Friedel-Crafts Reaction of Aromatic Compounds with Lactone and Unsaturated Acid by Acid Catalyst
|Course||Physical and chemical|
|Keywords||F-C reaction Lactone Unsaturated organic acid Acid catalysis Multi-functional groups Arylalkanoic acids Indanone|
The Friedel-Crafts reaction is an important reaction both in fundamental research and industrial application, so it is keeping be a hotspot in the research from its birth to the present. Conventionally, this reaction is catalyzed by Lewis acids （such as FeCl3, AlCl3 et al. ）. However, this reaction process will produce large amounts of acidity water, which is contaminated waste and not friendly to the environment. Therefore, much more attention is focused on the improvement and replacement for the conventional catalysts by new catalysts which are recylceable.The Friedel-Crafts alkylation and acylation reactions are very useful tools for the synthesis of numerous aromatic compounds, which are important intermediates in Pharmaceuticals, fragrances and agrochemicals. The reactions are commonly carried out with alkylating reagents such as alkenes, alkyl chlorides and alcohols et.al, and with acylating agents such as acyl halogens, carboxylic acids, anhydrides et.al. However, the reactants with two function groups such as unsaturated acids, lactone, hydroxyl carboxylic acids etc. and the reaction selectivity of mulit-groups are less reported.In this paper, the research objects are focused on the reaction of lactone and unsaturated acid with aromatic compounds, mainly discuss the effects of reaction conditions and the reaction mechanisms catalyzed by liquid acid and solid acid catalysts respectively. The main contents and results are as fowllows:The alkylation product 4-（2,4,6-trirnethylphenyl）butyric acid could besynthesized via the reaction of 1,3,5-trimethylbenzene with y-Butyrolactone catalyzed by AICI3 at room temperature. The amount of catalyst and reaction time were important factors for affecting the product yield. The y-butyrolactone could be converted to the target product quantitatively under certain reaction conditions. Some solid acid catalysts were screened in this reaction. Nafion-H was the best in terms of both the product selectivity and yield. The yield of 4-（2,4,6-trimethylphenyl）butyric acid increased with reaction temperature and reached the maximum value of 84.5% at 200°C, while the selectivity was about 90%. Nafion-H could be reused after simply washing and drying and is a green catalyst. The acid catalyst made the C-0 bond in the 4-position of y-Butyrolactone broken to form an active intermediate, which further reacted with 1,3,5-trimethylbenzene to produce 4-（2,4,6-trimethylphenyl）butyric acid.e-Caprolactone and y-butyrolactone did not react with 1,3,5-trimethylbenzene catalyzed by triflates. A self polymerized dimer of e-caprolactone was detected by using E-caprolactone as reactant, while similar product was not be found in the system of y-butyrolactone. This is due to the more stable structure of 5-member cycle in y-butyrolactone than that of 7-member cycle in s-caprolactone.The effects of reaction conditions such as reaction time, temperature and catalyst amounts were examined in the reaction of 1,3,5-trimethyl benzene with acrylic acid over AICI3. An B-addition alkylation product of 3-（2,4,6-trimethylphenlyl）propionic acid was also ’prepared, and the maximum mole-yield was about 33%. But some by-products were detected in GC analysis, and the selectivity of the objective product was low. Some solid acids were screened in this reaction. The results indicatedthat some zeolites （ZSM-5, H-Beta, SAPO-11） and superacids （SO4 7ZrO2） were inactive to produce the objective product, while Nafion-H, HPW and HSiW were active at certain temperature. The mole yield of product got to 32% over 0.4g HPW at 200°C for 4h, which was closed to that over AICI3, and the low-boiling point by-products were less than AICI3. So it was propitious to separate comparing with AICI3. But the reaction activity of methyl acrylate with 1,3,5-trimethyl benzene over HPW was very low under similar reaction condition. The reactivity of p-xy\ene was less than 1,3,5-trimethyl benzene because of the substitute effects. p-Cresol, which could be taken as the substitution of a methyl by hydroxyl in p-xylene, was used to react with acrylic acid under azeotropic condition of toluene to remove the water produced during the reaction, and finally obtained an ester. While the reaction of resorcinol with acrylic acid gave coumarin. It is demonstrated that an ester intermediate produced in the Pechmann reaction and Fries rearrangement.The butenoic acid is the homolog of acrylic acid or the isomer of lactone. Its reactivities over soild acid catalysts make us pay much more attentions. Butenoic acid has two isomers （crotonic aicd and vinylacetic acid） because of its different double bond position. In acid catalysis system, both of them gave the same second carbonium intermediate, and made the same product （3-mesitylbutyric acid） as they reacted with 1,3,5-trimethylbenzene, which was not reported before. The experimental results showed vinylacetic acid had better activity than crotonic acid because the later has a more stable conjugation structure than the former. Nafion and HPW were the two effective catalysts to get an alkylation product. The yield of 3-mesitylbutyric acid gotto 46% at 200°C for 4h for the reaction of vinylacetic acid and 1,3,5-trimethylbenzene over 0.4g HPW catalyst. As HPW was supported on SiC>2, the yield of product increased with the loading amount of HPW. 60%HPW/SiC>2 showed better activity than HPW. While other carriers such as AI2O3, active carbon and MCM-41could not promote the activity of HPA after supported.Two products of 3-（2,5-dimethylphenyl）butyric acid and 3,4,7-trimethylindan-l-one were detected from the reaction between p-xylene and vinylacetic acid. In the case of H-Beta, 3-（2,5-dimethylphenyl）butyric acid was the exclusive product, while the above two products were formed over HSiW/SiO2 at 160°C. As the reaction temperature was increased to more than 200°C, 3,4,7-trimethylindan-l-one was selectively formed over both HSiW/SiO2 and H-Beta. The results indicated that the reaction was a typical consecutive reaction, that is, the intermolecular alkylation was the first step, and the successive reaction was the intramolecular acylation of arylalkanoic acid. The rate of intramolecular acylation was restricted because of the pore structure and less acidity of H-Beta at lower temperture. therefore, an intermediate of 3-（2,5-dimethylphenyl）butyric acid was captured. But the rate of intramolecular acylation increased with the reaction-temperature to get the final product of indanone.In conclusion, the reactions of aromatic compounds with lactone or unsaturated acid catalyzed by an acid catalyst provide a promising and short route for the synthesis of arylalkanoic acids, indanones or cycloketones. In general, HPW and Nafion are efficient solid catalysts for this reaction and have promising application inindustry. Certainly, in order to make the ideal green process come true, further research should be done to make the solid acid catalysts with higher activity and reusability.