Progress in organic functional group analysis: 1959

MICROCHEMICAL

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Analysis:

1959 T. S. MA,

Department

c# Chemistry, Brooklyn New York

Cotbege, Brooklyn,

This review follows the last one1 without any duplication of references. A summary of the literature dealing with determinzltions of organic functional groups on the micro scale (approximately 0.1 meq.) which came to the attention of the reviewer during the past year will be found in Table I. Most of these papers are discussed in the text below, together with some publications on maCro (> 1 meq.) and ultramicro (approximately 1 peq.) m&hods which may 1)~ adapted to the micro scale. OXYGEN

FUNCTIONS

Acyl Groups The use of ion-exchange resins has greatly extended the scope of acyl group determination beyond the acetyl and benzoyl groups. Ma and Gary2 have developed a general micromethod for the analysis of 0-acyl and N-aryl compounds. The sample is dissolved in n-amyl alcohol and heated with sodium hydroxide in a sealed tube. The reaction mixture is then transferred onto an ion-exchange column containing Rmberite-IR-120 and eluted wit.h water-isopropyl alcohol mixed solvent. The free organic acid in the eluate is determined by titration with 0.02N sodium hydroxide. Kainz3 has described a procedure for the semi-automatic determination of acetyl groups. Automatic control of the steam distillation of acetic acid, after the hydrolysis of the sample, is accomplished by adding successive amounts of water through a pump cont,rolled by a relay. The distillation takes 20 to 30 minutes and 50 to 60 ml. of distillate are collected. 373

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TABLE I on Microdetermination

Summary of Current Literature

of Functional Groups References

Functional Group Oxygen functions Acyl Alkoxyl Carbonyl Carboxyl Hydroxyl Esters Peroxides Nitrogen functions Amid0 Amino Hydraxido Hydrazino Hydrazo Nitro Nitroso Quaternary ammonium Sulfur functions Mercapto Sulfides Sulfonates Unsaturated functions Etbylenic Benzylidene Miscellaneous functions Acidic Basic Active hydrogen

2,3 4-11 12-16 17 18,21-27 2,28 29 30 32-34 35,36 35 37 38,39 38 40 41,42 43 44 4547 48 4931 5555 56

Alkoxyl Groups Two papers have appeared which advocate the use of solid absorbents for the removal of iodine and hydrogen iodide in alkoxyl deVeEer& and Spevak4 employ a bent tube (see Fig. terminations. 1, C) which is packed with antimony potassium tartrate impregnated on kieselguhr. Filipovic and Stefana@ use an absorption tube (see Fig. 2, C) charged with ascarite. When it is desirable to perform carbon and hydrogen analysis on the alkyl iodide, the absorption tube (Fig. 2, E) is half filled with ascarite and half with anhydrone. The alkyl iodide is driven into the connecting combustion tube by a MICROCHEMICAL

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1 Fig. 1. Alkoxyl

Fig. 2. Alkoxyl

apparatus

apparatus

ANALYSIS

375

I of Verera and Spevak.4

of Filipovic

and Stefanac.5

stream of air. These workers propose to use the carbon and hydrogen ratio to ascertain whether the sample contains methoxyl or ethoxyl group, or a mixture of both. Separation of methoxyl and ethoxyl groups based on the solubility difference between tetramethyl-

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ammonium and ethyltrimethylammonium iodides has been reinvestigated by Makens, Lothringer, and Donia,6 who claim that nitrobenzene is the solvent of choice. Kratzel and Gruber7 have reported on the quantitative separation of alkoxyl groups by gas chromatography. Alkyl iodides are absorbed on tri-m-tolyl phosphate or polyoxyethylene glycol and separated at 84’. Using 10 mg. samples of the alkoxyl compound an accuracy of + 1% has been obtlained for methoxyl, ethoxyl, and propoxyl groups. Determinat,ion of alkoxyl groups in compounds containing a tertiary alkyl branched chain should be interpreted with precaution, as Campbell and Chnttleburgh8 have found that tert-butyl substituted phenols give anomalous alkoxyl values. Because sulfur in the sample interferes with the gravimetric method for alkoxyl analysis due to the precipitation of silver sulfide, Sobue, Hatano, and Araig have proposed that methyl iodide be absorbed in pyridine and that the absorption of the methyliodide pyridinium salt be measured at 366 rnp.

