Updated 21-Aug-2023
Disclaimer: Unregulated preparation and/or sale of methamphetamine or other controlled substances is illegal. The catalyst ideas presented below are speculative.
If you’ve read Enantiomer and also watched Breaking Bad, we’re ready to talk about Walter White’s blue meth. Among TV shows trying to “keep it real” scientifically, Breaking Bad has been the gold standard for decades. Even so, it has left a few Flaws stuck in the craws of skeptical viewers. Here are two of the biggest ones (until now!):
Flaw 1: Perfectly pure methamphetamine is colorless, not blue.
Flaw 2: The aluminum-amalgam catalyst Walt uses produces a 50-50 mixture of desired and undesired enantiomers, severely limiting the yield and purity of his method (“meth”-od?).
These apparent Flaws are usually dismissed as plot devices, implemented with wanton disregard for the underlying science. But while recently watching the series again, I thought of something that not only addresses both Flaws, but even fits nicely within the story.
About the color. It’s true that perfectly pure crystal meth should be colorless, and Walt’s “Sky Blue” is reported to be 99.1% pure (Season 5, Episode 7). But importantly, he never claims that it is blue because it is pure. It is blue, and it is pure. That’s not a contradiction. Color is funny that way. The color of a product reveals almost nothing about its purity. For example, put a drop of food coloring in a gallon of water; the color changes, but the decrease in purity is miniscule—and it’s still quite safe to drink. So, it’s entirely feasible that the blue meth is 99.1% pure, yet it contains a trace of some intensely blue component. More about that later.
About the enantiomer. Like Kyra’s Zeti in Enantiomer, methamphetamine is chiral, and only one of the enantiomers works for Walt’s purpose. The conditions of his synthesis should produce a 50-50 mixture of right- and left-handed methamphetamine, but only the right-handed version works to get his junkies high. Is this inconvenience simply ignored to streamline the plot? It sure doesn’t seem like it. Walt understands enantiomers. He tells his high school class about them (Season 1, Episode 2), and spitefully quizzes Victor about their importance to crystal meth “cooks” (Season 4, Episode 1). So, the writers are not ignoring Flaw #2; in fact, they are explicitly describing the underlying principle.
The final step in Walt’s route is called reductive amination, in which he reacts 1-phenyl-2-propanone (“P2P”) with methylamine and hydrogen (either added or generated in situ) to make the final product. This chemical reaction requires a catalyst, for which the aluminum amalgam described on the show is a viable choice. The problem is that the catalyst is not enantioselective; it makes a 50-50 mixture of enantiomers, severely limiting yield and/or purity of the reaction product. But here’s the thing. Catalysts can be enantioselective. In other words, it is chemically feasible that some catalyst other than (or in addition to) aluminum amalgam could selectively produce the desired enantiomer. In fact, some such catalysts have been reported in the scientific literature, just none with the activity and selectivity required to obtain the product in 99.1% purity. But such a catalyst performance is scientifically possible, and catalyst advances really have come in sudden, giant leaps at times. It’s a plausible story element that Walt (or some colleague) discovered such a catalyst, perhaps while doing graduate school research, yet never published the result.
Fixing the Flaws. Obviously, no one really knows the exact chemical formula of this hypothetical high-performance catalyst. But as someone who has done decades of catalyst research in his past, I can tell you that it is likely to include a transition metal. And this is where the two Flaws comes together. In addition to being useful for catalysis, many transition metal complexes are highly colored—maybe even blue! That’s the short answer: a blue, enantioselective catalyst.
About the catalyst. Let’s get more specific. First, which transition metal? Walt sure demonstrates a lot of knowledge about oxides of manganese (a transition metal) and their colors when he lectures Hank and Walter, Jr. about rhodonite (Season 4, Episode 4). Maybe the writers are trying to tell us something there? But I don’t like manganese for this. Blue is a rare color for manganese complexes, and they’re not often used for sophisticated catalysis. I like to think it’s cobalt, specifically cobalt(II), because it is useful in several catalytic applications, relatively inexpensive, easily "procured" from chemistry labs, and famously brilliant blue.
As for the details of the Co(II)-containing catalyst formulation, let’s heap some additional speculation onto the enormous mound we just created. Most chemists would want the transition metal catalyst to do all the work by itself, rather than using it along with aluminum amalgam. But Walt and Jesse mention the amalgam often, even comparing its merits to a platinum oxide alternative (Season 3, Episode 4). If the Co(II) catalyst is viable to use with either of them, that means it isn’t incorporated into the amalgam; it’s provided separately.
