How is carbolic acid made from aniline



Structural formula
General
Surname phenol
other names

Carbolic acid (historical), hydroxybenzene, coal tar creosote

Molecular formula C.6H6O or C6H5OH
CAS number 108-95-2
Brief description white crystals, yellowish to pink due to oxidation
properties
Molar mass 94.11 g mol−1
Physical state firmly
density 1.06 g · cm−3
Melting point 40.9 ° C
boiling point 181.9 ° C
Vapor pressure

0.2 hPa (20 ° C)

pKa value

9,95

solubility

well in water (84 g l−1 at 20 ° C)

safety instructions
MAK

7.8 mg m−3[1]

LD50

317 mg kg−1 (oral rat)[2]

WGK 2 [1]
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions.

The phenol (also Hydroxybenzene or historically carbolic acid, Coal tar creosote, acidum phenylicum, acidum carbolicum) is the simplest compound of the group of phenols.

presentation

Different synthetic routes are known, two of which are important. On an industrial scale, the basic chemical is called phenol by the cumene hydroperoxide process, also known as Phenol synthesis according to Hock known, manufactured:

Benzene and propene are first converted into cumene by a Friedel-Crafts alkylation in an acid, i.e. i. Isopropylbenzene, transferred. Cumene is oxidized by the oxygen in the air, producing a hydroperoxide. The subsequent acidic work-up produces phenol and acetone in a rearrangement reaction. This process is only economical because of the acetone that is produced in the process. If acetone could not be sold on the market, the following important processes, which are mainly used on a laboratory scale, could also be worthwhile industrially:

Phenol can be synthesized by boiling diazonium salts, which are formed by the diazotization of aniline with nitrous acid in the cold.

Another way of presenting phenol is to melt the sodium salt of benzenesulfonic acid with alkali hydroxide:

properties

Phenol is hydroxy substituted benzene. Its melting point is 41 ° C and the boiling point is 182 ° C. Pure phenol forms colorless crystal needles at room temperature, but the commercially available product is i. d. Usually pink to reddish-brown in color due to minor, but intensely colored impurities. It has a characteristic, aromatic odor. The hydroxyl group is relatively acidic for an alcohol and phenol is a weak acid. The cause is the mesomerism stabilization of the corresponding base, the phenolate ion. The negative charge can be delocalized into the ring.

In contrast to aliphatic alcohols, phenols do not undergo nucleophilic substitution reactions with replacement of the hydroxyl group by other nucleophiles. The hydroxy function shows a pronounced + M effect, especially in the deprotonated state. In addition, it shows an −I effect. However, since this is significantly smaller than the + M effect, phenol is very easily attacked by electrophiles. The attack takes place preferably in the ortho and para position to the hydroxyl group. Because of the electron-donating nature of the hydroxy group, phenol is about a thousand times more reactive than benzene.

The preference for ortho- or para-attack by electrophiles can be understood by looking at the boundary structures of the phenolate anion. The negative charge is delocalized in the aromatic ring to the ortho and para positions. Since electrophiles prefer to attack electron-rich positions, the observed regioselectivity occurs. Substitution in the para position is also preferred, since there is no steric interaction of the attacking electrophile with the lone electron pairs of the oxygen.

use

Sir Joseph Lister first used it in 1865 as an antiseptic for disinfecting wounds; However, because of its skin-irritating effect, it was soon replaced by other antiseptics in surgery. Phenol causes chemical burns and is a nerve / cell poison. Because of its bactericidal effect, it was used as a disinfectant in the past. It was also used to make drugs, as a herbicide, and to synthesize synthetic resins. One of the first synthetically manufactured synthetic resin products is Bakelite, a polycondensate made from phenol and formaldehyde.

During the Second World War, concentration camp doctors killed prisoners with intracardiac phenol injections.

In microscopy, it is used to produce phenol water, consisting of ten parts phenol and one part water.

Historical description

“It is a substance that has become extremely important for the paint industry and medicine (as a disinfectant). The trade name is still carbolic acid while the scientific name is now phenol; Although this substance has the properties of a weak acid and is able to combine with bases, it is therefore also called phenylic acid or phenic acid, but at the same time and to an even greater extent it plays the role of a monatomic alcohol, hence the name phenyl alcohol, which is also known as phenyl alcohol cut into phenol. Carbolic acid is mainly obtained from coal tar and lignite tar, only extremely small amounts of it are contained in wood tar, because the creosote of wood tar does not consist of phenol, as was believed for a time, but of the structurally similar cresol, as well as a few others Fabrics. In order to obtain the carbolic acid, the part of the tar that passes between 150-200 ° C is treated with caustic soda, which combines with the carbolic acid and the cresol, which is also contained in coal tar, separates this solution from the other tar components and decomposes them with an acid. The oily product which has separated out is then distilled off and what is above 190.degree. C. is collected. passes over, especially on; the latter is sold as raw cresol, that which passes below 190 ° C as raw carbolic acid. Both substances in this state are still brown, very foul-smelling, oily liquids. This raw carbolic acid (acidum carbolicum crudum) is partly further purified, partly it is used to preserve wood and to disinfect cesspools. "

- from: Merck's Warenlexikon, Verlag von G. A. Gloeckner, Leipzig, Third Edition, 1884, page 250 f.

swell

  1. ab GESTIS substance database
  2. NOAA Material Safety Data Sheet

Categories: Toxic Substance | Corrosive substance | phenol