Anal. Chem. 1980, 52, 28R-31 R
Functional Group Analysis Walter T. Smith, Jr." and John M. Patterson Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506
The analytical methods discussed in this review have been selected from the literature which has become available to the reviewers from December 1977 through November 1979. The following topics are not listed under the classifications which follow but are of general interest. A new edition of a book on functional group analysis has been released (80). The use of ion-selective electrodes in organic elemental and functional group analysis has been reviewed (79). The use of polymer-supported functional groups for the selective concentration of organic compounds and for functional group analysis has been discussed recently (45). Photoacoustic spectroscopy offers a possible way to determine materials on thin-layer chromatography plates without solvent extraction and without sample destruction (9). The sections below on amines and aldehydes and ketones should be consulted for new applications of molecular emission cavity analysis (MECA) to functional group analysis. Acids. Water insoluble carboxylic acids can be titrated conveniently in aqueous surfactant solutions using a visual indicator (90). Potentiometric titrations are reported to be very slow in these solutions. A negative ion mass spectrometric method has been developed for the analysis of fatty acids (32). The acids are converted to their p-nitrobenzyl esters thus providing drastic enhancement of carboxylate anion production in the mass spectrometer. T h e conversion of carboxylic acids to their benzylthiuronates followed by alkaline decomposition to benzyl mercaptan via benzylisothiourea is the basis for an analysis of acids (71). The benzyl mercaptan thus formed is titrated iodometrically. The determination of picomole amounts of carboxylic acids has been accomplished by conversion of the acid to its fluorescent ester by treatment with 4-bromomethyl-7-methoxycoumarin in the presence of crown ether catalysts. The ester is purified either by thin-layer chromatography and estimated by fluorimetry (17) or by high performance liquid chromatography usin a fluorimetric detector (50). Reversed-phase hig! performance liquid chromatography has been found a useful procedure for the analysis of Cz-2afatty acids which have been converted to their p-bromophenacyl, p-nitrophenacyl, p-chlorophenacyl, or 2-naphthacyl esters (36). T h e analysis of mixtures of benzoic and phthalic acids is accomplished by measuring their carbon-13 NMR spectra in basic DzO solutions (47). A calibration curve is used. Alcohols. Small amounts of hydroxy- and amino-containing compounds activate the manganese-catalyzed chemiluminescent reaction between Luminol and hydrogen peroxide (65). The extent of the catalytic effect was used to determine alcohols and phenols with a standard deviation of 0.04. Polyhydric alcohols, such as arabitol and mannitol, could be determined with a n error of 0.5-0.670by measuring the extent to which these substances quenched the chemiluminescence of the copper-catalyzed reaction between Luminol and hydrogen peroxide (67). An improved acetylation procedure for the determination of alcohols has been reported (13). Application of the method, which utilizes N-methylimidazole in dimethylformamide, results in much shorter reaction times compared to the pyridine procedure. The formation of appropriate derivatives of alcohols and phenols permits the characterization and determination of these substances in complex mixtures by NMR spectroscopy. In one method, the trimethylsilyl ethers are produced by reaction with hexamethyldisilazane and the 250-MHz proton spectra measured (77), while in another procedure, the hydroxy compounds are converted to the trifluoroacetyl derivatives and the fluorine-19 NMR spectra are used to analyze for hydroxyl content (81). 20 R
