V O L U M E 23, NO. 4, A P R I L 1 9 5 1 We now know: The substance is an ester, presumably of phenol. By the hydrolysis a n ammo acid and another acid (benzoic acid) are formed. As the substance does not contain free amino or carboxylic groups, it must contain a benzoylated amino group. The Kjeldahl determination and the formol titration of the hydrolyzed substance show that no acid groups other than the benzoic acid and the amino acid are present. The structure of the substance must be C&COPXIRCOOC6-
Hj.
From the equivalent weight of 255 are shbtracted C&CONH = 120 and COOCBH~= 121. R, therefore, can only be a methylene group, and the substance must be the phenylester of hippuric acid, the melting point of which (104” C.) is that found for the substance. A further proof for the correctness of the identification is obtained by hydrolyzing the substance with sodium carbonate. Hereby only the phenylester is hydrolyzed, and hippuric acid (melting point 190” C.) may be isolated. The second substance given to the student was hydratropaldehyde, the identification of which is somewhat easier. LITERATURE CITED
(1) Bacon, C.W., J . Am. Chem. SOC.,31,49 (1909). (2) Baubigny, H., and Chavanne. G., Compt. Tend., 136, 1198 (1 903).
667 (3) Bergmann, M.,and Stein, W. H., J . Bid. Chem., 129, 609 (1939). (4) Donleavy, J. J., J . Am. Chem. SOC.,58,1005 (1936). ( 5 ) Grote, W., and Krekeler, H., Angew. Chem., 46, 106 (1933). (6) Hoeke, F., Rec. trau. chim., 54,505(1935). (7) Huntress, E.H., and Autenrieth, J. S., J. Am. Chem. SOC.,63, 3446 (1941). (8) Huntress, E.H., and Carten, F. H., Zbid., 62,511 (1940). (9)Ibid., p. 603. (10) Kirsten, W., Svemk Kern. Tzd., 56, 248 (1944); 57, 69 (1945). (11) Liebermann, C., Ber., 7, 247 1098 (1874). (12) Liebermann. C.. and Kostanecki, S.v., Ibid., 17, 285 (1884). (13) Sah, P.P.T., and Woo, T.-F., Rec. trav. chim., 58, 1013 (1939). (14) Siggia, S.,ANAL.CHEM.,22,378 (1950). (15) Siggia, S.,“Quantitative Analysis via Functional Groups,” New York, John Wiley & Sons, 1949. (16) Stepanov, A,, Be?., 39, 4056 (1906). (17) Veibel, S., Acta Chem. Scand., 1, 54 (1947). (18) Veibel, S., Bull. SOC. chim. France, [4]41,1410 (1927). (19) Veibel, S.,J . Am. Chem. Soc., 67,1867 (1945). (20) Veibel, S., and Lillelund, H., Bull. SOC. chim. France, [5]5, 1153 (1938). (21)Veibel, S.,and Lillelund, H., Dansk Tids. Farm., 12,236 (1940). (22) Veibel, S., and Ottung, K., Bull. SOC. chim. FTance, 151 6, 1434 (1939). (23) Veibel, S., and Schmidt, H. W., Acta Chpm. Scand., 2, 545 (1948). (24) Zeisel, S.,and Fanto, R., 2.anal. Chem., 42, 554 (1903). RECEIVED July 10, 1950.
Quantitative Functional Group Determination In the Identijication of Organic Compounds SIDNEY SIGGIA, General Aniline & Film Gorp., Easton, Pa. DENTIFICATION of organic compounds has been largely
I dependent, in past years, on elemental analyses and on the properties of derivatives. The usefulness of quantitative functional group determinations has been realized, as shown by the introduction of micromethods for alkoxy], alkimino, acyl amino, hydroxyl, and other groups. It is the purpose of this paper to emphasize further the advantages of the latter concept, t o consider the scope of present methods, and to suggest new applications of quantitative functional group analysis. Identification problems lie in two main categories. The f i s t category concerns verification of the identity of a compoundfor example, the chemist may be rather sure of the identity of his compound inasmuch as he carried out a known reaction with known reagents, yet he needs verification of the identity before he can proceed with his work. The second category concerns the identification of unknowns. I t has been standard practice for many years for the chemist who has been working on a synthesis to send his product for the usual elemental analyses to verify the identity. I n recent years it has become iwognized as more advantageous to verify the identity of an organic compound by quantitatively determining the functional groups which should be on the molecule. It is a more meaningful analysis if it is determined that the synthesized compound contains the theoretical amount of nitro group or amino group rather than just the theoretical amount of nitrogen. iilong the same lines, the identity of a hydroxy acid is more firmly established by a hydroxyl group determination and a carboxyl group dtJttirmination than by a carbon and hydrogen determination. Functional group analysis also eliminates the uncertainty which exists when the elemental analyses are close to the theoretical. If a carbon analysis is 1% low out of a theoretical 50.070 carbon, the compound could be 98% pure, but often it is much less pure since organic interferences also contain carbon. Elemental analysis has a definite role in organic analysis, and the above should not be construed as meaning that functional group analysis should replace elemental analysis. However, the emphasis is laid on the greater specificity of the functional group determination.
