Review of Fundamental Developments in Analysis
AcidlBase Titrations in Nonaqueous Solvents John
A. Riddick
Commercial Solvents Corp., Terre Haute, Ind.
T
HE INTEREST in nonaqueous chemistry is increasing as evidenced by the number of basic and analytical studies reported. During the past two years there has been a considerable advance in the understanding of acids, bases, and solvents. There has been some correlatjon of this information toward a scientific selection of a solvent and titrant for a specific analytical use. An increase in scope of acid-base titration in nonaqueous systems and some improvement in methodology have occurred, but the largest increase has been in specific applications. The most significant analytical advance has been the differentiating titration of acids and bases. Several extensive studies have been reported that contained only one or two bits of novel infordation, or they repeat previously reported findings. Reviews have been numerous. Approximately one third of the published articles are not included in this review because they did not contain any novel information. This review includes published information through August Chemical Abstracts and other readily available journals.
THEORETICAL
Janz and Danyluk (69) studied the ionization processes of hydrogen halides in acetonitrile by conductance measurements and analysis of the solid substrates. Two mechanisms are proposed :
+ HX e CHsCN.HX
(1)
CHaCN.HX e CHaCNH+X-
(2)
CHaCN
CHaCNH +XHX
CHJCNH+
+ X-so~v.
+ X-80~v. (3)
HX-2
solv.
(4)
or from Equations 1 and 2: C H S k N H +X-
172 R
0
+
ANALYTICAL CHEMISTRY
+
The increased polarizability of hydrobromic and hydroiodic acids favors the enhancement of the imino-type interaction over that of hydrochloric acid, which favors the nitrilium type. A novel concept of acid-base reaction in nonsolvating solvents was presented by Looy and Hammett (SO), based on the study of basic nitroaniline-type indicators, B, and sulfuric acid, HA, in nitromethane. Although nitromethane has a dielectric constant of 38, it is nonsolvating to acids. In the absence of a solvent molecule with the necessary properties, the transfer of the proton from the acid to the base may require the drafting of an additional molecule OT molecules of the acid to perform the function fulfilled by the solvent in a water-like system. I n acid concentrations above 0.lM the reaction is B 3HA e BH+. A(HA)?-. I n lower acid concentrations the reaction apparently is B HA G BH+. A-. The picture of the salt in solutions of sulfuric acid concentrations over 0.1M would be in fact:
+
+
H-0
O-HN+HzR
\/ S
H03SOH-0
/\
0-HOSOsH
IzmaiIov (64) presents a theory concerning the effect of solvents on the strength of base-cation acids. Dissociation of bases follows the scheme (B is base, M is solvent), B nM s BM,, which is solvated and then dissomM e BH+,lv, ciates as: BM, (M-H)-Bolv., in which (M-H)- is a diatom ion. I n solvents with low dielectric constants, ionic pairs, BH+.,l,. (M-H)-~OI~. BH+~,IV. (hf-H)-Boly., are formed. The conventional dissociation constant depends on the equilibrium constants of the three reactions above. Considering the free energy involved in the processes, a n equation is derived characterizing the
+
+
+
e CHaC +=NH.X(5)
CH,C+=NH.X-
I
C H ~ = N H ~ +x - , ~ ~ ( 7 )~ .
+
-
+
relation between the strength of the base and the properties of the solvent. A derived equation characterizes the strength change of the base changing from solvent to solvent. The effect of solvents on the strength of cationic acids is not according to the Brgnsted universal scheme, B H + M s MHf B. It should occur with the change of base strength and the ion quantity generated by the medium; an equation is derived. de Ligny and Luykx (32) point out that p H in nonaqueous solutions cannot be interpreted the same way as those in aqueous solutions because there are no standards for the former. Other difficulties are attributed to liquid junction potentials. The electromotive forces of standard solutions in methanol were determined in a cell with hydrogen and silver-silver chloride electrodes. The electrolytes consist of mixtures of standard solutions with varying amounts of alkali chloride. The values were extrapolated to zero concentration. The interpretation was based on the fact that p H is a function of -log m H y * , where mH is the molality of the H + and T~ is the activity coefficient. To obtain p H it is necessary to add log ycl to the limiting value of pwH. The p H determined is equal to -mHy*. The pH values of several acid-alkali halide solutions are given. van der Heijde (147) explains the anomalous behavior of many carboxylic acids and phenols when titrated potentiometrically in inert and weakly basic solvents as due to insufficient shielding of the highly polar molecules by the solvent, resulting in association effects in solution and adsorption onto the electrodes. Bruckenstein and Kolthoff (15) have derived equations to show the effect of water on potentiometric and indicator end points in acid-base titrations in acetic acid. Barrow (9) concluded from a study of the infrared spectra of N,Ndiethylglycine, N ,N-diethyl-,%aminopropionic acid, and N,Ndiethyl-y-aminobutyric acid in carbon tetrachloride, chloroform, and 1-butanol that alpha-amino acids occur as zwitterion dimers in 1-butanol
+
+
and in concentrated chloioform solution; in dilute solution in chloroform and carbon tetrachloride they appear as internally hydrogen-bonded monomer. The beta- and gamma-amino acids showed a chelated monomer in chloroform and 1-butanol, which exhibited a 'tautomeric equilibrium between a hydrogen-bonded complex and a zwitterion species. Mandel (85) explained why the difference in pK of two acids compared in different solvents varies linearly with the inverse of the dielectric constant of the solvent if the acids have the same functional group. The interactional part of the energy of transfer depends primarily on the functional group of the acid. Sims and Peters (128) calculated that with two acids present as end groups in polyamides and similar substances, the ratio between the dissociation constants must exceed 59.7 before they can be distinguished by a differentiating titration. This was verified experimentally. Izmailov and \'all (66) found that mixed iodides and bromides may be differentiated frequently by potentiometric titration with silver nitrate in acetone or acetonitrile. It is postulated that the salts form ion pairs of varying strengths and that the titrations are of the same nature as those of weakstrong acid mixtures with bases.
