Patent GB-666186-A (GB)
Title: Improvements in or relating to the process for the production of organic acid esters of cellulose and catalysts therefor
IPC: C08B3/02
Filed: 1949-06-15
Abstract: Cellulose is esterified in the presence of a mixed catalyst comprising an equilibrium mixture of (1) perchloric acid and a metallic salt of hydrochloric, hydrobromic, phosphoric or a sulphonic acid or (2) a metal perchlorate and hydrochloric, hydrobromic, phosphoric or a sulphonic acid, the metal of the metallic salt or perchlorate having an electrode potential between +1.7 and -0.7. Suitable metals include aluminium (+1.7), zinc (+0.76), cobalt (+0.28) and copper (-0.34).  Suitable sulphonic acids are paratoluene sulphonic, ethionic, methionic and methane sulphonic acids.  The acids and salts may be used in aqueous solution.  The preferred catalyst comprises zinc chloride and perchloric acid.  Using this mixture the total catalyst may be between 0.25 and 8.0 per cent of the weight of cellulose, preferably about 0.5 to about 3.0 per cent, the perchloric acid/zinc chloride ratio being between 1 : 8 and 4 : 1, preferably between about 1 : 4 and about 1 : 1.  Acetyl, propionyl, butyryl, caproyl, stearyl, acetyl-propionyl, acetyl-butyryl and acetyl-stearyl radicles may be introduced into the cellulose.  In an example, 30 g. of cellulose are pretreated with 12 g. glacial acetic acid and then acylated with 78 mls. acetic anhydride, 110 mls. methylene chloride, 1 ml. of a 7.5 per cent solution of zinc chloride in glacial acetic acid and 1 ml. of a 7.5 per cent solution of perchloric acid in glacial acetic acid.  The mass is stirred and kept at 20 DEG  C. for half an hour and then heated to 40 DEG  C., at which temperature it is maintained.  After 5 1/2 hours a fibre-free acylation dope is obtained.  The product is hydrolysed and washed in accordance with conventional practice. Example (3) describes the preparation of cellulose propionate using a zinc perchlorate/hydrochloric acid catalyst.  The Specification as open to inspection under Sect. 91 includes a reference in example (2) to a zinc sulphate/perchloric acid catalyst.  This subject-matter does not appear in the Specification as accepted.ALSO:A catalyst comprising an equilibrium mixture of (1) perchloric acid and a metallic salt of hydrochloric, hydrobromic, phosphoric or a sulphonic acid; or (2) a metal perchlorate and hydrochloric, hydrobromic, phosphoric or a sulphonic acid, the metal of the metallic salt or perchlorate having an electrode potential between +1.7 and -0.7, is used in the esterification of cellulose (see Group IV(a)).  Suitable metals include aluminium (+1.7), zinc (+0.76), cobalt (+0.28) and copper (-0.34). Suitable sulphonic acids are paratoluene sulphonic, ethionic, methionic and methane sulphonic acid.  The acids and salts may be used in aqueous solution.  A preferred catalyst comprises about 0.25-0.75 per cent of perchloric acid and about 0.5-2.0 per cent of zinc chloride, based on the weight of cellulose to be esterified.  The Specification as open to inspection under Sect. 91 includes a reference in Example 2 to a zinc sulphate/perchloric acid catalyst.  This subject-matter does not appear in the Specification as accepted.