Read ChemII_Comp_Report_Expt4_Sem1.PDF text version

Your name here Experiment 4 ­ Isolation of Natural Products Extended Report Abstract Eugenol (1) was isolated from cloves by extraction in a 5 % recovery and was converted to its benzoate derivative (4) in a 73 % yield. Caffeine (2) (50 mg) was recovered from two tea bags. Introduction Natural product chemistry is an important area of research in Organic Chemistry. Compounds obtained from natural sources have been found to have a wide range of properties from anti-cancer activity to local anaesthetics and a multitude of uses from flavourings to dyes.1 The aim of this experiment is to isolate two relatively abundant natural products; eugenol (1), which is the major component in clove oil and caffeine (2), which is found in tea, coffee and cola nuts.2 Clove oil is a mild local anaesthetic, and was previously used by dentists to relieve toothache by dabbing a small amount onto the sore tooth. Eugenol is also a source for the commercial preparation of the flavouring vanillin (3).2 Caffeine is valued for its stimulant properties, and is a well-known additive to soft drinks.

O OCH3 H2C CH CH2 (1) OH H3C O N N CH3 (2) CH3 N N CHO (3) OH OCH3

Eugenol is a liquid, so to aid in its identification it will be converted to the benzoate derivative (4) following the pathway outlined in Scheme 1.

OCH3 1. NaOH / H 2O R OH 2. (1) R = CH 2CH=CH 2 O Cl R O O (4) R = CH2CH=CH 2 Scheme 1 OCH3

Crystalline derivatives such as (4) are of great use in helping to identify a compound, as solids are much more easily purified and characterised than liquids. The preparation of esters using the method shown in Scheme 1 is a widely applicable reaction.3 The hydroxyl group of eugenol is deprotonated by sodium hydroxide and the resulting phenolate ion Extended Report 1

Your name here "attacks" the carbonyl group of the acid chloride. This gives a tetrahedral intermediate that collapses to form the ester by eliminating a chloride ion. Results and Discussion Part 1: Eugenol (1g, 5 % recovery) was isolated from 20 g of cloves. The recovery was slightly lower than expected due to spillage. Eugenol showed the expected absorptions in its infrared spectrum for phenol OH, C=C alkene and C=C aromatic functional groups. The IR spectrum of eugenol also showed a signal for a carbonyl group at approximately 1760 cm-1 . This signal is due to the presence of acetyleugenol, a common impurity in eugenol, in which the phenol oxygen of eugenol has been acetylated. The eugenol obtained gave a positive test for the presence of a phenol group with ferric chloride solution, giving a blue-green colour. This result is consistent with the presence in the IR spectrum of a phenol OH signal. Eugenol benzoate (0.6 g) was obtained as white needles in a 73 % yield, mp 66-67ºC (lit.4 70ºC). An IR of the product confirmed its structure, showing absorptions for a carbonyl C=O, alkene C=C and C=C aromatic groups. The slight lowering of the melting point is probably due to residual solvent from recrystallisation. The absence of a phenol OHsignal in the infrared spectrum was noted as an indication of the successful conversion of the eugenol to the benzoate ester. Mechanism of formation of eugenol benzoate (4):

Extended Report 2

Your name here

OCH3 H2C CH CH2 O H OH

OCH3 H 2C CH CH2 O

Cl

O

OCH3 H 2C CH CH2 O O (4)

Part 2:

