Study On The Synthesis And Absorption Spectra Of Coumarins

Coumarins are mainly used as ragrances, and intermediates for drug and dyestuff, and yet as photosensitive dye widely used in many fields, such as electroluminescent Material and solar cells. The research on synthetize and spectral characteristics of coumarins are of great practical applications and theoretical significance for developing new coumarins and expand its applications. On the basis of optimizing the process conditions of Pechmann reactions in synthetizing 4-methyl coumarins, the DFT and TD-DFT of quantum chemistry were used to calculate the bond length, bond angle, charge distributions, frontier molecular orbital, vibrant frequency, ultraviolet spectrum. By contrasts with the theoretical calculations and the experimental results, the relationship of electron structure andλmax of 4-methyl coumarins was analysised.7-hydroxy-4-methyl coumarin was used as emplate to research influences of the type, amount and repeated times of catalyst and reaction temperature, reaction time and proportion of raw meterial on synthetizing coumarins. The results showed the yield of 7-hydroxy-4-methyl coumarin was 93.8% when using 1.0g DT-852 macroporous sulfonic acid resin,0.1 mol resorcin,n(resorcin):n(ethyl acetoacetate) =1.0, reaction temperature was 105℃, the reaction time was 2.5 h. Compared with traditional catalytic process of sulphuric acid as catalyst, this was a clean proces with no solvent, little catalyst, fewer side-effects of sulfonation and oxidation reaction, produce no discard acid and waste water, low corrosion rate to equipments, recycled catalyst and little environmental pollution. On this basis, a series of were synthetized: 4-Methyl-6,7-benzocoumarin,4-Methyl-7,8-benzocoumarin,7-acetoxylgroup-4-methyl-coumarin,6-nitryl-7-hydroxy-4-methyl coumarin,8-nitryl-7-hydroxy-4-methyl coumarin.The geometry of 4-methyl coumarin were fully optimized and meanwhile their frequencies analyzed by Gaussian 03, Then the quantum chemical parameters, bond length, dihedral angle, the natural charge population, frontier molecular orbital energy and composition were obtained, the molecular absorption spectrometry were calculated by the method of TD-DFT/PCM. The main results obtained from this study were summarized as follows:(1) Introduced groups onto 4-methyl coumarin can make C-C key long redistribution of coumarin, to achieve more stable condition, the number of free charge about the carbon atoms in compound directly related to strength of substituent's sucked electricity, theoretical calculation result predicted 7-hydroxyl-4-methyl coumarin C(8) position is the main electrophilic point by electric attacked, the synthesis of 7-hydroxyl-4-methyl-8-nitro coumarin showed 8 bits of 7-hydroxyl-4-methyl coumarin can smooth nitration in room temperature. (2) The highest occupying molecular orbital energy decreased as introduction of suction electronic substituents for 4-methyl coumarin, increased as introduction of donating electronic substituents, but the same results were front rail gap are lower result in absorption spectra gaps redshift. (3) The vibration spectra of 4-methyl coumarins was consistent with infrared spectrum analysis experimental results. The absorption intensity reach 644～690 of 4-methyl coumarins at wave number 1823～1825cm-1 in IR vibrating, the strongest absorbtion mainly caused by C=O stretching vibration.Visible ultraviolet absorption experimental results and theoretical analysis showed theλmax experimental values in keeping with calculated values of 4-methyl coumarins.λmax red shift enhanced for coumarins molecular as the number of substituent groups increased. The correlation coefficient of theλmax experimental values and the frontline rail gap/gaseous values about 4-methyl coumarins was respectively 0.9311/0.9946, the correlation coefficient was 0.8741 of theλmax experimental values and the calculation values in alcohol solution, these results stated solvent effects has important influence for the maximum absorption wave length of 4-methyl coumarins.The research results showed the synthesis of 4-methyl coumarins compounds with macroporous sulfonic acid resin catalytic has green environmental characteristics, TD-DFT/PCM for 4-methyl coumarin compounds structure and the spectrum oretical calculation have very good correlation with experimental results, and has certain directive significance for synthesis and application of 4-methyl coumarin compounds.