RPA - Nitrogen Compounds Flashcards
Why must diazotisation and coupling reactions occur below 10 C?
To prevent decomposition. The diazonium salt is unstable
What are primary, secondary and tertiary amines?
Primary - one carbon group
secondary - two carbon groups
3 - three carbon groups bonded to nitrogen
Are amines soluble in water?
yes, because they form hydrogen bonds between H of NH2 and O of H2O
Is there a regular pattern of boiling points of amines?
No, as VdW forces add to the hydrogen bonding,
Are there hydrogen bonds on tertiary amines?
no, as no hydrogens on amine groups
What can ammonia be described as?
Alkali - releases OH- ions in solution
How do you prepare aliphatic amines? (Mechanisms, reagents,)
Nucleophilic substitution of halide with NH3 nucleophile
Ethanol conditions (No water to form OH- ions –> alcohol)
high pressure
hot
What are possible impurities in aliphatic amines?
Secondary/tertiary.
primary amines have lone pair on nitrogen so can act as nucleophiles to attack halogenoalkane
How can you reduce chance of impurities?
large excess of NH3 means more change of NH3 encountering halogenoalkane than primary amine
What is the method for preparation of phenylamine?
reduction of nitrobenzene using Sn/HCl reducing agent
What is the second stage in preparation of azo dye?
Reaction of phenylamine with NaNO2 to form diazonium ion
How is NaNO2 formed?
HCl + NaNO2 –> HNO2 + NaCl
What is the second stage in azo dye production, following diazonium ion formation?
Coupling reaction with phenol in alkaline conditions
Why are alkaline conditions used in coupling?
increases phenol reactivity by producing phenoxide ion by loosing one of the ring’s hydrogen
What is characteristic of an amino acid?
Amine and carboxylic acid group
What is an alpha amino acid?
one where NH2 and COOH is bonded to same carbon
What is a zwitterion?
a dipolar form of amino acid with NH3+ and COO- ions. Exists at isoelectric point of amino acid
What form do zwitterions exist in at their isoelectric point?
solids due to ionic bonding between molecules
What happens when an amino acid is placed in alkaline conditions?
it acts as an acid, donates any protons on COOH groups to form negative ions
What happens when an amino acid is placed in acidic conditions?
it acts as a base, and any NH2 groups accept protons to form NH3+ groups.
What causes the intermolecular forces in amines to be intermittent?
Permanent dipole/H-bond interactions require direct alignment, which is not always the case.
What is the mechanism for the production of secondary amines having produced primary aliphatic amine by nucleophilic substitution?
The nitrogen on primary amine still has lone pair, so can go on to react as a nucleophile with halogenoalkane, producing secondary amine
What are the conditions when halogenoalkane undergoes nucleophilic substitution with NH3?
Ethanol (stop OH- ions forming)
High pressure
Hot
What happens if an amino acid with a COOH group as the R group is placed in alkaline solution?
Both COOH groups act as acids, hence proton donors, hence BOTH become COO- groups
What is required for a chiral centre?
Four different groups on a central carbon
What are optical isomers?
2 non-superimposable mirror images (i.e. reflections)
Given one molecule, how do you find the stereoisomers?
identify # chiral carbons, reflect the first, reflect the second, reflect both
What does the (+) enantiomer of a stereoisomer do to plane polarised light?
Rotates by 90 clockwise
What does the (-) enantiomer of a stereoisomer do to plane polarised light?
Rotates by 90 anticlockwise
What does a racemic mixture of +- enantiomers do to plane polarised light?
Nothing, as the rotations cancel out
What can be said about the optical activity of amino acids?
All alpha amino acids are optically active, except for glycine as this has only three different groups
What is the actual shape of the molecules of an amino acid surrounding chiral carbon?
tetrahedral
What happens when CH3CH2NH3 reacts with H2SO4?
Forms a salt:
CH3CH2NH3+ HSO4-
Why are amines described as bases?
lewis bases as they donate protons,
Bronstead-Lowry bases as they accept protons to form NH4+ + OH-
Can tertiary amines form hydrogen bonds?
No, as there must be a +ve H bonded to N/O/F, and there is not.
What is the difference in boiling point between primary, secondary and tertiary amines?
Decreases as hydrogen bonding sites decrease
What are the reactants in the first stage of synthesis of azo dyes?
HCl + HNO2
What is the reaction to form HNO2, nitrous acid, in the synthesis of azo dyes?
HCl + NaNO2 –> HNO2 + NaCl
What are the reactants in the second stage of formation of azo dye? What are the products other than the dye?
NaOH to produce H2O + NaCl
Define condensation reaction
Joining of two + monomers to make a polymer by the elimination of a small molecule e.g. H2O/HCl
Why is nitrogen a base?
NITROGEN electron pair accepts proton
What must you consider when reducing a ring with multiple nitro groups?
How many moles of reducing agent and how many moles of water are produced
What happens when a compound including amine groups is reacted with acid?
ALL the amine groups form ammonium ions. It does not matter whether they’re hydrolysed or not.
