How do you make Benzoic Acid from Phenol?

Answer 1

Firstly we React with Zinc Granules to Convert Phenol to Benzene

Then We React with Methyl Chloride in presence of AlCl3 and Oxidise with Alkaline KMnO4 in Drastic Conditions and Hydrolyse with Acid.

The first answer is correct, but there are two other possible ways to convert phenol into benzoic acid without first reducing it to benzene:

There is no direct method of converting phenol to benzoic acid because there is no benzylic carbon on phenol. There is one indirect way of starting with phenol and ending up with benzoic acid that will definitely work, and there are two additional, two-step methods, one of which will most likely work. The second step of one of the two additional methods gives 1-hydroxyethyl benzene, and that reaction has been published. The other indirect way may or may not work since I thought of it, but was not able to find any information about it via an internet search. Information on the reaction may be found searching Chemical Abstracts either on-line (for which I do not have an account), or at a university library.

Method 1. See the first Contributor's answer.

Synthesis of the Intermediate. The intermediate is 2,3-dihydrobenzo[ß]furan. To see the structure of this, imagine a benzene ring that has two of its carbons in common with one molecule of tetrahydrofuran. The "ß" means that the oxygen of the tetrahydrofuran moiety is bonded to either of the common benzene-ring carbons.

To make the intermediate, phenol is allowed to react with 1,2-dibromoethane in very dry ether or methylene chloride to yield 1-bromoethyl phenol and HBr. Slowly adding a slight excess of AlBr3 should easily cause a Friedel-Crafts alkylation to occur to give the intermediate and more HBr. Separate the intermediate by evaporating off the solvent and HBr.

Method 2. From the intermediate, there is a known method to produce 1-hydroxyethyl benzene, or C2H5CH2CH2OH, which is easily oxidized by potassium permanganate to benzoic acid.

Dissolve the intermediate in methylene chloride and allow it to react with triethylsilane in the presence of a catalytic amount of tris-pentafluorobenzene borane at room temp. for 22 hours. This will give 1-hydroxyethyl benzene in very high yield. Allow this to react with potassium permanganate to give benzoic acid.

Method 3. I am not sure this method will give the product I would like. I know that it would not if the oxygen were attached to an aliphatic carbon, but the phenyl ring prevents the base, which I figured needs to be a strong one, from attacking the phenyl carbon.

Add approximately 10% of the stoichiometric amount of sodium metal, relative to the amount of intermediate, to very dry tert-butyl alcohol. This will form sodium tert-butoxide, a very strong base, but a poor nucleophile thanks to its steric bulk. Add the intermediate drop-wise over a couple of hours while stirring rapidly. Distilling the reaction products is probably the easiest way to separate the product from the tert-butyl alcohol. The product should be phenyl acetaldehyde. An IR spectrum or a proton NMR will easily determine if the desired product were formed. Allowing the desired product to react with chromic acid will give benzoic acid.

Answer 2

Benzoic acid can be synthesized from phenol by oxidizing phenol with chromic acid or potassium permanganate. This reaction results in the hydroxylation of the benzene ring on phenol, producing benzoic acid.