Patent GB-792653-A (GB)
Title: Hydroxylated benzophenone mixed ether process
Filed: 1956-06-11
Abstract: Benzophenones of general formula: <FORM:0792653/IV (b)/1> where R is a primary alkyl group of more than 1 carbon atom, R1 is a primary alkyl group of less than 3 carbon atoms and R and R1 are different, are prepared by reacting a substituted benzoyl chloride of general formula: <FORM:0792653/IV (b)/2> and a 1,3-dialkoxy benzene in which the alkoxy groups have less than 3 carbon atoms and are the same, in the presence of a Friedel-Crafts type catalyst, and heating the mixture above room temperature.  The acid chloride used as a starting material is prepared from unsymmetrical dialkoxy benzoic acids which have been prepared by selectively alkylating the p-hydroxyl of resorcylic acid with an alkyl group having more than 2 carbon atoms, followed by alkylation of the ortho hydroxyl group with a methyl or ethyl group.  Suitable acids are 4-butoxy-2-methoxy benzoic acid, 4-hexoxy-2-ethoxy benzoic acid, 4-amyloxy-2-methoxy benzoic acid, and 4-ethoxy-2-methoxy benzoic acid.  The preparation of the benzophenones takes place in two stages, in the first stage the acid chloride is condensed with resorcinol dimethyl or diethyl ether using a Friedel-Crafts type of catalyst, and in the second stage the ortho alkoxy groups are dealkylated, also in the presence of a catalyst. The same catalyst may be used in both the condensation and dealkylation step, although it is preferable that different catalysts be employed.  Suitable Friedel-Crafts type of catalysts are aluminium chloride, aluminium bromide, zinc chloride, stannous chloride, zirconium tetrachloride, boron trifluoride, antimony pentachloride, stannic chloride, tellurium tetrachloride, bismuth trichloride, and titanium tetrachloride.  A preferred catalyst for the dealkylation step is titanium tetrachloride.  The condensation step is preferably carried out in the presence of an inert solvent, e.g. chlorobenzene, and after adding the catalyst gradually at about 10 DEG  C. the mixture is heated to above 50 DEG  C., dry hydrogen halide is passed through the reaction mixture, and the product of the condensation becomes dealkylated.  The dealkylation takes place under essentially anhydrous conditions.  Suitable hydrogen halides are hydrogen chloride and preferably hydrogen bromide.  By using hydrogen chloride in the presence of titanium tetrachloride, only one ortho alkoxy group is readily dealkylated.  Treatment of the alkoxy benzophenone with hydrogen bromide in the absence of the Friedel-Crafts catalyst similarly gives the mono-dealkylated product, viz. 2-hydroxy 21,4,41-trialkoxybenzophenones, in which the para alkoxy groups may be the same or different.  In the preparation of these compounds the alkyl groups removed by the dealkylation must be methyl or ethyl. Examples are given of the preparation of 2-hydroxy, 4-butoxy benzoic acid; 2-methoxy 4-butoxy benzoic acid; 2-methoxy, 4-isopropoxy benzoic acid; 2-ethoxy 4-n-hexyloxybenzoic acid; 2-methyl 4-isobutoxy benzoic acid; 4-ethoxy 2-methoxy benzoic acid; 2,21-hydroxy, 4-methoxy 41-butoxy benzophenone; 2,21-hydroxy 4-ethoxy, 41-hexoxy benzophenone; 2,21-hydroxy 4-methoxy, 41-isopropoxy benzophenone; 2,21-hydroxy 4-methoxy 41-ethoxy, benzophenone; 2-hydroxy 21,4,41-trimethoxy benzophenone; 2-hydroxy, 21,4,41-tributoxy benzophenone; 2-hydroxy, 21-methoxy 4-isobutoxy 41-methoxy benzophenone or its 2-methoxy 4-isobutoxy isomer, 2-hydroxy 21-methoxy 4-ethoxy 41-methoxy benzophenone or its 2-methoxy 4-ethoxy isomer; 2-hydroxy 21-ethoxy 4-methoxy 41-hexoxy benzophenone; 2,21,4-trimethoxy 41-ethoxy benzophenone.  Specification 789,070 is referred to.ALSO:Benzophenones of general formula: <FORM:0792653/IV (a)/1> where R is a primary alkyl group of more than 1 carbon atom, R1 is a primary alkyl group of less than 3 carbon and R and R1 are different, and benzophenones of general formula: <FORM:0792653/IV (a)/2> in which R1, R2 and R3 are alkyl groups which may be the same or different, are incorporated with, e.g. polyvinyl chloride, styrene polymers, styrene-acrylonitrile polymers, and polymers of acrylates such as methyl acrylate and methyl methacrylate to give resistance to U.V. light.  An example is given of a composition of <FORM:0792653/IV (a)/3> with polymethyl methacrylate powder.