Chemistry Reference
In-Depth Information
The alcohol test used by the police in former times is based on this color change:
the detector tube contains the dichromate reagent, which oxidizes the exhaled
alcohol vapor from the traffic offender. It should not be talked about the primary
oxidation product (acetaldehyde) before the students could gain experience with
this substance (see [
1
], p. 90 ff.).
9.5 Discovery of Other Synthesis Relations
In the next step, we will test how the six standard substances react with sodium
hydroxide solution ([
1
], p. 249).
Ethanoic ethyl ester (substance C) reacts quickly with sodium hydroxide solution.
The ester phase and the ester smell have already disappeared after a couple of
minutes. The reaction mixture has to be distilled for further testing. Distillate and
residue are to be tested with the standard tests.
In contrast to these observations, propanoic propyl ester (substance F) reacts
very slowly with sodium hydroxide solution. The volume of the ester phase has
reduced only by half after 1 week. Ester phase and aqueous phase are to be tested
without distillation.
The results of these two experiments can be found in Table
9.3
.
The following can be concluded from Table
9.3
:
- Ethanol can be found in the distillate in experiment 5 (it might also contain
propanol).
Acetic acid can be found in the residue (after acidifying with sulfuric acid).
Therefore, the following reaction has taken place:
Ethanoic ethyl ester has been transformed by sodium hydroxide solution to a
mixture of acetic acid and ethanol (and possibly propanol).
- Apart from remaining ester, propanol can be found in the upper phase in
experiment 6. The presence of ethanol can be excluded due to the negative
result of the iodoform test. Propanoic acid can be found in the lower phase (after
acidifying with sulfuric acid). The following reaction has taken place:
Table 9.3
Investigation of the reactions of esters with sodium hydroxide solution
Alcohols Esters Carboxylic acids Exp. 5 Exp. 6
A D C F B E Dist. Res. UP LP
Dichromate test + + + + - - + - + -
BTB test - - - - + + - + - +
Cerium nitrate test + + - - - - + - + -
Rojahn test - - + + - - - - + -
Iron chloride test - - - - +
L
+
u
- +
L
- +
u
Iodoform test + - + - - - + - - -
Exp. 5: Reaction of ester C (both the distillate and the residue are tested). Exp. 6: Reaction of the
ester F (both the upper phase (UP) and the lower phase (LP) are tested)
