Chromic anhydride test

They are distinguished from alcohols and other oxygen-containing compounds by their failure to dissolve immediately in cold concentrated sulfuric acid, and from primary and secondary alcohols by their failure to give a positive chromic anhydride test (Sec. 6.30). 

Since allyl alcohol is a primary alcohol, it will give a positive chromic anhydride test, whereas allylbenzene will not. Primary and secondary alcohols are oxidized by chromic anhydride, CrOa, in aqueous sulfuric acid. The clear orange solution turns blue-green and becomes opaque within two seconds in the presence of these alcohols. Hence, allyl alcohol and allylbenzene may be distinguished by the former s ability to give the color change in chromic anhydride. 

Chemical Tests. Benzoin contains an aromatic ring. Confirm this fact by performing the ignition test (Chapter 9). To confirm the presence of the alcohol and ketone functions in benzoin carry out the chromic anhydride test for the —OH group and the 2,4-dinitrophenylhydrazine test for the C=0 group. Isolate the solid 2,4-dinitrophenylhydrazone derivative and compare its melting point to the literature value. 

The reagent also reacts with primary and secondary alcohols (see Chromic Anhydride Test Jones Oxidation, p. 640). 

Dissolve part of the chromic anhydride crystals in water. Pour 2-3 ml of the solution into a test tube and add a potassium iodide solution. What is observed Write the equation of the reaction. 

Alkynes and dienes respond to characterization tests in the same way as alkenes they decolorize bromine in carbon tetrachloride without evolution of hydrogen bromide, and they decolorize cold, neutral, dilute permanganate they are not oxidized by chromic anhydride. They are, however, more unsaturated than alkenes. This property can be detected by determination of their molecular formulas (CnH2n-2) and by a quantitative hydrogenation (two moles of hydrogen are taken up per mole of hydrocarbon). 

Simple alkyl halides respond to the common characterization tests in the same manner as alkanes they are insoluble in cold concentrated sulfuric acid they are inert to bromine in carbon tetrachloride, to aqueous permanganate, and to chromic anhydride. They arc readily distinguished from alkanes, however, by qualitative analysis (Sec. 2.25), which shows the presence of halogen. 

Refer to the isomeric pentyl alcohols of Problem 1(a), p. 515. (a) Indicate which (if any) will give a positive iodoform test, (b) Describe how each will respond to the Lucas reagent, (c) Describe how each will respond to chromic anhydride, (d) Outline all steps in a possible synthesis of each, starting from alcohols of four carbons or less, and using any necessary inorganic reagents. 

The sublimed anthracene is dissolved by heating in a test-tube with a little glacial acetic cid it is treated with about double its weight of chromic anhydride, and heated a short time to boiling. The solution is then diluted with several times its volume of water, the anthraquinone separating out is filtered off, washed with some dilute sulphuric acid, then with water, and is finally crystallised in a test-tube from a little glacial acetic acid. Long colourless needles of anthraquinone, which melt at 2770, are thus obtained. 

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... 

---