Determination of Oxyalkylene Groups In Glycols and Glycol and Polyglycol Ethers and Esters SIDNEY SIGGIA, A. C. STARKE, Jr., J. J. GARIS, Jr., and C. R. STAHL Central Research laboratory, General Aniline & Film Corp., Easton, Pa.
b A procedure has been developed for determining the oxyalkylene groups in glycols, and in glycol or polyglycol ethers and esters. The procedure involves the use of hydriodic acid to react with the oxyalkylene group, thus forming one mole of 1,2-diiodoalkane for each group. These diiodo compounds are unstable and split off a mole of iodine to form the corresponding alkylene. The iodine liberated in the reaction is titrated with standard tbiosulfate. exist for the determination of oxyalkylene groups. Dichromate oxidation (1, 3) has been used, but lacks the desired specificity. Morgan ( 2 ) , who used hydriodic acid t o split the oxyethylene groups of polyethylene glycol ethers and esters, found ethylene to be liberated and also a n alkyl iodide presumed to be ethyl iodide. The alkyl iodide was caught in silver nitrate solution and determined via a Volhard-type titration. The ethylene was caught in a separate receiver and determined by using bromine. The total of ethylene and alkyl iodide represents the total oxyethylene groups in the sample. Morgan postulated the reaction to proceed as follows: ERY FEW METHODS
-( CH&HzO)=-
+ 2 z HI
-P
x ICH2CHJ ICHZCHJ decomp. CHz=CHp
-+
+ z HzO +
12
Some of the diiodoethane is thought to react with hydriodic acid: ICHzCHZI
+
HI
+ CHICHzI
+ Is
Early work in this laboratory had indicated that a stoichiometric amount of iodine was formed during treatment of polyoxyalkylene-containing compounds with hydriodic acid. A method was devised around the measurement of the liberated iodine. This work substantiates the postulations of Morgan. This approach permits determination of oxyalkylene groups in a shorter time, with less manipulation than with the earlier method, and with much simpler equipment. The method was extended beyond the oxyethylene groups t o oxypropylene groups as well.
REAGENTS
Table 1.
Determination of Oxyalkylene Groups
Assay,
%
Butyl Carbitol (diethylene glycol monobutyl ether) Phenyl Cellosolve (ethylene glycol monophenyl ether) Methyl Carbitol (diethylene glycol monomethyl ether) Carbowax 400 (polyethylene glYcol) Dioxane Polypropylene glycol Ethylene glycol Propylene glycol Diethylene glycol dimethyl ether Hydroxyethyl acetate Stearic acid ester of polyethylene glycol, 5.24 moles of ethylene oxide per mole of acid 8.00 moles of ethylene oxide per mole of acid Stearic acid ester of polypropylene glycol, 8.4 moles of propylene oxide per mole of acid e
% ’
as
99.9 97.5 98.9 98.5 97.8 98.4 99.0 98.6 94.5a 93.5a 97.3 99.5 97.0 97. l b 94.4* 96. I* 98.2 98.1 99.2 87.2c 90. 2c 88. 3c 102.4 105.2 105.2 99.1 99.5 99.2 100.9d
103.2d 102.6*
100.2d 98. I d 99.ld 94.9d 97. I d
(OCHZCH~).Theoretical value
for oxyethylene content is 96.4 as deter-
mined from hydroxyl group determination and corrected for terminal groupings. b % as (-OCH2CH-). Theoretical I
CH3 value for oxypropylene content is 98.4 determined from hydroxyl group determination and corrected for terminal groups. chssay by periodic acid method for 1,2-glycol came to 91.47,. d Based on theoretical value calculated from synthesis ratios used.
Hydriodic acid (55 to 58%, specific gravity 1.7) as used for methoxyl determinations is required. It is preferable t o use hydriodic acid with as little free iodine as possible, in order to obtain low blanks and results with optimum precision and accuracy. Freshly opened bottles of hydriodic acid have a free iodine content equivalent t o 2 to 4 ml. of 0.1N thiosulfate per 5 ml. of hydriodic acid. The free iodine increases rapidly once the bottle is opened and it is not advisable to use acid with a free iodine content equivalent t o over 10 ml. of 0.1N thiosulfate per 5 ml. of acid. This impure acid will cleave the ether and ester linkages and can be used, but the high blanks prevent optimum results. Hydriodic acid can be distilled to lower its free iodine content; however, it was found more expedient to purchase the acid in 0.25-pound bottles. Each bottle lasts for a few determinations and not enough time elapses for the blank to become excessive. Hydriodic acid containing hypophosphorus acid as a stabilizer must not be used. Aqueous potassium iodide solution, 20%. Standard sodium thiosulfate, 0.1N. Carbon dioxide. Cylinder gas or dry ice in a Dewar flask can be used. Unopened cylinders should be rapidly vented t o the atmosphere until frost forms on the nozzle of the valve. This reduces the oxygen content of the remaining gas and results in lower blanks. PROCEDURE
Into a 50-ml. round-bottomed flask is pipetted 5 ml. of hydriodic acid. The flask contains a ground-glass joint t o accommodate a vertical condenser, and is equipped with a side arm through which carbon dioxide can be passed t o blanket the solution. A weighed sample containing 0.001 to 0.002 mole of oxyalkylene group is added to the hydriodic acid. The sample is best weighed in a tared glass thimble (1-ml. beaker works well) and then is dropped into the acid, thimble and all. The vertical condenser is connected with a thin grease seal at the outermost edge t o cause a good seal. Too much grease should be avoided, as iodine tends to dissolve in the excess grease. The flow of carbon dioxide is commenced and kept a t a rate of a few (1 to 5) bubbles per second. A bubbler must be used in the carbon dioxide line, in order t o avoid excessive amounts of gas, and t o prevent iodine from being VOL. 30, NO. 1, JANUARY 1958
0
115
