Chapter 28 Further Practical Techniques

Buchner Flask and Funnel Pressure tubing Vacuum pump (tap) Filter Paper

High temperatures allow solutes to dissolve more easily

They lower the melting point of the substance The compound will melt over a range

Both the impurities and compound dissolve in the hot solvent As the solution cools, the solubility of the compound decreases until it becomes solid The impurities will stay dissolved in the cool solution, leaving behind purer crystals when filtered.

To ensure the solution is saturated thus allowing crystals to form (too dilute and they cannot form)

So the yield does not decrease, decreases when warm Crystals will form too quickly if straight to ice Impurities will still remain trapped within the crystals, and small crystals will form

This removes any soluble impurities that may remain

Scratch the surface with a glass rod to start the process

Air passes through the sample and not just around it, so better drying

Melting point- if pure, distinct sharp melting point at data value, impure melts over a lower range Spectroscopy- Run NMR/IR, if pure, peaks will match, no other peaks TLC- Check the Rf value, if pure, will be similar to the data book

Alkylation - react a haloalkane with a halogen carrier Acylation- react an acyl chloride with a halogen carrier

React with KCN/H2SO4, forms HCN in situ Forms a Cyanohydrin/Hydroxynitrile via nucleophilic addition For acyl chlorides addition elimination

NaCN in ethanol solvent Forms a nitrile and NaX Nucleophilic substitution

React with H2 in the presence of a nickel catalyst R- C///N + 2H2 —/ R-CH2NH2 Or reduction with LiAlH4

React with aqueous Hydrochloric acid, and heat R- C///N + 2H2O + HCl —/ R-COOH + NH4Cl

Mg + Haloalkane —/ R-MgBr Very reactive, needs a nitrogen environment

First add a Br via UV and Br2 Then in situ, react with Mg and CO2 Grignards reagent formed, nucleophilic addition to the O=C=O New step, Protonate with an acid

If hot, allow the solid to cool Filter under reduced pressure and let dry Heat up the chosen solvent Add the minimum amount of hot solvent to the solid to allow it to dissolve fully Allow to cool to room temperature, then using an ice bath until crystals form Filter under reduced pressure again Run with cool solvent Allow to air dry Check purity by comparing melting point to a data base or TLC and recrystallise if necessary

Heat up the solvent Add the minimum amount to the solid to allow it to fully dissolve Cool to room temperature then with an ice bath. If crystals do not reform, scratch with a glass rod. Filter under reduced pressure. Wash with cold solvent Allow to dry

Nitration with HNO3/H2SO4 Reduction with SN/HCl then NaOH React with HCl/NaNO2 to form diazonium salt NH2 a good ortho/para director, and can be removed at the end

React with CuX to replace with a halogen React with H3PO2 for replace with hydrogen React with H2SO4/H2O to replace with O-H

Run TLC, compare the Rf value of the sample to the database, pure will have a very similar Rf. Also no other spots e.g starting material or catalyst Run NMR/IR, compare to a spectral database, and the pure sample will contain the same peaks as the database

Take a small amount of solid and place into a capillary tube Tap/flick the capillary tube so the solid falls to the bottom Place into the melting point apparatus and heat, observe the temperature when the solid melts Take out the machine to allow the liquid to solidify, repeat, taking care close to the recorded melting points