Functional Group Analysis W a l t e r T . Smith, Jr., William F. W a g n e r , and l o h n University of Kentucky, lexington, Ky. 40506
T
discussed in this review have been selected from the literature which has become available to the reviewers from December 1967 through November 1969. Acid Anhydrides. A determination of carboxylic anhydrides, carboxylic acid chlorides, and phosgene is based on t h e reaction of t h e compounds with a known amount of piperidine in excess. T h e remaining unreacted piperidine is determined colorimetrically b y means of 3,sdinitrobenzoyl chloride. T h e anhydrides or chlorides 21 X 10-511f can be determined with a relative error of 0.6-7% (172). Polarography is recon mended for the quantitative analysis of a niisture of pyrenic acid anhydride and 1,4,5,8naphthalenetetracarbosylic acid anhydride in various solvent systems (57). Acid Halides. Reduction of sulfochlorides t o sulfinate bj- tiii(II), zinc, and iodide or sulfide was tested for t h e quantitative determination of alkylsulfochloritlcs. T h e simples were titrated in aqueous acetone medium a n d t h e end point was the appearance of :L bright yelloiv color as a result of the formation of 1)olysulfides (243). The determinatioii of benzyl chlorocarbonate is I m e d on the saponification in ethaiiolic alkali, followed by a determination of the free chloride ion by the Volhard procedure (238). Acids. T h e general principles and special methods for deternii!iing individual acids are reviewed b y Carles (34). Aspects of column chroniatography, including solvent selection are given, and the use of the Auto.halyzer, coloriiiietric, and potentiometric deterriiiiiatioiis are esploretl. IIicrocosmic salt, SaNH4HP04, has been used as a new titrant for the mici,odeterniination of bmzoic, salicylic, and phthalic acids. The sample is titrated in an aqueous solution to a pink end point using bromcresolpurple indicator (198). The r~iicrodetermiiiatjon of hippuric acid was achieved by titration with a standard solution of iiidium sulfate to form a 1: 3 indium-hippuric acid complex Catechol violet was used as the indicator (240). l l m i y procedures eniploying potentiometric titrations in nonaqueous solvents have been reported. Po~entioinetrictitrations in dimethylsulfosidc using a bismuth electrode have been accomplished using sodium niethosicte (104) aiid t etrabut ylaniiiioniuiii HE ANALYTICAL MZTHODS
M. Patterson, Department o f Chemistry,
hydroxide (105) as titrants. The procedures were applied to a wide variety of carbosylic acids and phenols. Carbon indicator electrodes (carbon black impregnated with Teflon) were used for titration of acidic compounds dissolved in pyridine. Before every titration, the bottom active surface of the electrode was roughened by a finegrain abrasive paper and activated chemically by immersion into an aqueous solution of 0.231 K h l n 0 4 in 0.551 H2S04 (21). A cliff erentiated potentiometric titration of sulfanilic, metanilic, and sulfuric acids is based on the different solubilities of the acids in water, organic solvents, and aqueous mistures (142). The effect of tert-butyl alcohol and AT,S-diiiiethylforiiiamide on the potentiometric titration of several dicarbosylic acids was studied. X high difboth solvents (1%). in mistures with their monoesters based on a titration in 1 : 4 isopropyl alcoholchloroform using 0.lX alcoholic KOH. The acids give t r o potential jumps. the 50 to -100 niV first in the range of and the second in the range of -100 to -350 mV which coincides ivith the neutralization of the second carbosylic grouli of the ester in the inisture (139). Two potential jumps are observed in the titration of perfluorodicarboxylic acids in acetone, methyl ethyl ketone, or N,S-dimethylformamide, using a tuiigsten indicator electrode aiid tetraethylammonium hydroside titrant (41). Conditions for the quantitative determination of pyromellitic, hemimellitic, and trimellitic acids in a mixture with HNOJ by poteiitiometric titration with alcoholic KOH in methanol medium were investigated. Other solvent systems were studied (233). The concentration dependence of the half-neutralization potential (Eo 5 ) of a variety of acids in butyl alcohol, acetone, and 507, acetone using glass and calomel electrodes was studied. Varying the concentration of the acid ten fold changed the Eo.s by 30 mV. Equations relating the concentrations and dissociation constants of the acids were developed t o predict the feasibility of differential titrations of mixtures (88). A method i p described for the determination of fatty acids b y a constant current potentiometric titration in 4:1 benzene-methanol with 0.1Jf sodium
+
methoxide, or in isopropyl alcohol with 0.1M tetrabutylammonium hydroxide (149).
