Isomerization of alkyl phenol with a solid acid catalyst

Abstract: The isomerization of an alkylated phenol composition that contains an ortho-alkyl substituted phenol component to isomerize and reduce the level of ortho-alkyl substituted phenol component therein can be accomplished by heating that composition in the presence of a catalytically effective amount of a solid acid catalyst to carry out such isomerization and reduction in the level of ortho-alkyl substituted phenol. Examples of suitable solid acid catalysts include H-form zeolites, supported sulfonic acids, and supported heteropoly acids. The resulting isomerized product can be subsequently phosphorylated.

Description: The present invention relates to the isomerization of an alkylation product, formed by the alkylation of phenol with an olefin in the presence of a super acid catalyst containing Brønsted acid functionality. The term " isomerization" as used herein, is meant to indicate the change in overall isomer distribution of an alkylated phenol composition by intra- and/or intermolecular mechanism(s). Such a product normally contains a certain level of undesired mono, di and trisubstituted ortho-alkylphenols (or mixture thereof). It is desired to reduce the level of such ortho-substituted alkylphenols, in such an alkylation product since such ortho-substituted components are significantly less reactive in any later desired phosphorylation reaction using the alkylated phenol and also may be deemed by some persons to be more undesired from a toxicological viewpoint. The phosphorylation of such materials is a well-known reaction and involves treating them with a phosphorylating reagent (such as phosphorus oxytrichloride) at moderately elevated temperature (such as about 100°C to about 200°C), preferably in the presence of a Friedel-Crafts catalyst. One prior art reference that relates to the use of trifluoromethane sulfonic acid (also termed "triflic acid" ) as the catalyst to achieve the general type of isomerization that forms the subject matter of the present invention is U.S. Patent No. 4,103,096 to S.L. Giolito et al., which is incorporated herein in its entirety. This patent illustrates, in general terms, one conventional way in which this isomerization reaction has been practiced. While the use of trifluoromethane sulfonic acid catalyst, as just described, has been utilized commercially, its use is attendant with certain disadvantages. The use of relatively high levels of this catalyst (e.g., 800 to 1000 ppm) may be needed for the desired level of isomerization to take place, and the use of such levels of this acid can cause unacceptable color change in the product of the reaction. Trifluoromethane sulfonic acid is a strong acid that can cause corrosion damage in the process equipment that is used. This catalyst cannot be recovered and hence the catalyst costs are not trivial. Finally, the isomerization reaction using this acid is rather slow (e.g., 40 to 60 hours) in order to reach the target isomer distribution. Other methods which have been proposed for practicing analogous isomerization reactions are shown in the following patent and literature references: Japanese Patent Publication No. 45-30091/1970; U.S. Pat. No. 3,014,079; and J. Org. Chem., 38, 1929 (1973). The present invention relates to the isomerization of an alkylated phenol composition comprising ortho-substituted C 3 - or C 4 -alkyl phenol, which comprises heating said composition in the presence of an effective amount of a solid acid catalyst wherein a composition comprising from about 10% to 20% by weight of mono-ortho-substituted alkylated phenols, from about 5% to about 20% by weight of mono-meta-substituted alkylated phenols, from about 10% to about 30% by weight of mono-para-substituted alkylated phenols, and from about 0.5% to 3% 2,6-di-alkylphenol is formed. In general terms, the alkylation product which is treated herein will comprise