Very little laboratory synthesis of caffeine is undertaken for one main reason: the growing trend for decaffeinated coffee means that there is an abundance of the pure compound as a residue from this process. Extraction from waste tea leaves and poor quality coffee beans is also a source of pure caffeine, as the process is cheaper than synthesis.
False colour photograph of caffeine under the microscope
If you want to do the laboratory synthesis, though, the full method would use dimethylurea and malonic acid...
Methylation of the extracted methylxanthines, using, say methyl iodide is often used instead, and several research papers published recently have used increasing exotic methylating reagents to do this.
Pure caffeine crystals are white, often a fleecy powder, or long silky crystals. At room temperature it is odourless and slightly bitter, and sublimes at 178 ºC. ¹
Most of the world's purified caffeine, used to spike soft drinks (the caffeine in coca-cola is not from cola at all, but added afterwards) and used in over-the-counter medicines comes from extracted caffeine from poor quality coffee beans and tea leaves, or the by-product from decaffeination. There are two major techniques in use; bean decaffeination (using supercritical carbon dioxide) and extract decaffeination (using near boiling water).
Pure caffeine is extremely toxic, and chemical supply companies are not allowed to sell to individual purchasers. Jars containing pharmaceutical grade caffeine come with the following message:
"WARNING! MAY BE HARMFUL IF INHALED OR SWALLOWED. INHALATION CAUSES RAPID HEART RATE, EXCITEMENT, DIZZINESS, PAIN, COLLAPSE, HYPOTENSION, FEVER, SHORTNESS OF BREATHE. MAY CAUSE HEADACHE, INSOMNIA, NAUSEA, VOMITING, STOMACH PAIN, COLLAPSE AND CONVULSIONS...FATALITIES HAVE BEEN KNOWN TO OCCUR"
In coffee terms, the lethal dose is the equivalent
to about fifty double espressos in one go, an amount that would induce
vomiting well before the blood concentration reached dangerous levels.
¹University of California Chemical Data Sheet @ http://www.erowid.org/chemicals/caffeine/caffeine_data_sheet.shtml
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Caffeine crystals http://www.microscopy.fsu.edu/pharmaceuticals/pages/caffeine.html
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