STRENGTHS
OF ACIDS AND BASES
Forman and Hume (39)demonstrated heats of neutralization to be a good relative measure of the strengths of aromatic amines as well as aliphatic primary and straight-chain secondary amines in acetonitrile. The B-strain hypothesis appears to explain deviations of branched chain secondary and tertiary aliphatic amines An empirical acidity potential scale for 12 solvents has been reported by van der Heijde and Dahmen (149). I t is based on the potential ranges which are covered when strong acids are titrated with strong bases. Generally, the feasibility of a potentiometric titration de. pends primarily upon both the intrinsic strength of the acid or base being titrated and the potential range of the solvent. Pearson and Vogelsong (102) have made a substantial contribution to the effect of the solvent on order of basicity. Equilibrium constants were determined spectrophotometrically for 2,4dinitrcphenol and some primary, secondary, and tertiary amines. Tertiary amines are the strongest bases in chloroform, chlorobenzene, and 1,2-dichloroethane; secondary amines are the strongest in n-heptane, benzene, and pdioxane; primary amines are the strongest in ethyl acetate. Metrade,
I
~.CH,.CH,.CH,.CH,.CH,N N II-
hT=N-
2
in acetic acid shows a rather shallow inflection when titrated with perchlonc acid, and Popov and Holm (107) report that it does not have any strong nucleophylic properties toward the proton or metal ions. Acidity in the water-acetic acid system was studied by Stenby (I%), with perchloric, hydrochloric, hydrobromic, and hydriodic acids and sodium acetate. The acidities of perchloric, hydrobromic, and hydrochloric acids increase slightly as the amount of acetic acid increases 50 to SO%, after which they increase sharply. The acids are all equally strong to about 90% acetic acid, then the strengths begin to be differentiated. The increase in the proton activity in solutions containing only II little water is especially remarkable. The proton activity in aqueous sodium acetate increases rapidly with the addition of acetic acid, then it becomes linear a t higher acetic acid concentrations. Eavin and Canady (10) measured the oxygen-hydrogen stretching frequencies of 21 phenols in to 10-2M carbon disulfide solutions. The values were plotted against the pK. values of the phenols in water and formed two straight lines, one for aliphatics and the steeper-sloped of the two for polar substituents. It was shown by correlation with other data that deviation frorn a single straight line was not due to electrostatic effects but to structural factors. Bayles and Chetwyn (11) studied spectrometrically the equilibrium between mono-, di-, or tributylamine and 2,4dinitrophenol in chlorobenzene. The equilibria were of the form E 4EIA s BHA. 2,4Dinitrophenol is present in the ionized state with excess amine. The following values were calculated: lOV3d log K / b T-*,log K , hFo, AHo,and Go. If - A F o is taken as a measure of the base strength, then EuNHz < BuzNH < Bu3N against 2,4dinitrophenol. The steric factors were not of determining importance. The relative acidities of organic acids in pyridine were correlated with their strengths in water by Streuli and Miron (136). The differential half-neutralization potential (AIINP) has been defined. Most ortho-substituted benzoic acids are weaker in pyridine .than in water. The calculation of the pK. water values of nieta- and para-substitued benzoic and aliphatic monocarboxylic acids from the AHNP values by using the equation] pK. (HzO) = 0.00642 X AHNP 4.15, agrees with literature values. Davis and Hetzer (29) report a new spectrophotometric method, using 1,s diphenylguanidine as reference base and
+
tetrabromophenylphthalein ethyl ester as reference acid, for determining relative strengths of acids similar in strength to benzoic acid. The method is applied t o the determination of the relative strengths of 31 monosubstituted derivatives (including ortho, meta, and para substitution with NHz, I, Br, Cl, F, OH, OCH3, CHI, or NOz), seven disubstituted derivatives, and trimethylbenzoic and benzoic acid. The plots of the determined equilibrium constants against pK in water were linear, giving different slopes for the meta and para series. Tutunzhich et al. (142) found that the basicity of dicarboxylic acids toward sulfuric acid is malonic > o-phthalic > succinic > adipic, ,that benzoic acid is a weaker base than the dicarboxylic ecids, and that phthalic anhydride is a very weak base. The ionization constants of several aliphatic carboxylic acids are reported for 82% dioxane-water mixtures a t several temperatures (26). The strengths of sulfuric and hydrofluoric acids were determined by Hyman and Garber (63) in trifluoroacetic acid. Izmailov and Aleksandrov (65) determined the normal potential, zero potentials, and common activity coefficients of hydrogen chloride from experimental determinations of e.m.f. within a wide concentration range of the Pt(H2):HClAgCl, Ag cell in 1-butanol, 2-methyl-1-propanol, and 2-propanol. The acid ionic energy a t infinite dilution depends on the dielectric constant and the basicity of the solvent. Dahmen (25a) determined the ranges of half-neutralization of strong acids and strong bases in 12 solvents using glass and calomel electrodes. The effect of half-neutralization potential (HNP) of weak acids is relatively slight. The leveling effects in the several solvents are correlated by HNP. H N P does not depend on the dielectric constant for cationic acids, but it does for neutral or anionic acids. Oiwa (97) made extensive studies of the properties of hydrochloric acid in organic solvent-water mixtures. An equation for the acidity coefficient was derived for concentrated electrolytic solutions of nonaqueous solvent-water mixtures taking into account the influence of the ion-solvent interaction. Shkodin, Karkuzaki, and Khimenko (127) determined the effect of various mixtures of formic and acetic acids on perchloric and toluenesulfonic acids. As the concentration of acetic acid increases] the dielectric constant of the mixture and the strength of the acids decrease. Natoli (93) determined the acidities of strong acids in nitromethane. The strengths, as expressed by the half-neutralization point, AEK,of the Ntrityl and/or N-benzyl derivatives of VOL 32, NO. 5, APRIL 1960
0
173 R
13 amino acids were determined in 1,2propanediol, chloroform, and 2-propanol, 4 : 4 : 1 (with 1% water added), by Legrand, Delaroff, and Bolla (79). Some related peptide derivatives were also studied. The value of AE allowed the determination of the position of the tritj-1 or benzyl substituent introduced into alpha- or omega-diamino acids. Roberts, McBee, and Hathaway (110) determined the pK, values in aqueous solutions for CF3CH20H, CF3CH(OH)C H ~ N H Z , CF3CH(OII)CHJ’?(C2HJz, and C2H50H. C F ~ C H Z O Hin butylamine was titrated with sodium 2aminoethylate in 2-aminoethanol and ethylenediamine. Butylamine enhanced the acidity of the fluoro alcohol. hIaher and Yohe (82) found, by potentiometric titration in ethylenediamine with sodium 2-aminoethanol, that 5-phenyltetrazole is a monobasic acid of about the same strength as benzyl alcohol and that 5-acetamidotetrazole is a dibasic acid with the second hydrogen of about the same strength as 1,3,5hydroxydimethylhenzene. Dulova and Kim (33) determined the strengths of formic, acetic, mono-, di-, and trichloroacetic, I-, 2-, and 3-nitrobenzoic, salicylic, 1-, 2-, and 3-nitrophenol, and picric acids and phenol. .They were determined in cyclohexanone except for the last three acids, which were determined in acetone. The phenolic group in salicylic acid is only weakly acidic in butylamine, whereas the phenolic group in the para position is so strongly acidic that it titrates with the carboxyl group (87’). The strengths of some mineral acids were determined in acetic acid ( 1 1 1 ) . Ang (3) describes a spectrophotometric method for the determination of overlapping ionization constants. SOLVENTS A N D TITRANTS
Solvents. I-Iarlow, Bruss, and Wyld (63) studied the influence of solvents on the potentiometric titration of weak acids in a number of solvents. Quaternary ammonium hydroxide can be used as the titrant for acid in inert aprotic solvents using a glass-calomel electrode pair and a vibrating reed electrometer. Sterically hindered and unhindered phenols were successfully titrated by conductometry in a variety of aprotic and amphiprotic solvents. Unhindered phenols exhibit conductance mid-point maxima indicating association of exceptional strength. Formation of an ion pair betm-een the titrant cation and the hydrogen-bonded acid-anion complex is postulated. The inflections obtained for the potentiometric titration of weak acids in such solvents as acetone or phenol are greatly affected by the acidity of the titrant solvent. Tetrabutylammonium hydroxide is more effective in 2-propanol than in methanol, 174 R
ANALYTICAL CHEMISTRY
