bluuebunny/crossref_metadata_2025_split huggingface dataset:
Über die Reaktion von Phenolen mit N‐substitutierten Maleinimiden
Authors: Renner Alfred , Forgo Imre , Hofmann Walter , Ramsteiner Klaus 
Published: December 2004

The Reaction of Phenols with N‐substituted MaleinimidesPhenoxysuccinimides are formed by the base catalysed addition of phenols to N‐substituted maleinimides. In the presence of catalytic amounts of tertiary aliphatic amines yields as high as 90% are obtained. A series of adducts of mono‐and di‐phenols to mono‐ and bismaleinimides is described. Pure phenoxysuccinimides are stable compounds but the basic catalysts of their formation give rise to their decomposition into the phenolic component and oligomeric maleinimide. A nucleophilic reaction mechanism both for the formation and the decomposition is discussed. A new crosslinked addition polymer from a diphenol and a bismaleinimide with a surprisingly high heat stability is described.
Complexes of the Lighter Lanthanoid Nitrates with 15‐crown‐5 and 18‐crown‐6 ethers: Synthesis and characterization
Authors: Bünzli Jean‐Claude G. , Wessner Denis 
Published: December 2004

AbstractComplexes of lanthanoid trinitrates Ln(NO3)3 with 15‐crown‐5 ether 1 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) and with 18‐crown‐6 ether 2 (Ln = La, Ce, Pr, Nd) having a 1:1 stoichiometry as well as 4:3 complexes with 2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) have been synthesized and characterized. All the isolated complexes are solvent free. At 170–220° the 1:1 complexes of 2 are quantitatively transformed into 4:3 complexes. X‐Ray powder diagrams of the neodymium complexes with 2 indicate that both the 1:1 and 4:3 complexes are genuine compounds. All the 1:1 complexes show a characteristic IR. absorption band at 875–880 cm−1 absent from both the spectra of the free ligands and of the 4:3 complexes.The spectroscopic properties (IR. and electronic spectra, fluorescence lifetimes) of the complexes and the low magnetic moments of the Ln(III) ions in the complexes with Ln = Ce‐Eu are indicative of a strong interaction between the lanthanoid ions and the crown ethers 1 and 2.
Struktur und Eigenschaften von 5‐epi‐Flavoxanthin und 5‐epi‐Chrysanthemaxanthin
Authors: Cadosch Herbert , Vögeli Ulrich , Rüedi Peter , Eugster Conrad Hans 
Published: December 2004

Structure and properties of 5‐epi‐flavoxanthin and 5‐epi‐chrysanthemaxanthinThe absolute configurations of 5‐epi‐flavoxanthin (6) and 5‐epi‐chrysanthemaxanthin (7) prepared by acid catalysed rearrangement of semi‐synthetic lutein epoxide 5 are shown to be (3S, 5S, 8R, 3′R, 6′R) and (3S, 5S, 8S, 3′R, 6′R), respectively. Contrary to published data [5] the relationship of the polyene chain and H3(18) on the dihydrofurane ring is cis for the pair of stereoisomers having a Δδ = δ (HC(7)) − δ (HC(8)) = 0,22 ppm and 3J ≡ 0. These conclusions are in full accord with the chiroptical data.
Etude des composés flavoniques et xanthoniques dans les feuilles de Gentiana ciliataL
Authors: Goetz Michel , Maniliho Faustin , Jacot‐Guillarmod André 
Published: December 2004

Study of the flavonic and xanthonic compounds in the leaves of Gentiana ciliata L.Fifteen 1,3,7,8‐oxygenated xanthones (1–15) were isolated from the leaves of Gentiana ciliata L. (genus Gentianopsis). Among these were six new glycosides: glucosyl‐1‐decussatin 6, glucosyl‐1‐gentiacaulein (8), primeverosyl‐8‐isogentiacaulein (9), glucosyl‐3‐isogentiacaulein (10), glucosyl‐1‐swertianin (12) and primeverosyl‐7‐swertianin (13). Three known flavone C‐glucosides were also found (16–18).
Ein synthetisches Modell für die Aktivstelle der Coenzym‐B12‐abhängigen Methylmalonyl‐CoA‐Mutase
Authors: Flohr Helmut , Pannhorst Wolfgang , Rétey János 
Published: December 2004

