lithium Aluminum Hydride as a Reagent for the Determination of Water BERTSIL B. BAKER, JR., AND WILLIAM AlARSHALL M A ~ N E V I X The Ohio State University, ColunibiLs, Ohio
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'IKHOLT, Bond, and Schlesingor ( 2 ) state that lithium aluminum hydride reacts vigorously with water according to the following equation: I,i:IIH,
+ 4 H 2 0+Ti011 + .Al(OH)3 + 4H2
reactions proposed below. Schlcainger added an excess (exact amount not specified) of mater dropnise to a dilute (concentration not given, but solubility is only 0.1 gram in 100 grams of dioxane) solution of a weighed amount of lithium aluminum hydride in dioxane and then measured the amount of hydrogen evolved and analyzed the solution for lithium and aluminum to establish the formula Li.llH4. The most likely oxplanation for the disagreement between the 1.00 ratio of Schlesinger's equation and the 1.4 to 1.6 of this investig:ttion is that when lithium aluminum hydride instead of water is in excess, the reaction does not stop with Reaction 1 but proceeds further h>-rither of the two courses given below.
(1)
The reagent was subsequently r(.portetl suitable for the determination of active hydrogen iii organic compounds (6, 11 ), and Reartion 1 was used to detcsrmine thc strength of lithium aluminum hydride-ether solutions ( 5 ) . So study has hecn reported, holvciver, of the possibility of using the reagent t o detcrmint. n-atclr. Such a method apprarcd to offcr the advantages of rapid reaction and high sensitivity, inasmuch as a 10-gram sample containing 0.1% x a t e r would, by Reaction 1, give, ovrr 10 ml. of hydrogen. The prospect of rapid reaction is of sprckal interest, for alniost d l other hydrogen evolution methods require from 1 to 48 hours' r.(wtion time, usually owing to the insolubility of the reagent in the sample. This dificulty is not mcountered here l)c.causc lithium aluminum hydride is soluble in diethyl ether ( 2 ) and vertain other organic solvents ( 2 , 9, I I ) . The reagent would thus nppear to be especially suitable for the determination of trams of water in organic liquids with which it is unreactive. Alcohol:: (9), acids (9),and amines ( 8 )react to release hydrogen and must be absent. Aldehydes, ketones, esters, acid chlorides, acid anhydrides, and nitro compounds react ( 7 ) with lithium aluminum hydride, but do not evolve hydrogen. If an excess of iwgent were employed, small amounts of such compounds might be permitted. Completely unreactive toivard the reagent arc' cthcrs and aliphatic and aromatic hydrocarbons. An investigation was therefore undertaken to determine the suitability of lithium aluminum hydride as a reagent for water. The experiments didnot lead to a prerise analytical procedure, but the reagent does seem to be suitable for an approximate analysis (about +0.005% in a concentration of 0.1%). Perhaps more important, however, the experiments furnished data to shoLv that the reaction in the presence of excess lithium aluminum hydride does not st,op with Reaction 1, but proceeds further, probably by one of the paths discussed below.