ethanol, or water. .4n explanation is given. The influence of the solvent on the resolution of acids is illustrated. The manner in which the properties of the solvent can be utilized in the analysis of acid mixtures is discussed. Cliffad, Beachell, and Jack ( 1 9 ) made a thorough and extensive qualitative survey of acids in the hydrogen fluoride solvent system. This is the most complete study the reviewer has been privileged to see in a single publication. It was found that Zn, Fe(III), and Co(II1) were completely basic, whereas Pb(I1) and Sn(I1) showed amphoteric tendencies. The strengths of the fluoroacids found are Sb(V) > .Is(V) = Bi(II1) > P(V) = Sn(IV) = Re(V1) = W(V1) = Mo(V1) = V(V) > I(V) = Te(V1) = Ge(1V) = Ta(V) = S b ( V ) > Se(1V) = Si = Ti(1V) > Sb(II1) = AI = Cr(II1) = Be(I1) > F = CI(II1) = 0 = S(V1) = ?j = C . Burmell and Langford (16) studied the solvent characteristics of tetramethylene sulfone (sulfolane) by cryoscopy and conductance. It has a dielectric constant of 44 and a r-erj’ small autoprotolysis constant. Tetramethylammonium iodide is extensively dissociated, tetraphenylarsonium chloride and phenyltrimethylammonium iodide are apparently completely dissociated, while lithium nitrate is largely undissociated. Jander and Rinkler (68)found molten acetamide to be an ionizing solvent. It dissolves organic and inorganic compounds. Acids and bases can be tir trated in it potentiometrically, conductometrically, and with indicatork. At 94’ C. the dissociation constant of acetamide is 3.2 X lo-“ and the dissociation B+CH3CONH- appears to be confirmed. Equivalent conductance measurements showed complete dissociation of all salts evcrpt the chlorides of zinc, cadmium, and mercury(I1). According to Allen and Geddes ( 2 ) , dimethylformamide is a suitable solvent for phenols and gives a titration curve with an inflection of a t least 75 niv. with tetrabutylammonium hydroxide in benzene and methanol as titrant. Dawson and coworkers (30) studied the conductance behavior of 20 m i valent electrolytes in A’-methylacetamide. The results indicated that 2,4,6trinitrophenol, hydrogen chloride, and all of the salts were completely dissociated a t infinite dilution. I n contrast to the differentiating action of isomeric dimethylforniamidc, A?-methylacetamide is a leveling solvent toward acids and partially substituted ammonium salts. An extensive study of titration of acids in various neutral and basic solvents was made by Mathews and Welch (87’). The solvents studied Ivere benzene and methanol, 3 to 1 : benzene and 2-propanol, 3 to 1; acetone, ethylenediamine, and benzene, 3 to 1; and butyl-
amine. Potassium methylate in benzene and methanol was the titrant. Thymol blue was the indicator used in neutral solvents and o-nitroaniline was the one used in basic solvents. Part of the study included evaluation of combinations of the glass, calomel, platinum, and antimony electrodes. The titration of hydroxybenzoic acids and dihydropiienols in butylamine was studied and several electrode pairs were evaluated. Spandau and Hattwig (131) studied tin(1V) chloride as an ionizing solvent. It was found that antimony(V) and arsenic(II1) chlorides and iodine monochloride are monobasic solvoacids and that phosphorus oxychloride, hydrogen chloride, and ketones are solvobases. Molten antimony(II1) bromide was found to be a good ionizing solvent by Jander and Keis (67). Many inorganic salts, bromine, iodine, sulfur, phoaphorus (white), salts of carboxylic acids, amines, ketones, nitriles, phenols, aldehydes, and nitro compounds n ere dissolved. Vaicum (145) reports a method for determining water in acetic acid based on the photoelectric determination of turbidity R hen acetic acid containing up to 27, water is mixed with toluene. Lapshin and Gus’kova (77‘)investigated the sulfuric-acetic acid system potentiometrically. It is indicated that the following ions exist, CH3COOH2+and HSOd-. Chand, Handard, and La1 (18) confirmed the ionic structure of sulfur monochloride as -ClS==S+-Cl and C1-S I-=Cl-. The effect of adding benzene to formic acid on the strength of mineral acids wae studied potentiometrically by Shkodin, Izmailov, and Dzyuba (124). The potentiometric titrations in formic acid were compared to those in a mixture of formic acid and benzene, 1 to 9. The change of potential from the acid to the alkaline region was greater in the mixed solvent than in formic acid, 190 and 74 mv., respectively. The improvement in titration is attributed to the decrease of the ion product of the medium as the molar fraction of formic acid decreases. CundifT and JIarkunas (23)found that pyridine is a completely satisfactory solvent for acids titrated with tetrabutylammonium hydroxide. The behavior of sulfuric and hydrochloric acids with 4-methyl-2-pentanone, dimethylformamide, acetonitrile, and pyridine was studied, and the first three were found to react with the acids to some extent. With mixtures containing strong and weak acids, a marked effect was noted on the accuracy of analyses when the strong acids reacted with the solvent. Salomaa (116) measured the value of the Hammett and Paul acidity function, H,, for solutions of hydrogen chloride in water, methanol, and binary mixtures thereof. It was found that
the proton-donating power of the solution decreased at first with increasing methanol content, passed through a minimum 11hen the methanol concentration was about 50 mole %, and then increased as pure mdhanol was approached. The acidic properties of the solutions are more pronounced in anhydrous methanol than in water, and the nddition of even small amounts of water to the methanol appreciably lowers the proton availability. Hcnnart and llerlin (55) report that titration of sodium acetate and pyridine nith perchloric acid in propionic acid gave about twice as large a potentionietric break as is obtained in acetic acid. However. this observation is not consistent with previous reports. Shkodin et al. (126) studied the effect of dielectric susceptibility of the solvent on acid strength in acetic and formic acids as mixed solvent. Streuli (135) reports that a linear relation exists between pK, for water and the half-neutralization potential for neutral and anionic bases in acetic anhydride. The relation for the neutral bases is different from that for the ions. Anions are stronger bases in the anhydride than in water in relation to the neutral compounds. Anions which form weak acids in Ivater are leveled in base strength in the anhydride. It is stated (49)that strong bases can be titrated better (perchloric acid in p-dioxane as titrant) in such solvents as chlorobenzene, acetone, and acetonitrile than in acetic acid, and that a differentiating titration of a weak and a strong base can be made in these solvents. Benzene, toluene, or p-dioxane containing 30 to 40% acetic anhydride are suitable solvents for the differentiation titration of caffeine and strong or medium strength bases (117 ) . Pernarowski and Blackburn (105) studied the titration of bases in chlorobenzene n i t h acetous perchloric acid both potentiometrically and with indicators. Glass sleevetype calomel electrodes were used; neutral red, brilliant green, and methyl red indicators can be used but bromophenol blue is the most satisfactory. Formic acid-p-dioxane, 8 to 17, was used (88) as the solvent for s e a k bases for conductometric titrations. A 1 to 1 mixture of nitrobenzene and acetic acid was used as the solvent for the analyses of purine compounds (61).
Flores and Brunner (38) report that titration values for sodium carbonate and strychnine do not change appreciably in the acetic acid system, titrating with 0.1-Vperchloric acid, nhen u p to a 10% excess of water or acetic anhydride is present. Amounts in excess of 10% result in higher values for indicator than for potentiometric titrations. (The hndings for water are a t variance with all other studies made.)
Titrants. Cluett (20) studied tetrabutylammonium iodide titrant as prepared by Markunas a n d Cundiff (1958 review). It was concluded that the titrant was a 50 to 50 mixture of the hydroxide and methylate, probably formed according to:
The probable composition of tetraalkylammoniuni base titrants prepared by other methods is discussed. Sakurai, Yoneda, and Nomura (115) successfully use periodic and p-toluenesulfonic acids as the titrant using various combinations of ethylene glycol, 2propanol, and p-dioxane as the titrant and sample solvent. Perchloric acid in formic acid-p-dioxane, 8 to 17, was used (88) as the titrant in conductometric titration of weak bases. INDICATORS A N D ELECTRODES
Indicators. A novel method is presented (99) for the analysis of organic acids, anhydrides, acyl halides, strong inorganic acids, reactive alkyl halides, and various mixtures thereof using three titrants and thymol blue as a single indicator. Thymol blue is red in the presence of strong acids, yellow with weak organic acids, their chlorides, and their anhydrides and amines and their salts, and blue with strong bases such as sodium methoxide and trimethylbenzylammonium hydroxide. -4study was made to find which indicators function in acetone and which ones can be used for titrating in various other solvents (85). Buffers of acids varying in strength from perchloric acid to phenol were made by titrating to one half neutralization and then adding the indicator. Twenty-three indicator properties are tabulated. Yokoyama and Chatten (155) used methylene bluequinaldine red as the indicator to titrate tetracycline antibiotic and some of its pharmaceutical preparations dissolved in a nitromcthane-formic acidbenzene mixture. Tropoline I and crystal violet n ere used for the differentiating titration of caffeine and strong bases; methyl red, instead of Tropoline I was used for medium strength bases (117). Caffeine, theobromine, and theophyllin were titrated in acetic acid to 609-mw color of malachite green (140). Crystal violet and benzanthrone were used. as indicators in acetyl chloride for titrating tin(1V) and titaniuni(1V) chlorides with bases (129). Apomorphine hydrochloride acts as its own indicator in acetic acid when titrated hot (101). Electrodes. Tutunzhich and Putanov (144) pwpared saturated Hg, Hg2C12/€Ig2+2 and Hg, HgSOllHg2+2 solvents in several solvents and determined their potential a t 22" C.