a mixture of alkylated phenols: from about 10% to about 30%, by weight of the mono-ortho-substituted alkylated phenols; from about 0% to about 5%, by weight of mono-meta-substituted alkylated phenols; from about 5% to about 15%, by weight of mono-para-substituted alkylated phenols; from 2% to 10% by weight 2,6-dialkylated phenol; and from 1% to 5% tri-alkylated phenol. The present invention relies upon a solid acid catalyst, as will be described below in further detail, to lower the amount of such mono and di-ortho-substituted species so that the final product has the following composition: from about 10% to about 20%, by weight of mono-ortho-substituted alkylated phenols; from about 5% to about 20%, by weight of mono-meta-substituted alkylated phenols; from about 10% to about 30%, by weight of mono-para-substituted alkylated phenols; and from about 0.5% to 3% 2,6-di-alkylphenol. The present invention is useful, for example, in the isomerization of mono-ortho-alkylsubstituted phenols, such as monoisopropylphenol, of di-orthoalkylsubstituted phenols, such as 2,6-diisopropylphenol, or mixtures containing such alkylated species. The alkyl group or groups on the phenols which are treated has three or four carbon atoms, such as exemplified by the isopropyl and tert-butyl groups. Most preferaby, it is an isopropyl group. The general type of isomerization reaction is shown in the aforementioned Giolito et al. patent in which the catalyst is employed at a level of from about 0.01% to about 5%, by weight of the alkylphenol, preferably from about 300 to 3000 ppm (about 0.03 to 0.3% by weight), and the reaction temperature for the isomerization reaction will be in the range of from about 170°C to the reflux temperature of the alkylphenol-containing composition which is treated preferably from about 100°C to about 250°C. The reaction can be performed advantageously at atmospheric pressure or elevated pressure (e.g., up to about 500 psig (34.4x10 5 Pa)). The present process is practiced in the absence of an alkylating agent, such as an olefin. In accordance with the present invention, a variety of solid acid catalyst types, which are well known to the person of ordinary skill in the art for other chemical reactions, can be used herein. Included as general types of such solid acid catalysts are the H-form zeolites, the supported sulfonic acids, and the heteropoly acids. Representative examples of H-form zeolites, which form a well-known class of commercially available materials, which find preferred utility in the present invention are the Y-type zeolites and the beta zeolites. Such materials contain Brønsted acid functionality that is needed in the process of the present invention. The ZSM (ex Mobil) type and mordenite class of zeolites also can be used, but they have been found to have somewhat lower activity. The zeolites that are used herein preferably have a silica/alumina ratio of from about 5 to about 100, most preferably from about 5 to about 80. Representative supported sulfur acid catalysts include the sulfonic acid catalysts, sulfated zirconia (commercially available, for example, from MEI Chemicals) and the perfluorinated ionic exchange polymers that are available from DuPont under the trademark NAFION. The latter type of material is described at Col. 2, line 24 to Col. 3, line 47 of U.S. Patent No. 5,001,281 to S.M. Li, which description is incorporated herein by reference. Preferably, the supported sulfur acid catalyst is a sulfated zirconia catalyst. A supported heteropoly acid catalyst can also be used in connection with the present invention. The description of these materials that appears at Col. 2, line 46 to Col. 5, line 24, for example, of U.S. Patent No., 5,300,703 of J.F. Knifton, is incorporated herein as describing such known catalytic materials. The Knifton patent deals with the use of such heteropoly acid materials in the synthesis, rather than in the isomerization, of