The Preparation of Adipic Acid by the Oxidation of Cyclohexanone We usually thin

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The Preparation of Adipic Acid by the Oxidation of Cyclohexanone We usually think of ketones as being rather stable towards oxidation. For example secondary alcohols can be oxidized to ketones without much concern about the ketones being further oxidized. This is certainly the case under mildly acidic conditions. However, under strongly acidic or basic conditions ketones that have enolizable hydrogens can be further oxidized. It is the carbon-carbon double bond of the enol tautomer that is attacked by the oxidizing agent. In fact, permanganate ion, under mildly basic conditions, will attack the enol double bond forming an inorganic cyclic ester. Decomposition of the ester results in cleavage of what was the carbon to carbon double bond of the enol. This produces an aldehyde carboxylate. Further oxidation of the aldehyde functionality by the permanganate ion converts it into a second carboxylate group. Subsequent acid work-up produces the dicarboxylic acid The mechanism for the oxidation of cyclohexanone by permanganate ion is outlined in Scheme 1. Manganese in the form of the permanganate ion is water soluble and a hazard to the environment and must not be flushed down the drain. However, when it is in the form of manganese dioxide it is water insoluble and can be filtered from the reaction mixture and disposed of with the chemical waste. MnO4 OH cyclohexanone enol tautomer cyclic ester OH H3O MnO or hexanedioic Acid (adipic acid) an aldehyde carboxylate Scheme 1 Safety Considerations: In this lab you will be working with cyclohexanone which is a flammable liquid and you will also be working with an open flame. Therefore, and as in all labs, do not take more cyclohexanone than you will be using (2.5 mL.). You will also be working with potassium permanganate, a very powerful oxidizing agent; sodium hydroxide, a strong base; and concentrated hydrochloric acid, a very corrosive acid. You must take care that none of these reagents comes in contact with your skin and, of course, you must wear your goggles at al! times 47

Explanation / Answer

KMnO4 = 7.9 g ; amount in 60 mL

molar mass of kmno4= 158.034 g/mol

Number o f moles = amount / molar mass= 7.9 g/ 158.034 g/mol

=0.05 mol

KMnO4 as an oxidizer in basic media in presence of NaOH I to MnO2 by gained 3 electrons:

MnO4- + 2H2O + 3e- --> MnO2(s) + 4OH-

so in this case:

Eq. wt. of KMnO4 = 158.04/3 = 52.68 grams/equivalent

15 to 20 drops of NaOH of 3 M:

1 mL = 20 drops

Means here the volume of NaOH = 1 mL

Number of moles = volume in L * molarity

= 0.001 L * 3.0M

= 3*10^-3 moles NaOH

Cyclohexanone = 2.5 mL

Density of cyclohexanone= 0.9478 g/mL

Density = mass/ volume

Mass = density * volume

Mass = 0.9478 g/mL* 2.5 Ml

Mass= 2.3695 g

Molar mass 98.15 g/mol

Number of moles =2.3695 g / 98.15 g/mol

= 0.024 moles

Limiting agent : cyclohexanone

0.024 moles cyclohexanol *1.0 adipic acid / 1.0 moles cyclohexanol

=0.024 moles adipic acid

Molar mass of adipic acid: 146.1412 g/mol

Amount in g= 146.1412 g/mol* 0.024 mol

=3.50 g

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