Spectrophotometric Study on the Interaction of Water with Chloranilic Acid and its Analytical Applic

Chinese Chemical Letters Vol. 16, No.7, pp 931-934, 2005931http://www.imm.ac.cn/jourmalccl.htmlSpectrophotometric Study on the Interaction of Water withChloranilic Acid and its A nalytical ApplicationFeng Lin ZHAO'*, Xi Lan FENG, Xue Jing LIU, Na LI', Ke An LI' .1 Department of Chemistry, Peking University, Beijing 1008712 Vocational-Technical Teachers College, Henan 4530033 Experimental Center of Zaozhuang Teachers Collge, Shandong 277160A bstract: The reaction between chloranilic acid and water in alcohol was studiedspectrophotometrically. The conditions of reaction were investigated in detail. The stablepurple complex with an absorption wavelength at 530 nm was produced from the reaction betweenchloranilic acid and water. As a method for determination of H2O, Beer's law was obeyed in rangeof 0-6.0 % or 0-8.0 % (V/V) with the detection limit of 0.13 %. The relative standard deviation(RSD) was less than 2 %，The proposed method has been applied to determination of traceamount of water in ethanol, flour and food flavoring, respectively.The recoveries of water insamples were 97~ 102 %.Key words : Water, chloranilic acid, charge-transfer reaction, spectrophotometry.The determination of water is routine analytical requirement in chemical industry andfood industry.To measure moisture in chemical products， Karl Fischer method(GB-6283-86) is usually employed as a reference method in China and many othercountries'-. The method has several limitations: it is time-taking; the reagents areexpensive; Karl Fisher reagent needs to be calibrated daily. In order to improve theaccuracy of titration, dead-stop endpoint method of potentiometric titration is usuallyused. However, the method is less sensitive and reagents are toxic. Furthermore, theoperation procedure is complicated.To determine the moisture in food industry,oven-drying method and azeotropic distillation are often usedThese methods aretime-consuming and the reagent of benzene or toluene is toxic.Chloranilic acid is an electron-deficient agent (electron acceptor) and can react withelectron-rich agent (electron donor) to form charge-transfer complex. For example, itCL,OH20HH2O:+H20;.中国煤化工I0^~COTHCNMHG"E-mail: zf@chem.pku.edu.cn932Feng Lin ZHAO et al.can react with electron donor medicines to determine pharmaceutics .Water is anelectron-rich compound and can react with chloranilic acid to form a purple complex.The charge transfer reaction is shown to happen between chloranilic acid and water.This paper discussed the charge-transfer reaction between chloranilic acid and water.ExperimentalChloranilic acid(chemical purity, Beijing Chemical Factory, China) of 0.0200 mol/Lsolution in absolute ethanol, methanol, n-propyl alcohol, n-butyl alcohol, n-heptanol and1-hexanol, etc. (Analytical grade, Beijing Chemical Factory, China). All the alcoholswere dehydrated in laboratory before using.A Shimadzu Model UV-265 double-beam spectrophotometer with 1 cm cell (Kyoto,Japan), HHS- 2-NI constant temperature water-bath (Beijing Jingwei Science InstrumentFactory), KQ3200E ultrasonic washing appliance (Kunshan,China).A certain amount of sample solution containing water was pipetted into a 10 mLvolumetric flask, 2.00 mL chloranilic acid solution was added and the solution wasdiluted to volume with anhydrous solvent and mixed thoroughly. The flask was placedat room temperature for 10 min. The absorbance of the solution was measured at 530nm against the reagent blank prepared in the same way simultaneously.Solid sample of 1.5~ 2 g was weighed and put into a conical flask with a stopper,and 30 mL absolute alcohol was added. The mixture was then ultrasonically extractedfor 40 min. The supernatant was collected. Then 20.0 mL absolute alcohol was addedinto the conical flask and the mixture was ultrasonically extracted for 20 min. Thesupernatant was collected and mixed with the first collection. The collection wasdistilled to near dry and the distillate was used for determination.Results and DiscussionA certain amount of chloranilic acid was weighed and dissolved in water, methanol,absolute ethanol, 2-propanol, heptanol, dimethyl sulfoxide, ethyl acetate, methylmethacrylate, acetone and dioxane, respectively. Corresponding solvents were used asblank. The absorption spectra are presented in Figure 1. Solvent has a significanteffect on absorption spectrum of chloranilic acid. Amax and absorbance of chloranilicacid changes with solvent used for dissolving chloranilic acid. As the polarity ofsolvent (dielectric constant ε ) increases, the λ max value shifted to longer wavelength