Conductometric methods were used by several investigators to determine acids. Dichloroacetic acid was titrated conductometrically with 0.5-1.031 amines in acetone (107). Conductometric titration of a number of organic acids as well as mixtures of the acids with nitric acid in methanol, isopropyl alcohol, and N,N-dime thylformamide were investigated, by using potassium acetate or tetraethylammonium hydroside as titrants (106). Weak acids and di- and tri-nit,robenzenes dissolved in ethylenediamine were titrated conductornetrically and potentiometrically with 0.1N lithium 2-aminoethylaniide (18). Salicylic acid and salicylamide were deterliiiiied separately in a mixture by conductometric titration in 1:1 aniline-ethanol with 0 . 1 s potassium niethosidc in metlianol-benzene. Severn1 other solvents were found to be unsatisfactory (222). The separate deterniiiiation of carbosylic and phenolic hydrosyl groups present in humic acids was carried out by using high-frequency titrations in aqueous methanol solutions (184). Xi1 evaluation of nrcthods used for determining functional groups in humic acids showed that all the following methods could be used for determining the number of carbosylic groups in all the aaml)lcs: acetate method, the barite method for the sun1 of carbosylic aiid phenolic hydrosyl groups, determinntioii of cation exchange capacity, and 1iotclitionietric titrations. The potentiometric method was most rapid but could not be used for the esnct deterniiiiation of the suni of carbosylic and phenolic hydrosyl groups. Cation exchange gave the most reliable results ( 5 ) . .I semimicro method was developed for the determination of the carbosyl group in hydrosybenzoic acids, and in cinnamic acid and some of its derivatives by using the decarbosylation reaction and high frequency conductometry. Phosphoric acid and hydrochloric acid or 20.11 ZnC12 were used as decarbosylating agents and 0.l.V Ba (OH)? as titrant (&H). K h e n an acid reacts with a base in a low dielectric constant solvent, the formation of an ion pair can be detected by the increase in the dielectric constant of the solution. Measurement of the dielectric constant provides a good
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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method for detecting the end point of acid-base titrations in benzene when the reaction proceeds quantitatively as in the titration between picric acid and triethylamine or N,N-dimethylbenzylamine (159). An oscillopolarographic method was developed for the determination of aliphatic dicarboxylic acids by their catalytic current reduction in the presence of germanium(1V) b y using perchlorate in an acetic acid medium of p H 3.2 as a supporting electrolyte (62). Conditions are described for the polarographic determination of isocinchomeronic and nicotinic acids in 2,5dicyanopyridine hydrolysates containing ammonium ions and pyridine (204). The slight polarographic reduction of the carboxyl group of methacrylic acid in neutral 0.05.V tetraethylammonium iodide was found to be linearly dependent on the concentration of the acid. No reduction was observed in alkaline and acidic solutions ( I ) . Aliphatic dicarboxylic acids were oxidized b y heating with an excess of 0.1N Ce(C104)4in 131 HClOa and the excess oxidant was back-titrated with 0.1N Ka2C204in 1-11 HClOd by using an amperonietric end point with no external applied potential (160). Spectrophotometry is the basis for several procedures for the determination of acids. The decreased absorption a t 492 nm observed for the iron(II1) nitrosalicylate complex in an aqueous monochloroacetate medium a t a p H 2.6 to 2.7, with increasing concentrations of an added organic acid was used to determine acids spectrophotometrically
(144). Linear calibration curves for the spectrophotometric microdetermination of several acids were obtained by a method based on the Oxidation of the acid by cerium(1V) sulfate in sulfuric acid followed by measuring the absorbance of the excess cerium(1V) in the presence of ferroin a t 426 nm (152). Phthalic acid and its anhydride, ester, imide, and substituted monoamide derivatives can be determined photometrically in microgram amounts a t 488 nm after condensation with resorcinol in a 83y0 zinc chloride solution a t 210 "C (44). Mixtures of m- and p-nitrobenzoic acids were analyzed in methanolethanol medium by spectrophotometric titration with sodium methoside a t 330 nm (140). Twentytwo basic dyes were tested as reagents for the extraction and photometric determinations of several acids and their derivatives (130, 131). Some of the dye complexes were used for ultraviolet fluorescence analyses. Tartaric acid can be determined spectrophotometrically by reaction with 78R
P-naphthol in 90% H2S04and measuring the absorbance at 603 nm (46). The determination of tartrate in the presence of citrate is based on oxidation b y an excess of periodate ion. The iodate ion formed is reacted with iodide ion to form Is- which is determined spectrophotometrically at 350 nm (169). Milligram quantities of tartaric acid and citric acid can be determined by complexation with iron(II1) followed by measurement of the absorbance a t 380 nm (226). An automatic procedure for the determination of carboxylic acids is based on the esterification of the acids and the reaction of the esters with hydroxylamine to form the hydroxamic acids. These acids are measured spectrophotometrically as their iron complexes a t 480 to 520 nm. The method is suitable for the continuous monitoring of eluants from chromatographic columns (246). An automatic system for the chromatographic separation of acids, after conversion to their esters, on Celite columns is described. After elution, the esters are converted back to the acids which are determined colorimetrically by their decolorizing effect on an indicator dye a t p H 8.0 (35). Idonic and gluconic acids in a hydrogenation mixture of 5-osogluconic acid were separated by ion eschange chromatography and the eluate was fed to an AutoAnalyzer for spectrophotometric analysis of the acids a t 218 nm b y reaction with 0.01% aqueous KIOd
(4).
ii simple selective, sensitive fluorometric method for the determination of oxalate ion is based on the quenching by oxalate of the fluorescence a t 460 nm of a 1:1 zirconium-flavanol chelate in sulfuric acid solution (26). A similar method for the determination of citrate involves the quenching of the fluorescence a t 450 nm of the flavanol-tungstate comples by citrate ion (89). Rapid fluorometric methods are described for the determination of mixtures of twenty-one carboxylic acids which iiivolve six enzyme systems. The rate of production of the highly fluorescent resorufin is equated to the concentration of the acid (87). An infrared technique has been developed for the determination of halogenated impurity in substituted anthranilic acid by making use of the displacement of the carbonyl band frequency by the substituent groups (230)* A quantitative method based on the measurement of the peak intensities in the X-ray diffraction pattern, was developed for the determination of a- and p-N-allyl-dl-camphoramic acids in the presence of each other (95). A method for the determination of
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5 , APRIL 1970
