Di- or tri-chloracetaldehyde or their acetals are prepared by contacting ethyl alcohol in atomized condition with chlorine. Preferably the alcohol, in which may be dissolved or suspended a chlorination catalyst such as ferric chloride, is atomized with the aid of a fast rotary agitator to bring the alcohol in a finely-divided form into the space above the liquid in the reaction vessel and then chlorine gas is introduced into the atomized alcohol phase. Operating in a continuous fashion, the alcohol is passed in cascade through reaction vessels, preferably three, in series, each provided with a centrifugal agitator and having a higher temperature than the preceding vessel and introducing chlorine counter-current to it; these vessels may be maintained at 20-30 DEG C., 60-70 DEG C. and 90-100 DEG C., respectively. Alternatively, the alcohol may be atomized into the reaction space with the aid of chlorine gas. To minimize formation of ethyl chloride, the liberated hydrogen chloride is removed as rapidly as possible; this is facilitated by working at somewhat reduced pressures. By adjustment of the chlorine supply, di- or trichloracetaldehyde may be obtained but preferably chlorination is only carried to the alcoholate or acetal stage, the pure aldehyde being obtained by distillation of the reaction product with sulphuric acid or an organic acid such as acetic acid. In an example, ethyl alcohol containing ferric chloride as catalyst is atomized in a glass still by means of a centrifugal agitator and chlorine is passed into the atomized alcohol phase at 25-30 DEG C. until the reaction liquid has a specific gravity of 1.0, whereupon the temperature is raised to 90-100 DEG C. and chlorine then passed in rapidly until the specific gravity is 1.47 whilst evaporated alcohol is condensed and returned to the still and gaseous hydrochloric acid is discharged to a scrubber; the yield as compared with the lower yield obtained in a similar experiment using normal stirring. Specifications 629,699 and 644,916 are referred to.
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