swept out of the system, causing low results. The system has to be kept under an atmosphere of carbon dioxide to avoid air oxidation of the iodide ion to free iodine, which would yield high, irreproducible blanks. After allowing a few minutes for the system to be covered with a blanket of carbon dioxide, heating is commenced. The sample solution is boiled gently for 90 minutes; vigorous boiling causes loss of iodine through the condenser. Xinety-minute boiling mas sufficient for the most stubborn compounds encountered in this study; 45 minutes mas satisfactory for ethylene glycol, but slightly low values were obtained for the Cellosolw and Carbitol samples listed in Table I. Concurrent with the sample is run a blank in the same manner and in duplicate equipment. A glass bead is included in the blank to avoid bumping. Carbon dioxide from the same source is fed into the system containing the blank. The blank is heated for the same length of time, because the blank is sizable and variation must be kept at a minimum for optimum results. It \vas found advantageous from a time standpoint to run several samples a t one time, along with one blank. These are all heated a t one time, by using a manifold of glass tubing to deliver the carbon dioxide from one cylinder. The use of one cylinder is emphasized, as carbon dioxide from cylinders contains oxygen which affects the blank. Different cylinders Ivould contain different amounts of oxygen. After the 90-minute boiling period, the walls of the condenser are mashed down with 15 ml. of 20% potassium iodide solution. All crystals of iodine which may have formed in the condenser must be dissolved by the potassium iodide. The condenser is then washed with two 10-ml. portions of water and is disconnected from the flask. The tip is rinsed, and this TTashing is added to the
flask. The contents of the flask are washed into an Erlenmeyer flask and titrated with 0.1N thiosulfate to the disappearance of the iodine color. Some samples which contain large organic nuclei leave a tarry residue as a button. This is visible either in the titration flask or in the reaction flask. This residue usually contains a measurable amount of iodine dissolved in it. This butt,on should be dissolved in methanol and any iodine present should be titrated with thiosulfate. This increment is added to the original titration. DISCUSSION
Table I shows results on various oxyethylene and oxypropylene ethers and esters. In the case of dioxane, the sample boiled below the boiling point of the hydriodic acid. To avoid low results with this sample it mas necessary to circulate ice water through the condenser, and apply a loose-fitting cork to the top of the condenser. Carbon dioxide was allowed to pass into the flask only a t 5-minute intervals, to avoid flushing out significant amounts of sample. After 45 minutes of gentle boiling, another 5 ml. of hydriodic acid was added through the condenser t o rinse any condensed dioxane back into the reaction flask. The Butyl Carbitol, phenyl Cellosolve, and methyl Carbitol were purified by distillation. Distillation cuts were used whose carbon and hydrogen analyses checked the theoretical values. The other samples were used as received. Though 1,2-dihydroxy compounds operated satisfactorily with this method, compounds with more than tn.0 adjacent hydroxyl groups could not be determined. Thus glycerol, 1,2,4-trihydroxybutane, and dextrose gave re-
sults to which no stoichiometry could be attached. Dihydroxy compounds where the hydroxyl groups are not adjacent to one another do not behave like 1,2dihydroxy compounds. When 1,4-butanediol was used, only 4% of the theoretical amount of iodine was liberated. Evidently the diiodobutane is very stable. Compounds in which the oxyalkylene group is connected to a nitrogen [R2N(CH2CH20),Hwhere R can be hydrogen and 5 can be 1 or greater] cannot be entirely decomposed to liberate iodine. Ethanolamine and diethanolamine liberated no significant amounts of iodine. In the case of polyglycol amines (reaction products of amines and ethylene oxide) the results corresponded to the total oxyethylene groups on the molecule minus 1. This signifies that the hydriodic acid attacks the ether linkages but not the carbonnitrogen links. Erratic results were obtained with epoxides. ACKNOWLEDGMENT
Acknowledgment is made to L. T. Hallett, under whose supervision this work was accomplished, and to TV. E. Hanford for his suggestions during the course of the early program. LITERATURE CITED
(1) Elkins, H. B., Storlami, E. D., Hammond, J. W.;J . Ind. Hyg. Toxicol. 24,229 (1942). 12) Morean, P. W., IKD. ENG.CHEM., ~, .4;.4~: ED. 18, i o 0 (1946). (3) Werner, H. W., Mitchell, J. L., Ibid., 15, 375-6 (1943).
RECEIVED for review July 1, 1957. Accepted September 11, 1957.
Infrared Analysis of Emulsion Polishes JOHN E. MURPHY' and WARREN C. SCHWEMER? Applied Research Department, S. C. Johnson & Son, lnc., Racine, Wis.
There has been a need for a rapid method for the qualitative determination of wax, resin, polymer, and emulsifier in emulsion polishes. The techniques of infrared spectroscopy solve this problem in a satisfactory manner. The spectra of the common components of emulsion polishes and of a group of amine emulsifiers as their hydrochloride derivatives have been compiled. Complete and definite analyses of these formulated products can b e obtained by first separating
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ANALYTICAL CHEMISTRY
the product into its components and then determining the infrared spectra of these components.
Q
UALITATIVE information to the type of wax, resin, polymer, and emulsifier used in emulsion polishes is often desired. These products usually contain about 12% nonvolatile material, waxes, resins, and/or polymers; the rest is water. Complete analysis of these formulations by classical chemical
methods is a long, uncertain, and a t times impossible task. Infrared spectroscopy offers a means of determining the composition of these complex formulations. It is possible to determine the infrared epectrum of the nonvolatile portion of these products by depositing the emulsion on silver chloride disks and evaporating the water. The technique of determining 1 Present address, Research Center, Borg-Warner Corp., Des Plaines, 111.