against a saturated calomel electrode. The following solvents were used: acetic acid, pyridine, 2-picolineJ and 2,4and 2,6-lutidine. The usefulness of the electrodes for potentiometric titrations is illustrated. Schwabe (121) found the potential of the HgJHg2(C2H,0&(s), NaC2H302,HC2H302electrode against the standard hydrogen electrode to be +590.0 mv.; the Hg,Hg*(CzTI30~)?(s)', XaCLH302, CHIOH (99%), E = 4'23.0 & 0.5 mv.; the HglHg2(C2H302(s), 2C3H70H (96%)) LiCZH302, E = 453.0 i 0.5 mv. Kashima ( 7 1 ) reports a direct differential titration method with two glass electrodes (one of which is retardcd) in nonaqueous solvents t o avoid the, fluctuations of liquid junction potentials. The titration results are presented as the first and second derivative curves. The standard molal electrode potential of the silver-silver chloride electrode in ethyl alcohol was determined to be -0.08138 volt by Taniguchi and .Jam (139). The standard potential for this electrode has been determined in 90% ethyl alcohol (98). Aluminum r . 1 ~ ~ trodes were used for the potentionietric titration of aluminum alkyls with isoquinoline or butyl ether in benzene (36). Potentiometric titration curves with sharp voltage peaks were obtained in nonaqueous systems with the glaqssilver electrode pair by Yakubik, Safranski, and llitchell (154) using a proper combination of solvent and titrant. The potentials of the hydrogen and glass electrodes have been studied in the acetic acid-quinoline system (143). Stock and Purdy (133) have devised a simple antimony-antimony electrode titration system for making differential titrations in which a small portion of the original solution may be trapped around the reference electrode during the entire titration. lIcCurdy and Galt (88) studied the conductometric titration of weak bases in the solvent formic acid-p-dioxane, 8 to 17, using perchloric acid as titrant in the same solvent. The same type bases plus their hydrochlorides also can be titrated potentiometrically. A4mides,as a rule, do not titrate. Differentiating titrations can be made if the base strengths differ by as much as 1 ,pKaE+ unit. Rosset and Trhmillon (112) made coulometric titrations of mixtures of perchloric and acetic acids in a n 85% acetone-water mixture. LEWIS ACIDS
Porter and Baughan (108) studied antimony(II1) chloride as a solvent by the cryoscopic method. Anthracene, fluorine, benzophenone, and bibenzyl are normal solutes giving identical depressions in dilute solutions. The intense color of the solutions and the marked deviation from Raoult's law indicate some solvent interaction. StilVOL. 32, NO. 5, APRIL 1960
175 R
bene dimerizes. Potassium and cesium chlorides are completely dissociated only at infinite dilution, whereas trimethylammonium chloride and bromide and triphenylmethyl chloride are strong electrolytes. Acetyl chloride is a polar solvent used for Lewis acid titration with organic bases by Singh, Paul, and Sandhu (199). The color change of the indicators is explained by the existence of ionic species present. The salvo acids, tin(1V) chloride and titanium(1V) chloride, coordinate with the solvent to increase the concentration of the acetylium ion as follo~Ts: SnClr
+ 2CH3COCl s 2CH3CO+
+ SnClc-2
The bases solvate and ionize to increase the concentration of the chloride ion. The complexes of aluminum bromide v i t h nitromethane and three parasubstituted nitrobenzenes were studied by infrared absorption by Gagnaux et al. (48. The complexiny is between one of the oxygen atoms of the nitro group and the aluminum. Susz and Chalandon (1%) studied the compounds formed by acetophenone and benzophenone with zinc chloride, iron(II1) chloride, and boron trifluoride. The donor properties of POCl,, SeOCh, CHsCOCl, SOCL, and VOCL were tested by Sheldon and Tyree (123) and mere found to decrease in the order given against the acceptors TiC14, SnC14, AsC18, SiCll, and CCl,. The acceptor strength decreased in the order given. There was no differentiation between Sic14 and CC14. Farina, Donati, and Ragazzini (36) titrated aluminum alkyls visually, with isoquinoline in benzene, and potentiometrically, using aluminum electrodes. Triethylaluminum can he differentiated in mixtures n ith diethylaluminum chloride. When diethylaluminum hydride is present, the total is first titrated and then differentiated by titration with triethylaluminum butyl ether. Archambault and Rivest (4) studied the donor-acceptor reactions of titanium(1V) chloride with formamide and ,Y,N-dimetliylformanlide in carbon tetrachloride and in dichloromethane. Infrared spectra indicated coordination of the amide oxygen atoms to titanium. Singh, Paul, and Sandhu (129) studied the titration of tin(1T.’) and titsnium(1V) in the polar solvent, acetyl chloride. Crystal violet and bcnzanthrone were used as indicators titrating with quinoline, 0-picoline, and N ,A'-dimethy lanilhe. Tin (IV) chloride is a stronger acid than titanium(1V) chloride and the base strengths found were quinoline, 0-picoline, W,X-dimethylaniline. Satchell (119) found that the acidity of the complex H2SnCld(OOCCH& is as strong as that of sulfuric and acetic acid 176 R
ANALYTICAL CHEMISTRY
mixtures. The ionizations nere obtained from the ultraviolet spectra of five indicators in up to 3M solutions of tin(1V) chloride in acetic acid. Paul and Singh (IOU) attribute the solvolysis of metal and other salts to form pure chlorides to the ionization of benzyl chloride. Neutralization of tin (Iv), zirconium(IV), titanium(IV), and tellurium(1V) as acids and the neutralization of dimethylphenylbenzylammonium chloride, pyridine, and other bases are reported. Brown and Tierney (14) studied the reaction of Lewis acids of boron with sodium hydride and borohydride in diethylene glycol dimethyl ether. Susz and Lachavanne (138) studied by infrared absorption the addition coinpounds of titanium(1V) chloride, benzophenone, and acetophenone. The bond apparently is formed through the carbonyl. Vaillant (146) explained the titration of triethylaluminum with isoquinoline.
