The anisole or methoxybenzene is an organic compound consisting of an aromatic ether whose chemical formula is C6H5OCH3. Its physical state is that of a colorless liquid, which may present yellowish colorations. It is easily recognized by its characteristic anise odor.
It is then a volatile compound and not very high cohesion forces; common characteristics in light ethers, which are stored in small sealed containers. Specifically, anisole is the simplest of the alkyl aryl ethers; that is, those with an aromatic component (Ar) and another alkyl component (R), Ar-O-R.
Group C6H5- comes to denote Ar, and -CH3 to R, thus having C6H5-O-CH3. The aromatic ring, and the presence of -OCH3 As a substituent group called methoxy, it gives anisole a nucleophilicity superior to that of benzene and nitrobenzene. Therefore, it serves as an intermediate molecule for the synthesis of compounds with pharmacological activity..
Its characteristic anise smell has been used to add anisole to cosmetic and hygiene products that demand a pleasant fragrance..
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The upper image shows the molecular structure of anisole using a spheres and bars model. The aromatic ring is appreciated, whose carbons are sptwo and therefore it is flat, like a hexagonal sheet; and attached to it is the methoxy group, whose carbon is sp3, and its hydrogens are above or below the ring plane.
The importance of the -OCH group3 in the structure it goes beyond breaking with the plane geometry of the molecule: it confers polarity on it, and consequently, the apolar molecule of benzene acquires a permanent dipole moment.
This dipole moment is due to the oxygen atom, which attracts the electron densities of both the aromatic and methyl rings. Thanks to this, anisole molecules can interact through dipole-dipole forces; Although, it lacks any possibility of forming hydrogen bonds, as it is an ether (ROR does not have H linked to oxygen).
Its high boiling point (154ºC), experimentally certifies the strong intermolecular interactions that govern its liquid. Likewise, the London dispersion forces are present, dependent on the molecular mass, and the π-π interactions between the rings themselves.
The structure of anisole, however, does not allow it to interact strongly enough to adopt a solid at room temperature (mp = -37ºC). This may also be due to the fact that when the intermolecular distances are reduced, the electrostatic repulsions between the electrons of neighboring aromatic rings begin to gain a lot of force..
Therefore, and according to crystallographic studies, the anisole molecules in crystals at a temperature of -173ºC cannot be arranged in such a way that their rings are facing each other; that is, their aromatic centers are not aligned one on top of the other, but rather a group -OCH3 is above or below a neighboring ring.
Colorless liquid but that may present slight shades of straw color.
Smells slightly similar to anise seeds.
Candy; however, it is moderately toxic, so this test is dangerous.
108.140 g / mol.
0.995 g / mL.
3.72 (relative to air = 1).
-37ºC.
154ºC.
125ºC (open cup).
475ºC.
0.778 cP at 30 ° C.
34.15 dynes / cm at 30ºC.
1.5179 at 20ºC.
Poorly soluble in water (around 1mg / mL). In other solvents, such as acetone, ethers and alcohols, it is however very soluble.
The aromatic ring of anisole is rich in electrons. This is because oxygen, despite being a highly electronegative atom, contributes with the electrons from its π cloud to delocalize them through the ring in numerous resonance structures. Consequently, more electrons travel through the aromatic system and therefore its nucleophilicity increases..
The increase in nucleophilicity has been experimentally demonstrated by comparing its reactivity, against aromatic electrophilic substitutions, with that of benzene. Thus, the remarkable effect of the -OCH group is evidenced.3 on the chemical properties of the compound.
Likewise, it should be noted that the electrophilic substitutions occur in the positions adjacent (-orto) and opposite (-para) to the methoxy group; that is, it is ortho-para director.
The nucleophilicity of the aromatic ring of anisole already allows a glimpse of its reactivity. The substitutions can occur either in the ring (favored by its nucleophilicity), or in the methoxy group itself; in the latter the O-CH bond is broken3 to replace the -CH3 by another alkyl group: O-alkylation.
Therefore, in an alkylation process, the anisole can accept an R group (fragment of another molecule) by substituting an H on its ring (C-alkylation), or by substituting the CH3 of its methoxy group. The following image illustrates what has just been said:
In the image the R group is located in the -orto position, but it can also be in the -para position, opposite to the -OCH3. When O-alkylation happens, a new ether with another -OR group is obtained.
The name 'anisole' is the best known and most accepted, most likely derived from its anise-like smell. However, the name 'methoxybenzene' is quite specific, since it establishes at once what is the structure and identity of this aromatic ether; this is the name governed by the systematic nomenclature.
Another less used, but equally valid name is 'phenyl methyl ether', which is governed by traditional nomenclature. This is perhaps the most specific name of all, since it directly indicates which are the two structural portions of the ether: phenyl-O-methyl, C6H5-O-CH3.
Medical studies have not yet been able to demonstrate the possible deadly effects of anisole in the body at low doses. However, like almost all chemicals, it causes irritation when exposed for too long and in moderate concentrations to the skin, throat, lungs and eyes..
Also, due to the nucleophilicity of its ring, a part of it is metabolized and therefore is biodegradable. In fact, as a result of this property, simulations showed that it cannot concentrate in aqueous ecosystems since its organisms first degrade it; and therefore, rivers, lakes or seas can accumulate anisole.
In soils, given its volatility, it evaporates quickly and is carried away by air currents; being so, neither does it considerably affect the vegetal masses or plantations.
On the other hand, atmospherically it reacts with free radicals, and therefore does not represent a risk of contamination for the air we breathe..
From anisole other derivatives can be obtained by aromatic electrophilic substitution. This makes it possible for it to be used as an intermediate for the synthesis of drugs, pesticides and solvents, to which it is desired to add its characteristics. Synthetic routes can consist of mostly C-alkylation or O-alkylation.
In addition to its use for organic synthesis, it can be used directly as an additive for creams, ointments and perfumes, incorporating anise fragrances to such products..
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