6.2 Organic chem and analysis 27.1-28.3 Flashcards
what are amines?
organic compounds, derived from ammonia, NH3, in which one or more hydrogen atoms in ammonia have been replaced by a carbon chain or ring
what are the two types of amines?
aliphatic
aromatic
aliphatic amine
the nitrogen atom is attached to at least one straight or branched carbon chain (alkyl group, R)
what is the simplest aliphatic amine?
methylamine
CH3NH2
one methyl group attached to the nitrogen atom
aromatic amine
the nitrogen group is attached to an aromatic ring (aryl group, Ar)
what is the simplest aromatic amine?
phenylamine
C6H5NH2
with a phenyl C6H5 group attached to the nitrogen atom
primary amines
1 R group
2 H groups
secondary amine
2 R groups
1 H group
tertiary amine
3 R groups
0 H groups
naming primary amines with NH2 group on the end of the chain
add suffix -amine to the name of the alkyl chain
e.g. ethylamine , propylamine
naming primary amines with NH2 group not on end of chain
use prefix amino- and a number is added to indicate the position of the amine group along that chain
e.g. 2-aminobutane
naming secondary of tertiary amines containing the same alkyl group
prefixes di- or tri- are used to indicate the number of alkyl groups attached to the nitrogen atom
e.g. (CH3)2NH is dimethylamine
naming secondary or tertiary amines when 2 or more different groups are attached to a nitrogen atom
the compound is named as a N-substituted derivative of the larger group
e.g. CH3NHCH2CH2CH3 is N-methylpropylamine and CH3N(CH2CH3)CH2CH2CH3 is N-ethyl-N-methylpropylamine
amines as bases
amines behave as bases in their chemical reactions as the lone pair of electrons on the nitrogen atom can accept a proton
when an amine accepts a proton, a dative covalent bond is formed between the lone pair of electrons on the nitrogen atom and the proton
salt formation- amines
amines are bases and they neutralise acids to make salts
e.g. CH3CH2CH2NH2 + HCl –> CH3CH2CH2NH3+Cl-
formation of primary amines
ammonia has a lone pair of electrons on the nitrogen atoms which allows ammonia to act as a nucleophile in a substitution reaction with a haloalkane
the product of the reaction is an ammonium salt
aqueous alkali is added to generate the amine from the salt
two stages:
1. salt formation. haloalkane + ammonia –> salt
2. amine formation. salt + aq alkali (e.g.NaOH) –> amine + sodium Cl/Br/I + H2O
conditions- ethanol used as solvent
- excess ammonia used
conditions for formation of primary amines
- ethanol used as solvent. prevents any substitution of the haloalkane by water to produce alcohols
- excess ammonia is used. reduces further substitution of the amine group to form secondary and tertiary amines
formation of secondary and tertiary amines
primary amine reacts with haloalkane to make ammonium salt
secondary amine is obtained from the salt by reacting the product with sodium hydroxide
tertiary amines can also be formed by further reduction of the secondary amine
preparation of aromatic amines- phenylamine
phenylamine made by the reduction of nitrobenzene
nitrobenzene is heated under reflux with tin and HCl to form the ammonium salt, phenylammonium chloride, which is then reacted with excess sodium hydroxide to produce the aromatic amine phenylamine
tin and HCl act as a reducing agent
reducing agents for preparation of aromatic amines
HCl
tin
amino acids
organic group containing both amine, NH2, and carboxylic acid, COOH, functional groups
body has 20 common AAs that can be built into proteins
these are all alpha AAs in which the amine group is attached to the alpha carbon atom (second carbon atom next to the COOH group)
these 20 AAs differ by the side chain R attached to the same a-carbon atom
a-amino acid general formula
RCH(NH2)COOH
reactions of the amine group in amino acids
amine group is basic and reacts with acids to make salts
so amino acids will also react with acids to form salts
reactions of the carboxylic acid group in amino acids
