Dediazoniation of Arenediazonium Ions in Homogeneous Solutions. Part XVII. Kinetics and mechanisms of dediazoniation of p-chlorobenzenediazonium tetrafluoroborate in weakly alkaline aqueous solutions in the presence of oxygen

The kinetics of dediazoniation of p-chlorobenzenediazonium tetrafluoroborate have been studied in buffer solutions in the pH-range 9.0–10.0, ionic strength I = 0.10, at 20.0° in glass and polytetrafluoroethylene vessels. The presence of oxygen (<5 ppb of O₂, 60 to 100 ppb of O₂, air, > 99% of O₂) has a decisive influence on the rate and kinetic order of the dediazoniation. Iodoacetic acid inhibits the reaction, whereas p-chlorophenol has a catalytic effect, and in air and >99% of O₂ it acts as an autocatalyst. The reaction is subject to general-base catalysis by water, hydroxyl ions, hydrogen carbonate and carbonate ions. The kinetic results are interpreted in conjunction with data concerning the reaction products [2] and a ¹⁵N-CIDNP. investigation of a related system [3]. Specific radical chain mechanisms are consistent with the results.     

Dediazoniations of Arenediazonium Ions in Homogeneous Solution. Part XIV. 15N-CIDNP. Investigation of the reactions of diazonium ions in weakly alkaline aqueous solutions

¹⁵N-CIDNP. spectra recorded during the reaction of diazonium cations with OH^? in weakly alkaline aqueous solutions show that the dediazoniation is at least partially homolytic. The polarizations observed for the diazonium and trans-diazotate ions can be explained by reaction proceeding via a cage involving diazenyl and diazotate radicals using Kaptein's rules and simple intensity considerations.     

Nucleophilic Aromatic Substitutions. Part XIV.. Investigation of the mechanism of hydroxy-denitration of 4,2-and 2,4-chloronitrobenzenediazonium ions as a function of pH

4,2-Chloronitrobenzenediazonium ions in aqueous buffer solutions between pH 2.9 and 7.9 do not hydrolyze by dediazoniation as previous authors have assumed, but by denitration. The isomeric 2,4-compound reacts by denitration (ca. 70%) and dechlorination (ca. 30%). The reactions are general base catalyzed. The products and kinetics are consistent with an S_NAr-mechanism in which the general base-catalyzed addition of a hydroxyl group at the reacting C-atom is rate-limiting. The rate maxima at or near the pH-values corresponding to (pK₁ + pK₂)/2 of the diazonium ? cis-diazotate equilibria can be rationalized on the assumption that the diazonium ion is the only equilibrium form of the diazo compound which enters the substitution proper, and the superposition of the rate term k_B[B] of all nucleophiles involved (H₂O, OH^? and buffer bases).     

Dediazoniation of arenediazonium ions in homogeneous solution. Part VIII. Reaction kinetics and products in dimethyl sulfoxide

p-Nitrobenzenediazonium tetrafluoroborate dissolved in dimethylsulfoxide (DMSO) at 50° forms p-nitrophenol in 88–90% yield. The phenolic oxygen atom originates exclusively from the oxygen atom of DMSO as demonstrated by the use of ¹⁸O-labelled DMSO. The first-order rate of dediazoniation is the same under N₂ as it is in the presence of air. The rate is little influenced by the addition of benzene or iodobenzene. However, the products formed in the presence of these additives are significantly different. UV. spectra and the reactivity of diazonium salt solutions in DMSO when mixed with reagents in aqueous solution demonstrate that a relatively stable charge-transfer complex is formed between the diazonium ion and DMSO. The product analyses and the kinetic and spectral results of dediazoniation in DMSO with and without additives are consistent with a mechanism in which the rate-limiting step is the formation of a p-nitrophenyl radical from the charge-transfer complex. p-Nitrophenol and the products with benzene and iodobenzene are formed in subsequent fast competition steps. In the presence of small amounts of pyridine the dediazoniation is much faster and follows a different kinetic law. Pyridine effectively competes with DMSO in the reaction with diazonium ions.     