an alkylphenol composition. The present invention's catalyst selection has a number of advantages, as compared to the use of the liquid catalyst trifluoromethane sulfonic acid previously described. The use of a solid catalyst precludes the possibility that it will become lost by dissolution in the liquid reaction media. There is also no need to use the more difficult means needed to separate a liquid catalyst from a liquid reaction product. The solid acid catalyst is more amenable to a continuous reaction process as compared to the use of a liquid catalyst. The solid catalyst used herein is more easy to regenerate than the trifluoromethane sulfonic acid catalyst that has been previously described. Finally, the solid acid catalysts that are described for use herein have been found to generally yield a product having lower color characteristics than were achieved in many cases using the trifluoromethane sulfonic acid catalyst of the prior art. When a zeolite is selected as the solid acid catalyst for use herein, it has been found that certain novel compositions can be obtained. Such compositions comprise a mixture of alkylphenols wherein the ratio of mono-ortho- to mono- meta- and mono-para- isomers is 2 or lower, preferably 1.5 or lower, more preferably 1 or lower, most preferably 0.85 or lower. Such compositions could also be obtained when a sulfated zirconia was used as the catalyst. The use of the latter catalyst, however, has disadvantages over the use of the zeolite catalysts in respect of cost and ease of regenerability. The present process can be practiced using a variety of reaction schemes. For example, it is possible to implement the present invention using batch reaction, fixed bed reaction, or reactive distillation reaction techniques, or a combination of those techniques. In those cases where a zeolite catalyst is employed, it has been found that such catalysts undergo varying levels of deactivation, due to the formation of carbonaceous species that block the active sites. Such a catalyst can be easily regenerated using known regeneration procedures. For example, a controlled burnout of the carbonaceous species can be achieved using air/nitrogen mixtures that are lean in oxygen at temperatures of from about 200°C to about 500°C. The invention will be further illustrated in the following non-limiting Examples. EXAMPLES Isomerization reactions were carried out using catalysts both in a fixed bed reactor and in a stirred batch reactor. Tests using the fixed bed reactor were carried out at the desired temperatures (150-250°C) and pressures (atmospheric to 150 psig (10.3x10 5 Pa)). Catalysts used were powders or crushed particles in a narrow mesh range or commercial extrudates. Alkylated phenol was pumped into the reactor as a liquid and was heated to about 180°C before contacting the catalyst. Nitrogen was used sometimes as an inert carrier gas. The reactants were fed into the top of the catalyst bed. Liquid isomerized phenol was collected in a gas/liquid separator, and the liquid samples were analyzed with a gas chromatograph, using a flame ionization detector. The results reported are in GC area % and can be converted into the wt% by using the appropriate response factors, i.e. 1.07 for phenol, 0.96 for 2-IPP (i.e. o-IPP), 2,6-di-IPP, 2,4-di-IPP, 2,5-di-IPP, and tri-IPP, 1.00 for 4-IPP (i.e. p-IPP), and 0.98 for 3-IPP (i.e. m-IPP) and 3,5-di-IPP (IPP stands for isopropylphenol). Catalysts were pretreated in situ as needed prior to the isomerization reaction. LHSV means Liquid Hourly Space Velocity. The ratio o/m+p is calculated from the amount (GC area % or wt%) of o-IPP divided by the amount of m-IPP plus the amount of p-IPP. Example 1 This Example illustrates the isomerization of an isopropylated phenol composition using a SO 4 /ZrO 2 (sulfated zirconia) catalyst. 