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Preparation of Propanone

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EXP4 - Preparation of Propanone Aim: The purpose of this experiment is to synthesis propanone (58 g/mol) from propan-2-ol (60 g/mol). Principle: This synthesis is an oxidation reaction of secondary alcohol. Secondary can be oxidized by either acidified potassium dichromate (VI) or acidified potassium permanganate (VII). In our synthesis, we oxidize propan-2-ol which is the smallest secondary alcohol available; its oxidation will form a propanone (commonly called acetone) according to the below equation. The most common reagent used for oxidation of secondary alcohols to ketones is chromic acid, H2CrO4. Chromic acid is produced in situ by reaction of potassium dichromate (VI), sulphuric acid and water. K2Cr2O7 + H2O + 2H2SO4 ? 2 H2CrO4 + 2 NaHSO4 The oxidation mechanism is outlined below, the propan-2-ol and chromic acid produce a chromate ester, which then reductively eliminates the Chromium species and produce the propanone product. Method: The experiment is a oxidation reaction where a secondary alcohol (propan-2-ol) is oxidized by acidified potassium dichromate. The reaction readily occurs in room conditions. The product is propanone and the reaction stops at that stage, no catalyst is needed for the reaction and the reaction completes within a few minutes. The reaction is started by adding acidified potassium dichromate to the alcohol. The colour of the oxidizer is initially orange and the colour changes to dirty green upon mixing. ...read more.


Calculations The predicted amount of products formed = 0.0528 mol X 58 g mol-1 = 3.064 g However, product loss due to incomplete reaction, side reactions, evaporation, spillage or residue on glassware could significantly reduce the percentage of yield. Number of mole of actual product formed = 1.93 g / 58 g mol-1 = 0.0332 mol The actual product formed has 0.0332 mol. Thus the percentage yield was about 63.0% of the theoretical value. Discussions Characteristics of this experiment This experiment is a oxidation reaction of secondary alcohol which its mechanism is mentioned in the principle section. The oxidation of secondary alcohol always produces a ketone while that of a primary alcohol, a aldehyde is formed. This experiment choose a secondary alcohol to demonstrate the production of ketone is a wise choice as the oxidation process is stopped at the ketone stage, where if a primary alcohol is used, the reaction will first produce an aldehyde. However, the aldehyde will continue to be oxidized to a carboxylic acid. This oxidation requires a strong oxidizing agent such as potassium permanganate, potassium dichromate or other agents containing Cr(VI). Heating is applied to quicken the reaction. This method is the most common known method for preparing ketones in the laboratory, however there are numbers of other methods which ketones could be produced: * Ketones are also prepared by Gem halide hydrolysis. ...read more.


This is a carbonyl-protecting reaction. * reaction of RCOR' with sodium amide results in cleavage with formation of the amide RCONH2 and the alkane R'H, a reaction called the Haller-Bauer reaction * Electrophilic addition, reaction with an electrophile gives a resonance stabilized cation. * the reaction with phosphonium ylides in the Wittig reaction gives alkenes * reaction with water gives geminal diols * reaction with thiols gives a thioacetal * reaction with a metal hydride gives a metal alkoxide salt and then with water an alcohol * reaction of an enol with halogens to ?-haloketone * reaction at an ?-carbon is the reaction of a ketone with heavy water to give a deuterated ketone-d. * fragmentation in photochemical Norrish reaction * reaction with halogens and base of methyl ketones in the Haloform reaction * reaction of 1,4-aminodiketones to oxazoles by dehydration in the Robinson-Gabriel synthesis * reaction of aryl alkyl ketones with sulfur and an amine to amides in the Willgerodt reaction Ketones are often used in perfumes and paints to stabilize the other ingredients so that they don't degrade as quickly over time. Other uses are as solvents and intermediates in chemical industry. Examples of ketones are acetone, acetophenone, and methyl ethyl ketone. Notes on experiment techniques When handling corrosive concentrated acids such as the concentrated sulphuric acid, a dropper is recommended for its transferral. Addition of concentrated sulphuric acid to aqueous potassium dichromate in this experiment should be done slowly to avoid spillage due to the generation and local acumination of heat. ?THE END? ?? ?? ?? ?? ...read more.

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