Reactivite et distribution moleculaire dans les copolycondensats lineaires-II: Effet de substitution

The development in Part I is extended to linear step polymerizations where the functional groups exhibit unequal reactivities induced by substitution effects in the course of the polymerization. An R(A)₂/R′(B)₂ copolycondensate is examined to determine how the polydispersity index varies with the strength and positive or negative sense of the substitution effect.     

Influence of Isotope Substitution on Lattice and Spin‐Peierls‐Type Transition Features in One‐Dimensional Nickel Bis‐dithiolene Spin Systems

Four new 1D spin‐Peierls‐type compounds, [D₅]1‐(4′‐R‐benzyl)pyridinium bis(maleonitriledithiolato)nickelate ([D₅]R‐Py; R=F, I, CH₃, and NO₂), were synthesized and characterized structurally and magnetically. These 1D compounds are isostructural with the corresponding non‐deuterated compounds, 1‐(4′‐R‐benzyl)pyridinium bis(maleonitriledithiolato)nickelate (R‐Py; R=F, I, CH₃, and NO₂). Compounds [D₅]R‐Py and R‐Py (R=F, I, CH₃, and NO₂) crystallize in the monoclinic space group P2₁/c with uniform stacks of anions and cations in the high‐temperature phase and triclinic space group P$\bar 1$ with dimerized stacks of anions and cations in the low‐temperature phase. Similar to the non‐deuterated R‐Py compounds, a spin‐Peierls‐type transition occurs at a critical temperature for each [D₅]R‐Py compound; the magnetic character of the 1D S=1/2 ferromagnetic chain for [D₅]F‐Py and the 1D S=1/2 Heisenberg antiferromagnetic chain for others appear above the transition temperature. Spin‐gap magnetic behavior was observed for all of these compounds below the transition temperature. In comparison to the corresponding R‐Py compound, the cell volume is almost unchanged for [D₅]F‐Py and shows slight expansion for [D₅]R‐Py (R=I, CH₃, and NO₂) as well as an increase in the spin‐Peierls‐type transition temperature for all of these 1D compounds in the order of F>I≈CH₃≈NO₂. The large isotopic effect of nonmagnetic countercations on the spin‐Peierls‐type transition critical temperature, T_C, can be attributed to the change in ω₀ with isotope substitution.     

Reactivity and gelation. I. Intrinsic reactivity

The method of Case is used with the Flory-Stockmayer gelation criterion to derive a critical transition equation for polycondensation of multifunctional reactants bearing coreactive functional groups of two species A and B, where the B groups may be of unequal intrinsic reactivity. Systems of the types R(A)₂/R′(B)₄ and R(A)₂/R′(B)₄/R′′(B)₂ are considered with the B groups divided into two classes characterized by a reactivity ratio in the range 0.1 to 10. If the reactivities are sufficiently different the polymerization can be regarded as a multistage process. Intramolecular reactions are not considered.     

Synthesis of peri-annelated heterocyclic systems based on 3-substituted 1-aryl-4,6-dinitro-1H-indazoles

A method for the synthesis of peri-annelated trinuclear heterocycles, including 14-electron heteroaromatic systems, namely, 1H-thiopyrano[4,3,2-cd]indazoles and 1,5-dihydropyrazolo[3,4,5-de]cinnolines, from 3-R-1-aryl-4,6-dinitro-1H-indazoles was developed. The method is based on the high mobility of the NO₂ group in position 4 and consists of either selective nucleophilic substitution of the 4-NO₂ group on treatment with the HSCH₂CO₂Me—K₂CO₃ system followed by intramolecular cyclization of the resulting sulfide (R = CHO) or the corresponding sulfone (R = CN) formed upon its oxidation or direct intramolecular substitution of the 4-NO₂ group (R = CH=NNHPh).     