the carboxylic acid group can react with alkalis to form salts and with alcohols to form esters
carboxylic acid group in AAs reacting with aqueous alkalis
amino acids reacts with aqueous alkalis such as sodium or potassium hydroxide to form a salt and water
carboxylic acid group in AAs reacting with alcohols
amino acids are easily esterified by heating with an alcohol in the presence of conc sulfuric acid
amides
products of reactions of acyl chlorides with ammonia and amines
amide groups are common in nature
in proteins the amine and carboxylic acid groups of amino acids are bonded together to form amide groups
RC(O)N
primary amide
one carbon atom bonded to N
secondary amide
two carbons atoms bonded to N
tertiary amide
three carbons bonded to N
stereoisomerism
compounds with the same structural formula but different a arrangement of atoms
another type of stereoisomerism is optical isomerism
optical isomerism
found in molecules that contain a chiral centre
chiral centre is a carbon atom that is attached to 4 diff atoms or group of atoms
the presence of a chiral carbon atom in a molecule leads to the existence of two non-superimposable mirror image structures
these two molecules are known as optical isomers
chiral centre
a carbon atom that is attached to four different atoms or groups of atoms
chirality in a-AAs
with an exception of glycine, all a-AAs contain a chiral carbon atom with the a-carbon atom bonded to four different atoms or groups
drawing optical isomers
drawn to show the 3D tetrahedral arrangement of the four different groups around the central chiral carbon atom
once one isomer has been drawn, the other isomer is drawn as a mirror image, reflecting the first structure
zwitterions
within the structure of the AA, the basic amine group can accept a proton from the COOH group to form an ion containing both a positive and negative charge
this ion is known as a zwitterion
zwitterions have no overall charge because the pos and neg charges cancel out
the isoelectric point is the pH at which the zwitterion is formed, and each AA has its own unique isoelectric point
isoelectric point
the pH at which the zwitterion is formed, and each AA has its own unique isoelectric point
- if an AA is added to a solution with a pH greater than it’s isoelectric point, the AA behaves as an acid and loses a proton
- if an AA is added to a solution with a pH lower than it’s isoelectric point, the AA behaves as a base and gains a proton
condensation polymerisation
the joining of monomers with loss of a small molecule, usually water or hydrogen chloride
two different functional groups are needed
polyesters
monomers are joined together by ester linkages in a long chain to form the polymer. polyesters can be made from one monomer containing both a carboxylic acid and an alcohol group, or from two monomers- containing two COOH groups and the other containing two OH groups
polyesters made from one monomer containing two different functional groups
only one monomer is involved, containing both different functional groups, a COOH and OH group
condensation polymerisation
the COOH in one molecule reacts with the OH of another molecule to form the ester linkage and water
polyesters made from two monomers each containing two functional groups
two different monomers are involved, each with diff functional groups
-one monomer is a diol, with two hydroxyl groups
-one monomer is a dicarboxylic acid, with two carboxyl groups
a hydroxyl group on the diol reacts with a carboxyl group on the dicarboxylic acid forming an ester linkage and water
polyamides
are condensation polymers formed when monomers are joined together by amide linkages in a long chain to form the polymer
can be made from one monomer containing both COOH and an amine group- or from two monomers, one containing two COOH and the other containing two amine groups
polyamides from one monomer with two functional groups
AAs contain both an amine group and a COOH group
AAs undergo condensation polymerisation to form polypeptides or proteins.
