Abstract:
Hydroxy and alkyloxy benzophenones, also known as arylphenones, are efficiently and economically purified by contacting them with inorganic phosphorous compounds in the presence of a non-polar solvent. Best results are obtained when the arylphenone is then treated with an activated carbon and/or activated clay.

Description:
BACKGROUND OF THE INVENTION 
     This invention pertains to a novel method of purification of highly colored crude hydroxy and alkyloxy benzophenones (arylphenones) by contacting them with an inorganic phosphorous compound in a non-polar solvent. 
     DESCRIPTION OF THE PRIOR ART 
     Arylphenones, such as 2,4-dihydroxy benzophenone, and related substituted benzophenone products are widely used as ultra-violet light absorbers in coating and polymeric compositions, such as polyvinylchloride, polyester, polyacrylate, etc. They are also useful in protection of certain dyes and adhesives against the effects of ultra-violet light. 
     It is desirable that such products be as light in color as possible in order to not affect the color of the material to which it may be applied. U.S. Pat. Nos. 3,526,666 and 3,850,988 discuss attempts to purify a colored crude product. In particular, good discussions of prior art purification methods can be found in U.S. Pat. No. 3,850,988. However, none of the prior art methods achieve the desired results of purifying and decoloring the crude product without substantial amounts of purifying agents and/or multiple purification attempts. Prior art purifying and decoloring methods therefore tend to be time consuming and expensive, and it is not commercially feasible to purify crude product with particularly high levels of impurities or discoloration to an acceptable level. 
     Although multiple repetitions may eventually produce a product with acceptable purity, multiple repetitions are time consuming, increase the required quantity of purifying agents, and each repetition typically reduces the eventual yield of purified product by 10-15%. 
     SUMMARY OF INVENTION 
     One object of this invention is to provide a method for purification and decolorization of crude arylphenones which contain colorants and/or impurities at a level which previously known methods are not effective in purifying without multiple repetitions. 
     Another object is to provide a method of purification and decolorization of arylphenones that is more economical and efficient than previously known methods. 
     A further object of the invention is to provide a method for the purification of arylphenones which comprises contacting the crude arylphenone with phosphoric acid (H 3  PO 4 ), phosphorous acid (H 3  PO 3 ) or phosphorous pentoxide (P 2  O 5 ) in a non-polar solvent. 
     Further objects and advantages of the invention will become apparent as this disclosure proceeds. 
     In satisfaction of the foregoing objects and advantages there is provided a method for the purification of arylphenones, which comprises contacting the impure arylphenones with inorganic phosphorous compounds such as phosphoric acid, phosphorous acid or phosphorous pentoxide in the presence of a non-polar solvent. As used in this application, the phrase phosphoric acid is intended to include concentrations ranging from 75% to 115%, and includes the super concentrated form commonly known as poly phosphoric acid. Best results are obtained by further contacting the arylphenone with an activated carbon and/or activated clay, removing the inorganic phosphorous compound and carbon/clay, and then recovering the decolorized/purified arylphenone from the resultant solution. The amount of inorganic phosphorous compound needed depends on the level of impurities, but will not exceed 15% by weight of the arylphenone, with as little as 2% being adequate. 
     For best results the ratio of the solvent to the impure arylphenone should be within the range of from 2:1 to 10:1, and the ratio of the carbon/clay to impure arylphenone should be within the range of from 1:100 to 10:100 by weight. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     According to this invention it has been found that if inorganic phosphorous compounds such as phosphoric acid, phosphorous acid or phosphorous pentoxide are used in the treatment and purification of arylphenones, prior to treatment with activated clays and/or activated carbons, that decolorization and purification is simple, inexpensive, and effective. The quality of the inorganic phosphorous compound only needs to be a good technical grade. Technical grades of 75% to 115% phosphoric acid are acceptable and are desirable due to their commercial availability and low water content. Low water content is desirable because it allows the solution to be mostly water-free with only a small amount of distillation of the non-polar solvent. Applicant has successfully used phosphorous acid and phosphorous pentoxide of 95-97% purity. 
