6.2 Nitogen Compounds, Polymers And Synthesis Flashcards
What are amines?
Organic chemicals where one or more of the hydrogen atoms on ammonia have been replaced by alkyl chains
What are the 3 types of amines?
Primary- one hydrogen atom on ammonia has been substituted. The structural formula can be summarised as RNH2 where R is an alkyl chain
Secondary- two hydrogen atoms have been substituted. The structural formula can summarised as RNHR’ where R and R’ are alkyl chains which may be the same or different
Tertiary-all three hydrogen atoms have been substituted. The structural formula can be summarised as RNR’R’’ where R, R’ and R’’ can be the same or different hydrocarbon groups.
How do you name primary amines?
-determine the root by the longest hydrocarbon chain
-add any prefixes for other groups. Finally add the suffix amine
How do you name secondary amines?
-determine the root by naming the two alkyl chains
-add any prefixes for additional groups and write them in alphabetical order
-add the suffix ‘amine’
-secondary amines often have the prefix N-
How do you name tertiary amines?
-determine the root by naming the three alkyl chains, if there is more than one of the same group add the appropriate prefix: di- or tri-
-add the prefix N,N-
Are amines bases?
Yes
-when an amine reacts with an acid the nitrogen lone pair acccepts a proton. A covalent bond is formed by the nitrogen atom donating its lone pair of electrons to the proton to form a dative covalent bond
- amines react with dilute acids e.g. HCl (aq) to form an alkylammonium salt
What is the general formula for amino acids?
RCH(NH2)COOH
How do you form aliphatic amines?
-using a sealed tube a haloalkane, excess ammonia and ethanol are heated together to make an amine
-the haloalkane will undergo nucleophilic addition in a 2 stage process
1- the ammonia reacts with the haloalkane to make an ammonium salt
2-an additional ammonia molecule reacts to form the propylamine product and ammonium chloride salt
-it is a reversible reaction so excess ammonia will increase the yield of the desired product
-additional substitutions on the hydrogen atoms on the nitrogen can occur
-when preparing amines by this method there is always a mixture of the products produced
How do you prepare aromatic amines?
-nitroarenes (e.g. nitrobenzene) can be reduced to produce an amine
-the reducing agent is made in situ by using a mixture of tin and concentrated hydrochloric acid
-the reaction occurs at reflux at 100 degrees Celsius
-after about half an hour a strong alkali is added, this undergoes a neutralisation reaction to remove excess hydrochloric acid and produce the amine
-separating the amine is a multi-stage process it includes: steam distillation, solvent extraction and further distillation
When do zwitterions form?
They form at the isoelectric point, which is the pH at which the overall charge of the molecule is zero
What is the zwitterionic form of an amino acid?
-when the amine group has a positive charge (NH3+) and the carboxylic group has a negative charge (COO-)
What is the zwitterionic form of an amino acid?
-when the amine group has a positive charge (NH3+) and the carboxylic group has a negative charge (COO-)
What is condensation polymers?
-a long chain molecule formed when monomers react together with the elimination of a small molecule such as water
What is addition polymerisation?
-monomers have at least one C=C, which breaks and joins the other monomers together
-there is only one product from this type of polymerisation
-they are non-biodegradable due to the absence of polar bonds in the main chain
-common examples- poly(ethene), PVC, poly(propene)
What is condensation polymerisation?
-where two different monomers with different functional groups react to form a polymer and release another small molecule, often water
-they are biodegradable due to the presence of polar C-N or C-O bonds in the main chain
-common examples- polyesters (e.g. terylene) and polyamides (e.g. nylon, Kevlar)
If you are given a monomer and it contains _______ then it must form an _________ _________. If the monomer contains two ________ functional groups or more than one monomer is present each with different _________ _________ then they must make a ______ _________.
-C=C
-addition polymer
-different
-functional groups
-condensation polymer
What are polyesters and how are they formed?
-they are condensation polymers
—made by the chemical reaction of a dicarboxylic acid (COOH) and a diol (OH)
-when the carboxylic acid group on one monomer reacts with the alcohol group on the other monomer an ester link (R-COO-R’) is formed between the two molecules, this happens many times and produces a long chain molecule called a polyester
-it is possible to have a molecule that contains both an alcohol group and a carboxylic acid group, this allows just one monomer to be used to make the polyester
What are polyamides and how are they formed?
-they are condensation polymers
—made by the chemical reaction between a dicarboxylic acid (COOH) and a diamine (NH2)
-when the carboxylic acid group on one monomer reacts with the amine group on the other monomer an amide link (R-CONH-R’) is formed between the two molecules. This happens between many molecules and produces a long chain molecule called a polyamide
-it is possible to have a monomer that contains both an amine group and a carboxylic acid group e.g. an amino acid this allows just one monomer to be used to make a polyamide
Draw a labelled diagram to show apparatus set up for filtration under reduced pressure (vacuum filtration)
(4 marks)
-CH3CH2CH2NH2 - No branches/has a longer chain therefore has more points of contact/ more surface interaction so stronger induced dipole-dipole interactions /London forces
-CH3CH2CH2NH2 and (CH3)2CHNH2 have hydrogen bonding
-(CH3)3N does not form hydrogen bonds, hydrogen bonds are stronger than London forces
-more energy is needed to break hydrogen bonds
-NH2 and COOH react to form an amide
What are primary amines formed from?
