Methamphetamine - Illicit Production - Synthesis

Synthesis

Methamphetamine is most structurally similar to methcathinone and amphetamine. Synthesis is relatively simple, but entails risk with flammable and corrosive chemicals, particularly the solvents used in extraction and purification; therefore, illicit production is often discovered by fires and explosions caused by the improper handling of volatile or flammable solvents. The six major routes of production begin with either phenyl-2-propanone (P2P) or with one of the isomeric compounds pseudoephedrine and ephedrine.

One procedure uses the reductive amination of phenyl-2-propanone (phenylacetone) with methylamine, P2P was usually obtained from phenylacetic acid and acetic anhydride, though many other methods have been considered, and phenylacetic acid might arise from benzaldehyde, benzylcyanide, or benzylchloride. Methylamine is crucial to all such methods, and is produced from the model airplane fuel nitromethane, or formaldehyde and ammonium chloride, or methyl iodide with hexamine. This was once the preferred method of production by motorcycle gangs in California, until DEA restrictions on the chemicals made the process difficult. Pseudoephedrine, ephedrine, phenylacetone, and phenylacetic acid are currently DEA list I and acetic anhydride is list II on the DEA list of chemicals subject to regulation and control measures. This method can involve the use of mercuric chloride and leaves behind mercury and lead environmental wastes. The methamphetamine produced by this method is racemic, consisting partly of the unsought levomethamphetamine isomer.

The alternative Leuckart route also relies on P2P to produce a racemic product, but proceeds via methylformamide in formic acid to an intermediate N-formyl-methamphetamine, which is then decarboxylated with hydrochloric acid.

Two infrequently used reductive amination routes have also been reported. The "nitropropene route", in which benzaldehyde is condensed with nitroethane to produce 1-phenyl-2-nitropropene, which is subsequently reduced by hydrogenation of the double bond and reduction of the nitro group using hydrogen over a palladium catalyst or lithium aluminum hydride. The "oxime route" reacts phenyl-2-propanol with hydroxylamine to produce an oxime intermediate which likewise is hydrogenated using hydrogen over a palladium catalyst or lithium aluminum hydride.

Illicit methamphetamine is more commonly made by the reduction of ephedrine or pseudoephedrine, which produces the more active d-methamphetamine isomer. The maximum conversion rate for ephedrine and pseudoephedrine is 92%, although typically, illicit methamphetamine laboratories convert at a rate of 50% to 75%. Most methods of illicit production involve protonation of the hydroxyl group on the ephedrine or pseudoephedrine molecule.

Though dating back to the discovery of the drug, the Nagai route did not become popular among illicit manufacturers until ca. 1982, and comprised 20% of production in Michigan in 2002 It involves red phosphorus and hydrogen iodide (also known as hydroiodic acid or iohydroic acid). (The hydrogen iodide is replaced by iodine and water in the "Moscow route") The hydrogen iodide is used to reduce either ephedrine or pseudoephedrine to methamphetamine. On heating the precursor is rapidly iodinated by the hydrogen iodide to form iodoephedrine. The phosphorus assists in the second step, by consuming iodine to form phosphorus triiodide (which decomposes in water to phosphorous acid, regenerating hydrogen iodide). Because hydrogen iodide exists in a chemical equilibrium with iodine and hydrogen, the phosphorus reaction shifts the balance toward hydrogen production when iodine is consumed. In Australia, criminal groups have been known to substitute "red" phosphorus with either hypophosphorous acid or phosphorous acid (the "Hypo route"). This is a hazardous process for amateur chemists because phosphine gas, a side-product from in situ hydrogen iodide production, is extremely toxic to inhale. The reaction can also create toxic, flammable white phosphorus waste. Methamphetamine produced in this way is usually more than 95% pure.

The conceptually similar Emde route involves reduction of ephedrine to chloroephedrine using thionyl chloride (SOCl₂), followed by catalytic hydrogenation. The catalysts for this reaction are palladium or platinum. The Rosenmund route also uses hydrogen gas and a palladium catalyst poisoned with barium sulfate (Rosenmund reduction), but uses perchloric acid instead of thionyl chloride.

The Birch reduction, also called the "Nazi method", became popular in the mid-to-late 1990s and comprised the bulk of methamphetamine production in Michigan in 2002. It reacts pseudoephedrine with liquid anhydrous ammonia and an alkali metal such as sodium or lithium. The reaction is allowed to stand until the ammonia evaporates. However, the Birch reduction is dangerous because the alkali metal and ammonia are both extremely reactive, and the temperature of liquid ammonia makes it susceptible to explosive boiling when reactants are added. It has been the most popular method in Midwestern states of the U. S. because of the ready availability of liquid ammonia fertilizer in farming regions.

In recent years, a simplified "Shake 'n Bake" one-pot synthesis has become more popular. The method is suitable for such small batches that pseudoephedrine restrictions are less effective, it uses chemicals that are easier to obtain (though no less dangerous than traditional methods), and it is so easy to carry out that some addicts have made the drug while driving. It involves placing crushed pseudoephedrine tablets into a nonpressurized container containing ammonium nitrate, water, and a hydrophobic solvent such as Coleman fuel or automotive starting fluid, to which lye and lithium (from lithium batteries) is added. Hydrogen chloride gas produced by a reaction of salt with sulfuric acid is then used to recover crystals for purification. The container needs to be "burped" periodically to prevent failure under accumulating pressure, as exposure of the lithium to the air can spark a flash fire; thus an abandoned reaction becomes a severe hazard to firefighters. The battery lithium can react with water to shatter a container and potentially start a fire or explosion.

Producing methamphetamine in this fashion can be extremely dangerous and has been linked to several fatalities. Because users frequently carry out the reaction in a two-liter bottle held close to their bodies, which can explode if the cap is removed too soon or if it accidentally perforates, the procedure has led to a large number of severe burns — for example, approximately 70 in Indiana during 2010 and 2011. As 90% of these cases in the United States lack health insurance, and the average cost for their treatment is $130,000 (60% more than the average), which is only partially compensated by Medicaid, this method of synthesis has been blamed for the closure of hospital burn units and a cost to taxpayers of tens or hundreds of millions of dollars.