A synthetic model of the active site of the coenzyme B12 dependent methylmalonyl‐CoA mutaseThe synthesis of a bridged cobaloxime with a built‐in methylmalonic ester moiety is described. 2‐Brommethyl‐2‐methylmalonic acid dichloride (5) afforded upon reaction with 5‐heptin‐1‐ol (4) the corresponding diester 6. Subsequent treatment of 6 with ozone, dimethylsulfide and hydroxylamine hydrochloride led to the pentadentate ligand: 10‐brommethyl‐10‐methyl‐9, 11‐dioxo‐8, 12‐dioxa‐nonadecane‐2, 3, 17, 18‐tetraone tetraoxime (8). Reaction of 8 with cobalt (II) chloride, pyridine and sodium borohydride furnished in 7% yield the bridged cobaloxime 10, which was spectroscopically characterized. Short term irradiation of 10 in methanol caused the exchange of the axial pyridine ligand by a solvent molecule affording 10a, the structure of which has been determined by X‐ray crystallography. Long term irradiation of 10 in methanol or ethanol led to irreversible cleavage of the Co, C‐bond. Upon alkaline hydrolysis the degradation product afforded methylsuccinic acid in 82–95% yield. No incorporation of solvent protons into this product could be observed. Implications of these findings for the mechanism of the coenzyme‐B12 catalysed rearrangement of methylmalonyl‐CoA are discussed.
Die Aminoalkylierung von Carbonylverbindungen mit Hilfe der Wittig‐Reaktion
Authors: Marxer Adrian , Leutert Thomas 
Published: December 2004

The Aminoalkylation of Carbonyl Compounds by the Wittig‐ReactionThe Wittig reaction would be a very suitable way to replace the carbonyl group in aldehydes and ketones by a 2‐amino‐ethylidene group if a simple and convenient method could be devised for synthesizing (2‐amino‐ethyl)triphenylphosphonium bromides 3. We have synthesized compounds of type like (2‐dialkylaminoethyl)‐, (2‐morpholino‐ethyl)‐, (2‐(1‐imidazolyl)ethyl)‐, and (2‐(1‐triazolyl)ethyl)‐triphenylphosphonium bromides (cf. Table 1), by melting at 150° the hydrobromides of triphenylphosphine and of the appropriate 2‐amino‐ethanol. The phosphonium bromides of type 3 could be converted with ketones by the Wittig reaction into the desired amino‐ethylidene compounds of type 2, e.g. 18–22 (Table 2). In the case of the reaction with 4‐chlorobenzaldehyde the steric course of the transformation was studied, and conditions were found favoring either cis or trans compounds (e.g. 27a or 27b in the reaction of the phosphonium bromide 11, cf. Table 3).
Dediazoniation of Arenediazonium Ions in Homogeneous Solution. Part XII. Solvent effects in competitive heterolytic and homolytic dediazoniations
Authors: Szele Ivanka , Zollinger Heinrich 
Published: December 2004

AbstractIn heterolytic dediazoniations arenediazonium salts form aryl cations. The reaction rates are relatively slow; they depend only to a small extent on the solvent. It is shown that the solvents in which the heterolytic dediazoniation mechanism is predominant have a low nucleophilicity, whereas in solvents of high nucleophilicity homolysis of arenediazonium salts, i.e. the formation of aryl radicals and related intermediates, is favoured. Under comparable conditions, homolytic rates are faster than the corresponding rates of heterolysis. Homolysis is strongly enhanced by addition of nucleophiles which form relatively stable radicals by electron transfer. The ability of additives to catalyze homolysis of arenediazonium salts can be explained using the concept of a nucleofugicIn the original proposal [32] we used the word nucleofugal. In keeping with a forthcoming proposal on nomenclature in physical organic chemistry by Commission III.2 (Physical Organic Chemistry) of IUPAC we now use the word nucleofugic.
homolytic leaving group.
Schiff‐Basen aus 1,3‐Dicarbonylverbindungen und Triaminen und ihre Fe (III)‐, Co (III)‐, Ni(II)‐ und Cu(II)‐Komplexe
Authors: Flückiger Jean‐Rodolphe , Schläpfer Carl Wilhelm 
Published: December 2004

