Amines, amides, amino acids and proteins

Reduction of aromatic nitro compound conditions second step

heat

Reduction of aromatic nitro compound reagents second step

Sn, HCl

amine functional group

NH2

Amide functional group

CONH2

amino acid

H2N-CHR-COOH

primary amines

one H of NH3 is replaced by an alkyl group

secondary amines

two H of NH3 are replaced by an alkyl group

tertiary amines

all H of NH3 are replaced by an alkyl group

naming amines

alkyl chain length - amine eg. methyl amine

naming of amines when two or more amine groups are present

-amino prefix used. Amine becomes premodifying group eg. diaminobutane

IR absorption of N-H

3500-3300cm-1

amines with water (acting as a base)

RNH2 + H2O ⇌ RNH3+ + OH-

amines with acids equation

CH3NH2 (aq) + HCl (aq) → CH3NH3+Cl-

amines with acids

amine+acid-> alkyl ammonium chloride
- reversible as addition of NaOH converts back to the amine
- These ionic salts will be solid crystals, if the water is evaporated, because of the strong ionic interactions
- The ionic salts formed in this reaction means that the compounds are soluble in the acid e.g. Phenylamine is not very soluble in water but phenylammonium chloride is soluble

butyl amine and ethanoyl chloride equation

C4H9NH2 + CH3COCl -> CH3CONHC4H9 (n-butyl ethanamide)

amines with acyl chlorides

amine+acyl chloride -> amide (CONH2)

naming compounds of acyl chloride and amides

N prefix always, amine gives alkyl prefix eg. butyl, acyl gives suffix eg. ethanoyl = N-butyl ethanamide

amines with halogenoalkanes equation

RNH2 + CH3Cl → RNHCH3 + HCl (H from amine and Cl from chloroalkane)

amines with halogenoalkanes

a substitution reaction in which the organic product is a secondary amine and the inorganic product is a hydrogen halide

amines to form complex ions (as ligands)

Lone pair of electrons on N means it can form dative covalent bonds to transition metal ions.

amines to form complex ions equation

[Cu(H2O6]2+ +2C2H5NH2-> [Cu(H2O)4(OH)2] pale blue precipitate + 2C2H5NH3+ (takes two hydrogens from complex). In excess of amine, gives deep blue complex as amine replaces 2 more H2O and the 2 OH.

Preparation of primary aliphatic amines

Reaction of ammonia with halogenoalkanes, the reduction of nitriles and reduction of aromatic nitrocompounds

ammonia with halogenoalkanes reagents

halogenoalkane and excess concentrated ammonia dissolved in ethanol

ammonia with halogenoalkanes conditions

heat under reflux

ammonia with halogenoalkanes nucleophile

NH3

Ammonia with halogenoalkanes step 1

lone pair on N atom of ammonia is attracted to positive charge in carbon in halogenoalkane. Lone pair forms a covalent bond between N-C producing a quaternary salt. (CH3-N+H2- CH3)

Ammonia with halogenoalkanes step 2

amine is released from the salt by removal of a proton using excess ammonia which attacks H on NH3 to make it an amine and form the salt NH4Br

reduction of nitriles by hydrogenation catalyst

nickel

reduction of nitriles by hydrogenation

nitrile+hydrogen-> alkyl amine (eg. butane nitrile+hydrogen-> butyl amine)

reduction of nitriles by LiAlH4 reagents

LiAlH4 catalyst in ethoxyethane, followed by dilute acid

reduction of nitriles by LiAlH4

nitrile+reducing agent->amine

basicity of amines as the chain length increase

increases as an increase in alkyl groups cause the nitrogen to be more electron rich/electrognegative due to inductive effect

strength of base decided by

availability of lone pairs of electrons on the N atom to accept a proton

why phenyl amine does not act as base

lone pair on N gets donated into delocalised ring so does is not readily available to accept a proton

order of basicity of amines

aliphatic>ammonia>aromatic

reduction aromatic nitro compounds

first turn benzene into nitrobenzene, then turn nitrobenzene into phenyl amine by replacing NO2 with NH2

to form nitrobenzene from benzene

concentrated H2SO4, concentrated HNO3, and heat under reflux at 50-60c

Reduction of nitrobenzene to phenyl amine

Sn and HCl and heat

total reduction of aromatic nitro compounds

1. conc. H2SO4 and HNO3, heat under reflux 50-60c
2. Sn, HCl and heat

preparation of amides

from acyl chlorides and ammonia/amine

acyl chloride+ammonia

acyl amide + HCl

acyl chloride+amine

N- alkyl acylamide + HCl

reaction for formation of a polyamide

condensation polymerisation

dicarboxylic acids+ diols

polyester + water (lose OH from acid and H from diol)

amino acid+amino acid

polypeptide + water

dicarboxylic acid+diamines

polyamide+water

isoelectronic point

the pH at which molecules of the amino acid will be in the zwitterion form

different isoelectronic points of amino acids

due to different character of their R groups

Zwitterion

a molecule or ion having separate positively and negatively charged groups.

amino acid zwitterion

H3N+ - CHR - COO-

Amino acid at neutral pH

zwitterion

amino acid at acidic (low) pH

H3N+ - CHR - COOH

amino acid at alkaline (high) pH

H2N - CHR - COO-

chirality of amino acids

all but glycine so will rotate polarised light

in aqueous solutions carboxyl group

is ionised, releasing H ions

in aqueous solutions amino groups

act as a base and accept hydrogen ions

in aqueous solutions amino acids

form zwitterions

peptide bond/Amide link (C=O NH)

formed when amino acids combine by condensation polymerisation

polypeptide

10-50 amino acids

protein

50+ amino acids

hydrolysis of proteins reactants/conditions

water, conc. HCl, heat under reflux

hydrolysis of proteins method

chromatography

Chromatography method

1. set up chromatography paper, draw start line in pencil (prevent ink leaking and altering results)
2. add dots of test solution (protein) onto start line
3. lower the paper into beaker with solvent and wait for it to travel up the paper
4. dry chromatography paper and spray with ninhydrin paper
5. analyse chromatogram

use of ninhydrin in chromatogram

a locating agent which is sprayed onto paper to react with separated amino acids to form coloured products so they can be seen

ninhydrin effect on amino acid colour

colourless to purple then fades to brown

type of solvent in chromatography

use according to polarity - polar substance use polar solvent (but not too soluble so surpasses paper)

amino acids are zittwerions

in aqueous solution and solid

amino acids mp

high melting points due to being crystalline solids as there are strong ionic attractions between one ion and its neighbour (stronger than hydrogen)