Review of Fundamental Developments in Analysis
Volumetric and Gravimetric Analytical Methods for Organic Compounds W a l t e r 1. Smith, Jr., W i l l i a m F. W a g n e r , a n d John
M.
Pafferson
University o f Kentucky, l e x i n g f o n , Ky.
T
analytical methods discussed in this reyier have been selected from the literature mhich has become available to the reviewers from Kovember 1959 to Sol-ember 1961. HE
DETERMINATION OF ELEMENTS
Carbon and Hydrogen. Research in this area has been confined primarily to the extension, modification, and more critical evaluation of the more recently developed methods reported in preyious rexiem-s. The dftermination of carbon by an oxygen-flask method vas reported by Juvet and Chiu (66). In general, organic compounds containing sulfur, nitrogen, boron, and alkali metals are analyzed rpadily, but halogens interfere. hlacdonald (81) has reviewed the oxygen-flask method, including 62 references. Carbon dioxide from the combustion of organic compounds u-as determined by a titrimetric procedure after absorption in a solution of barium hydroxide. Sources of error were examined and discussed ( E ) . In a semimicromanometric method (127) the water and carbon dioxide from the combustion are collected in dry ice and liquid nitrogen traps, respectively, then separately volatilized into an evacuated mercury manometer. From calibration curves the percentages of carbon and hydrogen are determined from the observed pressures. Analyses of typical samples gave standard deviations of 0.06170 for carbon and 0.0477, for hydrogen. Another manometric procedure for the determination of carbon dioxide follows the combustion of the compound in a sealed tube (18). Carbon-14 in the sample is determined from the radioactivity. wet ignition of organic substances in a closed flask yields carbon dioxide, which is determined manometrically by equalizing the pressure in the volumetric manometer (128). The effectiyeness of mixed preparations of CuO and Crz03, coarse CuO and Ag, a recheck of work using VeEeEa's catalyst (Co304on asbestos), and the decomposition product of iiglCln04 were studied by measuring the temperature a t
n hich methane was completely oxidized (68). The mixed preparation was not more effective than the single component. Klimova et al. (69, YO) described procedures for the simultaneous determination of carbon, hydrogen, halogens, and sulfur by a modification of the procedures of Korshun and Sheveleva (7'2). The sample is burned by passing the vapors over a platinum foil plug; the sulfur oxides are absorbed in a boat containing COO; the halogens are absorbed a t 420" by electrolytic silver in a platinum boat. The simultaneous determination of carbon, hydrogen, and nitrogen was accomplished by a combustion procedure using the Korbl silver permanganate decomposition product as catalyst (74). The water is absorbed in magnesium perchlorate; nitrogen dioxide, in manganese dioxide; carbon dioxide, in Xscarite. Kitrogen with oxygen and added carbon dioxide passes into a tube containing copper powder and copper oxide wire, and the resulting mixture of nitrogen and carbon dioxide passes to the nitrometer. VeEefa (142) found that Cos04 is a superior catalyst for the rapid (1 to 2 minutes) combustion of organic compounds for carbon, hydrogen, and nitrogen determinations in an automatic apparatus. Although it is beyond the scope of this review article, of particular interest is the development during the past two years of gas chromatographic methods for the determination of carbon and hydrogen, reported in several articles (34, 136, 1Q7), and of nitrogen (114). Halogens. The halides in organic compounds may be determined by reaction with dispersed sodium in a benzene solution. After removal of excess sodium by reaction with methanol the solution is acidified with nitric acid and the aqueous layer is titrated potentiometrically (83). Labile halogens may be hydrolyzed by sodium hydroxide in ethylene glycol and titrated by the Volhard method (13). Results are low by 0.2 to o.9YO. A similar method was used in the presence of Raney nickel, which may be omitted for the easily hydrolyzed compounds ( 2 2 ) .
