Vanillin
| Vanillin has a soothing, pleasant aroma. Its molecular weight is relatively low, and it is fairly volatile. Cooking with vanilla vaporizes some of the vanillin molecules and fills the room with its aroma. Molecules containing only carbon and hydrogen are mostly insoluble in water. The oxygen-containing groups attached to the ring in vanillin can form strong hydrogen bonds with water, making it water soluble (about a gram of vanillin can be dissolved in 100 mL of cold water). Vanillin's solubility in water is responsible for the "finish" acquired by wines aged in oak casks. Vanilla present in the wood lignin of the wine barrels slowly leaches into the wine over time. |
Eugenol
| Although eugenol is practically insoluble in water, it freely mixes with fats and oils. Its fat solubility allows it to penetrate tissues and bind more tightly to the vanilloid receptor, which is believed to have a fatty side chain. The tail gives eugenol a stronger odor than vanillin has. More than one or two ground cloves overpower a pumpkin pie. Eugenol has a numbing, analgesic effect. It is used as a dental antiseptic (it's one component of that strange smell some dentist's offices have). Why is the molecule an antiseptic? Apparently the hydrocarbon tail in combination with the polar functional group on the ring make eugenol rather soap-like, and it can disrupt the cell membranes of bacteria the way soap disrupts a spot of grease. |  |
Zingerone
 | Zingerone puts the zing in ginger and is also a flavor ingredient in mustard oil. The hydrocarbon tail attached to its vanillin foundation ring doesn't lower the solubility of zingerone much because it contains a carbonyl group that can form strong hydrogen bonds with water molecules. Zingerone is sparingly soluble in water, but also freely soluble in fats and oils. The higher molecular weight of zingerone in combination with the polar side-chain carbonyl group makes zingerone molecules attract each other more strongly than eugenol and vanillin molecules do. As a result, zingerone is less volatile than either eugenol or vanillin. The odor of ginger isn't strong, but the hydrocarbon tail gives it a more intense flavor when it does come into contact with its receptor. |
In a dry 250 mL round-bottomed flask equipped with a magnetic stirring bar and a reflux condenser fitted with a calcium chloride guard tube, introduce guaiacol (31.1 g), 3-bromo-1-propene (31 g), anhydrous potassium carbonate (34.6 g), and dry 2-propanol (50 mL). Reflux the mixture for 8 h then bring it back to room temperature and add water (100 mL). Stir well until all the solids are dissolved and transfer the biphasic mixture into a separatory funnel. Separate the organic layer and extract twice the aqueous layer with diethyl ether (2 x 50 mL). Gather together the 3 organic phases and wash them twice with 10% aqueous sodium hydroxide (2 x 50 mL), then with water until pH is neutral. Dry the etheral solution over anhydrous potassium carbonate and remove the solvents on a rotary evaporator. Distill the residue under reduced pressure to obtain the pure intermediate as a pale yellow oil (b.p. 117-118 deg.C/19 mm Hg). Typical yield is 80%.
ortho-Eugenol
Place 30 g of the intermediate obtained from the previous step in a 100 mL round-bottomed flask equipped with a reflux condenser. Heat progressively (the reaction is slightly exothermic) until a steady reflux is achieved. Maintain the reflux for 1 h then cool down to room temperature and dilute the reaction mixture with diethyl ether (50 mL). Transfer the etheral solution into a separatory funnel and extract it thrice with 10% aqueous sodium hydroxide (3 x 50 mL). Gather together the 3 aqueous phases and slowly add 18% hydrochloric acid until pH 1. Extract thrice the acidic aqueous solution with diethyl ether (3 x 25 mL). Gather together the 3 organic phases, dry them with anhydrous sodium sulfate, and remove the solvents on a rotary evaporator. Distill the residue under reduced pressure to obtain pure ortho-eugenol (b.p. 123-125 deg.C/19 mm Hg). Typical yield is 72%.
Mix 5 drops of compound and 1 mL of dichloromethane into a small test tube. Add one drop of a 2% bromine solution in dichloromethane to the tube and observe the results. A positive test is indicated by the disappearance of the red-brown color of the bromine.
Ferric Chloride Test
Mix 5 drops of compound and 1 mL of methanol into a small test tube. Add one drop of neutral 1% iron(III) chloride solution in water, stopper, shake, and observe the results. A positive test is indicated by the formation of a highly colored solution, usually purple, blue, or green, although other colors are possible depending upon the identity of the substituents.
[2] K. L. Williamson, Macroscale and Microscale Organic Experiments, 2nd ed., D. C. Heath: Lexington (Massachusetts), 1994, 106-107.
[3] M. Chavanne, A. Jullien, G. J. Beaudoin, E. Flamand, Chimie organique expérimentale, Modulo: Mont-Royal (Québec), 1986, 751-756.
[4] B. S. Furniss, A. J. Hannaford, P. W. G. Smith, A. R. Tatchell, Vogel's Textbook of Practical Organic Chemistry, 5th ed., Longman: Harlow, 1989, 1213 and 1226.
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Prénom : ..........................
Sart-Tilman, le 9 novembre 2001
Sur base du schéma réactionnel et des modes opératoires ci-joints, répondez de façon brève, claire et précise aux questions suivantes.
Vos réponses doivent se trouver uniquement dans les espaces
prévus à cet effet, sur les faces recto des feuilles. Les faces
verso peuvent être utilisées comme brouillons.
Thème I. Nomenclature chimique:
1) Donnez le nom systématique du gaïacol. (1 point)
4) La réaction du gaïacol avec le 3-bromo-1-propène est-elle plus probablement de type SN1 ou SN2? Justifiez votre réponse. (3 points)
6) Dans la synthèse de l'intermédiaire, quel est le but des lavages avec la solution d'hydroxyde de sodium? (3 points)
11) Quel(s) groupement(s) fonctionnel(s) le test au brome permet-il de détecter? Justifiez votre réponse. (2 points)
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