6.2 Nitogen Compounds, Polymers And Synthesis

Question 1

What are amines?

Answer 1

Organic chemicals where one or more of the hydrogen atoms on ammonia have been replaced by alkyl chains

Question 2

What are the 3 types of amines?

Answer 2

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.

Question 3

How do you name primary amines?

Answer 3

-determine the root by the longest hydrocarbon chain
-add any prefixes for other groups. Finally add the suffix amine

Question 4

How do you name secondary amines?

Answer 4

-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-

Question 5

How do you name tertiary amines?

Answer 5

-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-

Question 6

Are amines bases?

Answer 6

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

Question 7

What is the general formula for amino acids?

Answer 7

RCH(NH2)COOH

Question 8

How do you form aliphatic amines?

Answer 8

-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

Question 9

How do you prepare aromatic amines?

Answer 9

-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

Question 10

When do zwitterions form?

Answer 10

They form at the isoelectric point, which is the pH at which the overall charge of the molecule is zero

Question 11

What is the zwitterionic form of an amino acid?

Answer 11

-when the amine group has a positive charge (NH3+) and the carboxylic group has a negative charge (COO-)

Question 12

What is the zwitterionic form of an amino acid?

Answer 12

-when the amine group has a positive charge (NH3+) and the carboxylic group has a negative charge (COO-)

Question 13

What is condensation polymers?

Answer 13

-a long chain molecule formed when monomers react together with the elimination of a small molecule such as water

Question 14

What is addition polymerisation?

Answer 14

-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)

Question 15

What is condensation polymerisation?

Answer 15

-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)

Question 16

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 ______ _________.

Answer 16

-C=C
-addition polymer
-different
-functional groups
-condensation polymer

Question 17

What are polyesters and how are they formed?

Answer 17

-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

Question 18

What are polyamides and how are they formed?

Answer 18

-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

Question 19

Draw a labelled diagram to show apparatus set up for filtration under reduced pressure (vacuum filtration)

Answer 19

Question 20

(4 marks)

Answer 20

-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

Question 21

Answer 21

-NH2 and COOH react to form an amide

Question 22

What are primary amines formed from?

Answer 22

-ammonia

Question 23

What are secondary/tertiary amines formed from?

Answer 23

Amines

Question 24

Are amino acids basic or acidic?

Answer 24

-they are amphoteric (they can act as both an acid and a base)

Question 25

What is charged on an amino acid at a low pH? What is charged on an amino acid at a high pH?

Answer 25

-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

Question 26

How does the carboxylic acid group in an amino acid react with: -metal oxides -alkalis -carbonates -alcohol

Answer 26

-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

Question 27

How does the amine group in an amino acid react with acids?

Answer 27

-acts as a base -produces an ammonium salt

Question 28

What are amides? Draw out the amide functional group

Answer 28

-a class of compounds with an acyl group (RC(O)-) attached to an amine group (NH2)

Question 29

What is a primary amide?

Answer 29

The nitrogen group has two hydrogen atoms and one acyl group attached

Question 30

What is a secondary amide?

Answer 30

-the nitrogen atom has one hydrogen atom, one acyl group and one alkyl group attached

Question 31

What are tertiary amides?

Answer 31

-the nitrogen atom has no hydrogen atoms attached

Question 32

Draw out the general formula of a primary amide, a secondary amide and a tertiary amide?

Answer 32

Question 33

How do you name primary amides?

Answer 33

-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

Question 34

How do you name secondary amides?

Answer 34

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

Question 35

What are optical isomers?

Answer 35

-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

Question 36

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.

Answer 36

‘+’ ‘-‘

Question 37

What is a racemic mixture/ racemate?

Answer 37

-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

Question 38

What is a chiral carbon?

