Patent GB-694217-A (GB)
Title: Improvements in or relating to the production of flame-proof cellulose derivatives
IPC: C08B3/22
Filed: 1951-05-18
Abstract: Flame - resistant cellulose derivatives are obtained by esterifying cellulosic materials with compounds capable of introducing haloalkyl phosphate ester groups into the cellulose molecules.  Cellulose derivatives containing free hydroxyl groups may be subjected to the treatment.  The esterifying agent may be a haloalkyl ester of a halo-phosphonic acid; esterification takes place with elimination of hydrohalide acid.  Chlorine or bromine compounds may be used. Specified compounds are bis - (2 : 3 - dichloropropyl) - chlorophosphonate, bis - (2 - chloroethyl) - chloro - phosphonate, and bis - (2 : 3 - dibromopropyl)-chloro-phosphonate (see Group IV (b)).  The cellulosic material is preferably dried before being subjected to the esterification, e.g. it may be treated with boiling toluene so that the water is removed by azeotropic distillation.  In the case of a cellulose derivative, such as cellulose acetate, containing free hydroxyl groups, the esterification with a haloalkyl halophosphonate is preferably carried out in solution and in presence of an organic base which will combine with the hydrohalide acid set free.  Pyridine may serve both as solvent for the cellulose derivative and as neutralizer of the hydrohalide acid.  The reaction may take place at -10 DEG  to +60 DEG  C.  The product may be precipitated from the reaction mixture by means of water. Products suitable for moulding or extrusion may be obtained.  They may be dissolved or swollen to a gel with organic solvents or swelling agents, e.g. acetone or ethylene dichloride.  In an example, cellulose acetate having an acetyl value of 54.5 per cent calculated as acetic acid is heated in toluene until all moisture has been removed by distillation with the toluene.  The water-free cellulose acetate is dissolved in water-free pyridine and then esterified with bis-(2-chloroethyl)-chlorophosphonate at 50 DEG  C.  The solution is poured into water to precipitate the bis-(2-chloroethyl)-phosphate ester of cellulose acetate.  The product is washed with ethyl alcohol and toluene.  It swells in acetone and forms a gel in ethylene dichloride.  In another example, the cellulose acetate used has an acetyl value of 45.8 per cent and the bis-(2-chloroethyl)-phosphate ester of cellulose acetate obtained is soluble in acetone, 1 : 4-dioxane, and pyridine.ALSO:Bis-(haloalkyl)-halophosphonates are obtained by reacting phosphorus trichloride or tribromide with an alkylene oxide, a halogenated aliphatic alcohol, or a halogenated alkylene oxide, so as to form a tri-haloalkyl ester of phosphorous acid, and then chlorinating or brominating the product to convert it into the chloride or bromide of the corresponding bis-haloalkyl phosphonic acid.  Thus phosphorus trichloride is reacted with ethylene oxide, epichlorhydrin, or 2 : 3-dichlor-1-propanol to form the trialkyl phosphite, which is then chlorinated and converted into the bis-chloralkyl ester of chlorphosphonic acid.  Specified chlorophosphonates are bis - (2 : 3 - dichlorpropyl) -, bis - (2 - chlorethyl)-, and bis-(2 : 3-dibrompropyl)-chlorophosphonate. The compounds may be caused to react with cellulose or cellulose derivatives containing free hydroxyl groups so as to form flame-resistant compounds (see Group IV (a)).