Turgut Gündüz

Titrations in non-aqueous media. Part X. Potentiometric and conductimetric titrations of amino acids with tetrabutylammonium hydroxide in pyridine and acetonitrile solvents

Of the 22 α-amino acids studied, all but three (tyrosine, cystine and cysteine) have been titrated potentiometrically using a standard solution of tetrabutylammonium hydroxide in two solvent systems, 90% pyridine-water and 90% acetonitrile-water. The half-neutralisation potentials and the corresponding pK′a1 and pK′a2 values of the amino acids in these solvent systems have been calculated. Potentiometric titrations of binary mixtures of the two dicarboxylic amino acids, glutamic and aspartic acid, with the other monocarboxylic amino acids have also been carried out. The end-points of the titrations performed in the 90% acetonitrile-water solvent system were found to be much sharper than those of the titrations carried out in the 90% pyridine-water solvent system. All the determinations of amino acids, either in single or in binary mixtures, have been shown to have an error of less than ±2%.The α-amino acids and their binary mixtures with glutamic and aspartic acids have also been titrated conductimetrically in the same two solvent systems. Almost all the titrations gave either no end-points or non-stoicheiometric end-points. It has been shown that the solvent systems used in this work are suitable for potentiometric titrations of amino acids, but are not suitable for the conductimetric titrations.

A New Method for Synthesis of Manganese(III) Acetate Dihydrate

Abstract A new method is reported for the synthesis of manganese(III) acetate dihydrate from manganese(II) acetate tetrahydrate, lead(IV) oxide and acetic acid as solvent. Melting point, mixed melting point with manganese(III) acetate dihydrate obtained by the well–known Christiensen method, elemental analyses, and potentiometric titration with a standard hydroquinone solution in acetic acid showed that the compound obtained by the new method was very pure (99.6%). In addition a solution of the compound in acetic acid was used to titrate potentiometrically some hydrazine derivatives and excellent results were obtained.

Titrations in non-aqueous media. Part II. Basicity order of aliphatic amines in nitrobenzene solvent

The relative basicity order of methyl-, ethyl-, propyl- and butylamines has been determined potentiometrically with perchloric acid in nitrobenzene solvent and found to be R3N > R2NH > RNH2 > NH3, where R = Et, n-Pr or n-Bu. However, for the methylamines, the order is Me2NH Me3N > MeNH2 > NH3. The orders in primary, secondary and tertiary amines are EtNH2 > MeNH2 > n-PrNH2 > n-BuNH2 > NH3; Et2NH > Me2NH > n-Pr2NH > n-Bu2NH > NH3; and Et3N > n-Pr3N n-Bu3N > Me3N > NH3. These results show that, in general, an increase in the number of alkyl groups increases the basicity of the amine, and that an increase in the size of the alkyl group decreases the basicity. n-Butylamine is a stronger base than branched-chain primary butylamines.

Titrations in non-aqueous media. Part I. Determination of factors influencing the basicity of schiff bases in nitrobenzene solvent

Potentiometric titrations of Schiff bases with perchloric acid in nitrobenzene solvent were carried out in order to obtain information about the factors that influence the basicities of the Schiff bases. The Schiff bases were synthesised from aromatic aldehydes and amines bearing an aromatic ring. Some contained a methylene group between the aromatic ring and the imino group and others contained a hydroxy group ortho to the imino group. For each Schiff base, an S-shaped potentiometric titration curve was obtained. From these curves half-neutralisation potentials were determined and from the latter the pKa′ values. In these determinations the half-neutralisation potential of 0.001 M hexa(p-toluidino)cyclotriphosphazatriene [N3P3(NH-p-tol)6] in nitrobenzene with perchloric acid was taken as the standard.

