Examples of Organic Halides 2,3-dichloro-2,3-difluoro-1,1-diiodobutane H Cl Cl I I I I I H - C - C - C - C - I I I I I H F F H

Ozone Depletion An environmental concern has been raised by this type of reaction, which ends up producing products known as chlorofluorocarbons (CFC’s). These molecules have been used widely in foam products, as aerosol propellants and refrigerator/air conditioning coolants. Their use has been banned in the last 10 years or so but they are still present in many older refrigerators and AC units. Proper disposal of these appliances is essential to prevent further release of CFC’s.

CFC’s react in the atmosphere to destroy ozone molecules. As a result of this destruction, deadly UV radiation passes through our atmosphere and causes skin cancer. CFC’s have also been identified as a greenhouse gas and are so contributing to global warming.

Answers to Activity 1.bromobenzene 2.chloroethane 3.3-chlorobut-1-ene 4.1,4-dichlorobenzene (p-dichlorobenzene)

Organic Halide Reactions Halocarbons are chemically reactive. They are involved in a number of different reactions such as addition, substitution and elimination. We will look at elimination reactions after looking at alcohols.

Addition Reactions These occur when a substance is added to double or triple bonds in alkenes or alkynes, since these bonds are reactive. Addition reactions add a new functional group to a compound.

Addition When water is added, this is called a hydration reaction. This can occur when an alkene and water are heated to 100 o C in the presence of a trace amount of a catalyst, such as nickel metal. H OH Ni I I H - C = C – H + HOH (l)  H - C - C - H I I I I H H ethene + water ethanol

Test for Unsaturation The addition of bromine to the carbon- carbon double or triple bonds is often used as a test for unsaturated organic molecules. Bromine has a brownish-orange colour. The loss of this colour when bromine is added to an organic compound is a positive test for unsaturation. Although benzene has double bonds, it is stable and does not give a positive test for unsaturation with bromine.

Example-Reaction 1 Br Pt I H - C ≡ C - H + Br 2(l)  H - C = C - H I Br ethyne+ bromine 1,2 - dibromoethene The addition of halogens to alkynes results in alkenes or alkanes.

Example-Reaction 2 Br Br Br l Pt I I H - C = C - H + Br 2(l)  H - C - C - H I I I Br Br Br 1,2-dibromoethene + bromine  1,1,2,2 -tetrabromoethane Since addition reactions are very fast, the alkene produced, can undergo a second addition reaction.

Substitution Reactions Under the right conditions alkanes will undergo chemical reactions with halogens, such as chlorine: UV light Eg: CH 4 (g) + Cl 2 (g)  CH 3 Cl (g) + HCl (g) chloromethane Note that in situations such as this, ultraviolet light (UV light) is included as a catalyst.

Substitution Reactions A chemical reaction in which an atom or a group of atoms replace another atom or group of atoms is called a substitution reaction. In these reactions, the product of the previous reaction is reacted with chlorine again. We continue this process to end up with products such as chlorinated solvents, paint removers and degreasing agent.

Substitution Reactions This involves the replacement of an atom or group of atoms by another atom or group of atoms. For example: a halogen substituting hydrogen on an alkane to give a halocarbon: H H Cl H I I UV I I H - C - C - H + Cl 2(g)  H - C - C - H + HCl (g) I I I I H H H H ethane + chlorine chloroethane

Substitution Example 2: This reaction is so slow that it requires both light and a catalyst.

Substitution Example 3: Alcohols may be produced by the substitution of a halogen by hydroxide ions: water & heat CH 3 CH 2 Cl (l) + NaOH (s)  CH 3 CH 2 OH (l) + NaCl (aq) chloroethaneethanol

Activity Section 10.2 Questions 2-5 & 7.