A reasonable candidate is a chiral complex, prepared by surrounding the cobalt(II) metal centers with chiral organic molecules (called ligands). As for the ligand, there are millions of options. A conventional choice would be something like a chelating diphosphine. But the most convenient one is something available to Walt in great abundance: d-methamphetamine, crystal meth itself! So, maybe Walt makes his enantioselective catalyst from cobalt(II) chloride hexahydrate and a bit of meth retained from a previous batch, via reaction in some solvent (e.g., water, methanol, ether) at some controlled acidity level (pH). But even if meth doesn't work as a ligand and Walt has to bring his own ligand to the party, he may only need to secretly make a pound or so in his garage in order to produce 50,000 lb of meth throughout his criminal career. That's not magical thinking; catalysts really do work that way!
About the Process. Walt likely needs to use a multi-phase reaction (or even separate reactors) to keep the amalgam separated from the Co(II) catalyst to avoid reducing the oxidation state of cobalt. In this case, the only real function of the aluminum amalgam is to generate hydrogen from water (simplistically, 2Al + 6H2O --> 2Al(OH)3 + 3H2)—and to distract from the “real” catalyst. Walt seems to anticipate this eventuality when he specifically requests electrolytically-produced hydrogen for his first “P2P” cook (Season 1, Episode 7), which should match the high purity of the hydrogen generated by amalgam + water, free of impurities which could poison a Co(II) catalyst.
As might be expected, the details of Walt’s process seem to have evolved and improved over time. His first P2P cook was done at a relatively small scale, and he didn’t seem to use any amalgam. Pause S1E7 at the 16:15 mark, when Walter holds up the “shopping list” for his first P2P cook, and you can see the following (x = blocked by Walt’s fingers):
“One Autotransformer
6 Liters An Hydrous Meth Methylmine
xxxx 35MM tube furnaces
xxx grams Thorium nitrate
xxxx pseudoephedrine
xxxxx feenal/acitone
xxxxx in a tube furnace
xxxx reductive amination
xxxx yield methamphetamine”
Amusingly, the list seems to have doubled as a phonetic script prompter, since I would expect Walt to spell “anhydrous methylamine” and “phenylacetone” correctly. But importantly, look at what’s absent from the list: aluminum, mercury, platinum oxide. There’s no hydroamination catalyst on the list, because Walt has it already. Later, he realizes it’s more obfuscating to generate his own hydrogen from water, and starts using the amalgam. Protecting his secret is worth the added cost and complexity.
Fit with the Story. A highly-active catalyst would produce high-purity meth with very low residual cobalt, perhaps only a few parts per million, just enough to color it blue. While the amalgam components are likely filtered off, such a small amount of dissolved Co(II) catalyst in the product should not be a concern—especially because Walt is not worried about governmental regulations! (Walt and Gretchen should have mentioned the 0.000002% of cobalt in the human body in the flashback scene of Season 1, Episode 3, but they didn't.)
A complicated catalyst system like this one would be rather tricky to employ, especially at large scale, so it’s not surprising that lesser chemists struggle to reproduce Walt’s method. After many repetitions, Jesse masters it. Appropriate, considering his personal and scientific growth throughout the series. But even Gale, competent and well-educated, remains uncomfortable with the preparation after a few runs. And inexperienced/hamhanded operators, like Todd and Declan’s cook, can’t get it right. Notably, all of them still get over 50% purity, so they seem to be using Walt’s catalyst, just not preparing or implementing it as carefully.
Flaws or Features? Both "Flaws" in the plot can be addressed by a single catalyst. The meth is blue because of the catalyst; the meth is a pure enantiomer because of the catalyst. It’s a feasible explanation that fits well with the characters and plot, perhaps even turning these Flaws into Features. Sometimes, science and story can both win. Is this Co(II) catalyst really what the writers and scientific advisors had in mind? I don’t know. Then again, I don’t really care. Without ever being incontrovertibly wrong, Breaking Bad brings us a titillating mixture of well- and sparsely-described scientific phenomena, which add intrigue to the show and provide years of conversation fodder for the scientifically-minded. There’s nothing wrong with leaving a few gaps for viewers like us to fill in.
Disclaimer: Unregulated preparation and/or sale of methamphetamine or other controlled substances is illegal. The catalyst ideas presented below are speculative.