Schiff bases of 1,3‐dicarbonyl compounds with triamines and their Fe(III), Co(III), Ni(II) and Cu(II) complexesThe preparation of new hexadentate ligands obtained by the reaction of cis, cis‐1,3,5‐triaminocyclohexane (tach) or 1,1,1‐tris (aminomethyl)ethane (tame) with an 2‐ethoxymethylidene‐1,3‐dicarbonyl compound as well as their Fe(III), Co(III), Ni(II) and Cu(II) complexes is reported. Fe(III) and Co(III) yield neutral complexes with an octahedral N3O3‐coordination sphere, Ni(II) and Cu(II) complexes with a square‐planar coordination‐sphere. In the later complexes one of the bidentate branches of the ligand is not deprotonated and stays uncoordinated.
Radikalinduzierte intramolekulare 1, 4‐Verschiebung einer Formylgruppe
Authors: Kalvoda Jaroslav , Grob JÜRgen 
Published: December 2004

Radical‐induced Intramolecular 1,4‐Transfer of a Formyl GroupA further example of a radical‐induced intramolecular shift of a functional group in steroids is described. In analogy to the sequence leading to the 1, 4‐transfer of cyano groups [3], 11 β‐nitrite photolysis was used to generate the appropriate C (18) radical in the 20‐hydroxy‐11 β‐nitrosyloxy‐pregnene‐21‐al 6. Intramolecular addition of the radical center to the double‐bond of the specially adjacent aldehyde function, followed by fragmentation of the intermediate cyclic alkoxy radical and subsequent oxidation lead directly to the rearranged 18‐formyl compound 10.
Electronic states of di‐t‐butylpolyacetylene radical cations
Authors: Heilbronner Edgar , Jones Taylor B. , Kloster‐Jensen Else , Maier John P. 
Published: December 2004

AbstractThe π‐ionization energies of the di‐t‐butylpolyacetylenes with two, three, four and five conjugated triple bonds have been determined by He (Iα) photoelectron spectroscopy. The assignment of the bands to the Π‐states of the corresponding radical cations follows from simple correlations in agreement with previous experience. The influence of the t‐butyl groups on the ionization energies is rationalized in terms of traditional, qualitative arguments assuming an inductive and/or hyperconjugative mechanism. However, a more careful analysis shows that the ‘The ‐higher‐the‐ionization‐energy‐the‐higher‐the‐alkyl‐induced‐shift’ rule is not always true.
Chemistry of Benzocyclopropenes. 1H‐and 13C‐NMR. Spectra of 2, 5‐dideuterio‐1‐fluorobenzocyclopropenium ion
Authors: Müller Paul , Pfyffer Jean , Wentrup‐Byrne Edeline , Burger Ulrich 
Published: December 2004

AbstractPreparation of 1, 1‐difluorobenzocyclopropene (4) and of its 2, 5‐ and 3, 4‐dideuterio derivatives 4a and 4b is reported. Upon ionization in cold fluorosulfonic acid, 4 affords 1‐fluorobenzocyclopropenium ion (6). 1H‐ and 13C‐NMR. spectra of 4 and 6 are assigned on the basis of the data for the specifically deuteriumlabelled compounds 4a and 6a. Hydrolysis of 6a leads to 2, 5‐dideuteriobenzoic acid (7a).
Reaktionsprodukte aus 3‐Dimethylamino‐2, 2‐dimethyl‐2H‐azirin und Phthalohydrazid bzw. Maleohydrazid
Authors: Link Helmut , Bernauer Karl , Chaloupka Stanislav , Heimgartner Heinz , Schmid Hans 
Published: December 2004

Reaction Products from 3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine and Phthalohydrazide or Maleohydrazide3‐Dimethylamino‐2, 2‐dimethyl‐2H‐azirine (1) reacts in dimethylformamide at room temperature with the six‐membered cyclic hydrazides 2, 3‐dihydrophthalazin‐1, 4‐dione (2) and 1, 2‐dihydropyridazin‐3, 6‐dione (15) to give the zwitterionic compounds 3 and 16, respectively (Scheme 1 and 7). The mechanism of these reactions is outlined in Scheme 1 for compound 3 (cf. also Scheme 8). The first steps are thought to be similar to the known reactions of 1 with the NH‐acidic compounds saccharin and phthalimide (cf. [1]). Instead of ring expansion to the nine‐membered heterocycle i (X=CONH, Scheme 8), a proton transfer followed by the loss of water gives 3 (Scheme 1).The structure of the zwitterionic compounds 3 and 16 is deduced from spectral data and the reactions of these compounds (see Schemes 2, 3, 4, 6 and 7). Methylation of 3 yields the iodide 4, which is hydrolysed easily to the 2‐imidazolin‐5‐one derivative 5 (Scheme 2). Hydrolysis of 3 under basic conditions leads to the amide 6, which undergoes cyclization to 7 at 220–230° (Scheme 3). The analogous cyclization has been realized under acidic conditions in the case of 17 (Scheme 7).Catalytic reduction of 3 yields the tertiary amine 14 (Scheme 6), whereas the reduction with sodium borohydride leads to a mixture of 14 and the 2‐imidazoline derivative 13. The alcohol 11, corresponding to the amine 14, is obtained by sodium borohydride reduction of the 2‐imidazolin‐5‐one 7 or of the amide 6 (Scheme 3). This remarkably easy reaction of 7 shows the unusual electrophilicity of the lactamcarbonyl group in this compound. The reduction of 6 to 11 is understandable only by neighbouring group participation of N (2′) in the dihydrophthalazine residue.
Reaction of aminoalcohols with butadiene catalyzed by palladium complexes. Preliminary communication
Authors: Umpleby J. David 
Published: December 2004