hydride is added to another aliquot, the mixture is refluxed, and the secondary and tertiary amines are titrated. A third aliquot is refluxed with acetic anhydride and the tertiary amine is titrated. Gyenes (51) used acetic anhydride in acetic acid to acetylate primary and secondary amines present with tertiary amine hydrochlorides; then mercury (11) acetate was added and the tertiary amine was titrated with perchloric acid. A method for determination of aliphatic primary amino nitrogen compounds was developed by Critchfield and Johnson (21). A measured excess of 2,4pentanedione, a weak acid, reacts with primary amines to form imines. The excess reagent is titrated v, ith sodium methylate in pyridine with phenol or thymolthalein indicator. The scope and limitations are discussed. Wimer (153) contributed additional information on the titration of amides in acetic anhydride. Perchloric acid METHODS exhibits increased acidic behavior in acetic anhydride so that a number of Patchornik and Rogozinski (99) preamides and acetylated and formylated sent an excellent and comprehensive amides can be titrated using a modified paper on the nonaqueous titration of glass-calomel electrode system. The organic acids, anhydrides, acyl halides, structural configuration of certain strong inorganic acids, and reactive amides prevents them from being tialkyl halides in various mixtures. It is trated. not possible to review this work adeC u n d 8 and Rlarkunas (25) report a quately. Three standard base solumethod for the potentiometric differentions: sodium methylate in methanoltiating titration of mixtures of strong benzene, 1 to 4, trimethylhenzylamacids in pyridine with tetrabutylammonium hydroxide in pyridine, and trimonium hydrouide. Binary mixtures butylamine in p-dioxane are used with a of sulfuric, perchloric, nitric. hydrochlosingle indicator, thymol blue. The ric, arylsulfonic, sulfamic, methaneover-all procedure is illustrated by consulfonic, and phosphoric acids and bensidering a hypothetical mixture conzenesulfonyl chloride were reported. taining HC1 RCOCl (RC0)20 Das and hfukherjee (28) potentiRCOOEI RC1. Experimental eviometrically titrate sulfuric acid as a dence is given for two- and three-commono- or dibasic acid in G-H sdvent ponent mixtures to show applicability with sodium hydroxide or a base such and reliability. Three applications are as piperidine. It is possible to differcited. Titration with tributylamine entiate sulfuric acid in mixtures with will determine free strong acids in acid nitric, hydrochloric, perchloric, acetic, chlorides. The acid chloride is monop-toluenesulfonic, phosphoric, and salibasic toward sodium methylate in cylic acids. nonbasic organic solvents such as p Conductometric differentiating titradioxane, but is dibasic when dissolved in tions of acids with tetramethyl- and pyridine and titrated with a tetratetrabutylammonium hydroxides were akylmrnonium hydroxide. Alkyl halreported by van Meurs (150), using ides react with aniline; thus RCl 2CsHsNH2 + CBHSPJH,C~ C ~ H S N R H several sample solvents. Dibasic acids gave a n N-shaped curve. The titration and the anilinium chloride can be curve for a mixture of maleic and adipic titrated with sodium methylate. Caracids showed four distinguishable neuboxylic acid anhydrides are monobasic tralization points. when titrated with sodium methylate Milne (90) developed methods for and dibasic when titrated with tetrathe assay of mono- and dibasic phenoalkylammonium hydroxide in the abthiazine derivatives. The former was sence of alcohols; therefore, mixtures titrated in acetone and hexane-acetone, of carboxylic acid anhydrides and other 2 to 1, and the latter in benzene-nitroacidic components may be analyzed. methane, 2 to 1. A method for the determination of Cundiff and Markunas (24) have deprimary, secondary, and tertiary amines veloped a procedure for the titrimetric was developed by Gal’pern and Bezdetermination of inorganic salts. It inger (49). Total alkalinity is first deis based on a precipitation of the intermined on a n aliquot of a weighed organic cation with sulfuric acid in sample in acetic acid. Phthalic an-
+
+
+
+
+
+
pyridine or acetone, and potentiometric differentiating titration ($66)of the excess sulfuric acid and the liberated acid. Carbonate and hydroxide impurities do not interfere. They may be determined by adding a n exact amount of sulfuric acid. Reaction products of MCO, and MOH do not titrate. Casey and Starke (17) made a n extensive and thorough study of the titration of metal acetates in acetic acid. Many of their observations have already been reported. The novel features are: The calomel electrode can not be used to titrate lead or silver; cobalt and nickel can be titrated with perchloric acid in p-dioxane but not in acetic acid; zinc and silver must be determined by adding an excess of perchloric acid and back-titrating with sodium acetate using a silversilver chloride electrode; the acetates of copper, tin, antimony, bismuth, and uranium behave as though they were undissociated and cannot be titrated. The inflections in the titration curve for aluminum, chromium, and iron are clearly defined and reproducible but indicate a purity of only 11 to 12%. A complex of the type XIa(OH)~(CH&OO)tjCH&OO is postulated. Malmstadt and Vassallo (83) found that carboxylic acids, sulfonamides, imides, mercaptans, phenols, and enols can be titrated rapidly and accurately with a single solvent-titrant combination by automatic derivative potentiometric or spectrophotometric end point detection. Acetone is the sample solvent chosen and the titrant is tributylmethylammonium base in benzene-2-propano1, 4 to 1. A list of indicators for spectrophotometric titration is given to cover acid strengths from perchloric acid to phenol. -4rapid method for determining acetylenic hydrogen was developed by Barnes ( 8 ) . Free acidity of methanolic silver perchlorate is neutralized. The acetylenic hydrogen sample is dissolved in neutral methanol, the silver perchlorate solution is added, and the liberated perchloric acid is titrated to indicator end point R ith tris(hydroxymethy1)aminomethane. Potentiometric titration may be used with a modified indicating electrode. Jlodifications of the method are given when the sample contains acids or bases. Pickard and Iddings (104) determined ketimines by potentiometric or crystal violet indicator titration with perchloric acid in acetic acid. Delatte ( S I ) describes methods for titrating amines, chlorohydrates, sulfates or nitrates of amines, organic and inorganic salts, and heterocyclics. Fritz, Moye, and Richard (40) titrated anilines with a t least two nitro groups or one nitro and one or more chloro groups substituted in the 2,4-
or 2,4- and &positions as acids in pyridine n-ith triethyl-n-butylammonium hydroxide. Diphenylamines with a t least one nitro group in the four position and trinitrotoluene also can be titrated. Titration of some mixtures is possible. Fritz, Yamamura, and Bradford (41) oximated carbonyl compounds in methanol-2-propanol solution and titrated the excess hydroxylamine with perchloric acid in methyl Cellosolve. With martius yellow indicator, the end point is sharp either potentiometrically or visually. Nakamura (92) determined carbonyl compounds by reacting them with 4 nitrophenylhydrazine in p-dioxane and acetic acid below 20" C., and titrating the excess reagent with perchloric acid. Kundu and Das (75)studied the use of mercury(I1) acetate (Pifer and Wollish, 1954 review) in the G-H solvent system. This solvent system extends the usefulness of the reagent because of the wider solubilizing power. Cationic soaps-Le., long-chain quaternary halides--%-ere analyzed, as were binary mixtures of acetates containing mercury(I1) acetate. Hydrochloric acid in mixtures of strong mineral acids is easily determined. hIercaptans react with mercury(I1) acetate and the excess reagent can be titrated with hydrochloric acid in butanol. SPECIFIC METHODS
General.
The determination of salts present in vegetable tan liquors was studied by Xayudamma and Ramaswamy (95). The sample was dissolved in ethylene glycol and butanol, 1 to 1. One milliliter of water can be used to dissolve the sample first. The titrat ion was made potentiometrically with hydrochloric acid in the same solvent. The determination of organic acids and their salts in basic chrome (tanning) liquors was reported by Xayudamma and coworkers (94). The solid, after adding sodium hydroxide, removing chromium, and evaporating to dryness, was dissolved in a G-H solvent and titrated potentiometrically with perchloric acid. Ramaswamy et al. (109) used several nonaqueous titrimetric methods and techniques for the analyses of sulfated oils used in fat liquoring (tanning). The oils contain RCOONa, R(OS03)Na, RS03Ka, Na2S04,and RCOOH. The acidic constituents of coal processing products were determined in several solvents by KAlm&n and Ujhidy (70) by potentiometric titration with potassium methylate. Greenhow and S a i t h (48) studied the significance of the phenolic analysis of coal tar and pitch fractions. Consideration was given to the fact that the phenols would be mono- and polyhydric, having a wide molecular weight
range; hydrogen bonding may be present which would result in a large proportion of the phenolic hydroxyls being relatively inaccessible to chemical reagents. Maher (81) determined the total acidic groups in coal tar by titrating in ethylenediamine with sodium aminoethoxide. Kukin ('74) reports the determination of acids and basic nitrogen in petroleum products. The acids are determined by titrating the sample in benzene-2-propanol with alcoholic sodium hydroxide to the p-naphthobenzein end point. The sample is titrated in benzene-acetic acid with perchloric acid to the methyl violet end poipt for the basic components. Zinc in lubricnting oils was titrated photometrically by Marple and coworkers (86) in benzene-methanol with dithizone a t 610 mp. Other heavy metals can be tletected by a change in the shape of the titration curve. Skrynnikova and coworkers (130) determined the acid number of shale oils in ethyl alcoholbenzene solvent, 1 to 1, using a quinhydrone-and-oxide electrode and titrating with alcoholic potassium hydroxide. The acidic groups in lignin were determined potentiometrically by Enkvist, Alm, and Holm (%) in ethylenediamine or N,A'-dimethylformamide as solvent. Sarson (118) found that T N T , DKT, PETN, and R D X can be titrated as acids in 4-methyl-2-pentanone; nitroglycerin, nitrocellulose, mononitrotoluene, and ammonium nitrate are titratable acids in dimethylformamide. Inorganic nitrates are bases in acetic acid. Means of differentially resolving explosive mixtures are given. Gavriloff (46) determined free amine and soap present in ;l'-(hydroxyethyl) lauramide in an alcohol medium, titrating n-ith hydrochloric acid in alcohol. The acidity of catalyst surfaces was determined by Benesi (13) by suspending the material in benzene and titrating with butylamine using adsorbed Hammett indicators. Atteberry (6) states that it is indicated that decaborane exhibits a tautomeric equilibrium in nitrogenous solvents. It is a weak monoprotic acid, pK. = 3.5, in acetonitrile and can be titrated in this solvent to a lemonyellow or stran. end point. Decaborane is a diprotic acid in dimethylformamide with inflection points at p H of 1.2 and 6.0. Turska and Wolfram (141) report a decided improvement in the method for the determination of the amine end groups in polyamides. The sample is dissolved in 20 ml. of benzyl alcohol a t 135" to 150" C. in an atmosphere of nitrogen and cooled rapidly to 20" C. Then 3 ml. of propanol are added and the sample is titrated either potentiometrically or to the phenolphthalein end point. VOL. 32, NO. 5 , APRIL 1960
