Author Topic: Oxidization by Beach Instead of Chromium Salts  (Read 966 times)

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ADDkid

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Oxidization by Beach Instead of Chromium Salts
« on: January 03, 2004, 03:46:00 PM »
Primary and secondary alcohols are oxidized to the corresponding aldehydes and ketones by various oxidizing agents, e.g., dichromates, t-butyl hypochlorite,
hypochlorous acid, potassium permanganate, and nitric acid. The aldehydes derived from primary alcohols can be further oxidized to carboxylic acids by some of these
oxidizing agents (including HOCl), while the ketones derived from secondary alcohols are stable to further oxidation.

    The most widely used oxidizing agent is chromic acid, which is prepared by mixing sodium dichromate with sulfuric acid. However, chromium salts are suspected
mutagens and carcinogens, and strict EPA regulations exist for the handling and disposal
of chromium compounds.  Hypochlorous acid (HOCl), an alternative oxidizing agent, is readily available, inexpensive, safe, and environmentally sound as compared to the dichromates. Although HOCl is unstable and decomposes slowly to upon storage, it can be prepared from a common household item: bleach. Household bleach contains sodium hypochlorite which, when treated with acetic acid, produces the active oxidizing agent:

NaOCl + CH3CO2H HOCl + CH3CO2Na

Example:
Place 10 mmoles of cyclohexanol and a stir bar in an Erlenmeyer flask. Place over a
stir motor and stir while you carefully add 2.5 mL of acetic acid (conc.). Place 15 mL of bleach (approximately 5.25% sodium hypochlorite) in your separatory funnel, position the separatory funnel above the Erlenmeyer flask, and add the bleach dropwise to the cyclohexanol/acetic acid mixture. The addition of bleach should take about 15 min. If the reaction flask becomes hot to the touch during the bleach addition, use an ice bath to cool it down. When the addition of the bleach is
complete, the solution will be pale yellow to yellow-green in color. Test the solution for excess hypochlorous acid and, if necessary, add additional bleach.
    Stir the reaction mixture for an additional 15 min at room temperature. Then, quench excess oxidant by adding about 0.5 mL of saturated sodium bisulfite solution. Test for excess hypochlorous acid and, if necessary, add additional sodium bisulfite.  Add 2 drops of thymol blue (an indicator), then add 6N NaOH until the solution is
just basic. Add solid NaCl until the solution is saturated with salt, then decant the liquid into your separatory funnel. Extract with 5 mL of methylene chloride, save
the organic layer, then extract the aqueous layer one more time with 5 mL of methylene chloride.

Rhodium

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helpful hints
« Reply #1 on: January 03, 2004, 07:11:00 PM »
The grammar and spelling of your subject line is so bad as to create confusion about what the post contains. It wouldn't be a bad thing if you edited the body of your post and divided it into segments/paragraphs (writing "Example:" in boldface would also increase readability).

The title of your post

Post 480245

(ADDkid: "Function Group vs Solvation", Chemicals & Equipment)
also needs to be edited to reflect the content, as it stands now it is completely useless.


stratosphere

  • Guest
i believe when primary alchols are oxidized...
« Reply #2 on: January 05, 2004, 09:00:00 PM »
i believe when primary alchols are oxidized with NaOCl or HOCl in addition to aldhydes there is some carboxylic acid produced as well, this can be controlled by using excess alcohol, and any carboxlic acid can be removed by basification followed by distillation (leaving behind the sodium carboxlate salt).

the main problem with household bleach is its quite dilute (~5% or ~1 molar).
i don't know if it can be concentrated by simply boiling off water, or if that causes decompostion. if boiling is to harsh another option besides vacuum distillation might be to connect a flask of bleach by a short hose to a caintainer of dessicant (e.g. anhyd CaCl2) and warm the bleach say to about 40C), i would imagine you could obtain a fairly concentrated bleach solution after a day of this.

and yet another otc option is pool chlorinator which is usually somthing like dry 60% Ca(OCl)2+40% CaCl2.