Summary of Key Organic Chemistry Reactions Flashcards
Aldehydes with HCN/KCN
Reagents: HCN/KCN
Conditions: Carefully buffered at pH 9, room temperature, in a fume cupboard
Hydroxynitrile produced
Reduction of aldehydes
Reagents: LiAlH4 and dry ether (at 0°C) OR H2 and a platinum catalyst
Primary alcohol produced
Aldehydes with 2,4-DNPH
Orange precipitate of 2,4-dinitrophenylhydrazone produced
Aldehydes with K2Cr2O7^2- (potassium dichromate) and H^+ ions
Carboxylic acid produced, colour change from orange to green seen
Aldehydes with Fehling’s solution
Aldehyde is oxidised
Red precipitate of copper (I) oxide produced when aldehyde is warmed with Fehling’s solution
Aldehydes with Tollens’ reagent (ammoniacal silver nitrate)
Aldehyde is oxidised
Add a few drops of sodium hydroxide to silver nitrate solution then dissolving the precipitate in dilute ammonia
The silver is reduced to silver metal on warming with the aldehyde
Silver mirror seen on inside of test tube
Aldehydes with iodine and NaOH
Iodoform reaction
CHI3 and salt of a carboxylic acid produced
ONLY works with ethanal
Ketones with HCN/KCN at pH=9
Reagents: HCN/KCN
Conditions: Carefully buffered at pH 9, room temperature, in a fume cupboard
Hydroxynitrile produced
Reduction of ketones
Reagents: LiAlH4 and dry ether (at 0°C) OR H2 and a platinum catalyst
Secondary alcohol produced
Ketones with 2,4-DNPH
Orange precipitate of 2,4-dinitrophenylhydrazone produced
Ketones with K2Cr2O7^2- and H^+ ions
No reaction, solution stays orange, ketones cannot be oxidised
Ketones with Fehling’s solution
No change, ketones cannot be oxidised
Ketones with Tollens’ reagent
No change, ketones cannot be oxidised
Ketones with iodine and NaOH
Iodoform reaction
CHI3 and salt of carboxylic acid produced
ONLY works with methyl ketones
Halogenoalkanes with aqueous KOH
Nucleophilic substitution to form an alcohol, heat.
Halogenoalkanes with KCN
Heat under reflux with ethanol. Forms a nitrile by replacing halide ion
Halogenoalkanes with NH3 in ethanol
Heat in a high pressure, sealed apparatus. Forms a primary amine
Halogenoalkanes with ethanolic KOH
Heat under reflux. Elimination reaction to form an alkene, halide ion and water
Chlorination of alcohols
Vigorous reaction with PCl5 to produce a chloroalkane, POCl3 and HCl, which gives off steamy fumes when HCl is exposed to ammonia. Acts as a test for the hydroxyl group,
Bromination of alcohols
Heat under reflux with concentrated/50% sulfuric acid and KBr. 2 stage reaction to eventually form a bromoalkane and water (HBr and K2SO4 are formed from first reaction, HBr goes on to react with alcohol)
Iodination of alcohols
Heat under reflux with phosphorus and red iodine. 2 stages to eventually form iodoalkane and phosphoric acid (phosphorus (III) iodide made in situ in first reaction)
Oxidation of primary alcohols
Heat with potassium dichromate (VI) and dilute H2SO4
In a distillation apparatus, an aldehyde is formed.
In a reflux apparatus, a carboxylic acid is formed.
Both reactions have a colour change from orange (Cr^6+) to green (Cr^3+)
Oxidation of secondary alcohols
Heat under reflux with potassium dichromate (VI) and dilute H2SO4. A ketone is formed and an orange to green colour change is seen
Practical techniques: Heating under reflux
- The reflux apparatus is used to heat a reaction mixture safely for long periods of time
- It ensures that the reaction is complete
- Vapours condense in the condenser and fall back into the reaction vessel
- Ensure the apparatus is open (!!) or it may explode - important when drawing apparatus
Practical techniques: Solvent extraction using a separating funnel
- Ideal for use when product is more soluble in organic solvents but contains impurities that readily dissolve in water (like ionic compounds)
- Transfer your product to a separating funnel, add water and shake
- 2 layers will form, one organic and one aqueous, and the impurities will move into the organic layer where they are more soluble
- Open the tap of the separating funnel to remove the lower layer which will separate the purified product from the impurities.
- This method is not completely exact.
- As a general rule, water is more dense than organic solvents that do not form hydrogen bonds, so it will be the lower layer
Practical techniques: Distillation
- Can be used to separate mixtures of substances with different boiling temperatures
- When drawing apparatus, make sure thermometer is in the right place, water goes in at the bottom of the condenser (which is diagonal) and the apparatus cannot be sealed
- The temperature reading on the thermometer will match the boiling temperature of the substance being distilled at that time
Practical techniques: Drying with an anhydrous salt
- ‘Drying’ means removing water
- There will always be a small amount of water mixed with the product, especially if if you have carried out solvent extraction using water
- Add an anhydrous salt (e.g. anhydrous magnesium sulfate) shake, then leave to settle and filter off the solid
- The salt will absorb any water
Practical techniques: Boiling point determination
- Used to find out how pure a product is
- Boiling points of pure substances at atmospheric pressure have been accurately measure and are listed in data booklets
- Measuring the final product’s boiling temperature and comparing it with the data book’s value will let you know how pure the sample is
- Pure substances will boil at precise temperatures rather than over a range
Production of an alkane from an alkene
Heat at 150°C with hydrogen and a nickel catalyst
Thermal cracking
High temperature (up to 1000°C) and high pressure (up to 70 atm). Produces lots of alkenes
Catalytic cracking
Zeolite catalyst (hydrated aluminosilicate), slight pressure and high temperature (450°). Mainly produces aromatic hydrocarbons and motor fuels
Reforming straight chain alkanes
Converting straight chain alkanes into branched chain alkanes and cyclic hydrocarbons, using a catalyst like platinum stuck on aluminium oxide
Halogens with alkenes
Form dihalogenoalkanes, halogens add across the double bond. Decolourises bromine water