     The arylphenones to which the present invention is directed may be defined by the following general formula: ##STR1## wherein, in the above formula, R 2  is H or OH, R 1  and R 3  are H, OH, or OR, wherein R is C 1  to C 12  alkyl group. The preferred compounds to which the invention is applicable, but not limited, include the following: 
     2,4-dihydroxybenzophenone 
     2,2&#39;,4-trihydroxybenzophenone 
     2,2&#39;4,4&#39;-tetrahydroxybenzophenone 
     2,2&#39;-dihydroxy-4-methoxybenzophenone 
     2,2&#39;-dihydroxy-4,4&#39;-dimethoxybenzophenone 
     2-hydroxy-4-methoxybenzophenone 
     2-hydroxy-4-octyloxybenzophenone 
     2-hydroxy-4-dodecyloxybenzophenone. 
     These compounds are well known in the art and can be prepared by any conventional method. 
     A particularly important feature of the decolorization and purification method of this invention is that it be done in a non-polar solvent. The extraction and/or removal of the phosphorous compound is almost impossible in polar solvents. A non-polar solvent is a compound of the type whose molecules possess no permanent electric moments and primarily are those solvents which either do not ionize, or ionize very weakly in solution. 
     Preferred solvents of this type which may be used include, but are not limited to, aromatic hydrocarbons, aliphatic hydrocarbons, nitro substituted hydrocarbons, halogenated aromatics, halogenated aliphatics or mixtures thereof. Particularly preferred non-polar solvents are benzene, toluene, chlorobenzene, n-heptane, n-hexane, 1,2-dichloroethane and mixtures thereof. 
     It has been found that contact time of the arylphenone with the phosphorous compound need only be as long as is needed to distill most of the water from the non-polar solvent at or near atmospheric pressure. Water is contained in the solvent, the crude arylphenone and in some phosphorous or phosphoric acid. All or most of the residual water can be removed using simple distillation at reduced or atmospheric pressure. This is accomplished by heating the mixture to the reflux temperature of the solvent. Experience has shown that as little as ten minutes is adequate, but exposure of several hours is not harmful. 
     The common rating parameters for measuring the purity of products such as arylphenones are the varnish color scale (VCS) and the Hunter Lab ΔE (ΔE). For most known commercial applications it is generally desirable that the VCS rating be ≦5.0, and that the ΔE rating be ≦60.0. Di-substituted arylphenones are measured at 10% by weight of appropriate clear solvent (such as acetone, methanol, ethanol, toluene, etc.), whereas tri-substituted and tetrasubstituted arylphenones are measured at 5%. Highly pure disubstituted arylphenones are virtually white in color, whereas highly pure tri- and tetra-substituted arylphenones are light yellow. 
    
    
     The following examples are presented to illustrate the method of the present invention. All starting arylphenones were highly colored and contained a high concentration of impurities. All parts are by weight unless otherwise indicated. 
     EXAMPLE I 
     A. 55 grams (g) of impure 2,4,-dihydroxybenzophenone with a melting point (m.p.) of 132° C., varnish color scale (VCS) of 9+in a 10% by weight solution of Acetone, and a Hunter Lab ΔE (ΔE) greater than 115, was added to 275 g of toluene under stirring at room temperature. 
     B. 5.5 g of 85% phosphoric acid was added and heating began. Most material dissolved at 85° C. with a pink viscous oil forming and at 92° C. all material was dissolved except for the pink viscous oil which continued to darken as material was heated to 110° C. 
     C. Stirring was continued to 10 minutes at 112° C. whereupon the viscous red oil was totally suspended throughout the solution, with the solution being a golden color. 
     D. All of the above solution was poured into a hot decanting flask whereby all the viscous &#34;red oil&#34; separated to the bottom almost immediately. The upper layer was now a golden clear solution. 
     E. The bottom layer, consisting of phosphoric acid and impurities, was extracted and discarded. 
     F. The remaining solution was returned to a stirring vessel and reheated to 100° C. whereupon 3 g of activated clay and 2 g of activated carbon were added. Decolorization occurred almost immediately, but the solution was stirred 30 minutes at 100°-102° C. 
     G. The solution was then filtered through a hot ceramic filter to remove carbon, clay, residual phosphoric acid, and impurities. 
