Volumetric and Gravimetric Analytical Methods for Organic Compounds W a l t e r T. Smifh, J r . , William F. W a g n e r , and John M. Patterson, Department o f Chemistry, University o f Kentucky, Lexington, Ky.
T
discussed in this review have been selected from the literature which has become available to the reviewers from Kovember 1963 through November 1965. HE ANALYTICAL METHODS
DETERMINATION OF ELEMENTS
Carbon and Hydrogen. Relatively few methods for carbon and hydrogen were reported other than micro- and instrumental techniques which are covered in t h e other review articles. The microcombustion method developed by Backeberg and Israelstam ( 7 ) was estended to the semimicro-scale for fourteen aromatic and heterocyclic compounds containing nitrogen, sulfur, bromine, and chlorine (58). Organic carbon in sediment may be determined directly by removing carbonate carbon by treatment with HCl for 24 hours and combusting the filtered and dried residue in a tube to obtain the organic carbon content (31). Halogens. Previously reported methods for halogens using sodium reduction have been modified and extended (51, 111). Details are given for the preparation of a biphenyl-sodium-dimethoxyethane complex reagent for a semimicro method for chlorine and fluorine (91). A patent for the determination of halogens, nitrogen, and sulfur is based on known methods after decomposition of the sample in the presence of active metals a t 300-50' ( $ 3 ) . I n addition to the many reported uses of the Schoeniger oxygen flask method on the inicroscale the method was used by 13ennewitz (14) for the semimicro determination of chlorine, bromine, sulfur, and phosphorus. After ignition, chloride was titrated potentiometrically with AgK'Os, bromide by titiation of bromate iodometrically, sulfur by titration of sulfate with Ba(CIOn)z,and phosphorus by titration of magnesium with EDTA. Standard deviations were 0.17, 0.14, and 0.217, absolute for chlorine, bromine, and phosphorus, respectively, and varied from 0.08 to 0.14% for sulfur. A semimicro titrimetric determination of iodine, bromine, and chlorine is based on the selective oxidation of the halide ions by various oxidants followed by removal of the elemental halogen with oxygen. The oxidants are CuS04 and
Fe2(S04)3 for iodine, K2Crn07for bromine, and Khln04 in H2S04for chlorine. The halide ions are titrated with Hg(x03)~ in the presence of diphenylcarbazone. Fluoride ion is titrated with Th(X0a)b (85). Kozlowski (78-80) has developed semimicro iodogravimetric methods for the determination of chlorine and bromine by quantitative displacement of iodine from AgI or Ag2012in a combustion tube. The liberated iodine is absorbed by silver granules and weighed. XgI \vas unsatisfactory for chlorine owing to the slow conversion of HCl to Clnin the combustion by oxygen. Directions are given for the preparation of .Ag2012 which is much superior for both chlorine and bromine. Oxides of sulfur interfere. Bromine and iodine in aliphatic compounds are determined using the Gabriel synthesis by treatment with potassium phthalimide in .VZ',S-dimethylformamide to release the halide ion which is then titrated by the Volhardmethod (116). A light-weight Wurzschniitt bomb (149) was used by Muenster (103) for the combustion of organic compounds in the determination of halogens, sulfur, phosphorus, and silicon. Solid or liquid samples u p to 500 mg. are ignited, using 160-70 mg. of ethylene glycol as a primer. Conventional methods for the determination of fluorine in highly volatile compounds may be improved by using a polyethylene capsule for transferring the sample to the combustion bomb (136). Hennart (53) has prepared a review of the determination of fluorine in organic compounds with 526 references. Metals. The use of 50% hydrogen peroxide for t h e wet oxidation of organic matter preliminary to t h e determination of metallic elements was investigated. T h e method was found to be especially useful for polymeric materials (130). Nitrogen. Nitrogen was determined in organic compounds after decomposition by metallic potassium in a steel bomb a t 900" t o 1000° C. The cyanide formed was extracted with ethanol and converted to [Si(CX),]-* by treatment with ?;iSO4, the excess of which was titrated complexometrically (23).