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Reference gas chromatographic data have been recorded for the analysis of alcohols and phenols as trimethylsilyl ethers (55). In the catalytic thermometric titration of quinoline and caffeine with HC104 in acetic acid, hydroxy compounds in acetic anhydride are used as indicator reagents. It has been found that the nature of the hydroxy compound affects the shapes of the titration curves obtained and that these differences in shapes can be related to the reactivity of the hydroxy compound and molecular environment of the hydroxy group (26). The success of gas chromatographic analysis depends upon the easy formation of volatile derivatives. Fatty alcohols are conveniently converted to acetates without the formation of by-products by reaction with ketene (20) and 1,2-ethanediol is converted into its cyclic n-butylboronate by reaction with n-butylboronic acid (58). For increased sensitivity through the use of electron capture detection, 4-iodobutaneboronic acid or 2,4-dichlorobenzeneboronic acid are recommended as derivatizing agents for glycols (68). A method for the determination of hydroxyl group content in poly(ethy1ene glycols) has been developed which has about the same precision as the acetylation method but which is about 1000-fold more sensitive (22). The hydroxyl groups are silanized with dimethylaminosilanes and the derivatives determined photometrically. Hydroxyl group content in polymers has been determined by conversion to the phenyl carbamate by reaction with phenyl isocyanate and the derivative concentration measured by high-performance liquid chromatography (8)or by ultraviolet spectroscopy (96). Aldehydes and Ketones. Formaldehyde, acetaldehyde, and acetone have been determined in dilute aqueous solution by means of molecular emission cavity analysis. In the presence of sulfite and phosphoric acid, the Sz emission of the sulfite adducts of carbonyl compounds is delayed and can be distinguished from the emission due to unbound sulfite (2). Amines. Aromatic and aliphatic amines can be determined photometrically with a relative standard deviation of ca. *l.870 after reaction with 5-isothiocyanato-1,3-dioxo-2-ptolyl-2,3-dihydro-1H-benzo[d e ]isoquinoline (37). 1-Pyrenealdehyde and 2-fluorenealdehyde were found to form very stable Schiff bases with primary amines (35). The Schiff bases, which exhibited intense fluorescence in acidic ethanol, were determined spectrofluorometrically. Mixtures of aliphatic amines have been determined by a two-phase titration method (water/octanol) with relative errors of less than 3.4% (28). A variety of mono-, di-, trialkylamines, arylamines, nitrogen heterocycles, and polyfunctional amines were determined by hydrogenolysis at 2OC-280 "C followed by gas chromatographic analysis of the products (62). Amino compounds have been analyzed by measuring the catalytic effect the amine has on the manganese-catalyzed chemiluminescent reaction between Luminol and hydrogen peroxide (65). A fluorine-19 NMR method can be used to determine amines which have been converted to the amide by reaction with trifluoroacetyl chloride (81). Aliphatic primary amines react with o-phthalaldehyde and 2-mercaptoethanol to produce N-substituted 1-(hydroxyethy1thio)isoindoles. The concentration of the amine reactant is determined by measuring the absorption of this substituted indole (7). A study of the salicylaldehyde method for the differentiation of primary and secondary amine mixtures revealed that high results can be expected for primary amines and low results for secondary amines (78). An acetonitrile solvent is recommended. 0 1980 American
Chemical Society
FUNCTIONAL GROUP ANALYSIS Walter 1.Smith, Jr., professor in the Chemistry Department at the University of Kentucky, Lexington, has had industrial experience with Maiiinckrodt Chemical Works and Ethyl Corp. Before joining the Kentucky faculty, he taught at State University of Iowa. His education was obtained at the University of Illinois and Indiana University. He was a Lilly Fellow at Indiana in 1944-46 and a Fels Fund postdoctoral Fellow at Chicago in 1946-47. He is author or co-author of several publications in scientific journals. During 1963-64. he was visiting professor and chairman of the Department of Chemistry at the University of Libya, Tripoli, and in 1965-66 was a Fulbright-Hays visiting professor at the American University of l3eirut, Lebanon.
