6.2 Nitrogen compounds, polymers and synthesis Flashcards
What is an alkyl ammonium salt?
A compound where the hydrogens on an ammonium ion have been substituted by alkyl chains
What is a Lewis base?
has a lone pair of electrons for donation
What is a Bronsted-Lowry base?
proton acceptor
What happens when primary amines react with an acid?
alkyl ammonium salt is made
How are aliphatic amines made?
Haloalkane, ethanol, ammonia mixed in a heated seal tube, undergo a 2 step nucleophilic substitution reaction
Why are amines made in heated sealed tubes rather than by reflux?
Ammonia is too volatile and escapes condenser
What are products of the reaction to make an amine?
The intended amine, an ammonium salt, and further substituted amines
What does increasing the amount of ammonia in a reaction to make an amine do?
Increases the yeild of the amine
How are aromatic amines made?
Reduction of Nitroarene (benzene with NO2 attached),
reducing agent: tin + conc HCl, refluxed at 100*C
How do you extract aromatic amine from solution of products?
Add NaOH to remove excess HCl and neautralise solution, seperate product by steam distillation, solvent extraction then further distillation.
What is an a-amino acid?
When a carboxylic acid group and an amine group are attached to the same carbon atom in an organic compound
Why are amino acids amphoteric?
The -COOH group is a weak acid, the H+ ion partially dissocciates in water.
The nitrogen atom in the -NH2 group can donate a pair of electrons (to a H+ ion) and so is a base
What is a zwitter ion?
When the H+ ion dissociates from the -COOH and attaches to the -NH2, this results in opposite charges on either end of the compound
What is the isoelectric point?
The isoelectric point is when the pH is such that there is no net charge on the amino acid as the positive charge on the nitrogen and negative charge on the oxygen completely cancel out.
What happens either side of the isoelectric point?
At a lower pH than that of the isoelectric point, a lot of H+ ions are present, -COO(-) becomes -COOH and -NH2 becomes -NH3(+)
At a higher pH, the opposite happens
What is the general formula of an amide?
RC(O)-NH2
How do secondary and tertiary amides differ from primary amides?
The hydrogen atoms on the nitrogen are substituted for ‘R’ groups
How are polyamides formed?
They are condensation polymers made by the reaction of carboxylic acids and amines
Why does the CN- nucleophile attack haloalkanes?
The difference in electronegativity between the carbon and halogen atoms causes dipole, carbon has a partial positive charge
Why does the CN- nucleophile attack carbonyls?
Carbon has partial positive charge as oxygen draws electrons in double bond closer to it
Why do you get a racemic mixture of isomers when the carbon chain length of a carbonyl is increased?
Because the C=O bond is planar, cyanide can attach either side and so an equal amount of each is produced
How do nitriles form amines?
Reduction (LiAlH4), 2 hydrogen atoms attach to the nitogen, nickel needed to lower activation energy, heated 150*C
What does acid hydrolysis of nitriles form?
Carboxylic acids
What are optical isomers?
Molecules which are non-superimposable images of each other, same chemical properties but polarise light differently
What is a racemic mixture?
A mixture of isomers in which exactly half are one optical isomer and the other half are another optical isomer of the same compound (effects cancel out)
How do we make primary amides?
By mixing acyl chlorides with ammonia
How do we make secondary amides?
By mixing acyl chlorides with primary amines
What are optical isomers?
Non superimposable mirror images about a chiral centre
When can the CN- act as a nucleophile?
When the solution has been acidified to increase the polarity of the C=O group and make it more reactive
Why do we use a sealed tube to make amines from haloalkanes?
Because ammonia is volatile and could escape
What are the two nucelophilic substitution steps that make a primary amine from a haloalkane?
- an alkyl ammonium salt is formed
2. a further molecule of ammonia reacts to form the amine
What are aromatic amines used for?
The production of dyes
Similarities between enantiomers?
Same chemical properties
Difference between enantiomers?
Drastically different biological properties
One will rotate plane polarised light clockwise and the other will rotate it anticlockwise
What must we have to form optical isomers?
a carbon with four different groups attached - a chiral centre
How do we make polyesters?
Reacting dicarboxylic acids and diols
How can we increase the rate of hydrolysis of a polymer?
Using either an acid or an alkali
Is the acid hydrolysis of polyesters fast or slow?
Slow
Is the basic hydrolysis of polyesters fast or slow?
Fast
What does the acid hydrolysis of polyesters form?
diol and dicarboxylic acid
What does the alkali hydrolysis of polyesters form?
diol and the salt of the dicarboxylic acid
Is the acid hydrolysis of polyamides fast or slow?
fast
Is the basic hydrolysis of polyamides fast or slow?
slow
What does the acid hydrolysis of polyamides form?
diammonium salt and a dicarboxylic acid
What does the alkali hydrolysis of polyamides produce?
diamine and the salt of the dicarboxylic acid
What type of hydrolysis is faster in polyamides and polyesters?
- alkali hydrolysis is faster in polyesters
- acid hydrolysis is faster in polyamides
Why do we use ethanol as a solvent when using potassium cyanide to increase carbon chain length?
It is not a nucleophile so will be interfere with the reaction, unlike water
What can be attacked by cyanide ions?
haloalkanes
carbonyl functional groups
Why is a cyanide ion equally likely to attack above and below the plane of a C=O bond?
Because the C=O bond is planar
When do we get racemic mixtures different hydroxynitriles?
When we carry out the nucleophilic addition of cyanide on asymmetric ketones and aldehydes other than methanal
Why do we use a strong acid in the hydrolysis of nitriles?
It causes a carboxylic acid to be formed instead of an ammonium salt as it fully ionises, producing lots of H+
If there is not a dilute acid present, what does the hydrolysis of nitriles produce?
What is bad about this reaction?
- an amide which then becomes a ammonium salt
- it is so slow that it is not significant
How to increase chain length with nucleophilic addition?
-haloalkane mixed with potassium cyanide under reflux
How to increase chain length by nucleophilic addition?
- hydrogen cyanide generates cyanide nucleophile
- attracted to carbonyl group
- hydroxynitrile produced
types of steroeisomerism
cis trans
optical