the disodium salt of 2,2'-dicinchoninic acid has been reported. The lead salt may be precipitated and weighed after drying a t 120 "C, or the excess of a standard solution of lead ion used for the precipitation may be titrated with EDTA for a volumetric procedure (80). Alcohols. Primary and secondary alcohols may be determined with relative standard deviations of 2.02 and l.SO%, respectively, b y oxidation with BrCl (125). The excess BrCl is titrated iodometrically . The conditions for the quantitative oxidation of various alcohols have been investigated (22). The oxidation of methanol is carried out in 3N KOH, ethanol and propanol in 4.5N H2SOa, and isopropanol in 6N H2S04. Butyl alcohol and isobutyl alcohol do not react quantitatively. A mixture of chromic and sulfuric acids has also been used as oxidant in the determination of alcohols (108). The formation of hydrogen peroxide during the oxidation of methyl, ethyl, allyl, and propyl alcohols in the presence of alcohol oxidase has been used for the estimation of these compounds (86). Peroxidase and p-hydroxyphenylacetic acid are employed in the fluorometric determination of the hydrogen peroxide. thermocatalytic procedure has been applied to the determination of alcohols (75). The perchloric acidcatalyzed acetylation reaction was employed. Cycloalkanols form a stable intensely colored solution on interaction with phenols in the presence of sulfuric acid (110). The reaction is the basis of a spectrophotometric determination of these alcohols. The colored comples formed on the interaction of normal Cs to C18 alcohols with di-(8-quinolyl) orthovanadate in nitrobenzene has been used as the basis of their analysis in alcohol-ester mixtures (3). The sensitivity of the colorimetric determination of alcohols by the di(8-quinolyl) vanadate procedure is said to be improved if the alcohol complex is hydrolyzed in chloroform and the 8-hydroxyquinoline released is coupled with p-nitrobenzenediazonium fluoborate (181). A number of halo substituted di(8-quinolyl) vanadates were prepared and evaluated as reagents for the determination of alcohols (126). The complex derived from 5,7-dichloro8-hydroxyquinoline was the most sensitive of those tested. Small quantities of alcohols have been determined by their conversion to nitrites with nitrous acid (31). The nitrites, in turn are analyzed spectrophotometrically with Griess reagent. The methods used in the determina-
tion of terpene alcohols in flotation oils have been compared (188). Dehydration methods are stated to offer advantages over acetylation methods. Glycols have been determined by oxidation with gold(II1) chloride in the presence of excess alkali (212). The excess AuClp is estimated by adding KaFe(CN)G artd back titrating with C e (SO*)using A‘-phenylanthranilic acid as indicator. Periodic acid oxidation of glycols is the basis of several procedures for glycol analysis. These methods differ primarily in the method used to estimate excess reactant or quantity of product formed. I n one procedure, the aldehydes produced are determined h y the bisulfite-cyanide method (162) while in another they are determined colorimetrically after reaction with 2,4-dinitrophenylhydrazine (146). I n a third procedure, the iodate produced on oxidation of the glycol is determined spectrophotometrically by reaction with iodide to form triiodide (168). Hydroxy groups in phenol-carbohydrate compounds have been determined with alkyl borates b y a transesterification reaction (72). Excess unreacted alkyl borate is removed b y distillation and titrated with standard aase. The determination of mannitol and sorbitol b y polarimetry of their molybdate complexes has been studied (90). Polyhydric alcohols have been estimated b y an acetylation procedure (263) or by a lead tetraacetate oxidation procedure ( 2 ) . I n the lead tetraacetate procedure, unreacted I’b(OAc)c is hydrolyzed to a colloid which is determined turbidometrically or the formaldehyde formed is estimated with chromotropic acid. Hydroxy end groups in poly(ethy1ene terephthalate) have been determined b y reaction with 3,5dinitrobenzoyl chloride followed by titration of the excess hydrolyzed acid halide (255). Aldehydes and Ketones. Chemical a n d physical methods of analysis for carbonyl compounds have been comprehensively reviewed by Hanna (91).
T h e hydroxylamine method for carbonyl determination has been applied to the determination of ketones in the presence of ketals (209). Conductivity measurements have also been used with the hydroxylamine method (60) and the effect of dielectric constant change on the titration end point has been evaluated (158). Dinitrophenylhydrasine has been employed in carbonyl group determinations using either spectrophotometric methods (16, 225) or a potentiometric method (100). IXmedone (5,5-dimethyl-l,3-~yclohexanedione) has been used in a titrimetric method for the determination of
aldehydes (63). The aldehyde is precipitated by an excess of dimedone and the excess reagent is titrated amperometrically with standard nitrite solution. For the spectrofluorometric determination of aldehydes with dimedone, the work of Sawicki and Carnes, in which several methods are compared, should be consulted (197). I n colorimetric determinations of formaldehyde and glycolic acid 1,8-dihydroxy-3,6-naphthalenewith disulfonic acid or 2,7-dihydroxynaphthalene, interferences from ethanol have been reported (215). Amides. F a t t y alkanolamides give two moles of weak base for every mole of K O H during saponification. This serves t o distinguish t h e m from amines, amine derivatives, and other byproducts present in t h e mixtures, which yield only one mole of weak base for each mole of KOH. A differential rate technique can be applied to measure the formation of the extra base (148). Amines. Procedures available for the analysis of amines (216) and alkanolamines (191) have been reviewed. The decomposition process in the determination of amines and other nitrogen compounds by the Kjeldahl method (121) has been studied. The quantity of sulfuric acid consumed and the amount of ammonia produced has been correlated with the mode of decomposition. Chromic anhydride in sulfuric acid cleaves amines to ammonia. If halides and nitro groups are present in the amine, these can be determined simultaneously (134) since these groups are oxidized to halcgen and nitric acid, respectively. The procedure has been applied to eighteen compounds. The acetylation of amines with isopropenyl acetate is used for the determination of amines (245). The excess isopropenyl acetate is estimated by reaction with bromine followed by a titration with Na2S203 of the iodine produced when K I is added. Submicrogram quantities of primary amines can be e a d y determined by gas chromatography with good precision after conversion to the corresponding pyrrole with 2,Shexanedione (247). The reaction of diborane with aliphatic amines in tetrahydrofuran permits the analysis of amines with ca. 3% error (151). The excess of diborane is estimated b y measurement of the hydrogen liberated on hydrolysis with water or methanol. Success of the method depends upon the stability of the amine borane to the hydrolysis conditions. Aromatic amines do not give satisfactory results. Amines catalyze the reaction of nitromethane with 1,3,5-trinitrobenzene to form a red compound (16). Since the intensity of the color produced is pro-
