CAFFEINE Caffeine is a widely used pharmaceutical with the molecular formula C8H10N4O2. It is an alkaloid, and according to http://www.answers.com/topic/alkaloid 5/11/10 an alkaloid is defined as “Any of various organic compounds normally with basic chemical properties and usually containing at least one nitrogen atom in a heterocyclic ring” Caffeine is naturally found in 60 plants including coffee beans, tea leaves, cacao beans and cola nuts (Source: http://kidshealth.org/kid/stay_healthy/food http://kidshealth.org/kid/stay_healthy/food/caffeine.html /caffeine.html 5/11/10 5/11/10)) and the full chemical name for caffeine is Trimethylxanthine. Here is the molecular structure of caffeine. Now, within this structure are a few different functional groups. Namely, an Imide, Amide, Secondary Aldimine, Tertiary Amine and an Alkene. First up is the Imide. An Imide consists of two carbonyls, A carbon double bonded to an oxygen, double bonded to a nitrogen atom. As you can see here, this imide is located on the larger ring. Next is the Tertiary Amide. An amide is defined as an acyl group (R-C=O) bonded to a nitrogen atom. The number of hydrogen atoms bonded to the nitrogen atom determines whether the amide is primary, secondary or tertiary. When 2 hydrogens are bonded, it is primary. 1 is secondary, and none is referred to as tertiary. As you can see, there are no hydrogens bonded to the nitrogen atom here, and thus this is a tertiary amide. The associated peaks for amides are as follows. A C=O bond stretch produces a peak in the range of 1690 – 1630 cm^-1 and this peak is typically strong in intensity. An N-H stretch would produce peaks in the range of 3700 to 3500cm^-1, but as tertiary amides have no hydrogens, there would not be any peaks observed in this region on a caffeine spectra. Next is the secondary aldimine. A secondary aldimine consists of a nitrogen double bonded to a carbon atom, to which one hydrogen atom is bonded. As you can see here, the nitrogen atom in the smaller ring is double bonded to a carbon atom, to which 1 hydrogen atom is bonded. A tertiary amine, is defined as a nitrogen atom bonded to 3 organic groups. The associated peaks with a tertiary amine are as follows For an N–H stretch, the general range is from 3400-3250 cm -1 For a primary amine, two peaks are expected from 3400-3300 and 3330-3250 cm -1 For a secondary amine, one peak is expected from 3350-3310 cm -1 For a tertiary amine, there are no peaks in this region as there is no hydrogen atom present.
The amine present in caffeine is classed as an aliphatic amine as it is part of an aromatic ring, not directly bonded to one. The C-N stretch associated with aliphatic amines produces peaks in the range of 1250 to 1020cm^-1 with a medium to weak intensity expected. An alkene is also present, seen here in the middle of the two rings. An alkene is defined as a carbon chain of any length with a carbon=carbon double bond. The stretching of the C=C bond produces peaks ranging from 1680 – 1640 cm^-1 with a medium intensity expected. How is caffeine formed? Caffeine is in abundance due to the large demand for decaffeinated beverages, but, if desired caffeine can be synthesised using cyanoacetyl dimethylurea and cyanoacetic acid. Here is the process undergone. As you can see, the process is quite complex, and is completely unpractical in a real life situation. The first analytical technique I will introduce you to today is mass spectrometry Mass Spectrometry is an analytical technique in which the sample in question is bombarded with high speed electrons in order to break it up into its fragment ions. These ions are then separated according to their mass to charge ratio. The result of this process is a mass spectrum, which displays the mass to charge ratio and relative abundance. Each peak represents a fragment ion, and thus the fragment ions present can be determine using previous knowledge on their mass to charge ratios. Once these ions have been determined, the structure of the molecule in question can then be determined – often done in conjunction with other analytical techniques. Here is are the fragment ions of caffeine. Here is the mass spectrum of caffeine Now the original caffeine, as you can see has a mass to charge ratio of 194 m/z, so it correlates with the peak seen here. Next, this ion can lose a CHO ion, which in turn produces the peak at 29m/s – shown in brown and the peak at 165 m/z as shown in orange. Alternatively, the original molecule could give up this group here, producing the peak shown in green at 57 m/z and the peak in blue at 137 m/z. From here, a CO ion can be lost, resulting in a peak at 43 m/z when bonded to a methyl group ion that can be formed. The ion formed by this loss has a mass to charge ratio of 109 m/z resulting in the large peak shown in yellow. From here, an ion with mass to charge ratio of 82 m/z can be formed, resulting in the peak shown by beige here. From here, the methyl group I was talking about before can be lost, resulting in a peak at 15m/z and at 67m/z shown here. Alternatively this group here can be lost, resulting in the ion shown here in purple, producing a peak at 55m/z. Infrared Spectroscopy involves a beam of infrared light (wavelength between )being passed through a sample. The extra energy associated with this light excites the atoms within the molecule. This in turn leads to the bending, stretching and scissoring of the bonds within the
atom. Each bond and movement combination leads to a specific absorption of energy at a specific frequency. The transmittance of the light through the substance is also characteristic of the bonds present and is used in combination with the absorption frequencies to determine the functional groups present and, in combination with other analytical techniques, determine the overall structure of the molecule.
