| Borneol is an important intermediate for perfume and medicine.The steps of synthetic borneol in industry are as follows: synthesizing bornyl esters from pinene and oxalic acid by rearrangement-addition reaction under the action of catalyst,saponifying bornyl esters,steam distillating and recrystallizing.Eventhough the study of synthetic borneol was mainly focused on catalysts rather than the original technology at present,it is still necessary to find influence factors on quality of synthetic borneol for improving,monitoring and controlling original technology.Therefore,it is designed to synthesize and characterize several main ester compounds consisted in crude synthetic bornyl oxalate,which can be used as reference substances for establishing a qualitative and quantitative method to analyze the main ester compounds in crude synthetic bornyl oxalate by gas chromatography(GC).The researches are as follows:The indirect esterification technology was studied on fenchyl oxalate.Fenchyl oxalate was synthesized by the reaction of fenchyl alcohol and oxalyl chloride,under optimum conditions as: the molar ratio of oxalyl chloride to fenchyl alcohol 0.6 : 1,reaction temperature 55 ?,reaction time 10 h.The yield of fenchyl oxalate is 93.9 %,and the purity is 99.9 % while recrystallized.The structure of fenchyl oxalate was identified and characterized by GC-MS,FT-IR,1H NMR and 13 C NMR.A green catalyst was selected for synthesis of fenchyl oxalate by a direct esterification method,and the esterification process was optimized.The catalytic effect of several catalysts,such as H2SO4,metatitanic acid,cation exchange resinsE105,NKC-9 and D-72 were compared for the fenchyl oxalate synthesis from fenchyl alcohol and oxalic acid.The optimum reaction conditions are: the suitable catalyst cation exchange resin NKC-9,dosage of NKC-9 50 % based on the mass of fenchyl alcohol,reaction temperature 55 ?,reaction time 96 h,molar ratio of oxalic acid to fenchyl alcohol 4 : 1.Under the conditions,the selectivity and yield of fenchyl oxalate are 93.5 % and 86.1 % with 92.1 % conversion of fenchyl alcohol.Furthermore,the selectivity and the yield of fenchyl oxalate are still kept as 89.4 % and 78.0 % in 87.2 % conversion of fenchyl alcohol while the catalyst was reused for 7 times.Dibornyl oxalates with different optical activities were synthesized by indirect esterification method,and their spectral properties were compared.Three optical active dibornyl oxalates were prepared with different chiral borneols and oxalyl chloride,and the target products can be easily purified to 99.9 %(GC)through recrystallization in alcohol.The composition of the synthesized dibornyl oxalates were analyzed by a chiral high-performance liquid chromatography(HPLC),and it was proved that there were mesomer and racemic isomers in the synthesized racemic dibornyl oxalate.The hydrogen and carbon atoms of(-)-dibornyl oxalate was located by means of 1H-1H COSY?HSQC and HMBC.The spectra of different chiral dibornyl oxalates were contrasted,including GC-MS,FT-IR,1H NMR and 13 C NMR.Furthermore,the synthesized racemic dibornyl oxalate was compared to the mixture of equal(+)and(-)dibornyl oxalates.As results,the spectral properties of(+),(-)and racemic dibornyl oxalates are very similar,but these oxalates can be distinguished via their optical activities.Apart from the above three oxalates,it was comfirmed that there is another compound which was contained in the synthesized racemic dibornyl oxalate from the reaction of racemic borneol and oxalyl chloride,while the carbon and hydrogen atoms on both sides of the mesomer molecular owned different chemical environment and spectral properties.Fenchyl oxalate,dibornyl oxalate and diisobornyl oxalate were synthesized as reference substances to establish a qualitatively analytic method for the main ester compounds such as bornyl oxalate,fenchyl oxalate etc.in crude bornyl oxalate by gas chromatography(GC)based on an external standard method.The results showed that,the reference substances bornyl and fenchyl oxalates were stable while dissolved in inert solvent such as hexane,but instable in alcoholic solvents;and the main ester compounds in crude bornyl oxalate were determined and identified as dibornyl oxalate,diisobornyl oxalate,fenchyl oxalate,crossed bornyll isobornyl oxalate,crossed bornyl fenchyl oxalate,crossed isobornyl fenchyl oxalate and so on.The calibration curves for references fenchyl oxalate and dibornyl oxalate were linear in the ranges of 1-25 g/L and 5-25 g/L(r>0.99),respectively.The mean recoveries of reference compounds were 103.2 % and 106.9 % with the relative standard deviations(RSDs)of 1.72 % and 0.76 %,respectively.What is more,the GC external standard method would be applied to determine the crude esters with high precision,good repeatability,and good solution stability.The mass fractions and the total of the six main ester components in crude bornyl oxalate were determined by the external standard curves of fenchyl oxalate and dibornyl oxalate with GC on basis of the principle that isomers own approximate response factor.The results were compared with those of area normalization method,and it is showed that: the total mass fraction of the six esters is in a sequence as standard curve of fenchyl oxalate>area normalization method>standard curve of dibornyl oxalate,and the results were in a reasonable error range of GC,though there are slight differences among the total mass fractions determined by the three different methods.That is to say,an appropriate quantitative method would be selected to analyze the main ester compounds depending on real requirements,and the area normalization method would meet the requirement to control industial process in general. |
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