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KNOCKHARDY PUBLISHING 2015 SPECIFICATIONS AN INTRODUCTION TO THE CHEMISTRY OF AMINES.

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Presentation on theme: "KNOCKHARDY PUBLISHING 2015 SPECIFICATIONS AN INTRODUCTION TO THE CHEMISTRY OF AMINES."— Presentation transcript:

1 KNOCKHARDY PUBLISHING 2015 SPECIFICATIONS AN INTRODUCTION TO THE CHEMISTRY OF AMINES

2 INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... Navigation is achieved by... either clicking on the grey arrows at the foot of each page orusing the left and right arrow keys on the keyboard AMINES KNOCKHARDY PUBLISHING

3 CONTENTS Prior knowledge Structure and classification Nomenclature Physical properties Basic properties Nucleophilic properties Amino acids Peptides and proteins Amides Check list AMINES

4 Before you start it would be helpful to… know the functional groups found in organic chemistry know the arrangement of bonds around atoms recall and explain nucleophilic substitution reactions AMINES

5 STRUCTURE & CLASSIFICATION StructureContain the NH 2 group Classification primary (1°) amines secondary (2°) amines tertiary (3°) aminesquarternary (4°) ammonium salts Aliphaticmethylamine, ethylamine, dimethylamine Aromatic NH 2 group is attached directly to the benzene ring (phenylamine) R N : H H R H R R R + R N R R

6 NOMENCLATURE NomenclatureNamed after the groups surrounding the nitrogen + amine C 2 H 5 NH 2 ethylamine (CH 3 ) 2 NHdimethylamine (CH 3 ) 3 Ntrimethylamine C 6 H 5 NH 2 phenylamine (aniline)

7 PREPARATION Amines can be prepared from halogenoalkanes Reagent Excess, alcoholic ammonia(WHY USE EXCESS?) ConditionsReflux in excess, alcoholic solution under pressure Product Amine (or its salt due to a reaction with the acid produced) NucleophileAmmonia (NH 3 ) Equation C 2 H 5 Br + NH 3 (alc) ——> C 2 H 5 NH 2 + HBr ( or C 2 H 5 NH 3 + Br¯ )

8 PREPARATION Amines can be prepared from halogenoalkanes Reagent Excess, alcoholic ammonia(WHY USE EXCESS?) ConditionsReflux in excess, alcoholic solution under pressure Product Amine (or its salt due to a reaction with the acid produced) NucleophileAmmonia (NH 3 ) Equation C 2 H 5 Br + NH 3 (alc) ——> C 2 H 5 NH 2 + HBr ( or C 2 H 5 NH 3 + Br¯ ) WHY USE EXCESS AMMONIA? Ammonia attacks halogenoalkanes because it has a lone pair and is a nucleophile. The amine produced also has a lone pair C 2 H 5 NH 2 so can also attack a halogenoalkane; this leads to the formation of substituted amines. Using excess ammonia ensures that all the halogenoalkane molecules react with the ammonia before having the chance to react with any amines produced.

9 PHYSICAL PROPERTIES The LONE PAIR on the nitrogen atom in 1°, 2° and 3° amines makes them... LEWIS BASES - they can be lone pair donors BRØNSTED-LOWRY BASES - they can be proton acceptors RNH 2 + H + ——> RNH 3 + NUCLEOPHILES - provide a lone pair to attack an electron deficient centre

10 PHYSICAL PROPERTIES Boiling pointBoiling points increase with molecular mass Amines have higher boiling points than corresponding alkanes because of their intermolecular hydrogen bonding Quarternary ammonium salts are ionic and exist as salts SolubilityLower mass compounds are soluble in water due to hydrogen bonding with the solvent. Solubility decreases as the molecules get heavier. Soluble in organic solvents.