todifferent degrees.The absorption curves of chloranilic acid-water complexes in methanol, absolutealcohol, 1-propanol, 2-propanol, 1-butanol, 1-heptanol, 1-hexanol, dioxane, acetone andethyl acetate were recorded, respectively. The results showed that polarity of solventaffected λmax and absorbance value of chlc中国煤化工eIn solventwith higher polarity, the absorbance sens-water complexbecame higher. In alcohol solvents, the absMHCNMHGacidwasat440nm, Amax of chloranilic acid-water complex moved to a longer wavelength at 530 nmwith a shift of 90 nm. In acetone, ethyl acetate and dioxane, the absorbance sensitivitySpectrophotometric Study on the Interaction of Water933with Chloranilic Acidwas low and the maximum absorbance wavelength moved to shorter wavelength. Itmay be that the drawing electron effect of carbonyl group in acetone and ethyl acetatereduced electron supplement capability of solvents. In this experiment, absoluteethanol was used as solvent and the absorbance of chloranilic acid-water complex wasmeasured at 530 nm.According to the experimental procedure, the absorbance of complex wasdetermined at 18-65C. The results indicated that the reaction speed of chloranilic acidwith water was not influenced by temperature.The absorbance of complex reachedmaximum in 10 min and kept unchanged in 3 h.Ten aliquots of distilled water were tested in ethanol solvent to evaluaterepeatability of the method. The result indicated that the relative standard deviationwas 1.56 %. The detection limit was φ (H2O)= 0.13 % (V/V) (3σ).Different volumes of distilled water were added into 2.0 mL chloranilic acidsolution, respectively, and the solution was diluted to volume with different alcohols.Absorbance at 530 nm was measured after 10 min. The results are shown in Table 1.Figure 1 Absorption spectra of chloranilic acid in some organic solventsc(chloranilic acid) = 4.0x 103 mol/ L15rS[、|/d500700300a - dimethyl sulfoxidea- waterb- methanolb - methyl methacrylateC- ethanol anhydrous d - ethyl acetatec - 2-propanole - dioxanef- acetoned -1- heptanolTable 1 Regression equations for standard curves in alcoholsCorrelationLinear rangeSolventRegression equationcoefficient[p(H20)/%]methanol4=0.018+ 19.7p(H2O)0.99990~8.0ethanol4--0.005+25.40(H2O)0~6.0n-propyl alcoholA=0.041+22.4q(H2O)中国煤化工n-butyl alcohol4-0.008+19.1q(H2O)gylcolA=0.071+19.7p(H2O)MHCN MHG 0~6.0 .gylcerol4--0.023+22.0φ(H2O)0.9981934Feng Lin ZHAO et al.Analytical A pplicationDetermination of moisture content in ethanolAccording to the experimental section, 5.0 mL ethanol (95.5 %) was added intoa 10 mLflask, and 2.0 mL chloranilic acid ethanol solution was added, and then the mixture wasdiluted to volume with absolute ethanol. The absorbance of the solution was measuredat 530 nm against the reagent blank. The moisture content in ethanol was 4.45 %, RSD=1.6 %, the relative error E:= 1.0 %;Two millilitesr of chloranilic acid and 0.1 mL~0.4 mL of distilled water were mixed, and diluted to volume with absolute ethanol. Theabsorbance of the solution was measured for recovery test at 530 nm against the reagentblank. The recoveries were 98.0 %-101.7 %.Determination of moisture content in flour and in food flavoringThe test solution 8.0 mL was mixed with 2.0 mL chloranilic acid solution. The mixturewas diluted to volume with absolute alcohol. The absorbance of the solution wasmeasured at 530 nm against the reagent blank. The moisture of flour was determinedwith GB method' simultaneously. The moisture content in flour was 10.82 %, RSD =2.0%, E, was 1.6 %. The recoveries were 98.0 %- 102.0 %.Moisture contents of 3 food flavoring were measured by the suggested method.The results were comparable with that from standard method*, E, was 1.0 %-2.0 %.The recoveries were 97.0 %-101.0 %.The experimental results indicated that the reaction of chloranilic acid with watercould produce charge-transfer complex, it could be used not only to determine traceamount of water in alcohol, but also to determine trace amount of water in solid samples.This method is simple, reproducible and sensitive. The toxicity of reagent is low. Nospecial appliance is needed. This method could be a effeciat procedue to determinemoisture in samples.References1. M. H. Deng, B. Z. Wang, Analysis and Determination of Water, Beijing: High education Press,1992.2. W. T. Wang. Analysis of Trace Water: Beijing: Science Press, 1982.3. Wuxi Light Industry College, Tianjin Light Industry College. Food Analysis, Beijing: LightIndustry Press 1987.4. National Standard of China (GB5009.3-85), 1985.5. W.B. Zhou, H.K. Li, GZ. Zhao, Y.M. Rong. Chin.J.Anal. Chem, 2000, 28(6), 783.Received 19 Augest, 2004中国煤化工MYHCNMHG