Specification from OCR o Explain the basicity of amines in terms of proton acceptance by the nitrogen lone pair. o Describe the reactions of amines with acids to form salts o Describe the preparation of: i) aliphatic amines by substitution of halogenalkanes with excess ethanolic ammonia ii) aromatic amines by reduction of nitroarenes using tin and conc. hydrochloric acid o Describe the synthesis of an azo-dye o State the use of reactions in the formation of dyestuffs
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Specification from OCR oExplain the basicity of amines in terms of proton acceptance by the nitrogen lone pair. oDescribe the reactions of amines with.
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Specification from OCR
o Explain the basicity of amines in terms of proton acceptance by the nitrogen lone pair.
o Describe the reactions of amines with acids to form saltso Describe the preparation of:
i) aliphatic amines by substitution of halogenalkanes with excess ethanolic ammoniaii) aromatic amines by reduction of nitroarenes using tin and conc. hydrochloric acid
o Describe the synthesis of an azo-dyeo State the use of reactions in the formation of dyestuffs
AminesAmines
Amines are essentially molecules of ammoniaAmines are essentially molecules of ammonia One or more of the hydrogen atoms have been One or more of the hydrogen atoms have been
replaced with an alkyl group.replaced with an alkyl group.
1. PREPARATION OF ALIPHATIC AMINES1. PREPARATION OF ALIPHATIC AMINES
Aliphatic amines can be prepared from substitution of halogenoalkanes with substitution of halogenoalkanes with excess ethanolic ammoniaexcess ethanolic ammonia
Reagent Excess alcoholic ammonia
Conditions Reflux in aqueous, alcoholic solution under pressure
Why excess ammonia?A large excess ammonia also ensures that further substitution doesn’t take place - see below
ProblemAmines are also nucleophiles (lone pair on N) and can attack another molecule of halogenoalkane 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.
Amino acids can join together to form peptides via an amide or peptide link
2 amino acids joined dipeptide
3 amino acids joined tripeptide
many amino acids joined polypeptide
a dipeptide
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
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 HCl NH2 becomes NH3+Cl¯
H+ NH2 becomes NH3+
NaOH COOH becomes COO¯ Na+
OH¯ COOH becomes COO¯
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
CH3
CH3
Which amino acids are formed?
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
CH3
CH3
CH3
H
H2N C COOH
H
H
H2N C COOH
CH3
CH3
H2N C COOH++
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
H
CH3
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
Which amino acids are formed?
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
H
CH3
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
CH3
H
H2N C COOH
H
H
H2N C COOH2 x +
PROTEINSPROTEINS
• 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