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Reaction of alkenes

Reaction of alkenes. More reactions of alkenes Objective: To know some more electrophilic reactions of alkenes Success criteria:

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Reaction of alkenes

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  1. Reaction of alkenes

  2. More reactions of alkenes Objective: To know some more electrophilic reactions of alkenes Success criteria: understand the addition reactions of alkenes with: hydrogen, in the presence of a nickel catalyst, to form an alkanehalogens to produce dihalogenoalkanessteam, in the presence of an acid catalyst, to produce alcoholspotassium manganate(VII), in acid conditions, to oxidise the double bond and produce a diol understand that heterolytic bond fission of a covalent bond results in the formation of ions understand the mechanism of the electrophilic addition reactions for the reaction of alkenes with halogens including using curly arrow notation and other given binary compounds

  3. Testing for alkenes The presence of unsaturation (a carbon–carbon double bond) can be detected using bromine water, a red/orange coloured solution of bromine. A few drops of bromine water are added to the test liquid and shaken. If a carbon–carbon double bond is present, the bromine adds across it and the solution turns colourless.

  4. Electrophilic Addition of Br2 to Ethene • The same mechanism with one small difference… • Br2 has an induced dipole. • Draw out the mechanism • Connect the stages with  just like an equation.

  5. Halgoens reacting with alkenes Halogens react with alkenes to form dihalogenalkanes

  6. Heterolytic Fission • In heterolytic fission the bond breaks unevenly • One of the bonded atoms receives both electrons from the bonded pair • Two different substances can be formed • E.g. A positively charged cation (X+) and negatively charged anion (Y-) X – Y  X+ + Y- The curly arrow shows the movement of an electron pair

  7. Halgoens reacting with alkenes Mechanism 1) The double bond repels the electrons in Br2 polarising Br - Br

  8. Halgoens reacting with alkenes Mechanism 2) Heterolytic (unequal) fission of Br2. The closer Br gives up the bonding electrons to the other Br and bonds to the C atom

  9. Halgoens reacting with alkenes Mechanism 3) You get a positiviely charged carbocation intermediate. The Br- now zooms over……

  10. Halgoens reacting with alkenes Mechanism 4) ….. And bonds to the other C atom, forming 1,2-dibromoethane

  11. Halgoens reacting with alkenes But-1-ene is an alkene. Alkenes contain at least one C=C double bond. • Describe how bromine water can be used to test for C=C double bonds. • Name and draw the mechanism for involved in the above test.

  12. More reactions of alkenes Objective: To know some more electrophilic reactions of alkenes Success criteria: understand the addition reactions of alkenes with: hydrogen, in the presence of a nickel catalyst, to form an alkanehalogens to produce dihalogenoalkanessteam, in the presence of an acid catalyst, to produce alcoholspotassium manganate(VII), in acid conditions, to oxidise the double bond and produce a diol understand that heterolytic bond fission of a covalent bond results in the formation of ions understand the mechanism of the electrophilic addition reactions for the reaction of alkenes with halogens including using curly arrow notation and other given binary compounds

  13. Alkenes reacting with hydrogen • Ethene will react with hydrogen gas in an addition reaction to produce ethane • It needs a nickel catalyst and a temperature of 150oC • Margarine is made by “hydrogenating” unsaturated vegetable oils • By removing some double bonds you raise the melting point of the oil so that it becomes solid at room temperature

  14. Alkenes reacting with hydrogen • Ethene will react with hydrogen gas in an addition reaction to produce ethene • It needs a nickel catalyst and a temperature of 150oC Ni H2C = CH2 + H2 CH3CH3 150oC

  15. Alkenes reacting with steam • Alkenes can be hydrated by steam at 300oC and a pressure of 60 – 70 atm • The reaction needs a solid phosphoric (V) acid catalyst • The reaction is used to manufacture ethanol from ethene • It is an electrophilic addition reaction and an example of a hydration reaction H3PO4 H2C = CH2 (g) + H2O (g)  CH3CH2OH (g) 300oC, 60 atm

  16. Alkenes reacting with steam Mechanism Can you suggest a mechanism?

  17. Alkenes reacting with acidified potassium manganate (VII) H2C = CH2 + [O] + H2O  CH2OH-CH2OH ethane-1,2-diol • If you shake an alkene with acidified potassium manganate (VII), the purple solution is decolourised (no change is observed with alkanes). • You’ve oxidised the alkene and made a diol (an alcohol with two –OH groups) • The oxidising agent is potassium manganate (VII), KMnO4, acidified with dilute H2SO4. • This is represented [O].

  18. Questions Write the equation, and name the organic product, for the reaction between but-2-ene and: Steam Acidified potassium manganate (VII)

  19. More reactions of alkenes Objective: To know some more electrophilic reactions of alkenes Success criteria: understand the addition reactions of alkenes with: hydrogen, in the presence of a nickel catalyst, to form an alkanehalogens to produce dihalogenoalkanessteam, in the presence of an acid catalyst, to produce alcoholspotassium manganate(VII), in acid conditions, to oxidise the double bond and produce a diol understand that heterolytic bond fission of a covalent bond results in the formation of ions understand the mechanism of the electrophilic addition reactions for the reaction of alkenes with halogens including using curly arrow notation and other given binary compounds

  20. Reactions of alkenes plenary What can you remember about the reactions of alkenes? Anything from the last two lessons

  21. More reactions of alkenes Objective: To know some more electrophilic reactions of alkenes Success criteria: understand the addition reactions of alkenes with: hydrogen, in the presence of a nickel catalyst, to form an alkanehalogens to produce dihalogenoalkanessteam, in the presence of an acid catalyst, to produce alcoholspotassium manganate(VII), in acid conditions, to oxidise the double bond and produce a diol understand that heterolytic bond fission of a covalent bond results in the formation of ions understand the mechanism of the electrophilic addition reactions for the reaction of alkenes with halogens including using curly arrow notation and other given binary compounds

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