Hi, that's a good question regarding the oxidation of ethyne. This question was asked before (see the message thread here) but unfortunately I have not learned any more about this reaction. Here are a few statements on the Internet that you may have seen: http://mattson.creighton.edu/C2H2/index.htmlEthyne and permanganate react with cleavage of the carbon-carbon triple bond and formation of the formate ion and the carbonate ion. The stoichiometry for the oxidation by permanganate under neutral or slightly acidic conditions is:
3 C2H2 (g) + 8 MnO4�?/SUP> (aq) + 8 H+ (aq) ––�?gt; 3 HCOOH (aq) + 3 CO2 (g) + 8 MnO2 (s) + 4 H2O (l)
If the conditions are neutral or acidic, the formate ion is converted to formic acid and the carbonate ion forms carbon dioxide. Indeed, as the reaction proceeds, tiny bubbles are observed in the aqueous phase.
http://www.ucc.ie/academic/chem/dolchem/html/dict/alkynes.htmlEthyne is oxidised by a dilute aqueous solution of potassium permanganate to form oxalic acid. Thus, if ethyne is bubbled through a solution of potassium permanganate the solution is decolourised. This is Baeyer's test for unsaturated organic compounds.
No doubt the reaction outcome heavily depends on the conditions used: hot vs. cold; acidic vs. basic vs. neutral; concentrated vs. dilute. Concentrated, hot, acidic permanganate would favor complete oxidation to CO2 and H2O, while milder conditions could give formic acid and/or oxalic acid.
>> And how about if iodine water is added to the ethyne sample? Its 10 drops so I think its considered excess amount. <<
Since alkenes do not generally undergo addition reactions with I2, and since alkynes are considerably less reactive towards addition of halogens, ethyne may not react at all with a dilute solution of iodine in water. The difficulty is the unfavorable formation of the alkene halonium ion intermediate, the first step in the reaction.
Steve
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