A gasoinetric determination of nit,rogen was achieved by pyrolyzing a misture of the compound with Si0 in a stream of carbon dioxide. Only nitrogen is formed, and the analysis may be accomplished in 30 minutes. Over 3000 compounds were analyzed viith an error of ~kO.1-0.27, ( 2 4 ) . The Kjeldahl procedure for heterocyclic nitrogen reportedly gives results equivalent to the Dumas method provided the digestion is carried out for a sufficiently long period of 12 to 24 hours. The period may be reduced by using a combined V20j-Se catalyst (202). Nader and Hoyle de portable unit that may be used for perchloric acid digestions of organic compounds including a semimicro Kjeldah1 digestion. Fumes are removed without the need for a hood (83). h patent has been issued for a n allparatus for the autoniatic Iijeldahl nitrogen determination (129). Oxygen. For the determination of oxygen in organic compounds, the effectiveness of different preparations was measured of HIO3.I?Osand 1206 by the completeness of the oxidation of carbon monoxide. Important factors were the method of preparation and particle size. 1205was more effective (66). Platinized channel black and anthracene black were compared as the catalyst in the direct deterinination of oxygen. +inthraceneblack was superior in both quantitative results and life of catalyst (82). Holt has described a n apparatus for the direct determination of oxygen in organic phosphates, phosphonates, the phosphinates by use of some hot graphite in a graphite pipe furnace ( 5 5 ) . Silicon. Methods for the analysis of silico-organic compounds containing Si-H bonds were reported by Bork and Shvyrkova. One method is based on t h e reaction of the Si-H bond with HgC12 in a nonaqueous medium t o form Hg2Cl2 which may be measured turbidimetrically or gravimetrically. Two other methods are based on the reaction of the Si-H bond with IiMn04 by titration or colorimetry (19).
Sulfur. Sulfur in organic compounds was determined as sulfate by decomposition with KNnO,. The VOL. 38, NO. 5, APRIL 1966
479 R
sulfate was titrated with lead nitrate using dithizone indicator. Chlorine and bromine may also be determined from aliquots of the combustion ( 1 ) . FUNCTIONAL GROUPS
The principles and methods curientlj- employed for the determination of functional groups have been summarized (97). Acid Halides. An aquametric procedure has been reported for t h e determination of easily hydrolyzable acid chlorides ( 3 7 ) . A standardized water solution in pyridine is added to the sample in methanol, and the excess water is titrated with Karl Fischer reagent. Acids. The methods reported for the determination of carboxylic acid are not generally applicable. o-Phthalic acid has been determined by precipitation with mercury(I1) nitrate folloJved by titration of excess mercury(I1) nitrate with potassium ferrocyanide (43) or by weighing the dried mercury(I1) phthalate ( 4 2 ) . Easily oxidized acids and their salts, such as formic, tartaric, citric, and lactic acids can be oxidized quantitatively nith dichromate (68). The escess dichromate is titrated with an iron (11) ammonium sulfate solution. Ascorbic acid can be titrated quantitatively to a starch end point with IC103 (106) in solutions containing u p t o 1.ON HC1 and 0.055 KCN. Cerium(1V) perchlorate can be used to titrate pyruvic acid using a ferroin indicator (122). The reaction is carried out in HC104 solution containing (SH1)2hI004. Carboxyl groups in pectin can be