How is aniline made from chlorobenzene
Experiment: differentiating between diesel fuel and heating oil (furfural reaction)
Experiment: Qualitative detection of sugars with the DC
Experiment: Qualitative detection of carbohydrates with aniline
Experiment: dyeing with aniline black
aniline is aminobenzene. It is the simplest aromatic amine (Phenylamine).
The term `` aniline '' stands for all amino aromatics (Arylamines), just like the term `` phenols '' stands for all hydroxyl aromatics.
Manufacture of aniline
Aniline was first named by a pharmacist in 1826 Otto Untouched produced. The heated indigo along with limestone powder. Discovered eight years later F. F. Runge Aniline also found in coal tar and was the first to notice its coloring properties by oxidizing it with chromate to a blue-green dye. But it was not until the rediscovery of the indigo decomposition that aniline was named today, many years later, and thus to its definitive fixation in science. Its name is based on the Arabic word an-nil (means `` blue '', but also `` indigo ''). The name common in Latin countries for indigo is also anil.
Technically, aniline is mainly produced by reducing nitrobenzene. A reducing agent is hydrogen (in statu nascendi), which is made available through a reaction between hydrochloric acid and iron.
A modern process (Halcon process) is based on the catalyzed ammonolysis of phenol.
Catalysts include cerium-doped silicates and metal oxides.
A process similarly proceeds in that chlorobenzene is used instead of phenolate.
Aniline is a liquid that, like almost all amines, has an unpleasant odor. It is also a blood poison that is also absorbed through the skin. It is also suspected of being carcinogenic.
Autoxidation sets in after a short period of standing in the air; polymerisation occurs with the formation of brown products. Therefore, aniline must always be freshly distilled before use (boiling point 184 C).
Aniline is a weak base
From a chemical point of view, aliphatic amino compounds are indeed weak Br nsted bases, but they work with pKaValues around 9-10 are very basic. In contrast, aniline only reacts as a base in a clearly acidic environment.
The pKaValue is therefore only 4.63. In other words: It takes a high proton pressure to protonate aniline. This is also related to the fact that aniline hardly forms hydrogen bonds and is therefore poorly soluble in water. Ultimately, aniline hydrochloride (or that Anilinium cation) about as acidic as acetic acid, whose pKaValue is 4.76.
All of this is due to the fact that the non-binding (`` free '') pair of electrons in nitrogen is `` busy '' elsewhere and is not readily available to bind protons or to form hydrogen bonds. We describe the reason in the next section.
The mesomerism of the aniline molecule
The amino group is in close interaction with the aromatic ring. Its N atom does not make its non-binding electrons completely available to the ring (as is the case with N-heterocycles, for example), but more or less establishes a double bond between itself and the C atom. It is a 1st order substituents, that is, someone who pushes electrons into the already existing aromatic system. With this positive inductive effect (+ I effect) the amino group promotes the mesomerism of the entire ring system. One speaks of one + M effect.
We see that the amino group tends to be positively charged on average over time and prevents protons from docking. That is the reason for the low basicity of aniline. From the mesomeric boundary structures one can further read that aniline even acts as an acid in an alkaline environment, because the amino group can give up protons rather than absorb them.
Some reactions of the aniline
Above all, aniline is known as a starting material in paint chemistry (and thus also in the drug industry). Already his proof through Stanchion belongs here: If you add chlorinated lime to aniline, the mixture turns red-violet. Chlorinated lime acts as an oxidizing agent; it is calcium chloride hypochlorite Ca (ClO, Cl)2.
The leather and textile dye aniline black is produced by oxidative polymerization of aniline in the presence of potassium chromate. Due to the length of the chromophore, all visible light is absorbed; consequently the dye is black.
Aniline forms the basis of the processes for technical indigo syntheses. After all, aniline was first produced by decomposing indigo.
Dyes based on aniline play a role in the customs proof of furfural, which is used to `` mark '' heating oil to distinguish it from diesel oil. The qualitative evidence of carbohydrates with thin layer chromatography and as a test tube experiment are also based on this reaction.
Further reactions that lead to dyes require the diazotization of the aniline. For this purpose, aniline is reacted with sodium nitrite in an acidic environment:
The resulting diazonium salt couples with other substituted aromatics such as phenols to form dyes. The best-known group of dyes is probably that of Azobenzenes.
It is sterically about that trans-Isomers.
Another well-known example of colored azo compounds is the detection reaction for nitrite and nitrogen oxides with Saltzman's reagent.
In the past, clothes were dyed with the azo dye congo red.
The red trousers of the French infantrymen are known from history.
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