C.10. Organic Reactions

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  • Created by: sana.aaa
  • Created on: 18-01-18 16:45

Reactions of the Alkenes.

  • organic molecules all contain carbon atoms
  • the C=C grouping is an example of a FUNCTIONAL GROUP. A  functional group gives a "family" of organic compounds their characteristic reactions.
  • a family of organic compounds with the same functional group is called a HOMOLOGOUS SERIES. e.g the homologous series of alkenes are (methene, ethene, propene, and butene).
  • The general formula for alkenes is C(n)H(2n)
  • You can test the ethene gas using a lighted spill
  • alkenes do burn but with a smokier, yellow (luminous) flame compared with alkanes because there is incomplete combustion.
  • they also release less energy per mole in combustion than alkanes.
  • during complete combustion you get (ethene+oxygen-----> carbon dioxide +water)
  • the C=C double bond makes the alkenes more reactive than alkanes.
  • when you test ETHENE with bromine water, it reacts. Ethene takes the orange colour out of the mixture and leaves it colourless. The orange colour in bromine water comes from Br2 (aq) molecules, which are converted into a colourless product called DIBROMOETHANE when they react with ethene.
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Reactions with Hydrogens :

  • the alkenes are unsaturated compounds, because of the C=C bond, their molecules do not contain the maximum number of hydrogen atoms possible in a hydrocarbon molecule.
  • But the addition of a hydrogen molecule, H2, across the double bond with form a saturated hydrocarbon- an alkane.
  • the reaction takes place at 60*C in the presence of a nickel catalyst.
  • for example, pentene (C5H10) + hydrogen (H2)---> pentane (C5H12)
  • this reaction is used to add hydrogen across the C=C bonds in unsaturated oils to straighten their molecules
  • and it is also used so that the melting points are increased.
  • for example, the right amount of hydrogen is added to make a margarine that can be spread easily straight from the fridge.
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Reactions with Water (steam) :

  • ethanol (an alcohol) for industrial use as a fuel or solvent can be made from ethene gas.
  • ethene is the main by-product produce by cracking. ethene gas can react with steam to make ethanol. These reactions require energy to heat the gases and to generate a high pressure. The reaction is reversible, so ethanol can break down back into ethene and steam. So unreacted ethene and steam are recycled over the catalyst.
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Structures of Alcohols :

  • remove an H atom from an alkane molecule and replacing it with an -OH group, this would be an ALCOHOL molecule.
  • the -OH group of atoms is another example of a FUNCTIONAL GROUP.
  • for ethanol, a chemist will often show its formula as - CH3CH2OH (instead of C2H5OH).
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Structure of Carboxylic Acids :

  • ethanoic acid is the main acid in vinegar.
  • All carboxylic acids contain the -COOH functional group.
  • methanoic acid - HCOOH
  • ethanoic acid - CH3COOH
  • propanoic acid- CH3CH2COOH
  • butanoic acid- C3H7COOH
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Structure of Esters :

  • esters are closely related to carboxylic acids.
  • if you replace the H atom in the -COOH group by a hydrocarbon (alkyl) group, such as -CH3 or -C2H5, you get an ester.
  • an ester's structural formula always contain the -COO- functional group.
  • the structural formula of ethyl ethanoate is CH3COOCH2CH3
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Uses of Alcohols :

  • alcohols, especially ethanol, are commonly used in everyday products.
  • ethanol is the main alcohol in alcoholic drinks.
  • it is made by fermenting sugars from plant material with yeast and is becoming an important alternative fuel to petrol and diesel.
  • ethanol made by fermentation is termed a biofuel.
  • Ethanol can also be made in an industry from reacting ethene and steam in the presence of a catalyst
  • this method uses up some of the diminishing supplies of crude oil, a non- renewable source.
  • alcohols dissolve many of the same substances as water
  • the alcohols with smaller molecules mix very well with water, giving neutral solutions.
  • the alcohols can also dissolve many other organic compounds
  • this property makes them useful as solvents. for example, you can remove ink stains from permanent marker pens using methylated spirits
  • methylated spirits is mainly ethanol, but has the more toxic methanol mixed with it, it also has a purple dye.
  • alcohols are also used as solvents in products such as perfume, mouthwashes, and aftershaves. 
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Reactions of alcohols : Combustion :

  • the use of ethanol as fuels shows that the alcohols are flammable.
  • ethanol is used in spirit burners, and can be used as biofuels in cars
  • it burns with a 'clean' blue flame, (ethanol + oxygen --> carbon dioxide +water(c2h5oh + 3o2---> 2co2 +3h2o))
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Reaction with Sodium :

  • the alcohols react in a similar way to water when sodium metal is added, with ethanol the sodium effervesces (gives off bubbles of gas), producing hydrogen gas. it gets smaller and smaller as if forms a solution of sodium ethoxide in the ethanol. their reactions are not as vigorous as the reactions you observe between sodium and water. (sodium +ethanol ---> soidum ethoxide +hydrogen(2na + 2c2h5oh ---> 2c2h5oNa +h2))
  • if sodium ethoxide or any sodium alkoxide, is dissolved in water, you get a strongly alkaline solution.
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Reactions of Alcohols : Oxidation :

  • combustion is one way to oxidise an alcohol
  • an alcohol is oxidised to a carboxylic acid when boiled with acidified potassium dichromate (VI) solution, so ethanol can be oxidised to an ethanoic acid:
    • ethanol + oxygen atoms from oxidising agent --> ethanoic acid +water
    • c2h5OH +2o---> ch3cooh+ h2o
  • the same reaction takes place if ethanol is left exposed to air, microbes in the air produce ethanoic acid from the ethanol. that is why a bottle of beer or wine taste like vinegar when they are left open for too long. 
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Carboxylic Acids and Esters:

  • carboxylic acids, form acidic solutions when they dissolve in water.
  • carboxylic acids have their typical reactions of all acids
  • reactions with a metal carbonate forms a salt, water and carbon dioxide.
  • carbon dioxide gas is given off more slowly when a metal carbonate reacts with a carboxylic acid, as compared with hydrochloric acid of the same concentration
  • that is because the carboxylic acids are weak acids, as opposed to STRONG acids, such as sulfuric acid or hydrochloric acids.
  • in water all acids ionise(split up), their molecules split up to form h+ (aq) ions and negative ins (such as the ethanoate ions, ch3COOH- (aq) from the ethanoic)
  • strong acids ionise completely, whereas weak acids do not, in carboxylic acids, most of the molecules stay as they are, and only a small proportion will ionise in their solutions.
  • a reversible reaction takes place
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Making Esters :

  • carboxylic acids also react with alcohols to make esters
  • water is also formed in this reversible reaction
  • an acid, usually sulfuric acid, is used as a catalyst.
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