If you’ve read Enantiomer and also watched Breaking Bad, we’re ready to talk about Walter White’s blue meth. Among TV shows trying to “keep it real” scientifically, Breaking Bad has been the gold standard for decades. Even so, it has left a few Flaws stuck in the craws of skeptical viewers. Here are two of the biggest ones (until now!):
Flaw 1: Perfectly pure methamphetamine is colorless, not blue.
Flaw 2: The aluminum-amalgam catalyst Walt uses produces a 50-50 mixture of desired and undesired enantiomers, severely limiting the yield and purity of his method (“meth”-od?).
These apparent Flaws are usually dismissed as plot devices, implemented with wanton disregard for the underlying science. But while recently watching the series again, I thought of something that not only addresses both Flaws, but even fits nicely within the story.
About the color. It’s true that perfectly pure crystal meth should be colorless, and Walt’s “Sky Blue” is reported to be 99.1% pure (Season 5, Episode 7). But importantly, he never claims that it is blue because it is pure. It is blue, and it is pure. That’s not a contradiction. Color is funny that way. The color of a product reveals almost nothing about its purity. For example, put a drop of food coloring in a gallon of water; the color changes, but the decrease in purity is miniscule—and it’s still quite safe to drink. So, it’s entirely feasible that the blue meth is 99.1% pure, yet it contains a trace of some intensely blue component. More about that later.
About the enantiomer. Like Kyra’s Zeti in Enantiomer, methamphetamine is chiral, and only one of the enantiomers works for Walt’s purpose. The conditions of his synthesis should produce a 50-50 mixture of right- and left-handed methamphetamine, but only the right-handed version works to get his junkies high. Is this inconvenience simply ignored to streamline the plot? It sure doesn’t seem like it. Walt understands enantiomers. He tells his high school class about them (Season 1, Episode 2), and spitefully quizzes Victor about their importance to crystal meth “cooks” (Season 4, Episode 1). So, the writers are not ignoring Flaw #2; in fact, they are explicitly describing the underlying principle.
The final step in Walt’s route is called reductive amination, in which he reacts 1-phenyl-2-propanone (“P2P”) with methylamine and hydrogen (either added or generated in situ) to make the final product. This chemical reaction requires a catalyst, for which the aluminum amalgam described on the show is a viable choice. The problem is that the catalyst is not enantioselective; it makes a 50-50 mixture of enantiomers, severely limiting yield and/or purity of the reaction product. But here’s the thing. Catalysts can be enantioselective. In other words, it is chemically feasible that some catalyst other than (or in addition to) aluminum amalgam could selectively produce the desired enantiomer. In fact, some such catalysts have been reported in the scientific literature, just none with the activity and selectivity required to obtain the product in 99.1% purity. But such a catalyst performance is scientifically possible, and catalyst advances really have come in sudden, giant leaps at times. It’s a plausible story element that Walt (or some colleague) discovered such a catalyst, perhaps while doing graduate school research, yet never published the result.
Fixing the Flaws. Obviously, no one really knows the exact chemical formula of this hypothetical high-performance catalyst. But as someone who has done decades of catalyst research in his past, I can tell you that it is likely to include a transition metal. And this is where the two Flaws comes together. In addition to being useful for catalysis, many transition metal complexes are highly colored—maybe even blue! That’s the short answer: a blue, enantioselective catalyst.
About the catalyst. Let’s get more specific. First, which transition metal? Walt sure demonstrates a lot of knowledge about oxides of manganese (a transition metal) and their colors when he lectures Hank and Walter, Jr. about rhodonite (Season 4, Episode 4). Maybe the writers are trying to tell us something there? But I don’t like manganese for this. Blue is a rare color for manganese complexes, and they’re not often used for sophisticated catalysis. I like to think it’s cobalt, specifically cobalt(II), because it is useful in several catalytic applications, relatively inexpensive, easily "procured" from chemistry labs, and famously brilliant blue.
As for the details of the Co(II)-containing catalyst formulation, let’s heap some additional speculation onto the enormous mound we just created. Most chemists would want the transition metal catalyst to do all the work by itself, rather than using it along with aluminum amalgam. But Walt and Jesse mention the amalgam often, even comparing its merits to a platinum oxide alternative (Season 3, Episode 4). If the Co(II) catalyst is viable to use with either of them, that means it isn’t incorporated into the amalgam; it’s provided separately.