Dehydration of Al(OH),:
+ + -I.kl(OH)3 + 16112 ( 1 ) lAl(OH), + BLiAlH, --+ 2LiOII + 3.41203 + H?O + 8FT, (2) (X) ciLiA1Hc + 15H20--+ tiI,iOH + 3A1203 + 24IIy 41AiA1H4 16H20 ---+-fIiO€I
Mole ratio II,:H,O
= 1.60
Amphoteric Reaction of Al(OH),:
+ 8 H 2 0---f 2LiOlI + 2.41(OH)3 + 8112 LiOH + 2iZ1(0€11i --+ T,i11(A102)2 + 31120 21,iAlHa + 5 H ~ + 0 LiOIl + LiFI(AIO?)? + 8152 21,i;ilHd
Mole rittio 11,/1120
=
(1) '4)
(5)
1.60
Because the ratio of lithium :iluminum hydride to hydrogen i n both Reactions 3 and 5 is the same as in Reaction 1, their postulation is not in conflict with Schlesingrr's data. Schlesinger did not report any investigation of the hydrogen-water ratio. In regard to the first of the tn-o possible courses dehydration'^. i f one considers aluminum hydroxide :is .41203.3H?O, a n cxp1air:ition for the above-mentioned decrease in reaction rate when the ratio 1.40 is reached may lie in stepwise reaction of tho three water molecules, the third being more difficult to remove and reacting more slowly. As for the second possibility (amphoteric reaction), a rercnt article by Gibb ( S ) , which appeared after the majority of this work had been completed, stat,ed that the reaction with water i? approximately representrd by the equations:
EXPERIMENTAL PROCEDURE AND RESULTS
1Ie:tsurements 4 ere made of the pressure of the hydrogen evolved in a closed brass vessel upon reaction of known amounts of water with excess reagent. From 10 to 40 ml. of approximately 1% solution of lithium aluminum hydride in diethylene glycol diethyl ether were added to the vessel and from 15 to 50 mg. of water were introduced by means of a hypodermic syringe through a serum bottle-type stopper. The weight of water n a s determined by difference from the weights of the syringe. The mole ratio of hydrogen to water was calculated. Values ranged between 1.40 and 1.60, depending upon the exact conditions of the experiment. For analytical purposes i t was found possihlc to establish an empirical mole ratio, which, B ith careful duplirntion of temperature, degree of agitation, and reaction time, could he leproduced to * 5 % . The reaction occurs very rapidly a t first and runs sufficiently far in about 1 minute to give mole ratio values of around 1.40. It then slows down considerably, but continues perceptibly for about 1 hour. At the end of thls time pressure readings are constant and give mole ratio valucs approaching 1.55 to 1.60.
+ 21120 +Li.4102 + 4H2 + 4HZ0--+ I i O H + Al(0H)n + 4H2
LiAlH, LiAlH,
S o discussion or data were given. Although the amphoteric rr:tction of aluminum hydroxidc with lithium hydroxide has not been studied under conditions similar to those existing in this experiment, i t would appear from the work of Allen and Rogers ( I ) , I'rooiv ( I O ) , and especially Horan that the acid aluminate, LiH(A102)p (Rcactiori and Damiano (4), 5 ) , is normally formed instead of LiAIOs as suggested by G i h h SUMMARY
STOICHIOMETRY OF REACTION
The reaction of excess lithium aluminum hydride with n a t r r differs from that reported by Schlcsinger ( 2 )as taking place when water is in excess. The stoichiometry of the reaction is discussed and possible equations arc proposed. .I mole rrttio of H I / H 2 0of 1.50 to 1.60 \vas found after the reaction had been allowetl to go to completion. This is i n fair
Both Schlesinger ( d ) and Iirynitsky ( 6 )gave Equation 1 for the reaction of lithium aluminum hydride with water. However, Krynitsky's hydrolysis was cairied out, not with water, but n i t h an excess of 10% sulfuric acid. The acid neutralized the aluminum hydroxide formed and prol):ibly prrvc,nted any of the further
364
V O L U M E 2 2 , NO. 2, F E B R U A R Y 1 9 5 0
365 Gibb, T. It. P . , J . Cheni. Education, 25, 577 (1948). Horan, H. A., and Damiano, J. B., .I. Am. Chem. Soc., 57, 2431
agreement with the calculated ratio from either of two proposed reactions. T h e est:tblishment of a n empirical ratio of hydrogen-water shows the reagent can be used for an approximate determination of water. T h e reagent may find application in the determination of tr:tcw of \v:Lter in hydro(-arbons.
(1935).
Krynitsky, J. .4., Johnaon. ,J. b:,, and Carhart, H. W., -is.tr,. CHEY.. 20, 311 (1948). Iirynitsky, J. A , , Johiison, %J.I,;., :tiid (:arhart, H. IT., .1.A m , Chem. Soc.. 70. 486 (1948). Nystrorn, R. F., 'and Growi'i, K . G . , Ibid., 69, 1197 (1947). Ibid., p. 2548. Nystrom, I?. F., Yaiiko. \V. 11.. and Brown, \V. C . , Illid., 70,
ACKSOWLEDGMENT
441 (1948).
l ' h ~authors arc indebtcd t o Hanns I-drolyzed to urea and for~ ~ ~ a l d c h y dthe e ; resulting solution is then analyzed for formaldehydc. It was found t h a t sodium phosphate at a concentration of approximately 0.3 S in the neutral p€I range will accelerate the tlissoriation of mono- or dimethylo1 urea nearly 100 timrs, and if the solutions are sufficiently dilute so t h a t the equilibrium and the polymrrization effects are negligible the dissociation is 99% complete. The advantages of a ncwtral solution are obvious, for in acid solution the nicithylol urcas are transformed to a \rhite insolulilc solitl.
