6.2 Nitrogen compounds, polymers and synthesis Flashcards
how to name amine
primary: identify number of carbons in alkyl chain, suffix -amine (e.g. methylamine)
secondary: for shorter alkyl chain add prefix “N-alkyl” e.g. N-methyl propylamine
tertiary: add “N-“ prefix for each shorter alkyl chain (e.g. N-methyl N-ethyl propylamine
if amine group is side chain, add number before “-amine” suffix
why amines are bases
lone pair on N atom
accept hydrogen ions to form alkyl ammonium salts
reacts with acids
formation of ammonium ion example with methylamine and water
methylamine + water -> methylammonium ion + hydroxide ion
methylamine accepts hydrogen ion from H2O due to lone pair
phenylamine solubility
only slightly soluble due to non-polar benzene ring
how to classify amines
primary: attached to 1 alkyl group
secondary: attached to 2 alkyl groups
tertiary: attached to 3 alkyl groups
formation of primary amines conditions
ethanol as solvent (prevents substitution of haloalkane by water to produce alcohol)
excess ammonia used (reduces further substitution of amine group to secondary and tertiary amine)
not reflux as gas would escape
formation of primary (aliphatic) amines method
haloalkane + ammonia -> alkylammonium salt
alkylammonium salt + aqueous alkali -> amine + salt + water
NH3 has lone pair (acts as nucleophile to substitute with halogen in haloalkane)
to form alkylammonium salt
aqueous alkali added to form amine, salt, water
formation of secondary, tertiary, quaternary (aliphatic) amines
haloalkane + primary amine -> ammonium salt
ammonium salt + alkali -> secondary amine + salt + water
tertiary and quaternary formed by repeating processes (continuing reaction)
how to separate primary, secondary, tertiary amines
distill as more chains = more boiling point
primary has lowest boiling point, tertiary highest
formation of quaternary amine conditions
excess haloalkane
ethanol as solvent
don’t reflux
formation of primary amines with nitriles
reduce nitriles
H3C-CN + 4[H] -[LiAlH4] -> primary amines
Na (alcohol), LiAlH4 = reducing agent
can add hydrogen gas and Ni catalyst as well
formation of aromatic amines
heat nitro compounds (nitrobenzene) with tin + conc. HCl under reflux for 30 minutes
C6H5NO2 + 7[H]^+ + 6e^- -> C6H5NH3^+ +2H2O
nitrobenzene + 7[H]^+ + 6e^- -> phenylammonium ion + water
add sodium hydroxide to remove hydrogen ions from phenyl ammonium ion
C6H5NH3^+ + OH^- -> C6H5NH2 + H2O
phenyl ammonium + hydroxide -> phenylamine + water
chirality definition
atoms in the enantiomers are joined up in the same order but have different spatial arrangement
molecules that are non-superimposable mirror images on one another
what is required for chirality
chiral centre (4 different groups attached to a carbon atom)
chiral molecule features
non-superimposable images
enantiomers
form of stereo isomerism
carbon atom with 4 different groups attached
optical isomers
only with chiral centred isomers
optical isomers rotate plane-polarised light differently (one clockwise, one anti-clockwise)
racemic
racemic = racemate
mixture containing 1:1 mix of both optical isomers
no effect on plane-polarised light as they cancel each other out
amino acid general structure
carboxylic acid functional group
amine functional group
central hydrogen ion
varying R group
reaction of amino acid with acids
amine group is basic
accepts hydrogen atom to form ammonium salt + negative ion
amino acid + acid -> salt + negative ion
reaction of amino acid with aqueous alkali
carboxylic acid group is acidic
amino acid + aqueous alkali -> ammonium salt + water
reaction of amino acid + alcohol
amino acid + alcohol -[concentrated sulfuric acid]-> ester + water
amine group is protonated due to acidic conditions
polyamides uses
nylons: fishing nets, ropes, parachutes, fabrics, guitars
Kevlar: armour
