Re: ORGLIST: Conditions for the conversion of phenol into benzene (non-chemist's question)

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From: Jacob Zabicky (zabicky$##$bgu.ac.il)
Date: Mon Oct 20 2008 - 12:24:33 EDT


Dear Joshua,

The reaction you mention can be attempted (i do not see for what
purpose) in a 'chemical' plant but is out of the capabilities of any
distillery. BTW, benzene quite undesirable in your beverage. You got
scared by 'phenol' but in the fermentation and distillation process
are produced tens if not hundreds of toxic compounds, including
ethanol, that are avidly ingested by people buying your products. It
is wise to take the middle cut where you got rid of most of the toxic
light components (e.g. methanol, formaldehyde, acetaldehyde) and most
of the heavy ones remained in the kettle (e.g. fusel oil). If a
standard operation such as drying the grain introduces unwanted
components, try to modify it to reduce that risk, perhaps changing
the particular peat you are using.

Let me ask you a question of somebody ignorant of the deep secrets of
whisky production. Why use peat fire for drying grain? Why not with
hot air that would not add the unwanted pollutant (you probably want
the added taste values of smoke)? Cannot something be learned from
wine producers, who abandoned the traditional oak barrels for
stainless steel containers and still produce excellent wines?

Cheers!

Jacob

On 20 Oct 2008, at 08:12, Joshua McGee wrote:

> I am not an organic chemist. I do not have a firm command of the
> vocabulary, and my question, in three parts, is likely to be
> imprecise and badly-worded. I appreciate your tolerance of my
> intrusion.
>
> For the context in which my question arose, I was having a
> discussion with another non-chemist about the production of scotch
> whisky. In some cases, grain is dried over a peat fire. This
> impregnates the grain with phenolic compounds, including simple
> phenol, which is retained in the final product following distillation.
>
> Yes, the resulting product is consumed intentionally by some
> people. :^)
>
> The first part of my question is to establish under what conditions
> simple phenol can be converted into benzene. If I understand
> correctly, this would entail the replacement of a hydroxyl group
> with a hydrogen atom.
>
> I understand that the reverse conversion -- benzene to phenol --
> can be accelerated by (or is impossible without, I don't know)
> copper-containing compounds. The conditions of the distillation
> under discussion involve the presence of ethanol and other yeast
> metabolites (including other alcohols), various organic compounds,
> elemental copper from the still, and the application of direct
> heat. Thus, the second part of my question (which may, to answer,
> require more information than I have provided) is whether the
> conversion of phenol to benzene would be likely to arise
> accidentally in the process of commercial whisky distillation.
>
> Finally, I am wondering the likelihood of benzene surviving into
> the final bottled product, which is the "middle cut" (the period of
> the still run including the portion containing the highest
> percentage of ethanol) diluted with water.
>
> I do not have access to an adequate textbook. I have been
> unsuccessful in answering this question through search engine
> queries, likely because I am not providing the correct keywords. I
> have read the charter and believe that my question is within the
> bounds of discussion.
>
> Thank you,
>
> Joshua McGee
> http://www.mcgees.org
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