Determination of Hydroxyl Groups with Grignard Reagent J
J
I
FALTER FUCHS, NORMAN H. ISHLER, AND ALL4N G. SANDHOFF School of 3Iineral Industries, The Pennsylvania State College, State College, Penna.
Iioliler experienced difficulties with various substances, some of which gave more than the theoret,ical amount of methane, no matter how carefully they were dried. Insolubility of the original substance and of intermediate addition products also gave trouble. He states that these rarely interfered with the determination of active hydrogen. Difficulties were encountered in reactions involving oxidation-reduction. Successive reactions, revealed by a slon-1y diminishing evolution of gas, also gave trouble.
A
METHOD for the deteriiiinatioil of active hydrogen was
developed in 1907 by Zerewitinoff ( 3 ) , who based his procedure on the evolution of methane from a Grignard reagent of methyl magnesium iodide upon reaction Tpith a compound containing active hydrogen: CHsMgI
+ ROH +CHI + ROMgI
Early apparatus consisted of a reaction vessel with a side arm connected to a gas buret by a glass tube through the stopper. The Grignard reagent was placed in the side arm and the sample in the vessel; the stopper and tube were inserted, and the vessel was tipped so as to bring the Grignard in cont,actwith the sample. The methane evolved was measured directly in the gas buret. Isoamyl ether was used in place of ethyl ether as a solvent for the Grignard reagent because of its lon- vapor pressure and, further, because at that time it vas one of the felv ethers available in quantity . An accuracy of about 5 per cent n-as obtained xith many substances. In cases where the sample n-as insoluble in the solvent of t'he Grignard reagent, it was dissolved in pyridine ( 3 ) . Xylene, mesitylene, or anisole (1) were sometimes used as solvents for the methyl magnesium iodide. Kohler ( 2 ) developed a highly refined apparatus for determination of active hydrogen with which he attained accurate results. This apparatus is hardly suitable for work where fern determinations are to be run, because its operation is involved and it is not readily adapted to an occasional determination. This apparatus permits standardization of the Grignard solution, addition of a measured amount, free from air and moisture, and addition of water after the reaction is complete. Thus, he is able t o measure not only methane evolved by active hydrogen and other groups, but also the amount of reagent used by addition react,ions such as the addition to a carbonyl group.
Apparatus In view of the fact that the Zeremitinoff procedure is inaccurate and the Kohler apparatus is too intricate and involved for occasional use, it was thought desirable to develop a simplified device which would give quick and precise results. The apparatus shown in Figure 1 offers a fast, accurate determination of active hydrogen by the Zerewitinoff method. In designing this, the authors desired to retain the speed and simplicity of the Zerewitinoff device, and to niake its accuracy comparable to t h a t of the usual carbon, met'hoxyl, and hpdrogen determinations. The apparatus differs from conventional design chiefly in that the samples are weighed out in steel cups, which are hung from nubs on the capillary tube above the Grignard reagent. They are introduced into the reagent by means of an electromagnet, which was constructed by winding several hundred turns of KO.26 enameled copper wire on one end of a laminated core of transformer iron. The core is 17.5 cm. (7 inches) in length and 1.25 em. (0.5 inch) square, which makes it very convenient for delicate manipulation. It may be connected in series with a variable resistance t o a 110-volt alternating current line. Pure drynitrogen is introduced through the capillary directly above the solution. Thus the entire system can be flushed free of air and moisture before the samples are dropped. By heating during flushing, t h e Grignard solution can be made completely stable in its atmosphere of nitrogen. The system is rigid, so that no volume change occurs with manipulation. The dibutyl phthalate manometer makes pressure a d j u s t m e n t s q u i c k and accurate. The results obtained \-indicate the precautions taken to ensure their accuracy.
Procedure
FIGURE 1. DIAGRAM O F APPARATUS 507
After drying in an Abderhalden vacuum-drying apparatus a t 100' C. and 2-mm. vacuum, or in case of volatile compounds a t a suitable lower temperature and higher pressure, a sample is weighed into a steel cup, care being taken t o avoid getting moisture on the cup and sample. Traces of moisture which may be
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absorbed in spite of quick weighing and proper transfer to the apparatus are removed during the flushing operation a t 70' C., as shown by experience. The cups are hung facing each other on the glass nubs located on the capillary tube. The reaction vessel containing 15 to 20 cc. of Grignard solution, and with the ground-glass joint properly sealed, is quickly fastened in place with brass springs. Stopcocks 1 and 4 are closed to the atmosphere, 2 is opened to the reaction vessel, and 3 is opened to the atmosphere and the eudiometer. Nitrogen is passed through a drying tube, bubbled through the same dry ether which is used as Grignard solvent, and passed through the capillary tube. After flushing for 5 minutes a t a rate of 2 or 3 bubbles per second, the reaction vessel is immersed in a water
The second sample can be introduced immediately after the first has been run, without further flushing, but merely by emptying the eudiometer and using the same procedure. I n the interests of accuracy, calculations were based strictly on the density of methane a t the temperature a t which the system n-as held during the reaction. These calculations were based on the formula
where t = degrees centigrade, a = 0.003683, and 2, = molecular volume a t t . From Equation 1, Equation 2 is easily derived
where do is given as 0.000716. Values for the density of methane a t various temperatures mere calculated in this way and consolidated in Table I for convenience. Vapor pressures of n-butyl ether mere taken from the curve in Figure 2, which was furnished by the courtesy of the Carbide and Carbon Chemicals Corporation.
