[Regular Paper] Formylation of Methylnaphthalene Compounds with CO in HF-BF3 Medium

石油学会誌 Sekiyu Gakkaishi, 40, (2), 115-123 (1997) 115 [Regular Paper] Formylation of Methylnaphthalene Compounds with CO in HF-BF3 Medium Yoshiji DOKO†1), Kiyoshi KUDO†2)*, Yohei MINAMI†3), Sadayuki MORI†2), and Nobuyuki SUGITA†2) †1) Sumitomo Metal Industries, Ltd., Hikari, Kashima, Ibaraki 314 †2) Institute for Chemical Research, Kyoto University, Uji, Kyoto 611 †3) Sumikin Chemicals Co., Ltd., Hikari, Kashima, Ibaraki 314 (Received August 27, 1996) The formylation of naphthalene compounds, including 2-methylnaphthalene (1a), 1-methylnaphthalene (1b), 1,2,3,4-tetrahydro-2-methylnaphthalene (1c), and 5,6,7,8-tetrahydro-2-methylnaphthalene (1d), with pressurized CO was investigated in HF-BF3 medium at ambient temperature. With pressurized BF3 (6atm) and CO (50atm) at 25℃, 1a was formylated readily to yield a mixture of five isomers of aldehydes in total yield of 72%, in which 6-formyl-2-methylnaphthalene was produced as the major regioisomer in selectivity of 33%. In contrast, 1b produced predominantly 4-formyl-1-methylnaphthalene in yield of 60% together with a small amount (2.8%) of 2-formylated product. In the cases of tetralin ompounds, 1c produced ca. 1:1 of 6- and 7-formyl-1,2,3,4-tetrahydro-2-methylnaphthalenes, in total yield of 98%. On the other hand, 1d produced only one product, 3-formyl-5,6,7,8-tetrahydro-2- methylnaphthalene, in yield of 64%. In the formylation of 1a, the effects of the reaction variables, such as the pressure of BF3 and reaction temperature, on the yield and positional selectivities were examined, and also compared with the results in other acid media. 1. Introduction higher positional selectivity (98% p-tolualdehyde), indicating that the HF-BF3-CO system produces a Formylation of aromatic compounds are known more reactive and bulky electrophilic species. to occur with mixtures of CO and hydrogen The authors' continuing interest, both in the chloride in the presence of AlCl3 and a small mechanism and synthetic usefulness of the amount of Cu2Cl2, i.e., Gattermann-Koch condi- superacid-catalyzed aldehyde synthesis, led us to tions1)-3). Other catalyst systems such as HF- this study on the formylation of naphthalene BF34),5), and HF-SbF56) were also investigated compounds. relative to this reaction, and Olah and co-workers7) Recently, Souma et al.8) have reported that the compared the reactivity and positional selectivity diformylation of polynuclear aromatic com- of various catalyst systems for formylation of pounds, such as naphthalene and methylnaphtha- an equimolar mixture of benzene and toluene. lenes, could be achieved using HF-SbF5 medium Among the most frequently used methods of in pressurized CO (20atm). For example, the Formylation, the Gatterman-Koch reaction dis- reaction of naphthalene selectively produced played the highest selectivity as shown by the high 1,5-diformylnaphthalene together with 1-formyl- rate ratio of toluene and benzene (kT/kB=155-319) naphthalene. These formylation, however, often observed, as well as a high degree of para sub- require the acidic catalyst in excess of the stoichio- stitution (88.7-92.6%)3). The authors previously metric amount with respect to the substrate. reported results of studies on kinetics and mechan- Antimony pentafluoride catalyst cannot be ics of the formylation of aromatics, including recycled and causes enormous disposal and toluene5a), m-xylene5b), anisole5c), and phenol5d), environmental problems in industrial processes. with CO in HF-BF3 medium in pressurized On the contrary, anhydrous HF or BF3 can be conditions. The formylation with HF-BF3-CO recycled almost quantities in case of Friedel-Crafts system at 0℃ displayed a much lower substrate type reactions. The 2,6-disubstituented naphtha- selectivity (kT/kB=12), but exhibited a much lenes, especially having a carbonyl group at the 6- position, were found to be highly useful in the * To whom correspondence should be addressed. pharmaceutical and polymer industry9). For ex- 石油学会誌 Sekiyu Gakkaishi, Vol. 40, No. 2, 1997 116 Table 1 Effect of Reaction Temperature on the Formylation of 2-Methylnaphthalene (1a)a) a) Conditions, 1a (16mmol), BF3 (6atm), HF (2mol), CO (50atm), 4h. b) Determined by GLC and based on 1a employed. c) Determined by GLC peak area ratio. d) Reaction time was 3h. ample, 2,6-naphthalenedicarboxylic acid repre- sents an important component of several com- mercial liquid crystal polymers. It is of interest, therefore, to investigate whether or not the HF-BF3 medium is applicable to a selective formylation of 2-methylnaphthalene (1a) with CO (Eq. (1)). There were only a few patent literatures10), how- (1) ever, on the preparation of alkylformylnaphtha- lene compounds by the HF-BF3-catalyzed reaction of alkylnaphthalenes and CO. In this paper, authors would like to report on when the reaction was maintained for 4h. At low synthesis of 6-formyl-2-methylnaphthalene (2) temperature (<0℃), the