determined gravimetrically by precipitation as the insoluble copper pectinates and pectates (73). Calcium pectate can be titrated chelatometrically a t a pH of 12 to 13 with a 0.01X EDTA solution by using 2-hydroxy-l-(2-hydroxy-4-sulfo-l-naphthylazo)-3-naphthoic acid as indicator (57). Aniline has been recommended as a solvent for the acidimetric titration of carboxyl groups in poly(ethy1eneterephthalate) (32). Active Hydrogen. A modification in t h e Zereaitinoff method is reported to give more accurate and precise results (83). Active hydrogen can be determined with LiAlH4 in the presence of nitroso and nitro groups (91) since the amount of gas corresponding to the active hydrogen can be differentiated from the amount of gas liberated by the nitro or nitroso groups. Ar-Ethylmorpholine or butyl ether is used as the solvent. Alcohols. The methods available for t h e determination of hydroxyl groups in organic compounds have been reviewed (140). 480 R
ANALYTICAL CHEMISTRY
K'ew modifications in the acylation procedure involve alterations in the reaction solvent. One procedure for primary alcohols employs 3-nitrophthalic anhydride in a dimethylformamide solvent (36). The excess anhydride is hydrolyzed and titrated with t e t r ab u t ylammonium hydroxide. Water, primary and secondary anlines interfere. Another acylation procedure uses pyromellitic dianhydride in dimethyl sulfoxide containing pyridine (48). After hydrolysis, the excess anhydride is titrated with XaOH solution. Hydroxyl groups in high molecularweight alcohols have been determined by acetylation with acetic anhydride using a HC10, catalyst (64). Primary and secondary alcohols, glycols, and phenols react rapidIy with p-toluenesulfongl chloride in the presence of pyridine but in many examples the reaction is not quantitative (99). X direct titration procedure for the determination of alcohols involves the use of lithium aluminum dibutylamide in dimethosyethane as titrant (63). The sample is dissolved in tetrahydrofuran and titrated to a S-phenyl-paminoazobenzene end point. hcids, water, and oxygen interfere. Tertiary alcohols which can be dehydrated may be determined with a mean error of +05% ( 7 2 ) . The alkene produced is titrated potentiometrically with bromine. The phenyl isocyanate method for hydroxyl group determination (114) has been modified by the use of toluene diisocyanate as the reagent (108). A ;l;aVO3-H2SO4 solution has been used to study the oxidation of aliphatic monohydric alcohols (109). The excess oxidizing agent was back-titrated with iron(I1) solution. Glycerol forms a copper(I1) complex which may be used in its determination (98). The complex is decomposed by acidification, and the copper(I1) is determined iodometrically. Sorbitol and glycerol can be determined in mixtures by periodic acid oxidation (18). Glycerol is removed by distillation and determined in the distillate. Aldehydes and Ketones. It is reported t h a t the hydroxylamine hydrochloride method of Bryant and Smith (20) may be improved by using a pH meter and a calibration curve relating pH to aldehyde concentration after a standard reaction period (49). Aldehydes can be determined with an accuracy of 99.570 in the presence of acids, acetals, and ketones (96) by using a silver oxide-tert-butylamine complex. After addition of the complex to the sample, the excess Ag ion is titrated with standard KSCN to a ferric alum end point. Anisaldehyde and cinnamaldehyde give low results.