Alkylated styrene ionomers with variable length spacers. I. Synthesis

Two analogous series of ionomer precursors based on 4-substituted styrene copolymers were prepared with substituents R = -(CH_2)nCO₂Me (n = 1, 5, 10), or R = -O(CH₂)_nCO₂Me (n = 1, 4, 10), and degrees of substitution from 10 to 15 mol%. The synthesis of the alkyl series compounds involved either chloromethylation of polystyrene or bromoalkylation via lithiation of a styrene-4-bromostyrene copolymer, followed by conversion to the nitriles. Methyl esters were then produced by reaction of the nitriles with methanol/HCl gas. The ether series compounds were obtained directly by reacting a styrene-4-hydroxystyrene copolymer with the methyl esters of the corresponding ω-bromoaliphatic carboxylic acids in a Williamson ether-type synthesis.     

Halomethylated polysulfone: Reactive intermediates to neutral and ionic film-forming polymers

Halomethylation of polysulfone (PS) with C₈H₁₇OCH₂X (X = Cl, Br) in the presence of SnX₄ (X = Cl, Br) led to PS–CH₂X (X = Cl or Br or both) (Scheme 1). Under controlled conditions, PS–CH₂X could be isolated and retains the good film forming properties of PS itself. Interhalogen exchange reactions occur in the presence of SnX₄ (X = Cl, Br) under anhydrous conditions (Scheme 1), or a quaternary ammonium phase transfer catalyst R^*R₃N⁺X^?, under aqueous conditions (Scheme 2). The exchange reactions with R^*R₃N⁺X^?, are favored when R = C₈? C₁₀, and with R = C₄ only if n-octanol is added; otherwise gelation occurs. Exchange in CHCl₃ is attributed to dehydrohalogenation (and generation of dichlorocarbene) of the solvent in the presence of tetrabutyl ammonium hydroxide. Further chemical modifications of PS–CH₂X by reaction with strong nucleophiles, led to hydroxymethyl polysulfone, acetoxymethyl polysulfone, and t-butyl-oxymethyl polysulfone (Scheme 3). Hydroxymethyl polysulfone sometimes gels under basic hydrolytic conditions and is best obtained by methanolysis of PS–CH₂-OAc. Both PS? CH₂? OAc and PS? CH₂O-t-Bu are very stable, and provide a way to generate PS? CH₂Br on need by cleavage with HBr in acetic acid. Direct oxidations with DMSO or tetrabutyl ammonium dichromate (Scheme 4) or indirect oxidations (Scheme 5) produce polysulfone with pendent CHO, CO₂R and PO₃R groups. Finally, polysulfones with linker arms including, carboxy alkyl, hexaglycol or sulfonamido crowns are described (Scheme 6). The reaction products were characterized by ¹H- and ¹³C-NMR. Double irradiation experiments, proved unequivocally, that the first substitution occurred on the B ring of the bisphenol A moiety (see Table I); the second substitution occurs on the A ring in position a. Thermogravimetric analysis generally shows for all modified polysulfones an extra transition at a lower temperature. The area of this band agrees generally with the values expected from calculated substitution degrees.     

Bimolecular Homolytic Substitutions at Nitrogen: An Experimental and Theoretical Study on the Gas‐Phase Reactions of Alkyl Radicals with NF3

The X‐ray irradiation of binary mixtures of alkyl iodides R?I (R=CH₃, C₂H₅, or i‐C₃H₇ radicals) and NF₃ produces R?NF₂ and R?F. Based on calculations performed at the CCSD(T), MRCI(SD+Q), G3B3, and G3 levels of theory, the former product arises from a bimolecular homolytic substitution reaction (S_H2) by the alkyl radicals R, which attack the N atom of NF₃. This mechanism is consistent with the suppression of R?NF₂ by addition of O₂ (an efficient alkyl radical scavenger) to the reaction mixture. The R?F product arises from the attack of R to the F atom of NF₃, but additional contributing channels are conceivably involved. The F‐atom abstraction is, indeed, considerably more exothermic than the S_H2 reaction, but the involved energy barriers are comparable, and the two processes are comparably fast.     

cine‐Substitution Reactions of Metallabenzenes: An Experimental and Computational Study