Carbonyl Groups Budesinsky and co-workers have suggested two oxidimetric methods for determining carbonyl groups. In one method,12 the sample is treated with a known amount of phenylhydrazine and t,he unreacted reagent is back titrated potentiometrically with standardized cupric acetate solution according to the following equation : CsHsNH-NH2

+ 2Cu2+ + 20H-

-

2Cu+ + C~HG + N, + 2HzO

In another method,13 the carbonyl compound is converted to the oxime and the excess hydroxylamine is determined potentiometrically by titrati,)n with potassium ferricyanide or iodine in strongly alkaline solution. The sample size is in the range of 0.15 to 0.20 mey. but the titrant used is 0.05 to 0. IN. It is noted that the normality of the reagent changes after a few days. Klimova and Zabrodina14 have determined 10 to 15 mg. of carbonyl compounds by oximation and acidimetry. The sample is shaken with 5 ml. of reagent solution containing hydroxylamine hydrochloride, triethanolamine, and ethanol until it dissolves, then set aside for 30 min. Saturated sodium chloride solution is added and the reaction mixture is tit,rat,ed with 0.02N hydrochloric acid using bromophenol blue as indicator. In an attempt to adapt the conventional macro MICROCHEMICAL

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oximation technique to the micro scale using O.OlN titrant, sharp color changes with Martius yellow indicator have been observed.15 However, these color changes do not correspond to the equivalence points and the results are erratic.

Carboxyl Groups AndersonI has described a procedure for the determination of carboxyl groups by decarboxylat’ion in which 1 to 5 mg. of carbon dioxide is produced. The sample is heated with hydrochloric acid and the carbon dioxide formed is removed by a stream of nitrogen The excess base is then and absorbed in 0.05N barium hydroxide. back titrated with 0.05N hydrochloric acid.

Hydroxyl Groups Berka and Zyka18flg have compared potassium periodate and lead tetraacetate for the quantitative oxidation of hydroxy acids and polyhydroxy compounds. The former appears to be the reagent of choice since the reaction proceeds according to stoichiometric ratios. On t,he other hand, oxidation of hydroxy compounds by means of lead tetraacetate is complicated by the subsequent oxidation of the resulting formic acid. These workers also reportzO that the excess potassium periodate (10 to 20 mg.) can be determined by potentiometric titration with hydrazine sulfate solution in the presence of a 20-fold amount of i0dat.e ions. West and Skoogzl have determined 4 to 34 mg. of glycerol by oxidation with quinquevalent vanadium, the excess reagent being back titrated with ferrous sulfate using N-phenylanthranilic acid as indicator. A t,urbidimetric micromethod for determining tertiary hydroxyl groups has been proposed by A.shworth.22 The reagent consists of mercuric sulfate in dilute sulfuric acid. The method is based on the dehydration of the tertiary alcohol to an alkene which forms an insoluble complex with mercuric sulfate. A calibration curve is necessary, and duplicate or triplicate determinations are recommended for an analysis. Coulometric titration of mono- and dihydroxy phenols using electrolytically generated bromine has been investigated by Cuta and Kucera. 23 Phenol and cresols exhibit sharp endpoints when one mole of bromine per mole of sample is consumed. o-Cresol also can

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be brominated until three hydrogen atoms have been substituted, as in the case of resorcinol. The use of infrared spectrometry for the determination of phenolic hydroxyl and other hydroxy compounds are described in several papers.24-27 Like the bromination method for phenols, the infrared absorption procedures are limited to the analysis of known compounds and cannot serve as a general method for the determination of hydroxyl groups.

Esters A microprocedure for the determination of saponification number has been described by Lee.2* About 40 mg. sample of the oil is heated at 75” in a micro-Kjeldahl flask with 0.5 ml. of 4Oa/cpotassium hydroxide in ethanol for 50 min. The excess alkali is then titrated, while warm, with O.lN hydrochloric acid using phenolphthalein as indicator. Ma and Gary* have suggested a method to determine both the ester and acyl functions with one sample. After heating the sample with a known amount of sodium hydroxide in a sealed tube, the residual alkali is titrated with 0.02N hydrochloric acid. The free organic acid is then separated on the ion-exchange column and determined by titration with 0.02N sodium hydroxide.

