1026
ANALYTICAL CHEMISTRY
This diagram is an enlargement of the portion of the apparatus around inlet B and shows a platinum capsule, W , suspended from the stopple in B by two needles held together a t the top by the soft wire loop, Q. The weighing stand, X, for the platinum capsule is also shown. The release mechanism for the platinum capsule is made by forcing two ordinary 1.5-inch sewing needles through opposite sides of the cork (Figure 2) of a sleeve stopple (following the taper of the cork as nearly as possible) until the points of the needles project approximately 1 em. below the bottom of the cork. The points of the needles are then held in a gas flame for a few seconds and bent outwards, as close to the ends as possible, by means of a pair of fine tweezers. W is made of platinum foil 0.004 inch thick (1.41 grams per square inch), and consists of a hollow cylinder 4.9 mm. in diameter and 1.0 em. in length, open a t both ends, but with a bottom sealed in 2.5 mm. from the lower end. The weighing stand, X, for the platinum capsule consists of a short stub of glass rod fitting snugly into the hollow bottom of the capsule and sealed to a thin glass rod long enough to extend up through most of the length of tube B. This thin rod is coiled a t the lower end to form a stable supporting stand of suitable size to fit on a balance pan. Procedure. The release mechanism is put in place a t B. The sample to be reduced is then weighed into W , supported on X , and care is taken to prevent any of the sample from adhering to the upper part of W . The capsule containing the sample is inserted up through the lower end of B until the two bent needle points just extend inside the top part of W . The eyes of the two needles are then pushed together. This results in spreading the points and suspending W from them. X is withdrawn from B and the eyes of the needles are held together by means of Q. The reaction vessel, D (Figure l), containing the stirring ball, solvent, and a weighed amount of catalyst is then attached to C. Hydrogen is passed into the apparatus through U and out through b. After all the air is displaced, and temperature equilibrium in K and J is brought about, the first reading of I is taken in the usual manner a t a convenient level near the loiver end. 9 slight pressure in the system is produced by raising the leveling bulb, and stirring is started. After the catalyst is completely reduced, stirring is stopped, the second buret reading is taken, and Q is removed from the tops of the two needles. As a result W falls into D. Stirring is started again and continued until hydrogen absorption ceases, when the third and last buret reading is noted.
If the reduction is carried out a t room temperature, more effective agitation of the reduction mixture can be attained by removal of K . Direct contact of the core of L with the outside of D a t a point exactly even with the internal liquid level results in vigorous stirring of the reaction mixture, whereby the liquid surface is broken with each oscillation of the stirring ball. For use with the hydrogenation procedure a commercially available rotary type of magnetic stirrer (Arthur H. Thomas Co., Philadelphia 5, Pa., List Xo. 9235-R) proved satisfactory. A small nail cut to proper length, bent to conform to the shape of the bottom of the reaction vessel, and sealed in glass was used as the qtirrer. ACKYOWLEDGMENT
The authors wish to thank E. F. Greinke of the University of Minnesota for much of the original glass blowing involved in the development of the apparatus. To E. B. Vliet, E. F. Shelberg, and R. Jordan, all of the Abbott Laboratories, the authors wish to express appreciation for help and suggestions in construction of the final apparatus. To E. H. Volwiler of the Abbott Laboratories thanks are expressed for provision of the opportunity to complete the work. LITERATURE CITED
(1) Chem. Eng. S e w s , 20, 1648 (1942).
(2) Johns, I. B., and Seiferle, E. J., IND.EXG.CHEM.,A s . 4 ~ ED., . 13, 841 (1941). (3) Kohler, E. P., Stone, J. F., and Fuson, R. C., J . Am. Chem. Soc.. 49, 3181 (1927). (4) McCutcheon, F. H., Science, 102, 7 1 (1945). (6) Niederl, J. B., and Niederl, V., “Organic Quantitative Microanalysis,” p. 263, John Wiley & Sons, New York, 1942. ( G ) Noller, C. R., and Barusch, M. R., IND.ENG.CHEU.,- ~ K . L L .ED., 14, 907 (1942). (7) Scholander, P. F., J . Biol. Chem., 146, 169 (1942). (S) Senn, J. B., Science, 101, 392 (1945).
RECEITED March 29, 1948. Part of this work was made possible by a research grant from the Graduate School of the University of Minnesota. July 194
lithium Aluminum Hydride As a Quantitative Reagent in the Modified Grignard Apparatus H4ROLD E. Z iL?!GC,
AND
BRUCE R
. HORRO31,
l b b o t t Laboratories, Vorth Chicago, 111.