portional t o the amine concentration, amines may be estimated colorimetrically b y this procedure. Hydrochlorides, liberated from their salts with silver oxide, may also be determined. Treatment of an amine with a sodium bisulfite-formaldehyde complex liberates an equivalent quantity of HSO1which can be determined iodometrically. Methylamine (78) and 4-methylaminoantipyrine (77) have been estimated in this way. It has been reported that substances containing both primary and secondary amino groups could not be titrated in the usual way (115). These compounds, however, could be titrated to within 5y0 error using a methanolichydrochloric acid titrant and methanol, methanol-isopropanol or dimethylformamide-methanol solvents. I n an investigation of the titration of bases in acetonitrile (122), it was found that mixtures of aliphatic amines with aromatic amines can be titrated to the first equivalence point using a potentiometric end point or a neutral red indicator. Acetonitrile is also used as the solvent in the titration of aliphatic amines with cinnamic anhydride (47). The end point is determined spectrophotometrically. Water interferes but methanol does not. Amines have been determined by potentiometric titration in the following solvents: nitromethane (133), aqueous acetic acid (187), and acetone (81). .4n interface cell and electrode have been used in the potentiometric titration of organic bases (11 1 ) . Anhydrous benzene, petroleum ether, chloroform, or acetone are used as solvents. Microamounts of primary and secondary aliphatic amines have been determined b y a fluorometric procedure (180). The neutralized amine is heated with sodium 1,2-naphthoquinone-4-sulfonate and the blue fluorescence a t 410 nm is measured. The temperature increase arising from neutralization has been used to determine the end point in the titration of amines with HC1 in isopropanol (234). A sharp drop in temperature rise marks the end point. A related catalytic thermometric titration has been applied to the determination of amines and other organic bases (232). The titration is carried out in acetic acid containing water and acetic anhydride. Excess titrant (HClOa) catalyzes reaction of acetic anhyride with water, thus producing a temperature rise after the equivalence point. The end point is detected from a plot of temperature us. volume of titrant. Methods used in the estimation of aniline and aniline derivatives have been discussed (176). il spectrophotometric titration of
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
79 R
nitro derivatives of aniline using glacial acetic acid as solvent and HC104 as titrant is reported to offer advantages over a potentiometric procedure (141). The relative error is 4% or less, The oxidation reaction of various secondary aromatic amines b y Cu(1I) in anhydrous and 1% aqueous acetonitrile has been studied potentiometrically (1S5).
The sodium bisulfite-formaldehyde complex procedure (78) has been applied to the determination of aniline and its hydrochloride (79). X,N-Dialkylphenylenediamines in the presence of sLV HC1 can be determined with a maximum error of &0.3% when titrated potentiometrically with ?;aKOz (166). An automated procedure has been developed for the determination of primary aromatic amines (195). The amine hydrochloride is diazotized with XaKO, and the excess XaN02 estimated with Safranine GF. Both indirect and direct bromometric titration procedures for the estimation of A7-alkylanilines were investigated (155). The direct method mas unsatisfactory. The indirect method involved the addition of KBr03 and KBr with the excess determined iodometrically and was satisfactory only for S-methylaniline. Other N-substituted anilines were oxidized instead. Aromatic amines can be estimated with an absolute error of -1 to -4oj, using N-bromosuccinimide (227). The excess is determined iodometrically. The most N idely used procedures in the determination of aromatic amines are spectrophotometric methods which differ primarily in the way a chromophore is introduced into the molecule. Thus p-aminophenol is determined by reaction with &xo3 in aqueous acetone (IO), primary aromatic amines by reaction with ethanolic 9-chloroacridme (214),X,-N-dimethylaniline by reaction with N a N 0 2 in the presence of PdCI2 in a dimethylforniamide solvent (ZO), secondary aromatic amines b y reaction with quinone dichlorodiiniide (229)) m-phenylenediamine by reaction with chloranil and CuC12-PPha complex in acetone (93), o-phenylenediamine by reaction with CuC12-PPh3 complex (94), and p-phenylenediamine b y reaction with RuC13-PPh3 complex. The coupling reaction is used extensively for the development of colored substances in spectrophotometric procedures. I n one approach the amine to be determined is diazotized aiid coupled with a phenol. The isomeric toluidines (128) and cy- and P-naphthylamines (127) are coupled with cy-naphthol, and aniline is coupled with phydroxyquinoline (1SW). Diphenylamine is estimated by reaction with p-nitrobenzenediazonium fluoborate (241). 80 R
A number of aromatic amines have been determined by coupling with the diazonium salt of 3-methylbenzothiazolin-2-one hydrazone in the presence of Fe(II1) ion (17 7 ) . Heterocyclic bases and amines are determined by the same procedures applied to the aliphatic and aromatic amines. Pyridylureas (123) and pyridine and quinoline bases (124) have been determined by potentiometric titration with HC104 in acetic anhydride aiid methanol-methyl ethyl ketone, respectively. The behavior of 2,2’-bipyridyl, 4,4’bipyridyl and 1,lO-phenanthroline in the potentiometric titration of these substances with HC104 in acetic acid was studied (12). The potentiometric curve of 2,2’-bipyridyl showed two breaks and the break in the curve of 1,lO-phenanthroline corresponded to one K atom. The 4,4’-bipyridyl behaved as expected. Homatropine, hyoscyamine, cypicoline, 2,6-lutidine, and n-dodecylamine have been titrated with picric acid or trichloroacetic acid (248) using a Kamienski interfacial voltaic cell. Oxazines have been investigated as indicators to be used in the titration of weak bases in nitromethane and in chloroform-dioxane mixture (217). A determination of alkaloids and nitrogenous bases depends upon their precipitation with NaBPha (175). The precipitate is dissolved in acetone and the BPh4- measured b y argentiometric coulometry. Ovalbumin,, gelatin, casein, histamine, histidine, uric acid, cyanuric acid, guanine, adenine, cytosine, and thymine can be estimated by the extent to which these compounds quench the fluorescence of tetramercurated fluorescein (252). The development of a color in the presence of NaOEt by 3,s-dinitrobenzoyl derivatives of primary and secondary amines of the pyrrolidine series and some amines of the furfural, pyrazole, and pyrone series is the basis of their spectrophotometric determination (171). Microgram quantities of pyridine can be estimated spectrophotometrically after reaction with BrCN and 4,4’-diamino-2,2’-stilbenedisulfonicacid (68). A spectrophotometric determination of 3-aminopyridine is based on diazotization followed by coupling with naphthol or naphthylamine (129). The methods used in the determination of piperazine and its salts have been reviewed (173). A characteristic set of infrared absorptions of piperazine permits its detection in ethyleneamines, poly(ethy1eneamine), and polyethyleneimine (210). An amperometric titration of diethylammonium chloride with KOBr gave
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