The factors influencing the quantitative production of iodoform from acetophenone have been studied (60). ' 1 large excess of NaOH, a moderate excess of iodine, slow addition of reagents, and half-hour reaction times are recommended. A rapid determination of chloral involves cleavage with KOH followed by a volumetric measurement of the chloroform produced (38). h calibration curve is recommended for the determination of furfural by titration with iodic acid (132) since the aldehyde is incompletely oxidized. The decomposition of trioxane by sulfuric acid, followed by a determination of the formaldehyde produced on treatment with base is the basis of an analysis of triosane (1.46). An alternate procedure for trioxane in aqueous solutions involves a dichromate oxidation followed by an iodometric titration of excess oxidant (144). Although halogenated and nonhalogenated aromatic Schiff bases can be determined by a nonaqueous titration, it has been found (112) that Schiff bases containing the thiocyanate group do not give satisfactory results. These substances may be determined as the 2,4dinitrophenylhydrazones after hydrolysis. The hydroperoxide interference in the determination of carbonyl by 2,4-dinitrophenylhydrazine can be reduced (34) by the use of purified tert-butyl alcohol and by using reaction temperatures of 5' ==! 1' C. Thiosemicarbazones in acetic acid can be titrated with mercury(I1) nitrate solution (74). The indicator, copper 4-phenylthiosemicarbazide, was used in the presence of 5 to 12 drops of a 0.02M CuS04 solution. Amides. The differential reaction rate method has been applied to t h e analysis of mixtures of amides (124). Samples were heated in water-tetrahydrofuran containing S a O H and then subjected to a Kjeldahl-type distillation. Modifications in the saponification method of amide analysis continue to be studied. Amides which are derived from volatile acids can be determined by removing the acid by distillation followed by titration with standard base (6). I n another procedure, the resulting acid is removed from excess alkali by the use of an ion exchange resin and then titrated with standard base (12). A method for the determination of caprolactam, which is simpler and more accurate than other methods, involves reaction of the lactam with acetyl chloride in toluene containing pyridine (113). After the addition of water upon completion of reaction, the reaction mixture is titrated with standard KaOH. Amines. RIodifications in the acylation procedure involve different
acylating agents or nonaqueous solvents. Succinic anhydride offers advantages over other acylating agents in that it is more reactive than phthalic anhydride and less subject to interferences such as aldehydes, ketones, ethers, esters, amides, and water (106). Dimethyl sulfoxide has been recommended as a solvent (48) for the pyromellitic dianhydride method of determining amines. l h e amine nitrogen in aromatic amines is quantitatively converted in (SH&SOd on oxidation with CrOa in H2S04 solution (107). Treatment of the reaction mixture with base generates ammonia which is distilled and titrated in the usual manner. h'itro, nitrobo; and azo groups do not interfere. The reaction of primary and secondary amines with phenyl isothiocyanate permits the direct titration of tertiary amines in mixtures containing the three classes of amines (101). The titrant is anhydrous HCl in methyl isobutyl ketone. The folloning procedure ( 2 ) can be used to determine 2-naphthylamine in the presence of 1-naphthylamine with an error of =1=1.5%. , 7
T o an aliquot of 0.001 to 0.1Ji solutions of ethanolic 2-naphthylamine, add an excess of 0.lJf CdS04 or ZnS04, dilute with water to 200 ml., and agitate Ivithout separating the precipitate. To a 10-ml. aliquot, add Eriochrome Black 'r indicator, 1 t o 2 ml. of S H I O H and water, and titrate with 0.05N EDTA to a blue color. Sodium tetraphenylborate titrations of quaternary ammonium salts differ primarily in the solvent and indicator employed. One method (67) utilizes a borate buffer along with a dichloroethylene solvent and a Rile Blue indicator while another method ( 1 7 ) employs an acetic acid-sodium acetate buffer, a chloroform qolvent, and Neutral Red as indicator. Compounds such as cetyldimethylethylaninioniuni ethyl sulfates have been titrated (137') with sodium lauryl sulfate in chloroform solution to a bromophenol blue end point. Amino Acids. Alanine, valine, leucine, isoleucine, phenylalanine, and methionine can be determined by a variation of the method of Virtanen (139) in which the amino acids are refluxed with ninhydrin and the resulting aldehydes determined iodometrically after absorption in bisulfite solution (119). llodifications included the use of a CO? atmosphere and a n air condenser. Factors influencing the reaction of nitrous acid with amino acids have been investigated (56). The speed of shaking the reaction mixture after addition