177 R
lleyers (89) developed a method for the determination of nonbasic nitrogen impurities in high molecular weight amine products. The amine number is determined in acetic acid. The amine or its salt is precipitated as the oxalate from benzene and is filtered. The nitrile in the filtrate is hydrogenated to the amine and titrated. Examples are given. Hennart and Merlin (59) devised a novel method for determining the amounts of sodium and calcium in disodium calcium(ethylenedinitri1o)tetraacetate. Kubias (73) reports a method for the determination of mixtures of mono-, di-, and triethanolamines. Acetic anhydride was analyzed by K'ovikova and Petrova (96) by hydrolyzing in a known volume of water catalyzed by pyridine or an acid and titrating the excess water by the Karl Fischer method. Das (27) studied the anilineacetic anhydride method for the determination of water in acetic acid. Bellen and Sekowska (12) combined titration in nonaqueous solvents, polarographic, and redox techniques to determine mivtures of succinic, fumaric, and maleic acids. ilmmonium halides were titrated (57) in propionic acid to the IIetanil-yellow end point 'with perchloric acid in the presence of mercury (11) propionate. Chlorides and iodides can be resolved in acetic anhydride (135). Methods for differentiating titration of cyclohexylamine, ' dicyclohexylamine, and aniline in the hydrogenation product of aniline has been devised by Gribova and Levin (@) by combining basic procedures given in previous reviews. (Sufficient detail is given in Chemical .4hstracts, volume 53, page 9904.) Hennart and Merlin (58) showed that benzimidazole and its 2-methyl, 5methyl, 2,5dimethyl, 2-ethy1, and 2ethyl-&methyl derivatives can be titrated in propionic acid with perchloric acid using methyl yellow indicator. konoff (5) titrated porphyrins in nitrobenzene with perchloric acid. Huhn and Jenckel (62) analyzed mixtures of maleic acid and maleic anhydride by first titrating in water and then titrating again with sodium methylate t o the salt of the half ester. Errors ranged from 1 0 . 0 5 to 10.39%. The method was used for styrene-maleic acid-maleic anhydride copolymers. Zaugg and Garven (156) determined diethyl malonate in the presence of substituted malonates in dimethylformamide by titrating to the azo violet end point with potassium methylate. Diethyl monoalkylmalonates in the presence of disubstituted malonic esters are determined by titrating with potassium methylate in ethylenediamine with o-nitroaniline as the indicator. Minczewski and Mlodecka (91) de178 R
0
ANALYTICAL CHEMISTRY
termined guanidine nitrate in a technical product and also its ammonium salt by titrating t n o portions, one with perchloric acid and the other with sodium methylate. Benzotriazoles can be deterfnined in dimethylformamide titrating with potassium methylate in methanol-benzene with azo violet as the indicator (56). Pharmaceuticals. Salts of barbiturates and their dosage forms were passed through a n Amberlite IRC-50 cation exchange resin column by Vincent and Blake (151). The sample was dissolved in dimethylformamide, the solution passed through the column and titrated. Substituted barbituric acids were assayed by several procedures by Goldstein and Dodgen (47). The sample was dissolved in dimethylformamide and titrated with lithium methylate in benzene-methanol or potassium hydroxide in methanol using thymol blue as the indicator. Various methods are given for the determination of 5-ethyl-5-crotylbarbituric acid in mixtures of other medicinals and in dispensing forms without previous separations (60). Gautier, Pellerin, and Pineau (45) dissolved barbiturates in pyridine, added silver nitrate in pyridine and thymol blue indicator, and titrated with ethanolic sodium hydroxide. A blank is required. 4 - Diethylamino - 2,3 - dimethyl - 1phenyl - 5 - pyrazolone (amidopyrine) forms 1 to 1, 1 to 2, and 1 to 3 compounds with perchloric acid. Lang and Tavaszy (76) dissolved the pyrazolone in benzene and acetic acid, 3 to 1, and titrated n ith perchloric acid in acetic acid; results with diphenylamine orange indicate the 1 to 1 salt with results agreeing to 10.2%. The base constituents of ergot alkaloid salts were determined by Gyenes and Szasz (52) in acetic acid by titrating with perchloric acid to the crystal violet end point. The acidic constituents were determined in pyridine by titrating with potassium methoxide to the thymol blue end point. The 3methoxy - 4 - hydroxybenzylidine hydrazide derivative of isonicotinic acid (phthivazide) can be titrated in acetic acid with perchloric acid (113). Isolysergic acid hydrazide in acetic acid containing 15% acetic anhydride can be titrated with perchloric acid to the crystal violet end point (50). Alkaloids of the atropine group were extracted from a n alkaline medium with ethyl ether and titrated with hydrochloric acid in acetic acid (34). A simple procedure is given for the analysis of a mixture of ephedrine hydrochloride and pentamethylenetetrazole (106). Sakurai and Sahashi (114) developed a method for the determination of lidocaine (Zdiethylamino - 2',6' - acetoxylidide) in pharmaceutical preparations. Salvesen
(117) determined caffeine mixed with sodium salicylate, sodium benzoate, or diphenj-lhydramine chloride by differentiation titration in nitromethane and acetic anhydride (25%) or toluene, benzene, or p-dioxane and acetic anhydride (30 to 40%). Two sharp inflections were obtained by potentiometric titration. Mixtures containing the sodium salts were titrated first using tropaeolin indicator, then crystal violet was added and the titration was continued. Methyl red was used as the first indicator for the diphenylhydramine moiety. Titration of ethyl p-aminobenzoste with perchloric acid in acetic acid is recommended (37) as a more accurate and rapid method than iodometric or photocolorimetric assay. A method applicable for the determinat:on of medicaments in such ointment bases as petrolatum, polyethylene glycol, and hydrophylic ointment, USP, was reported by Wang, Starr, and Hoffman (152). The ointment is dissolved in a mixed solvent (chlorobenzene and chloroform 5 to 1))acetic acid is added, and then the mixture is titrated. Tetrabutylammonium hydroxide was used by Leavitt and Autian (78) to analyze barbituric acids dissolved in either benzene and 2-propanol or benzene and chloroform. The titration was made potentiometrically or to the thymol blue end point. Sulfuric acid may be determined in crystalline food acids (citric and malic) dissolved in acetic acid and acetic anhydride, but a distinct inflection is obtained in a mixture of acetic and formic acids (125). MISCELLANEOUS
Stock and Purdy (133) propose the term potentiometric derivative titrimetry instead of differential titrimetry to designate the titrimetric technique first proposed by Cox (see 1956 review). (iidequate and definitive terms are in existence and a change to the proposed does not seem advisable.) Sodium hydrogen diglycolate is proposed as an alkalimetric standard by Keyworth and Hahn (72). It has an equivalent weight of 156.075, is easily prepared, and is inexpensive along n i t h the other properties that recommend i t as a standard. van der Heijde (148) presents tables of systematically coded information enabling the selection of the proper combination of solvent and titrant of a large number of acids and bases; differentiating titrations of mixtures are included. Bacarella et al. (7) showed that previous discrepancies between pK, values obtained potentiometrically and conductometrically for acetic acid in methanol-water mixtures are incorrect. The accuracy was established for p H meas-
urements with the glass electrode to 95% weight methanol. Malmstadt and Vassallo (84) describe an automatic derivative spectrophotometric titration assembly consisting of a Sargent-Malmstadt derivative central unit and a modified titration stand equipped to isolate and detect narrow bands of radiation which makes it possible to titrate automatically using indicators. Haslam and Squirrel1 (54) developed an automatic titrator that records the full-scale titrations. It consists of a constant rate titrant delivery system, a n indicating system for p H or e.m.f., and a recorder. Titrations of acids, bases, halogens, and redox reactions were reported. Pocker (105) found that triphenylmethyl chloride on dissolving in nitromethane develops hydrogen chloride. It is indicated that the free ions are formed and not ion pairs. Sensabaugh, CunditT, and Markunas (122) titrated 2,4-dinitrophenylhydrazones of aldehydes and ketones as acids in pyridine with tetrabutylammonium hydroxide. REVIEWS
Cruse (22) reviewed the concepts and development of p H and the attempts to carry over this concept into nonaqueous systems; the relationship between the dielectric constant of the solvent and the dissociation constants of acid-base indicators and various strength acids in nonaqueous media; the limitation and requirements of electrodes in various solvents; the behavior of the hydrogen electrode in various solvents; the behavior of the glass electrode in organic solvents with reference to acid-base titrations. Gautier (44) presents a review with an interesting slant “Acids and Bases as Seen by the Analyst.” Schwabe (120) discussed electronic p H measurements under extreme conditions in nonaqueous liquids. Akiyama ( I ) gave extensive review of titration in nonaqueous systems. Stock and Purdy (134) reviewed potentiometric electrode systems in nonaqueous titrimetry and included 231 references. LITERATURE CITED
(1) Akiyama, T., Kyoto Yakka Daigaku Gakuhb 5, 1 (1957). (2) Men, J., Geddes, E. T., J. Pharm. and Pharmawl. 9, 990 (1957). (3) Ang, Kok-Peng, J. Phys. C h a . 62, 1109 (1958). (4) Archambault, J., Rivest, R., Can. J . Chem. 36,1461 (1958). (5) Aronoff, S., J. Phys. Chem. 62, 428 (1958). (6) Atteberry, R. W., Zbid., 62, 1458 (1958). (7) Bscarella, A. L., Grunwald, E , Marshall, H. P., Purlee, E. L., Zbid., 62,856 (1958).
