Ketones chromic acid test

Chromic acid test. This test is able to distinguish primary and secondary alcohols from tertiary alcohols. Using acidified dichromate solution, primary alcohols are oxidized to carboxylic acids secondary alcohols are oxidized to ketones tertiary alcohols are not oxidized. (Note that in those alcohols which are oxidized, the carbon that has the hydroxyl group loses a hydrogen.) In the oxidation, the brown-red color of the chromic acid changes to a blue-green solution. Phenols are oxidized to nondescript brown tarry masses. (Aldehydes are also oxidized under these conditions to carboxylic acids, but ketones remain intact see Experiment 31 for further discussion.)... 

Chromic acid test. Aldehydes are oxidized to carboxylic acids by chromic acid ketones are not oxidized. A positive test results in the formation of a blue-green solution from the brown-red color of chromic acid. 

The chromic acid test for primary and secondary alcohols exploits the resistance of tertiary alcohols to oxidation. When a primary or secondary alcohol is added to the chromic acid reagent, the orange color changes to green or blue. When a nonoxidizable substance (such as a tertiary alcohol, a ketone, or an alkane) is added to the reagent, no immediate color change occurs. 

The answer is B. Chromic acid test is a qualitative test that can be used to confirm whether a given unknown compound is an aldehyde or not. Even though aldehydes give a positive response to this test, ketones do not. A sample reaction is shown below ... 

Many chromium (VI) compounds are suspected carcinogens. If you would like to run this test, talk to your instructor first. Most often, theTollens test will easily distinguish between aldehydes and ketones, and you should do that test first. If you run the chromic acid test, be sure to wear gloves to avoid contact with this reagent. 

Another method for distinguishing between aldehydes and ketones is the chromic acid test. Because chromic acid is unstable when stored for extended periods of time, the test reagent is prepared as needed by dissolving chromic anhydride in... 

Although primary alcohols are first oxidized to aldehydes, the aldehydes are further oxidized to carboxylic acids. The ability of chromic acid to oxidize aldehydes but not ketones is taken advantage of in a test that uses chromic acid to distinguish between aldehydes and ketones (see Experiment 52D). Secondary alcohols are oxidized to ketones, but no further. Tertiary alcohols are not oxidized at all by the reagent hence, this test can be used to distinguish primary and secondary alcohols from tertiary alcohols. Unlike the Lucas test, this test can be used with all alcohols regardless of molecular weight and solubility. 

Thus, the chromic acid reagent gives a clear-cut distinction between primary and secondary alcohols and aldehydes on the one hand and tertiary alcohols and ketones on the other. Aldehydes may be distinguished from primary and secondary alcohols by means of Schiff s, Tollens s, Benedict s (Sec. 23.4), and Fehling s tests, and primary and secondary alcohols of lower molar mass may be differentiated on the basis of their rates of reaction with concentrated hydrochloric acid containing zinc chloride—the Lucas reagent (Sec. 25.11B). 

In organic chemistry, dilute solutions of hexavalent chromium can be used to oxidize primary or secondary alcohols to the corresponding aldehydes and ketones. Tertiary alcohol groups are unaffected. Because of the oxidation is signaled by a color change from orange to a blue-green, chromic acid is used as a qualitative analytical test for the presence of primary or secondary alcohols. 

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