The efficiency of lithium aluminum hldride is compared with that of methyl magnesium iodide as a reagent for the quantitative determination of active hydrogen and of reactive functional groups in thirteen organic compounds. With few exceptions the former reagent is superior, particularly where hindered or enolizable functional groups are involved. In many rases where it may be desirable to determine approximate degrees of hindrance o r to establish the presence of enolizable groups in unknown structures, use of both reagents can be more informative than use of either one alone.
T
HE purpose of the present nTork \vas t\vofold: to determine whether lithium aluminum hydride ( 2 , ?, dissolved in a suitable solvent could be used successfully in the apparatus described in (9) and if so to compare its efficacy with that of methyl magnesium iodide as a quantitative reagent not only for active hydrogen atoms but more particularly for reactive functional groups in organic compounds. After the present work was completed, a paper by Krynitsky, Johnson, and Carhart ( 5 ) appeared, in which lithium aluminum hydride was compared with methyl magnesium iodide as a quantitative reagent for active hydrogen in organic compounds. Still in an more recently Hochstein and paper ( 3 ) reported a more exhaustive study of the use of lithium aluminum
hydride in the conventional Grignard apparatus. The present work offers a different analytical technique. Although some duplication of results regarding active hydrogen is reported, application to measurement of organic functional groups is of primary concern; and little repetition of previous findings in this connection is described, a t least in so far as individual compounds are concerned. The first aim wa5 realized by successful standardization of a solution of lithium aluminum hydride and by testing its action on a compound (benzoin) Jvhich reacts normally a i t h the Grigthe action of lithium alumiorder to nard reagent, num hydride with that of methyl magnesium iodide, determinations were carried out on a number of compounds that have been
V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8
1027
Table I. Thesevalues in turn are derived from the more detailed experimental data summarized in Tables I1 and 111. Any deviation from theory of less than 3% is probably not significant, as this seems to be the approximate limit of experimrntal rwor of the procedure. From Table I it can be seen that in the case of benzoic acid the RESULTS AND DISCUSSIOK hydride reagent is superior to the Grignard reagent for measurcsThe stoichiometrical relationships involved in the reac~tioii ment of both the active hydrogen and the carbonyl function. Heating is required for quantitative reaction in reasonable timt. between functional groups and the Grignard reagent are well of the carbonyl group with the hydride. Similar conditions with known. The quantitative nature of the corresponding lithium the Grignard reagent, however, do not result in quantitative aluminum hydride reactions has been recently established ( 2 , reaction, although the discrepancy between reactions TId and 7 , 8). The number of moles of lithium aluminum hydride required for the quant.itative reduction of 1 mole of R functional [If would indicatts that with use of a much larger excess of group is: ketone, 0.25: ester (or lactone), 0.50; carhoxylic Grignard reagent (SW Table III), a more nearly quantitativc acid (carbonyl function only), 0.50; and nitrile, 0.50. In thr, reaction (2.0 moles) could be achieved. nirasuremrnt of active hydrogen with lithium aluminum hydride, Likewise with aniline it is evident that the hydride is a better as with methyl magnesium iodide, the number of moles of gas reagent than the GrigIiard for the detection of both hydrogens evolved is equivalent to the number of gram-atoms of activf, of the amino group. A series of tivc~nitriles of varying complexity was chosen for hydrogrn in the compound. comparison of the two rcwgents. With the Grignard reagent, The rwults of the Inrasurenierits with both lithium aluminurn in tlipherivlac~tonitl.ilc~TI- givcls 59% active hydrogen and 397, hydritle and with nwthyl magnesium iodide are su~nmariz:r~d addition on heating. With ______~_ ___-_______-the hydride reagent a t room temperature, only 47% active 'rahle 1. (:omparison of Lithium Aluniiniini H>dride w i t h 3Iethyl Magnesiunl Iodide hydrogen is observed together, Moles Reagent ivith 58% reduction. HowS o . of Actire Consumed per Conditions ~ iT~~~~ ~Hydrogens , Mole Compound tver, on heating with the Compound Reartion Min. OC." LiAlHd CHaMel LiAlHd CI31lleI hydride abnormally high reBenzoin I 98 1.04 . 0.2.5 ., d t s for reagent consumed arc 11 Rrnzoir arid in 27 1.01 0.28 a ohtained, possibly because of h 1 98 1.02 0 4i c and d 10 98 1.02 1.1i 0 ;70 1 61 further reduction of the salt P a 26 . 0.94 . (See f ) f 20 98 .. 1.13 . . 1 2R form. In this case the hydridc. TI1 .knililie d 20 26 1.62 ., (See b) appears to provide no advanb 1 98 1.84 ., 0.02 .. tirge over the Grignard reagent. CIS 2.04 n.ot r d 26 .., 0