(8) Barnes, L., Jr., ASAL. CHEW 31, 405 (1959). (9) Barrow, G. M., J. Am. Chem. SOC.80, 86 (1958). (10) Bavin, P. hI. G., Canady, W. J., Can. J. C h a . 35, 1555 (1957). (11) Bayles, J. W., Chetwyn, A., J. Chem. SOC.1958,2328. (12) Bellen, Z., Sgkowska, P., PrzemysE Chem. 11, 523 (1955). (13) Benesi, H. A., J. Phys. Chem. 61, 970 (1957). (14) Brown, H. C., Tierney, P. A., J. Am. Chem. SOC.80, 1552 (1958). (15) Bruckenstein, S.,Kolthoff, I. M.; Ibid., 79, 5915 (1957). (16) Burwell, R. L., Jr., Langford, C. H., Zbid., 81, 3799 (1959). (17) Casey, A. T., Starke, K., ANAL. CHEM.31, 1060 (1959). (18) Chand, R., Handard, G. S., Lal, K., J . Indian Chem. SOC.35, 28 (1958). (19) Clifford, A. F., Beachell, H. C., Jack, W. M., J. Znorg. & Nuclear Chem. 5, 57 (1957). (20) Cluett, M. L., ANAL. CHEM. 31, 610 (1959). (21) Critchiield, F. E., Johnson, J. B., Zbid., 29, 1174 (1957). (22) Cruse, K., Arch. Tech. Messen. Lfg. 245, 125; Lfg. 247, 169; Lfg. 248, 203; Lfg. 249, 217 (1956). (23) CundiE, R. H., Markunas, P. C., ANAL.CHEM.30, 1447 (1958). (24) Cundiff, R. €I., Markunas, P. C., Anal. Chim. Acta 21, 68 (1959). (25) Cundiff, R. H., Markunas, P. C., Ibid., 20, 506 (1959). ( 2 5 4 Dahmen, E. A. M. F., Chim.anal.40, 378 (1958). (26) Danyluk, S. S., Taniguchi, H., Janz, G. J.,J. Phys. Chem. 61, 1679 1957). (27) Das, M. N., J. Indian &em. SOC. 34,248 (1957). (28) Das, M. N., Mukherjee, D., ANAL. CHEM.31, 233 (1959). (29) Davis, M. M., Hetzer, H. B., J. Research Natl. Bur. Standards 60, 569 f19581. (30) Dan-&, L. R., Wilhoit, E. D., Holmes, R. R., Sears, P. G., J. Am. Chem. SOC.79, 3004 (1957). (31) Delatte, M. F., Zng. chim. (Milan) 39. 43 (19571. (32) ‘de Ligny,’ C. L., Luykx, P. F. M., Rec. trav. chim. 77, 154 (1958). (33) Dulova, V. I., Kim, I. N., Khim. Nauka i Prom. 4,’ 134 (1959). (34) Dzyuba, N. P., Shralber, M. S., Aptechnoe Delo 6, No. 6, 17 (1957). (35) Enkvist, T., Alm, B., Holm, B., Paperija Puu 38, 1,8, 12 (1956). (36) Farina, M., Donati, M., Ragamini, M., Ann. chim. (Rome) 48, 501 (1958). (37) Fernando, M. J. de Sa, Rev. port. farm. 8, 1 (1958). (38) Flores, E. S., Brunner, C., Galenicu Acta IMudrid) 11. 21 11958). (39) Foknan, E. J:, Hume, D. N., J. Phys. Chem. 63, 1949 (1959). (40) Fritz, J. S., Moye, A. J., Richard, M. J., ANAL.CHEM.29. 1685 (1957). (41) Fritz, J. S., Yamamura, S.‘ S., Bradford. E. C.. Zbid..31. 260 (1959). (42) Gagnaux, P.,‘Janjk, D., Su&, B.P., Helv. Chim. Acta 41, 1322 (1958). (43) Gal’pern, G. D., Bezinger,. N. N., Zhur. Anal. Khim. 13,603 (1958). (44)Gautier, J. A., Chim. ei tech: 1954, ’
. - - - - I -
5.
(45) Gautier, J. A., Pellerin, F., Pineau, J., Ann. pharm. franc. 16,625 (1958). (46) Gavriloff, A., Oleagineuz 13, 135 (1958). (47) Goldstein, S. W., Dodgen, D. F., Drzdg Standards 26, 113 (1958). (48) Greenhow, E. J., Smith, J. W., Analyst 84, 457 (1959). (49) Gribova, E. A., Levin, E. S., Zavodskaya Lab. 25,38 (1959).