of the reagents affected the rate of reaction. Under conditions used for the major number of amino acids, lysine and creatine reacted incompletely while cystine produced excessive quantities of gas. Aziridines. Aziridines can be titrated directly with perchloric acid (61) by dissolving the sample in a suitable solvent, by adding a quaternary bromide reagent, and by using a crystal violet indicator. Azo Groups. A selective procedure for azo group analysis has been developed (75). The sample is oxidized with Cr03-H2S04in a C 0 2 atmosphere a t 150' C. The gases are passed over copper and nitrogen determined by the Dumas method. Excess H2Cr04is back titrated with FeS04. .Li titanous sulfate reduction of azo compounds is the basis of a determination of these compounds (133). The excess titanous sulfate is determined by titration with iron(II1) sulfate solution using a KSCN indicator. Diazodinitrophenol can be determined azotometrically by treatment with a large excess of copper(1) chloride (121). The gas evolved is measured in a buret. Carbon - Methyl Groups. The Kuhn-Roth method (81) has been improved for the determination of methyl groups in steroids by the use of pyridine as a cosolvent (127). Esters. Information about the number of ester groups in a molecule may be determined by observing the change in boiling point after ethanolysis (52). Results are moderately accurate. Esters containing acetyl groups can be determined on a submicro scale by acid hydrolysis and distillation of the acetic acid ( 6 ) . The acetic acid in the distillate is titrated with standard NaOH solution. A specific determination of carbobenzyloxy groups in high-molecularweight peptides containing carbobenzyloxy and benzyloxy groups (143) may be accomplished by cleavage with HBr in a closed system followed by titration of the COz produced. The cinnamoyl group in poly(viny1 cinnamate) has been determined (135) by saponification with a mixture of aqueous NaOH and tetrahydrofuran. The alkyl-group portion of sulfonic acid esters is converted into the alkyl iodide by heating the sample with phenol, KI, and &PO4 (71). The alkyl iodide is distilled and determined by the usual alkoxy group method. A similar procedure has been employed (97) in the determination of alkyl groups in alkylthiophosphoric acid esters. Ethers. Ethers have been determined by direct titration with pyridinium bromide perbromide (141) using HgClz as catalyst. The end point is detected photometrically.
Modifications in the apparatus used for the semimicro determination of methoxyl groups have been described ($0).
Cyanoethoxy groups do not interfere in the methoxy group determination (77) by the Zeisel-Vieboeck method when methyl cyanoethyi ethers are analyzed. .Ilkoxy groups (C,-C4) and osyalkylene groups can be determined by cleavage with boiling H I (29). The oxyalkylene groups produce gases which are determined azotometrically while the alkyl iodides are collected in a freezing trap over silica gel. The alkyl iodides are then separated by gas chromatography and determined iodometrically. The cleavage of 2,4-dichlorophenoxyacetic acid with anhydrous H3P04and KI is the basis of a determination of this compound (146). The 2,4-dichlorophenol is aiinlyzed with 4-aminoantipyrine. Alkoxy groups in alkoxysilanes are quantitatively converted into alkyl acetates by reaction with acetic anhydride in the presence of HC104 (89). The unreacted acetic anhydride is hydrolyzed and the resulting acid titrated with base. X blank is required. Hydrazine Derivatives. Aromatic hydrazines, hydrazones, and hydrazides on heating with a Cr03-H2S04 mixture containing Ag2S04 produce nitrogen (76) which is then determined volumetrically. & i n iodometric procedure has been employed in the determination of 2,2diphenyl-1-picrylhydrazyl and 2,2-dip-tolyl-1-picrylhydrazyl (131). Nitriles. The differential reaction rate method has been applied to the determination of mixtures of nitriles and mixtures of nitriles and amides (124). +Imethod which is limited to compounds capable of undergoing tautomerism has been developed for the determination of the cyano group in cyanoguanidines (60). The cyanoguanidine is dissolved in a mercury(I1) acetate-acetic acid mixture and titrated with HC104. Nitroso Compounds. The titanous sulfate procedure previously described for the determination of azo groups is also applicable t o the analysis of nitroso compounds (133). Organometallic Compounds. The factors affecting the precision of the benzyl chloride titration of alkyllithium compounds have been studied (10). Alcoholates and oxidation products formed during the synthesis of alkyllithium compounds do not interfere. The use of a four-fold excess of benzyl chloride, a reaction time of 5 minutes, and 1 :1 solvent-sample ratio represents optimum reaction conditions. Oxiranes. The direct titration procedure utilizing a quaternary amnioVOL. 38, NO. 5 , APRIL 1966
481 R
nium bromide for the determination of aziridines may also be used for the analysis of oxiranes (61). The addition of HC1O4 generates HBr which interacts with the oxirane. A crystal violet indicator is used. -4similar procedure has been applied to the analysis of glycidic esters and ethers (26). The usual oxirane determinations show only one oxirane grouping in dicyclopentadiene dioxide (59). The use of excess anhydrous HBr in dioxane followed by back titration gives correct results. A direct titration with HBr has been used in the determination of absorbed ethylene and propylene oxides (46). The oxiranes are removed from the absorbing material by distillation in chlorobenzene. Hydrochloric acid saturated with CaClz has been used for the determination of propylene oxide in the presence of tetrahydrofuran (115). Peroxides. A study of the methods for the determination of peroxides by the liberation of iodine recommends optimum solvent systems for peroxides of different reactivity (90). Isopropanol is suggested for easily reduced peroxides, acetic acid-6% water for aralkyl peroxides, and acetic acidHC1 for the most stable peroxides. The iodometric method of Silbert and Swern (126) has been applied to the analysis of dibenzoyl and dilauroyl peroxides (110). Hydroperoxides and dialkyl peroxides can be determined in the presence of compounds which react with iodine by the use of excess triphenylphosphine (28). The peroxides oxidize Ph3P to Ph3P0 in benzene a t 80' C. The excess Ph3P can be determined gravimetrically or photometrically after conversion to (Ph3CH20H)+C1- with HC1 and formaldehyde. Phenols. Pyridinium bromide perbromide can be used to titrate phenols quantitatively if a 1,1,3,3-tetramethylguanidine catalyst is present (141). The end point is determined photometrically. Small quantities of m-cresol may be determined by the following procedure (100). Heat 0.7 to 1.5 grams of sample and 150 ml. of HzS04in a boiling water bath for 30 to 40 minutes, cool, add 9 ml. of HN03. After the evolution of nitrogen oxides is complete, heat on a boiling water bath for 20 minutes, add 10 ml. of HzO and crystallize, Titrate the crystalline product in aqueous alcohol with alkali. The error is 2 to 3%. Phenolic groups in condensation products with formaldehyde have been assayed by an acylation procedure using benzenesulfonyl chloride (134). Sulfonamides. Sulfonamide, sulfanilamide, sulfaguanidine, and so482 R
0
ANALYTICAL CHEMISTRY
dium sulfacetamide can be titrated to within & l % using 1% N-bromosuccinimide as titrant (8). Sulfoxides. Dialkyl, diaryl, or substituted aralkyl sulfoxides on reduction with H I in a hydrogen atmosphere produce iodine which is titrated with Na2S203(54). The mean error was *l%. Sulfides and sulfones do not interfere. Thioureas. Thiourea and alkylthioureas could be titrated quantitatively with iodine monobromide to an amylose end point (126). Arylthioureas were oxidized quantitatively using a bromide-bromiate oxidant ( 4 7 ) . Chloramine T oxidizes thiourea in both neutral iind alkaline media (4). Unsaturation. Unsaturated compounds can be titrated photometrically with pyridinium bromide perbromide in the presence of a HgClz catalyst (141). A new ozonolysis procedure for unsaturation (45) determination involves a division of the ozone stream, one passing into KI solution and the other into sample and then into KI solution. The differences in the iodine concentrations gives the alkene concentration. Amines, which interfere with the Kaufmann iodine-value determination, do not interfere when converted to their hydrochlorides ( I S ) . The mercury(I1) acetate method is reported to give better precision than the iodometric method in the determination of p-nitro-a-methoxystyrene (66).