Gases and volatile liquids containing fluorine, chlorine, and iodine were decomposed in isopropyl ether solution by the biphenyl-sodium-dimethoxyethane complex, with subsequent passage of the aqumus extract of the product through a cation-exchange resin and determination of the halide. by the oxycyanide method (27). A semimicromethod (4) for chlorine in highly chlorinated compounds uses the decomposition of the compound by powdered magnesium a t 600°, an adaptation of the macroprocedure by Fedoseev and Ivashora (40). Further studies in the mineralization of organic compounds with magnesium in the determination of iodine have been made. The mineralized material is dissolved in acetic acid, and an aluminum salt is added before filtering off the carbon to bring about a quantitative desorption in order to prevent low results. The iodide is oxidized by bromine to iodine, which is titrated nith sodium thiosulfate (62, 63). Chlorine was determined in highly volatile liquids by vaporization of the sample in a stream of nitrogen and oxidation by MnOZ in a tube a t 450". After combustion the packing and absorbent liquid (8y0 NaOH containing sodium bisulfite) are combined and the excess MnOz is reduced by oxalic acid. The chloride is determined either gravimetrically or volumetrically (119). The mercurimetric determination of halogens in organic compounds after fusion with sodium in a closed bomb was found to be superior to other methods (46-48)
Metals. A semimicromethod for the determination of arsenic was described in which the sample is digested with 28% chloric acid. After the arsenate is reduced to arsenic(II1) by iodide ion, and the iodine formed is removed by adding sodium thiosulfate, the arsenic(II1) is determined iodometrically. Bismuth interferes by forming yellow BiI4- (1.40). Organomanganese compounds were analyzed for manganese by dissolving the samples in nitric acid or aqua regia. After evaporation the residue is treated with hydrogen peroxide and sulfuric acid to reduce the manganese oxides t o manVOL. 34, NO. 5, APRIL 1962
* 333 R
ganous ion; the solution is then partially neutralized with zinc oxide and titrated with permanganate (115). Nitrogen. In a modification of the Kjeldahl digestion, where an internal reducing system is present, the use of sucrose in place of salicylic acid-thiosulfate is recommended, because reduction can be carried out a t much lower temperatures. By adding phosphoric acid with sucrose, pyridine ring compounds can be determined. Pyrazolone, antipyrine, benzotriazole, and nitroaliphatics in which the nitrogen is attached to a secondary or tertiary carbon cannot be determined (15)'
The various catalysts suggested for the Kjeldahl digestion of proteins were critically reviewed by Sietz (129). Selenium and copper sulfate are not generally useful. Low results were obtained in the analysis of residues from soybean and rapeseed oils. The distillation step of the Kjeldahl process may be eliminated by oxidizing the ammonium ion with sodium hypochlorite by a volumetric procedure (2,s). A similar procedure involves the oxidation of the ammonia by hypobromite, the excess of which is determined iodometrically (56, 57). Schulek et al. claim that the partial pressures of ammonia solutions are sufficiently low to permit the ammonia from the Kjeldahl distillation to be collected in freshly distilled cooled water instead of acid, thus permitting the ammonia to be titrated directly by a standard acid solution (123). The use of Co304 catalyst in the combustion of samples for the determination of nitrogen is described (143). Two procedures are reported for the determination of nitrogen in nitrocellulose and nitric acid by titration with ferrous sulfate (96, 97). Phosphorus. Tributyl phosphate is converted into an orthophosphate salt by low temperature alkali fusion. The phosphate is then titrated with standard bismuthyl perchlorate (118). Sulfur. Sulfur in organic compounds, rubber, and fuel may be determined by burning the sample in a quartz tube a t 800" in a stream of oxygen and absorbing the sulfur oxides directly in the combustion tube a t 700" by the silicates of alkali or alkaline earth metals placed in small boats. Nitrogen does not interfere but halogens do, since the hydrogen halides are also absorbed by the silicates (60). The determination of sulfur in organic substances in the absence of nitrogen and halogens was accomplished by burning the sample in a current of oxygen, and passing the products through a tube filled with barium chloride. The hydrogen chloride and sulfur trioxide formed are absorbed in a 3y0 hydrogen
334 R
0
ANALYTICAL CHEMISTRY