formyl group was mainly in a specific high positional selectivity, on the introduced into 1-position (isomer 3), and the formylation of 1a, in HF-BF3 medium under pres- order of the isomer distribution is 3>4>5>2, sure of CO at ambient temperature. Further- which agrees with the results expected from more, the formylation of these methyltetralins to electronic effect of the methyl group in common produce the corresponding formylated products, at electrophilic substitutions of 1a12). Increasing the high yield, are also reported. temperature, to 25℃, greatly enhanced both the total yield and selectivity of 2, and then the order of 2. Results and Discussion the distribution of isomers is 2>5>3>6>4. Fur- thermore, the higher temperature (>50℃) brought 2.1. Formylation of 2-Methylnaphthalene (1a) about the adverse effect on the formation of 2, and In the authors' previous studies11), it was found an isomer 6 was had as a major product. The best that anhydrous HF-BF3 medium is a highly useful result, with respect to the yield and selectivity of catalyst system for selective formylation of naph- desired product 2, was achieved at 25℃. thalene, to produce 1-formylnaphthalene at excel- The favorable formation of 6, at higher tem- lent yield. The formylation of 1a, in conditions perature, suggests that the isomerization of 1a to 1- similar to those of our previous studies produced a methylnaphthalene (1b) proceeded during the mixture consisting of several isomers as described formylation, as in the case of Friedel-Crafts in Eq. (1): i.e., when 1a (16mmol) was reacted with alkylations (vide infra)13). Besides the isomeric CO (50atm) in HF (2mol) under pressurized BF3 products, GLC analysis of the organic extract (6atm), as the standard conditions, 2, 1-formyl-2- (benzene) revealed the formation of considerable methylnaphthalene (3), 4-formyl-2-methylnaph- amount of other high boiling products which thalene (4), 8-formyl-2-methylnaphthalene (5), were not examined in further detail. These by- and 4-formyl-1-methylnaphthalene (6) were pro- products accounted for about 20-30% of the duced as the formylated products together with reaction mixture at 50℃. In control experi- small amounts of some unidentified compounds. ments, none of these by-products were found when First, in order to search the optimum conditions CO was replaced by argon. The formation of the for the formation of 2, the effect of the reaction by-products, therefore, is attributed to secondary temperature on the total yield and isomer reaction of protonated aldehyde with excess distribution was examined under pressurized CO substrate 1a, similar to the case of toluene in (50atm) and BF3 (6atm). As shown in Table 1, it superacid14). became obvious that the positional selectivity The influence of the pressure of BF3 on the significantly varied with reaction temperature, conversion of 1a, the total yield of aldehydes, and 石油学会誌 Sekiyu Gakkaishi, Vol. 40, No. 2, 1997 117 Table 2 Time Dependence of the Product Yield and Distribution for the Formylation of 1aa) a) Conditions: 1a (16mmol), BF3 (6atm), HF (2mol), CO (50atm), 25℃. b) Determined by GLC and based on 1a employed. c) Determined by GLC peak area ratio. sharply increased at an early stage (-1h), and then the reaction rate gradually decreased with progress of time (2-4h). This reaction was complete within about 2h, and afforded 2 in yield of 24%. The decrease in total yield at a later stage could be attributed to the polymerization via secondary reaction of the protonated aldehydes with the starting substrate 1a, by a mechanism similar to the case of toluene14). The formylation of 1a in other acid media were further investigated. As shown in Table 3, the total yield and the isomer distribution, which varied directly with the acidity of the medium, and yields increased by increasing the acid: substrate Reaction conditions: 1a (16mmol), HF (2mol), CO mole ratios. In contrast to the case of HF-BF3 (50atm), 2h at 0℃. ○: Conversion of 1a, ●: Total yield of aldehydes, medium, in the case of HF-SbF5 medium, which ▲: Selectivity of 2-methyl-6-formylnaphthalene (2). was known as the strongest superacid15), the addition of about 2.5 equivalent SbF5 to the Fig. 1 Effects of BF3 Pressure on the Formylation of substrate led to total yield of 90%; but the selectivity 2-Methylnaphthalene (1a) of 2 surprisingly plunged to a very low figure (4%), while the order of isomers distribution is 3>4>5≫2 (Run 4). the selectivity of 2 at 0℃, are shown in Fig. 1. Solvent often affects the positional selectivity of Here, the mole fraction of BF3 dissolved in electrophilic substitution of aromatics. It has anhydrous HF changes linearly relative to its been reported that when Friedel-Crafts acylation is partial pressure, in the range examined (i.e., carried out in nitrobenzene16), which is presumed 4.86×10-3mol of BF3 per 1mol HF at latmand to increase steric requirement by solvation, the 0℃)11).

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