Caffeine sublimation

The trimethylated xanthine, caffeine, sublimes at 1800°C, which is a lower temperature of sublimation than theobromine.10 Temperatures of melting and sublimation are given in Table 1. 

Cuffeine is extracted from tea dust and during coffee roasting, caffeine sublimes. Caffeine has above all a centrally stimulant (analeptic) effect on the cerebrum, produces tachycardia and has a diuretic effect. 

One advantage of sublimation is that no solvent is used, and therefore none needs to be removed later. Sublimation also removes occluded material, such as molecules of solvent, from the sublimed substance. For instance, caffeine (sublimes at 178°C, melts at 236°C) absorbs water gradually from the atmosphere to form a hydrate. During sublimation, this water is lost, and anhydrous caffeine is obtained. If too much solvent is present in a sample to be sublimed, however, instead of becoming lost, it condenses on the cooled surface and thus interferes with the sublimation. 

If your melting point apparatus uses capillary tubes to determine the melting point, an evacuated sealed tube is necessary, since caffeine sublimes the melting point is above the sublimation temperature (see Chapter 4). The melting point may be obtained using the Fisher-Johns apparatus without this precaution. 

Using The Merck Index or Handbook of Chemistry and Physics or a suitable site found on the web, look up the temperature at which caffeine sublimes at standard atmospheric pressure. 

C8H10N4O2. An alkaloid occurring in tea, coffee and guarana, from which it may be prepared by extraction, It is also manufactured by the methylation of theobromine and by the condensation of cyanoacetic acid with urea. Crystallizes with H2O or anhydrous from organic solvents. M.p. (anhydrous) 235"C, sublimes at 176 C. Odourless, and with a very bitter taste. Caffeine acts as a stimulant and diuretic, and is a constituent of cola drinks, tea and coffee. 

Caffeine (Theme), C8H10N4O2 + H20.—Colourless needles M.P. 234° sparingly soluble in cold water and in alcohol, readily soluble in chloroform sublimes unchanged. 

Caffeine (melting point 238°C, sublimes at 178°C density 1.23), theobromine, and theophylline are xanthine derivatives classified as central nervous stimulants, but differing markedly in their properties. They can be extracted from a number of natural sources. 

Sublimation. This involves heating a solid until it passes directly from the solid phase into the gaseous phase. The reverse process, when the vapor goes back to the solid phase without a liquid state in between, is called condensation or deposition. Some solids which sublime are iodine, caffeine, and paradichlorobenzene (mothballs). 

Sublimation is a process that involves the direct conversion of a solid to a gas without passing through the liquid state. Relatively few solids do this at atmospheric pressure. Some examples are the solid compounds naphthalene (mothballs), caffeine, iodine, and solid carbon dioxide (commercial Dry Ice). Water, on the other hand, sublimes at — 10°C and at 0.001 atm. Sublimation temperatures are not as easily obtained as melting points or boiling points. 

Caffeine forms white hexagonal crystals by sublimation. Caffeine has a melting point of 238 Celsius, but the crystals begin to sublime when heated to 178 Celsius. Caffeine is only moderately soluble in water, but more soluble in hot water. The crystals are also moderately soluble in alcohol, acetone, but are much more soluble in methylene chloride, chloroform, and practically insoluble in ether. Caffeine is capable of forming a hydrate, which looses it water of hydration when heated to 80 Celsius. Caffeine is a widely used stimulant, ingested by millions in the form of coffee, tea, ect.,... 

Silky white crystals, usually matted together, or a white crystalline powder. It sublimes at about 180°. M.p. 234° to 239°. When crystallised from water, caffeine contains 1 molecule of water of crystallisation, but it is anhydrous when crystallised from ethanol, chloroform, or ether. It is decomposed by strong solutions of caustic alkalis. 

Sublimation is a fast and easy way to purify caffeine. Using the apparatus depicted in Fig. 13 in Chapter 7, sublime the crude caffeine at atmospheric pressure following the procedure in Part 2 of Chapter 7. 

One way to confirm the identity of an organic compound is to prepcne a derivative of it. Caffeine melts and sublimes at 238°C. It is an organic base and can therefore accept a proton from an acid to form a salt. The salt formed when caffeine combines with hydrochloric acid, like many amine salts, does not have a sharp melting point it simply decomposes when heated. But the salt formed from scilicyclic acid, even though ionic, has a sharp melting point and can thus be used to help characterize caffeine. 

To 50 mg of sublimed caffeine in a tared test tube add 38 mg of scilicyclic acid and 2.5 mL of dichloromethane. Heat the mixture to boiling and add petroleum ether (a poor solvent for the product) dropwise until the mixture just turns cloudy, indicating the solution is saturated. If too much petroleum ether is added then clarify it by adding a very small quantity of dichloromethane. Insulate the tube in order to allow it to cool slowly to room temperature, and then cool it in ice. The needle-like crystcils are isolated by removing the solvent while the reaction tube is in the ice bath. Evaporate the last traces of solvent under vacuum and determine the weight of the derivative and its melting point. Caffeine salicylate is reported to melt at 137°C. 