results which were comparable to those obtained by argentiometric or by POtentiomet’ric titration (237). A rotating micro Pt electrode in buffered solutions (pH 8.3-9.6) gave best results, Methyl red has been recommended as a spectrophotometric reagent for the determination of long-chain quaternary ammonium salts (163). The reagent is said to provide a highly sensitive method and a stable complex. An analysis of mixtures of amine oxides and hydrogenated aiid aromatic heterocyclic bases can be accomplished b y an acidomet’ric potentiometric titration in acetic anhydride and in a 4 : l mixture of dioxane and acetonitrile (23)‘ X new method for the production of the color in the Dische-Borenfreund determination of hexosamines (62) has been developed (228). The deamination product of the hexosamine is treated with 3-met’hyl-2-benzothiazolone hydrazone followed b y iron(II1) chloride. Amino Acids. I n a report describing the conversion of several functional groups to fluorescent derivatives (for subsequent determination by fluorometry), amino acids are converted into fluorescent derivatives of dihydrolutidine (186). This report should also be consulted for fluorometric determinations of alkylamines, indoles, furfural, and A4 and A1f4-3,11-diketost’eroids. Some fairly specific methods for t’he microt,itration of certain amino acids in the presence of others have been described. Thus, lysine can be titrat,ed with HzPtC16 in a mixture of amino acids (239); glutamic acid, valine, and alanine can be determined in each other’s presence by a combination of titrations with gold chloride, sodium tungstate, and potassium tellurate (200); aspartic or glutamic acids can be titrated with microcosmic salt, h’a?;H4HPOa.Hn0 in the presence of glycine, alanine, and leucine (199); and asparagine and valine may be determined in the presence of each ot’her by t,itrations with In2(804)3 and Kp TeOs (201). A new determination of amino acids is based on conversion of the amino acid to a copper derivative followed b y determination of the copper by neut’ron activation ( 2 7 ) . Aromatic Hydrocarbons. Ultraviolet spectra are used in a number of cases for determination of several aromatic components of mixt’ures. A rapid method (30 minutes) for benzene, toluene, and xylene gives errors of less than 15% (196). Analysis of a four-component system consisting of 0 - , m-, p-xylene and ethylbenzene was improved by int’roduction of empirical correction coefficients ( 3 7 ) . I n this way the mean error was decreased to
1.3-4.7%. The influence of errors in absorbance measurements on this same system has also been discussed (219). The optimum analytical wavelengths for a ternary mixture of naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene are oreported to be 3040, 3195, and 311 A, respectively (251). For the analysis of aromatic mixtures containing u p to ten components, a combination of ultraviolet spectra down to 190 nm with infrared spectra in the 0.8- to 2 . 5 - p range is reported to improve reliabilit'g (202). Quasilinear luminescence spectra has been utilized for the determination of a series of polycyclic hydrocarbons (64). This method has been studied in some detail for the determination of benzo[alpyrene (51, 118), Fluorescence spectro,vopy has been used for the determination of benzo[a]pyrene (61) and other poynuclear aromatic hydrocarbons ((143). Electroluminescence techniques have been applied to the determination of 9-pheiiylaiithracene, pyrene, coronene, and anthracene. I t is claimed that the technique must ultimately be superior to conventional spectrofluorometry for organic trace analysis (66). The determination of phenanthrene (over the range 0.1-15%) in anthracene has been accomplished by a combination of infrared and ultraviolet techniques (220). -4 compensation method for the infrared determination of anthracene, phennnthrene, and carbazole mistures uses absorptions a t 888, 820, and 1245 cm-' ( 1 4 7 ) . Carbohydrates. An approach t o t h e analysis of periodate oxidized polysaccharides utilizes sodium borohydride reduction of t h e oxidized polysaccharide followed b y conversion of t h e resulting polyalcohols t o trimethylsilyl derivatives for determination by gas chromatography (58). The method has been worked out for the products expected from ethylene glycol, glycerol, erythritol, t'hreitol, arabinose, sylose, mannose, galactose, and glucose and has given good agreement with espected results \$-hen applied to simulated product mistures of arabiiiosylan, gluco~iiannan,galactoglucomannan, and arabinoga1act:in. The effects of borate on the colorimetric determination of carbohydrates with the phenol-sulfuric acid reagent has been studied with 41 carbohydrates (49). Borate has no effect on the abs o i b n c e of ketose solutions, but lowers the absorbance of aldose solutions. 1he possibility of determining mixtures of ketoses and aldoses is suggested. modification of the colorimetric mc'thod of IXsche and Devi (53) has been used for the determination of fructose in the prewice of a hundredfold escess of glucose with an error of about loyo. I11 the modificatiou, the 7 ,
color formed after addition of the cysteine-sulfuric acid reagent is measured at intervals for 6 hours. The linear portion of the curve is extrapolated to zero time to obt'ain the absorbance due to fructose (166). Epoxides. A monograph on t h e determination of epoxide groups has been published (54). The determination of a-pinene oxide is based on its rapid and quanbitative hydration a t a neutral pH followed b y a titration of the excess water by Karl Fischer reagent (186). X a n y factors influencing the accuracy and precision of the determination of a-epoxides by the hydrochloric acidN,N-dimethylformamide method were studied (221). Esters. T h e determination of RCOO groups in di- and trialkyl tin derivatives of carboxylic acids and dicarboxylic acid heniiesters was achieved b y titration in pyridine with 0.1S sodium methoxide, using an mitimony indicator electrode or thymolphthalein visual indicator ( 8 4 ) , Xeutral esters of aliphatic and aromatic acids are hydrolyzed in ethanol b y 20% KOH, th? escesi of which is titrated with 0 . 1 S HC104 i n 1: 4 ethanol-isopropyl alcohol. Esters of aromatic hydroxy carboxylic acids are titrated directly potentiometrically in acetone with 0.1S tetrabutylammonium hydroxide in benzene-methanol (138). A polarographic method for the determination of glycol esters of phthalic acids has been reported (103). The ester bonds in lipids are split b y sodium methoxide. The corresponding methyl esters formed in a trans-esterificatioii reaction are identified by gas and thin layer chromatography (66). h method for the determination of acetyl groups in the 0-acetyl derivatives of mono- and disaccharides by reaction with hydrosg-laminc is described. The iroii(II1) complex of the acetylhydroxamic acid is measured spectrophotometrically (24). For the quantitative determination of the total carboxylic acid esters in a mixture, a sample is dissolred in methanol, and treated with hydroxylamine in a basic solution. The iron(II1) complexes of the hydroxamic acids formed are determined spectrophotometrically at 510 nm. For the determination of phthalic acid esters in the mixture, a sample is reacted with hydroxylamine and converted to the sodium salt of A'-hydrosyphthalimide which is deterniined spectrophotometrically a t 410 nm (145). A similar Colorimetric procedure based on the condensation of benzyl benzoate with hydroxylamine to give the corresponding hydrosamic acid xhich forms the iron(II1) coniples, was used to determilie small amounts of esters in benzoic acid (9).
