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LAB REPORT :

STEAM DISTILLATION AND AROMATIC ELECTROPHILIC SUBSTITUTION

INTRODUCTION :

The aims of this experiment were to separate a small quantity of ortho-vanillin from vanillin by steam distillation, to run a TLC to check the extent of that separation and to react vanillin with iodine to give a mono-iodo derivative in which one of the hydrogens of the ring had been replaced by iodine.

METHOD :

Steam distillation :

1,00 g (+/- 0,02 g) of vanillin and 1,00 g (+/- 0,02 g) of ortho-vanillin were placed into the same 250 mL round-bottomed flask, in which was poured approximately 100 mL of water. The steam distillation apparatus was assembled for distillation from this flask and half of the water was distilled.

During the distillation, an IR spectrum of vanillin in nujol was run (see results section).

When half of the water was distilled, the flask was stoppered and placed in an ice/water bath for 30 minutes. A small crystal of ortho-vanillin was then added to the chilled filtrate, which caused a solid to precipitate. The latter was filtered through a buchner funnel under suction at a waterpump.

The solid and the filter paper were removed from the funnel and placed on a Petri dish to air-dry for 30 minutes. However, after these 30 minutes, the solid still seemed very wet, it was therefore decided to leave it in a desiccator overnight.

The next morning, the crystals seemed dryer and had a weight of 0,20 g (+/- 0,005 g). Their melting point was also determined (see results section). The rest of the sample is attached to this lab report.

Thin layer chromatography :

A small amount of the solid obtained after the steam distillation, a small amount of vanillin and a small amount of a mixture of each were dissolved in 0,5 mL of dichloromethane in separate sample tubes. The three different solutions were applied to a thin layer chromatoplate and the chromatogram was run in the following solvent : Petroleum ether ; Ethyl acetate in the proportions 3 ; 1. The compounds were revealed by UV and the position of the spots was recorded (see results section).

Mono-iodination of vanillin :

The borate buffer was made by dissolving 2,14 g (+/- 0,005 g) of boric acid in a solution of 0,28 g (+/- 0,005) of sodium hydroxide in 5 mL of distilled water. However, as the solid were not completely dissolved when 90 mL of distilled water were added, a demonstrator recommended to heat the mixture on a hot plate.

Meanwhile, the iodinating mixture was prepared by adding 2,2 g (+/- 0,05 g) of potassium iodine and 1,8 g (+/- 0,05 g) iodine in 35 mL of distilled water.

When the borate buffer was homogeneous, the latter and the iodinating mixture were mixed in a 250 mL round-bottomed flask and to this mixture were added 0,53 g (+/- 0,05 g) of vanillin.

The resultant suspension was stirred for 35 minutes and then treated with 2 mL of 20% aqueous sodium bisulphite. It was left, lightly stoppered, at room temperature overnight.

The next morning, the solution was still a bit dark, so 5 mL of 20% aqueous sodium bisulphite were added to the solution which turned to a light cream color. The product was then filtered through a buchner funnel and washed with two portions of distilled water. Air was allowed to suck through the solid for one minute, and the filter paper and the cake of solid were placed on a Petri dish. The melting point of the product was then determined (see results section). Moreover, an infra-red spectrum of that product was also run. The rest of the sample is attached to this report.