Here is the infrared spectra of caffeine. The peak at the highest wave number, 3110cm^-1, could be attributed to a C-H stretch between the carbon double bonded to a nitrogen atom. This could cause the bond to react in a similar fashion to an alkene C-H stretch which has a frequency range of 3080-3020cm^-1 with medium intensity as seen. The sharp peaks at 2954, 2925 and 2864cm^-1 could be attributed to the stretching of the CH bond in the attached methyl groups. This frequency range for such is 2960 - 2850cm^-1 with a strong intensity as seen. The peaker at wave number 1699cm^-1 is most likely due to a C=O stretch of the bond located between the two nitrogen atoms. This is because the expected wavenumber ranges from 1760 - 1670 cm^-1 with a strong intensity expected.
The peak at 1659 was also due to a C=O stretch of the bond located between the ‘upper’ nitrogen atom and the carbon atom. This peak was lower that the previous C=O stretch due to conjugation with the C=C bond According to http://webcache.googleusercontent.com/search? q=cache:dZf7sElatQoJ:www.uncp.edu/home/mcclurem/courses/chm550/ir_notes.pdf+infrare d+spectroscopy+conjugation&cd=4&hl=en&ct=clnk&gl=au, Conjugation decreases the CO bond order and therefore decreases the stretching frequency As you can see from this diagram, conjugation involves the movement of the double bonds such that positive and negative poles are produced. Now, The peak at 1549 was likely due to a C=N stretch. The range for a C=N stretch is normally 1615-1700cm^-1. But C=N bonds can experience similar conjugation effects as C=O bonds, causing this lower value. The Peak at 1457cm^-1 was most likely due to a C=C stretch in the alkene portion of the molecule as it is part of an aromatic ring. The frequency range for aromatic C=C stretches is 1700-1500cm^-1. A medium peak height is expected for this – correlating with the transmittance of 31% seen.
The peaks at 1457, 1431, 1404 and 1360 were likely due to C-H scissoring and bending, in the alkyl groups present. The expected frequency range for an alkyl group C-H scissoring or bending is 1470 – 1350 cm^-1 with variable transmittance or peak height as seen.
The peak at 1379 is characteristic of a C-H3 Umbrella Deformation with an expected frequency of 1380cm^-1 and medium to weak transmittance – Seen is 49% transmittance, supporting this theory. The peak at 1240 was likely due to a C-N stretch – Aliphatic amine with an expected frequency range of 1340-1020cm^-1 and medium intensity. The final analytical technique is, of course, gas chromatography. In gas chromatography, the sample is first vaporized. This vaporized sample is then carried by a carrier gas – typically an inert gas, through a long column coated in an ester. Each compound takes a different time to pass through the column. This time is known as the retention time. The least soluble compounds are detected first as they take the least time to travel through the column. Each compound has its own characteristic retention time. The area under each peak describes the relative amount of each compound present in the sample. Now the retention time of each chemical is subject to much change depending on the conditions under which the procedure is carried out. For example, in the following graphs, let’s say that peak number 3 is caffeine. This can be used to identify caffeine in the sample. This is done using the retention time. As you can see, this peak has the same retention time. Therefore this peak here is caffeine. The area under the peak describes the amount of the compound present. As you can see, on the standard chromatogram it can be see that the peak area is greater than in the sample chromatogram. Therefore, relatively, there is a greater amount of caffeine present in the standard than in the sample. The number one use is, of course, as a stimulant. In the body, caffeine acts upon the central nervous system, speeding up the messages to and from the brain. This makes the user feel more awake and active. Unfortunately, the use of caffeine can induce dehydration, anxiety, rapid heart rate, increased breathing rate, restlessness, lack of concentration, gastro-intestinal pains and irritability Long term, caffeine can be incredibly addivtive. If a long term user stops using it, they may experience severe withdrawal symptoms including fatigue, muscle pain, sweating and anxiety. A few fun facts for you. Did you know that over 450 million cups of coffee are consumed in the USA each and every single day?
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Caffeine was first isolated in 1820
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10g of caffeine is considered a lethal overdose
Finally, here are a few caffeine contents of some drinks you may have consumed •
Coca Cola – 0.098mg/mL
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Brewed Coffee – 0.453mg/mL
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Espresso – 1.735mg/mL
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Red Bull – 0.321mg/mL
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Rockstar – 0.338mg/mL
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Brewed Tea – 0.200mg/mL
Thank you for listening.
