DIENE VALUE BY MALEIC ANHYDRIDE ADDITION REACTION UOP Method 326-82 SCOPE This visual indicator titration method is for determining maleic anhydride reactivity with a wide variety of oils ranging from debutanized light hydrocarbon distillates to heavy drying oils. The method gives a measure of the conjugated diolefin diolefin content of the sample. The determination is 1 somewhat empirical since some diolefins may not react completely, while certain compounds other than conjugated diolefins may be reactive, also. For example, anthracene, many of its homologs, and the corresponding alkylated compounds react quantitatively as dienes with maleic anhydride. Similarly, certain vinyl aromatics react. The molecular weight of the conjugated diolefins must either be known or estimated. Therefore, the results obtained by this method must be carefully interpreted in the light of these specified limitations.
OUTLINE OF METHOD Maleic anhydride is refluxed with sample in boiling toluene for 3 hours. The unreacted maleic anhydride is hydrolyzed to maleic acid, extracted from the reaction mixture, and titrated with 1 M sodium sodium hydroxide. A blank is run using the same amount of maleic anhydride as charged to the reaction flask. The amount reported as having reacted with the sample is the net value obtained by titration difference, and from this the diene value and/or the percent dienes can be calculated.
DEFINITION Diene Value is Value is defined as the number of grams of iodine equivalent to the amount of maleic anhydride that reacts with 100 g of sample (on the basis of 2 atoms of iodine per mole of maleic anhydride) under the specified reaction conditions of 3 hours in boiling toluene solution.
APPARATUS Bottle, Bottle, polyethylene, 1000-mL, Sargent-Welch Scientific Co., Cat. No. S-8482-A, or equivalent Buret , 50-mL, with Teflon plug stopcock, 0.1-mL subdivisions IT IS THE USER’S RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TO DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE IN THE MANNER PRESCRIBED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS (MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE).
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Condenser , Liebig, with T s 24/40 ground-glass joint, Sargent-Welch Scientific Co., Cat. No. S-22655-C, or equivalent Flask , Erlenmeyer, 250-mL, with T s 24/40 ground-glass joint, Sargent-Welch Scientific Co., Cat. No. S34114-F, or equivalent, (2 required) Flask , volumetric, 1000-mL Funnel , separatory, 150-mL Hot plate Pipets, volumetric transfer, 3-, 5-, 10- and 20-mL
REAGENTS AND MATERIALS All reagents shall conform to the specifications established by the Committee on Analytical Reagents of the American Chemical Society, when such specifications are available, unless otherwise specified. References to water mean deionized or distilled water. Boiling chips, carborundum, Arthur H. Thomas Co., Cat. No. 1590-D30, or equivalent Filter paper , qualitative, medium, Whatman No. 1, Sargent-Welch Scientific Co., Cat. No. S-33215, or equivalent Maleic anhydride in toluene. Dissolve 60 g of maleic anhydride (mp 52-54 C) in warm toluene. Cool, transfer to a one-liter volumetric flask, and dilute to the mark with toluene. Allow the solution to stand at least one day, and filter through a qualitative-grade filter paper before using. Methyl-tert-butyl ether , (MTBE), or tert -butyl methyl ether, 3 degree boiling range, Fisher Scientific Co., Cat. No. E-128, or equivalent Phenophthalein indicator solution. Dissolve 1 g of phenolphthalein in 100 mL of denatured ethyl alcohol. Sodium hydroxide, 1.0- M , Fisher Scientific Co., Cat. No. SO-S-266, or equivalent, or weigh 80-90 g of a purchased 50% sodium hydroxide solution into a beaker, add 200 mL of water and transfer the mixture to a one-liter volumetric flask. Dilute to the mark with water. Standardize this solution against one gram of pure maleic acid dissolved in 100 mL of water, using phenolphthalein as the indicator. Store in a polyethylene bottle.
PROCEDURE Pipet or weigh a sample of appropriate size, usually 5-20 g, into the dry 250-mL Erlenmeyer flask. With a volumetric pipet add 20 mL of the filtered maleic anhydride-toluene solution, and a few carborundum chips to prevent bumping. Lubricate the joint on the condenser with a thin layer of graphite by marking with a soft pencil. Fit the Erlenmeyer flask to the condenser and suspend the assembly over a hot plate. Adjust the boiling rate by raising or lowering the assembly. Reflux for 3 hours. Allow to cool to ambient temperature, pour 5 mL of water into the flask through the top of the condenser, then gently boil the contents for an additional 15 minutes. Allow to cool to ambient temperature and then add 5 mL of MTBE through the top of the condenser, followed by 20 mL of water. 326-82
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Remove the condenser and carefully transfer the contents of the flask into a 150-mL separatory funnel. Wash the flask with 20 mL of MTBE in 3 portions, then with 25 mL of water, also added in 3 increments. Add the washings in each case to the separatory funnel. Shake the contents of the separatory funnel 4-5 minutes, then let stand until separation of the 2 phases has taken place. Draw off the aqueous layer into a 250-mL Erlenmeyer flask. Extract the residual liquid in the separatory funnel 3 times with successive 25-, 10- and 10-mL portions of water, in each case adding the water extracts to the 250-mL flask containing the aqueous layer drawn off previously. Titrate the combined aqueous extracts with the s tandard sodium hydroxide solution, using phenolphthalein as the indicator. In some cases an insoluble substance forms which makes the recovery of the maleic acid difficult. In the event this has occurred, break up the insoluble compound with a stirring rod and extract with hot water. Extract by adding 15 mL of water to the reflux flask, heat to boiling and continue boiling for several minutes. Cool and transfer the water extract to the separatory funnel. Repeat at least twice more, adding each extract to the separatory funnel. Continue as in the preceding paragraph. Run a blank on the reagents in an identical manner to the samples.
CALCULATIONS Diene value
(B A )( M )(12.69) −
=
W
Conjugated dienes, mass-%
=
C M (B
−
A)
20W
where:
A = volume of sodium hydroxide solution required to titrate sample, mL B = volume of sodium hydroxide solution required to titrate blank, mL C = molecular weight of conjugated dienes M
= molarity of the sodium hydroxide solution W = mass of sample, g
PRECISION The estimated standard deviation (esd) based on 10 duplicate analyses at each level is shown in the following table. Duplicate results by the same operator should not differ by more than the allowable difference shown (95% probability).
Diene Value
esd
Allowable Difference
<5 5-50 >50
0.07 0.25 0.40
0.2 0.8 1.3
TIME FOR ANALYSIS The elapsed time for one determination is 5 hours. The labor requirement is one hour. 326-82
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REFERENCES 1. Norton, J. A., Chem. Rev. 31, 319 (1942) 2. Ellis, B. A. and Jones, R. A., Analyst 61, 812 (1936) 3. McKinney, R. S., Hallbrook, N. J., and Rose, W. G., Oil and Soap 19, 141-143 (1942) 4. Official and Tentative Methods Manual of the American Oil Chemists’ Society, Ka 12-55
SUGGESTED SUPPLIERS Arthur H. Thomas Co., P.O. Box 779, Philadelphia, PA 19105 Fisher Scientific Co., 1600 W. Glenlake Avenue, Itasca, IL 60143 Sargent-Welch Scientific Co., 7300 N. Linder, Skokie, IL 60077
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