Table I.
Anal) sis of Dimethylol Urea
Time of Ileatina, M i n . 15
30 60
Theoretical
Iodine. 311. .54,3 :>a.R 57.2 58.1
__
H2C0,
%
46.5 48.0 49.3 50.0
holutions iwre mixed in a 250-1111. I~rlcnmeyerflask with a reflux tube. Thcl flask was heatrtl on a steam bath for periods of time Trim 15 niiiiutes t o 1 hour. .kt the end of the heating period the d u t i o i i s were cooled and analyzed for formaldehyde, using 0.003T1 .\-iodinc solution, by thc method of Donnallg ( 2 ) . This consists of adding a small esc('ss of sodium hisulfite solution ivliich contains no excess sulfur diosidc, allowing to stand 15 uiiiiutes at room temperatwe, ac*idifyingthe solution to nmet,hyl orange, titrating with iodin(, t o remove the esccss hisulfitc. nc~ntt:alizingwith sodium carbotiatcs solution, and titrating the. cwniliinrd sulfite with iodiiir.
Table I gives the results ol~t:~iricd.
'I'ahle 11.
Effect of Concentration on Analysis of and Dimethylo1 Urea
Concentration, G./L.
Jfotio-
c: I'orinaldehyde Observed 3Ionurrietl~ylolurea Diinethylol -.i;ri
19.8 2.5.8 29.0
3 3 ,2 5.3 . 2 :35 :1
30.2 43.0 47.0 49.0 49.8 49.8 49.9
At higher concentrations t h t s tlirnetliylol or monomethylol ureiL I'orms insoluble substances \vhich cannot be analyzed by this method. Table I1 gives results of determinations of mononietliylol aiid dinic.thylo1 urea a t concentratioiis up t o 10 grams per liter :tnd the percentage of formnltlehyde observed. For better than 0 5 9 , accuracy the solutions on heating should be less than 1 gram 1)er liter: for 99% they should be less than 0.2 gram per liter. \Vith undue delay between dissolving the methylol urea anti completion of the analysis the amount of formaldehyde avai1:tI)le l)y this method decreases. Horvewr, thc dccrease is usually not o1)scrvcrl in less than 24 hours. LlTEH 41'lJHE CITED
Method of Synthesis. Monomethylol and dimethylol urea liavc I)crn synthesized by the method of Einhorn and Hamburger (3,4 ) . However, the preferred method is a variation of one given I)y IValker (8) rvhich was taken from Ripper ( 6 ) , Schniibing ( 7 ) , and JValter ( 9 ) , and is carried out in substantially neutral solution. T h r melting points for the thoroughly dried material n . e ~ ( ~ 125' C. for dimethylol and 111 C. for monomethylol urea.
Analytical Procedure. T h e sample (0.0655 gram) of dimethylol urea was dissolved in 100 ml. of water, 40 ml. of 1 M sodium dihydrogen phosphate were added to 20 nil. of 1 M sodium hydroxide, and 40 nil. of water were added to make 100 nil. T h e t y o
I
1)
( 'rowe,
G. 8 . ,Jr., and L ~ . n c hC. . C., .I. Am. Chem. Soc., 70, 3795
(1948).
(2) Doiiirally, L. H., IND. Lsc;. ('HEM., ASAI..ED.,5, 91 (1933). ( 3 ) Einhorn, A.,A n n . , 361,113--18 (1908). (4) Einhorn, A., and Warnburger, A , , Ber., 41, 24-8 (1908). (5) Folin, O., Z. physiol. Chem., 32, 305 (1901). (0) Ripper. K., U. S. Patent 1,400,606 (1923). (7) Schmibing, M., Ibid., 1,989,628 (1935). (8) Walker, J. F., "Formaldehyde," p. 211, A.C.S. Monograph !IS5 New York, Reinhold Publishing Corp., 1944. (9) Walter, G., Brit. Patent 202,148 (1927). (10) R'alter, G., Trans. Fa?'ada!/ Soc., 32,377 (1935). I ~ E C E I V E D February 21,1949,