AbstractThe aminoalcohols 1, react with 2 equivalents of butadiene in the presence of catalytic quantities of bis (acetylacetonato)palladium/triphenylphosphine to give exclusively the corresponding N‐octadienyl amninoalcohols. In the presence of excess butadiene, subsequent O‐octadienylation occurs only for N‐octadienylimino‐diethanol 2g, affording the monoether 4g. O‐octadienylation of 2a‐f and 4g can be effected by the addition of molar quantities of triethylamine to the reaction mixture.
The intramolecular ene reaction: The thermal rearrangement of linalool and 1, 2‐dehydrolinalool
Authors: Pickenhagen Wilhelm , Ohloff GÜNther , Russel Ronald K. , Roth Wolfgang D. 
Published: December 2004

AbstractA kinetic analysis of the thermal rearrangement of linalyl trimethylsilylether (1b) shows that four diastereoisomeric 1, 2‐dimethyl‐3‐isopropenyl‐l‐cyclopentyl trimethylsilyl ethers (2b‐5b) are formed directly in parallel first order reactions. Kinetic analysis of the thermal rearrangement of dehydrolinalool (6) shows that two diastereoisomeric 1‐methyl‐2‐methylidene‐3‐isopropenyl‐1‐cyclopentanols (7 and 8) are formed in parallel first order reactions. The configurations of 7 and 8 are determined by correlations with the known iridenols.
Thiosucres. III. Réactions du substituant (benzylthio)‐acétyle. Communication préliminarie
Authors: Tronchet Jean M. J. , Eder Hansjörg 
Published: December 2004

Thiosugars. III. Some reactions of the (benzylthio)‐acetyl substituent Preliminary CommunicationThe (benzylthio)‐acetyl substituent as found in 6‐benzylthio‐6‐deoxy‐1, 2‐O‐isopropylidene‐3‐O‐methyl‐α‐D‐xylo‐hexofuranos‐5‐ulose (1) constitutes and useful synthon which can be transformed into ‘second generation’ synthons as, for example, the sulfylidene 10 or the chlorinated derivative 14. S‐Debenzylating C‐acylation of 10 leading to 11 is described as well as the ring‐forming condensation of 10 with the sulfene 12. Depending on the nature of the nucleophile reacted with 14, one can obtain the product of the substitution of the chlorine atom or of the chlorine atom and the benzylthio group or reactions taking place at both the carbonyl group and the terminal carbon atom, among them binucleophilic cyclizations. Some reactions of the conjugate base of 14 are also described.
Is water critical to the formation of micelles in apolar media??
Authors: Eicke Hans‐Friedrich , Christen Heinz 
Published: December 2004

AbstractPhoton correlation studies in H2O/sodium di‐2‐ethylhexylsulfosuccinate (AOT)/i‐C8H18‐systems, pertinent IR. investigations, and vapor pressure osmometric measurements with alkylated quaternary ammonium di‐2‐ethylhexylsulfosuccinates strongly suggest water to be pre‐requistite for the micellization in apolar media.
A convenient high yield version of the ester Claisen rearrangement. Preliminary communication
Authors: Petrilka Martin 
Published: December 2004