a polypeptide or protein contains many different AAs all linked together by amide bonds
when an amide bond is formed water is lost
polyamides from two monomers each with two functional groups
can be made by the reaction of a dicarboxylic acid with a diamine
during the condensation reaction an amide bond forms between the amine on one monomer and the carboxyl group on the other monomer
hydrolysing condensation polymers
polyesters and polyamides can be hydrolysed using hot aqueous alkalis such as sodium hydroxide or by hot aqueous acid such as HCl
hydrolysing polyesters
acid and base hydrolysis
base- NaOH/H2O
acid- H+/H2O
hydrolysing polyamides
base and acid hydrolysis
base- NaOH/H2O
acid- H+/H2O
nitrile
-CN
nitriles from haloalkanes
reacting haloalkanes with sodium cyanide, NaCN, or potassium cyanide, KCN, in ethanol
reaction follows a nucelophilic substitution mechanism
nitriles from aldehydes and ketones
react with hydrogen cyanide in a nucelophilic addition reaction
produces a hydroxynitrile
mix of sodium cyanide and sulfuric acid used
reduction of nitriles
reduced to amines by reacting with hydrogen in the presence of a nickel catalyst
hydrolysis of nitriles
form carboxylic acids by heating with dil aq acid, e.g. HCl
alkylation of benzene
transfers an alkyl group from a haloalkane to a benzene ring
takes place in presence of a friedel-crafts catalyst such as aluminium chloride
forms C-C bonds to benzene ring
forms HCl
acylation of benzene
when benzene reacts with acyl chloride in the presence of an aluminium chloride catalyst, a ketone is formed
forms HCl
filtration under reduced pressure
- connect one end of the pressure tubing to the vacuum outlet or to the filter pump whilst attaching the other end of the rubber tubing to the Buchner flask
- fit the Buchner funnel to the Buchner flask ensuring that there is a good tight fit
- switch on the vacuum pump or the tap
- check for good suction by placing your hand across the top of the funnel
- place a piece of filter paper inside the Buchner funnel and wet this with the same solvent used in preparing your solid. you should see the paper being sucked down against the holes in the funnel
- to filter your sample, slowly pour the reaction mixture from a beaker into the centre of the filter paper.
- rinse out the beaker with the solvent so that all of the solid crystals collet in the Buchner funnel
- rinse the crystals in the Buchner funnel with more solvent and leave them under suction for a few mins so that the crystals start to dry
filtration under reduced pressure apparatus
Buchner flask
Buchner funnel
pressure tubing
access to filter or vacuum pump
recrystallisation
the solid product obtained after filtration will contain impurities which can be removed by carrying out recrystallisation
- pour a quantity of the chosen solvent into a conical flask. if the solvent is flammable, warm the solvent over a water bath. if the solvent is water, place the conical flask on a tripod and gauze over a Bunsen and warm the solvent
- tip the impure sample into a second conical flask of beaker
- slowly add the solvent to the impure sample until it dissolves in the solvent. you should add the minimum volume of solvent needed to dissolve the solid
- once the solid has dissolved, allow the solution to cool. crystals of the desired product should form in the conical flask. when no more crystals form, filter the crystals under reduced pressure to obtain the dry crystalline solid.
melting point determination
chemists determine the MP of solids to identify whether a solid compound is pure
if the compound is impure, the solid melts over a wide range of temps
1. before taking the MP of a solid you should ensure that the sample is completely dry and free flowing
2. take a glass capillary tube or MP tube. hold one end of the tube in a hot flame of a Bunsen burner. rotate the tube in the flame until the end of the tube is sealed
3. the capillary tube is allowed to cool, and is then filled with crystals to about 3mm depth. this is usually carried out by pushing the open end of the capillary into the solid sample to force some of the solid into the tube
4. once you have prepared the sample you will need to take its MP. two methods: using electrically heated MP apparatus or using an oil bath
using electrically heated MP apparatus
- place the capillary tube containing the sample into a sample hole and a 0-300 degree thermometer in the thermometer hole of the MP apparatus
- using the rapid heating setting, start to heat up the sample whilst observing the sample through the magnifying window
- once the solid is seen to melt, record the MP. allow the MP apparatus to cool
- prepare a second sample in a new capillary tube and place in the MP apparatus and again heat up the sample
- as the MP is approached, set to low and raise the temp slowly whilst observing the sample. an accurate determination of the MP can then be obtained
using an oil bath method- determining the MP
- set up the oil bath
- attach the capillary tube containing the sample to a thermometer using a rubber band
- clamp the thermometer. the end of the thermometer and the end of the capillary tube should dip into the oil
- using a micro-burner, slowly heat the oil bath whilst observing the solid
when the solid starts to melt, remove the heat and record the temp.