Peroxides Hock and Kropf2g have presented a method for determining hydroperoxides. The sample is dissolved in 10 ml. of acetic acid and treat,ed Solid carbon dioxide with 0.5 ml. of 500/, potassium iodide solution. is introduced to remove air and a granule of cuprous chloride is The iodide liberated is titrated with O.OlN added to act as catalyst. sodium thiosulfate. Satisfactory results are given for cumyl hydroperoxide.

NITROGEN FUNCTIONS Amino and Amide Groups In the microdetermination of amido groups in proteins, Stegemann30 reports that alkaline hydrolysis at 20” gives quantitative yields of ammonia. Cystine is decomposed under this condition and interferes with the analysis. Bier and Teitelbaum3i have investigated the application of gas chromatography to amino acid analysis. Some MICROCHEMICAL

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amino acids can be quantitatively oxidized to volatile aldehydes by means of ninhydrin. Another approach is the decarboxylation of the amino acids to the corresponding amines, but the conversion is not quantitative. An enzymatic method for the determination of the primary amino group of n-amino acids on the micro scale has been developed by Ma and Breyer.32 The sample is decomposed by n-amino acid oxidase and catalase in a phosphate buffer. This oxidative deamination process yields ammonia which is driven into boric acid solution by a current of steam and titrated with O.OlN hydrochloric acid. The presence of n-amino acids does not interfere with the deThe gasometric method for determining primary termination. amino groups by diazotization has been extensively studied by Kainz and Huber.33 Various types of compounds which do not possess the primary amino group may cause anomalous readings in the nitrometer. Thus it is shown that the amide linkage and oximes react with nitrous acid to produce nitrogen and nitrous oxide. A coulometric method for determining secondary amines has been described by Przybylowicz and Rogers.34 The sample is converted t,o the dithiocarbamic acid which is titrated with electrolytically generated mercury in acetone solution, according to the following set of reactions : 2RzNH + CSz k

2RzN-C-Si!

R,N-V-S-

+ Hgf2 -

+ RtNHz+

(R3-C-S

)sHg

J

Primary amines constitute an interference in this procedure but can be removed by forming the Schiff bases with salicylaldehyde prior t,o the reaction with carbon disulfide.

Hydrazido, Hydrazino, and Hydrazo Groups A micro apparatus has been constructed by Ma and Mattei for the gasometric determination of hydrazino and hydrazido groups, The sample is dissolved in a neutral or acidic medium and oxidized by a suitable oxidizing agent. The liberated nitrogen is flushed into a micro azotometer by a stream of carbon dioxide. The choice of oxidizing a,gent, and of solvent, affects the results greatly. No single

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oxidizing agent or solvent is generally effective for all types of hydrazine derivatives. Gowda and Rao36 have determined acid hydrazide by titration with 0.05N sodium vanadate in 8N sulfuric acid solution. The excess oxidant is back titrated with ammonium ferrous sulfate solution. Reiss37 has suggested the determination of 0.1 meq. quamities of hydrazobenzene by means of O.lN potassium permanganate in alkaline solution. The excess permanganate is back titrated iodimetrically Aniline and phenylhydroxylamine using O.lN sodium thiosulfate. interfere with the analysis; azo, azoxy, nitro, and nitroso compounds have no effect.

Nitro, Nitroso, and Azo Groups Tandon has presented a method for the direct titration of nitro, nitroso, and azo compounds with chromous sulfate using neutral red or phenosafranine as indicator. Alternately, an excess of chromous sulfate solution is added and the excess is back titrated with a ferric It should be solution, with ammonium thiocyanate as indicator. mentioned that chromous sulfate solution is extremely unstable. Kruse39 has developed a method to determine aliphatic and aromatic nitro compounds by controlled potential coulometry. The best solvent system for the reduction of mononitro compounds is 4 to 1 methanol to 0.5N aqueous lithium chloride solution.

