amines are polar compounds and both primary and secondary amines associate by intermolecular hydrogen bonding. H N H R H R N H R H N H Hydrogen bonding
* Comparing the boiling points of 1o,2oand 3oamines - for isomeric amines, the boiling points decreases in the order, 1° amine > 2° amine > 3° amine - reason: decrease in intermolecular hydrogen bonding. - example, CH3CH2CH2NH2 1-propanamine (1o amine) 48.6o C CH3 CH3CH2N H N-methylethanamine (2o amine) 37.0o C CH3 CH3 N CH3 N, N-dimethylmethanamine (3o amine) 3.5o Cboiling point: molecular formula: C3H9N molecular mass: 59
* Comparing the boiling points of amines with other organic compounds -the boiling points of aliphatic amines are higher than those of alkanes or haloalkanes of similar relative molecular mass due to intermolecular hydrogen bonding. -the N-H bond is more polar than the C-H bond but less polar than O-H bond. -Hydrogen bonding in amines are weaker than that of alcohols or carboxylic acids. -Boiling points of amines are lower than those corresponding alcohols or carboxylic acids. Comparison of boiling points of some organic compounds with similar molecular weight alkane < ether < alkyl halide < amine < ketone, aldehyde < alcohol < acid
ii) Solubilities of 1o, 2o and 3o amines: -all three classes of aliphatic amines are capable of forming hydrogen bonds with water molecules. -the lower amines (with chain length up to four carbon atoms per molecule) are very soluble in water because they can form hydrogen bonds with water molecules. -the solubilities of amines is decrease with increasing number of carbon atoms in the chain. - amines are soluble in organic solvents.
• Amines can act as: -a nucleophile (a Lewis base) because its lone pair none bonding electrons can form a bond with an electrophile. -a Brønsted-Lowry base because it can accept a proton from a proton acid. Reaction of an amine as a nucleophile R N H CH3 I H nucleophile R H N CH3 H I- electrophile new N-C bond formed Reaction of an amine as a proton base NR H H H X R H N H H X- base proton acid protonated THE BASICITY OF AMINES
• • Amines are fairly strong base and their aqueous solutions are basic. An amine can abstract a proton from water, giving an ammonium ion and a hydroxide ion. The equilibrium constant for this reaction is called base-dissociation constant, symbolized by Kb. • NR H H H O H R H H N H OH -Kb Kb = [RNH3 +] [-OH] [RNH2] bpK = - log K10 b Stronger base have smaller values of pKb
• The basicity of the amines depends on the ability of the lone pair none bonding electrons at nitrogen atom to form bond with an acid. The more easier the lone pair electrons formed bond with the acid, will make the amines a stronger base. Factors that effect the basicity of the amines: • • i) substitution by alkyl groups -the presence of alkyl groups (electron-donating group) such as (CH3-) and (CH3CH2-) will make the amine become more basic. - for example, methylamine is more basic than ammonia. ii) substitution by electron-withdrawing groups -the presence of electron-withdrawing groups or atom will decrease the basicity. - for example, nitroaniline is less basic than aniline
Basicity of aromatic amines *Aromatic amines is less basic than aliphatic amines and ammonia. -the lone pair of electrons on the nitrogen atom is delocalised into the benzene ring. -As a result, the lone pair of electrons is less available for donation to an acid. -The reaction is shifted toward the left and makes aniline a weaker base than ammonia or aliphatic amines.