11 BASIC PROPERTIES BasesThe lone pair on the nitrogen atom makes amines basic; RNH 2 + H + ——> RNH 3 + a proton acceptor Strength depends on the availability of the lone pair and its ability to pick up protons the greater the electron density on the N, the better it can pick up protons this is affected by the groups attached to the nitrogen

12 BASIC PROPERTIES BasesThe lone pair on the nitrogen atom makes amines basic; RNH 2 + H + ——> RNH 3 + a proton acceptor Strength depends on the availability of the lone pair and its ability to pick up protons the greater the electron density on the N, the better it can pick up protons this is affected by the groups attached to the nitrogen electron withdrawing substituents (benzene rings) decrease basicity as the electron density on N is lowered and the lone pair is less effective C 6 H 5 N : H H

13 BASIC PROPERTIES BasesThe lone pair on the nitrogen atom makes amines basic; RNH 2 + H + ——> RNH 3 + a proton acceptor Strength depends on the availability of the lone pair and its ability to pick up protons the greater the electron density on the N, the better it can pick up protons this is affected by the groups attached to the nitrogen electron withdrawing substituents (benzene rings) decrease basicity as the electron density on N is lowered and the lone pair is less effective electron releasing substituents (CH 3 groups) increase basicity as the electron density is increased and the lone pair is more effective CH 3 N : H H C 6 H 5 N : H H

14 BASIC PROPERTIES Measurementthe strength of a weak base is depicted by its pK b value the smaller the pK b the stronger the base the pK a value can also be used; it is worked out by applying pK a + pK b = 14 the smaller the pK b, the larger the pK a. Compound Formula pK b Comments ammonia NH methylamine CH 3 NH methyl group is electron releasing phenylamine C 6 H 5 NH electrons delocalised into the ring strongest base methylamine > ammonia > phenylamine weakest base smallest pK b largest pK b

15 CHEMICAL REACTIONS - WEAK BASES WaterAmines which dissolve in water produce weak alkaline solutions CH 3 NH 2 (g) + H 2 O(l) CH 3 NH 3 + (aq) + OH¯(aq) AcidsAmines react with acids to produce salts. C 6 H 5 NH 2 (l) + HC l (aq) ——> C 6 H 5 NH 3 + C l ¯(aq) phenylammonium chloride This reaction allows one to dissolve an amine in water as its salt. Addition of aqueous sodium hydroxide liberates the free base from its salt C 6 H 5 NH 3 + C l ¯(aq) + NaOH(aq) ——> C 6 H 5 NH 2 (l) + NaC l (aq) + H 2 O(l)

16 CHEMICAL REACTIONS - NUCLEOPHILIC Due to their lone pair, amines react as nucleophiles Reagent Product Mechanism haloalkanes substituted aminesnucleophilic substitution acyl chloridesN-substituted amides addition-elimination

17 NUCLEOPHILIC SUBSTITUTION HALOALKANES Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt. C 2 H 5 NH 2 + C 2 H 5 Br ——> HBr + (C 2 H 5 ) 2 NH diethylamine, 2° amine

18 NUCLEOPHILIC SUBSTITUTION HALOALKANES Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt. C 2 H 5 NH 2 + C 2 H 5 Br ——> HBr + (C 2 H 5 ) 2 NH diethylamine, 2° amine (C 2 H 5 ) 2 NH + C 2 H 5 Br ——> HBr + (C 2 H 5 ) 3 N triethylamine, 3° amine

19 NUCLEOPHILIC SUBSTITUTION HALOALKANES Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt. C 2 H 5 NH 2 + C 2 H 5 Br ——> HBr + (C 2 H 5 ) 2 NH diethylamine, 2° amine (C 2 H 5 ) 2 NH + C 2 H 5 Br ——> HBr + (C 2 H 5 ) 3 N triethylamine, 3° amine (C 2 H 5 ) 3 N + C 2 H 5 Br ——> (C 2 H 5 ) 4 N + Br¯ tetraethylammonium bromide a quaternary (4°) salt

20 NUCLEOPHILIC SUBSTITUTION HALOALKANES Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt. C 2 H 5 NH 2 + C 2 H 5 Br ——> HBr + (C 2 H 5 ) 2 NH diethylamine, 2° amine (C 2 H 5 ) 2 NH + C 2 H 5 Br ——> HBr + (C 2 H 5 ) 3 N triethylamine, 3° amine (C 2 H 5 ) 3 N + C 2 H 5 Br ——> (C 2 H 5 ) 4 N + Br¯ tetraethylammonium bromide a quaternary (4°) salt UsesQuarternary ammonium salts with long chain alkyl groups are used as cationic surfactants in fabric softening e.g. [CH 3 (CH 2 ) 17 ] 2 N + (CH 3 ) 2 C l ¯

21 AMINO ACIDS Structure Amino acids contain 2 functional groups amine NH 2 carboxyl COOH They all have a similar structure - the identity of R 1 and R 2 vary H 2 N C COOH H H CH 3 H H 2 N C COOH R2R2 R 1