Quaternary Ammonium Groups Sodium tetraphenylboron has been reported to be a satisfactory reagent for the determination of quaternary ammonium compounds. Pate1 and Anderson40 have observed that Mraalkyl or alkylaryl ammonium ions form salts with bromophenol blue which can be extracted from alkaline solutions. These workers describe a titrimetric method in which the quaternary ammonium compound is mixed with bromophenol blue in chloroform and aqueous sodium hydroxide solution. The mixture is titrated with 0.02M sodium tetraphenyl boron, with frequent shaking, until the blue color disappears from the chloroform layer. A gravimctric method is also suggested. The sample is treated with 2.5% sodium tetraphenylboron solution and the precipitate is allowed to stand overnight, collected on a filter, dried at 105”, and weighed. MICROCHEMICAL

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FUNCTIONS

Kunkel, Buckley, and Gorin 41 have det’ermined alkyl mercaptans in hydrocarbons by titration with ammoniacal silver nitrate in ethanol. Ammonium dithizonate is used as indicator. Sant and Sant42 have described a procedure to determine mercaptoacetic acid by titration with O.lN copper sulfate until permanent yellow precipitate is formed. Results are given for 0.1 meq. samples, but the titration endpoint is difficult to ascertain for such quantities. Mixtures of alkyl mercaptans and dialkyl sulfides have been determined titrimetrically by Jaselskis43 using two aliquots. The first aliquot is titrated for mercaptan with iodine. The second aliquot is treated with basic acrylonitrile to convert the mercaptan to sulfide, acidified, and the total sulfide content determined by titration with bromate-bromide solution. The amount of dialkyl sulfide is found by difference. A method is also described for the analysis of mixtures containing alkyl mercaptans and alkyl disulfides. Mercaptan alone is titrated with iodine solution. Then the total mercaptan is titrated after the reduction of alkyl disulfide with zinc in a solution containing acidic and hydrochloric acids and alcohol. The determinations were carried out on the semimicro scale using O.lN titrants. This method probably can be adapted to the microscale using 0.02N standard solutions. Sulfonates have been determined by Gardner and co-workers4’ by burning the sample to yield sulfur dioxide which is then absorbed and titrated with 0.03N potassium iodate. UNSATURATED Ethylenic

FUNCTIONS Groups

Chapheker and Gore45 have used a modified active hydrogen apparatus of Roth to determine unsaturation by hydrogenation. The reaction is carried out in acetic acid solution with 30% palladium on carbon as catalyst. A fully automatic coulometric method for determining olefinic groups by bromination has been presented by Walisch and Ashworth. These workers claim that it is possible to ascertain by means of a simple operation, whether the addition reaction is complete and unaccompanied by side reactions, and that the concen-

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trations of different olefins in a mixture can be determined when their bromination speeds differ sufficiently from each other. Cuta and Klozar4’ have determined methyl oleate in the presence of styrene by coulometric bromination. The rate of bromine addition to oleate in acetic acid is 13 times faster than that to styrene. On the other hand, addition of chlorine to both compounds is too fast while the reaction of iodine too slow to be practicable. Benzylidene

Groups

Jurecek and Obruba4s have described a method for the determination of benzylidene groups attached to oxygen or nitrogen. The sample (4 to 15 mg.) is hydrolyzed in dilute sulfuric acid under reflux in a modified Kuhn-Roth acetyl apparatus. The benzaldehyde formed is steam distilled into 10 ml. of standardized O.OlM 2,4dinitrophenylhydrazine solution. After standing for 1 hour, the hydrazone is separated by filtration and washed 6 times. Hydrochloric-hydrofluoric acid mixture is added to the filtrate, followed by 4 ml. of 0.4N titanous chloride. The solution is boiled for 30 min. under carbon dioxide, cooled, and titrated with O.lN ammonium In spite ferrous sulfate using ammonium thiocyanate as indicator. of the complicated procedure using unstable reagents, the results reported for 8 test compounds all agree to within h2y0 relative. MISCELLANEOUS

FUNCTIONS

Acidic Groups Shain and Svoboda4g have applied constant current potentiometry to titrate O.OlM solutions of weak acids with O.lN tetra-n-butylammonium hydroxide. In most cases typical peak shaped titration curves are obtained which permit direct location of the end point from the meter reading. Differential titration of acid mixtures has Patchornik and RogozinskFO not been successful with this technique. have employed tri-n-butylamine in dioxane, sodium methoxide in methanol, and benzyltrimethylammonium hydroxide in pyridine to determine mixtures of acids, anhydride and acyl halides. The amount of sample taken is between 15 to 50 mg. and the titrant used is O.lN. Using strong basic ion exchange resins, Shelley and Umbergersl have separated compounds of different acidity by eluting them with MICROCHEMICAL

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either alcohol only or with applied to acidic aromatic derivatives. Identification compounds are performed by

GROUP ANALYSIS

383

acidic alcohol. This method has been and heterocyclic compounds and their and determination of the individual ultraviolet spectrophotometry.

