V O L U M E 2S, N O
1, J A N U A R Y 1 9 5 4
(331) Walter, J . L., and Freiser, Henry, Ibid.,24, 984-6. (332) Ihld., 25, 127-30 (1953). (333) Warlu, V. C., and Rao, BH.S.V.R., J. I n d i a n Chem. SOC.,28, 354-6 (1951). (';: 4) Watanabe, hIanjiro, Science Repts. TGhoku Unic., Third Ser., 4, 81-6 IlR.52) \----,.
(335) Weel,%., van der, C h t m . Weeliblad, 47, 845-8 (1951). (336) Wengert, G. B., Walker, R. C., Louks, 11.F., and Stenger, V. A., A x . 4 ~CHEM., . 24, 1636-8 (1952). (337) Werner, O., Metall, 4, 9-12 (1950). (338) Wernet, Joeef, Z . anorg. t i . allgem. Chem., 267, 213-37 (1952).
155 (339) (340) (341) (342) (343) (344)
West, T. S., Metallurgia, 47, 97-106 (1953). Ibid., 43, 41-6 (1951). Willard, H. H., A 4 CHEM., ~ ~ ~22,. 1374 (1950). Willard, H. H., and Gordon, Louis, Ibid., 25, 170-2 (1953). Yatsimirskif, K. B., Zhur. Anal. K h i m . , 6, 2111-17 (1951). Yatsimirskif. K. B.. and hstasheva. A. A.. Ibid.. 7. 43-7 (1952). (345) Yebra Montagut, J. de, and Rich, G. M. M., Afinidad, 27, 488-93 (1950). (346) Young, B. S., and Simpson, H. R., MetaZlurgia, 45, 61 (1952). (347) Zhivopistev, V. P., Zavodskaya Lab., 16, 118C9 (1950).
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Volumetric Analytical Methods For Organic Compounds WALTER T. SMITH, JR., WILLIAM F. WAGNER, and JOHN M. PATTERSON University o f Kentucky, Lexington, Ky.
T
HIS discussion endeavors to cover the literature from Octo-
ber 1951 to October 1953. A few earlier items which were not covered in previous reviews are also included. Although a large number of articles have appeared in this field, many of them are concerned primarily with modifications and adaptations of the more or less standard procedures. Some of these will be found to be useful improvements. DETERMITSATION OF ELEMENTS CARBON
An improvement in the Van Slyke-Folch wet carbon combustion procedure increases the stability of reagents and convenience of handling by adding the chromic acid as potassium dichromate R ith the potassium iodate in the combustion tube instead of predissolved chromic oxide in the sulfuric-phosphoric acid solution (263). A new apparatus for wet carbon combustion in which the sample is heated with the combustion reagent under reduced pressure is described (161). The carbon dioxide formed is diffused through a tube containing potassium iodide and zinc turnings into standard sodium hydroxide, the excess of which is titrated with hydrochloric acid after the addition of barium chloride. HALOGENS
The results of about 100 experiments on the micro and semimicro-determination of halogens are tabulated to show the accuracy attainable by the following improved procedure ( 8 4 ) : Samples of 10 to 20 mg. are burned a t 1000° C. in a stream of 50 mi. of oxygen per minute. Chlorine is absorbed in a tube containing 2 ml. of 2 N sodium hydroxide and 0.5 ml. of 30y0hydrogen peroxide. The inlet tube and glass worm are washed with 1 ml. of 12% hypochlorous acid followed by GO ml. of absolute ethyl alcohol. Five drops of 2,G-dinitrophenol and just enough 1 N sodium hydroxide to give a yellow color are added, followed by 1 ml. of 0.4Y0 mercuric chloride solution and 0.3 ml. of a 1.57, solution of diphenylcarbazide in absolute ethyl alcohol. The solution is then titrated with 0 . 1 4 silver nitrate in ethyl alcohol to a violet color. Bromine is absorbed in 5 ml. of 1 S sodium hydroxide and the hydrogen peroxide is not added until after the combustion. Iodine is absorbed in 5 ml. of 1N sodium hydroxide without the addition of hydrogen peroxide. After the combustion and transfer, 10 drops of bromine are added, followed by 3 ml. of 9.V sulfuric acid, formic acid, and sodium acetate. The final titration is made with sodium thiosulfate solution. The usual inconveniences of some of the common methods for the determination of chlorine are reportedly avoided by placing the sample in a small porcelain crucible filled R-ith halogen-free
slaked calcium oxide and covering with a larger crucible and inverting. The small crucible is completely covered with calcium oxide and heated a t a red heat for about 25 minutes until the mass is disintegrated. The contents are cooled, dissolved in 100 ml. of 2 X nitric acid, filtered, and washed. The chloride is precipitated with silver nitrate and determined gravimetrically or volumetrically. The method is particularly convenient for polyvinyl chloride (134). A modification of Votocek's method (168) for the determination of chlorine in organic compounds is based on the combustion of compounds wrapped in filter paper in a bottle containing distilled water in an oxygen atmosphere. The chloride is titrated mercurimetrically (107). The reaction for the titration of fluoride with thorium nitrate is not the same as that between the fluosilicate ion and thorium nitrate. I n the first case thorium tetrafluoride is formed, but hexafluothoric acid results for the most part in the latter reaction. hloreover, the second reaction varies, depending upon the way in which the fluosilicic acid is removed by distillation. The determination of fluorine when associated with organic matmial ie accomplished by destroying the organic matter, removing t h e fluoride as fluosilicic acid by careful distillation from the ash mixed with 40 ml. of 18N sulfuric acid and 0.5 gram of silicon carbide, buffering a suitable aliquot of the distiIlate to pH 3.0, and titrating v,-ith thorium nitrate using sodium alizarin sulfonate as indicator (170). I n the determination of halo-organic compounds of the a b phatic series, the sample is placed in a rotating autoclave with 0.5N alcoholic potassium hydroxide and 10% aqueous sodium hydroxide for 1 hour a t 200' (131). METALS