I n the case of the second category, where the problem is the identification of an unknown, quantitative functional group determination is of value in not only establishing the structure of the sample by giving the ratio of groups to one another, but in obtaining the molecular weight of the material. Saponification equivalent and neutralization equivalent determinations have been used for many years to obtain the molecular weights of esters and acids or bases. However, any functional group determination can be used in the same fashion-for instance, hydroxyl, carbonyl, and amide equivalents are just as useful in obtaining the molecular weight of organic compounds containing these groups. I t is best to illustrate the above points with an example of an actual identification. It was discovered that in the reaction HCECH
+ CH,O+HC-CCH&H
several side reactions took place, and the by-products had to be identified. The product of the reaction was distilled, and two materials were isolated which did not have the physical constants of any of the known materials from the reaction mixture. All the functional groups involved in the system were known, and, no matter which functional groups were consumed in forming the by-products, there should still be some unreacted groups which would be determinable. I n the case of these by-products, the following determinations were run: hydroxyl, acetylenic hydrogen, unsaturation, and free and combined carbonyl groups (the combined carbonyl groups are acetal-like compounds). The hydroxyl and free carbonyl values were zero. However, definite values were obtained for acetylenic hydrogen, for unsaturation, and for combined carbonyl. From these values, the corresponding equivalent weight was calculated. (The term “equivalent weight” is used herein in the same sense as neutralization and saponification equivalents are used. The equivalent is actually the molecular weight of the compound when only one of the determined functional groups is on the molecule. It is one half the molecular weight if there are two such functional groups on the molecule, and it is one third the molecular weight if three groups are present, etc.)
ANALYTICAL CHEMISTRY
668 From the equivalent weights determined by these analyses and also from the known reactants and conditions present in the original reaction mixture, the identity of the two materials was ePtablished as HC=CCH( OCH& and H2C(OCH,C=CH)2. For HC=CCH( OCH3)2, the functional group analysis not only indicated what groups were present and which of the starting groups were absent, but yielded the equivalent weight according to each group. This showed that there was one acetylenic hydrogen for each acetal-like group, and that there was either one triple bond for each of the above groups or two double bonds. Then, assunling the molecular weight of the compound equal to the equivalent weight, the formula was reached. From the knowledge of the system, i t was known that propargyl alcohol, the desired product of the reaction, oxidizes on standing to the corresponding aldehyde. Also it was known that methanol was present in the formalin used in the synthesis. The reaction mixture was also slightly acidic; thus, there were all the prerequisites to obtain the compound indicated by the functional group determination. For H2C(OCH2C=CH)2, again the functional group determination indicated the groups present and which of the starting groupq were absent. The equivalent weight according to each group indicated that two acetylenic hydrogens were present for each acetal-like group and also that there were two triple bonds (or an unlikely four double bonds) for each acetal-like group. It was evident then that the molecular weight was at least the equivalent weight as calculated from the acetal analysis with two acetylenic hydrogens and two triple bonds, or that the molecular weight had t o be some multiple of that value. From these data and from the fact that i t was knov n that formaldehyde and propargyl alcohol were present in the original reaction and that they form
formals under slightly acid conditions (which were present in the reaction) the identity of the compound was arrived at. Functional group determination does not make an absolute identification. It does, however, yield data which serve to indicate the probable identity of the compound. The absolut'e identification is made by act,ually synthesizing by known methods the compound indicated by the funct,ional group determination and then comparing the known against the unknown by st,andard techniques such,as comparison of the infrared curves of each, the x-ray diffract,ion patterns in the case of cryst,alline solids, and microscopical examination for crystalline solids in order to compare crystalline form, refractive indexes, and other optical behavior. Other physical properties such as boiling point, freezing point, refractive index, and density can be used to compare the known and the unknovm. Quantitative detr~rminatioriof the functional groups can be a valuable aid in identifying complete unknowns as well as in verifying the identity of suspected compounds. I n the latter type of identification, the functional group determination, because of its specificity, yields a more meaningful idrntification than does an elenirantal analysis. The main value of functional group analysis in identifying complete unknowns is in determining the ratio of the groups t,o one another and determining the functional equivalent weight of the compound, a factor in the molecular weight. RECEIVEDJuly 25, 19.50.
