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Marta Girma

Synthesizing 2-methyl-2-butanol

Adam Jacholkowski  Follow

Isopropyl lithium and ethyl bromide would be my go-to if I were to try to prepare this stuff (which I will call TAA). This requires a solid fume hood, and the resulting mixture of salt, TAA, and isopropyl lithium solvent (usually n-hexane) should be easy to separate. The hexane can be stripped from the TAA via fractional distillation, with more distillation passes resulting in a more pure product. TAA boils at $\pu{102 ^\circ C}$ (Sigma Aldrich), and n-hexane boils at around $\pu{70 ^\circ C}$ - this $\pu{30 ^\circ C}$ gap in BP passes the rule-of-thumb "can I separate with distillation?" question.

All that said, even pricey Sigma Aldrich can get you 99% for $115 a liter.

I am aware that TAA is an experimental recreational drug, and a possible replacement for ethanol. I advise caution in sourcing this material for that purpose, as the impurities present are likely to be more toxic than TAA itself. I believe the industrial synth is from 2-methyl-2-butene (2m2b) with the addition of water (this would be cheapest); TAA prepared this way can be purified further by refluxing with an open condenser, enabling any unreacted alkene to evaporate (Boiling point = $\pu{39 ^\circ C}$). Acetone and ethyl Grignard would also form TAA, but with much more hassle and hazard, so the remnant ethyl chloride and acetone from such a synthesis are not likely impurities in any cheap sample.

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Caleb Rose  Follow

Or, cheaper alternative: I suspect that the acid dehydration of isoamyl alcohol would yield a carbocation with a subsequent 1,2 hydride shift, thus giving (to a yield that I don't know, and with reaction conditions that I don't know) 2-Methyl-2-butene (caution: flammable and with a bp of 40°C).

Further treatment with aqueous acid could yield, via Markovnikov hydration of the alkene, the desired product.

Any trace of a secondary alcohol product (derived from a elimination without hydride shift), if isolable, could be added to a reaction environment described in the first step, as it would easily convert to a trisubstituted alkene, that via Markovnikov hydration, again, gives 2-Methyl-2-butanol.

Please don't perform these reactions without a proper fume hood, anyway.

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