2.0 g of SO 4 /ZrO 2 extrudates obtained from Magnesium Elektron Limited, was loaded into a stainless steel reactor and was calcined in dry air at 600°C - 650°C for two hours. The catalyst was then brought to 180°C and the system was purged with a N 2 stream prior to the isomerization reaction. The results of the isomerization are summarized in Table 1. Day 1.0 1.0 1.0 2.0 2.0 Time (h) 0 (Feed) 2.0 3.0 5.0 6.3 8.5 Liquid Rate (ml/min) 0.1 0.1 0.1 0.1 0.1 LHSV (h -1 ) 3.0 3.0 3.0 3.0 3.0 Temperature (°C) 185.0 185.0 185.0 185.0 185.0 Phenol (GC Area %) 55.88 58.19 55.41 55.16 54.68 53.65 o-IPP (GC Area %) 23.11 15.82 17.45 17.70 16.65 18.13 m+p-IPP (GC Area %) 9.19 19.27 19.55 19.06 17.96 18.75 2,6-di-IPP (GC Area %) 4.48 0.84 1.14 1.23 1.39 1.57 2,4-di-IPP (GC Area %) 4.88 3.49 4.11 4.48 5.70 5.36 2,5-di-IPP (GC Area %) 0.85 1.16 1.17 1.21 1.71 1.29 3,5-di-IPP (GC Area %) 0.87 0.77 0.71 1.00 0.53 tri-IPP (GC Area %) 1.62 0.00 0.41 0.45 0.65 0.52 o/m+p ratio 2.51 0.82 0.89 0.93 0.93 0.97 Example 2 This Example illustrates the isomerization of an isopropylated phenol composition over a beta zeolite catalyst obtained from Zeolyst International (CBV 861E). First, 2.0 g of beta zeolite pellets was loaded into the stainless steel reactor. The catalyst was used without any pretreatment. The results are summarized in Table 2. It is clear from the Examples 1 and 2 described above, that these two types of catalysts, i.e. sulfated zirconia and beta zeolite, respectively, are effective for the isomerization of alkylated phenol compositions. The amounts of o-IPP and 2,6-di-IPP are reduced whereas the amounts of m-IPP and p-IPP are increased leading to a reduced o/m+p ratio. They also offer several advantages over the triflic acid-based process: a) the process is noncorrosive, b) catalysts can be separated from the reaction mixture and be reused and hence catalyst costs are more economical, c) no color formation is observed, as compared to the case of the triflic acid catalyzed isomerization process. Example 3 This Example illustrates the isomerization of an isopropylated phenol composition on a perfluorinated ion-exchange polymer (NAFION brand from DuPont) on a silica support. In this Example, about 1.0 g of the NAFION brand/SiO 2 extrudates, was loaded into a stainless steel reactor and dried in a nitrogen gas stream at 150°C for four hours prior to the evaluation. The catalyst was then brought to 155°C while in the nitrogen gas stream. Isomerization was carried out at 55°C and at atmospheric pressure. The results are summarized in Table 3. It is clear from the results obtained that at relatively mild temperatures, the catalyst was quite active for the isomerization of isopropylated phenol. Liquid hourly space velocities (LHSV) has an effect on the isomerization activity, but it is noteworthy that the catalyst was remarkably stable for an extended period. Example 4 Zeolite type Y is also effective, as shown herein, at catalyzing the isomerization of ortho-substituted isopropylphenols to more stable meta isomers. HY Zeolite obtained from Zeolyst International (CBV 712 Si/Al ratio 12) was used as 14-30 mesh size particles. The following Table 4 summarizes the results. Day 1 1 1 1 1 1 1 Time (h) 0 (Feed) 0:40 1:20 2:25 3:25 4:25 5:25 20:30 LHSV(h -1 ) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Composition (GC Area %) Phenol 40.15 32.23 31.71 30.98 31.34 31.19 30.42 31.11 o-IPP 27.50 16.92 16.12 14.40 15.27 16.43 16.48 20.41 m+p-IPP 8.92 28.70 30.31 31.96 31.26 29.85 29.39 24.14 2,6-di-IPP 7.36 2.03 1.17 0.93 1.03 1.18 1.23 1.95 2,4-di-IPP 8.99 6.71 6.16 5.38 5.81 6.37 6.59 8.56 2,5-di-IPP 1.38 4.25 4.50 4.46 4.49 4.56 4.67 4.88 3,5-di-IPP 5.94 6.25 7.27 7.02 6.60 6.67 5.16 tri-IPP 4.80 2.48 2.40 2.24 2.30 2.55 2.69 3.34 o/m+p ratio 3.08 0.59 0.53 0.45 0.49 0.55 0.56 0.85 Example 5 Another HY Zeolite (Zeolyst CBV 600 - Si/AI ratio: 5.2) was used as 14-30 mesh size particles for the isomerization reaction. Table 5 summarizes the results obtained in this test. The catalyst is