Determination of Small Amounts of Water-Reactive Hydrides in Presence of Inert Salts Containing Base >I. DOUGLAS BANUS AND JAMES B. VETRANO Chemical Research Laboratory, Metal Hydrides, Inc., Beverly, Mass. ~ C R O quantities
of water-reactive hydrides such as the alkali
& and alkali Iearth hydrides have long been determined by measuring the pressure or volume of gaseous hydrogen evolved when these hydrides are allowed to react with water or dilute aqueous acid in a closed system. An example of the pressure method is the Q-ork of Krynitsky, Johnson, and Carhart ( 1 ) on the determination of lithium aluminum hydride in ethereal solution. At lrrtal Hydrides, Inc., a modification of this method, developed by A. E. Finholt, and employing a volume measurement by water displacement has been successfully used for all these hydrides where about 1000 cc. of hydrogen are evolved in an average determination. However, when such a method is applied to the determination of very small amounts of alkali hydrides in a matrix of alkali halide, including small amounts of the hydroxide or oxide, many difficulties arise. The concentrations involved are of the order of 0.025 millimole of hydride per gram of sample. This concentration of hydride would evolve much less than 1 cc. of hydrogen using the same technique. The universal gasometric method of Pepkowitz and Proud ( 2 ) would probably not be suitable, since it could not distinguish between hydride and hydroxide hydrogen because of the reaction
MHz
+ M(OH)z
+
2.210,12
+ XHZ
The evolution flask is grasped by tongs (to minimize body heat transfer), unstoppered, and quickly attached to the a paratus at the greased standard taper joint. Wire springs h o b it firmly in place. Any air that is trapped in the apparatus during this transfer should be automatically vented through the bulb, causing no change in L1. If L, does change, the delivery column tip was probably blocked with a droplet of water. Stopcock G is immediately turned to allow delivery of the water to the evolution flask. The system cannot remain vented through the bulb for too long a period without a loss of precision, since the air in the apparatus is saturated with water vapor which would decompose the sample. A magnet is used to agitate the stirrer and aid in rapid and complete decomposition of the sample. The water is leveled in the gas buret by opening stopcock F (and lowering the reservoir if necessary), and the entire apparatus is left once more to come to thermal equilibrium. A convenient aid to leveling the tR-0 arms of the buret is pictured ( H in Figure 1). It is made of stiff paper and slides over the gas buret and leveling arm. .4t this time, the temperature on the Beckman differential thermometer, t2, is recorded, and the gas buret is releveled if necessary. This level is recorded as L1. The difference between tP and tl should be close to zero to obtain the best precision. The atmospheric pressure is now recorded. CALCULATIONS
(1)
This is also true of microcombustion, simple titrimetric, or pH measurement techniques. However, by modification of the macromethod and apparatus, a technique has been developed which will be specific for hydride hydrogen and which will give the analysis to a precision of 2%.
The analytical results are reported as millimoles of hydride per 100 grams of sample. From the equation for the reaction, MHz
+ xHOH
-*
MOHz
+ zH?
(2)
and the familiar gas law, then
APPARATUS
The semimicroapparatus (Figure 1) is constructed of borosilicate glass and mounted on a ring stand. It consists of an evolution flask, A , made from a 19/38 7 joint, the male portion acting as the bulb; a delivery column, B, with a stopcock for adding the hydrolyzing liquid; a 25-cc. buret, C, with a leveling column; and storage bulb, D. I t is necessary that the two uprights of the gas buret be of the same internal diameter to avoid any capillary effect and a false leveling. [This effect may be minimized by the addition of a small amount of Aerosol OT (American Cyanamid Co., New York) to the liquid in the gas buret.] A Beckman differential thermometer and a 0- to110" C. mercury thermometer arc clamped in position alongside the gas buret. Since temperature fluctuation is the most important source of error in the determination, the entire apparatus is placed in a closed room that is free from radiators, drafts, direct sun, and traffic. The laboratory dark room provided an ideal site. A temperature change of 1.0" C. during an analysis can cause an error of 0.08 cc. of hydrogen evolved. Since less than 3 cc. is evolved in an average determination, this causes a significant error.
i-? D V
A
PROCEDL R E
The sample of about 3 to 4 grams (handled only in the dry box) is weighed by difference into the stoppered evolution flask, A (Figure l ) , containing a magnetic stirrer. The evolution flask is thzn placed alongside the apparatus, which is prepared by filling the delivery column to the top mark with water and stoppering. The excess mater collected in the inner tip of the delivery column from the previous determination is then forced out by squeezing the atomizer bulb, and the gas buret is leveled a t a convenient mark. This level is recorded, L1, stopcock F is closed, and the reservoir is dropped a few milliliters below L1. (This should cause no change in L1 if stopcock F is tight.) The entire apparatus and sample are then left to come to thermal equilibrium in a closed room (about 15 minutes). At this time, the temperatures shown by both the Beckman differential, tl, and 0-to-110" thermometers, T, are recorded.
I
H Figure 1. Microhydrolysis Apparatus
1268
V O L U M E 2 5 , NO. 8, A U G U S T 1 9 5 3 Table I.
Summary of Analytical Data
Average Millimoles MHz/100 G. 4.55 2.89 1.92 1.22 21.65 .50 3.09 2.66 1.91 2.66 2.75 3.99 3.13 4.95 4.25
Sample NO.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1269
Average Deviation 0.055 0.09 0.02 0.02 0.105 0.035 0.140 0.070 0.050 0.065 0.025 0.005 0.055 0.060 0.015
Av.