22 AMINO ACIDS – OPTICAL ISOMERISM Amino acids can exist as optical isomers If they have different R 1 and R 2 groups Optical isomers exist when a molecule Contains an asymmetric carbon atom Asymmetric carbon atoms have four different atoms or groups attached Two isomers are formed - one rotates plane polarised light to the left, one rotates it to the right Glycine doesn’t exhibit optical isomerism as there are two H attached to the C atom H 2 N C COOH CH 3 H H 2 N C COOH H H GLYCINE 2-aminoethanoic acid

23 AMINO ACIDS - ZWITTERIONS Zwitterion a dipolar ion has a plus and a minus charge in its structure amino acids exist as zwitterions give increased inter-molecular forces melting and boiling points are higher H 3 N + C COO¯ R2R2 R1R1

24 amino acids possess acidic and basic properties this is due to the two functional groups COOH gives acidic properties NH 2 gives basic properties they form salts when treated with acids or alkalis. H 2 N C COOH R2R2 R1R1 AMINO ACIDS - ACID-BASE PROPERTIES

25 Basic properties: with H + HOOCCH 2 NH 2 + H + ——> HOOCCH 2 NH 3 + with HClHOOCCH 2 NH 2 + HC l ——> HOOCCH 2 NH 3 + C l ¯ Acidic properties: with OH¯HOOCCH 2 NH 2 + OH¯ ——> ¯OOCCH 2 NH 2 + H 2 O with NaOH HOOCCH 2 NH 2 + NaOH ——> Na+ ¯OOCCH 2 NH 2 + H 2 O

26 PEPTIDES - FORMATION & STRUCTURE Amino acids can join together to form peptides via an amide or peptide link 2 amino acids joineddipeptide 3 amino acids joinedtripeptide many amino acids joinedpolypeptide a dipeptide

27 PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis attack takes place at the slightly positive C of the C=O the C-N bond is broken hydrolysis with water is very slow hydrolysis in alkaline/acid conditions is quicker hydrolysis in acid/alkaline conditions (e.g. NaOH) will produce salts with HC l NH 2 becomes NH 3 + C l ¯ H + NH 2 becomes NH 3 + NaOHCOOHbecomes COO¯ Na + OH¯COOHbecomes COO¯

28 PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis H 2 N C CO CH 3 H NH C CO H H NH C COOH CH 3 Which amino acids are formed?

29 PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis H 2 N C CO CH 3 H NH C CO H H NH C COOH CH 3 H H 2 N C COOH H H CH 3 H 2 N C COOH ++

30 H 2 N C CO CH 3 H NH C CO H H NH C COOH H CH 3 PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis Which amino acids are formed?

31 H 2 N C CO CH 3 H NH C CO H H NH C COOH H CH 3 PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis CH 3 H H 2 N C COOH H H 2 x +

32 PROTEINS are polypeptides with high molecular masses chains can be lined up with each other the C=O and N-H bonds are polar due to a difference in electronegativity hydrogen bonding exists between chains dotted lines represent hydrogen bonding

33 AMIDES Structurederivatives of carboxylic acids amide group is -CONH 2 NomenclatureWhite crystalline solids named from the corresponding acid (remove oic acid, add amide) CH 3 CONH 2 ethanamide (acetamide) C 2 H 5 CONHC 6 H 5 N - phenyl propanamide -the N tells you the substituent is on the nitrogen Nylons are examples of polyamides PreparationAcyl chloride + ammonia CH 3 COC l + NH 3 ——> CH 3 CONH 2 + HC l ethanoyl chloride ethanamide

34 AMIDES - CHEMICAL PROPERTIES Hydrolysis general reaction CH 3 CONH 2 + H 2 O ——> CH 3 COOH + NH 3 acidic soln. CH 3 CONH 2 + H 2 O + HC l ——> CH 3 COOH + NH 4 C l alkaline soln. CH 3 CONH 2 + NaOH ——> CH 3 COONa + NH 3 IdentificationWarming an amide with dilute sodium hydroxide solution and testing for the evolution of ammonia using moist red litmus paper is used as a simple test for amides. Reduction Reduced to primary amines: CH 3 CONH 2 + 4[H] ——> CH 3 CH 2 NH 2 + H 2 O

35 © 2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHING AN INTRODUCTION TO THE CHEMISTRY OF AMINES THE END


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