stearyl sulfate content in a mixture of cetyl and stearyl alcohols can be determined with a precision of *0.7y0 (41) by adding chloroform and sulfuric acid followed by titration with papaverine hydrochloride to a methyl yellow end point . When an acetic acid solution of hydrazine and monomethylhydrazine is treated with salicylaldehyde in the presence of perchloric acid, only the unsubstituted hydrazine reacts with salicylaldehyde. The excess perchloric acid is titrated with standard sodium acetate solution and the perchloric acid consumed is a measure of the monomethylhydrazine present (223). 1,l-Dimethylhydrazine can be determined in the presence of either hydrazine or methylhydrazine by titration with HC104 (quinaldine red indicator) after acetylation with acetic anhydride in acetic acid. Hydrazine and methylhydrazine are acetylated immediately, but 1,l-dimethylhydrazine is acetylated only slowly under these conditions (94). A differential method for the analysis of mixtures of hydrazine apd methylhydrazine makes use of the fact that the reaction of hydrazine and methylhydrazine with chloramine-?' and of hydrazine with hypochlorite involve3 a 4electron change, whereas the reaction of methylhydrazine with hypochlorite involves an 8-electron change (25). For the determination of small amounts of methanol in the presence of aldehydes and ketones the sample is treated with nitrous acid (from sodium MISCELLANEOUS METHODS nitrite and hydrochloric acid). The resulting methyl nitrite is absorbed in a This section does not include comhydrogen iodide solution and the liberpounds that normally are reviewed in ated iodine is titrated with sodium the Review of Applications Analysis appearing in ANALYTICAL CHEMISTRY thiosulfate solution (120). '1 somewhat complex procedure for (z?), such as food, coatings, pesticides, the determination of ethanol in the petroleum, pharmaceuticals, and rubber. presence of methanol, acetaldehyde in Mixtures. An analysis of mixtures the presence of formaldehyde, or acetic of hydrazine, 1,l-dimethylhydrazine acid in the presence of formic acid, is and diethylenetriamine is based on based on the fact that each of the 2the difference in titration behavior of carbon compounds mentioned above is the reaction products obtained when oxidized only to acetic acid by HzCrOl the mixture is treated with salicylwhile each of the 1-carbon compounds is aldehyde in methanol and in acetic oxidized to carbon dioxide (95). acid. I n an acetic acid solvent sysA rapid method for analysis of mixtem, salicylaldehyde gives a neutral tures of methanol-dimethyl phthalate azine with hydrazine, a basic hydrazone or of butanol-dibutyl phthalate is with 1,l-dimethylhydrazine, and a Schiff based on the appearance of turbi :ity base with diethylenetriamine in which when the samples are titrated with all three nitrogens can be titrated as water (70). bases. I n the methanol solvent system, At least 45 binary solutions have been hydrazine gives a neutral azine, 1,l-didetermined recently by phase titration methylhydrazine gives a neutral hywith water (217, 118). The method drazone, and diethylenetriamine gives appears to be particularly useful for a Schiff base in which only the secondthe analysis of binary solutions which ary amino group can be titrated as a base are chemically similar. (93). The compositions of binary solutions *4similar method has been used for of ethyl acetoacetate in ethyl alcohol, the determination of diethylenetriisopropyl alcohol, acetone, and dioxane amine mixed with hydrazine, ethylhyhave also been determined by titration drazine, or 1,I-diethylhydrazine (92). with water (128). The sodium cetyl sulfate-sodium
The turbidimetric tit ration of polystyrene in butanone with isopropyl alcohol ha5 been studied , especially with iegard to its value in determining the molecular n eight of the dissolved polystyrene (138). Xixturea of 2,4,6-trichloro-s-triazine, 2,4-dichloi o-6-alkylainino-s-triazine, and 2-chloro-4,6-bis(alkylaniino)-s-triazine can be analyzed by a method based on the difference in reactivity of the chlorines in each compound. The trichloro compound reacts with inethariol and the liberated hydrogen chloride can be titiated with 0 . 1 s KaOH, using p-ethoxy-a-naphthyl red as indicator. The dichloro compound does not react n i t h methanol but reacts quantitatively \\it11 SaOCH3 in 30 minutes at room temperature. The resulting acidified solution can be titrated with 0.1s .\gsos to give a measure of trichloro and dichloro compounds combined (84). Water. X determination of trace amounts of water uses a n azeotropic diqtillation to collect the water in a n inert solvent, followed by a Karl F i s h e r titration (86). The Karl Fischer reagent has alzo been used for determination of water in condensates of sodium tetraphenylborate and diols (sa),and in terphenyls (11 ) . -4 recent patient describes apparlttus for a continuous Karl Fischer titration (9).
