Dow process (phenol)
The Dow process is an industrial chemical process for the manufacture of phenol (C6H5OH) from chlorobenzene (C6H5Cl). It was developed by The Dow Chemical Company in the early 20th century and was a significant improvement over earlier methods.
The process involves the nucleophilic aromatic substitution of chlorine in chlorobenzene with hydroxide. Chlorobenzene is reacted with a concentrated aqueous solution of sodium hydroxide (NaOH) at high temperature (around 340°C) and high pressure (around 3,000 psi). This reaction yields sodium phenoxide (C6H5ONa) and sodium chloride (NaCl).
The sodium phenoxide is then acidified with hydrochloric acid (HCl) or another suitable acid to produce phenol and sodium chloride. The overall reaction can be summarized as:
C6H5Cl + NaOH → C6H5ONa + HCl C6H5ONa + HCl → C6H5OH + NaCl
The Dow process allowed for the large-scale, efficient production of phenol, which is a vital precursor in the production of a wide range of chemicals, including plastics (e.g., Bakelite), epoxy resins, and pharmaceuticals. The process is notable for requiring relatively harsh conditions, illustrating the challenges of nucleophilic aromatic substitution. Alternative methods for phenol production, such as the cumene process, have become more prevalent due to their lower energy consumption and milder reaction conditions, although the Dow process remains in use.