Alkali‐resistant osmabenzene [(SCN)₂(PPh₃)₂Os{CHC(PPh₃)CHCICH}] ( 2 ) can undergo nucleophilic aromatic substitution with MeOH or EtOH to give cine‐substitution products [(SCN)₂(PPh₃)₂Os{CHC(PPh₃)CHCHCR}] (R=OMe ( 3 ), OEt( 4 )) in the presence of strong alkali. However, the reactions of compound 2 with various amines, such as n‐butylamine and aniline, afford five‐membered ring species, [(SCN)₂(PPh₃)₂Os{CH?C(PPh₃)CH?C(CH?NHR′)}] (R′=nBu( 8 ), Ph( 9 )), in addition to the desired cine‐substitution products, [(SCN)₂(PPh₃)₂Os{CHC(PPh₃)CHCHC(NHR′)}] (R′=nBu( 6 ), Ph( 7 )), under similar reaction conditions. The mechanisms of these reactions have been investigated in detail with the aid of isotopic labeling experiments and density functional theory (DFT) calculations. The results reveal that the cine‐substitution reactions occur through nucleophilic addition, dissociation of the leaving group, protonation, and deprotonation steps, which resemble the classical “addition‐of‐nucleophile, ring‐opening, ring‐closure” (ANRORC) mechanism. DFT calculations suggest that, in the reaction with MeOH, the formation of a five‐membered metallacycle species is both kinetically and thermodynamically less favorable, which is consistent with the experimental results that only the cine‐substitution product is observed. For the analogous reaction with n‐butylamine, the pathway for the formation of the cine‐substitution product is kinetically less favorable than the pathway for the formation of a five‐membered ring species, but is much more thermodynamically favorable, again consistent with the experimental conversion of compound 8 into compound 6 , which is observed in an in situ NMR experiment with an isolated pure sample of 8 .     

Reaction of α,β-unsaturated ketones with guanidine. Substituent effects on the protonation constants of 2-amino-4,6-diarylpyrimidines

1,3-Diaryl-2-propen-1-ones, I, reacted with guanidine hydrochloride (II) in the presence of 3 moles of sodium hydroxide to give the corresponding 2-amino-4,6-diarylpyrimidines, III. The structure and configuration of the products are based on chemical and spectroscopic evidence. The protonation constants of these compounds (series A and series B) have been determined in 50 volume percent ethanol-water medium. Excellent linear correlations are obtained when pK_a values of the two series of 2-amino-4,6-diarylpyrimidines, IIIa-j and IIIk-r, are plotted against the substituent constant, ^σx, and the polar substituent constant, ^σ* xC₆H₄, for substituted phenyl groups. The pK_a values have also been correlated with the extended Hammett equation. The correlation follows the equations: Series A; pK_a = 3.273 - 0.820σI,X - 0.662σR,X Series B; pK_a = 3.169 - 0.424σI,X - 0.137σR,X     

Two‐Coordinate Magnesium(I) Dimers Stabilized by Super Bulky Amido Ligands

A variety of very bulky amido magnesium iodide complexes, LMgI(solvent)_0/1 and [LMg(μ‐I)(solvent)_0/1]₂ (L=‐N(Ar)(SiR₃); Ar=C₆H₂{C(H)Ph₂}₂R′‐2,6,4; R=Me, Prⁱ, Ph, or OBu^t; R′=Prⁱ or Me) have been prepared by three synthetic routes. Structurally characterized examples of these materials include the first unsolvated amido magnesium halide complexes, such as [LMg(μ‐I)]₂ (R=Me, R′=Prⁱ). Reductions of several such complexes with KC₈ in the absence of coordinating solvents have afforded the first two‐coordinate magnesium(I) dimers, LMg?MgL (R=Me, Prⁱ or Ph; R′=Prⁱ, or Me), in low to good yields. Reductions of two of the precursor complexes in the presence of THF have given the related THF adduct complexes, L(THF)Mg?Mg(THF)L (R=Me; R′=Prⁱ) and LMg?Mg(THF)L (R=Prⁱ; R′=Me) in trace yields. The X‐ray crystal structures of all magnesium(I) complexes were obtained. DFT calculations on the unsolvated examples reveal their Mg?Mg bonds to be covalent and of high s‐character, while Ph???Mg bonding interactions in the compounds were found to be weak at best.     