peroxide solution and titrated with 0.1N alkali. The analysis requires 15 to 60 minutes and gives an error of A0.2 to 0.3% (41). A method for the determination of sulfur is based on high temperature ignition in oxygen in an induction furnace followed by titration of the sulfur dioxide formed with potassium iodate (77). Wr6nski reported that compounds containing CS, S S , NCS, or SCN groups, when heated with o-hydroxymercuribenzoic acid in the presence of sodium hydroxide, readily split up the total sulfur or its sulfide component which forms complexes with o-hydroxymercuribenzoic acid. The excess reagent is back-titrated with thioglycolic acid, using ammoniacal thiofluorescein indicator (152). FUNCTIONAL GROUPS
Several recent reviews are available in which the methods useful in the determination of organic substances by functional group analysis are surveyed and discussed (79,116,144,145). Acetyl Groups. Acetyl groups may be determined rapidly and accurately in organic compounds (91) by saponifying the substance, suspended or dissolved in CHIOH, with excess KOCH,. The unreacted KOCH, is hydrolyzed to KOH, which is determined by titration to a phenolphthalein end point. Acetyl and sulfonic acid groups in acetylated and sulfonated poly(viny1 alcohol) (111) are determined titrimetrically and gravimetrically, respectively, after hydrolysis with propanolic KOH. Acid Halides. The quantitative reaction of absolute ethanol with a carboxylic acid chloride is the basis for the determination of the acid chloride ($3) in the presence of HCI and carboxylic acid. The saponification of the ester formed consumes a quantity of alkali equivalent to acid chloride in the sample. A modification of the Neitzel method (98) for the determination of aromatic sulfonyl chlorides involves a hydrolysis of the acid chloride in a pyridine-water solvent (6), followed by titration of the freed HCl and arenesulfonic acid with NaOH to a phenolphthalein end point. The short hydrolysis period (15 minutes instead of 3 hours) is the chief advantage of the modification. Sulfonyl, sulfinyl, and sulfenyl chlorides have been determined titrimetrically with NazS in aqueous acetone (1@), forming the sodium sulfinate, sulfenate, and mercaptide, respectively. The end point is detected by the yellow color or by amperometric methods. Alcohols. Alcohol functional group analyses continue to employ acylation procedures. Perchloric acid catalyzes the complete acetylation of primary or second-
ary alcohols in ethyl acetate or pyridine (44). Alcohols soluble in ethyl acetate are acetylated within 5 minutes, while hindered and secondary alcohols in pyridine require longer reaction times. Pyromellitic dianhydride, whose reaction rate with alcohols is comparable to that of acetic anhydride, is said to be a superior reagent (130) for alcohol determinations, since aldehydes and phenols do not interfere. The method provides results which are comparable to those of the acetylation method. The polyhydric alcohols, glycerol, erythritol, and pentaerythritol, have been determined with a standard deviation of 0.3 to 0.5% by oxidation with Ce(SO& in HC104 containing a Ag(1)Mn(I1) catalyst system (50). The reaction required 3 to 5 minutes a t 90" and the end point was indicated by the formation of permanganate ion. A dichromate oxidation can be used for the analysis of dilute aqueous solutions of diethylene glycol or triethylene glycol, if the reaction time and acid concentration are carefully controlled (150). Two procedures, involving a periodic acid oxidation, for the determination of 1,2-glycolsand polyhydroxy compounds have been reported which differ primarily in the manner by which the formaldehyde product is determined. In one (86),the formaldehyde is converted to, and separated as, the bisulfite addition product, followed by decomposition with KCN and iodometric titration of the sulfurous acid. In the other (88), the formaldehyde is measured directly using a H&-KCN-iodometric system. Aldehydes and Ketones. The methods available for the analytical determination of the carbonyl group have been reviewed recently by Budesinsky (19). Aldehydes are oxidized by the mercury(I1) (ethylenedinitri1o)tetraacetic acid complex in alkaline solution (20), liberating an equivalent of (ethylenedinitrilo)tetraacetate. The quantity liberated is determined by titration with a lead(I1) salt using a methyl thymol blue indicator. Both aromatic and aliphatic aldehydes may be determined by their reaction with o-toluidine (107). The water produced in the reaction is titrated directly with Karl Fischer reagent when aromatic aldehydes are estimated or is removed by azeotropic distillation with benzene, followed by titration of the water in the distillate when aliphatic aldehydes are estimated. Two modifications in the analysis of aldehydes by the bisulfite addition reaction method involve isolation and decomposition of the bisulfite addition product followed by an iodometric titration of the sulfurous acid formed. The procedures differ primarily in the reagent used to decompose the bisulfite addition
