SEPTEMBER 15, 1940
AKALYTICAL EDITION
Pyridine was tested as a possible solvent for some of the substances, but i t was found to 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
309
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 that 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) Hibbert, H.. and Sudborough. J. J.. J . Chem. Soc., 95, 477 (1909). ( 2 ) Kohler, E. P., Stone, J. F., J r . . and Fuson, R. C., J . Am. Chem. SOC.,49, 3181 (1927). (3) Zerewitinoff. Th.. 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 an 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.
INDUSTRIAL A N D ENGINEERING CHEMISTRI-
510
TABLE I.
Rr.4TER OBTAINED BY
Water added. ml.
0.00
2.00
DI~TILLATIOS
4.00
6.00
8.00
10.00
Renaene Water recovered. nil. Average apparent gain,
1111.
.. .. ..
.. ..
..
-1.04
4.04 0.01
ti.05
6.0;
6.06
8.08
0.055
0.075
10.09
10.10 0 09:
Toluene Water recovered. rill. h v e r a g e apparent gain, n i l .
.. .. ..
,
.
. .,
,
4.09 6.10 4.10 6.10 0.095 0.10
8.12
10.1; 10.17
0.113
0. l i
8.11
Xyiene IVa t 6.v recovered,
II I
I,
? ~ e r i l e i . 3 1 ) i ) i i i i ' n f ~ ~ ii111. ii,
1 00 1.10 1 05
2 Yh 29!r
4.9-1
G 91 Ii.92
h UI 8.90
0 983
0.9.5
0.91.5
0.905
i.$lC;
10 ti7 10.60
0.647
dnhydrous Glycerol for Tests The first part of this work mas limited to glycerol-water combinations. Preliminary tests upon glycerol from several sources revealed that enough water could be removed by distillation with benzene to cause objectionable error, and it became necessary to prepare specially dehydrat,ed glycerol for these experj ments. The glycerol i ~ a sdehydrated b? the Dean and Stark ( 2 ) method, only on a larger scale. About 500 granis of pure glycerol were placed in a 1-liter, short-necked flask, together with 150 ml. of benzene. In addition to the ivater receiver and condenser custoniarily used in the Dean and Stark assembly, the flask was provided with a mechanical stirrer. This was made by inserting a glass stirrer through a closely fitting glass tube which dipped below the surface of the liquids, thus providing an adequate seal. Rapid stirring of the liquids kept them intimately mixed and permitted a smooth and rapid distillation. Dehydration was continued until a clean moisture trap showed no cloudiness when distilled benzene was collected in it.
VOL. 12, NO. 9
chiefly by water vapor, as the data indicate. I n the case of xyleiie, whose boiling point is much higher than the other two liquids, ~ o m eglycerol is undoubtedly brought over with the xylene, as tests upon the distillate showed. The tabulated data suggest, in the case of xylene, the possibility of calculating the positive error in a water deterniination. For example, let us consider a coconut oil soap containing 35.0 per cent of water, the balance being soap plua glycerol. The composition of this soap would be, approximately, 55.5 per cent soap, 9.5 per cent glycerol, antl 35.0 per cent Tyater. Khen distilled with xylene the glycerol in it could be expected to behave somewhat like the test containing 10 ml. of water. If 10 grams of glycerol (in the test) produced an error of 0.48 nil. compared with a >imilar toluene distillation, then 0.95 gram of glycerol in a 10-gram w n p l e of soap would cause a proportional error of 0 046 ml. of water, equal to 0 46 per cent.
;inalyLical Comparisons The indicated discrepancy between water determinations made with benzene and with toluene does not exceed 0.1 per cent. Therefore, since dehydration is much more rapid with toluene, this liquid is preferred, and for this reason analytical comparisons were made only between toluene and xylene as distillation media. A series of duplicate moisture determinations was made upon a variety of boaps. Ten-gram samples of these soaps n-ere distilled in duplicate, using anhydrous barium chloride ( 9 ) for an antifoaming agent. The data thu.; ohtnined are - 1 i o n ~in Tahle 11.
TABLE 11.
hIOIslrRE
DETERMINATIOXS O S 80 91'
Experimental Moisture Tests The anhydrous glycerol thus prepared was stored in a separatory funnel. The surface of the glycerol was kept covered with a layer of benzene, and for further protection against moisture the stem of the funnel xas inserted through a rubber stopper into a test tube. Ten-gram portions of this glycerol were carefull?weighed into a 500-ml. round-bottomed flask, and immediately covered with benzene, toluene, or xylene as the experiment required. A measured amount of water from a calibrated buret tws then added to each weighed portion of glycerol. The moisture receiver was calibrated in respect to the measuring buret. The contents of theflask were carefully swirled for a moment and then distilled for recovery of water. The same precautions and technique were used as described in the author's previous paper (S).
The quantities of water obtained upon distilling measured amounts of Iyater from glycerol by means of the three hydrocarbons are shovn in Table I. Duplicate tests were made in each case, and the distilling time for each test was 4 hours. The data obtained for distillations with benzene compare relatively well wit'h those made with toluene. It is probable that, while the maximum indicated errors are only 0.095 antl 0.17 ml., the actual entrainment of glycerol is greater, since the volume of two miscible liquids is less than the sum of theii, individual volumes. The additive error increases v-ith the increase of water, when either benzene or toluene is ujetl. With xylene the effect is different. The apparent error is greater in the absence of water, anti least when the weight's of water and glycerol are equal. This is partly accounted for by the decrease in volume as the amount of water increases. However, this does not explain the rather abrupt drop from 0.905 ml. (for 8 ml. of water) to 0.65 ml. in the final test using 10 ml. of water. I t might be assumed that the increase in \.ohme when benzene and t,olnene are used is brought a.bout
Summary and Recommended Method When xylene is used instead of toluene for distilling out the water content of soap containing glycerol, the additive m o r in the ainount of water found may exceed 1 per cent. A larger error will be observed in the analysis of soaps derived from the fatty oils of the coconut oil type than in the analysis oi other soaps made from longer-chain fatty acids. This is due to the larger yield of glycerol from the former type of oils. Toluene and xylene give identical results upon glycerol-free 3oaps. In order to obtain universal accuracy in ascertaining anhydrous soap, the distillation test for moisture should be made with toluene. The commercial variety known as 10" toluene is recommended.
Literature Cited (1) Church and Wilaon, Soap, 7, No. 11, 3.57 (1931). (2) Dean and Stark,J. IND. ENO.CHEM., 12, 486-90 (1920). (3) Truder, R B., Oil & Soap, 16, No. 12, 239-41 (1939).