Organometallic polymers. III. Organometallic modifications of diene polymers

A process for the chemical modification of polybutadienes and natural rubber by various metallocene compounds is described. Soluble products of up to 43% ferrocene content were obtained. The effect of substrate, metallocene, and reaction conditions on the course and extent of substitution was investigated. The glass transition temperature T_g was found to increase considerably with the degree of substitution, e.g., cis-polybutadiene substituted with ferrocene (18 mole-%) has a T_g of 30°C, as compared with ?91°C for the unsubstituted polymer.     

Contribution to the mechanism of copolymerization of phenylvinyl alkyl ethers and thioethers with maleic anhydride

The equilibrium constants of the charge-transfer complex monomers of phenylvinyl alkyl ethers (I) and thioethers (II) with maleic anhydride (MAn) were determined by the transformed Benessi—Hildebrand NMR method, and it was found that the bulkiness of alkyl groups had no significant influence on the equilibrium constant. The rate of copolymerization, however, was largely dependent on the bulkiness of the alkyl groups in the phenylvinyl alkyl ether series. The rate of copolymerization of I (R = Et; sec-Bu) and II (R = Et; sec-Bu) with MAn was proportional to the square root of AIBN concentration, and intrinsic viscosity of poly-I (R = Et)-co-MAn was proportional to the reciprocal square root of AIBN concentration. Spontaneous copolymerization did not occur, but I (R = Et) copolymerizes with MAn in the presence of oxygen; II did not copolymerize with MAn in the presence of oxygen; nor in the presence of peroxide initiators. In the copolymerization of I (R = Et) and MAn, it was found that molecular weight increases with conversion. By applying the generalized model described by Shirota and co-workers, the reactivity ratios k_1c/k₁₂ and k_2c/₂₁ for copolymerization of I (R = Et) and II (R = Et) with MAn were calculated from the change of copolymerization rate with monomer feed at constant total monomer concentration.     

Copper(I) nitrile complexes,part IV. Mechanism of copper(II) acetate and trifluoroacetate reduction by copper in acetonitrile in the presence of free carboxylic acid

Summary Copper(II) carboxylates, Cu(O₂CR)₂, R = Me or CF₃, in acetonitrile are reduced to copper(I) complexes by copper metal in the presence of RCO₂H. No reduction however, was observed in the absence of the acid. The CuO₂CMe, Cu(O₂CCF₃)(MeCN) and Cu(O₂CCF₃)(CF₃CO₂H)₂(MeCN)₄, complexes were isolated from the reaction mixture. Copper(I) species are stabilized by coordination of diacetamide or isoamide, a reaction product of the free acid and nitrite. Copper(I) carboxylate is obtained after decomposition of the coordinated species to the original acid and nitrite.Part III: R. J. Hurtado, R. V. Casillas and T. Ogura,Transition Met. Chem.,2, 91 (1977).To whom correspondence should be directed. Reprints of the article are not available.     

γ-Radiolysis of ketone polymers. I. Studies of symmetrical aliphatic ketones as model compounds

γ-Radiolysis of model ketones of the general structure R(C?O)R, neat and in hydrocarbon solution, show that the radio-chemical degradation of these aliphatic ketones can be explained by mechanisms analogous to those generally accepted for the photochemical decompositions of the same compounds. The G (type I) and G (type II) yields are found to decrease with increasing total chain length of the ketone as monitored by the products (R? H) and (CH₃CO? R), respectively. Differences in the relative yields of type I and II products are attributed to the higher incident energies involved in γ-radiolysis as compared to ultraviolet photolysis. Evidence is presented for energy transfer from paraffinic solvents to aliphatic ketonic solutes. Solid- and condensed-phase studies show the importance of rotational and diffusional mobility to the yields of the type II and I processes, respectively.     

Inorganic reaction mechanisms. vol. 4 (A chemical society specialist report) : A. McAuley,Senior reporter,The Chemcial Society,London, 1976, xviii + 398 pages, £ 23.00, $63.25.

The palladium(I) and platinum(I) complexes [(CH₃NC)₆M₂]²⁺ undergo substitution reactions with isocyanides, phosphines and halide or pseudohalide ions. With triphenylphosphine, axial substitution is preferred. The product [(CH₃NC)₅(Ph₃P)Pd₂]²⁺ is fluxional.     