AbstractRegiospecific addition of benzeneselenenyl bromide to ethyl vinyl ether followed by alcoholysis of the initially formed β‐bromoalkyl selenide 1 by primary, secondary or tertiary allylic alcohols 2a‐e gave the mixed acetals 3a‐e. Subsequent oxidation and thermal treatment of the corresponding selenoxides 4a‐e furnished after saponification the γ, δ‐unsaturated acids 7a‐e in excellent overall yields. The entire sequence (Scheme 2) represents a new version of the ester Claisen rearrangement.
Photochemische Reaktionen 100. Mitteilung. Photochemistry of N‐Acylimidazoles. V. Photolysis of the N‐Acylimidazoles of Dehydroabietic Acid and of 13‐Deisopropyl‐10‐epi‐dehydroabietic Acid
Authors: Iwasaki Shigeo 
Published: December 2004

AbstractThe irradiation of 1‐(dehydroabietoyl) imidazole (3) gave no Type II elimination product but yielded instead compounds 6 and 7 by migration of the imidazolylcarbonyl group from C(4′) to C(6′) of the abietan moiety, probably via a cyclobutanol intermediate. Similarly, irradiation of 1‐(13′‐deisopropyl‐10′‐epi‐dehydro‐abietoyl)imidazole (13) gave only a small amount of Type II fragmentation product 20, the main products derived from γ‐hydrogen abstraction being the cyclobutanol derivatives 16 and 17.
On Excited States of Alkyl Bridged [14] Annulenes
Authors: Spanget‐Larsen Jens , Gleiter Rolf 
Published: December 2004

AbstractThe linear dichroic absorption spectrum of 1,3,6,8‐trans‐15, 16‐hexamethyl‐dihydropyrene has been measured in stretched polyethylene at 77K, and CNDO‐CI calculations with inclusion of singly and doubly excited configurations have been carried out on a series of alkyl bridged [14] annulenes with pyrene‐ and anthracene‐shaped perimeters. Transitions to e3g → e4u type 1B states are well described, and the results indicate that additional low‐energy excited states originate from e3g→ e5g and e2u → e4u type configurations interacting strongly with doubly excited configurations of the e3g, e3g → e4u, e4u type. The second excited singlet state responsible for the weak transition observed between the 1L bands may be assigned to one of these additional states, but it is probably of complex nature, similar to the ‘phantom’ state in linear polyenes.
The Conversion of α‐Hydroxythioacetals to Functionalized Ketene Thioacetals
Authors: Lottenbach Willi , Graf Walter 
Published: December 2004

AbstractThe conversion of α‐hydroxythioacetals to ketene thioacetals possessing an unprotected carbonyl function is described. Besides the intrinsic utility of this transformation it is of interest to recognize that ketene thioacetals are protected carboxyl groups.
Etude dans la série des radicaux hétérocycliques. Partie XV. Décomposition aprotique de l'amino‐6‐éthyl‐2‐benzothiazole dans des substrats aromatiques et hétéroaromatiques: préparation des mésityl‐6‐ et furyl‐6‐éthyl‐2‐benzothiazoles, des sels quaternaires et des spiropyrannes correspondants
Authors: Vernin Gaston , Kister Jacky , Metzger Jacques 
Published: December 2004

AbstractStudy of heteroaromatic radicals. Part XV. Partie XIV: cf. [1].
Aprotic decomposition of 6‐amino‐2‐ethylbenzothiazole in aromatic and heteroaromatic substrates: preparation of 6‐mesityl‐ and 6‐furyl‐2‐ethylbenzothiazoles and of the corresponding quaternary salts and spyropyransIn the presence of excess isopentyl nitrite in aprotic solvent, the 6‐amino‐2‐ethyl‐benzothiazole leads to 6‐aryl‐ and 6‐heteroaryl‐2‐ethylbenzothiazoles 1 to 14 in ca. 20–50% yield (Scheme 1, Table 1). The 2‐ethyl‐6‐benzothiazolyl radicals generated during these reactions exhibit a weak electrophilic character (Table 2).Preparatively this method has been applied to the synthesis of 6‐mesityl‐ and 6‐furyl‐2‐ethylbenzothiazoles 6 and 7, which were used to prepare the corresponding quaternary salts 15, 16 and the spiropyrans 19, 20 (Scheme 4).
γγ‐Disubstituted Itaconic Acids. Part 1. The Stobbe condensation of 1‐arylnaphthyl ketones with diethyl succinate
Authors: Baghos Victorine B. , Nasr Farid H. , Gindy Munir 
Published: December 2004

