Alcohols

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  • More about Alcohols
    • Alcohols are classified by counting how many other carbon atoms are bonded to the carbon that bears the -OH
    • Primary Alcohol
      • The carbon atom to which the -OH group is joined is joined to one other carbon atom
      • General Formula: RCH2OH
    • Secondary Alcohol
      • The carbon atom to which the -OH group is joined is attached to two other carbon atoms
      • General Formula: R2CHOH
    • Tertiary Alcohol
      • The carbon atom to which the -OH group is joined is also bonded to three other carbon atoms
      • General Formula: R3COH
    • Oxidation and Reduction
      • 'Oxidation involves the gain of one or more oxygen atoms and/or the loss of one or more hydrogen atoms'
        • The oxidising agent used to convert alcohols to other organic compounds is hot aqueous acidic potassium dichromate (K2Cr2O2)
        • The colour change when an alcohol is oxidised by K2Cr2O2 is orange to green. This is because while the alcohol is oxidised, the orange dichromate ions are reduced to green Cr3+ ions
        • A primary alcohol is oxidiesd in two stages;
          • It first loses two hydrogens to form an aldehyde (-CHO). They are named with the root name of the carbon skeleton and the ending -al
            • These reactions are performed by heating the alcohol briefly with aqueous acidic potassium dichromate
              • If heating is carried out for a long time, with excess oxidising agent, the aldehyde can be oxidised furthur to form a carboxylic acid
          • The oxidation of a primary alcohol can be controlled to obtain either an aldehyde or a carboxylic acid
            • Distillation
              • Method used to make aldehydes from primary alcohols. You boil the aldehyde as soon as it is formed and condense it elsewhere, away from the oxidising agent so furthur oxidation does not occur
            • Refluxing
              • Method used to make carboxylic acids from primary alcohols or ketones from secondary alcohols
                • Involves a continuous cycle of boiling, condensing and returning to the reaction flask
                  • It ensures that the reaction can continue for a long time with the oxidising agent while avoiding losing material through evaporation
                    • This helps ensure that you get a good product yield if the reaction is slow and the oxidation of a primary alcohol continues to make a carboxylic acid
                      • At the end of refluxing the product can be purified from the reaction mixture by distillation
        • Secondary alcohols are oxidised to ketones (RCOR) and are not oxidised any furthur
          • Ketones are named with the root name of the carbon skeleton and the ending -one
        • Tertiary alcohols are not oxidised by hot aqueous acidic potassium dichromate
      • 'Reduction involves the gain of one or more hydrogen atoms and/or the loss of one or more oxygen atoms'

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