found to be effective for the isomerization of ortho-isopropyl phenol and 2,6-di-isopropyl phenol. Time (h) 2:00 4:00 6:00 7:00 23:00 24:02 Day 1 1 1 1 1 1 LHSV (h -1 ) 1 1 1 1 1 1 Component (GC Area %) Phenol 40.15 41.82 39.54 38.93 39.16 34.44 37.53 o-IPP 27.50 13.87 13.80 15.15 15.64 16.49 19.05 m+p-IPP 8.92 26.97 28.99 28.22 27.50 29.48 24.59 2-6-di-IPP 7.36 1.15 0.69 0.74 0.80 0.90 1.22 2,4-di-IPP 8.99 3.33 3.27 3.65 3.83 4.31 5.00 2,5-di-IPP 1.38 2.47 2.91 3.18 3.28 3.67 3.63 3,5-di-IPP 3.69 4.42 4.59 4.59 5.10 4.13 tri-IPP 4.80 2.55 2.87 3.19 3.24 3.62 3.72 o/m+p ratio 3.08 0.51 0.48 0.54 0.57 0.56 0.77 Example 6 HY Zeolite (Zeolyst CBV 780 - Si/Al: 80) was used as described in the previous example and also found to be effective for the isomerization reaction. The following Table 6 summarizes the results. Time (h) 2:00 3:00 4:00 6:00 7:00 19:40 23:30 Day 1 1 1 1 1 1 1 LHSV (h -1 ) 1 1 1 1 1 1 1 Temp. (°C) 220 220 220 220 220 220 220 Component (GC Area %) Phenol 40.26 33.06 32.68 34.33 37.26 37.71 38.44 38.83 o-IPP 27.46 19.56 19.94 20.87 22.39 23.01 24.02 23.89 m+p-IPP 8.95 25.53 24.94 23.97 21.71 20.82 19.27 19.44 2,6-di-IPP 7.30 1.70 1.80 1.85 1.89 1.98 2.15 2.09 2,4-di-IPP 8.96 7.46 7.86 7.82 7.50 7.49 7.64 7.41 2,5-di-IPP 1.44 4.66 4.76 4.47 3.93 3.81 3.58 3.51 3,5-di-IPP 5.38 5.30 4.53 3.45 3.11 2.50 2.44 Tri-IPP 4.84 1.55 1.71 1.74 1.88 2.06 2.40 2.39 o/m+p ratio 3.07 0.77 0.80 0.87 1.03 1.11 1.25 1.23 Example 7 The HY Zeolite brand catalyst, as described in Example 4, was tested at higher pressures, i.e. about 100 psig (6.8 x 10 5 Pa), to determine the effect of pressure. The results are summarized in the following Table 7. Time (h) 4:00 6:00 22:00 26:00 48:00 63:30 70:00 Day 1 1 1 2 2 3 3 LHSV (h -1 ) 1 1 1 1 1 1 1 Temperature (°C) 220 220 220 220 220 220 220 Composition (GC Area %) Phenol 39.34 38.40 40.05 38.49 38.13 39.55 38.72 38.60 o-IPP 27.35 13.38 10.93 13.61 13.96 14.93 14.20 15.21 m+p-IPP 9.95 31.32 33.14 30.26 30.24 28.55 29.65 28.18 2,6-di-IPP 7.30 0.88 0.53 0.88 0.92 0.93 0.81 1.08 2,4-di-IPP 9.13 4.10 3.06 4.21 4.41 4.51 4.49 4.72 2,5-di-IPP 1.53 3.32 3.05 3.74 3.81 3.70 3.92 3.88 3,5-di-IPP 0.00 4.32 4.80 5.13 5.09 4.41 4.83 4.73 tri-IPP 4.73 2.62 1.93 2.65 2.72 2.76 2.92 2.81 o/m+p ratio 2.75 0.43 0.33 0.45 0.46 0.52 0.48 0.54 Example 8 Commercial HY Zeolite extrudates (Zeolyst CBV 712 XE) were tested in the isomerization reaction of the present invention, both in the crushed and uncrushed forms, to determine its activity for the isomerization reaction. The results are summarized in the following Table 8. Time (h) 0 (Feed) 24:45 40:00 80:00 202:00 297:00 405:00 487:00 Day 2 2 3 8 12 17 27 LHSV (h -1 ) 1 1 1 1 1 1 1 Temp. (°C) 190 190 190 195 200 200 210 Composition (GC Area %) Phenol 39.34 39.03 37.68 37.80 38.25 37.69 36.36 34.69 o-IPP 27.35 23.01 20.56 19.43 18.83 17.78 18.99 20.42 m+p-IPP 9.95 19.48 23.18 24.15 24.36 26.44 25.18 24.10 2,6-di-IPP 7.30 3.57 2.59 2.33 1.99 1.13 1.37 1.62 2,4-di-IPP 9.13 7.61 7.15 6.87 6.84 5.57 6.45 7.06 2,5-di-IPP 1.53 2.33 2.98 3.20 3.51 4.08 4.25 4.46 3,5-di-IPP 0.00 1.07 1.87 2.27 2.64 4.09 3.83 3.68 tri-IPP 4.73 3.69 3.73 3.66 3.33 3.19 3.32 3.72 o/m+p ratio 2.75 1.18 0.89 0.80 0.77 0.67 0.75 0.85 Example 9 The HY Zeolite extrudates, which are described in Example 8, after about 500 hours on stream were subjected to a rapid deactivation test and were regenerated using air at 450°C for about 4-6 hours. The regenerated catalyst was tested for its isomerization activity, and the results are summarized in Table 9. Time (h) 21:00 43:00 73:00 100:00 212:00 241:00 Day 1 2 3 4 8 10 LHSV (h -1 ) 1 1 1 1 1 1 Temperature (°C) 190 190 195 195 205 205 Composition (GC Area %) Phenol 37.74 36.96 32.09 32.63 35.94 37.51 39.53 o-IPP 27-54 18.28 19.90 21.34 23.38 23.03 23.97 m+p-IPP 10.23 25.50 25.38 22.71 18.62 19.21 17.81 2,6-di-IPP 7.51 1.43 1.83 2.36 3.05 2.41 2.54 2,4-di-IPP 9.35 6.33 7.81 8.66 8.61 7.67 7.41 2,5-di-IPP 1.62 