     H. The filtered material was cooled under stirring with a light nitrogen pad, and white, almost translucent crystals began to form at 70° C. 
     I. Material was cooled to room temperature under stirring and nitrogen, then filtered off under vacuum, and formed a damp white cake. 
     J. The damp white cake was dried at 70° C. and 20 mm vacuum for 4 hours. 
     K. Yield of white purified material (purified arylphenone) was 47.3 g (86%) with a m.p. of 144.7° C. and a varnish color scale of less than 2 at a 10% by weight solution in Acetone. Hunter Lab was 21. Material is of very high quality and suitable for any known use of such products. 
     EXAMPLE II 
     Same as Example I except 6.0 g of 75% phosphoric acid was used instead of the 5.5 g of 85% phosphoric acid. Yield was 46.9 g (85%) of material of virtually the same quality as Example I. 
     EXAMPLE III 
     Same as Example I except 5.0 g of polyphosphoric acid was used instead of 85% phosphoric acid. Yield was 47.3 g (86%) of material of virtually the same quality as Example I. 
     EXAMPLE IV 
     Same as Example I except no phosphoric acid was used. Resulting material was unacceptable for use, having a m.p. of 142° C., VCS of 8-9 in a 10% by weight solution in Acetone. The ΔE was 94. 
     EXAMPLE V 
     Same as Example IV but clay and carbon were increased to 6.0 g each. The m.p. increased to 144.2° C. but material was still highly colored and unacceptable with a VCS of 8+and a ΔE of 88. 
     EXAMPLE VI 
     Same as Example I except toluene replaced by chlorobenzene. Results were same as Example I. 
     EXAMPLE VII 
     Same as Example I except toluene was replaced by 1,2 dichloroethane. Results were same as Example I. 
     EXAMPLE VIII 
     Same as Example I except toluene was replaced by n-butanol. No oily separation and no color improvement occurred after carbon/clay addition. Results were poor and unacceptable. 
     EXAMPLE IX 
     Same as Example I except toluene was replaced by methyl isobutyl ketone. Same unacceptable results occurred as in Example VIII. 
     EXAMPLE X 
     Same as Example I except toluene was replaced with a 50/50 mixture of Acetone/methanol. Results were unacceptable, just as in Examples VIII and IX. 
     EXAMPLE XI 
     Same as Example I except toluene was replaced by perchloroethylene. Similar results as in Example I were obtained, producing excellent quality material. 
     EXAMPLE XII 
     Same as Example XI but no phosphoric acid was used. Same unacceptable results as Example IV. 
     EXAMPLE XIII 
     Same as Example I but no activated clay was used. Material was acceptable but not as high quality as Example I. M.P. 144.4° C., VCS 3, ΔE 34. 
     EXAMPLE XIV 
     Same as Example I but no activated carbon was used. Similar results as Example XIII. 
     EXAMPLE XV 
     Same as Example I except 2,4-dihydroxybenzophenone was replaced with a very crude 2,2&#39;-dihydroxy-4, methoxybenzophenone having a m.p. of 58° C., a VCS color of 9+, and a ΔE of 120+. 
     Toluene was also replaced with mineral spirits due to this benzophenone&#39;s high solubility in toluene. 
     Results obtained were similar to results of Example I. M.P. of 71° C., VCS of 2.0-2.5 and ΔE of 32. 
     EXAMPLE XVI 
     Same as Example XV except mineral spirits was replaced by n-heptane. Similar results as in Example XV. 
     EXAMPLE XVII 
     Same as Example XV except mineral spirits was replaced by ethanol. No separation was obtained and very little decolorization. Results were poor and unacceptable. 
     EXAMPLE XVIII 
     Same as Example I except 2,4-dihydroxybenzophenone was replaced by crude 2,2&#39;dihydroxy-4,4&#39;dimethoxybenzophenone with a m.p. of 126° C., VCS of 8, and ΔE of 92. A good quality material with a m.p. of 138° C., VCS 3.0-3.5 and ΔE of 39 was produced. 
     EXAMPLE XIX 
     Same as Example XVI except 2,2&#39;dihydroxy-4- methoxybenzophenone was replaced by crude 2-hydroxy-4- methoxybenzophenone. Excellent results were obtained as in Example XVI. 