product. In one (1.24) hydroxylamine is employed, while in the other (126) KCN is used. Errors in the determination of formaldehyde, due to sublimation of the formaldehyde-dimedon precipitate during drying, may be avoided by drying below 100" in a vacuum drying apparatus
A complexometric method for the determination of tertiary amines, quaternary ammonium bases, and their salts (21) is based on a precipitation reaction with a solution of bismuth (ethylenedinitri1o)tetraacetate and KI, followed by titration of the liberated (ethylenedinitrilo)tetraacetic acid with a thorium(132). (IV) salt a t pH 2 to 3 using a methyl A method for the determination of thymol blue indicator. furfural involving its condensation with Another complexometric method has excess cyclopentanone has been debeen applied to the determination of scribed (90). The excess cyclopentapiperazine which is accurate to within none is determined with the diazonium hl% (36). The piperazine is precipisalt of 8-hydroxy-l-naphthylamine-3,6- tated with excess mercury(I1) chloride, disulfonic acid. the excess being estimated with disodium Cyanohydrins have been estimated by (ethylenedinitrilo)tetraacetate. their reaction with nickel(I1) sulfate The methods for the determination of solution (11). The excess nickel sulfate the aromatic amino group, including is titrated with disodium (ethylenediacidimetry, acetylation, diazotization, nitrilo) tetraacetate to the murexide and gasometric analysis, have been discolor change from yellow to red-violet. cussed by Goupil (49). Vicinal dioximes are quantitatively Nicolas and hIansel (102) describe dehydrogenated to the corresponding procedures by which aromatic amines furoxane in nonaqueous media by excess can be determined by diazotization, iodine in the presence of mercuric followed by a volumetric measurement acetate (5). of the nitrogen produced on the dedomposition of the diazonium salt with cuprous chloride and sulfuric acid. Caffeine, antipyrine, and similar organic bases can be titrated directly with R-C---C-R perchloric acid in a propionic acidpropionic anhydride (1 to 1) or a propionic anhydride solvent (35). The errors in the estimation of p-phenylenediamine by its conversion to the The excess iodine is determined by tidichloroimine with excess sodium hypotration with thiosulfate to a starch end chlorite (54)arise from the reaction of point. the dichloroimine with sodium arsenite, Vicinal dioximes, as well as ketoximes, which is added to reduce the excess somay also be determined by an aciddium hypochlorite (108). This can be catalyzed acylation (121). The excess avoided by using sodium thiosulfate inacetic anhydride is hydrolyzed to acetic stead of sodium arsenite. acid, which is titrated with standard Amino Acids. The determination NaOH. of lysine in protein hydrolysates Amides. Simple esters of carbamic depends upon its quantitative deacid, such as ethyl and butyl carbamcarboylation by lysine decarboxylase ate, can be determined by boiling (71). The COz formed is measured the ester with 4 to 5y0 S a O H soluvolumetrically in a Warburg apparatus. tion in the presence of Raney nickel Serine and threonine can be oxidized containing 3 t o 4Y0 aluminum (139). quantitatively with periodate to formThe ammonia, which is produced quanaldehyde and acetaldehyde, respectitatively, is distilled into standard hytively (85). The amino acids are dedrochloric acid. The method cannot be termined by analysis of the aldehydes used for the analysis of N-substituted produced or by back-titration of the excarbamates or other carbonic acid decess periodate. The method is accurate rivatives, since the reaction is incomto within O.;Y0. plete with these compounds. Azo Groups. The reduction of azo Amines. The methods available compounds with copper and sulfuric for the determination of the amine acid is the basis of an analysis of function have been reviewed (93) and these compounds (67). The loss in modifications in these methods necesweight of the copper is equivalent to the sary for their application to the analysis organic nitrogen in the compound. of high molecular weight amines have Diazophenols may be estimated by been described. reduction in acid solution with excess Pyromellitic anhydride is reported to vanadium(I1) sulfate (99). The excess offer definite advantages over acetic vanadium sulfate is titrated with ferric anhydride or phthalic anhydride in the ammonium sulfate in an inert atmosdetermination of amines by the acylaphere. An acid concentration of about tion method (130). The accuracy of the procedure is comparable to the acid 4N is recommended for the reduction. titration method for amine determinaCarbon-Methyl Groups. The detion. termination of carbon-methyl groups
