Carboxylic acid Essay
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B. Chromic Acid Test/ Jones Oxidation This test is based on the reduction of chromium(IV), which is orange, to chromium(III), which is green, when an alcohol is oxidized by the reagent. A change in color of the reagent from orange to green represents a positive test. Primary alcohols are oxidized by the reagent to carboxylic aicds; secondary alcohols are oxidized to ketones. Tertiary alcohols are not oxidized at all by the reagent. Hence, this reaction can be used to distinguish tertiary alcohols form primary and secondary alcohols.
1. Place ethanol, isopropyl alcohol and tert-butyl alcohol in three different test tubes. Label them accordingly. 2. Add potassium dichromate solution to each of the test tube. Mix thoroughly. 3. Cautiously add concentrated sulfuric acid and mix. 4. Observe the change in color of the solution as soon as possible and the time required for such change to occur. 5. Note the odor of the product produced. 6. Rank the alcohols based on the 1-fastest and 3-slowest/no reaction.
Study Questions: 1. What is the principle involved in Chromic acid test?
What is the purpose? Answer: Chromic Acid test is a qualitative test used for the oxidation of primary and secondary alcohol to carboxylic acid and ketones, respectively. Used to determine the primary and secondary alcohol. 2. Provide the type equation used in Chromic acid test. Answers: Primary alcohols; alcoholaldehydescarboxylic acid Note: A mixture of sodium dichromate or potassium dichromate in dilute sulfuric acid and acetone can also be used as Jones reagent. Secondary alcohols are oxidized to its corresponding ketones. 3.
Show the sample equation involved in the reaction between Chromic acid agent and your samples/ which gave a positive result. Ethanol Isopropyl alcohol tert-butyl 4. Provide the possible explanation for: a. Positive results obtained with your samples b. Negative results obtained with your samples c. Different reactivities of your samples Answers: a. Positive results were obtained from ethanol and isopropyl alcohol because ethanol is a primary alcohol and isopropyl alcohol is a secondary alcohol and we all know that Chromic acid test is a test to classify primary and secondary alcohols from tertiary alcohol.
b. Negative results was obtained because tert-butyl alcohol is a tertiary alcohol and potassium dichromate does not react with a tertiary alcohol. c. Different reactivities from the samples were obtained because of the difference in type of alcohols; primary, secondary and tertiary. 5. What is the purpose of the reagent used? Answer: Potassium Dichromate is especially suitable for the oxidation of secondary alcohols to ketones and of primary alcohols to carboxylic acids and in a few cases to aldehydes.
References: http://cactus. dixie. edu/smblack/chemlabs/Chemical_Tests_for_Unknowns. pdf /namedreactions/jones-oxidation. shtm http://www. wellesley. edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/ClassificationTests/alcohol. html http://www. adichemistry. com/organic/organicreagents/jones/jones-reagent-reaction-1. html http://en. wikipedia. org/wiki/Jones_oxidation http://www. organic-chemistry. org/chemicals/oxidations/jones-reagent. shtm.