Page 40 - FPGEE Medicinal and Organic Chemistry Q&A Book

Krisman

477. (c) Acetophenone undergoes reduction re- which on acidification gives the corresponding
action in the presence of Zinc amalgam and is carboxylic acid.
concentrated HCl to form ethylbenzene. This Tollens’ reagent is also used to distin-
reaction is known in organic chemistry as guish an aldehyde from a ketone (except alpha-
Clemmensen reduction. hydroxy ketone, which gives a positive Tollens’
test). A test can be performed by adding the al-
O
dehyde or ketone to Tollens' reagent and then
C CH 3 CH CH putting the test tube in a warm water bath. If
2 3
the reactant under the test is an aldehyde, the
Zn (Hg) / HCl
Tollens' test results in a silver mirror. If the re-
Reduction actant is a ketone (except alpha-hydroxy ke-
tone), it will not react because a ketone cannot
Acetophenone Ethyl benzene be oxidized easily. A ketone has no available
hydrogen atom on the carbonyl carbon that can
478. (c) o-Benzoquinone, also known as o- be oxidized, unlike an aldehyde, which has this
quinone, can be prepared by the oxidation of hydrogen atom, (fig: 11.26, page 194).
catechol in the presence of silver oxide.
481. (d) All. The haloform reaction is a chemi-
OH O
cal reaction where a haloform (CHX , where X
OH 3
O
is a halogen) is produced by the exhaustive ha-
Silver oxide
logenation of a methyl ketone (a molecule
Oxidation containing the R-CO-CH group) in the
3
Catechol o-Benzoquinone presence of a base. R may be H, alkyl or aryl.
The reaction can be used to produce CHCl ,
3
479. (a) I only. In benzaldehyde, the -CHO CHBr or CHI . Since chloroform (CHCl ) and
3 3 3
group is a meta-director therefore nitration of bromoform (CHBr ) are liquid at room tempera-
3
benzaldehyde would result in m- ture whereas iodoform (CHI ) is solid at room
3
nitrobenzaldehyde as a major product. temperature, an iodine solution is commonly
used.
CHO CHO
The haloform reaction is used as a di-
HNO / H SO agnostic test for the presence of the -COCH
3 2 4
3
group. The test can be performed by the addition
NO of a solution of iodine to an unknown compound
2
Benzaldehyde m-Nitrobenzaldehyde in the presence of aqueous alkali (NaOH). A
presence of yellow precipitates of iodoform
480. (b) Tollens' reagent is an ammoniacal sil- indicates a positive iodoform test.
ver nitrate (Ag(NH ) OH) solution. It was
3 2
named after Bernhard Tollens. The This test is positive with the following
diamminesilver complex (Ag(NH ) OH) is an compounds:
3 2
oxidizing agent, which is itself reduced to sil-
ver metal, which in a clean glass reaction ves- 1. Methyl ketone
sel forms a "silver mirror." This feature is used 2. Acetaldehyde
as a test for aldehydes, which are oxidized to 3. Ethanol
carboxylic acids. It should be noted that the ac- 4. Secondary alcohol
tual oxidation product is the carboxylate ion,

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