Hilski
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Sodium Bisulfite in place of Sodium sulfite in Etard Reaction
One of the final steps of a typical Etard reaction is to decompose the C6H5CH3-2Cr02Cl2 complex
that is formed by adding the reaction mixture to a solution of sodium sulfite (Na2SO3). I would like to know if sodium bisulfite
(NaHSO3) could be substituted, and if so, would there be any disadvantages, or extra precautions that need to be taken.
| Quote: | | In a typical experiment the toluene (1/10-1/5 mole) was dissolved in carbon tetrachloride (5-6 volumes). Chromyl chloride (0.21-0.42 mole) in ail
equal volume of carbon tetrachloride \vas added slowly over 1 hour with stirring and external cooling in a bath of cold water so that the temperature
never rose above 35 degrees. Stirring was continued for another 2 hours and the mixture was then either allowed to stand at room temperature or
refluxed with stirring for a number of hours. If the reaction is not initially cooled or if stirring is discontinued too soon, a violent or explosive
reaction may take place. The reaction mixture was decomposed by pouring onto a stirred mixture of ice and saturated aqueous sodium sulphite solution.
The use of insufficient ice or stirring may lead to overheating and over oxidation of the benzaldehyde to the benzoic acid. The organic layer was
separated and the aqueous layer extracted several times with carbon tetrachloride. Extraction is sometimes made difficult by the precipition of basic
chromium salts, and these can best be removed by adding diluted (1 :1) hydrochloric acid. The products were isolated by distillation and their content
of benzaldehydes determined [...] |
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Nicodem
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This is a science forum, so have the decency to cite the quotation!
Like this:
Canadian Journal of Chemistry 1958, 36, 949-951. DOI: 10.1139/v58-136
The sulfite is used to quench the oxidant, so it is irrelevant if NaHSO4 is used.
It is not used "to decompose the C6H5CH3-2Cr02Cl2 complex". That does not make any sense (besides the symbol for oxygen is "O" and not "0"!).
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unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Hilski
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| Quote: | [quote=248894&tid=20135&author=Nicodem]This is a science forum, so have the decency to cite the quotation!
Like this:
Canadian Journal of Chemistry 1958, 36, 949-951. DOI: 10.1139/v58-136 |
Sorry about that. I had intended to post a link to the reference, which I downloaded from this website. Apparently I forgot to do so, so here it is.
www.sciencemadness.org/talk/files.php?pid=156237&aid=806...
| Quote: | The sulfite is used to quench the oxidant, so it is irrelevant if NaHSO4 is used.
It is not used "to decompose the C6H5CH3-2Cr02Cl2 complex". That does not make any sense (besides the symbol for oxygen is "O" and not "0"!).
|
Sorry about the typo. I copy/pasted that passage from the JCS article, and I guess the font didn't translate properly or something.
I'm not going to pretend to understand everything that's going on in the formation of the complex, and it's conversion to the aldehyde in this
reaction, but the phrase The reaction mixture was decomposed by pouring onto a stirred mixture of ice and saturated aqueous sodium
sulphite solution, or very similar phrases are also used in some of the other texts I have read about the Etard reaction. In this
case,if the author is only using the sulfite to quench the oxidant, and only the water is responsible for the 'decomposition' of the Etard complex, I
can see where my thought process went awry. For example, the author appears to be referring to the decomposition of the formed complex, as stated in
the following abstract. (The author uses only water for the decomposition in this instance.)
| Quote: | The Etard reaction. IV. Oxidation of ethylbenzene with chromyl chloride.
Rentea, C. N.; Rentea, Marina; Necsoiu, Ileana; Nenitzescu, C. D.
Inst. Org. Chem., Bucharest, Rom. Revue Roumaine de Chimie (1967),
12(12), 1495-501. CODEN: RRCHAX ISSN: 0035-3930. Journal written in
English. CAN 69:2591 AN 1968:402591 CAPLUS
Abstract
The Etard complex of ethylbenzene (I) was prepd. in CCl4 at 0°. Decompn. of the Etard complex of I by water yielded
phenylacetaldehyde (II) and acetophenone (III) in equal proportions, along with styrene and BzH. The same products were obtained by treatment of
styrene with chromyl chloride and hydrolysis of the complex, II being the major product. Chromyl chloride oxidn. of epoxyphenylethane yielded BzH and
II and a trace of III. Presumably all these compds. result from a common intermediate possessing an epoxide-like structure. The mechanism of these
reactions is discussed. |
Here are a few more areticles about the Etard that I have read.
KINETIC SOLVENT EFFECT IN ETARD'S REACTION R. A. STAIRS
www.sciencemadness.org/talk/files.php?pid=179917&aid=106...
KINETICS OF ETARD'S REACTION: PART III. EFFECT OF RING SUBSTITUTION
R. A. Stairs
Canadian Journal of Chemistry, 1964, 42(3): 550-553, 10.1139/v64-080
http://www.nrcresearchpress.com/doi/abs/10.1139/v64-080
ÉTARD REACTION: II. POLYCYCLIC AROMATIC AND HETEROCYCLIC COMPOUNDS
Owen H. Wheeler
Canadian Journal of Chemistry, 1958, 36(6): 949-951, 10.1139/v58-136
http://www.nrcresearchpress.com/doi/pdf/10.1139/v58-136
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Nicodem
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Though "decomposing the reaction mixture" is not really a proper phrase, I understood what you wanted to say. I was referring to your suggestion that
the sulfite is used to decompose some PhMe.2CrO2Cl2 complex, which does not make sense, because sulfite would reduce it to toluene, and not the Etard
reaction products.
As for that decomposition phrase, "quenching the reaction mixture" is a more descriptive and less ambiguous phrase for the process. Quenching can mean
both, decomposing the excess of a reagent (for example, an oxidant), or hydrolyzing an intermediate product to give the final one (for example,
hydrolyzing the complex of the product with AlCl3 in the Friedel-Crafts acylations).
Quote: Originally posted by Hilski  | | For example, the author appears to be referring to the decomposition of the formed complex, as stated in the following abstract. (The author uses only
water for the decomposition in this instance.) |
I suggest you to nevertheless quench with the sulfite. Cr(VI) compounds are genotoxic and can be carcinogenic. Also, depending on the product, after
addition of water, the various Cr(VI) species can further oxidize some products that are otherwise relatively stable under the anhydrous and properly
mild Etard reaction conditions (typically aldehydes).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Hilski
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| Quote: | | As for that decomposition phrase, "quenching the reaction mixture" is a more descriptive and less ambiguous phrase for the process. Quenching can mean
both, decomposing the excess of a reagent (for example, an oxidant), or hydrolyzing an intermediate product to give the final one (for example,
hydrolyzing the complex of the product with AlCl3 in the Friedel-Crafts acylations). |
OK. That makes sense. Thanks for the clarification.
\"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety. \"
- Benjamin Franklin
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