as acetic acid without interference from bcnzoic acid on samples of alkyl benzenes is accomplished by a chromic acid-sulfuric acid oxidation in sealed tubes a t 130'. Monoalkyl benzenes with up to 20-carbon side chains give good agreement with theory. When polyalkyl benzenes are oxidized by this method, ring methyl groups as well as side chain methyl groups give rise to acetic acid (16). Percheron has reviewed various methods for the determination of carbonmethyl groups, including oxidation to acetic acid, and physical methods such as infrared spectra (105). Diazonium Groups. The decomposition of diazonium salts, stabilized salts, and diazotates by their addition to boiling 30% HzS04 containing 0.75% CuzClz produces nitrogen quantitatively (102). The nitrogen evolved is measured volumetrically. Esters. A method (104) accurate to within 2% for the determination of the benzyloxy group in benzyl esters is based on the cleavage of the benzyloxy group with 30% HBr (9) in glacial acetic acid a t 80" to 100'. 0 II
R&OC?H,
+ HBr +
+
C7H7Br RCOOH The benzyl bromide formed is extracted into benzene after the addition of excess sodium hydroxide solution. An aliquot of the benzene solution is reacted with aniline, releasing an equivalent of HBr which is titrated with sodium methoxide. Ethers. Recent developments in alkoxyl determinations (194) and variations of methods now in use for alkoxyl determinations (38) have been reviewed. Variations in the method usually involve modifications in the procedure used for the decomposition of the sample or for the determination of the alkyl iodide produced. In one modification (76), the use of a Zeisel bomb in the decomposition step and the use of acetic acid, red phosphorus, and Decalin in the steam distillation step permit the determination of the higher alkoxyl groups. In another modification (46) the alkyl iodides are determined by the combustion method. Factors which influence the accuracy of the method are discussed. The usual alkoxyl procedure has been extended to the analysis of alkoxyl groups in organosilicon compounds (100). Ethoxy groups in organosilicon compounds and in organoaluminum compounds have been determined by the folloiving procedure ( 2 4 ) . An ampoule containing 0.12 to 0.15 gram of the sample is crushed under a VOL. 34, NO. 5 , APRIL 1962
335 R
mixture of 10 ml. of 5% K2Cr207and 5 nil. of 1 to 1 HzS04. After the mixture has been refluxed for 30 minutes, and cooled, 25 ml. of 10% iodide solution is added to the mixture and the liberated iodine is titrated with 0.1N Sa2S203. Hydrazines. Derivatives of hydrazine-e.g., semicarbazones, benzoylhydrazine, phenylhydrazine, and others-can be titrated directly IT-ith chloramine T using iodine chloridechloroform solutions as indicators (131). -4 complexometric method utilizes mercury(I1) (ethylenedinitrilo)tetraacetnte as oxidizing agent (20). The (ethylenedinitri1o)tetraaceliberated tste is titrated with a lead(I1) salt solution. Nitro Compounds. Another niodification in the Vanderzee-Edge11 method (141) involves the substitution of copper (67) for the tin in the reduction reaction. The loss in weight of the copper is equivalent to the organic nitrogen present. The accuracy and the precision of the method are to about 0.5%. d stabilized titanium(II1) chloride rragent has been found to give satisfactory analysis (precision to 10.3%) of aromatic nitro compounds (80). The addition of amalgamated zinc to the reagent keeps its concentration essentially constant for about 3 weeks. Nitroso Compounds. The methods summarized above for the determination of nitro compounds (67, 80) have been successfully extended to the determination of aromatic nitroso compounds. Oxiranes. Terminal epoxides, particularly styrene oxide, liberate an equivalent of alkali upon reaction n ith alcoholic magnesium sulfate-sodium thiosulfate (135). After the addition of water, the magnesium hydroxide produced in the reaction is titrated with acetic acid. The end point is detected by the use of a screened phenolphthalein-methyl red indicator containing methylene blue. Quinones. The reductive acetylation of quinones using zinc and acetic anhydride or copper and HzS followed by acetic anhydride has been successfully applied to the determination of these compounds (33). Thiols. Thiols (0.3 to 1 mmole) can be determined by a direct titration in neutral aqueous or acetone media nith mercury(I1) perchlorate using a 4,4'-bis(dimethy1amino) thiobenzophenone indicator (48). Sulfur, sulfide, iodide, cyanide, and thiocarbony1 compounds interfere. Solutions must be neutral prior to the addition of the acetone, since mercaptals are formed in the acidic media. A direct titration using a standard copper(I1) salt solution a t pH 4.0to 4.4 may be used for the determination of 336 R
ANALYTICAL CHEMISTRY