OCH3 Cl H2C CH CH2 O O

Two tea bags yielded 50 mg of caffeine as fine cream-coloured needles, mp 230-231ºC (lit.5 234-236ºC). The IR of caffeine showed the signals expected of the functional groups present at 1720 (C=O), 1700 (C=O), 1660 (C=N) and 1505 cm-1 (C=C). The melting point of the isolated caffeine was a few degrees below the literature value; this could be due to the presence of ethanol (used as a recrystallisation solvent) in the crystals. The presence of ethanol as an impurity is supported by the fact that the IR spectrum also showed a broad signal at ~3600 cm-1 , indicative of an alcohol ­OH group. Since caffeine does not contain an OH group, it must be present as an impurity. Experimental Part 1: Isolation of Eugenol (1): Crushed cloves (20 g) were placed in a 250 ml conical flask and dichloromethane (70 ml) and a few boiling chips were added. This mixture was boiled gently on a steam bath for 20 minutes. The resulting solution was filtered through a 2 cm pad of Celite; the solid residue was rinsed with dichloromethane (3x20 ml) with the rinsings also filtered. The solvent was carefully removed on the rotary evaporator using a warm water bath. Hexane (20 ml) was added to the residue and the resulting solution filtered to remove solid material. The hexane was removed under reduced pressure, again using a warm water bath, to give eugenol (1) (1 g, 5 % recovery) as a pale yellow oil. IR spectrum (neat liquid): 3500 (phenol OH), 1630 (C=C alkene), 1595 and 1500 cm-1 (C=C aromatic). Phenol test: eugenol (2 drops) was dissolved in ethanol (2 ml) in a test tube. Ferric chloride (2 drops) was added to this solution, giving a deep blue-green colour. Extended Report 3

Your name here Eugenol Benzoate (4): Eugenol (0.5 g, 3.05 mmol) was added to 10% aqueous sodium hydroxide (10 ml) in a 50 ml conical flask. After swirling the flask to dissolve the oil, benzoyl chloride (1 ml, 1.21 g, 8.59 mmol) was added in 0.5 ml portions with constant shaking. The flask was stoppered and the contents shaken for 5 minutes. The solid benzoyl derivative was collected by suction filtration and washed with cold water (5 ml). The crude product was recrystallised from ethanol to give eugenol benzoate (4) (0.6 g, 73%) as white needles, mp 66-67ºC (lit.4 70ºC). IR spectrum (nujol mull): 1735 (C=O), 1638 (C=C alkene), 1606 and 1509 cm-1 (C=C aromatic). Part 2: Isolation of Caffeine (2) from Tea Distilled water (40 ml) and two tea bags were placed in a 125 ml Erlenmeyer flask and brought gently to the boil. After 3 minutes, the flask was removed from the heat and the solution cooled by packing in ice. The cooled tea bags were squeezed to remove the remaining liquid and the resulting aqueous solution was extracted with dichloromethane (4 x 10 ml). The organic extracts were combined, dried over sodium sulphate and concentrated on the rotary evaporator until 5 ml of liquid remained. The residue was purified by column chromatography, using a slurry of 2 g silica gel in dichloromethane in a 1.9 cm i.d. column. The column was eluted with the following solvent mixtures: 5 ml each of 5%, 10%, 20% and 40% ethyl acetate/dichloromethane followed by pure ethyl acetate (6 x 5 ml). The contents of each tube were checked by TLC (3% methanol/ethyl acetate eluant) against an authentic sample of caffeine, with the caffeine-containing fractions combined and the solvent removed on a rotary evaporator. The crude product was recrystallised from ethanol to give caffeine (2) (50 mg) as cream-coloured needles, mp 230-231ºC (lit.5 234-236ºC). IR spectrum (nujol mull): 1720 (C=O), 1700 (C=O), 1660 (C=N) and 1505 cm-1 (C=C). Conclusions Eugenol and caffeine were isolated successfully from cloves and tea bags respectively, with reasonable recovery. The recovery of eugenol was reduced due to spillage. Eugenol was converted to a benzoate derivative, which confirmed the structure of the original compound. References 1. 2. 3. 4. 5. Bailey, P.S. and Bailey, C.A., Organic Chemistry (5th Ed.), Prentice-Hall Inc. (New Jersey, 1995). Organic Chemistry II Practical Manual, 2001. McMurrry, J., Organic Chemistry (5th Ed.), Brooks-Cole (California, 2000). Melting Point tables, Organic Chemistry II laboratory. Aldrich handbook of fine chemicals, 2000-2001.

Extended Report 4

Information

ChemII_Comp_Report_Expt4_Sem1.PDF

4 pages

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

431318