Elektronendonator-Akzeptor-Komplexe von Diazonium-Ionen und die Struktur von stabilisierten Diazonium-Salzen. 20. Mitteilung zur Kenntnis der Azokupplungsreaktion

1. In 0.1N HCl/H₂O, o- and p-nitrobenzenediazonium ions rapidly form a complex with 2-naphthol-6, 8-disulphonic acid anions. Visible and NMR, spectra show that it has the structure of a charge-transfer complex (π-complex). The latter is probably an intermediate in the electrophilic aromatic substitution (diazo coupling reaction). 2. Diazonium ions form charge-transfer complexes with naphthalene, 1-methylnaphthalene, naphthalene-1-sulphonic acid, 1-naphthyl-methanesulphonic acid and also 2-naphthol-1-sulphonic acid. The equilibrium constants of all these complexes have been determined. 3. The stabilisation of diazonium salts by arylsulphonic acids with regard to decomposition is due to charge-transfer complex formation and not to formation of diazosulphonates as assumed by former investigators. The sulphonic group is not essential for the stabilisation. 4. Charge-transfer complex formation decreases the electrophilicity of the diazonium ion (rate of diazo coupling reaction) only slightly.     

Electrophilic Aromatic Substitution of Groups other than Hydrogen. Part II: SN1-Type Desulfonation of 2-Naphthol-1-sulfonic Acid by Diazonium Ions in Aprotic Apolar Solvents. 27th communication on diazo coupling reactions

The rates of formation of 1-(4′-chlorophenylazo-)-2-naphthol by SO₃ of release from the π-complex [2-naphthol-1-sulfonate anion …? p-chlorobenzenediazonium cation] have been measured in chloroform and in methylene chloride; they are first-order with respect to the complex. They are catalysed by pyridine and co-catalysed by acetic acid. Acids alone, in stoichiometric or higher concentrations, inhibit the reaction. A mechanism is postulated involving proton transfer to the sulfonate group, followed by rearrangement to the σ-complex which, in the catalysed reaction, first loses a proton to the base and then releases SO₃, but in the uncatalysed reaction loses SO₃H^⊕. The function of the co-catalyst (pyridinium ion) is explained (see text). This reaction is - in contrast to electrophilic aromatic substitutions in which the leaving group is a protonan S_N1-type re-aromatization of the σ-complex to the product.     

Mécanisme de solvolyse des cis- et trans-(p-toluènesulfonates) d'aryl-2-cyclopentyle I. Etude de la première étape de la solvolyse: effets isotopiques de l' atone de deutérium en position 2, effets de sel basique et effet spécial de sel

Solvolysis Mechanism of cis - and trans-2-Arylcylopentyl p-Toluenesulfonates. The Step: 1-Deuterium Isotope Effects, Basic Salt Effects, and Special Salt Effect We have studied the first step of the solvolysis of cis and trans-2-arylcyclopentyl p-toluenesulfonates in HCOOH, AcOH, and EtOh. All substrates show a high kinetic 1-deuterium isotope effect (k_H/k_D(1) >1.15). This fact indicates that first step leads to classical intimate ion-pair Which dissociates to a solvet-separated ion-pair, without participation either of solvent, the 2-aryl group, or a H-atom at C(2). The slight influence of added basic ions on reaction rate allows us to exclude any direct solvent attack on the covalent substrate even in the most favorable case, i.e. ethanolysis of 2-(p-nitrophenyl)cylopentyl-p-toluenesulfonates. Furthermore, solvent-separated ion pair formation is indicated by the special salt effect induced by LiClO₄.     

Dediazoniations of Arenediazonium Ions. Part XXI. Dediazoniation of Arenediazonium Ions Complexed with Crown Ethers

The evaluation of the dediazoniation kinetics of various m- and p-substituted benzenediazonium tetrafluoroborates in 1,2-dichloroethane at 50° in the presence of 18-crown-6, 21-crown-7 and dicyclohexano-24-crown-8 demonstrates that the rate constant for the dediazoniation within the complex (k₂) is smallest, and the equilibrium constant for complex formation (K) is largest for the complexes with 21-crown-7 (cf. Scheme 1). The logarithms of the equilibrium constants (K) for complex formation with each of the crown ethers studied correlate well with Hammett's substituent constants, σ, to give reaction constants ρ = 1.18–1.38. A linear correlation between the logarithms of the rate constants for the dediazoniation within the complex with those of the dediazoniation rate constants of uncomplexed diazonium ions (log k₂ vs. log.k₁), found for most substituted diazonium salts, indicates that the dediazoniation mechanism of the complexed diazonium ions is not significantly different from that of the free ions. For very electrophilic diazonium ions (p-Cl, m-CN), k₂ was much larger than expected on the basis of the linear log k₂ vs. log k₁ relationship. Analysis of the dediazoniation products showed that this was due to a change in mechanism from heterolytic to homolytic dediazoniation. The complexation rate of diazonium salts by crown ethers (k_c) is practically diffusion controlled and does not change much with the size of the crown ether. The decomplexation rate (k_d), however, is significantly lower for complexes with 21-crown-7, than for those with 18-crown-6 and dicyclohexano-24-crown-8, and is therefore the reason for the variations in the equilibrium constant (K) and thus for the fact that complexes of arenediazonium salts with 21-crown-7 are the most stable. The amounts of the N_α-N_β rearrangement, as well as those of the exchange of the ¹⁵N-labelled diazonio group with external nitrogen during dediazoniation of p-toluenediazonium salt were independent of the addition of crown ethers. A dediazoniation mechanism involving a charge transfer, as well as an insertion-type diazonium ion-crown ether complex is proposed. In this mechanism, dediazoniation of the insertion complex does not take place directly, but through the charge-transfer complex.     

