2.  An alkane molecule such as ethane has a ‘backbone’ consisting of a chain of single C-C bonds.  An alkane molecule is non-polar as carbon and hydrogen have similar electronegativity.  Therefore they are insoluble in water, but are soluble in non-polar solvents.  The stability of the C-C bonds and the non- polar nature means that alkanes are quite non- reactive.  Most reactions involving alkanes are either combustion or substitution reactions.

3.  Alkanes can be used as fuel.  Combustion reactions involving alkanes release large amounts of heat energy.  Combustion of methane › CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O(g) + energy  Combustion of methane › 2C 8 H 18 (g) + 25O 2 (g) → 16CO 2 (g) + 18H 2 O(g) + energy

4.  One or more hydrogen atoms in an alkane is replaced by a different atom or functional group.  This involves breaking the C-H bonds and making new bonds with the substituting atom or group.  Chloroethane is a gas at room temperature and is used in a local anaesthetic spray.  CH 3 CH 3 (g) + Cl 2 (g) CH 3 CH 2 Cl(g) + HCl(g) Heat or light

5.  Page 146  Questions 1 and 2

6.  Alkenes: › Are unsaturated › Are non-polar › Are insoluble in water › Participate in addition reactions › Polymerises to produce polymers.

7.  The double covalent bond in ethene molecules has a significant effect on its chemical properties.  Ethene reacts more readily, and with more chemicals than ethane.  The reactions of ethene usually involve addition of a small molecule to produce a single product.  For example it reacts with bromine solution.

8.  Involve the C=C bond being converted to a single bond.  Ethanol can be produced by an addition reaction of ethene and water using a catalyst to speed up the reaction.

9.  A type of addition reaction of ethene is involved in making polyethene.  The number n in this reaction is very large (several thousand or more).  A molecule made by linking a large number of small molecules, is called a polymer.  The small molecule (in this case ethene) is called a monomer.  This type of reaction is known as addition polymerisation

10.  When the polymer is being formed the ethene molecules add to the end of growing polymer chains.  Ethene is used as a base for other addition polymerisation reactions. For example to make PVC and polystyrene.

11.  Page 149  Question 1-3

12.  Once a more electronegative atom such as chlorine has been substituted for a hydrogen atom in an alkane, the molecule becomes polar.  Electrons in the carbon-chlorine bond are attracted towards the more electronegative chlorine atom.  This makes the carbon atom at the other end of the bond susceptible to attack by negatively charge ions.

13.  For example chloromethane is converted to methanol when it is reacted with hydroxide ions.  The chlorine atom is substituted by an OH functional group to form methanol.

14.  Alkanols can be produced by addition reactions of alkenes or substitution reactions of chloroalkanes.  Ethanol has very different properties from ethane or chloroethane. › It is liquid at room temp. › It is widely used as a solvent in cosmetics and pharmaceuticals › It is the active ingredient in alcoholic drinks › It can act as a depressant on the human body, slowing reactions and responses. › Excess ethanol consumption also blocks the production of antidiuretic hormones, increasing urination and resulting in dehydration.

15.  Ethanol is soluble in water as a consequence of its highly polar OH group, which readily forms hydrogen bonds with water molecules.  Alkanols can be turned into amide groups by reacting ethanol with ammonia.  CH 3 CH 2 OH(g) + NH 3 (g) CH 3 CH 2 NH 2 (g) + H 2 O(g)  What type of reaction is this? alumina 400°C

16.  Alkanols can also be oxidised to form carboxylic acids: › CH 3 CH 2 OH(aq) CH 3 COOH(aq)  Not all alkanols will oxidise to form carboxylic acids. Carboxylic acid synthesise only occurs from primary alkanols. O 2 (g) PrimarySecondaryTertiary

17.  Carboxylic acids are weak acids, reacting with water to form weak acidic solutions.  CH 3 COOH(aq) + H 2 O(l)↔ CH 3 COO - (aq) + H 3 O + (aq)

18.  Page 151  Questions 8, 9 and 10

19.  Esters are a group of organic compounds responsible for some of the natural and synthetic flavours and smells in ice-creams, lollies, flowers and fruits.  Esters composed of small molecules are volatile and smelly. Esters of larger molecular size are oils and waxes EsterSmell or flavour Pentyl propanoateApricot Ethyl butanoatePineapple Octyl ethanoateOrange 2-methyl methanoateRaspberry Ethyl methanoateRum Pentyl ethanoateBanana

20.  Esters are made by a condensation reaction between carboxylic acids and an alkanol.  Reactions that involve the combination of two reactions and the elimination of a small molecule, such as water, are called condensation reactions.