Basic Groups Gutterson and Mas2 have reported on the use of O.OlN perchloric acid for the microdetermination of basic compounds in several solvents. In acetic acid, bases whose pKb’s in water are 12 or below can be titrated either visually or potentiometrically. Acetic anhydride permits extending the scope to bases whose pK:s in water are no greater than about 13.5. While formic and propionic acids appear to exert a greater leveling effect on bases than acetic acid or acetic anhydride, they are not practicable as solvents for routine analysis. Streulis3 has found that amides and ureas show extremely steep This latter may serve as solvent. titration curves in nitromethane. for very weak bases. When O.OlN perchloric acid is used for the titration of pmole quantity of basic compounds, Belcher and coworkerss4 have observed that primary aromatic amines and their hydrochlorides always give high results in acetic acid because of acetylation. This difficulty is not encountered in titrations on the 0.1 meq. scale. diisoTekar and Simonyl e3 have proposed chloroaluminum propylate hydrochloride as a new titrant for bases. It acts as monobasic acid in chloroform and is suitable for aromatic amines and alkaloids whose dissociation constants are larger than lo-lo. Ethyl orange and dimethyl yellow serve as indicators.

Active Hydrogen Arjungi, Kulkami, and Gore 66have made a slight modification of the Roth apparatus for active hydrogen. The reagent consists of lithium hydride dissolved in di-n-butyl ether. Since no separate solvent is used for dissolving the substance, the procedure is limited to compounds which are soluble in di-n-butyl ether. Radioactivity has been applied to active hydrogen analysis by Eastham and Raaen.67 The active hydrogen in the sample is exchanged with tritium from excess tritiated isopropyl alcohol by dissolving the sample in the alcohol and then evaporating this solvent. The measured radioactivities taken on by a variety of compounds

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agree well with that expected from the number of active hydrogens in the compound and the known radioactivity of the solvent. A procedure using 200 mg. sample is described. It probably can be adapted to the 0.1 meq. scale.

References 1. Ma, T. S., Microchem. J., 3, 415 (1959). “Progress in functional group quantitative organic analysis.” See H. H. Gary, Master’s 2. Ma, T. S., and H. H. Gary, unpublished work. Thesis, Brooklyn College, 1960. “The microdetermination of esters and acyl compounds.” 3. Kainz, G., 2. anal. Chem., 166, 32 (1959). “Partial automation of acetyl distillation.” 4. Verer&, M., and A. Spevak, Chem. listy., 52,152O (1958); Collection Czechoslov. Chem. Communs., 24, 413 (1958). “Quantitative organic analysis XIX. Microdetermination of alkoxyl groups.” “Deter5. Filipovic, L., and Z. Stefanac, Croat. Chem. Acta, 30, 149 (1958). mination of methoxyl and ethoxyl groups in organic compounds.” 6. Makens, R. F., R. L. Lothringer, and R. T. Donia, Anal. Chem., 31, 1265 “Microdetermination of methoxyl and ethoxyl.” (1959). “Quantitative 7. Kratzel, K., and K. Gruber, Monatsh. Chem., 89,618 (1958). separation and identification of alkoxyl groups by gas-liquid chromatography.” 8. Campbell, A. D., and V. J. Chattleburgh, Analyst, 84, 190 (1959). “Anomalous alkoxyl values for t-butyl substituted phenols.” 9. Sobue, H., A. Hatano, and T. Arai, J. Sot. l’extile and Cellulose Ind. Japan, “Determination of methoxyl groups.” 15, 21 (1959). 10. Nessonova, G. D., and E. K. Pogosyants, Zavodskaya Lab., 24,953 (1958). “Determination of alkoxyl groups in organo-silicon compounds.” “Quantitative 11. Brown, P., and A. L. Smith, Anal. Chem., 30,549 (1958). determination of methoxyl groups in siloxane polymers.” 12. Budesinsky, B., Chem. listy, 52, 2292 (1958). “Semimicro determination of the carbonyl group.” 13. Budesinsky, B., and J. Korbl, Microchim. Acta, 1959, 922. “Oxidimetric hydroxylamine method of carbonyl determination.” 14. Kliniova, V. A., and K. S. Zabrodina, Zzvest. Akad. Nauk S.S.S.R., 1959, 175. Microdetermination of the carbonyl group by oxime formation.” See 15. Ma, T. S., M. Gutterson, and R. W. Schneteinger, unpublished work. R. W. Schnetzinger, Master’s thesis, Brooklyn College, 1959. “Oximation of carbonyl compounds.” 16. Slouf, A., feskoslov. farm., 8, 77 (1959). “Photometric determination of ketonic substances in chloramphenicol.” 17. Anderson, D. M. W., Z’alanta, 2, 73 (1959). “An apparatus for routine semimicro estimation of uranic acid content.” “New volumetric 18. Berka, A., and J. Zyka, C’eskoslov. farm., 7, 141 (1958). MICROCHEMICAL

