Preparation of Quinoline using aniline, glycerol and iodine:
Yields in this prep are not as good as the one using nitrobenzene (50% vs ~80%)
Preparation of Quinoline
(Source: Vogel's Textbook of Practical Organic Chemistry, 4th ed.,pg. 910)
This preparation should be done in a fume cupboard.
1) CH2OH.CHOH.CH2OH __> CH2=CH.CHO
2) C6H5.NH2 + CH2=CH.CHO __> 'hydroquinoline' __> quinoline
Equip a 250ml three-necked flask with a double surface condenser, a sealed stirrer unit and a screw-capped adapter carrying a thermometer positioned so that subsequently the temperature of the reaction mixture may be noted. Place 10g (9.8ml, 107mmol) of pure aniline, 15g (163mmol) of glycerol (*) and 0.5g iodine in the flask. Stir the reaction mixture and add down the condenser from a dropping funnel 30g (16.4ml, 306mmol) of conc. sulphuric acid. Reaction soon commences, the temp. rises to 100-105°C. Heat the flask gradually, with stirring, in an air or oil bath to 140°C; the reaction proceeds with the evolution of SO2 and a little iodine vapour and the liquid refluxes. Continue heating at 170°C for 1 hr, allow to cool and then add cautiously with stirring sufficient 5 M NaOH soln (~ 85ml) to render the mixture alkaline. Rearrange the apparatus for steam distillation and steam distil until no more oily drops pass over. The distillate contains quinoline and a little aniline. Extract the distillate with 3x25ml portions of ether, combine the ethereal extracts and remove the ether on a rotary evaporator.
To remove the aniline present in the residual crude quinoline, advantage is taken of the fact that bis-quinolinium tetrachlorozincate(II) [(C9H8N)2+(ZnCl4)-2] is almost insoluble in water and crystallises out, whilst under the same experimental conditions, bis-anilinium tetrachlorozincate(II) [(C6H5.NH4)2+(ZnCl4)-2] remains in solution (**). Dissolve the crude quinoline in 100ml of dilute hydrochloric acid (1:4 by volume), warm the solution to 60°C and add, with stirring, a solution of 13g (95mmol) of zinc chloride in a 22ml portion of the diluted hydrochloric acid. Cool the well stirred mixture thoroughly in ice-water and, when crystallisation is complete, filter the bis-quinolinium tetrachlorozincate(II) with suction, wash with two 10ml portions of dilute hydrochloric acid and drain well. Transfer the solid to a 250ml beaker, add a little water and then 10% NaOH soln until the initial precipitate of zinc hydroxide dissolves completely. Extract the quinoline with 3x25ml portions of ether in a separatory funnel and dry the combined ethereal extracts with calcium sulphate. Remove the ether by flash distillation using a 10ml flask and finally distil the residue from an air bath using an air condenser. Collect the quinoline at 236-238°C as a colourless liquid: the yield is 6.9g (50%). If distilled under reduced pressure the b.p. is 118-120°C/20 mm Hg.
(*)Lab grade glycerol may be used since anhydrous glycerol is not necessary when iodine is used as the oxidising agent. Anhydrous glycerol may be prepared by heating commercial grade glycerol in a porcelain evaporating dish carfully over a wire guaze (preferably in a fume cupboard), stirring it steadily with a thermometer until the temperature rises to 180°C, allowing it to cool to about 100°C, pouring it into a pyrex beaker and transferring the beaker to a dessicator containing conc. sulphuric acid. It must be remembered that glycerol is a very hygroscopic substance.
(**)An alternative method of removing aniline is to add 8ml of conc. sulphuric acid carefully to the steam distillate, cool the soln to 0-5°C and add a concentrated soln of sodium nitrite until a drop of the reaction mixture colours potassium iodide-starch paper a deep blue instantly. As the diazotisation approaches completion, the reaction becomes slow; it will therefore be necessary to test for the excess of nitrous acid after an interval of five minutes, stirring all the while. About 3g of sodium nitrite are usually required.
The diazotised soln is then heated on a boiling water bath for an hour (or until active evlution of N2 ceases), treated with a solution of 15g of NaOH in 50ml water, the mixture steam-distilled and the quinoline isolated from the distillate by extraction with ether as above.
