Organic Preparations

Preparation of Ethene

Unsaturated: Decolourises Bromine water ⇒product 1,2 dibromoethane Aluminium Oxide White powder. Dehydrating Agent. Glass Wool holds Ethanol. Safety: Remove delivery tube when heating stopped to prevent suck-back. Burns with a luminous flame. Unsaturated: Decolourises Bromine water ⇒product 1,2 dibromoethane www.pdst.ie Ripening Fruit, Manufacture of Polymers

Ethene C2H4 Carbon atoms are planar

Preparation of Ethyne CaC2 + 2H2O → Ca(OH)2 + C2H2 Calcium Dicarbide: Grey lumpy solid Ca(OH)2 is a white solid. Acidified Copper Sulfate (CuSO4): removes phosphine and hydrogen sulphide. Burns with a Yellow Smokey Flame C2H2 + 2½ O2 → 2CO2 + H2O Unsaturation: Decolourises Bromine Water C2H2 + 2Br2 C2H2Br4 Oxyacetylene torch, cutting and welding Safety: gas flammable/no naked flame.

Preparation of Ethyne

Ethyne C2H2

Preparation of Benzoic Acid 3C6H5CH2OH + 4KMnO4 → 3C6H5COOH + 4MnO2 + H2O + 4KOH Flask: KMnO4 + Phenylmethanol(colourless liq.) + Na2CO3 The KMnO4 is saturated to ensure complete oxidation. The sodium carbonate ensures the solution is alkaline; Mn+7 (purple) → Mn+4 (brown) → Mn +2 (colourless) Benzaldehyde forms first then sodium benzoate. Conc. HCl is added in fume hood: convert sodium benzoate to benzoic acid to neutralise the excess sodium carbonate added and potassium hydroxide produced to provide an acidic medium to enable sodium sulphite to reduce Mn4+ to Mn2+.

C6H5COOH

3C6H5CH2OH + 4KMnO4 → 3C6H5COOH + 4MnO2 + H2O + 4KOH Sodium sulphite is a reducing agent and reduces Mn4+ to Mn2+ in acid conditions The brown MnO2 would contaminate the benzoic acid Flask placed in ice to accelerate crystallisation of acid. Benzoic acid is isolated by vacuum filtration. Crystals washed with ice water. Damp crystals placed in desiccator to dry. Phenylmethanol Mr=108 Benzoic acid Mr=122 Food Preservative/Antiseptic.

Sample: Benzoic acid + NaCl (Soluble) + charcoal (Insoluble) Dissolve in a Min. of hot water (ensures a better yield) Hot filter removes Charcoal on filter paper. Benzoic acid and sodium chloride in filtrate. Evaporate until crystals begin to form. Cool in ice: NaCl soluble in cold water. Benzoic acid crystals form in cold water. Vacuum filtration collects benzoic acid Wash with ice water NaCl in filtrate. Damp crystals placed in desiccator to dry.

Melting Point Determination of Benzoic acid

Melting Point Determination of Benzoic acid Observe the melting point range of the crystals. i.e the temperature at which liquid first appears and the temperature at which no solid remains. Melting point range of an impure substance is lower and broader than that recorded for a pure sample of the same substance. Impure sample melting points 115 –118 0C (bigger range less sharp) Pure sample 120 – 121 0C (smaller range, sharp)

Preparation of Soap (I)

Preparation of Soap (I) Flask contents: Oil (lard) + Ethanol + NaOH + antibumping granules. Ethanol is solvent for oil and sodium hydroxide Granules for smooth boiling. Reaction: Substitution. Base hydrolysis of ester (animal fat (lard) or vegetable oil) Reflux: evaporation followed by condensation. Ensures complete reaction between oil and sodium hydroxide and prevents any loss of reactants or products. KOH more soluble in ethanol than NaOH (need some water)

Preparation of Soap (II)

Preparation of Soap (II) Ethanol removed by distillation as it keeps soap in solution. Dissolve residue in flask with some hot water. Brine (NaCl) used to precipitate soap. Brine will contain ethanol, glycerol, sodium hydroxide and water at the end. Collect soap by vacuum filtration and wash with a little cold water or brine to remove NaOH. Dry in desiccator

Extraction of Clove oil (I) Eugenol

Extraction of Clove oil (I) The bottom of the safety tube should be well below the water surface in the steam generator, but not touching the bottom of the flask. Disconnect steam generator when heating stopped to prevent suckback. This method allows extraction of oil at a lower temperature than heating directly. Heating directly can cause decomposition or charring. Whole cloves have more oil than ground cloves. Cloudy milky emulsion (water + Eugenol)

Solvent Extraction of Clove oil

Solvent Extraction of Clove oil Solvent used is Cyclohexane Shake mixture and open tap to release any pressure built up. Open tap and collect aqueous layer Pour organic layer out through top of funnel. Add more cyclohexane to water layer and repeat procedure. Place all organic liquid in a flask and add a dehydrating agent. Anhydrous Magnesium Sulfate is drying agent. Forms clumps, Filter to remove salt and wash with a little cyclohexane Leave mixture in fume hood overnight to evaporate cyclohexane.

Paper Chromatography.

Paper Chromatography. Apply mixture using dropper (capillary tube) or spot on paper slightly above solvent Solvent moves up separating components. Different components of a mixture have different interactions with the stationary and mobile phases.

ORGANIC PREPARATIONS Preparation of Ethyne Extraction of Clove Oil Recrystallisation and Melting Point of Benzoic acid Preparation of Ethene Preparation of Soap Preparation of Benzoic Acid Paper Chromatography

Aldehydes v Ketones Test Aldehyde Ketone Mix Fehlings 1 and 2 Add aldehyde/ketone Heat gently. Blue to red precipitate of copper (I) oxide No reaction Add aldehyde/ketone to Tollens reagent in clean test tube Heat gently Silver mirror forms Add aldehyde/ketone to acidified potassium dichromate Orange solution turns green

Alcohol to Aldehyde to Acid Colour Change Cr2O72 – Cr3+ Orange Green

Reactions of Acids Reactions of Carboxylic Acids CH3COOH + Na2CO3 ➞ 2CH3COONa + CO2 + H2O CH3COOH + NaOH → CH3COONa + H2O 2CH3COOH + Mg ➞ (CH3COO)2Mg + H2 CH3COOH + CH3OH ➞ CH3COOC2H5 + H2O Turns universal indicator red

The End