(50) Gyenes, I., Magyar K h . Folyhat 62.26 (1956). (51) ‘Zbid., 63,’94 (1957). (52) Gyenes, I., Szasz, K., Zbid, 61, 356 (1955). (53) Harlow, G. A., Bruss, D. B., Wyld, G. E. A., ANAL.CHEM.30, 69, 73, 1833, 1836 (1958). (54) Haslam, J., Squirrell, D. C. M., J . Appl. Chenz. (London)9, 65 (1959). (55) Hennart, C., Merlin, E., Chim. anal. 40,20 (1958). (56) Ibid., p. 87, (57) Zbid., p. 161. (58) Zbid., p. 264. (59) Zbid., p. 345. (60) Horsch, W., Pharmuzie 12, 212 (1957). (61) Huang, W., Chu, H., Sun, S., Tu, K., Yao Hsueh Hsueh Pa0 4,217 (1956). (62) Huhn, H., Jenckel, E., Z. anal. Chem. 163, 427 (1958). (63) Hyman, H. H., Garber, R. A., J. Am. Chem. SOC.81, 1847 (1959). (64)Izmanov N. A., Trudy Znsl. Khim., Khar’kov. kosudarst Univ. 10, 5, 49 (1953). (65) IzmaIlov, N. A., Aleksandrov, V. V., Zhur. Fiz. Khim. 31, 2619 (1957). (66) IzmaUov, N. A., Vail, E. I., Ukrazn. Khim. 23, 662 (1957). (67) Jander, G., Weis, J., 2. Elektrochnz. 61, 1275 (1957). (68) Jander, G., Winkler, G., J. Znorg. & Nuclear Chem. 9, 24 (1959). (69) Janz, G. J., Danyluk, S. S., J . Am. C h m . SOC.81, 3846, 3850 (1959). (70) K(Qm&n, L., Ujhidy, A., Nehbzvegyipari Kutatd Zntezel Kozlemenyei 1,129 (1958). (71) Kashima, T., C h a . Pharm. Bull. (Tokyo) 6, 229 (1958). (72) Keyworth, D. A,, Hahn, R. B., ANAL.CHEM.30, 1343 (1958). (73) Kubias, J., Chem. listy 51, 2275 (1957). (74) Kukin, I., ANAL. CHEM.30, 1114 f19.581. ~~..-,. (75) Kundu, K. K., Das, M. E.,Zbid., 31, 1358 (1959). (76) Lang, B., Tavaszy, L., Z. anal. Chem. 158,339 (1957). (77) Lapshin, B. M., Gus’kova, L. V., Trudy Zvanovsk. Khim. Tekhnol. Inst. 5,23 (1956). (78) Leavitt, D. E., Autian, J., Drug Standards 26, 33 (1958). (79) Legrand, M., Delaroff, V., Bolla, P., Rec. trav. chim. 77, 1026 (1958). (80) Looy, H. V., Hammett, L. P., J . Am. C h a . SOC.81,3872 (1959). (81) Maher, T. P., Illinois State Geol. Survey, Circ. 264, 8 pp. (1959). (82) Maher, T. P., Yohe, G. R., J . Org. Chem. 23, 1082 (1958). (83) Malmstadt, H. V., Vassallo, D. .4., ANAL. CHEM.31, 862 (1959). (84) Malmstadt, H. V., Vassallo, D. A., Anal. Chim. Acta 16, 455 (1957). (85) Mandel,. M.,, Znd. chim. belge - 23,. 721 . (i958). (66) Marple, T. L., Matsuyama, G., Burdett, L. W., ANAL. CHEM. 30, 937 (1958). (87) Mathews, D. H., Welch, T. R., J. Appl. Chem. (London)8,701 (1958). (88) McCurdy, W. H., Jr., Galt, J., ANAL. CHEM.30, 940 (1958). (89) Meyers, R. T., Ohio J. Sei. 58, 34 (1958). (90) Milne, J., J. Am. Pharm. Assoc. 48, 117 (1959). (91) Minczewski, J., Mlodecka, J., Chem. anal. 2, 176 (1957). (92) Nakamura, N., BunsI.. Karkuzaki. L. . I.,, KhimenGo, M. T:, J . Gen. Ckem. U.S.S.R. 27, 31 (1957). (127) Shkodin, A. >I.) Karkuzaki, L. I., Khimenko, I f . T., Zhur. Obshchef Khim. 27, 29 (1957). (128) Sims, D., Peters, L., .Vature 180, 805 f1957). (129i Singh: J., Paul, R. C., Sandhu, S . S., J . Chem. SOC.1959, 815. (130) Skrynnikova, G. N . , hlatveeva, S . I., Ivshina, E. K., Trudy Vsesoyuz. Nauch.-Issledovalel. Inst. p o Pererabotke Slanlsev 1958. 227. (131) Spandau,H., Hattwig, H., 2. anorg. u. allgem. Chem. 295, 281 (1958). (132) Stenby, P. S., Ph.D. thesis, Eid-
genossische Technische Hochschule, Ziirich, 1957. (133) Stock, J. T., Purdy, W. C., Chemist Analyst 47, 37 (1958). (134) Stock, J. T., Purdy, W. C., Chem. Raw. 58, 1159 (1958). (135) Streuli, C. A., ANAL. CHEM. 30, 997 (1958).
(136) Streuli, C. A., Miron, R. R., Ibid., 30,997 (1958). (137) Susz, B. P., Chalandon, P., Helu. Chim. Acta. 41, 1332 (1958). (138) Susz, B. P., Lachavanne, -4., Ibid., 41, 634 (1958). (139) Taniguchi, H., Janz, G. J., J. Phys. Chem. 61 , 6% (1957). (140) Tsao, K., Loo, Y., Tang, T., l’ao Hsueh Hsueh Pao 4,281 (1956). (141) Turska, E., Wolfram, L., Zeszyty h’auk. Polztech. Lddi. KO.22. Chem. KO.7, 79 (1958). (142) Tutunzhich, P. S., Liler, M., Kosanovich, B., Glasnik Khem. Drushtva, Beograd 19, KO.9, 549 (1954). (143) Tutunzhich, P. S., Putanov, P., Ibid , 21, 33 (1956). (144) Ibid., p. 257. (145) Vaicum, Lydia, h a l e l e Univ. “C.I. Parhon” Bucurevti, Ser. Stiinf. nat. No. 10, 133 (1956). (146) Vaillant, II., Chim. anal. 39, 431 (1957). (147) van der Heijde, H. B., Bnal. Chim. Acta. 16. 392 (1957) (148) Ibid.; 17,512 (19i7) (149) van der Heiide. H. B., Dahmen, ‘ E.’A. hi. F., I W : , 16, 378 (1957). (150) van Meurs, N., Chem. Weekblad 54, 298 (1958). (151) Vincent, hf. C., Blake, hI. I., J . Am. Pharm. dssoc., Sci. Ed. 48, 359 (1959). (152) Wang, S. &I., Starr, H. W., Hoffman, R. J., Drug Standards 26, 116 (1958). (153) )Vimer< D. C.. ANAL. CHEM. 30, . 77; 453 (1958). ’ (1%) Yakubik, 31. G., Safranski, L. W., . Mitchell, J., Jr., Ibid., 30, 1741 (1958). (155) Yokoyama, F., Chatten, L. G., J . Am. Pharm. Assoc. 47, 548 (1958). (156) Zaugg, H. E., Garven, F. C., Ax.4~. CHEM.30, 1444 (1958).
of Fundamental Developments in Analysis
Amperometric Titrations ti. A.
laitinen
University o f Illinois, Urbana, 111.
S
INCE the
last review (66) (October 1, 1957, to October 1, 1959) the amperometric method has continued its steady rate of development. Emphasis has been placed on automation and scaling down to micro scale titrations. Relatively little work has been devoted t o the investigation of novel electrode systems; the brunt of the load has been carried by the time-honored rotating platinum and dropping mercury electrodes, designated as is customary by r.p.e. and d.m.e., respectively. In t h e present review, applied potentials are referred to the saturated calomel electrode (S.C.E.). According t o the tentative recommendation of the Commission on Electrochemical Data of the Analytical 180 R
0
ANALYTICAL CHEMISTRY
Chemistry Section of the IUPAC (22), the so-called “dead-stop” method is to be called a “bi-amperometric titration,” a term suggested by I. M. Kolthoff. I n this connection, Jlintti (41) proposed the name “diamperometric end point.” The theory of such titrations has been considered by Kao and Hsu (46) and Kies (54). Several reviews of the amperometric method have appeared (55, 86, 102, 109,I l l ) . Michalski (77) has reviewed the principles involved in titrations without the use of external applied e.m.f. APPARATUS AND METHODOLOGY
Several devices for carrying out
automatic amperometric titrations have been described. Juliard (44) titrated small amounts of chloride by means of a syringe buret and a detector for the minimum current in a titration involving a specially pretreated silver cathode and a mercury pool anode. The minimum detector consisted of a recorder with a microswitch set to operate when the recorder has just passed its minimum reading. An apparatus for automatically recording titration curves, in which a Selsyn servolinkage is used to synchronize a syringe buret and the chart drive, has been patented (88). Several automatic coulometric titraton with amperometric end point detection have been described. Cotlove, Tmntham, and Bowman (18) used anodically