• • • • Salt formation Reaction with nitrous acid Amide formation Ring halogenation of phenylamine REACTIONS OF AMINES
• • Reaction of amines and acid will give amine salt. Amine salt: - composed of two types of ions: i) the protonated amine cation (an ammonium ion) ii) anion derived from the acid Amine salts are ionic, have higher melting points, nonvolatile solids, more soluble in water than the parent amines and slightly soluble in nonpolar organic solvents. • Salt formation
EXAMPLES: CH3CH2CH2 NH2 n-propylamine CH3CH2CH2 NH3Cl n-propylammonium chloride HCl (CH3CH2)3 N triethylamine HCl (CH3CH2)3 NH Cl triethylammonium chloride R NH2 H Cl R2 NH H Cl R3 N tertiary amine H Cl R3 NHCl trialkylammonium chloride RNH3 Cl alkylammonium chloride R2 NH2 Cl dialkylammonium chloride primary amine secondary amine
• Nitrous acid (HNO2) is unstable and is prepared in situ by the reaction of dilute HCl or dilute H2SO4with sodium nitrite in the absence of heat. NaNO2(s) + HCl (aq) → NaCl (aq) + O=N-OH (aq) nitrous acid • Nitrous acid can be used to differentiate primary, secondary and tertiary aliphatic amines. Reaction with nitrous acid
Primary aliphatic amines • When aliphatic primary amines react with HNO2, nitrogen is evolved rapidly and an alcohol is produced. RNH2+ O=N-OH → R-OH + H2O+ N2(g) • For example, ethylamine gives nitrogen and a mixture of ethanol (60%), ethene and other products. C2H5NH2 + O=N-OH → C2H5-OH+ H2O+ N2(g) + other products • The reaction of propylamine with HNO2produces nitrogen and a mixture of 1-propanol (7%), 2-propanol (32%) and propene (28%). • The reaction of methylamine with HNO2produces only a little methanol, and the main products are methoxymethane and nitrogen.
• Aliphatic secondary amines react with HNO2at room temperature to form nitrosoamines / nitrosamines (yellow oils). R2N-H + HO-N=O → R2N-N=O + H2O nitrosoamine Example,• N H CH3 CH3 HO N=O CH3 CH3 2N N=O H O dimethylamine N-nitroso-N,N-dimethylamine Secondary aliphatic and aromatic amines
• - A tertiary aliphatic amines react with HNO2will produced ammonium salts which is dissolve readily in water as a clear solution. R3N+ HNO2→ [R3NH]+NO2 (aq) NH2 HNO2 HCl + N2 Cl - RT 2H2O N RT = room temperature 2 5o C benzenediazonium chloride mixture products Tertiary aliphatic amines Primary aromatic amines A primary aromatic amines react with cold HNO2 and dissolved in dilute HCl at 0-5oC will produced diazonium salt. When this cold salts heated at room temperature, nitrogen gas will evolved. •
Tertiary aromatic amines R N R HNO2 < 5o C ON R N R a nitosoamiline compound (yellow precipitate) • Tertiary aromatic amines reacts with nitrous acid by undergoing substitution at the para position of the benzene ring to form nitrosoaniline which is a yellow precipitate.
i) Reaction with acyl chlorides • Primary and secondary amines are acylated at room temperature by acyl chlorides to form N-substituted amides. RNH2+ CH3COCl → RNHCOCH3+ HCl R2NH + CH3COCl → R2NCOCH3+ HCl • Tertiary amines are NOT acylated because they do not have hydrogen atom attached to the nitrogen atom. Amide formation
Examples: H CH3N H O CH3C Cl H N H O CH3C Cl H O N C CH3 H O CH3N C CH3 HCl HCl N-methylethanamide N-phenylbenzamide ethanoyl chloride ethanoyl chloride
ii) Reaction with acid anhydrides • Primary and secondary amines are readily acylated by acid anhydrides to yield the corresponding N-alkyl or N-aryl amides. For example,• H CH3CH2CH2N H propylamine O O CH3 C O C CH3 H CH3CH2N CH2CH3 diethylamine O O CH3 C O C CH3 H O CH3CH2CH2N C CH3 N-propylethanamide O CH3CH2N C CH3 CH2CH3 N, N-diethylethanamide O HO C CH3 O HO C CH3 ethanoic anhydride ethanoic anhydride
• When bromine water is added to phenylamine (aniline) at room temperature, decolorisation of the bromine water occurs and a white precipitate of 2,4-6-tribromoaniline (C6H4Br3N) is obtained. This reaction is used as a test for aniline.• NH2 23Br (aq) NH2 Br Br Br 2,4,6-tribromoaniline (white precipitate) 3HBrroom temperature Ring halogenation of phenylamine
SYNTHESIS OF NYLON •Nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acids, so that peptide bonds form at both ends of each monomer in a process analogous to polypeptides biopolymers. • General reactions: DiaminesDicarboxylic acids Nylon USES OF AMINES
Basic concepts of nylon production • The first approach: -combining molecules with an acid (COOH) group on each end are reacted with two chemicals that contain amine (NH2) groups on each end. -Form nylon 6,6, made of hexamethylene diamine with six carbon atoms and acidipic acid, as well as six carbon atoms. • The second approach: -a compound has an acid at one end and an amine at the other and is polymerized to form a chain with repeating units of (-NH-[CH2]n-CO-)x. -Form nylon 6, made from a single six-carbon substance called caprolactam.
