Chemical of the Day: Phenol

Lol today's Chemical of the Day is phenol. At first I wanted to do benzene but I realized that wasn't as interesting :D Anyway lets get started.

Name: Phenol (wow!)
IUPAC name: Phenol (lol)
Other names: Carbolic acid, hydroxybenzene, benzenol, phenylic acid, phenic acid
*comment: strictly speaking, phenol is not an acid, but we'll talk about this later

Molecular formula: C6H5OH
Molar mass: 94.11g/mol
Appearance (at r.t.p.): transparent crystalline solid
Solubility in water: 8.3g/100mL (decent)
Dipole moment: 1.7D (rather large, but not unexpected)

Synthesis:
1. The most common synthesis pathway for phenol is the Cumene Process.
Benzene + Propene + [O] --> Acetone + Phenol
The intermediate in this reaction is cumene (isopropylbenzene) which is formed by the Friedel-Crafts alkylation of propene onto benzene. The reaction continues via a radical mechanism followed by a rearrangement (Hock's Rearrangement) and elimination reaction to produce acetone and phenol.

2. Another common industrial synthesis pathway for phenol is Dow's Process
Chlorobenzene + NaOH (aq) --340 degrees C, 170atm--> Phenol + NaCl
This reaction is interesting because it proceeds via a benzyne intermediate (HCl is eliminated from chlorobenzene, if you'd like) and OH- adds to the triple bond in to form phenol.

There are few synthesis routes available in the laboratory, since the benzene ring is inert to electrophilic addition and oxidation. As a result most of the phenol used in the lab is obtained via the petrochemical industry (lol).

Properties:
1. The hydroxyl group attached to the benzene ring is a strongly activating group due to oxygen being able to delocalize its lone pairs into the pi electron system. This makes the benzene ring extremely favourable to electrophilic substitution reactions. In fact, nitrating a benzene ring with a hydroxyl group attached no longer requires concentrated nitric acid; dilute nitric acid is sufficient. Furthermore, halogenation of phenol no longer requires the catalyst (it occurs spontaneously) and halogenates at all 3 o- and p- positions since the halide group is such a weak deactivator but hydroxyl is a strong enough activator to cause polysubstitution. Friedel-Crafts alkylation and acylation still require their Lewis acid catalysts, but occur in much milder conditions (e.g. phenol reacts with alcohols in the presence of an acid catalyst to add the alkyl group) and polyalkylation frequently.

2. Phenol is actually the enol tautomer of its keto-enol pair. The keto form is cyclohexa-2,4-dienone and is extremely unstable. The formation of a C=O bond rather than a C=C bond is favourable, but that is more than offset by the loss of resonance stability due to aromaticity. Phenol is hence a notable exception to the norm of keto-enol tautomerism, since most such pairs usually favour the keto form.

3. Phenol is not an acid, but the word "acid" commonly pops up in its name. Its pKa in water is 9.95, about 1 million times more acidic than most aliphatic alcohols such as ethanol (pKa 15.9). This is due to the stability of the phenoxide / phenolate anion which is resonance stabilized by the benzene ring. An alternate explanation is that there is orbital overlap between the lone pairs of the oxygen atom and the delocalized pi network.

4. Phenol is corrosive, but there is no evidence whether it is carcinogenic (benzene, however is a known carcinogen).

Reactions:
1. The obvious, electrophilic substitution. Phenol is a special case though, since it undergoes Friedel-Crafts acylation in 2 different ways. Phenol has 2 sites to which electrophiles may attack: the electrically rich benzene ring, and the lone pairs of the oxygen atom.
When the electrophilic attack occurs on the benzene ring, its termed C-acylation and the "normal" Friedel-Crafts acylation occurs. When the electrophilic attack occurs on the oxygen however, O-acylation occurs and an aryl ester is formed.

2. Phenol + zinc powder --> Benzene
One of the more useful reactions to know, when they ask for funny things like converting phenol into methyl phenyl ketone.

3. Use of the phenoxide anion:
Williamson ether synthesis with the phenoxide anion allows for easy synthesis of aryl ethers.
The phenoxide anion is a potent (though not very strong) base and a strong nucleophile. It can attack ketones and aldehydes.

Other random crap:
None I think. Most of the interesting stuff is up there already :D

Let's see what should Fan Yi do next.