Level 3: Organic Reactions Part I

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Level 3Organic Reactions Part I

• Aldehydes
• Ketones
• Haloalkanes
• Amines

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Aldehydes - Introduction

• Aldehydes are very similar to carboxylic acids in
  structure (but they are missing the OH)
• Their names have al as a suffix e.g. methanal,
  ethanal
• The smaller aldehydes are liquids (except for
  methanal a gas) because of their polar bonds
• The smaller molecules (below hexanal) are soluble
  in water
• Methanal is a gas that is dissolved in water to
  create a disinfectant, and to preserve biological
  specimens in jars

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Aldehydes - Production

• As we saw in the extension of level 2 organics
  section, aldehydes are made if you partially
  oxidise a primary alcohol
• This means that aldehydes can be oxidised further
  to create carboxylic acids
• Remember
• A thing that can be oxidised is called a reducing
  agent (because it reduces someone else)
• A thing that can be reduced is called an
  oxidising agent (because it can reduce someone
  else)
• Common oxidising agents (or oxidants) used to
  create aldehydes are
• Acidified dichromate (Cr2O72-/H)
• Acidified permanganate (MnO4-/H)

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Ketones - Introduction

• Ketones are very similar to aldehydes except the
  double bond is not at the end of a carbon chain
• Their names have one as a suffix e.g.
  propanone, butanone
• The smaller ketones are the same as aldehydes.
  They are liquids because of their polar bonding
• The smaller molecules (below hexanone) are
  soluble in water
• Ketones are good solvents and are often used for
  things like nail polish remover (propanone) or
  plastic model glue (butanone)

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Ketones - Production

• Ketones can be made by oxidising secondary
  alcohols
• Note Tertiary alcohols cannot be oxidised at
  all. The OH cant form double bonds with the
  carbon that it is attached to because that carbon
  is already bonded to three other carbons

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Aldehydes and Ketones The Tests

• Aldehydes can be oxidised a little further while
  ketones can not. This is the basis for the
  various tests for difference between these two
  chemicals
• Acidified permanganate/dichromate aldehydes
  will be oxidised and change the colour of these
  two chemicals. BUT the colour will also change if
  we have any primary or secondary alcohols present
  because they can be oxidised also
• Benedicts solution This blue solution (Cu2)
  turns red/orange (Cu2O) when boiled with
  aldehydes (but not with alcohols)
• Tollens (silver mirror) test This colourless
  (Ag(NH3)2) solution turns the test tube silver
  (Ag) when aldehydes are present

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Haloalkanes

• Can be classified as primary, secondary and
  tertiary just like alcohols.

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Haloalkanes

• Volatile, polar molecules but only slightly
  soluble in water as no hydrogen bonding can occur
  (except fluorocarbons)
• Melting points higher than alkanes
• Examples teflon non stick frying pans,
  chloroform CHCl3 used as a solvent and in
  movies as an anaesthetic, CCl4 solvent used in
  dry-cleaning fluid until it was found to cause
  liver damage

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Haloalkane preparation

• Prepared by
• substitution of an alcohol by thionyl chloride
• Addition of HX to an alkene
• Substitution of an alkane in UV light with a
  halogen eg Br2

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Haloalkane reactions

• Nucleophilic substitution A nucleophile is any
  species that loves nuclei or is attracted to a
  positive charge. Nucleophiles are species
  carrying a lone pair of electrons or a negative
  charge eg H2O, OH- or NH3
• The C-X bond is polar is haloalkanes and has a
  slightly positive charge. The positive carbon is
  vulnerable to attack by a nucleophile

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3 types of nucleophilic substitution reactions

1. OH-(aq) forms an alcohol with a primary or
   secondary haloalkane
2. H2O (l) forms an alcohol with a tertiary
   haloalkane
3. NH3(alc) forms an amine with a haloalkane. Note
   (alc) means dissolved in alcohol. Why not water?

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Chloroalkane elimination reactions

• Haloalkanes can form alkenes by reacting with
  KOH(alc) or NaOH (alc).
• Why alcoholic again solvent again?
• Reverse of Markovnikovs rule applies.

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Questions

• Write a balanced equation for the reaction of
  bromoethane with aqueous potassium hydroxide
• Write a balanced equation for the reaction
  between 2-iodobutane and alcoholic ammonia
• Write an equation for the reaction between
  2-methyl butan-2-ol and alcoholic potassium
  hydroxide.

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Properties of Esters

• Have pleasant fruity smells and occur naturally
  in plants. Used in manufacture of everyday items
  such as flavouring agents, perfumes.
• Have the general formula R-COOR.
• Polar molecules but no hydrogen bonding
• Colourless volatile liquids
• Insoluble in water

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• Naming Part that comes from the alcohol is an
  alkyl group, part from the acid is anoate on the
  end.
• Eg Ethanol and propanoic acid make ethyl
  propanoate

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Name the ester made from

• Propanoic acid and butanol
• Ethanoic acid and methanol
• Butanol and methanoic acid
• Decanol and hexanoic acid
• This one?

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Preparation of an ester

• Condensation reaction of a carboxylic acid with
  an alcohol, using concentrated sulfuric acid as a
  catalyst and dehydrating agent.
• Reaction carried out by reflux.

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Chemical Reactions

• Hydrolysis (split with water) with dilute acid to
  form the original acid and alcohol
• Hydrolysis with a basic solution eg NaOH to form
  the salt of the acid and the alcohol. Used in
  soap manufacture.
• React with ammonia or amines to form an amide
  (slow reaction)

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Making soap

• Soaps are the sodium salts of fatty acids (long
  chain acids). These salts are soluble in water as
  they are ionised, but they have a carbon chain
  end that is soluble in fats and oils. This allows
  them to dissolve and break down dirt.
• Sodium laurate is the name of the soap molecule
  made from coconut oil made by boiling it with
  sodium hydroxide.

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See page 97 for an example
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Amines - Introduction

• Amines are organic compounds that contain
  nitrogen in their structure (but no oxygen)
• There are three types of amines primary,
  secondary and tertiary. Unfortunately we use
  these words slightly differently than we do with
  alcohols
• Identify the trend
• Amines are bases (like ammonia) and smell like
  fish.
• Most amines liquids but aminomethane and
  aminoethane boil below 20ºC

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Amines Naming and Source

• We only look at primary amines this year. This
  makes life easier when it comes to things like
  naming and making amines
• The name of the primary amine comes from the
  length of the alkyl (alkane) chain attached to
  the NH2. For example, an amine with a propane
  chain attached is called aminopropane
  (CH3CH2CH2NH2)
• Primary amines are made using the nucleophilic
  substitution of haloalkanes (as we saw earlier)

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Amines - Reactions

• Neutralisation
• Because amines are bases they will neutralise
  acids to create salts (just like ammonia)
• Ionisation
• Amines dissolve in water to create ions (just
  like ammonia)
• Complex ion formation
• Amines will form complex ions with Cu2 (just
  like ammonia)

CH3CH2NH2 HCl CH3CH2NH3Cl
CH3CH2NH2 H2O CH3CH2NH3 OH-
4CH3CH2NH2 Cu2 Cu(CH3CH2NH3)2