Ethers. T h e basis for most alkoxyl group determinations cont'inues to be cleavage of t h e alkoxyl group with hydrogen iodide. T h e determination of t h e resulting alkyl iodide has been t h e subject of a number of investigations. For example, t'he alkyl iodide has been det'ermined b y gas chromatography aft'er init'ial adsorption on silica gel coat'ed with 10% Apiezon L (119), by combustion a t 900 "C for det,ermination of the iodine (33, 70) and by conversiou to hypoiodous acid for determination by titration (8, 46). I n another variation, the alkyl iodides are mixed with air and passed over cupric oxide a t 750 "C. Both the iodine and the carbon dioxide resulting from the combustion were determined gravimetrically (69). I n the coiiventional Zeisel determination of P-methoxynapht halene, low results due to formation of phosphine and have been avoided phosphate (P043-) by the use of hydrogen iodide alone rather than the usual hydrogen iodide and red phosphorus ( 5 5 ) . Estimation of the tril)henylinrthoxyl groups in carbohydrxte polymers has been accomplished b y measurcment of the color formed in 72yo sulfuric acid (211). method for tlialkoxybenzenes is essentially a determination of the reactive aromatic ring by bromination with an excess of bromide-bromate solution (161). N-Methyl Compounds. X modification of t h e 1nicrodeterminat.ion of AT-methyl groups uses an aluminum catalyst for the thermal decomposition of t h e hydroiodide of t h e N methyl compound to give methyl iodide (165). The method has been applied to a variety of compounds. I n a determination of .2'-methyl alkimideq, the sample is tlrcomposed to give methyl iodide, which is collected in a liquid nitrogen trap and then transferred to an evacuated infrared cell for determination of the spectrum. Nethyl iodide content is determined from the peak height a t 1265 cm-l by comparison with a calibration curve ( 1 1 6 ) . I t seems that this infrared determination of methyl iodide could be applied to methoxyl determinations aq well. The technique is an example of the increased application of spectral techniques to functional group determination which we can expect in the future. Nitro Compounds. Primary nitroalkanes can be determined rapidly and specifically b y conversion to t h e nitrolie acid (by base and nitrous acid) followed by photometric titration (190). The accuracy and precision of the method in aqueous a i d nonaqueous solvent. is 0.5%. -4 colorimetric anal\ and secondary nitroalkanes involves their oxidation with alkaline hydrogen
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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peroxide (14). The color is developed by adding sulfanilic acid and hydrochloric acld followed b y 2-hydroxy3-naphthoic acid in sodium hydroxide, Xitro groups and nitroso groups can be determined in the presence of one another by using a two-step polarographic procedure in which TiC13 is used as reducing agent (71). The nitroso group is reduced a t p H 0.5 and the nitro group a t p H 5.5, Titanium trichloride has been used to determine substituted nitrofurans (36). After the addition of TiC12 to the sample, the excess is titrated with NH4Fe(SOd)*. The spectral band centered a t 355 nm arising from the complex formed between hexanitroethane and p-chloroaniline is used to quantitatively estimate hexanitroethane (157). An error nithin 0.5% is obtained in the concentration to lO-5*lf. range of Dinitro- and trinitrobenzenes can be titrated to within 1% error with lithium 2-aminoethylamide (18). The end point is determined potentiometrically or conductometrically. Aromatic nitro compounds have been determined by potentiometric titration under COn with vanadium(I1) sulfate (40, 48). o-Nitrophenol, o- and p-nitrotoluene, and 2,4-dinitrophenol cannot be determined by a direct titration method (40). X polarographic procedure has been developed for the analysis of dinitrosec-butylphenyl acetate, pentachloronitrobenzene, and 1,2,4-trichloro-3,5dinitrobenzene (235). Hydrogen numbers (the weight of substance reacting n i t h one mole of hydrogen) have been determined for a number of nitro cornpounds (76) using the apparatus and procedure previously described (38). A P d / C catalyst was employed. A spectrophotometric analysis of polynitroaromatic compounds is based on the formation of a colored complex between the polynitroaromatic substance and ethylenediamine in dimethylsulfoxide ( 7 4 ) . The spectra are generally stable for 1 hour. Organometallic Compounds. -4 conductometric method was used t o determine triethylaluminum and diethylaluminum iodide in octane solutions by titration with ethers which form electrically conducting complexes. Dibutyl ether, tetrahydrofuran and dioxane were the most suitable titrants (153). The determination of diisobutylisobutoxyaluminum in toluene solutions of triisobutylaluminum is based on the decomposition of the sample with ethyl alcohol and gas-liquid chromatography of the isobutyl alcohol formed (19).