The caffeine can be purified by sublimation as has been done in the experiment in which it was extracted from tea (Fig. 2) or it can be purified by crystallization. Recrystallize the caffeine by dissolving it in the minimum quantity of 30% ethanol in tetrahydrofuran. It can also be crystallized by dissolving the product in a minimum quantity of hot toluene or acetone and adding to this solution ligroin (hexanes) until the solution is cloudy while at the boiling point. In any case allow the solution to cool slowly to room temperature, then cool the mixture in ice, and remove the solvent from the crystals with a Pasteur pipette. Remove the remainder of the solvent under aspirator vacuum, and determine the weight of the caffeine and its melting point. 

The fruit is, when ripe, a red drupe containing white seeds, the seed coat of which has a thin parchment-hke membrane, which is called silver membrane. The seed consists mainly of endosperm. The coffee-bean consists of the peeled seed, which is roasted at a temperature of 200-250°C, when the caffeine is partly sublimated, and the aromatic substances are formed. 

The separation of caffeine from coffee by entrainer sublimation... 

Your instructor has been given a new and simple entrainer sublimator that it is supposed to work quite well. You are to test it for him by separating caffeine from coffee. First you are to determine if anything can be sublimed from coffee. If there is any sublimate, you will try to identify it. 

About 2 to 3 g of coffee are placed in the sublimator, the pressure is reduced to 50 to 60 torr, and the temperature of a slow flow of entrainer air is raised to 170 to 180 "C. The entrainer gas is heated because, if cold gas passes over a hot sample, the caffeine will condense as a fog. Many of these particles then will be pumped through the system and not collected, thus causing low results. The caffeine will separate as white crystals in the cooled downwind side. These crystals are dissolved in chloroform and verified as being caffeine by infrared spectroscopy. 

Watch the collection tube and the thermometer. When the temperature reaches about 100 "C, a region of the collection tube will become eloudy as the caffeine begins to sublime. At 140 to 150 "C, the caffeine begins to collect fairly rapidly. Continue the sublimation for about 15 minutes after the temperature reaches 178 "C. NOTE If the collected material begins to turn brown, lower the temperature, because other compounds are subliming. 

Hexagonal prisms by sublimation, mp 238. Sublimes 178°. Fast sublimation is obtained at 160-165° under 1 mm press, at 5 mm distance, dj 1.23. pH of 1% soln 6.9. Aq solns of caffeine salts dissociate quickly. Absorption spectrum Hartley, J. Chem. Soc. 87, 802 (1905). One gram dissolves in 46 ml water, S.5 ml water at 80°, 1.5 ml boihag water, 66 ml alcohol, 22 ml alcohol at 60 . 50 ml acetone, 5.5 ml chloroform, 530 ml ether, 100 ml benzene, 22 ml boiling benzene. Freely sol in pyrrole in tetrahydrofuran contg about 4% water also sol in ethyl acetate slightly in petr ether. Soly in water is increased by alkali benzoates, cinna-mates, citrates or salicylates. LDM orally in mice, hamsters, rats, rabbits (mg/kg) 127. 230, 355, 246 (males) 137, 249, 247, 224 (females) (Palm). 

Caffeine, mp 263°C, sublimes on heating and is more soluble than dimethylxanthines. Caffeine has a stimulating effect on the central nervous system. It is extracted from green coffee beans with liquid CO2 [151]. Caffeine is synthesized by methylation of xanthine, theophylline or theobromine with methyl iodide or dimethyl sulphate [149]. 

Theobromine (3,7-dimethylxanthine, 3,7-dihydro-3,7-dimethyl-lW-purine-2,6-dione). C7H,N402, Mr 180.17 formula, see under theophylline. Monoclinic, bitter tasting needles, mp. 357 °C, sublimes at 290-295 °C, soluble in hot water, alkali hydroxides, concentrated acids, moderately soluble in ammonia, poorly soluble in cold water and alcohol. With acids T. forms salts which decompose in water detection by the murexid reaction. T. is the main alkaloid of cocoa (Theobroma cacao, 1.5-3 wt.-%), from which it is obtained - especially from the husks in which it accumulates during fermentation. The typical bitter taste of cocoa is the result of interactions between T. and the pip-erazinediones formed in the roasting process. T. has diuretic, vasodilatory, and stimulating effects on cardiac muscle. The activities are weaker than those of the structurally related caffeine (a methylation product of T.) with which it co-occurs in cola nuts. For further pharmacological properties, see table under theophylline. 

Radiometric measurement of the C levels therefore, while requiring sophisticated instrumentation, is nonetheless the method of choice in our view. The normal procedure used in radiocarbon C analyses is to combust the sample, recover the resultant CO2, and convert it first to acetylene and then to benzene, as described above for the cinnamic aldehyde analysis. However, caffeine cannot be treated in this fashion due to its tendency to sublime from the combustion chamber to the catalyst traps before combustion is complete. Thus, a direct liquid scintillation counting technique was required, and the low-level liquid scintillation counting apparatus described by Noakes (18) was used to make all measurements. 

---