Kinetics and mechanisms of the reactions of thiosulphato-amine complexes of cobalt(III). Part I. Isomerization and base hydrolysis ofcis andtrans isomers of dithiosulphatobis(ethylenediamine) cobalt(III) ion in aqueous solution

Summary Investigations were carried out on the isomerization and base hydrolysis ofcis andtrans forms of dithiosulphatobis-(ethylenediamine)cobalt(III) ions. Thecis form isomerizes to thetrans form in neutral aqueous medium, rates being 1.15, 2.30 and 4.0×10^–5s^–1, respectively at 42, 50 and 58 °C. Thetrans complex isomerizes to thecis form in basic solution only, the rate varying with pH in a sigmoid pattern. In presence of OH^–, an acid-base equilibrium of the complex ion sets in, but only the basic form takes part in the isomerization reaction. Hydrolysis of thecis isomer proceeds through a base-dependent path only, but that of thetrans isomer proceeds both through base-dependent and base-independent paths. The mechanisms are associative in nature. Thetrans form reacts faster thancis in all cases.     

Cis-trans isomerization of styrylpyrroles by stray light

A series of substituted N-methylstyrylpyrroles (H, p-Br, p-CN, o,p-diCl, m-CH₃, m-CN, m-NO₂) were prepared via the Wittig reaction of 1-methylpyrrole-2-carboxaldehyde and substituted benzyltriphenylphosphonium bromides. Both cis and trans isomers were found to be present in the reaction mixture and they were separable by column chromatography in a few cases (H, p-Br, m-CN, m-NO₂). Photochemical isomerizations of cis-styrylpyrroles to trans isomers were observed when the substituents were o,p-diCl and m-NO₂, while the opposite was the case with compounds having H, p-Br, m-CH₃, m-CN. It was difficult to separate the cis and trans mixture of p-cyanostyrylpyrroles and the equilibrium ratio did not change under similar photochemical reaction conditions.     

Graft polymerization kinetics of acrylamide initiated by ceric nitrate–dextran redox systems

The kinetics of the graft polymerization of acrylamide initiated by ceric nitrate—dextran polymeric redox systems was studied primarily at 25°C. Following an initial period of relatively fast reaction, the rate of polymerization is first-order with respect to the concentrations of monomer and dextran and independent of the ceric ion concentration. The equilibrium constant for ceric ion—dextran complexation K is 3.0 ± 1.6 l./mole, the specific rate of dissociation of the complex, k_d, is 3.0 ± 1.2 × 10^?4 sec.^?1, and the ratio of polymerization rate constants, k_p/k_t, is 0.44 ± 0.15. The number-average degree of polymerization is directly proportional to the ratio of the initial concentrations of monomer and ceric ion and increases exponentially with increasing extent of conversion. The initial rapid rate of polymerization is accounted for by the high reactivity of ceric ion with cis-glycol groups on the ends of the dextran chains. The polymerization in the slower period that follows is initiated by the breakdown of coordination complexes of ceric ions with secondary alcohols on the dextran chain and terminated by redox reaction with uncomplexed ceric ions.     

Der massenspektrometrische Zerfall isomerer Diacetamido-cyclo-hexane,ihrer N-Phenäthyl-Derivate und Bis (acetamidomethyl)cyclohexane. 32. Mitteilung über massenspektrometrische Untersuchungen,,