4.14 4.84 4.85 4.15 4.11 3.58 3,5-di-IPP 0.00 4.27 4.34 3.47 2.08 2.55 2.00 tri-IPP 5.00 2.68 3.43 3.98 3.96 3.52 3.17 o/m+p ratio 2.69 0.72 0.78 0.94 1.26 1.20 1.35 Example 10 In a similar fashion to Example 4, an H-form mordenite (Si/AI ratio: 20 and 30-14 mesh) at 200°C and LHSV of 1 hr -1 gave initial conversion rates of 45% for ortho to meta and para and 70% for 2,6-di-iso-propylphenol to 3,5-di-iso-propylphenol and others and, at 210°C and a LHSV of 2.51 hr -1 , gave initial conversion rates of 10% for ortho to meta and para and 25% for 2,6-di-iso-propylphenol to 3,5-di-iso-propylphenol and others. In both of these cases, the catalyst activity for isomerization was insignificant after twenty-four hours of operation. Example 11 In this Example, 20 g of SiO 2 pellets (Degussa -Support 350 product, surface area: 160 m 2 g -1 , pore volume: 0.75 cm 3 g -1 ) was impregnated with an aqueous solution of silicotungstic acid until incipient wetness. The impregnated support was then dried/calcined in air at 200°C for three hours prior to use in the reaction. An approximate loading of 30 wt% HPA on the SiO 2 was achieved. Then, 50 g of an alkylated phenol composition was weighed into a three neck round bottom flask. To this solution was added 5 g of HPA/SiO 2 pellets. The reaction was performed at 175-180°C, with constant stirring with a magnetic stirrer, under reflux conditions. The temperature of the reactant/product mixture was measured with a thermocouple immersed into the liquid. Samples were taken at regular intervals and analysis was done using a gas chromatograph. Results are tabulated in the following Table 10. EXAMPLE 12 This Example illustrates the phosphorylation of the isomerized product of the present invention. About 120 g of the isomerized product was phosphorylated with about 150 g of phosphorus oxytrichloride in the presence of 0.5 g of magnesium dichloride at atmospheric pressure and a temperature of about 180°C. The phosphorylated sample was stripped under vacuum to remove free phenolics and was washed with oxalic acid and caustic solutions to remove the catalyst. The product was then dried under vacuum for about four hours to reduce the water level in the product to about 100 ppm. The composition of the alkylated phosphate ester was determined to be (in GC area %): phenol: 42.7; o-IPP: 13.6; m+p-IPP: 35.3; 2,6-di-IPP: 0.1; 2,4-di-IPP: 1.4; 2,5- and 3,5-di-IPP: 3.9; 2,3-di-IPP: 0.1; 2,4,6-tri-IPP: 2.6; other tri-IPP: 0.2.

Claims: A process for the isomerization of an alkylated phenol composition comprising ortho-substituted C 3 - or C 4 -alkyl phenol, which comprises heating said composition in the presence of an effective amount of a solid acid catalyst wherein a composition comprising from about 10% to 20% by weight of mono-ortho-substituted alkylated phenols, from about 5% to about 20% by weight of mono-meta-substituted alkylated phenols, from about 10% to about 30% by weight of mono-para-substituted alkylated phenols, and from about 0.5% to 3% 2,6-di-alkylphenol is formed. A process according to claim 1, characterized in that the solid acid catalyst is an H-form zeolite, a supported sulfur acid, or a supported heteropoly acid. A process according to claim 2, characterized in that the H- form zeolite is a Y- or beta-type zeolite. A process according to claim 2, characterized in that the supported sulfur acid is a sulfated zirconia. A process according to any one of the preceding claims, characterized in that the C 3 - or C 4 -alkyl group is an isopropyl or tert-butyl group. A process according to any one of the preceding claims further comprising phosphorylation of the isomerized alkylated phenol composition.

Inventors: DESIKAN ANANTHA NARAYAN, WHITWELL GEORGE EDWARD, DESIKAN, ANANTHA NARAYAN, WHITWELL, GEORGE EDWARD
Applicants: AKZO NOBEL NV, AKZO NOBEL N.V.
Application year: 2000
Main classification: C07C39
IPC codes: C07C37, B01J27, B01J29, C07C39, C07B61