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methods in the analysis of organic compounds. V. Oxidizing tart,aric acid with potassium periodate and lead tetraacetate.” 19. Ibid., Collection Czechoslov. Chem. Communs., 23,2005 (1958). “On the oxidation of some a-hydroxy acids and mannitol with lead tetraacetate and potassium periodate.” 20. Ibid., ceskoslov. farm., 8,136 (1959). “Titration of periodates in the presence of iodate with hydraeine sulfate.” 21. West, D. M., and D. A. Skoog, Anal. Chem., 31,586 (1959). “Analysis of dilute aqueous glycerol solution with quinquevalent vanadium.” 22. Ashworth, M. R. F., Mikrochim. Acta, 1959,506. “Turbidimetric micromethod for analysis of tertiary butyl alcohol.” 23. Cuta, F., and Z. Kucera, Collect. Czechoslov. Chem. Communs., 24, 1467 “Coulometric titration of mono and di-hydroxy benzenes with halo(1959). gens.” 24. Burns, E. A., and R. F. Nuraca, Anal. Chem., 31,397 (1959). “Determination of hydroxyl concentration in polypropylene glycols by infrared spectroscopy.” 25. Hilton, C. L., Anal. &em., 31, 1610 (1959). ‘(Determination of hydroxyl numbers by near infrared absorption.” 26. Goddu, R. F., Anal. Chem., 30, 2009 (1958). “Determination of phenolic hydroxyl by near infrared spectrometry.” 27. Crisler, R. O., and A. M. Burrill, Anal. Chem., 31, 2055 (1959). “Determination of hydroxyl value of alcohols by infrared spectroscopy.” 28. Lee, F. A., J. Assoc. OjTc. Agr. Chemists, 41, 899 (1958). “Microdetermination of the saponification number.” 29. Hock, H., and H. Kropf, Chem. Ber., 92, 1115 (1959). “Iodimetric determination of organic hydro peroxides.” 30. Stegemann, H., Z. physiol. Chem., 312, 255 (1958). “Microdetermination of amide nitrogen especially in proteins.” 31. Bier, M., and P. Teitelbaum, Ann. N. Y. Acud. Sci., 72,641 (1959). “Gas chromatography in amino acid analysis.” 32. Ma, T. S., and R. Breyer, unpublished work. See R. Breger, Master’s determination of t,he primary amino thesis, Brooklyn College, 1960. “Micro group by an enzymatic method.” 33. Kainz, G., and H. Huber, Mikrochim. Actu, 1959,337, 563. “On reactions which cause anomalous results in the determination of amino group. Anomalous (‘The reaction of the KH-CO group with behavior of isonitroso compounds.” nitrous acid.” 34. Przybylowicz, E. P., and L. B. Rogers, An&. Chim. Actu, 18, 596 (1958). “Coulometric titrations with mercury (I) and (II). Determinations of secondary amines and mercaptans.” 35. Ma, T. S., and F. Mattei, unpublished work. See F. Mattei, Master’s of hydrazines.” thesis, Brooklyn College, 1960. “Microdetermination 36. Gowda, H. S., and G. G. R.ao, 2. anal. Chem., 165, 36 (1959). “Vanadametry. Assay of isonicotinic hydrazide.” 37. Reiss, R., Z. anal. Chem., 164, 402 (1958). “Determination of hydrazobenzene with alkaline permanganate solution.”

