In: Chemistry
2) Indicate the structural change and reaction that occurred to produce each positive test a. Bromine Unsatuation b. Baeyer Unsaturation c. Chromic Acid d. Tollen’s e. Iodoform
Bromine Unsatuation
This test is used for finding unsaturation (not aromatic unsaturation). Here bromine adds to alkene to give 1,2-dibromocompound.
Baeyer Unsaturation
This also a qualitative test for the presence of unsaturation, Baeyer's reagent is an alkaline solution of cold potassium permanganate, which is a powerful oxidant making this a redox reaction. Reaction with double or triple bonds (-C=C- or -C?C-) in an organic material causes the color to fade from purplish-pink to brown. It is a syn addition reaction. But Aldehydes and formic acid also give a positive test.
Chromic Acid Test
This test is for 1o and 2o alcohols and aldehydes. This test distinguishes primary and secondary alcohols from tertiary. Chromic acid will oxidize a primary alcohol first to an aldehyde and then to a carboxylic acid and it will oxidize a secondary alcohol to a ketone. Tertiary alcohols do not react. The OH-bearing carbon must have a hydrogen atom attached.
Since the carbon atom is being oxidized in primary and secondary, the orange chromium Cr6+ ion is being reduced to the blue-green Cr3+ ion.
Tollen’s Test
The Tollen’s test is used to test for the presence of aldehydes. In this reaction, an aldehyde is oxidized to a carboxylic acid while the Ag1+ is reduced to silver metal, which deposits as a thin film on the inner surface of the glass. The generic reaction is as follows and is specific for aldehydes:
lodoform test
It will show the positive test for acetaldehyde and methyl ketones. The methyl group of the ketone is removed from the molecule and produces iodoform (CHI3). The formation of a yellow precipitate or suspension of iodoform is a positive test.