21.  Gently heating a mixture of ethanol and pure ethanoic acid, with a trace amount of sulfuric acid as a catalyst, produces an ester (ethyl ethanoate) and water.  Ethyl ethanoate is more commonly known as ethyl acetate, it is used as a solvent in paints and nail varnish

22.  Below is the general equation for the esterification reaction involving a carboxylic acid and an alkanol.

23.  Esters have two-part names.  The first part derived from the name of the alkanol from which it is made › The ‘anol’ part is replace with ‘yl’ › Ethanol becomes ethyl  The second part comes from the carboxylic acid. › Where ‘ic acid’ is replace with ‘ate’ › Ethanoic acid becomes ethanoate.  Therefore we have ethyl ethanoate

24.  Read pages 153 – 155 on polyesters  Page 156  Questions 11 and 12

25.  Which pathway is the most effective to make ethanol???

26.  Production chemists need to find the most efficient pathway for making certain materials.  To do this there are certain areas to consider: › How readily available is the starting material › The yield (how much will it produce) › The purity of the final product › Can they minimise any unwanted side products › Can they minimise waste materials › Cost › How long will it take.

27.  What is ethyl propanoate made out of?  Suppose we only had alkanes and alkenes on hand how could we make ethyl propanoate?

28.  Ethanol is a two carbon compound that can be synthesised directly from ethene, or from ethene via the intermediate product chloroethane.

29.  Propanoic acid is a carboxylic acid containing 3 carbon atoms.  It is prepared by the oxidation of the primary alkanol propan-1-ol.  This in turn can be formed by the reaction of 1- chloropropane with NaOH.  1-chloropropane is formed by reacting propane with chlorine.  A number of products will be formed which are separated by fractional distillation.

30.  The substitution reaction of propane is chosen rather than an addition reaction of propene because the addition of HCl to propene will result in the formation of unwanted 2-chloropropane.  Having synthesised ethanol and propanoic acid we can now prepare the ester using a condensation reaction.

32.  The purity of the product needs to be evaluated. For this a lot of companies will use some of the analysis techniques looked at in first term.  The yield must be taken into account, as not all of the reactants are necessarily converted to product % Yield = Actual mass of product obtained Theoretical mass of product

33.  Page 159  Question 15, 17 and 18

34.  A technique used to separate liquids that have different boiling points.  Commonly used in a laboratory to separate volatile liquids from a reaction mixture.  Industrial application of fractional distillation include: › Separation of the fractions from crude oil › Production of oxygen and nitrogen by the fractional distillation of liquid air › Extraction of ethanol from water in the fermentation of sugar.

35.  The column is packed with glass beads or has glass shelves, providing a large surface area upon which the vapours condense.  There is a temparature gradient up the fractionating column; the column is cooler at the top than at the bottom.

36.  Looking at our example of synthesis of the ester ethyl ethanoate.  Pure ethyl ethanoate can be extracted from the reaction mixture by fractional distillation. Look at the boiling points of components in the reaction mixture ComponentBoiling Point CH 3 COOCH 2 CH 3 57°C CH 3 CH 2 OH78°C H2OH2O100°C CH 3 COOH118°C

37.  The reaction mixture is heated in the distillation flask.  The vapour rises up the fractionating column.  The temperature at the top of the column slowing increases until it stabilises at about 57°C, which is the boiling point of ethyl ethanoate.  The fraction condensing over a small range of temperature near the boiling point of ethyl ethanoate, 55°C - 59°C is collected.

38.  Page 161  Question 19

39.  Pharmaceutical products are often developed from substances found in a plant that has been used as a traditional medicine.  Aspirin is one such substance.  Its origins are from a naturally occurring substance called salicin found in the leaves and bark of willow trees and in the herb medowsweet.  As long ago as 400BC people have recommended ‘an infusion of willow leaves and bark to relieve aches, pains, inflammation and fever.’

40.  The body converts salicin into salicylic acid and this is the active substance that helps to reduce fever and acts as a pain killer.  Salicylic acid is more effective than salicin and by 1870 doctors were prescribing salicylic acid directly.  A lot of people could not tolerate salicylic acid directly and it tasted bad.

41.  In 1897, Felix Hoffmann, synthesised an improved modification of salicylic acid.  Once he had made salicylic acid he replaced the hydroxy functional group with an ester functional group to form acetylsalicylic acid.  This is the compound known commercially as aspirin.

42.  To make aspirin we could add a carboxylic acid and an alcohol.  This would form acetylsalicylic acid  However this is a slow reaction, with a low yield, as the water formed tends to drive the reaction backwards.

43.  In an alternative reaction pathway, which is faster and produces higher yields, the ethanoic acid is replaced with ethanoic anhydride (acetic anhydride).  This is the preferred pathway for aspirin synthesis

44.  The products, acetylsalicylic acid and acetic acid have to be separated and the product purified before it can be put into tablet form and packaged for sale.

45.  Although aspirin has a –COOH functional group, pure acetylsalicylic acid is not very soluble in water.  Converting the carboxylic acid functional group into the sodium salt changes the molecule into an ion and makes it much more soluble.  It is used in many headache and cold remedies in this form.

46.  A recent development is to make a polymer structure using a condensation reaction between salicylic acid and 1,8-octanedioic acid  Pretty much a polymer of aspirin which has a number of potential advantages: › It can be used as a controlled-release pain killer because the polymer breaks down slowly › Because it is a polymer with a similar molecular structure to polyesters it can be made into thread and used to stitch cuts or wounds together. › It has the potential to be used as a plastic coating for an injured bone or joint.

47.  Page 225  Question 1