Titrations in non-aqueous media. Part IV. Solvent effects on basicity of aliphatic amines

The relative basicity orders of methyl-, ethyl-, propyl- and butylamines have been measured potentiometrically with perchloric acid in cyclohexane and hexane solvents. The basicity orders of the amines in the series, including ammonia, were found to be NH3 > MeNH2 > Me2NH > Me3N; NH3 > EtNH2 > Et2NH > Et3N; NH3 > n-PrNH2 > n-Pr2NH > n-Pr3N; NH3 > n-BuNH2 > n-Bu2NH > n-Bu3N; and n-BuNH2 > i-BuNH2 > sec-BuNH2 > t-BuNH2. In addition to these, some interesting orders have also been found among primary, secondary and tertiary amines, e.g., MeNH2 > EtNH2 > n-PrNH2 > n-BuNH2; Me2NH > Et2NH > n-Pr2NH > n-Bu2NH; Me3N > Et3N > n-Pr3N > n-Bu3N; and MeNH2 > EtNH2 > i-PrNH2 > t-BuNH2. From these findings four important results have been obtained as follows: (1) an increase in the number of alkyl group decreases the basicity; (2) an increase in the size of an alkyl group decreases the basicity; (3) amines containing unbranched alkyl groups are more basic than their branched analogues; and (4) an increase in the number of methyl substituents on the methyl group of methylamine decreases the basicity in a regular manner. These results contradict results reported in the literature and also earlier results obtained in this laboratory.

Titrations in non-aqueous media: potentiometric investigation of the basicity of meso-porphyrins in nitrobenzene solvent

The basicity of the meso-porphyrins, namely meso-tetraphenylporphyrin (I), meso-tetrakis(4-methylphenyl)-porphyrin (II), meso-tetrakis(4-methoxyphenyl)porphyrin (III), meso-tetrakis(4-aminophenyl)porphyrin (IV), meso-tetrakis(4-chlorophenyl)porpyrin (V) and meso-tetrakis(4-nitrophenyl)porphyrin (IV), was investigated potentiometrically in nitrobenzene solvent. This investigation showed that these compounds are basic, rather than acidic. Whereas they cannot be titrated even with tetrabutylammonium hydroxide, they can readily be titrated with perchloric acid to give well shaped and stoichiometric end-points. In addition, they undergo two proton reactions per porphyrin molecule. However, IV shows a second end-point corresponding to a six-proton reaction per porphyrin molecule. Half-neutralization potentials (measures of their basicity) of these compounds are I = 321, II = 270, III = 255, IV = 155, V = 395 and VI = 480 mV. These values clearly indicate that, if para-hydrogen with respect to the bond found to be between the phenyl group and porphyrin core of meso-tetraphenylprophyrin (I) is replaced with basifying methyl, methoxy and amino groups, the basicity of I increases (270, 255 and 155 mV, respectively); if the same hydrogen atom is replaced with acidifying chlorine and nitro groups, the basicity of I decreases (395 and 480 mV, respectively). These observations show that the nitrogen atoms at the centre of the prophyrin molecules are strongly influenced by changes even at the perifery of the molecules, which is a good indication that prophyrin molecules are flat.

THE REACTIONS OF GEMINAL N3P3Ph2Cl4 AND N3P3(NHBut)2Cl4 WITH DIFUNCTIONAL REAGENTS. X-RAY CRYSTALLOGRAPHY, NMR SPECTROSCOPY AND BASICITY OF THE PRODUCTS

Abstract The reactions of geminal N3P3Ph2Cl4 and N3P3(NHBut)2Cl4 with difunctional reagents have been investigated. The N.M.R. spectra of the derivatives are reported. The basicity of these products in nitrobenzene solution is reported and the basicity substituent constants evaluated. X-ray crystallographic data are presented.

