Re: what color is sodium benzoate (aq)?


<mrdarrett@xxxxxxxxx> wrote in message
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HLS@xxxxxxxxxx wrote:
<mrdarrett@xxxxxxxxx> wrote in message
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Ok. Thanks. Someone said this is why Toyota radiator coolant is
pink... guess they were wrong.
Mike

Absolute bullshit! Yes, they were wrong.


All the ingredients on the coolant were given (ethylene glycol, yada
yada yada) and then two proprietary chemicals - but then they gave the
CAS numbers for these.

Those two CAS numbers turn out to be sodium benzoate and potassium
hydroxide (I'm pretty sure it was KOH, I'm going by memory now, don't
have the numbers in front of me anymore).

Oh well. Guess they forgot to add "FDC Red 3" to the list of
ingredients...

Actually, I had the impression that the pink antifreeze was based on
propylene glycol (non-toxic) rather than the ethylene glycol (toxic, deadly
to pets) that's used in normal antifreeze. Both colors are indeed due to
dyes added to distinguish it from water and from the other type of
antifreeze. I think I remember the green is rhodamine, anyone know what dye
is used in the pink stuff?

Also, I'd be surprised if KOH is an ingredient in any antifreeze, or any
alkali. Aren't most modern radiators made of aluminum, as well as some
engine blocks? If there are no acids present to neutralize the alkali
before the antifreeze is put in the engine, it would dissolve any aluminum
it comes in contact with. Try it with aluminum foil--even bicarb is
alkaline enough to slowly dissolve the foil...and that's at room
temperature. Dissolution will be much faster at the ~100 C temperatures in
your car's cooling system.

As to the OPs question...benzoate salts are colorless, at least judging by
the white crystalline sodium benzoate I use to stop fermentation when making
sweet wines. Crossed conjugation between the carboxylate and the phenyl
ring limits the effectiveness of conjugation, and extended conjugation is
generally the name of the game for color in organic compounds. Sodium
phenoxide is better conjugated, but still not colored (although it will turn
red in air, presumably due to oxidation to semiquinones, biphenoxides and
quinones.)

Eric Lucas


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