GB454013A - Manufacture of acetals of polyvinyl alcohol - Google Patents

Abstract

Polyvinyl acetals are manufactured, in a condition in which they can well be further treated, by dissolving, under pressure, a polyvinyl acetal, made in known manner, in a solvent which is gaseous at ordinary temperature and pressure but liquid under the pressure used in the dissolution, and releasing the solution obtained into a liquid or gaseous agent which does not dissolve the acetal, e.g. water, alcohol or alcohol diluted with water. Alternatively the acetal is produced in the solvent under pressure. Suitable volatile solvents are methyl chloride, ethyl chloride, dimethyl ether, ethylene oxide and similar bodies which owing to their content of halogen or oxygen have strong solvent properties, and also sulphur dioxide. The polyvinyl acetals may be prepared by reacting a carbonyl compound (e.g. acetaldehyde, p formaldehyde or a ketone, especially a hydroaromatic ketone) with a polyvinyl alcohol or ester in the presence of a strong acid as catalyst, e.g. a mineral acid such as sulphuric acid or an aromatic sulphonic acid such as toluenesulphonic acid. When the production of the acetal is effected in liquid sulphur dioxide, this substance itself acts as a catalyst, probably in the form of sulphurous acid, and also binds the water liberated in the reaction. In examples: (1) a formaldehyde acetal of polyvinyl alcohol, prepared by reacting polyvinyl acetate and formaldehyde in the presence of ethyl alcohol and sulphuric acid is precipitated in water, dried, and dissolved under pressure in sulphur dioxide, and the solution is released into water; (2) an acetaldehyde acetal prepared by reacting an aqueous solution of polyvinyl alcohol with acetaldehyde in the presence of hydrochloric acid is dried and treated as in (1); (3) a butyraldehyde acetal prepared by reacting polyvinyl alcohol in ethanol with butyraldehyde in the presence of sulphuric acid is worked up by steam distilling the solvent and drying under reduced pressure, and is then dissolved under pressure in methyl chloride and the solution is released into water; (4) polyvinyl alcohol and butyraldehyde or octoic aldehyde are reacted in a bomb in the presence of hydrochloric acid and dimethyl ether, and the solution is released into water; alternatively sulphur dioxide is used as solvent and the hydrochloric acid is dispensed with; (5) polyvinyl alcohol and acetaldehyde are reacted in a bomb in the presence of sulphur dioxide, and the solution is released into water; (6) polyvinyl alcohol and benzaldehyde are reacted in a bomb in the presence of hydrochloric acid and methyl chloride, and the solution is released into water. Samples have been furnished under Sect. 2 (5) of products obtained as follows: (1) polyvinyl acetate and formaldehyde are reacted in an autoclave in the presence of sulphur dioxide and hydrochloric acid, and the solution is released into water; (2) polyvinyl alcohol and isohexaldehyde are reacted in a bomb in the presence of propane and sulphuric acid, and the solution is released into a mixture of water and alcohol. The Specification as open to inspection under Sect. 91 contains an additional example according to which polyvinyl alcohol and paraformaldehyde are reacted in a bomb in the presence of sulphur dioxide, and the solution is released into water. This subject-matter does not appear in the Specification as accepted.