Experimental
T€MPE A ATU R E "C.
FIGURE 2 bath a t 70" while the flushing continues for 15 minutes. Stopcock 4 is then opened to the reaction vessel, stopcock 3 is closed to the atmosphere but opened t o the eudiometer, and thegas buret is filled with nitrogen. Stopcock 3 is again opened to the atmosphere and the buret is emptied. This is repeated two or three times. The last time the eudiometer is emptied to not less than 20 cc., stopcock 4 is opened to the reaction vessel, and stopcock 3 is closed to the atmosphere a t the same time that stopcock 2 is closed. The 70" bath is replaced by one a t room temperature, and the contraction due to cooling is taken up by raising the mercury level in the eudiometer. After half an hour, the pressure can be adjusted t o atmospheric by raising or lowering the leveling bulb, so that the mercury level in it and in the eudiometer are approximately the same. Stopcock 1 is carefully opened to the manometer and the final leveling adjustment is made by a screw clamp on the mercury tube according to the common gas analysis technique. When, after 5 or 10 minutes, there is no further contraction or expansion of the gas within the system, the apparatus is ready to use. Stopcock 1 is closed, 4 is opened to the atmosphere, and the mercury is raised in the eudiometer to expel all the enclosed gas. The mercury is allowed t o rise 5 mm. in the cup a t the top to form a safety seal. Stopcock 4 is opened to the reaction vessel and the mercury level in the eudiometer is lowered to about 10 cc. more than the amount of gas expected from the reaction. The screw clamp is left open. The bath is removed from the reaction vessel, and the lower cup is dropped into the Grignard solution by means of the electromagnet. The reaction is usually vigorous, expansion taking place into the eudiometer. After the reaction has ceased, the mercury levels are adjusted t o equality in the eudiometer and leveling bulb, stopcock 1 is again opened carefully, and adjustments are made as described above. Heat effects due to the heat of reaction, as well as incomplete reaction, cause the rise or fall of the manometer level. An equilibrium must be reached before a reading is taken. Temperature, volume, and barometric pressure are noted. The temperature must not vary more than l o from beginning to end of a run; eudiometer and bath must be adjusted t o the same temperature.
Grignard reagent prepared with n-butyl ether as a solvent reacted more quickly than the reagent in isoamyl ether. Equally precise results were obtained with either solvent. I n many cases in which n-butyl ether was used, a reading could be taken within 15 minutes after the sample had been dropped. Duplicate determinations are made without taking the apparatus apart. Stirring is accomplished by agitating the cup with the electromagnet instead of shaking the machine. Checks were obtained within 0.1 per cent of the average values given in Table 11. TABLEI. DENSITY O F hfETHANE Temperature
c.
20
21
22 23 24 25 26 27
Density of Methane X 10-3
Teniperatuir 0
0.667 0.665 0.662 0.660 0,658 0.656 0.G34 0.652
Density of Methane X 10 - 3
c.
28 29 30 31 32 33 34 35
O.61H 0.647 0.645 0.643 0.640
0,638 0.636 0,634
OF HYDROXYL DETERMINATIONS TABLE 11. RESULTS
Theoretical Value Value, Obtained, Substance Per Cent Per Cent 13.9 14.2 1 Benzoic acid 11.6 11.6 2@ Anisic acid 11.8 11.9 35 a-Naphthol 4 &Naphthol 11.8 11.9 30.9 30.8 5 Catechol 40.5 40.8 6 Pyrogallol 13.7 14.2 7 hlethoxyresorcinol Ethylacetoacetate 12.9 12.9 I1 80 7.0 7.0 9 3Ialonic ester o-Toluic acid 12.5 13.1 I11 10 m-Toluic acid 12.5 13.1 11 p-Toluic acid 12.5 13.1 12 Phthalic acid 20.6 .... IV 13' Isophthalic acid 20.5 .... 14 Terephthalic acid 20.5 .... 15 Trimesic acid 24.3 .... 16 Pyromellitic acid 26.7 .... 17 Benzene pentacarboxylic acid 28.5 .... 18 7.4 .... v 19 Picric acid Tribromophenol 5.1 5.4 20 30.9 15.2 VI 21a Resorcinol .... 30.9 22 Hydroquinone 27.4 23 Toluhydroquinone 40.5 .... 24 Phloroglucinol a Isoamyl ether was used as solvent for the Grignard reagent. No correction was made for vapor pressure in these cases. Group
Sumber
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SEPTEMBER 15, 1940
AKALYTICAL EDITION
Pyridine was tested as a possible solvent for some of the substances, but i t was found t o detract from the precision of the determination. No advantages were derired from its use. The results of the substances examined are contained in Table 11. Blanks signify nil values. I n these cases amounts of methane equivalent to 0.5 per cent hydroxyl or less were evolved, probably owing to impurities or traces of moisture.
