AMMONOLYSIS

MANUFACTURE OF ANILINE FROM CHLOROBENZENE BY AMMONOLYSIS

Raw materials

Basis:1 ton aniline

Chlorobenzene = 2,500 lb

Ammonia solution(28%) = 7,450 lb

Cuprous oxide = 350 lb

  Manufacture

Chlorobenzene is charged into a series of horizontal, rotating high - pressure rolled steel autoclave. Approximately 0.1 mole of cuprous oxide and 4 to 5moles of 28 to 30% aqueous ammonia per mole of chlorobenzene are added. The reaction is initiated at a temperature of 180oC and is later maintained at 210 to 220°C under constant agitation. The pressure rises to 750 to 850 psi. The active catalyst is cuprous chlorine produced from cuprous oxide by the product ammonium chlorine as follows:

Cu2O + 2NH4CI  →  Cu2CI2 + 2NH3 + H2O

A large excess of ammonia solution is used to suppress the phenol producing side reaction (C6H5CI + NH3 + H2O → C6H5OH + NH4CI). If the indicated ratio of reactants is used, the rate of aniline formation is about 20 times greater than the rate of phenol formation.

The reaction products are cooled below 100°C and run to a separator. The free ammonia continues to absorption and condensing system for recovery. The settled reaction mass separates into two layers: aniline rich lower and an aqueous upper layer. The approximate distribution of reaction products not including unreacted chlorobenzene in the two layers is as follows: aniline layer 82% aniline, 5% phenol, and 1% diphenylamine; water layer 5 % aniline, 0.5% phenol, 9% chlorine ion (NH4CI), 3% cuprous oxide and 14% ammonia.

The aqueous layer is drawn from the top of the separator and is run to a neutralizer, where it is treated with sodium hydroxide or lime. A sufficient amount of alkali is used to react with the ammonium chloride and phenol. The solution is fractionally distilled, and the liberated ammonia expelled first is recovered in an absorption system. The second fraction consists of aniline and water, which are separated by decantation. The residual solution of sodium phenate and sodium chloride is filtered to remove the precipitated copper oxides, which are reused in subsequent runs.

The aniline layer is withdrawn from the bottom of the separator and treated with 50% sodium hydroxide solution. Approximately 0.2 percent of the volume of the aniline layer is used. The solution is fractionally distilled, yielding first aniline -water mixture, which is further treated as described previously. The second fraction is technically pure (97 to 90%) aniline, the residue is steam distilled, yielding diphenylamine. The phenol is recovered by acidifying the residue mostly sodium phenate and distilling. The yield of aniline is 96% based on chlorobenzene.

 m-NITROANILINE 

100 parts of dinitrobenzene is added to 1000 parts of water at 900C contained in a reducer fitted with reflux condenser and a propeller type stirrer. Upon emulsification, 245 parts of sodium sulfide (9H2O), dissolved in a minimum of water, is gradually run in. The dinitro compound is gradually reduced to m-nitro aniline, the end point being determined by the formation of a definite black streak when ferrous sulfate solution is added to filter paper spotted with some of the reducer liquor.

A modification in the preceding process involves the use of an organic solvent, which is immiscible with water, for the m-dinitrobenzene. Accordingly, 100 parts of technical dinitrobenzene, 90% purity and 160 parts of either solvent naphtha or toluene are put into reducer, and the mixture is warmed to 600C to effect solution. Then, 4000 parts of hot water is added, and the m-dinitrobenzene solution is stirred and heated to 950C. A hot polysulfide (Na2S3) solution – made by heating 720 parts of 7% Na2S with 40 parts of flowers of sulfur – is then added rather rapidly. The reaction of polysulfide is distinctly exothermic, and the charge boils vigorously, but overheating is avoided because of vaporization of solvent. Reduction of the dinitrobenzene to m-nitro aniline is found to take place quickly under such conditions.

To hot reduction mass is first filtered to remove any free sulfur, and the solvent naphtha in the filtrate is distilled with steam. The dissolved m-nitro aniline crystallizes out in the form of bright yellow crystals when the residual liquor is cooled. After washing, the product has a melting point of about 1130C and can be used directly in the manufacture of azo dyes. A yield of approximately 90–92% of theory is attainable, and the process is applicable to other m-dinitro compounds, e.g., m- dinitro derivatives of toluene and xylene.