thioglycolic acid with an accuracy to 0.3% (117). Thiosulfate, thiocyanate, sulfide, and cyanide ions interfere. The argentometric titration of mercapto acids in ammoniacal solution leads to high results because of the formation of insoluble polysilver salts (26). In the presence of excess ammoniacal silver ion, P-mercaptopropionic acid can be quantitatively precipitated as the disilver salt (AgSRCOOAg). Silver nitrate in pyridine reacts with saturated and unsaturated thiols, releasing an equivalent of pyridinium nitrate (120). Titration of the pyridinium nitrate with standard alkali (phenolphthalein end point) gives the concentration of thiol in the sample. Unsaturation. The use of potassium permanganate in the oxidation of unsaturated organic compounds has been reyiewed and interpreted by Cordier (SO). Iodothiocyanate, IKCS, has been suggested as a reagent for the measurement of an unsaturation index (92). The reagent, however, appears to have limited application, since unsaturated aldehydes, ketones, acids, and halogen compounds interfere. 1 modified methoxymercuration procedure, suitable for compounds containing terminal double bonds or internal double bonds with the cis configuration, has been developed (66). Conjugated unsaturated acids, aldehydes, esters, ketones, and nitriles cannot be determined under the conditions employed and inorganic salts, especially, must be excluded. Conjugated unsaturated acids and esters can be determined rapidly by a bromination procedure, if they are first converted into the corresponding potassium or sodium salt (31). When applied to a determination of the purity of these compounds, the precision of the method is within *0.1%. Bromine chloride has been used to determine unsaturated aldehydes with an accuracy of A0.57, (24). Excess bromine chloride is generated from potassium bromate and hydrochloric acid and after a reaction period of 5 minutes, potassium iodide is added. The iodine liberated is titrated with thiosulfate to the starch end point. Acrylonitrile, in the absence of acrylic acid and its esters, can be determined by its reaction n ith piperidine in the presence of acetic anhydride (138). The product formed is then titrated with methanolic hydrogen chloride to a methyl red-methylene blue end point. The known methods available for the estimation of acetylene compounds have been discussed in a review containing 132 references (94). The three usual methods for the determination of terminal triple bonds (acetylenic hydrogen) have been reviewed and compared (110). None of
the methods are completely general, but the silver nitrate and silver benzoate methods appear to be best. The third method, which utilizes K2Hg14in alkaline media, tends t o give high results. Vinylacetylene is quantitatively precipitated with ammoniacal silver nitrate (146). The excess silver ions are titrated by the Volhard method. MISCELLANEOUS METHODS
Mixtures. Tartaric acid has been determined in the presence of citric acid by oxidation nith periodic acid, followed by determination of the glyoxylic acid which is formed by the periodate oxidation. The glyoxylic acid is determined by convrrsion to the bisulfite addition compound followed by its decomposition and iodometric titration of the sulfurous acid liberated (125). A rather complex procedure using permanganate has been described for the analysis of formic acid, oxalic acid, and acetic acid mixtures (109). In the determination of methanol in ethanol based on permanganate oxidation of the methanol to folmaldehyde followed by its determination with Schiff's reagent, a statistical study s h o w that the variability and the age of the reagent are important fsctors (103). For the analysis of mixtures of mater, ethylene oxide, ethylene glycol, and diethylene glycol, ethylene oxide is determined by the Deckert (32) or Lubatti (78) method, water by the Karl Fischer method, ethylene glycol by oxidation with periodic acid, and the total of ethylene glycol and diethylene glycol is determined by oxidation with dichromate (1). Some&-hat similar procedures hare been used for the determination of Cellosolve and of water, ethanol, and ethylene glycol in Cellosolve (106). Total nitrogen in butadiene-vinylpyridine-acrylonitrile terpolymers is determined by a modified Kjeldahl method, pyridyl groups are titrated by perchloric acid in glacial acetic acid, and acrylic acid units are titrated with sodium methoxide in pyridine (26). For the analysis of mixtures of cyclohexyl nitrite, cyclohexanone, and nitrocyclohexane, cyclohexyl nitrite is determined iodometrically, the cyclohexanone is determined by the hydroxylamine method, and the nitrocyclohexane is determined by reduction with hydrogen iodide followed by titration of the liberated iodine by thiosulfate (96). Since cyclohexyl nitrite interferes with the other determinations, it is removed by converting it to methyl nitrite by refluxing with methanol follon ed by distillation of the methyl nitrite. 1,3-Chlorobromopropane can be determined in the presence of its 1,2- isomer by a procedure based upon the fact that the 1,3- isomer reacts readily with
sodium iodide in acetone under conditions in which no more than 0.35% of the 1,2- isomer reacts (75). Chloramine T may be determined iodometrically in the presence of formaldehyde, if the solution is acidified nith acetic acid before addition of XI (64).
