GB418943A - Improvements in or relating to processes of making vinyl esters - Google Patents

Abstract

Vinyl esters are manufactured by reacting acetaldehyde, preferably in the form of paraldehyde, with an aliphatic carboxylic acid anhydride by heating the mixture and continuously distilling off the vinyl ester. The reaction may be carried out in the presence of a non-volatile inorganic acid catalyst, e.g., sulphuric, phosphoric or toluenesulphonic acids, preferably in amount between 0,25--2 per cent. In examples: (1) acetic anhydride and paraldehyde are boiled in the presence of sulphuric acid, the volatile products being removed through a fractionating column and the distillate refractionated several times to yield vinyl acetate; (2) the same reaction mixture is boiled in a flask connected for simple distillation, the vapours being introduced into a continuous still near the middle of the column; a mixture of vinyl acetate, acetaldehyde and acetic acid passes over and is fractionated after adding copper acetate and sodium acetate, whilst higher boiling and unreacted materials collect in the still kettle and are returned to the reaction vessel; (3) the reaction mixture is heated as in (2) and when the still head temperature reaches 133 DEG C. a further quantity of reagents is added continuously; the distillate is fractionated as in (2), whilst high boiling bye-products accumulating in the reaction vessel are removed by drawing of portions of the reaction mixture into a tar pot from which volatile products are returned to the reaction vessel; (4) the procedure is as in (3) except that the vapours are led into a continuous still provided with a tray-containing column, whence the higher boiling constituents are returned to the reaction vessel, whilst the vapours pass into a second continuous still where they are fractionated into a heads-cut containing vinyl acetate and acetaldehyde, and a tails-cut containing acetic acid and anhydride; these fractions are then fractionally distilled. The paraldehyde may be replaced by the equilibrium mixture of acetaldehyde and paraldehyde obtained by treating acetaldehyde with sulphuric acid, or the similar mixture found when the recovered acetaldehyde stands in contact with accompanying traces of sulphur dioxide. Vinyl propionate and butyrate may be similarly produced. Reduced pressures may be employed, especially when making the higher boiling esters.