John M. Patterson, professor in the Department of Chemistry at the University of Kentucky, received a Ph.D. from Northwestern University in 1953, after taking undergraduate work at Virginia MilHary Institute and Wheaton College. His fields of interest include investigations of high-temperature reactions, nitroparaffin chemistry, heterocyclic compounds, and photochemical reactions in solution.
o-Phenylenediamine is converted to volatile derivatives, suitable for analysis by electron-capture gas chromatography, with 4-iodobutaneboronic acid or with 2,4-dichlorubenzeiieboronic acid (68). Pyridine and certain substituted pyridines have been determined as their fluorescent hydroxyl derivatives (95). The hydroxyl derivatives are obtained by the action of hydrogen peroxide, catechol, and ferric perchlorate on pyridines having at least a 2- or 4-position unsubstituted. The method appears useful for 104-104 M aqueous solutions. The fluorimetric determination of secondary amines as their bansyl or dansyl derivatives will give high results in the presence of tertiary amine N-oxides because the dansyl and bansyl chlorides used to prepare the derivatives cause dealkylation and reduction of the tertiary amine N-oxides so that derivatives of the corresponding secondary amine are obtained (93).
Aliphatic amines and amino acids have been determined by conversion to dithiocarbonates by reaction with carbon disulfide, followed by determination of the products by their S2emission in molecular emission cavity analysis (3). Amino Acids. A fluorescence inhibition method, in which the reaction between amines and fluorescamine is competitively inhibited by proline, has been developed for a determination of proline and hydroxyproline (10). The procedure is said to be more sensitive than direct colorimetric methods based on ninhydrin or fluorescamine. Aromatic Hydrocarbons. Current methods (76) and recent developments in methods ( 7 3 ) and techniques (23) for the analysis of polynuclear aromatic hydrocarbons have been reviewed. Other reviews of analytical methods for polynuclear aromatic hydrocarbons which have appeared recently iriclude high pressure liquid chromatographic methods (86) and fluorescence methods as applied to oil spills (21). An extraction procedure coupled with gas chromatographic analysis has been developed for the detection and determination of polynuclear aromatic compounds (27). Another method for the analysis of this class of substances involves the combination of dry-coluinn chromatography, thin-layer chromatography, and fluorescence spectrometry ( 3 4 ) . The method can be used to determine benzo[a]pyrene in shale oil at levels above ca. 1.2 ppni. I t has been observed that in the thin-layer fluorescence method, the fluorescence intensity of various compounds changes during thin-layer separation and in the subsequent analysis (31). The effect of the thin-layer matrix and errors are described.
A low-temperature spectrofluorimetric method has been developed as a routine procedure for the determination of benzo[a]pyrene in aqueous media (57). Azo Compounds. The azo function in a number of azobenzenes was determined by a selective oxidation of the azo group with H2Cr04in sulfuric acid ( 4 3 ) . The nitrogen produced was determined by gas chromatography. Cyanates, Isocyanates, and Isothiocyanates. A recent review discusses the determination of organic cyanates, isocyanates, and isothiocyanates ( 5 ) . Diazonium and Diazo Compounds. The determination of diazo and diazonium groups has been reviewed recently (6). Esters. Esters of nonvolatile alcohols and volatile carboxylic acids, such as cholesteryl acetate and sucrose octaacetate, have been determined by an acid-fusion reaction gas chromatographic procedure (94). The ester is hydrolyzed in molten H3P04and the volatile acid estimated by gas chromatography after collection in a trap-loop. Ethers. Alkoxy groups in either ethers or esters are converted into alkyl iodides on treatment with HI. The alkyl iodides are then estimated by high-performance liquid chromatography (18) or by gas chromatography ( 2 4 ) . Hydrazines. Alkyl- and arylhydrazines and their salts have been determined with an average recovery of 99.4% and a relative standard deviation of f0.4% by a direct titration procedure using a CuS04 titrant (30). A copper ion-selective electrode was used to determine the end point. The H2CrO4oxidative procedure previously developed for azo compounds (43) has been adapted for the determination of hydrazine salts, arylhydrazines, and arylhydrazones (42). Reversed-phase high-pressure liquid chromatography has been used to detect hydrazine and N,N-dimethylhydrazine a t a 2 ,ug/niL level with a relative standard deviation of