A procedure is described for the separation of mono-, di-, and trialkyltin 82 R
compounds b y thin-layer chromatography, followed by a spectrophotometric determination. Monoalkyltin compounds were determined titrimetrically with EDTA (97). The analysis of butyllithium was accomplished by comparing the integrated triplet in the N M R spectrum of butyllithium in benzene with a peak of mesitylene added to the solution as a standard (231). A satisfactory and convenient S M R method for the estimation of Grignard and alkylmetal solution has been reported (109). Two thermometric procedures were developed for the determination of Grignard reagents. One was the titration of the Grignard compound in toluene by isopropyl alcohol. The other was by direct measurement of the temperature rise obtained in t,reating the Grignard reagent with an excess of isopropyl alcohol (174). An acidimetric double titration method for the determination of Grignard reagent was developed which compensates for the free basicity present in the solution (242). The determination of trace amounts of organic mercury compounds (RHg C1) in aqueous solutions was achieved by extraction into beiizene followed by a gas chromatographic analysis (2 6 7 ) . Dicyclopentadienyltitanium dichloride and cyclopentadienyltitanium trichloride were separated by paper chromatography and determined by a spectrophotometric analysis of the samples eluted from the paper (818). Peroxides. The analysis of mixtures of peroxides was accomplished b y titrating first t h e hydrogen peroxide with cerium(1V) solut'ion, then adding K I to react with the peracids to liberate iodine which was titrated with thiosulfate. Total peroxides were determined by the liberation of iodine from a separate sample (6). The quantitative KMR analysis of mixtures of organic peroxides, hydroperoxides, and alcohols was studied by measuring the 6-proton peaks. The chemical shifts of both the a- and pprotons are presented (249). Organic peroxides and hydroperoxides are determined colorimetrically by using zirconium naphthenate catalyst in a reaction with benzoyl leuco methylene blue in benzene solution (17). An automatic method and apparatus for an intermittent polarographic determination of cuniene hydroperoxide were developed using a diffusion flowmeter and dropping mercury electrode (120). h rapid method for the spwtrophotometric deterniination of traces of peroxides in ethers is described. Tetralkylammonium iodide is added to the ether, and the absorbance of the
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
liberated iodine (as I3-) is measured a t 295, 365, and 400 nm (82, 83). Hydroperoxides are determined by reaction with nitrous acid. -4 photometric method was developed by using bhe Griess reagent. Hydrogen peroxide, peroxy hydrogen esters, diacyl peroxides, dialkyl peroxides, and ketone dihydroxg peroxides do not interfere (30). The photometric determination of peroxy acids in the presence of hydrogen peroxide is based on a selective oxidation of ?n-phenylenediamine by the peroxy acid. The absorbance of t,he red-brown solution is measured a t 360 nm (205). Phenols. T h e end point of t h e potentiometric titration of sniall amounts of phenols and substituted phenols with bromate-bromide solution can be detected with a cathodically polarized platinum electrode (43). The bromate-bromide titration procedure is suitable for the determination of hydroxybenzophenones with an error of =t3% (112). Excess titrant is estimated iodimetrically. Alkylphenols can be determined to within 0.2'% error using iodine chloride (214). Dichloroquinoline hydrogen bromide perbromide has been used in the determination of phenol and phenolic acids (208), The following compounds have been investigated as possible solvents for the analysis of phenols using a kinetic bromina,tion procedure: ethanol (198), ethylene glycol (193), and 1,3-propanediol (194). Resorcinol may be determined by an amperometric titration with sodium ilkrite in the presence of hydrogen bromide using a platinum electrode (186) or by precipitation with lead(I1) acetate (254). I n the latter procedure the unreacted lead acetate is treated with Trilon B and the mixture titrated wit,h zinc chloride using a special Acid Chrome Black indicator. Acetone, acetonitrile, tert-butyl alcohol, dimethylformamide, dimethylsulfoxide, methyl ethyl ketone, isobutyl methyl ketone and pyridine were investigated as possible solvent's for the titrimetric determination of monohydric phenols (50). The titrant was tetramethylammonium hydroxide in a tert-butyl alcohol-ethanol solvent. The effect of water on the potentiometric titration of p-nitrophenol in tetramethylurea has been investigated (48). Beat results were obtained in the absence of excessive amount.: of water . Hydroxy groups in dihydroxyphenylsubstituted alkanes have been estimated by titration with sodium niethoxide using acetone or terf-butyl alcoholdimethylforniamide as solvent ( 3 9 ) . Hydrochloric acid in inethanol has been used in the potentiometric titra-
tion of sodium alkylphenoxides in a 4: 1 benzene-acetone solvent ( 7 ) . A polarographic procedure for the determination of phenol and resorcinol has been described (117). The sample is dissolved in dimethylformamide containing butyl acrylate and tetraethylammonium iodide and the polarogram measured. The concentration is obtained by a comparison with standard polarograms. m-Cresol has been determined with a relative error of ca. 2-301, using a cryoscopic procedure (85). The method involves comparing the freezing point of a urea-m-cresol adduct in mixtures with those obtained from mixtures of known composition. The formation of a complex between titanium(1V) chloride and phenolic hydroxy groups is the basis of their estimation (102). The concentration of the complex is determined spectrophotometrically. 2,6-Xylenol forms a 1 : 1 complex with tetracyanoethylene and can be titrated with a n error of 1-301, with this reagent (206). The end point is determined photometrically. The coupling reaction, using pnitrobenzenediazonium chloride, is the basis of the determination of resorcinol, 2-nitroresorcinol, 4-chlororesorcinol and 4,6-dichlororesorcinol (179). The concentration of the resulting dye is estimated colorimetrically. T h e effect of p H on the analysis of phenolic compounds by ultraviolet spectroscopy has been discussed (178). The ultraviolet spectrophotometric procedure has been applied to the analysis of the following mixtures: phenol in cyclohexanone (170), metol and hydroquinone (73), and 1- and 2-naphtho1 (96). An infrared spectrophotometric procedure has been used to determine cresol in alkylated phenol mixtures ( l i s ) , 1-naphthol in 1-naphthyl carbonate mixtures (213) and two component alkylphenol mixtures (183). A combined infrared and ultraviolet spectrophotometric procedure has been devised for the analysis of sodium alkylphenolate-alkylphenol mixtures (184).