A reasonable candidate is a chiral complex, prepared by surrounding the cobalt(II) metal centers with chiral organic molecules (called ligands). As for the ligand, there are millions of options. A conventional choice would be something like a chelating diphosphine. But the most convenient one is something available to Walt in great abundance: d-methamphetamine, crystal meth itself! So, maybe Walt makes his enantioselective catalyst from cobalt(II) chloride hexahydrate and a bit of meth retained from a previous batch, via reaction in some solvent (e.g., water, methanol, ether) at some controlled acidity level (pH). But even if meth doesn't work as a ligand and Walt has to bring his own ligand to the party, he may only need to secretly make a pound or so in his garage in order to produce 50,000 lb of meth throughout his criminal career. That's not magical thinking; catalysts really do work that way!
About the Process. Walt likely needs to use a multi-phase reaction (or even separate reactors) to keep the amalgam separated from the Co(II) catalyst to avoid reducing the oxidation state of cobalt. In this case, the only real function of the aluminum amalgam is to generate hydrogen from water (simplistically, 2Al + 6H2O --> 2Al(OH)3 + 3H2)—and to distract from the “real” catalyst. Walt seems to anticipate this eventuality when he specifically requests electrolytically-produced hydrogen for his first “P2P” cook (Season 1, Episode 7), which should match the high purity of the hydrogen generated by amalgam + water, free of impurities which could poison a Co(II) catalyst.
As might be expected, the details of Walt’s process seem to have evolved and improved over time. His first P2P cook was done at a relatively small scale, and he didn’t seem to use any amalgam. Pause S1E7 at the 16:15 mark, when Walter holds up the “shopping list” for his first P2P cook, and you can see the following (x = blocked by Walt’s fingers):
“One Autotransformer
6 Liters An Hydrous Meth Methylmine
xxxx 35MM tube furnaces
xxx grams Thorium nitrate
xxxx pseudoephedrine
xxxxx feenal/acitone
xxxxx in a tube furnace
xxxx reductive amination
xxxx yield methamphetamine”
Amusingly, the list seems to have doubled as a phonetic script prompter, since I would expect Walt to spell “anhydrous methylamine” and “phenylacetone” correctly. But importantly, look at what’s absent from the list: aluminum, mercury, platinum oxide. There’s no hydroamination catalyst on the list, because Walt has it already. Later, he realizes it’s more obfuscating to generate his own hydrogen from water, and starts using the amalgam. Protecting his secret is worth the added cost and complexity.
Fit with the Story. A highly-active catalyst would produce high-purity meth with very low residual cobalt, perhaps only a few parts per million, just enough to color it blue. While the amalgam components are likely filtered off, such a small amount of dissolved Co(II) catalyst in the product should not be a concern—especially because Walt is not worried about governmental regulations! (Walt and Gretchen should have mentioned the 0.000002% of cobalt in the human body in the flashback scene of Season 1, Episode 3, but they didn't.)
A complicated catalyst system like this one would be rather tricky to employ, especially at large scale, so it’s not surprising that lesser chemists struggle to reproduce Walt’s method. After many repetitions, Jesse masters it. Appropriate, considering his personal and scientific growth throughout the series. But even Gale, competent and well-educated, remains uncomfortable with the preparation after a few runs. And inexperienced/hamhanded operators, like Todd and Declan’s cook, can’t get it right. Notably, all of them still get over 50% purity, so they seem to be using Walt’s catalyst, just not preparing or implementing it as carefully.
Flaws or Features? Both "Flaws" in the plot can be addressed by a single catalyst. The meth is blue because of the catalyst; the meth is a pure enantiomer because of the catalyst. It’s a feasible explanation that fits well with the characters and plot, perhaps even turning these Flaws into Features. Sometimes, science and story can both win. Is this Co(II) catalyst really what the writers and scientific advisors had in mind? I don’t know. Then again, I don’t really care. Without ever being incontrovertibly wrong, Breaking Bad brings us a titillating mixture of well- and sparsely-described scientific phenomena, which add intrigue to the show and provide years of conversation fodder for the scientifically-minded. There’s nothing wrong with leaving a few gaps for viewers like us to fill in.
Note: While putting this idea together, I came across a multitude of excellent, scientifically-sound analyses of Breaking Bad chemistry. Jason Wallach's Comprehensive Guide details a lot of the chemistry, as well as insights into actual clandestine drug labs and manufacture. The Reddit AMA with HeisenbergSpecial provides an insider perspective, if you have the patience to sort through the usual Reddit dribble. I found weakinteractions Screen Science Explained episode-by-episode comments to be both entertaining and enlightening. There are many, many more. I found some posts that recognize a possibility of enantioselective catalysis, but I didn't see any that propose the kind of system I describe--surprising to me because the primary purpose of the Internet seems to be to show how someone already thought about my latest idea.