Discussion and Summary GROUPI. The results, n-hich correspond closely to the theoretical value, clearly indicate the accuracy obtainable with this apparatus. GROUP11. Keto-enol tautomeric substances of the aliphatic series gave hydroxyl values which correspond exactly with the calculated result if me assume complete enolization under the conditions of the determination. The reactions required only 2 or 3 minutes for completion. These results are suprising, yet these data were duplicated time and again by the different operators. GROUP 111. The three toluic acids gave results which were several tenths of a per cent too high, even after careful drying at 79" C. and 2-mm. pressure. The values checked with the usual precision of * O . l per cent. The chemicals, which were obtained from a Fell-known chemical supply house, may not have been of the highest purity, S o attempt a t purification was made. GROUPIV. The six benzene carboxylic acids did not give methane with the methylmagnesium iodide. The only readily apparent explanation is the obserred fact that these
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compounds are inqoluble in the medium. This imolves the assumption that the Grignard reagent does not react in these heterogeneous systems. GROUPV. Insolubility may also account for the inertness of picric acid in the Grignard reagent. The fact t h a t this compound does not react cannot be traced to steric hindrance, as shown by the coniplete reaction of tribromophenol. GROL-PTI. The phenols listed in this group were very slightly soluble in n-butyl ether. They are knon-n to be capable of keto-enol tautomery. Their failure or partial failure to react may be traceable to either fact. The most interesting result is that obtained n ith resoicinol, which seems to indicate that resorcinol in n-butyl ether acts as a monoketomonoenol.
Conclusions The apparatus and procedure give accurate results rather quickly and show considerable improvement over conventional apparatus. The authors' equipment has been used intermittently over several years and has been found convenient aiid efficient for occasional operation in this and other laboratories. Each hydroxyl-containing substance that was completely soluble in the Grignard reagent gave a methane evolution corresponding to some whole number of hydroxyl groups in its htructure.
Literature Cited (1) H i b b e r t , H.. a n d Sudborough. J. J.. J . Chem. Soc., 95, 477 (1909). ( 2 ) K o h l e r , E. P., S t o n e , J. F., J r . . a n d Fuson, R. C., J . Am. Chem. SOC.,49, 3181 (1927). (3) Zerewitinoff. T h . . Ber.. 40, 2053 (1907): 41, 2236 (1908).
Effect of Glycerol on Distillation Method for Water R;ILF B. TRUSCER The Daiies-1-oung Soap Co., Dayton, Ohio
The deterniinatioii of water in soaps b j the distillation method is affected by the presence of glycerol. The error is negligible when benzene or toluene is the distillation medium, but appreciable w h e n xylene is used. OISTURE determination, have been made upon a variety of substances by the well-known distillation method. Dean and Stark's (2) modification of this method was responsible for its expanded and diversified use, aiid Church and TT'ilson ( I ) were first to adapt i t to soap analyses. I n nearly every instance the distillation medium has been one possessing a lower specific gravity aiid generally a higher boiling point than water. Because the aryl hydrocarbons such as benzene, toluene, and xylene can be obtained reasonably pure, are easily available, and entrain a relatively large amount of water in their vapor phase, they have been most commonly used for this distillation. Since water can be removed from most substances faster a t more elevated temperatures, xylene was accordingly chosen for the distillation medium.
Hence, in procedures for the cletermiiiatioii of moisture in soaps by the distillation method. xylene is repeatedly recommended, except in the author's paper (3)in which toluene mas specifically mentioned as the distillation agent. The majority of bar, flaked, and powdered soaps do not contain glycerol, for there is no advantage in leaving thib costly by-product in them. On the contrary, glycerol is left in almost all liquid potassium soaps, especially shampoo soaps in vhich it is a n accredited ingredient, and many potassium-vegetable oil soaps aiid the so-called cold-made soaps retain the glycerol that is liberated during saponification. Can the analyst treat both kinds of soaps in the same manner for the determination of water? He has been advised not to overheat his sample for analysis in the drying oven; in fact, he has been specifically instructed not to exceed 105" C., partly to a m i d the loss or decomposition of any glycerol that might be present. Apparently no attention has been given to the effect of the distillation media upon glycerol when the moisture in soap is determined by the distillation method. The object of this research was to determine what error in a soap analysis is caused by glycerol when JTarious liquids are used for distilling out the moisture.