T h e reaction of m-aminophenol with KIOI and dilute produces a pink-violet color which can be used for the colorimetric determination of the m-aminophenol (92). The ortho and para isomers did not interfere if their concentrations were less than 10 and 70'%, respectively. The number of hydroxyl groups in phenolic adehydes, ketones, and carboxylic acids may be calculated from the infrared spectra of their 2,4-dinitrophenyl ethers (250). The ratio of the percentage maximum absorption of the nitro band at 1547-28 cm-1 to that of the carbonyl band at 1760 to
1690 cm-l gives values of 0.98-1.16, 1.30-1.56, and 1.68-1.78 for 1, 2, and 3 hydroxyl groups, respectively. Silicon Compounds. Alkylarylsilanols were determined b y dissolving the sample in anhydrous 1 : 1 Et2"HCOK(Me)* and titrating potentiometrically with a 0.02N solution of EtrNOH in 1: 20 alcohol-benzene (137). A potent'iometric method for the determination of triarylsilanols was extended to the determination of substituted hexaphenyldisiloxanes. The samples were dissolved in pyridine or a mixture of pyridine and isopropyl alcohol and titrated with 0.1N Bu4NOHdissolved in 4 :1 benzene isopropyl alcohol under a nitrogen atmosphere (203). il coulometric determination of impurities containing Si-H bonds in chlorosilanes is based on the reaction of the silicon bonded hydrogen with electrogenerated bromine (664). Hexaorganocyclotrisiloxanes and some other siloxanes can be titrated potent,iometrically as weak acids by Bu4NOH in pyridine using thymolphthalein (13). Sulfides. Sulfides have been determined b y oxidat'ion t o t h e corresponding sulfoxide followed b y titration of t h e resulting sulfoxide with perchloric acid in acetic anhydride (189). The oxidation is accomplished a t room temperature with hydrogen peroxide in acetic acid. Sulfonic Acids. Sulfonic acids or their salts have been determined b y fusion with potassium hydroxide at 380-400 "C under nitrogen or helium, followed b y determination of either t h e resulting sulfite or t h e resulting phenol (207). Measurement of the sulfite gives a measure of total sulfonate with high selectivity since the sulfite can come only from sulfonate. Phenols formed are determined by gas chromatography and this technique is valuable for analyzing mixtures of homologs and isomers. High frequency titration in 1:2 methanol-benzene using potassium methoxide in methanol as the tit'raiit permits the analysis of mixtures of oand p-toluenesulfonic acids and sulfuric acid (65). Sulfoxides. When sulfoxides are pyrolyzed in a nitrogen stream in t h e presence of copper, half of t h e sulfur is converted t o sulfur dioxide while t h e other half is converted to cupric sulfide (244). The amount of sulfur in the sulfoxide may be calculated from analysis of either the sulfur dioxide or the cupric sulfide. Dimethylsulfoxide has been determined by oxidation to the sulfone with excess chloramine-T, followed by measurement of the excess oxidizing agent by addition of potassium iodide and titration with standard thiosulfate solution.
Thiols. p - ( D i m e t h y l a m i n o ) phenylmercuric acetate and p-(diethy1amino)phenylmercuric acetate have been used for t'he titration of thiols (29). Diphenylcarbazone is used as the indicator, but t'he titration can also be done potentiometrically or amperometrically. I n the ac polarographic determination of methanethiol plus ethanethiol, Smethylisothiouronium sulfate is a useful primary standard for obtaining the calibration curve. The solid can be weighed and the solution converted to methaiiethiol with base just prior to the polarography (99). An apparatus for semiautomatic titration of thiols combines a coulometric silver tit,ration of the thiol with potentiometric determination of silver in the titration solution (59). -4 potentiometric titration of thiolactic acid, thioglycolic acid and pentachlorophenol uses a solution of cupric chloride in anhydrous dimethylformamide as the titrant (98). The yellow color formed Lvhen a thiol reacts with o-dinitrobenzene in an alkali carbonate-water-ethanol solution is the basis for a colorimetric determination of thiols in the presence of disulfides (150). Veibel (236) has reviewed the detection, characterization, and quantitative determination of thiols and also of disulfides, sulfides, thioacids, xanthates, sulfonic acids, sulfonamides, isothiocyanates, thioaniides, sulfoxides, and sulfones. Unsaturated Compounds. Several methods have been described for t h e automatic determination of unsaturation. One of these (25) uses electrolytically generated bromine. Others use hydrogen and a palladium catalyst (101) or sodium borohydride and a platinum catalyst, which is generated in situ from the borohydride and H2PtC16 in isopropyl alcohol. X large surfaced carbon is also present, providing a highly active catalyst. This last method is reported to give accurate and rapid results on a micro or ultramicro scale (28). Methanolic mercuric acetate reagent has been applied in an acidimetric tit'ration procedure for determination of T I C comunsaturation in vinyl and alljl' pounds (154). I n another use of this same reagent, radioactive methanol is used and after volatilization of the excess methanol, the residue is oxidized to carbon dioxide. From the radioactivity of the carbon dioxide, the unsaturation in the sample can be calculated (32). The method is sensitive to one micromole of double bond. It should be noted that methods using methanolic mercuric acetate are not suitable for all types of unsaturation. Simple olefins have been determined by a spectrophotometric titration using a solution of bromine in acetic acid as
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5 , APRIL 1970
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the titrant (67’). The method can be modified to provide a rapid procedure for the determination of small amounts of unsaturation. Aromatic amines, phenols, sulfides, disulfides, and thiols interfere. Dienes nliich will undergo the DielsAlder reaction have been determined by titration with tetracyanoethylene in dichloroethane, using Durol as the indicator (11). LITERATURE CITED
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