The Mass Spectral Decomposition of Isomeric Diacetamido-cyclohexanes, their N-Phenethyl-Derivatives and Bis(acetamidomethyl)cyclohexanes In the mass spectra of the six isomeric diacetamidocyclohexanes 2--4 (cis and trans each, Scheme 2) as well as of the six isomeric bis(acetamidomethyl)cyclohexanes 6--8 (cis and trans each, Scheme 5) are clear differences between the constitutional isomers, whereas cis/trans isomers show very similar spectra. The lack of stereospecific fragmentations is explained by loss of configurational integrity of the molecular ion before fragmentation. However, the mass spectral fragmentation of epimeric diamidocyclohexanes becomes very stereospecific by the introduction of a phenethyl group on one of the nitrogen atoms: this group avoids epimerization of the molecular ion prior to fragmentation. In the N-phenethyl derivatives 10, 11, 13 and 14 (Scheme 8) the typical fragmentations of the cis-isomer after loss of ·C₇H₇ from the molecular ion are the elimination of CH₂CO by formation of cyclic ions, and the loss of p-toluenesulfonic acid or benzoic acid, respectively, with subsequent elimination of CH₃CN (Scheme 9). In the trans-isomer the typical fragmentations are the loss of the side chain bearing a tertiary nitrogen atom, and the elimination of the tosyl or benzoyl radical, respectively, with subsequent loss of CH₃CONH₂ (Scheme 10).     

Stereochemical studies. Part 67. Saturated heterocycles. Part 52. The mass spectra of some condensed skeleton 1,3-oxazin-4-one derivatives

The mass spectrometric behaviour of twenty saturated heterocyclic compounds with a 1,3-oxazin-4-one moiety fused with cis or trans anellation to a cycloalkane ring (C₅-C₈) was studied. The roles of the C-2 and N-3 substituent(s) were found to be characteristic, while the size of the cycloalkane ring seemed to be unimportant. Some fragmentation processes involving breakdown of the oxazinone ring of the cis or trans isomers displayed significant stereoselectivity. A striking new decomposition process involving significant chlorine elimination from the molecular ion of some 2-p-chlorophenyl derivatives was observed and was studied in some detail.     

Cationic polymerization of cyclic dienes. X. Cationic polymerization of 1-vinylcyclohexene and 3-methyl-1,3-pentadiene

1-Vinylcyclohexene (VCH), which has one of the double bonds in the ring and the other outside the ring, was synthesized and polymerized by cationic catalysts. The reactivity of VCH was very large in the polymerizations catalyzed by boron trifluoride etherate (BF₃OEt₂) and stannic chloride–trichloroacetic acid complex. Similar to other cyclic dienes, the polymerization of VCH was a nonstationary reaction having a very fast initiation step. The polymerization proceeded by either a 1,2- or a 1,4-propagation mode in which vinyl group was always involved. Particularly when BF₃OEt₂ was used as a catalyst, an intramolecular proton or an intramolecular hydride ion transfer reaction took place, resulting in the formation of methyl groups in the polymer. The degree of polymerization of polymer formed was about 10. This indicates the preponderance of monomer transfer reaction. To investigate the reason for the high reactivity of cyclic dienes, cationic copolymerizations of VCH and 3-methyl-cis/trans-1,3-pentadiene (cis/trans-MPD) was carried out. The relative reactivity of monomers decreased in the order VCH > trans-MPD > cis-MPD. On the other hand, the resonance stabilization of monomers decreased in the order VCH > trans-MPD > cis-MPD. Therefore, it could be considered that the monomer reactivity is mainly determined by the stability of carbonium ion intermediate. The relative stability of carbonium ion must be VCH > trans-MPD > cis-MPD. Thus the influence of the conformation of ion on its stability was clearly demonstrated.     

Coupling rates and kinetics of arenediazonium cations with couplers utilized in the diazo reprographic process

Stoichiometric and, in most cases, absolute rates of coupling of a series of m- and p-substituted benzenediazonium ions with 2,3-dihydroxynaphthalene-6-sulfonate ion (1) have been determined (i) at pH 5.6 (when one OH group is partly monoionized) and (ii) at pH 9.9 (when one OH group is completely ionized and the second slightly so). The rates at both pH values correlate with the σ⁺ parameter (except for the most reactive ArN at pH 9.9) and the contributions of the two reactive forms of the coupler evaluated. Detailed pH dependences of the coupling rate of the p-chlorobenzenediazonium ion with (1) reveal a strong interaction between (1) and the borate ion, which strongly influences the coupling rate. Coupling rates have also been measured for both diazonium ions and couplers of importance in the diazo reprographic process.     