-ammonia
What are secondary/tertiary amines formed from?
Amines
Are amino acids basic or acidic?
-they are amphoteric (they can act as both an acid and a base)
What is charged on an amino acid at a low pH?
What is charged on an amino acid at a high pH?
-at low pH there are a lot of H+ so the carboxylic acid functional group becomes COOH and only the amine group is charged. The amino acid is acting as a base and accepts a proton from the acid. So it is a positive ion in acidic solution
-at high pH the amine group becomes NH2 and only the carboxylic group is charged. The amino acid is acting as an acid and donates a proton to the hydroxide ion. So it is a negative ion in alkaline solution
How does the carboxylic acid group in an amino acid react with:
-metal oxides
-alkalis
-carbonates
-alcohol
-carboxylic functional group is a weak acid
Metal oxides-neutralisation reaction occurs to produce a metal salt and water
Alkalis-neutralisation reaction occurs to form salt and water
Carbonates-neutralisation reaction produces a salt, water and carbon dioxide gas (effervescence is observed)
Alcohol- produces an ester and releases a molecule of water
How does the amine group in an amino acid react with acids?
-acts as a base
-produces an ammonium salt
What are amides?
Draw out the amide functional group
-a class of compounds with an acyl group (RC(O)-) attached to an amine group (NH2)
What is a primary amide?
The nitrogen group has two hydrogen atoms and one acyl group attached
What is a secondary amide?
-the nitrogen atom has one hydrogen atom, one acyl group and one alkyl group attached
What are tertiary amides?
-the nitrogen atom has no hydrogen atoms attached
Draw out the general formula of a primary amide, a secondary amide and a tertiary amide?
How do you name primary amides?
-the suffix is amide and the root is generated by the number of carbon atoms in the parent hydrocarbon chain which has the functional group.
-when numbering prefixes the functional group is considered to be on carbon 1
How do you name secondary amides?
When naming secondary amides, the suffix is ‘amide’ and the root is generated by the number of carbon atoms in the parent hydrocarbon chain which has the functional group. The alkyl chain is
attached to the nitrogen, so it is called an N-substituted compound
What are optical isomers?
-an example of stereoisomerism
-molecules which are non-superimposable images of each other
-the molecules must have a chiral centre
-they have the same chemical properties but each enantiomer interact with polarised light differently
Each enantiomer can be given a prefix to denote its effect on a plane of polarised light. If the enantiomer rotates the plane of polarised light in the clockwise direction it is given the prefix ___
The prefix __ is given if the rotation is in the anticlockwise direction. This can only be determined by
experiment and cannot be deduced from the structure.
‘+’
‘-‘
What is a racemic mixture/ racemate?
-a 50:50 mixture of enantiomers
-a racemic mixture will have no effect on polarised light as the rotations of the two isomers cancel each other out
What is a chiral carbon?
-a carbon that has 4 different groups attached to it
Carbons with a _________ __________ cannot be a chiral carbon as there are ____ __ _______ ________
-double bond
-not 4 groups attached
Describe the acid hydrolysis of polyesters
-when polyesters are reacted with a strong aqueous acid, the reaction produces a diol and a dicarboxylic acid
-the acid hydrolysis of a polyester has a slow rate of reaction
Describe the alkali hydrolysis of polyesters
-when a polyester is reacted with hot sodium hydroxide solution, the reaction produces the diol and the salt of the dicarboxylic acid
Describe the acid hydrolysis of polyamides
-when a polyamide is reacted with a strong aqueous acid, the reaction produces a diammonium salt and a dicarboxylic acid
Describe the alkali hydrolysis of a polyamide
-when a polyamide is reacted with hot sodium hydroxide solution, the reaction produces the diamine and the salt of the dicarboxylic acid
_______ hydrolysis is faster in polyesters. And __________ hydrolysis is faster in polyamides
-alkali
-acid
What are alkalis?
Bases that dissolve (are soluble) in water
Draw out the dot and cross diagram for the cyanide ion
Is Cyanide a nucleophile?
-yes it is a nucleophile as it is attracted to areas of positive charge in a molecule
What is the cyanide ion called in inorganic chemicals?
-it keeps the name cyanide .e.g. sodium cyanide (NaCN
What is the -CN group called in an organic molecule?
-it is called a nitrile functional group
How is the carbon length chain of a haloalkane increased?