SYNTHESIS OF DYE • Primary aromatic amines are used as a starting material for the manufacture of azo dyes. • Azo compounds: compounds bearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl. N=N group is called an azo group HNNH is called diimide • Aryl azo compounds have vivid colors, especially reds, oranges, and yellows Yellow azo dye
•Amines react with nitric(III) acid to form diazonium salt, which can undergo coupling reaction to form azo compound. •Azo-compounds are highly coloured, they are widely used in dyeing industries, such as: i) Methyl orange ii)Direct brown 138 iii)Sunset yellow FCF iv)Ponceau
Uses and important of azo dye  Methyl orange - used as acid-base indicators due to the different colors of their acid and salt forms  Artist’s paints – clays, yellow to red range Dye in food and textiles
E102: Tartrazine E107 : Yellow 2G E110 : Sunset Yellow E122 : Azorubine EXAMPLES OF AZO DYES USED IN FOOD
E123 : Amaranth E124 : Ponceau 4R E129 : Allura Red E151 : Brilliant Black
Sandmeyer reaction  The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts using copper salts as reagents or catalysts.  It is an example of a radical-nucleophilic aromatic substitution.  The Sandmeyer reaction provides a method through which one can perform unique transformations on benzene, such as halogenation, cyanation, trifluoromethylation, and hydroxylation.
Sandmeyer reaction  The substitution of an aromatic amino group is possible via preparation of its diazonium salt and subsequent displacement with a nucleophile (Cl-, I-, CN-, RS-, HO-).  Many Sandmeyer Reactions proceed under copper(I) catalysis, while the Sandmeyer-type reactions with thiols, water and potassium iodide don't require catalysis.
Mechanism Treatment of an aromatic amine with nitrous acid (or sodium nitrite, which is converted to nitrous acid in the presence of acid) in the presence of a strong acid like HCl results in the loss of H2O and the formation of a new N-N triple bond. The resulting species is called a “diazonium ion”:Step I: Formation of the nitrosonium ion
Nucleophilic Substitution
Step II: Formation of the benzenediazonium ion
Step III: Single electron transfer
Diazo Coupling  Because a diazonium salt is only weakly electrophilic, the reaction only occurs when the benzene ring has a strong electron donor group, such as NH2, NHR, NR2, or OH.  Although these groups activate both the ortho and para positions, substitution occurs unless the para position already has another substituent.  To determine what starting materials are needed to synthesize a particular azo compound, always divide the molecule into two components: one has a benzene ring with a diazonium ion, and one has a benzene ring with a very strong electron donor group.
Diazo Coupling Mechanism
Diazo Coupling Examples
TEST YOUR KNOWLEDGE
TEST YOUR KNOWLEDGE
TEST YOUR KNOWLEDGE
TEST YOUR KNOWLEDGE
TEST YOUR KNOWLEDGE
TEST YOUR KNOWLEDGE
Hinsberg test  A chemical reaction that can distinguish between primary, secondary, tertiary amines.  The amine is shaken well with Hinsberg reagent in the presence of aqueous alkali (e.g., KOH or NaOH).  The Hinsberg reagent is a solution of aqueous sodium hydroxide and benzenesulfonyl chloride.  In this test, the amine acts as a nucleophile and attack the electrophilic benzenesulfonyl chloride.  This reaction leads to the displacement of the chloride and the generation of the N- alkylbenzenesulfonamide.  When the primary amine forms a sulfonamide, this product is soluble in aqueous sodium hydroxide (NaOH).  On the contrary, secondary amine’s sulfonamide precipitates from the alkali solution as a solid.
Hinsberg test Summary  To summarize what your visual observations would be for the Hinsberg test:  Primary amines–Adding a primary amine to the Hinsberg test solution should give a clear solution which, on acidification with HCl, would form a precipitate.  Secondary amines‐ React to form a suspension of an insoluble solid or oil which does not dissolve on acidification with HCl.  Tertiary amines– Do not react with the benzene sulfonyl chloride in the Hinsberg test solution and thus initially provide an insoluble solid or oil(the unreacted amine) which, on acidification with HCl, dissolves to give a clear solution of the amine salt.