The method of Schulek and Villecy (140) was modified for the determination of arsenic in organic nitrogen compounds of t h e guanidino type, by doubling the sulfuric acid, using lem hydrogen peroxide, and adding the hydrazine sulfate in 10 ml. of water. Reproducible results were obtained with N-guanylarsanilic acid and its picrate (156). A review (13) with 172 references discusses the &termination of 38 metals in organic compounds. NITROGER
The Kjeldahl method is adapted to the analysis of azines, by-drazones, oximes, semicarbaxones, other compounds containing N-0 linkages, and derivatives of pyridine and quinoline. The material is dissolved in glacial acetic acid and methanol, reduced
156
ANALYTICAL CHEMISTRY
with zinc and hydrochloric acid, and digested, and the nitrogen is determined by Cole and Park's procedure (47). A special apparatus for the Kjeldahl determination is described and analytical results for many substances are reported. The gas-volumetric Kjeldahl method is also described (177). Nitrogen may be recovered quantitatively from a wide range of heterocyclic compounds and tetramethylammonium compounds by a Kjeldahl digestion using a mercury catalyst and a constant final ratio of sulfuric acid to sodium sulfate ( I06). The method previously described for the determination of ring and sidechain nitrogen has been applied to other heterocyclic compounds. Acridine is not destroyed by ashing with sulfuric acid, but rings of pyrrole, indole, imidazole, pyrimidine, purine, thiazole, benzothiazine, and triazine are completely destroyed (104). Preheating with thiosalicyclic acid assists the conversion of nitrogen to ammonia and permits the determination of nitrogen in nitro-type compounds in a method that appears to be suitable for all basic and neutral forms of nitrogen compounds found in petroleum (97). The Ronchese and Colobraro modification of the Kjeldahl method was investigated on a semimicro scale by analyzing samples of urea, amino acids, and natural products (16). Several investigations of factors influencing the Kjeldahl digestion have been reported. I n a study of the use of selenium oxychloride catalyst for the digestion of quinoline and quinaldine, it was observed that the time of heating and amount of catalyst were critical; an excess of either resulted in low results (110). I n a study of the effect of digestion temperature, it was found that a low temperature gives low results, while a high temperature results in loss of nitrogen. With the proper amount of potassium sulfate, the proper temperature of 410' C. may be obtained (91). A modification of the Kjeldahl-Wilfarth-Gunning method reduces the digestion period to about 15 minutes by use of a higher concentration of mercury, intense heating, and silica granules. The method will stand less abuse than the method of the Association of Official Agricultural Chemists and requires more careful control of heating and measuring of chemicals (119). Eight catalysts were used to determine nitrogen in samples of grasses, seeds, and leguminous plants. A mixture of selenium and mercuric oxide which gave maximum recoveries was selected as the best, although a mixture of selenium and mercury gave the shortest digestion period (3). A special apparatus, together with a combination of existing methods, has been used for semimicro-Kjeldahl determinations (145) A new method for the determination of nitrogen involves the combustion of the sample in the presence of powdered magnesium to form the nitride which decomposes in water to liberate ammonia, the latter being absorbed in a known volume of standard acid (41 ). In a preliminary report on the Dumas method, Kirsten (81) reported that nitrogen can be determined accurately without mixing the sample with cupric oxide if a temperature of 1000" is used for the combustion. I n a later report (83) nickel oxide was suggested as a better catalyst to replace cupric oxide, which gives incomplete combustion a t low temperatures and liberates oxygen a t higher temperatures to cause the retention of some oxides of nitrogen in the combustion tube. Experimental results obtained by using an electrically heated apparatus in the micro-Dumas method indicated that in the reversible reaction 2C02 % 2 C 0 O2 the equilibrium is completely to the left when carbon dioxide is passed a t the rate of 10 bubbles per second through cupric oxide in a tube over a fixed heater at 450" to 600" C. When a movable heater reaches a temperature of 850", the carbon dioxide rapidly dissociates to carbon monoxide and oxygen in the presence of cupric oxide and the nitrogen in the compounds is quantitatively reduced or oxidized to free ni-
+