0.054
Millimoles MH,/100 grams
=
Precision, Parts/ 1000 12.1 31.1 10.4 16.4 42.0 21.2 45.3 26.3 26.2 24.4 9.1 1.3 17.6 12.1 3.6 19.9
PV 105
RT.w.2
0.13 ml. a t STP (0.14 nil. at usual laboratory conditions) to be substracted from (Lz- h)to obtain V. This blank value of -0.13 nil. is very close to the predicted value. The difference in volume between 4 grams of the salt and 10 ml. of solvent to that of their solution is +0.20 ml. as calculated from literature values of density. (The assumption is made that the density of the hydride mixture is equal to that of the pure salt.) The volume increase for vaporization of water into the dry reaction tube has been experimentally determined by attaching a dry reaction flask to the apparatus and noticing the volume change to be several tenths of a milliliter. The predicted correction is, therefore, close to the experimental blank, indicating that all factors have been considered. The pressure, P, is the barometric pressure corrected for the temperature of the mercury column and for the vapor pressure of water a t the temperature of the experiment, 2‘. Tables are available for these corrections.
(3)
where P = pressure, atmospheres V = volume of hydrogen, cc. R = gas constant, 82.05 cc. X atm./‘ K. T = temperature, K. w = sample weight z = valence of ,?.I R, T , and w may be substituted directly in Equation 3, but corrections must be made for P and V. Any temperature change during an analysis would lead to an erroneous result due to the thermal expansion or contraction of free air and hydrogen in the apparatus. If the temperature fluctuation is not large and has been accurately measured (tz t l ) , a correction can be made for it. using Charles’ law. There are two additional corrections to be made to ( 4 L1) to obtain the true volume of hydrogen evolved, V . The first is a correction t o be added for the change in volume of the inert salt (the major constituent of the sample) on solution. The second is a correction to be subtracted for the increase of volume due to the vaporization of water into the dry reaction flask. These two fairly significant effects, along with any minor effects (such as solubility of hydrogen in water), are corrected for with a series of blank determinations. These blank determinations are carried out using commercial potassium bromide, following the same procedure outlined. The authors have found a blank of about
-
-
DISCUSSION
An average precision of 20 parts per 1000 has been found for samples in the concentration range of 1 to 5 millimoles of MH, per 100 grams of sample as shown in Table I, all determinations being carried out in duplicate. Below 1 millimole per 100 grams, the precision is erratic and poor; above 5 milIimoIes there are indications that it is significantly better. It is also possible to determine the oxide or hydroxide impurity on the same sample by a subsequent titration of the solution after hydrolysis is complete, the amount of hydroxide corresponding to the hydride being deducted from the total titrated base. ACKNOWLEDGMENT
This work was carried out under a research contract supported by the Department of the Navy, Bureau of Ships. The authors are indebted to H. W. Kruschwitz and R. W. Bragdon for their assistance and advice. LITERAIURE CITED
(1) Krynitsky, J. A., Johnson, J. E., and Carhart, H. W., ASIL. CHEM., 20, 311 (1948). (2) Pepkowits, L. P., and Proud, E;. R., Ibid., 21, 1000 (1949). RECEIVED for review October 14, 1962. Accepted April 6, 1953. Presented before the Division of Analytical Chemistry at the 122nd XIeeting of the Atlantic City, X. J. AMERICAN CHEXICALSOCIETY,
Analysis of lacquer Thinners by Fluorescent Indicator Adsorption Method W. €1. ELLIS AND R . L. L E T O U R N E A C ’ Calgornia Research Corp.. Richmond, Calg.
c
-Y ONMERCIAL
lacquer thinners and those prepared according to
U. S. Government specifications ( 2 ) contain approximately
equal proportions of primary solvents and diluent hydrocarbons. The primary solvents are mixtures of alcohols, esters, and ketones; the hydrocarbons are aromatics and saturates boiling in the range 200’ to 300’ F. Existing procedures for the analysis of lacquer thinners involve several separate steps to determine t,he percentages of the various compound types present. A rapid, accurate adsorption method for the simultaneous, direct determination of aromatics, saturates, total hydrocarbons, and total oxygenated compounds is presented. PROCEDURE
The procedure for the analysis of lacquer thinners is identical to that previously published by Criddle and LeTourneau ( 1 ) for the analysis of hydrocarbon mixtures, with the substitution of a new dye and a new displacing agent. Alcohols were used as displacing agents in the analysis of hydrocarbons; they are
replaced by n-butylamine in the analysis of lacquer thinners, which already contain alcohols and other strongly adsorbed, oxygenated compounds. The new dye component, Rhodamine &‘B”Base (E. I. du Pont de Nemours & Co., Inc.), is added to the fluorescent indicator to mark the boundary between the oxygenated compounds and the n-butylamine. The Rhodamine “B” Base is prepared by dissolving 400 mg. of the solid in 10 ml. of 200-proof ethyl alcohol. Both dyes, the Rhodamine “B” Base and the hydrocarbon indicator described by Criddle and LeTourneau, are added to the sample in concentrations of 0.5 to 5 parts per thousand. Further minor modifications follow. Before adding the displacing agent, 20 mm. of dry gel is added to prevent the heat of adsorption from distilling sample out of the column. Considerable heat will be evolved when the butylamine is initially adsorbed. The additional gel is tamped gently with a glass rod to eliminate gas pockets that may have formed and to guarantee a tightly packed column.