-the haloalkane is mixed with potassium cyanide and heated under reflux
-the solvent for this reaction is ethanol
-this is a nucleophilic substitution reaction
-a new C-C bond forms between the original haloalkane and cyanide, this increases the length of the carbon chain by one carbon atom, as well as this the new nitrile group can undergo more reactions and make a variety of different chemicals
Why is the solvent ethanol when extending the carbon chain length of a haloalkane?
-the solvent is ethanol as this ensures the nucleophile is the cyanide ion
-if water is used then the hydroxide ion tends to be the nucleophile and the carbon-chain length would not increase
Draw the mechanism of the reaction between 1-bromopropane and potassium cyanide
Name this mechanism
And write the equation for this reaction
-this is a nucleophilic substitution mechanism
How do you extend the carbon chain length on a carbonyl compound?
—react the carbonyl compound with HCN
-this results in a hydroxynitrile organic compound
-this is a nucleophilic addition mechanism
Draw the general mechanism of the reaction between a carbonyl compound and HCN
What type of mechanism is this?
-nucleophilic addition mechanism
When carbonyl compounds are reacted with HCN what happens due to the C=O planar bond?
-as the C=O is a planar bond there is an equally likely chance that the cyanide ion will attack from either side
-so a racemic mixture is produced when an asymmetric ketone or any aldehyde other than methanal is used in this reaction
Draw out ethanenitrile
Describe the reduction of nitriles
-nitriles form amines when they undergo reduction
-hydrogen gas can react directly with a nitrile to form a primary aliphatic amine, two hydrogen atoms are added to the nitrogen atom of the nitrile group
-the reagent is H2
-the catalyst is Ni
-the reaction mixture is heated to about 150 degrees Celsius, at a raised pressure
What do nitriles form when they undergo acid hydrolysis?
-they form carboxylic acids (and an inorganic ammonium salt)
-an aqueous strong acid is used as well as this the reaction is heated under reflux
In the acid hydrolysis of nitriles why are organic acids (carboxylic acid) formed rather than an organic ammonium salt
This is because the strong acid fully ionises in solution, forming hydrogen ions and chloride ions. Once the amide is formed, the bond between the nitrogen and the carbon is broken, making the ethanoate ion. This then reacts with the proton from the strong acid to form the carboxylic acid. All organic acids are weak acids and only partially ionise in solution. In these reactions the CN triple bond is completely broken through a series of steps via the amide. This gives the carboxylic acid and the ammonium salt as the major products.
What is distillation?
-a technique used to separate miscible liquids or solutions
What is reflux used for?
-heating under reflux is a technique used to ensure that volatile compounds are not lost from the reaction mixture
What is recrystallisation?
-a method for purifying organic compounds
Draw the set up for distillation
What is the method for filtration under reduced pressure?
Organic solids will often crystallise out of solution after an organic synthesis. Filtration under reduced pressure is one method of collecting the product. This is done as follows:
1 . Connect thick-walled rubber tubing to the vacuum pump and check that there is suction.
2. Put a Büchner funnel into the top of a filter flask
3. Connect the tubing from the vacuum pump to the side arm of the clamped filter flask and start the suction.
4. Place a piece of filter paper, just big enough to cover the holes, into the top of the funnel.
5. Using distilled water or the solvent from your organic synthesis if this is different, dampen the filter paper so that it sticks over the holes of the funnel.
6. Slowly pour your reaction mixture into the centre of the funnel.
- Wash out the reaction vessel and the funnel with the solvent and add this to the funnel.
- Rinse the collected solid with more solvent and maintain suction for a minute after all the washings have been added.
- Turn of the suction by removing the rubber tube from the side arm of the filtration flask.
- Invert the funnel onto a watch glass to collect the organic solid
What is the method for recrystallisation?
Recrystallisation is a purification technique that uses the differing solubilities of solid and impurities in different solvents.
• The solid is dissolved in a minimum volume of hot solvent. The solubility of the solute increases with temperature so it is important that the solvent is near its boiling point.
• The solution is immediately filtered through hot apparatus by gravity filtration. This removes insoluble impurities. The resulting solution is allowed to cool and crystallise.
• The purified crystals can then be obtained by vacuum filtration of this solution. This removes any impurities that were soluble in the solvent. It also helps to dry the crystals.
When choosing the solvent, it is important to choose a solvent in which the solute is insoluble at room temperature, but a lot more soluble at higher temperatures.
What is the method for measurement of melting points?
In a sealed capillary tube, put a few grains of the organic solid. Using a small rubber
band, attach the tube to a thermometer. Submerge the thermometer into the oil of the Thiele
tube, ensuring that the rubber band is above the oil line.
Using a microburner with a small gentle flame, heat the side arm of the Thiele tube. Note the
temperature range of when the organic solid starts and finishes melting.
-compare this value to data book melting point value, the purer the substance the coser to the data book value it will be
Draw out the mechanism for the alkylation of benzene to form ethylbenzene
Draw out the mechanism for the acylation of benzene to produce phenylethanone
What is a dimer?
A molecule consisting of two identical molecules (monomers) linked together