Titrations in non-aqueous media: potentiometric investigation of symmetrical and unsymmetrical tetra-aryl porphyrins with 4-nitrophenyl and 4-aminophenyl substituents in nitrobenzene solvent

The basicity of the symmetrical and unsymmetrical tetraphenylporphyrins, namely 5,10,15,20-tetraphenylporphyrin (I) (references), 5-(4-nitrophenyl)-10,15,20-triphenylporphyrin (II), a mixture of 5,10-bis(4-nitrophenyl)-15,20-diphenylporphyrin and 5,15-bis(4-nitrophenyl)-10,20-diphenylporphyrin (III), 5,10,15-tris(4-nitrophenyl)-20-phenylporphyrin (IV), 5,10,15,20-tetrakis(4-nitrophenyl)porphyrin (V), 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (VI), a mixture of 5,10-bis(4-aminophenyl)-15,20-diphenylporphyrin and 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin (VII), 5,10,15-tris(4-aminophenyl)-20-phenylporphyrin (VIII) and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (IX), was investigated potentiometrically in nitrobenzene solvent. This investigation showed that these compounds are basic rather than acidic. Although they can not be titrated even with tetrabuthylammonium hydroxide, they can easily be titrated with perchloric acid to give well shaped and stoichiometric end-points. In addition they all undergo two proton reactions per porphyrin molecule. However, compounds VI, VII, VIII and IX each shows a second end-point to give three, four, five and six proton reactions, respectively, per porphyrin molecule. Half neutralization potentials (measures of their basicity) of these compounds are: I=368, II=409, III=432, IV=461, V=520, VI=340, VII=302, VIII=238 and IX=225 mV versus Ag/AgCl in methanol. These potentials clearly indicate that, if para-hydrogen with respect to the porphyrin core of tetraphenylporphyrin (I) is replaced with an acidifying nitro group (II, III, IV and V) the basicity of I decreases. This decrease is approximately proportional to the number of nitro groups. Each nitro group decreases the half neutralization potential by about 35 mV. On the other hand, if para-hydrogen indicated above is replaced with a basifying amino group (VI, VII, VIII and IX) the basicity increases. This increase is also approximately proportional to the number of amino groups. Each amino group increases the half neutralization potential by about 36.7 mV. The values 35 and 36.7 mV indicate that in nitrobenzene solvent the electron releasing power of an amino group to the porphyrin system is a little stronger than the electron withdrawing power of a nitro group from the porphyrin system. All these observations reveal that the nitrogen atoms at the core of the porphyrin molecules are strongly influenced by changes at the periphery of the molecules, which is a very good indication that the substituted phenyl groups and the cores of the porphyrins are nearly in the same plane.

Titrations in non-aqueous media: Conductimetric and spectrophotometric investigation of reactions between iodine and aliphatic amines in acetonitrile

Abstract The reactions between iodine and methyl-, ethyl-, n-propyl- and n-butylamines were investigated conductimetrically and spectrophotometrically in acetonitrile. The mole ratios of iodine to the amines titrated are 1:2, 2:2, 3:2 and 4:2, respectively, indicating strongly the formation of anionic species of the types I−, I−3, I−5 and I−7 and cationic species of the type [R3N-I-NR3]+. Although the conductivities of the primary amines do not show a regular order, the secondary and tertiary amines show orders at least at the first end-points. The order for secondary amines is Me2NH>Et2NH>n-Pr2NH>n-Bu2NH and for tertiary amines n-Bu3N>Et3N>Me3N. The end-points of the conductimetric titrations are fairly sharp and can be used in the determination of these amines.

Titrations in non-aqueous media. Part III. Basicity order of aniline, N-Alkyl- and N-aryl-substituted anilines and pyridine in nitrobenzene solvent

The relative basicity order of ammonia, pyridine, aniline and N-methyl-, N,N-dimethyl-, N-ethyl-, N,N-diethyl-, N-aryl- and N,N-diaryl-substituted anilines have been determined potentiometrically with perchloric acid in nitrobenzene solvent and found to be NH3 > Py > PhNEt2 > PhNMe2 > PhNHEt > PhNHMe > PhNH2 > Ph2NH > Ph3N. This order in general conflicts with the results observed by other workers in either the gas phase or in the condensed phase. N-Alkyl substitution increases the basicity of the aniline, and N-aryl substitution decreases its basicity. Moreover, the number and size of the substituent influence the basicity of aniline. N-Ethyl-substituted anilines are more basic than the corresponding N-methyl-substituted anilines. The position of pyridine in the order is surprising and difficult to interpret.