The tertiary amines present in mixtures of amine hydrochlorides have been determined by acetylation in an acetic acid-acetic anhydride solution containing mercuric acetate, followed by perchloric acid titration of the liberated tertiary amine (51). The posqible use of certain acetylating reagents developed by Fritz and Schenk (44) for the determination of phenols, thiols, amines, and mixtures of these substances has been extensively investigated (122). Sugars and Related Substances. Procedures for the determination of fructose and glucose are based on a periodate oxidation followed by an iodometric titration of the aldehydes formcd by the oxidation. The aldehydes react with an excess of sulfite, the excess of sulfite is titrated and destroyed by iodine solution, and then the sulfite addition compound is decomposed by the addition of 20% XaOH and KCN. The resulting sulfite solution is acidified and titrated with 0 . W iodine with a starch indicator. This last titration is a direct measure of the aldehydes formed from the oxidation of the sugar (87, 89). Periodate oxidation has also been used for the determination of end groups in various glycogens (37). Modifications of the Ionescu-RiIatiu (58, 69) method have been utilized for the determination of lactose and other reducible sugars (10, 39). Water. The hydrolysis of excess tert-butyl vanadate in the presence of excess ammonia gives a quantitative yield of (XH4)41'4012 in which one vanadium atom results from each 2 molecules of HzO present. This provides the basis for a quantitative determination of HzO in organic solvents. (KH4)4V& is precipitated, redissolved in 2N HzS04, and titrated with ferrous ion using sodium N-methyldiphenylamine-p-sulfonate as indicator. Special apparatus is required (61). Moisture in xanthates has been determined by measuring the volume of hydrogen evolved when the sample is allowed to react with CaHzin anhydrous dioxane ( 6 5 ) . Water content of acetic acid in the range 0.009 to l.i% has been determined by a direct spectrophotometric titration based on the sulfuric acidcatalyzed hydrolysis of acetic anhydride (17 ) . Several secondary and tertiary amines have been claimed as stabilizers for the Karl Fischer reagent (12).
Unclassified. The method of Hofmann and Hochtlen (53) for the determination of benzene, in which the benzene is precipitated as the complex Ki(CS)? NH3.C6He,has been improved so that the method now gives a precision within 1% instead of the 2 or 3% previously obtained (84). The improvement involves operating a t a p H of 10.5 and drying the precipitate a t 110" for 2 to 3 hours. An aniline-mercuric acetate reagent has been used for the titration of thiosemicarbazide, thiourea, and phenyl-, diphenyl-, and 2-naphthylthiourea (153). The samples to be titrated are dissolved in 0.1N HC1O4 in HzO, CH30H, or CzH60H. The anilinemercuric acetate reagent is prepared by mixing 20 ml. of 10% alcoholic aniline with 125 ml. of mercuric acetate in 0.2n' acetic acid, boiling gently for 90 minutes, pouring into 500 ml. of H 2 0 containing 4 ml. of acetic acid, decanting, and diluting t o 1 liter. This sdution is standardized against pure thiourea. p-Dimethylaminobenzalrhodanine is used as the indicator for the titrations; its color change is from pale yellow to violet. Thiosemicarbazide and its 1-phenyl, 1,4-diphenyl, 1-phenyl-4-o-tolyl, and 1-phenyl-4-o-anisyl derivatives were determined by titration with mercuric nitrate using the copper derivative of thiosemicarbazide as indicator. This indicator is produced in the reaction mixture by adding cupric nitrate to the titrant. In those cases in which precipitates form in the titrated solution, it is necessary to add varying amounts of acetic acid to dissolve the precipitate (73)* Diacetyl is oxidized to acetic acid by alkaline hydrogen peroxide and the resulting acetic acid may be determined by titration of the excess alkali with standard sulfuric acid (161). Propyl gallate is determined by an indirect method in which the gallate is precipitated with bismuth nitrate and the excess of Bi(II1) is determined by titration with the disodium salt of EDTA using Pyrocatechol Violet or Xylenol Orange as indicator (82). Phthalocyanines are oxidized quantitatively to XH3 and phthalimide by vanadate, if conditions are carefully controlled ( I 12). The excess vanadate may be titrated with ferrous ion. -4 determination of thiophene in benzene is based upon the mercuration of the thiophene by 0.1S mercuric perchlorate in CH30Hcontaining perchloric acid (154). The excess mercury is titrated with HSCH2CO2H. A procedure for the determination of diacetylmonoxime is based on the conversion of the monoxime to nickel dimethylglyoxime by hydroxylamine hydrochloride, sodium acetate, and nickel acetate, followed by titration of the
excess nickel with the disodium salt of EDTA (52). The determination of amylsodium, butyllithium, and phenyllithium by an iodination process is claimed to be more accurate than acid titration methods and perhaps more accurate than the usual carbonation method. In this process the organometallic compound is treated with excess iodine in ethyl ether and the unrearted iodine is titrated with aqueous thiosulfate to a starch end point. Coupling is reduced by slow addition of the sample to the iodine solution. KO more than 2 3 % of biphenyl is formed (28). Butyllithium may be detcrinined by oxidation n-ith vanadium pentoxide, follorTed by titration of the reduced vanadium conipounds with standard sulfatoceric acid (29). A rapid method for the determination of the aluminum alkyls depends upon their reducing action with iodine in benzene solution ( 7 ) . Aluminum alkyls (A&) and their halogen derivatives (RAlC1and RAlClZ) form green solutions in oxygen-free toluene containing methyl violet indicator. The color of the methyl violet reverts to violet upon the addition of an organic base. This provides the basis for a method for determining these alkyl aluminum compounds by titration with suitable organic bases such as pyridine to the methyl violet end point just described (113). Compounds of the type S A l O R or RAl(OR)z do not produce the above color change. Various aspects of the analysis of organosilicon compounds have been discussed in a review by Smith (133). Methylchlorosilane, phenylchlorosilane, silicon tetrachloride, and similar compounds react quantitatively with acetone solutions of thiocyanate to give chloride. Silanes may be titrated with thiocyanate using an ether solution of FeC13 as indicator (137). The SiOR groups in various silicon compounds have been determined by a modification of the usual Zeisel alkoxy1 determination (42). The alkyl groups of poly(alkylsi1oxanes) may be determined by mixing a 0.1-gram sample with 2 to 3 grams of powdered KOH in a bulb connected to a glass buret and heating to 250" to 270" until no more gas is evolved. The gas is collected over mercury or saturated aqueous sodium chloride and is estimated as methane or ethane. Alkyl groups are eliminated selectively and aryl groups do not interfere (148). LITERATURE CITED
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Review of Fundamental Developments in Analysis
X-Ray Diffraction, Crystal Structure Analysis, and the- High-speed Computer G. A. Jeffrey and M a r t i n Sax, The Crystallography laboratory, The University of Pittsburgh, Pittsburgh 13, Pa.
T
analysis of the structure of matter by x-ray diffraction is an interdisciplinary technique which has applications in chemistry, biochemistry, biophysics, solid-state physics, geology, ceramics, mineralogy, and metallurgy (56). I n fact, in its emphasis on the basic structure of materials it tends to make the barriers between these sciences appear somewhat superficial. This was well illustrated by the range of topics covered by the 600 papers presented a t the Fifth Congress of the International Union of Crystallography (34), many of which were concerned with the use or results of x-ray diffraction methods. As with most techniques having such a broad application, it often happens that a cross fertilization of concepts occurs between rather distant sciences because of a common interest in the experimental method. As a pure technique, x-ray diffraction analysis requires a good knowledge of elementary physics and, in these days particularly, a sufficient grasp of applied mathematics to be able to harness to one’s requirements the facilities of the high speed computer. Nevertheless the real incentives for the investigation usually come from the scientific area where the results are fully understood and their significance is most appreciated. Hence the aphorism pertaining to crystal structural analysis HE
that only the physicist knows how to do it, but only the chemist knows why. For the more chemically oriented scientist interested in the atomic structure of materials, x-ray diffraction technique has a variety of applications, the more important of which can be classified as follows : Study of order in liquids and noncrystalline or partially crystalline solids Identification of single crystalline phases Quantitative measurement of certain chemical and physical data, such as density, molecular weight, stoichiometry, polymorphism, hydration, or solvation in crystals Determination of crystal structures. The majority of these investigations have as their objective the elucidation of an unknown chemical configuration or the study of the nature of the intraor intermolecular binding forces. Phase transformations can be studied by determining the structures on either side of the transitions and this has been applied mainly to ferroelectrics (81),orderdisorder in alloys (40), and molecular structures involving the onset of orientational or rotational disorder (66). The idea of following a solid-state reaction by observing the structural changes by means of the diffraction pattern of a single crystal is an attractive one, but instances where this might be possible are rare (22, 27, 37, 86).
With varying emphasis, these topics have been periodically reviewed in the previous articles in this series (30, 46-45, 779, together with some provocative remarks on the training of chemical crystallographers. The present review covers the period from 1958 to 1961. As regards the fundamental methods involved, there is not much to add to what has previously been said. The already comprehensive literature on xray diffraction methods has been brought up to date by new books (11,12, dl,56,67, 73, 85,88,85). The characteristic of the development in x-ray diffraction analysis during the period of this review has been an increase in complexity and specialization in the methods of interpretation and an improvement of existing experimental techniques and of the commercially A world-wide available equipment. index of crystallographic supplies was produced in 1959 (83), and another edition is planned for 1963. The increased sensitivity and convenience of the proportional and scintillation counter detectors over photographic film for recording x-ray diffraction spectra have been exploited for powder diffraction methods, but the revolution in single-crystal techniques has developed much more slowly. The most important technical development has been the effect of the high-speed comVOL. 34, NO. 5, APRIL 1962
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