Organic synthesis

Step Reason 1. Dissolve the impure compound in a minimum volume of hot (near boiling) solvent. An appropriate solvent is one which will dissolve both compound and impurities when hot and one in which the compound itself does not dissolve well when cold. The minimum volume is used to obtain saturated solution and to enable crystallisation on cooling 2. Hot filter solution through (fluted) filter paper quickly. This step will remove any insoluble impurities and heat will prevent crystals reforming during filtration 3. Cool the filtered solution by inserting beaker in ice Crystals will reform but soluble impurities will remain in solution form because they are present in small quantities so solution is not saturated. Ice will increase the yield of crystals 4. Suction filtrate with a buchner flask to separate out crystals The water pump connected to the Buchner flask reduces the pressure and speeds up the filtration. 5 Wash the crystals with distilled water To remove soluble impurities 6. Dry the crystals between absorbent paper Purifying an organic solid: Recrystallisation Loss of yield in this process • Crystals lost when filtering or washing • Some product stays in solution after recrystallisation • other side reactions occurring buchner flask. Used for purifying aspirin. f the sample is very pure then the melting point will be a sharp one, at the same value as quoted in data books. One way of testing for the degree of purity is to determine the melting “point”, or melting range, of the sample. Heat Heating oil- needs to have boiling point higher than samples melting point and low flammability Thermometer with capillary tube strapped to it containing sample Measuring melting point. Comparing an experimentally determined melting point value with one quoted in a data source will verify the degree of purity. Sometimes an error may occur if the temperature on the thermometer is not the same as the temperature in the actual sample tube. Melting point can be measured in an electronic melting point machine or by using a practical set up where the capillary tube is strapped to a thermometer immersed in some heating oil. In both cases a small amount of the salt is put into a capillary tube. If impurities are present (and this can include solvent from the recrystallisation process) the melting point will be lowered and the sample will melt over a range of several degrees Celsius. Thermometer with capillary tube strapped to it containing sample. Heating oil- needs to have boiling point higher than samples melting point and low flammability

Br2, Cl2 UV light Free radical Substitution amine alkane haloalkane alkene alcohol aldehyde ketone carboxylic acid dihaloalkane Br2, Cl2 room temp Electrophilic addition HBr ,HCl room temp Electrophilic addition If primary heat gently and distill partial oxidation If secondary heat under reflux oxidation Na2Cr2O7/H+ heat under reflux + excess oxidising agent Oxidation poly(alkene) high pressure Catalyst polymerization KOH aqueous heat under reflux Nucleophilic substitution H2, Nickel Catalyst addition/reduction NaBr/H2SO4 Heat under reflux substitution hydroxynitrile HCN + KCN Nucleophilic addition Acyl chloride ester Primary amide secondary amide H2O room temp Alcohol room temp NH3 room temp 1 o amine Alcohol + H2SO4 room temp heat esterification Esters and amides can be hydrolysed by NaOH and acids SOCl2 Acyl chloride room temp Nu add/elim 2 o amine 3 o amine haloalkane NuSub Na2Cr2O7/H+ NaBH4 Reduction NaBH4 Reduction nitrile Acid hydrolysis Heat with HCl H2O (g) Catalyst: Conc H3PO4 conc. H2SO4 or conc. H3PO4 Elimination, dehydration Caboxylic acid + H2SO4 heat esterification H2/nickel catalyst Reduction CN– and ethanol Nucleophilic substitution 6. Alcoholic NH3 heat under pressure Nucleophilic substitution. conc nitric acid + conc sulphuric acid Electrophilic substitution C O CH3 acyl chloride in the presence of anhydrous aluminium chloride catalyst Electrophilic substitution Sn and HCl NH2 reduction NH C O CH3 CH3COCl CH O CH3 H NaBH4 Red Nu Add NH CH3 CH3Cl Nu sub C O CH3 H CN NaCN + H2SO4 Nu Add A. Aromatic synthetic routes H3C CH O C O CH3 CH3CO2H + H2SO4 heat esterification N Goalby chemrevise.org Br Br2 FeBr3 Electrophilic substitution CH2CH3 chloroalkane and anhydrous AlC3 catalyst. Hydrogen Nickel catalyst