trogen without the use of reducing copper, although copper is necessary for compounds containing halogen (63). A titration procedure suitable for measuring the nitrate nitrogen content of nitrocellulose consists in dissolving the sample in hot acetic acid, boiling with a special ferrous salt reagent, and titrating the resulting ferric ion with standard titanous chloride solution using ammonium thiocyanate as the indicator (142). OXYGEN
Several modifications of the Schdtze-Unterzaucher method have been reported recently. A careful study of the method has led to the development of an improved compact apparatus requiring little skill for routine operation (28). The high blanks and extra corrections usually required can be eliminated by changing the volumetric iodine end point to a volumetric carbon dioxide one, and by improving the purity of the transport gas (55). Difficulties due to the reaction of hydrogen formed by the pyrolysis and reduction of organic material a i t h iodine pentoxide are avoided by the oxidation of the carbon monoxide to carbon dioxide by cupric oxide, and the collection of the carbon dioxide in a liquid nitrogen trap. After the residual gases are pumped out, the carbon dioxide is determined manometrically. Water is removed by freezing in a dry ice trap (67). An improved apparatus and procedure are described to overcome interference due to hydrogen, permitting accurate and rapid analysis of materials of both low and high oxygen content. The carbon monoxide formed is oxidized with iodine pentoxide, and the resulting carbon dioxide is absorbed in a measured excess of 0.05.V alkali hydroxide solution, which is back-titrated with 0.025-V arid after precipitation of the carbonate with barium chloride (62). PHOSPHORUS
After destruction of the organic matter in glycerophosphate8 and lecithin with sulfuric and nitric acids, the phosphate is precipitated with a measured quantity of magnesium chloride hexahydrate in the presence of ammonium ion and ammonia. I n the filtrate the excess of magnesium ion is titrated with 0.1.V complexon I11 (apparently Versene, ethylenediaminetetraacetic acid) solution with a 0.4% solution of Eriochrome Black T in ethyl alcohol as indicator. The complexon I11 solution is standardized by titration of a solution containing 0.1 gram of zinc ( 3 2 ) . SULFUR
I n a method for sulfur, the sample is oxidized with hot potassium dichromate in phosphoric acid. After the reduction of the excess dichromate by ethyl alcohol, the sulfate is precipitated with barium chloride. The barium sulfate which is contaminated with chromium is fused with sodium carbonate and potassium nitrate. The sulfate ion and other soluble material are extracted with hot water from the residual barium carbonate, which may be weighed, or dissolved in a measured volume of standard hydrochloric acid, and the excess acid then titrated (85). Sulfur impurities from 0.1 to 0.001 % in naphthalene, benzene, and phenol are determined by combustion of the sample in a hydrogen flame, The evolved gases are absorbed in hydrogen peroxide or sodium carbonate solution and titrated to a methyl orange end point. The analysis can be completed in 15 to 30 minutes. The accuracy decreases when larger amounts of sulfur are determined (169). I n a modification of the classical Carius method, potassium iodide is added to the sample, which is then moistened with water, treated with nitric acid, and fumed. Hydrochloric acid is added and the solution is boiled until colorless. The sulfur is then determined gravimetrically or by titration after precipitation with benzidine hydrochloride (126). Sulfur can be determined by a procedure similar to the modifi-
V O L U M E 2 6 , N O . 1, J A N U A R Y 1 9 5 4 cation of Votocek's method for chlorine described above, by dissolving the combustion gases in aqueous hydrogen peroxide (107). Sulfur is determined by combustion of the sample in the presence of magnesium to form magnesium sulfide by a process similar to that described above for nitrogen. When dissolved in acid, the hydrogen sulfide which forms is absorbed in a suitable train ( 4 2 ) . TELLURIUM
The sample is completely decomposed by heating p i t h nitric acid. After the addition of more nitric acid and phosphoric acid the sample is diluted and an excess of 0.lY potassium dichromate is added. After 30 minutes, an excess of standard ferrous solution is added and back-titrated with standard dichromate using diphenylaminesulfonate as indicator (90).
FUNCTION4L GROUPS ACIDS
-4method for the determination of formic acid has been described (100) uherein the mercurous salt, formed by reaction of mercuric acetate or chloride with the acid, is titrated with an iodide-iodate solution. The free and total acidity in commercial lactic acid (45) was estimated by titration followed by hydrolysis with excess standard alkali on another sample. I t was found in the determination of lactic acid in heavy corn steep liquor (151)that oxidation procedures employing potassium permanganate R ere more satisfactor), ACID ANHYDRIDES
Application of the Mahn-Sodeau procedure (148) for acetic anhydride to propionic, maleic, phthalic, camphoric, and butyric anhydrides was successful. Succinic anhydride gave anomalous results. Acid anhydrides, in the presence of organic acids, have been determined ( 6 6 ) by reaction M