Nucleophilic Reactions at Tertiary Carbon. Part 1. The 1,2-dimethyl-1-cyclohexyl cation

Stereoisomeric ion pairs are implicated as intermediates in the solvolysis of cis and trans-1-chloro-1,2-dimethylcyclohexane, cis- 4 and trans- 4 , respectively. This follows from the rates and products of these stereoisomeric tertiary chlorides in 80% ethanol and 50% acetone. The composition of elimination and substitution products from cis- 4 and trans- 4 differs markedly and the differences are accentuated by silver ion. Furthermore, substitution products are formed with predominant inversion of configuration. The equilibrium constant for isomerization of cis- 4 and trans- 4 shows the latter to be more stable by 0.7 kcal/mol. Since the solvolysis rates of the chlorides are equal, the transition state for trans- 4 is also more stable by 0.7 kcal. By inference the intermediates differ by a similar amount of energy which is ascribed to more efficient solvation of the trans ion pair 13 .     

Photooxygenation and photodimerization of 4-methoxystyrene in NaY. The role of co-adsorbed water and alkene–oxygen charge-transfer complex

On adsorption into NaY, 36% of 4-methoxystyrene (1) was consumed to yield its cis- and trans- chain dimers 2. Irradiation of the NaY sample under vacuum gave cyclic dimers 3, probably through the excimer of 1, and also caused trans-to-cis one-way isomerization of 2. When the NaY sample was irradiated under dry oxygen, 4-methoxybenzaldehyde (4) was given as the major product through photoinduced electron-transfer reaction on excitation of the contact charge-transfer complexes between the guest molecules and O₂. The effects of sodium ion and co-adsorbed water on the photodimerization and photooxygenation is also discussed.     

Stereocomplementary Synthesis of cis‐ and trans‐2‐(p‐Bromophenyl)‐5‐methylthiazolidin‐4‐ones: Useful Umpolung‐type Suzuki–Miyaura Cross‐coupling Partner and Donor

Novel cis‐ and trans‐2‐(p‐bromophenyl)‐5‐methylthiazolidin‐4‐ones, S,N‐containing heterocyclic compounds, were provided in a cis‐stereocomplementary and trans‐stereocomplementary synthetic manner. cis‐Selective cyclo‐condensation proceeded between 2‐sulfanylpropanoic acid (thiolactic acid) and an imine derived from 4‐bromobenzaldehyde and methylamine, whereas Ti(OiPr)₄ and Ti(OiBu)₄‐promoted trans‐selective cyclo‐condensation proceeded between benzyl 2‐sulfanylpropanoate and the imine. The obtained cis‐ and trans ‐ 2‐(p‐bromophenyl)‐5‐methylthiazolidin‐4‐ones were successfully converted to 2‐(3‐furyl)phenyl derivatives and bis(pinacolato)diborane derivatives utilizing Suzuki–Miyaura and Miyaura–Ishiyama cross‐coupling reactions, respectively, in an umpolung manner.     

Substitution reactions under NH3 chemical ionization conditions in cis-/trans-1,2-dihydroxybenzosuberans

The nucleophilic substitution reaction under NH₃ chemical ionization (CI) conditions in cis- and trans-1,2-dihydroxybenzosuberans (1–4) has been studied with the help of ND₃ CI and metastable data. The results indicate that in the parent diols 1 (cis) and 2 (trans), the substitution ion [M_sH]⁺, is produced mainly by the loss of H₂O from the [MNH₄]⁺ ion (S_Ni reaction) while in their 7-methoxy derivatives 3 and 4, the ion-molecule reaction between [M? OH]⁺ and NH₃ seems to be the major pathway for the formation of [M_sH]⁺. The substitution ion from 1 and 2 and the [MH]⁺ ion from trans-1-amino-2-hydroxybenzosuberan give similar collision-induced dissociation mass-analysed ion kinetic energy spectra. Interestingly, their diacetates do not undergo the substitution reaction.     

Cationic polymerization of α,β-disubstituted olefins. Part 17. Effect of polymerization conditions on the reactivity of alkenyl ethers relative to vinyl ethers

In order to clarify the propagation reaction, vinyl ether was copolymerized with the corresponding alkenyl ether under various conditions. cis-Propenyl ether (cis-PE) was several times more reactive than trans-PE and the corresponding vinyl ether in the copolymerization catalyzed by BF₃ · O(C₂H₅)₂ in toluene. However, the reactivity of cis-PE relative to trans-PE and the vinyl ether was found to be greatly decreased with increasing polarity of the solvent and to be very close to unity in such polar solvents as nitroethane. On the other hand, the reactivity of trans-IBPE relative to IBVE was scarcely changed by polymerization conditions. Also, the nature of the initiator and polymerization temperature affect the reactivity of cis-PE relative to the vinyl ether. These phenomena were explained by the relative stability of the bridged and open car bonium ions based on the polarity of the solvent and steric hindrance due to substituents in the trans isomer.