4-aminophenol

 

4-aminophenol

Chemical formula	C6H7NO
OTP appearance	white or red/yellow crystals
Molar Mass(g/mol)	109.126
Density(g/cc)	1.13
Melting Point(°C)	187.5
Boiling Point(°C)	284
Solubility in water(g/L)	15
NFPA 704	1 2 0

Uses

• Vital precursor to paracetamol

Natural occurrence

• 4-aminophenol does not occur naturally

Hazards

• Flammable
• Mutagen, Irritant, lowers blood oxygen via methemoglobin.

Production

Synthesis

Chemical reduction of nitrophenol

sodium borohydride

Combine the 4-nitrophenol and sodium borohydride giving 4-aminophenol

HO-C₆H₄-NO₂ + NaBH₄

{1 M/L NaOH,Pd/C

→

13-17°C}

HO-C₆H₄-NH₂ + NaBO₂ + H₂

tin / hydrochloric acid

1. Combine the 4-nitrophenol with tin in a reflux apparatus
2. Drip in hydrochloric acid

   2 HOC₆H₄NO₂ + 12 HCl + 3 Sn → 2 HOC₆H₄NH₂ + 3 SnCl₄ + 4 H₂O

3. Neutralize the solution with an icy saturated solution of sodium hydroxide
4. Separate the remaining materials via distillation, salting, and liq/liq extractions

Electroreduction of nitrobenzene

JAE

The Journal of Applied Electrochemistry outlines the electrolysis (375mV) of a solution of nitrobenzene in 20% sulfuric acid produces an amine which rearranges into 4-aminophenol and aniline

C₆H₅NO₂ + 4 H → C₆H₅NHOH + H₂O // benzene amino hydrate

C₆H₅NHOH + H → NH₂-C₆H₄-OH // 4-aminophenol

C₆H₅NHOH + 2 H → C₆H₅NH₂ + H₂O // aniline and water}

SCV

SCV

Purification

Phase I

This phase eliminates materials like ethers, esters, and analine. From an acidic aqueous solution of 4-aminophenol

1. Neutralize pH to ~5.0-5.5 using ammonia

   N.B. should keep the 4-aminophenol dissolved in water (higher pH will cause it to precipitate)

2. Repeat
   1. Exclude oxygen from the environment, maintain temperature at 60-70°C
   2. Mix thoroughly (countercurrent wash) with trichloromethane
   3. Evaporate the TCM and recycle
   4. Discard the acidic material left behind by the TCM
3. Until satisfied
4. Filter through carbon
5. Discard carbon residue

Phase II

This phase eliminates 2-aminophenol

1. Prepare an aqueous solutionof 4- and 2- aminophenol at 75°C
2. Increase pH of solution to 7.2 using ammonia
3. Lower temperature to 1°C
4. Filter
5. Discard filtrate, potentially containing 2-aminophenol
6. Retain residue, purified