Determination of Microgram Amounts of Calcium and Magnesium in Vanadium Metal JOSEPH RYNASIEWICZ, RVTH GUENTHER, M. E. SLEEPER, ~ V R D . H . GALE Knolls .Itomic Power Laboratory, General Electric Co., Schenectady, .V. Y . method of preparing high-purity vanadium metal to 0SEreduce vanadium pentoxide with calcium in a vessel someis
times lined with magnesia. Saturally, calcium and magnesium were suspected as major impurities in vanadium, but no suitable method of analysis could be found to verify this belief. Accordingly, this laboratory has developed a method for the determination of microgram quantitieq of calcium and magnesium in vanadium. The precipitation of small amounts of calcium as calcium oxalate in a thousandfold excess of vanadium was not feasible. It has been reported (3, 6) that calcium cannot be determined as oxalate in solutions of high ionic strength because of the large solubility of calcium oxalate under these conditions, and because of the coprecipitation of other constituents in the solution. Therefore, it was necessary to separate the calcium from vanadium, before the calcium could be determined microvolumetrically. Vanadium was separated from calcium with cupferron, the classical reagent reviewed b y Furinan and coworkers ( 1 ) . According t o the procedure described hy Guenther and Gale ( 2 ) , vanadiuni was precipitated from a n acid solution with cupferron and the cupferride was then extracted with chloroform. Calcium and magnesium were determined in the aqueous phase as calcium oxalate and as magnesium ammonium phosphate according to the method described by Marsden ( 4 ) . PROCEDURE
Dissolve as small a sample as possible up to 1 ram of vanadium metal (contrtining 0.1 to 5 mg. of calcium a n 3 0.1 to 2 mg. of magnesium) in 30 ml. of 1 to 1 nitric acid, evaporate the solution to dryness several times with hydrochloric acid, and take u p the vanadium chloride with 30 ml.'of 10% hydrochloric acid. Cool the vanadium solution, the cupferron solution, and a bottle of wash water in an ice bath. Transfer the vanadium solution to a 125-ml. separatory funnel, add 15 ml. of cold 5y0 cupferron solu-
tion, shake for 2' nliriutes, and extract the cupferride with 50 in1 of chloroform. Repeat the cupferride precipitation and extraction until the vanadium has been removed. About four or five extractions are necessary to remove 0.5 gram of vanadium. Test for the presence of any unextracted vanadium with a few drops of cupferron solution. A milky white precipitate, instead of thr brown vanadium cupferride, indicates adequate removal of vanadium. Kithdraw the a ueous phase into a 250-ml. beaker, evaporate the solution to %yness, and destroy any residual organic matter by repeated evaporation with nitric and hydrochloric acids. Dissolve the residue in 20 ml. of water plus a few drops of hydrochloric acid. Reflux the solution in the covered vessel, and transfer it to a 50-ml. beaker. At this point the volume should not be greater than 20 in]. Determine calcium and magnesium as previously described ( G , 6). RESULTS
Tables I and 11 show the recoveries of microgram amounts of calcium and magnesium from solutions containing 1 gram of vanadium as vanadium chloride. The extraction of vanadium was done in 10% sulfuric acid as well as in hydrochloric acid, but this lengthened the procedure because of the increape in time necessary to evaporate the sulfuric
Table I. Recoveries of Calcium from Vanadium Chloride Solutionsa by t h e Cupferron-Oxalate Method Calcium .4d=
Calcium Recoveredb
Mg.
7c
0.09
0.009 0.018 0.028 0.037
0.18 0.28 0.37
Mg. 0.06 0.17 0.26 0.36
% 0.006 0.017 0.026 0.036
Each solution contained vanadium chloride equivalent t o 1 gram of vanadium. b A value of 0.20 mg. for calcium in reagents and C.P. vanadium chloride was subtracted.
