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Preparation of propanone from propan-2-ol

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Introduction

Date: 11/10/2011 Exp. No.: 23 Title: Preparation of propanone from propan-2-ol Aim: The aim of this experiment is to prepare propanone by oxidizing propan-2-ol with acidified potassium dichromate solution. Introduction: Ketones and aldehydes are important series in preparation of other compounds and they are commonly prepared by oxidizing alcohol which is done in this experiment. The experiment is an oxidation reaction where a secondary alcohol (propan-2-ol) is oxidized by acidified potassium dichromate. The reaction does not need to be heated but should be placed in an iced water bath as the reaction is highly exothermic. The product is propanone and no catalyst is needed for the reaction. The propanone is serparated from the reaction mixture by simple distillation and is purified using anhydrous cacium chloride. The equation of this reaction is as follow: Chromic acid is produced in situ by adding potassium dichromate (VI) with sulphuric acid and water. K2Cr2O7 + H2O + 2H2SO4 ? 2 H2CrO4 + 2 NaHSO4 The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. ...read more.

Middle

The equation is as below: Why do we need to use ice bath? This is because the boiling point of propanone is only 56oC, during the oxidation, the boiling point of propanone would be reached as the oxidation was very exothermic. If the iced water bath was not used, most of the propanone would be vaporized and escape from the reaction mixture. This causes loss of the product. Therefore, we need to use an ice bath during the oxidation to minimize the amount of propanone vaporized. Why do we need to use anhydrous sodium chloride? This is because even after distillation, the product might contain some water. We need to use anhydrous sodium chloride as a drying agent to extract the water molecule mixed in the organic product. Why does the ketone further oxidize to form carboxylic acid? Ketone may undergo further oxidation to form carboxylic acid with acidified potassium permanganate and under reflux. This reaction has very high activation energy because this requires breaking the strong C-C bond Why do we use the suction flask instead of purely using the gravitational force to filter the crystals? This is because if we do not use the suction flask or any negative pressure, the filtration process will be too slow. ...read more.

Conclusion

Geminal halide hydrolysis The reactants are a geminal dihalide and water or a hydroxide. The reaction product is a ketone or an aldehyde. The first part of the reaction mechanism consists of an ordinary nucleophilic aliphatic substitution to produce a gem-halohydrin. Ruzicka Large Ring Synthesis Formation of large ring alicyclic ketones from dicarboxylic acids by thermal decomposition of salts with metals of the second and fourth groups of the periodic table (Ca, Th, Ce) Nef reaction Carbonyl compounds can also be formed using the Nef reaction. The Nef reaction is an organic reaction describing the acid hydrolysis of a salt of a primary or secondary nitroalkane (1) to an aldehyde or a ketone (3) and nitrous oxide (4). Precaution of this experiment 1. Concentrated sulphuric acid is highly corrosive and oxidizing, so it must be handled with care. 2. Acidified potassium dichromate is also very oxidizing, so it should also be treated carefully. 3. If any concentrated sulphuric acid or acidified potassium dichromate are in contact with our skin, we should wash it with running tap water immediately. 4. During the oxidation of propan-2-ol, safety goggles should be worn as this reaction is highly exothermic. Reference: http://en.wikipedia.org/wiki/Chromic_acid http://www.chemguide.co.uk/organicprops/alcohols/oxidation.html http://www.docbrown.info/page07/redox3.htm http://chemistry.boisestate.edu/people/richardbanks/organic/nomenclature/ethernomenclature1.htm http://www.angelfire.com/bc2/OrgChem/ethers.html http://www.chemicalforums.com/index.php?topic=32190.0 http://www.newworldencyclopedia.org/entry/Ketone http://www.lookchem.com/Chempedia/Basic-Chemical/Chemical-Reaction/8524.html http://www.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/ClassificationTests/aldehyde_ketone.html http://scmwaterproofporous.blogspot.com/2010/10/buchner-funnel.html ?? ?? ?? ?? ...read more.

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This is a highly detailed, well laid out experiment with excellent alternative methods.
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Marked by teacher Brady Smith 20/02/2012

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