Answer 38

-a carbon that has 4 different groups attached to it

Question 39

Carbons with a _________ __________ cannot be a chiral carbon as there are ____ __ _______ ________

Answer 39

-double bond -not 4 groups attached

Question 40

Describe the acid hydrolysis of polyesters

Answer 40

-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

Question 41

Describe the alkali hydrolysis of polyesters

Answer 41

-when a polyester is reacted with hot sodium hydroxide solution, the reaction produces the diol and the salt of the dicarboxylic acid

Question 42

Describe the acid hydrolysis of polyamides

Answer 42

-when a polyamide is reacted with a strong aqueous acid, the reaction produces a diammonium salt and a dicarboxylic acid

Question 43

Describe the alkali hydrolysis of a polyamide

Answer 43

-when a polyamide is reacted with hot sodium hydroxide solution, the reaction produces the diamine and the salt of the dicarboxylic acid

Question 44

_______ hydrolysis is faster in polyesters. And __________ hydrolysis is faster in polyamides

Answer 44

-alkali -acid

Question 45

What are alkalis?

Answer 45

Bases that dissolve (are soluble) in water

Question 46

Draw out the dot and cross diagram for the cyanide ion

Answer 46

Question 47

Is Cyanide a nucleophile?

Answer 47

-yes it is a nucleophile as it is attracted to areas of positive charge in a molecule

Question 48

What is the cyanide ion called in inorganic chemicals?

Answer 48

-it keeps the name cyanide .e.g. sodium cyanide (NaCN

Question 49

What is the -CN group called in an organic molecule?

Answer 49

-it is called a nitrile functional group

Question 50

How is the carbon length chain of a haloalkane increased?

Answer 50

-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

Question 51

Why is the solvent ethanol when extending the carbon chain length of a haloalkane?

Answer 51

-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

Question 52

Draw the mechanism of the reaction between 1-bromopropane and potassium cyanide Name this mechanism And write the equation for this reaction

Answer 52

-this is a nucleophilic substitution mechanism

Question 53

How do you extend the carbon chain length on a carbonyl compound?

Answer 53

—react the carbonyl compound with HCN -this results in a hydroxynitrile organic compound -this is a nucleophilic addition mechanism

Question 54

Draw the general mechanism of the reaction between a carbonyl compound and HCN What type of mechanism is this?

Answer 54

-nucleophilic addition mechanism

Question 55

When carbonyl compounds are reacted with HCN what happens due to the C=O planar bond?

Answer 55

-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

Question 56

Draw out ethanenitrile

Answer 56

Question 57

Describe the reduction of nitriles

Answer 57

-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

Question 58

What do nitriles form when they undergo acid hydrolysis?

Answer 58

-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

Question 59

In the acid hydrolysis of nitriles why are organic acids (carboxylic acid) formed rather than an organic ammonium salt

Answer 59

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.

Question 60

What is distillation?

Answer 60

-a technique used to separate miscible liquids or solutions

Question 61

What is reflux used for?

Answer 61

-heating under reflux is a technique used to ensure that volatile compounds are not lost from the reaction mixture

Question 62

What is recrystallisation?

Answer 62

-a method for purifying organic compounds

Question 63

Draw the set up for distillation

Answer 63

Question 64

What is the method for filtration under reduced pressure?

Answer 64

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. 7. Wash out the reaction vessel and the funnel with the solvent and add this to the funnel. 8. Rinse the collected solid with more solvent and maintain suction for a minute after all the washings have been added. 9. Turn of the suction by removing the rubber tube from the side arm of the filtration flask. 10. Invert the funnel onto a watch glass to collect the organic solid

Question 65

What is the method for recrystallisation?

Answer 65

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.

Question 66

What is the method for measurement of melting points?

Answer 66

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

Question 67

Draw out the mechanism for the alkylation of benzene to form ethylbenzene

Answer 67

Question 68

Draw out the mechanism for the acylation of benzene to produce phenylethanone

Answer 68

Question 69

What is a dimer?

Answer 69

A molecule consisting of two identical molecules (monomers) linked together