The reaction between chloral and chlorobenzene in yields:

The reaction of chloral (trichloroacetaldehyde) with chlorobenzene in concentrated sulfuric acid is the classic synthesis of DDT. The acid catalyzes the electrophilic aromatic substitution, where the aldehyde carbon of chloral is activated and attacks two molecules of chlorobenzene at the para positions (due to the chlorine substituent directing para), yielding 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, known as p,p-dichlorodiphenyl trichloroethane (DDT).