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38. Tandon, J. P., 2. anal. Chem., 167, 184 (1959). “Studies in hivalent chromium salts. VIII. Estimation of nitro, nitroso and azo compounds, quinones and carbohydrates wit,h chromous sulfate.” “Determination of organic 39. Kruse, J. M., Anal. Chem., 31, 1854 (1959). nitro compounds by controlled-potential coulometry.” 40. Patel, D. M., and R. A. Anderson, Drug Standards, 26,189 (1958). “Methods for the determination of benzethonium chloride.” 41. Kunkel, R. K., J. E. Buckley, and G. Gorin, Anal. Chem., 31, 1098 (1959). “Determination of alkane thiols in hydrocarbons with silver ion and dithizone.” “Titrimetric de42. Sant, S. B., and B. R. Sant, Anal. Chem., 31,1879 (1959). terminat,ion of 2-mercapto-acetic acid by copper(H).” 43. Jaselskis, B., And. Chem., 31, 928 (1959). “Titrimetric determination of alkyl mercaptan-dialkyl sulfide and alkyl mercaptan-alkyl disulfide mixtures.” 44. Gardner, C. M., C. H. Hale, E. A. Setzkorn, and W. C. Woelfel, Anal. Chem., 30, 1712 (1958). “Determination of combining weight of sulfonates.” 45. Chapheker, N. R., and T. S. Gore, Microchim. Beta, 1959, 664 “Microdetermination of unsaturation in organic compounds.” “Auto46. Walisch, W., and M. R. F. Ashworth, Mikrochim. Acta, 1959,497. matic coulometric microdetermination of unsaturation with kinetic proof of real equivalence point.” 47. Cuta, F., and V. Klozar, Collection Czechoslov. Chem. Communs., 24, 1482 (1959). “Simultaneous coulometric determination of styrene and methyl oleate.” 48. Jurecek, M., and K. Obruba, Collection Czechoslov. Chem. Communs., 24,2578 “On the identification and determination of benzylidene groups attached (1959). to oxygen and nitrogen.” “Application 49. Shain, I., and G. R. Svoboda, Anal. Chem., 31, 1857 (1959). of constant current potentiometry to nonaqueous titrations of weak acids.” “Non50. Patchornik, A., and S. E. Rogozinski, Anal. Chem., 31,985 (1959). aqueous titration of organic acids, anhydrides, acyl halides, strong inorganic acids, and reactive alkyl halides in various mixtures.” 51. Shelley, R. N., and C. J. Umberger, Anal. Chem., 31,593 (1959). “Behavior of acidic organic compounds in nonaqueous media on ion exchange resins.” 52. Gutterson, M., and T. S. Ma, Mikrochim. Acta, 1960, 1. “Microtitrations of organic bases in nonaqueous solvents.” 53. Streuli, C. A., Anal. Chem., 31, 1652 (1959). “Titration characteristics of organic bases in nitromethane.” 54. Belcher, R., J. Berger, and T. S. West, J. Chem. SOL, 1959, 2882. “Submicromethods for the analysis of organic compounds. Part IX. Titration of organic bases and amine hydrochlorides in glacial acetic acid.” 55. Tokar, G., and I. Simonyi, Magyar Kemiai Foly, 64, 94, 151, 379. “New reagent for titration in nonaqueous medium.” 56. Arjungi, K. N., R. S. Kulkami, and T. S. Gore, J. Sci. Znd. Research, 17B, 459 (1959). “Microdetermination of active hydrogen in organic compounds using lithium aluminum hydride.” “Deter57. Eastham, J. F., and V. F. Raaen, Anal. Chem., 31, 555 (1959). mination of active hydrogen in organic compounds by exchange with tritiated isopropyl alcohol.” MICROCHEMICAL

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