Dibenz [b,f]-1, 4-oxazepin-11 (10 H)-one und Dibenz [b,e]-1, 4-oxazepin-11 (5 H)-one. 12. Mitteilung über siebengliedrige Heterocyclen

The syntheses of dibenzo [b, f]-1, 4-oxazepin-11 (10 H)-ones (I) with electron-attracting substituents in position 2 by ring closure of the sodium salts of 2-halogeno-2′-hydroxy-benzanilides (II) are described. The reaction of II (R = SO₂·N(CH₃)₂) in N-methylpyrrolidone also led, by SMILES rearrangement, to the isomeric minor product dibenzo [b, e]-1, 4-oxazepin-11 (5 H)-one (III; R = SO₂·N(CH₃)₂), whose constitution was proven by synthesis from VI. In the case of II (R = SO₂·CH₃), the 5-methylsulfonyl-2-(2-hydroxyanilino)-benzoic acid (VI; R = SO₂·CH₃) was obtained directly after hydrolysis. The lactam I (R = NO₂) was rearranged to the corresponding acid VI by heating with dilute caustic soda.     

Reaktionen von Tetraphosphortrichalkogeniden mit Alkyliodiden

Reactions of Tetraphosphorus Trichalcogenides with Alkyl Iodides Reactions of alkyl iodides RI (R = CHI₂, CH₂I or tert-Butyl) with P₄E₃ (E = S or Se) under the influence of light resulted in cleavage of the basal P₃ ring. β-P₄E₃(I)R was formed initially, then it rearranged to the more stable α-P₄E₃(I)R structure. ³¹P NMR data of these products were measured and discussed, along with ⁷⁷Se data for α- and β-P₄⁷⁷SeSe₂(I)CHI₂. On reaction of P₄S₃ with tert-butyl iodide in CS₂ or with sec-butyl iodide or iso-propyl iodide in dioxane, the new type of compounds P₅S₂R was observed. In this a sulfur bridge of P₄S₃ is replaced by a P? R group. ³¹P-NMR data for these compounds are reported.     

Catalysis in aromatic nucleophilic substitution. Note II. Piperidino substitution reactions of some 2-l-3-nitrothiophenes and 2-l-5-nitrothiophenes in methanol and benzene

The rates of piperidino substitution of some 2-L-3-nitrothiophenes (I) and 2-L-5-nitrothiophenes (II) (L = Cl, Br, I, OC₆H₄NO₂-p, and SO₂Ph) have been measured in methanol and in benzene at various piperidine concentrations. The reactivity of compounds (I) is not affected by the piperidine concentration in both methanol and benzene, except for the case of L = I (Ic). Probably due to association effects, the reactivity of Ic in benzene decreases as the piperidine concentration is increased. The reactions of compounds II follow overall second order kinetics in methanol while in benzene a different behaviour is observed as a function of the nature of the leaving group. In fact, the piperidino substitutions of IIa-c (L = Cl, Br, I) are mildly accelerated at high piperidine concentrations (a moderate solvent effect); on the contrary the reactivity of IId and e shows a strong dependence on the piperidine concentration, pointing out a genuine base catalysis.     

Electrophilic aromatic substitution under chemical ionization conditions. Methylamine and ammonia as reagent gases

For compounds C₆H₅X (X?Cl, Br, I) under chemical ionization conditions, methylamine causes ipso substitution of X by [NH₂CH₃]⁺ and by [NH₂]⁺˙. C₆H₅F is less reactive; it gives some [C₆H₅NH₂]⁺˙. Nitrobenzene gives an adduct ion [M+CH₃NH₃]⁺, a reduction product ion [C₆H₅NO₂]⁺˙, and an ion at m/z93, probably a substitution product [C₆H₅NH₂]⁺˙, but no [C₆H₅NH₂CH₃]⁺. It is also shown that the ion m/z94, formed from nitrobenzene with ammonia as reagent gas, is a substitution product rather than a reduction product ion. Carbonyl compounds C₆H₅. CO. X give adduct ions and some substitution, mainly [C₆H₅NH₂]⁺˙.