     EXAMPLE XX 
     Same as Example XIX except 2-hydroxy-4-methoxybenzophenone was replaced by 2-hydroxy-4-octyloxybenzophenone. Similar results as in Example XIX. 
     EXAMPLE XXI 
     Same as Example XX but n-heptane was replaced by isopropanol. Very little improvement in color. Results poor and unacceptable. 
     EXAMPLE XXII 
     Same as Example I except phosphoric acid and impurities were not extracted prior to addition of clay and carbon. Although slower to filter off the clay, carbon, phosphoric acid, and impurities, an acceptable product was obtained with m.p. of 144.20° C., VCS of 3, and ΔE of 37. 
     EXAMPLE XXIII 
     Same as Example I except no activated clay or activated carbon was used after phosphoric acid and impurities were extracted. Although not acceptable, material has more improvement in color than when only activated clay and activated carbon were used without phosphoric acid or other phosphorous compound. Material has a m.p. of 142 with a VCS of 6-7, and ΔE of 69. 
     EXAMPLE XXIV 
     Same as Example I except the 5.5 g of 85% phosphoric acid (H 3  PO 4 ) was replaced with 1.5 g of phosphorous pentoxide (P 2  O 5 ). Yield was 46.7 g of excellent quality material having a m.p. of 145° C., VCS of 1.5 and ΔE of 19.0. 
     EXAMPLE XXV 
     Same as Example XXIV except no clay or carbon were used. Resulting material was of acceptable quality, having a m.p. of 144° C. VCS of 5.0 and ΔE of 56.3. 
     EXAMPLE XXVI 
     Same as Example XXIV except 2, 4, -dihydroxybenzophenone was replaced with 2,2 dihydroxy-4, 4 dimethoxy benzophenone. Resulting material was of acceptable quality, having a m.p. of 140° C., VCS of 3.0, and AE of 44.0. 
     EXAMPLE XXVII 
     Same as Example XXIV except 2, 4, -dihydroxybenzophenone was replaced with 2, 2, 4 trihydroxybenzophenone. Resulting material was of quality equal to or better than Example XXVI. 
     EXAMPLE XXVIII 
     Same as Example XXIV except clay and carbon were reduced to 1.0 g each. Yield was 47.5 g of excellent quality material, having a m.p. of 145° C., VCS of 2 and ΔE of 23.1. 
     EXAMPLE XXIX 
     Same as Example XXIV except 5.5 g of ortho phosphoric acid (H 3  PO 4 ) was replaced with 1.5 g of phosphorous acid (H 3  PO 3 ). Quality of resulting material was almost identical to Example XXIV, having a m.p. of 145° C., VCS of 1.5 and ΔE of 20.1. 
     EXAMPLE XXX 
     Same as Example XXIX except no clay or carbon was used. Resulting material was of acceptable quality, having a m.p. of 144° C., VCS between 4 and 5, and ΔE of 54. 
     EXAMPLE XXXI 
     Same as Example XXX except H 3  PO 3  was increased to 2.5 g. Resulting material was of slightly better quality, having a m.p. of 144 C, VCS of 4 and ΔAE of 48.1. 
     EXAMPLE XXXII 
     Same as Example XXIX except 2, 4-dihydroxybenzophenone was replaced with 2, 2 dihydroxy-4 methoxybenzophenone. Excellent material was produced having a melting point of 720° C., VCS of 2.5 and ΔE of 29.8. 
     EXAMPLE XXXIII 
     Same as Example XXIX except 2, 4 dihydroxy benzophenone replaced with 2, 2 dihydroxy-4, 4 dimethoxybenzophenone. Produced excellent material with m.p. of 140° C., VCS of 3.0 and ΔE of 43.3. 
     As can be seen from the foregoing examples the novel use of phosphoric acid, phosphorous acid, or phosphorous pentoxide is the key to obtaining a high level or purity. When used without either activated clay or carbon, the result is better than the existing conventional process of using only clay and/or carbon as the purifying agent. When phosphoric acid, phosphorous acid or phosphorous pentoxide are used prior to treatment with activated clay and/or carbon, vastly superior results are obtained.