condensation polymerisation definition
joining of 2 monomers, the monomers having 2 different functional group
functional groups in amide linkage
carboxylic acids
amine
how polyamides can be formed
condensation reaction between:
2 different monomers e.g. dicarboxylic acid + diamine
1 monomer with 2 functional groups
addition polymerisation definition
formation of a very long molecular chain, by repeated addition reactions of many unsaturated alkene molecules
how to make polyesters
condensation reactions between carboxylic acid and alcohol groups
either 2 monomers, one with 2 alcohols and the other with 2 carboxylic acids
or 1 monomer with both groups
hydrolysis definition
reaction where water is a reactant in a decomposition reaction
acid hydrolysis of polyester
polyester + water -> diol + dioc acid
conc. acid catalyst under feflux
base hydrolysis of polyester
polyester + water -> diol + dioate salt
NaOH(aq) catalyst
under reflux
acid hydrolysis of polyamide
polyamide + water -> diamine salt + dioic acid
conc. acid catalyst under reflux
base hydrolysis of polyamide
polyamide + water -> diamine + dicarboxylic salt
NaOH(aq) catalyst under reflux
importance of biodegradable polymers
break down easily (e.g. in landfills, less expensive)
don’t need to recycle (which is difficult to mechanise and automate)
no longer need to combust and release toxic emissions
degradable polymer definition
breaks down into smaller fragments exposed to heat, light or moisture
biodegradable polymer definition
polymer that breaks down completely onto CO2 and water
photodegradable polymer definition
becomes weak and brittle when exposed to sunlight
carbonyl groups in backbone of polymer make it photodegradable by bacteria
formation of nitriles from haloalkanes
nucleophilic substitution of haloalkane with cyanide ion formed from NaCN or KCN in ethanol
adds length to carbon chain
e.g.
1-chloropropane + KCN -> butanenitrile + KCl
formation of nitriles from carbonyls
nucleophilic addition of carbonyls with
cyanide ions (formed with NaCN/H+)
adds length to carbon chain when with aldehyde
aldehyde/ketone + CN- + H+ -> hydroxynitrile
what is used instead of HCN and why in formation of nitriles
HCN too poisonous
increased reaction rate (KCN faster than HCN)
mixture of NaCN + H2SO4
improves safety, increases reaction rate
reduction of nitriles
nitrile + 2H2 -[Ni]-> amine
e.g.
propanenitrile + 2H2 -[Ni]-> propylamine
hydrolysis of nitriles
heat with dilute aqueous acid e.g. HCl
nitrile + 2H2O + HCl -> carboxylic acid + ammonium chloride (NH4Cl)
e.g.
butanenitrile + 2H2O + HCl -> butanoic acid + NH4Cl
alkylation of benzene rings
haloalkane + benzene -[halogen carrier catalyst]-> alkylbenzene + HCl/Br
acylation of benzene
benzene + acyl chloride -> [AlCl3]-> phenylketone/phenylaldehyde + HCl
organometallic compound importance
compounds containing carbon-metal bond
important for increasing carbon chain length in organic compounds
Grignard reagents
made by reacting magnesium with haloalkane dissolved in ether solvent
e.g.
bromoethane + Mg -> ethylmagnesium bromide
Grignard reagents react as carbanion e.g. CH3CH2-
nucleophilic substitution of haloalkane and cyanide ion
ethanol as solvent (so hydroxide ions can’t act as nucleophile)
heat under reflux
CN- + haloalkane -> nitrile + halogen ion
why nucleophilic addition of carbonyls with cyanide and optical isomerism
C=O is planar
CN- can attack from either side
forms both optical isomers
racemic mixture is formed
other way of reducing nitriles
LiAlH4
lithium tetrahydridoaluminate (III)
nitrile + 4[H] -> primary amine
acid hydrolysis of nitriles
reflux with dilute hydrochloric acid
nitrile + 2H2O + HCl -> carboxylic acid + ammonium chloride
e.g.
ethanenitrile + 2H2O + HCl -> ethanoic acid + ammonium chloride
CH3CN + 2H2O + HCl -> CH3COOH + NH4Cl