The use of S-ethylpiperidine as a catalyst and the use of an electrode circuit attached to a p H meter and recorder for precise end point determination permits the Karl Fischer method to be used for determining water in the 10 to 60-p.p.m. range (6). d simple determination of water in liquids uses a modified hIcBain sorption balance ( 2 2 ) . The water in water-pyridine solutions has been determined by a phase titration using chloroform as the titrant (117).
h further application of the Karl Fischer reagent involves the determination of water in acetaldehyde (104). The sample is added to a pyridine-propylene glycol mixture, the acetaldehyde removed in a stream of nitrogen, and the water retained in the solvent titrated by the Karl Fischer method. Unclassified. A recent study ($9) indicates t h a t lJ2-dibrornoethane is the preferred halide for general use in the double titration method (40) of analysis of alkyllithium compounds and for phenyllithium. h method for determining alkoxysilanes and aryloxysilanes is based on their conversion to acetoxysilane by treatment with a known excess of acetic anhydride in perchloric acid and ethyl acetate.
The unreacted acetic anhydride is hydrolyzed by the addition of water and pyridine and titrated as acetic acid (27). The method is applicable to monomers or polymers, dependin, on the conditions used. For the deterinination of mercaptosilanes, either perchloric acid-catalyzed acetylation or reaction with mercuric acetate is reported to give satisfactory results for compounds having the general formula (CH3)3Si-S-R, where R is phenyl or primary or secondary alkyl. Apparently steric effects inhibit reaction when R is tert-butyl (15). S-Triniethylbetaines may be separated from certain other bases by precipitation in weakly acidic solutions by either sodium tetraphenylborate or sodium triphenylcyanoborate. The resulting precipitates are then titrated. While sodium tetraphenylborate is sensitive and precipitates the betaines which are present in low concentration, it is not so selective as sodium triphenylcyanoborate. The latter reagent is recommended for isolation of betaines from animal tissue (44). Semicarbazide is determined by adding an excess of 0.1M K3Fe(CS)6to an alkaline solution of the sample and titrating the acidified excess reagent with standard ascorbic acid, using 2oxyvariamine blue as indicator. A blank is required (69). Semicarbazide is oxidized to elemental nitrogen in this method. Two variations on the use of alkaline permanganate for the determination of organic compounds as well as oxidizable inorganic compounds have been reported. I n one of these the hydrous manganese dioxide resulting from oxidation of the sample in an excess of permanganate is separated and reduced by ascorbic acid to manganous ion which be titrated with EDTA, using Eriochrome Black T as indicator. Modifications of the procedure are necessary, depending on the nature of the substance being determined (%). I n the second method the hydrous manganese dioxide is treated with sulfuric acid, a saturated solution of Na4P207, and 0.5-21 MnS04. As shown by the following equation
+
+
+
LInO(OH)z ~HZPZOT-~ 4 H + -+ 2[Mn(H~P~07)31 -3 3Hz0
+
manganese(1V) is converted to manganese(II1). The resulting solution is titrated with 0.lN hydroquinone solution using diphenylamine indicator or potentiometrically (16). The equation for the titration is 2[Mn(HzPz0d~1 -3
+ CeH4(0H)2 + CeH4OZ+
---f
2[Mn(HzP,07)~1-2
2HzPz07-*
+ 2H+
LITERATURE CITED
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