AbstractArylnaphthyl ketones condense with diethyl succinate yielding the stereoisomeric half‐esters 2a–2d which were subjected to a series of reactions leading to 1‐phenylphenanthrene and 1,1′‐binaphthyl derivatives. (E)‐3‐Ethoxycarbonyl‐4‐(4‐methoxynaphth‐1‐yl)‐4‐arylbut‐3‐enoic acids (2b–d) were converted finally into the corresponding naphtho[1,2‐c]fluorenones (9). The structure of the products was established by IR. and UV. spectroscopy. The effect of substituents on the relative proportions of (E)‐ and (Z)‐half‐esters 2 was determined by chromatography and UV. spectroscopy.
(Z)‐4,7‐Octadiensäure‐äthylester und (Z)‐Buttersäure‐3,5‐hexadienylester, zwei neue Aromastoffe der roten Passionsfrucht
Authors: Winter Max , Näf Ferdinand , Furrer Anton , Pickenhagen Wilhelm , Giersch Wolfgang , Meister Alain , Willhalm Bruno , Thommen Walter , Ohloff Günther 
Published: December 2004

Ethyl (Z)‐4,7‐Octadienoate and (Z)‐3,5‐Hexadienyl Butyrate, two New Aroma Components of the Purple PassionfruitThe isolation of ethyl (Z)‐4,7‐octadienoate (1) and (Z)‐3,5‐hexadienyl butyrate (2), two new and important aroma constituents of the purple passionfruit (Passiflora edulis SIMS) is reported.Ester 1 was synthesized by two different routes: (1) via a Wittig reaction between the known 4‐oxobutyrate 4 and 3‐butenylidenephosphorane, and (2) by thermolysis of (Z)‐8‐acetoxy‐4‐octenoate 7 which was readily accessible from (Z,Z)‐1,5‐cyclooctadiene.Ester 2 was prepared from the known hex‐3‐yn‐5‐en‐1‐ol (8) by a stereoselective (Z)‐reduction of the triple bond to 9, using Rieke's active metallic zinc, followed by esterification.The organoleptic properties and the taste threshold values of 1 and 2 are given.
Photolyse des 3‐Phenyl‐2, 1‐benzisoxazols und einiger seiner Derivate in Salzsäure bzw. Schwefelsäure
Authors: Giovannini Edgardo , De Sousa Bernardo F. S. E. 
Published: December 2004

Photolysis of 3‐phenyl‐2,1‐benzisoxazole and some derivates in hydrochloric and sulfuric acidThe photolysis of 3‐phenylanthranils (3‐phenyl‐2, 1‐benzisoxazoles) in conc. hydrochloric or sulfuric acid leads to the formation of 5‐substituted 2‐amino‐benzophenones wherein the 5‐substituent is the anion of the acid employed. 5‐Halo‐substituted 3‐phenylanthranils, however, show a differing reaction pattern in the two acids. Whereas 2‐amino‐3, 5‐dihalo‐benzophenones are obtained when photolysis is effected in conc. hydrochloric acid, irradiation in sulfuric acid causes the hydroxy group to substitute the halogen which migrates to the 4‐position of the 2, 1‐benzisoxazole to yield 2‐amino‐5‐hydroxy‐6‐halo‐benzophenones. A similar behaviour in sulfuric acid is also observed with 5, 7‐dichloro‐3‐phenylanthranil. When the 5‐position of the anthranil is blocked by a phenyl group, irradiation in conc. hydrochloric acid leads to entry of the halogen mainly in this 5‐phenyl substituent, as can be expected from mesomeric structures.The reaction mechanisms for the photolytic behaviour of 3‐phenylanthranils in both conc. hydrochloric and sulfuric acid is discussed.
Pyrrole Ligands. III. The Stability of Dipyrromethenato Complexes of Cu (II) and Ni (II) in Aqueous Solutions
Authors: Stünzi Hans , Anderegg Giorgio 
Published: December 2004

AbstractThe protonation and complex formation of the new ligand 3,3′, 5,5′‐tetramethyl‐dipyrromethene‐4,4′‐dicarboxylate in aqueous solutions was investigated by alkalimetric titrations and spectrophotometric measurements (25°, I = 1 (KNO3)). The pK values for the NH groups are 8.03 and 16.1 and logβ2 of the complexes with Cu (II) and Ni (II) are 31.0 and 24.4, respectively. Comparison with other ligands shows that the dipyrromethenato group acts as a normal rigid aromatic dinitrogen ligand, despite the charge on one nitrogen atom.