Patent GB-656740-A (GB)
Title: Improvements in the manufacture of crotonic anhydride
IPC: C07C51/56
Filed: 1948-05-28
Abstract: Crotonic anhydride is produced by reaction between crotonic acid and acetic or propionic anhydride with the production of the corresponding saturated aliphatic acid, by a process which comprises continuously introducing crotonic acid, in admixture with an inert organic liquid diluent which forms an azeotropic mixture with said saturated aliphatic acid, into the vapour of the acetic or propionic anhydride boiling under atmospheric pressure and continuously removing a vaporous azeotropic mixture of said saturated aliphatic acid and said diluent to leave a liquid residue comprising crotonic anhydride.  Suitable diluents are benzene, ethyl benzene, toluene and meta-xylene.  In carrying out the process, acetic or propionic anhydride is heated to boiling in the base of a fractionating column and, when the column is filled with anhydride vapours, a mixture of crotonic acid and diluent is introduced at a point between 1/4 and 1/2 the length of the column above the base.  Acetic (or propionic) acid is formed by reaction with the crotonic acid and is removed as an azeotropic mixture with the diluent from which it may be separated by water-extraction, the diluent then being dried and recirculated with more crotonic acid.  The crotonic anhydride formed in the column is withdrawn from the base in liquid mixture with unreacted crotonic acid and unchanged acetic or propionic anhydride.  The mixture is fractionated to separate the three components, the crotonic acid and acetic or propionic anhydride being returned to the column.  The crotonic acid feed, which may be preheated, is preferably employed in the proportion of 1 part per 2.5-5.0 parts by weight of diluent and the acetic or propionic anhydride is preferably vaporized at a rate two or more times that theoretically necessary to react with the crotonic acid.  Examples are given.  Specification 612,790 is referred to.  The Specification as open to inspection under Sect. 91 relates to the production of crotonic anhydride by reaction between crotonic acid and saturated lower aliphatic acid anhydrides in general wherein crotonic acid in admixture with an inert organic diluent is introduced into the vapour of a saturated lower aliphatic acid anhydride boiling at atmospheric pressure, the diluent and conditions employed being such that the diluent boils and its vapour is removed from the reaction zone together with the vapour of the lower aliphatic acid produced.  This subject-matter does not appear in the Specification as accepted.ALSO:Crotonic anhydride is produced by reaction between crotonic acid and acetic or propionic anhydride with the production of the corresponding saturated aliphatic acid, by a process which comprises continuously introducing crotonic acid, in admixture with an inert organic liquid diluent which forms an azeotropic mixture with said saturated aliphatic acid, into the vapour of the acetic or propionic anhydride boiling under atmospheric pressure and continuously removing a vaporous azeotropic mixture of said saturated aliphatic acid and diluent to leave a liquid residue comprising crotonic anhydride.  Suitable diluents are benzene, ethyl benzene, toluene and meta-xylene.  In carrying out the process, acetic or propionic anhydride is heated to boiling in the base of a fractionating column and when the column is filled with anhydride vapours, a mixture of crotonic acid and diluent is introduced at a point between 1/4 and 1/2 the length of the column above the base. The acetic or propionic acid formed is removed in azeotropic mixture with the diluent and the diluent separated therefrom and recycled with further crotonic acid.  The crotonic anhydride formed is removed from the column base in liquid mixture with unreacted crotonic acid and unchanged acetic or propionic anhydride; the latter two components are separated from the crotonic anhydride by fractionation and recycled to the column.  Examples are given.  Specification 612,790, [Group IV (b)], is referred to.  The Specification as open to inspection under Sect. 91 relates to the production of crotonic anhydride by introducing crotonic acid in admixture with an inert organic diluent into the vapour of a saturated lower aliphatic acid anhydride boiling under atmospheric pressure, the diluent and conditions employed being such that the diluent boils and its vapour is removed from the reaction zone together with the vapour of the saturated lower aliphatic acid produced.  This subject-matter does not appear in the Specification as accepted.