Nucleophilic Solvent Participation in the Solvolysis of Tertiary Bromoalkanes

The solvolysis of 2‐bromo‐2‐methylpropane ( 1B ), 2‐bromo‐2‐methylbutane ( 2B ), 2‐bromo‐2, 3‐di‐methylbutane ( 3B ), 2‐bromo‐2, 3, 3‐trimethylbutane ( 4B ), 3‐bromo‐3‐methylpentane ( 5B ), 3‐bromo‐2, 3‐dimethylpentane ( 6B ), 3‐bromo‐2, 2, 3‐trimethylpentane ( 7B ), 3‐bromo‐3‐ethylpentane ( 8B ), 3‐bromo‐3‐ethyl‐2‐methylpentane ( 9B ) and 2‐bromo‐2, 4, 4‐trimethylpentane ( 11B ) in 15 to 21 solvents was studied, and correlation analyses by using the single‐ and dual‐parameter Grunwald‐Winstein equations (Eqns 1 and 2) were examined. Substrates 7B, 9B and 11B showed excellent linear relationship (R ≥ 0.997) in the logk ‐ Y_Br plots and indicated limiting S_N1 mechanism for the solvolysis. On the other hand, bromides 1B‐6B and 8B gave linear correlations (R = 0.987–0.996) with the dual‐parameter (Y_Br and N_OTs) equation (2) only, which indicated the presence of significant nucleophilic solvent participation. Normal trends of reactivity due to the relief of B‐strain could be found in the poorly nucleophilic trifluoroethanol. Similar to the corresponding chlorides, the overwhelming influence of nucleophilic solvent assistance results in the observed inverse order of reactivity: k( 2B ) > k( 3B ), k( 5B ) > k( 6B ) and k( 8B ) > k( 9B ).     

A 2D Metal‐Organic Framework Based on 9‐(Pyridin‐4‐yl)‐9H‐carbazole‐3,6‐dicarboxylic Acid: Synthesis,Structure and Properties

A metal‐organic framework (MOF ) formulated as [Cd₂(μ₃‐L)₂(DMF )₄]•H₂O ( CdL ) [H₂L =9‐(pyridin‐4‐yl)‐ 9H ‐carbazole‐3,6‐dicarboxylic acid, DMF =N ,N ‐dimethylformamide] was synthesized under solvothermal condition. Crystal structural analysis reveals that CdL features the layered 2D framework with L^{2 −} ligands as 3‐connected nodes. The compound CdL emits blue‐violet light with the narrow emission peak and the emission maximum at 414 nm upon excitation at the maximum excitation wavelength of 340 nm. The compound CdL has a similar emission spectrum curve to the free H₂L ligand that indicates the emission of compound CdL should be originated from the coordinated L^{2 −} ligands.     

C–C bridged Ni(II) complexes bearing β‐keto‐9‐fluorenyliminato ligands prepared by different in situ bonding mechanisms and their use in catalytic (co)polymerization of norbornene and styrene

Two C–C bridged Ni(II) complexes bearing β‐keto‐9‐fluorenyliminato ligands with electron‐withdrawing groups (─CF₃), Ni{PhC(O)CHC[N(9‐fluorenyl)]CF₂}₂ (Ni 1 ) and Ni{CF₃C(O)CHC[N(9‐fluorenyl)]Ph}₂ (Ni 2 ), were synthesized by metal coordination reaction and different in situ bonding mechanisms. The C–C bridged bonds of Ni 1 were formed by in situ intramolecular trifluoromethyl and 9‐fluorenyl carbon–carbon cross‐coupling reaction and those of Ni 2 were formed by in situ intramolecular 9‐fluorenyl carbon–carbon radical coupling reaction mechanism. The obtained complexes were characterized using ¹H NMR spectroscopy and elemental analyses. The crystal and molecular structures of Ni 1 and Ni 2 with C–C bridged configuration were determined using X‐ray diffraction. Ni 1 and Ni 2 were used as catalysts for norbornene (NB) polymerization after activation with B(C₆F₅)₃ and the catalytic activities reached 10⁶ g_polymer mol_Ni^?1 h^?1. The copolymerization of NB and styrene catalyzed by the Ni 1 /B(C₆F₅)₃ system showed high activity (10⁵ g_polymer mol_Ni^?1 h^?1) and the catalytic activities decreased with increasing feed content of styrene. All vinyl‐type copolymers exhibited high molecular weight (10⁴ g mol^?1), narrow molecular weight distribution (M_w/M_n = 1.71–2.80), high styrene insertion ratios (11.13–50.81%) and high thermal stability (T_d > 380°C) and could be made into thin films with high transparency in the visible region (400–800 nm).     

Effects of diamines and their fluorinated groups on the color lightness and preparation of organosoluble aromatic polyimides from 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]‐hexafluoropropane

To investigate the position and amount of the CF₃ group affecting the coloration of polyimides (PIs), we prepared 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]hexafluoropropane ( 2 ) with four CF₃ groups with 2‐chloro‐5‐nitrobenzotrifluoride and 2,2‐bis(4‐hydroxyphenol)hexafluoropropane. A series of soluble and light‐colored fluorinated PIs ( 5 ) were synthesized from 2 and various aromatic dianhydrides ( 3a – 3f ). 5a – 5f had inherent viscosities ranging from 0.80 to 1.19 dL/g and were soluble in amide polar solvents and even in less polar solvents. The glass‐transition temperatures of 5 were 221–265 °C, and the 10% weight‐loss temperatures were above 493 °C. Their films had cutoff wavelengths between 343 and 390 nm, b* values (a yellowness index) ranging from 5 to 41, dielectric constants of 2.68–3.01 (1 MHz), and moisture absorptions of 0.03–0.29 wt %. In a comparison of the PI series 6 – 8 based on 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane, and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane, we found that the CF₃ group close to the imide group was more effective in lowering the color; this means that CF₃ of 5 , 7 , and 8f was more effective than that of 6c . The color intensity of the four PI series was lowered in the following order: 5 > 7 > 6 > 8 . The PI 5f , synthesized from diamine 2 and 4,4′‐hexafluoroisopropylidenediphthalic anhydride, had six CF₃ groups in a repeated segment, so it exhibited the lightest color among the four series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 922–938, 2003     

Synthesis of 3‐(ω‐Hydroxyalkoxy)isobenzofuran‐1(3H)‐ones by Trifluoroacetic Acid‐Mediated Lactonization of tert‐Butyl 2‐(1,3‐Dioxol‐2‐yl)‐ or 2‐(1,3‐Dioxan‐2‐yl)benzoates

An efficient two‐step method for the preparation of 3‐(2‐hydroxyethoxy)‐ or 3‐(3‐hydroxypropoxy)isobenzofuran‐1(3H)‐ones 3 has been developed. Thus, the reaction of 1‐(1,3‐dioxol‐2‐yl)‐ or 1‐(1,3‐dioxan‐2‐yl)‐2‐lithiobenzenes, generated in situ by the treatment of 1‐bromo‐2‐(1,3‐dioxol‐2‐yl)‐ or 1‐bromo‐2‐(1,3‐dioxan‐2‐yl)benzenes 1 with BuLi in THF at ?78°, with (Boc)₂O afforded tert‐butyl 2‐(1,3‐dioxol‐2‐yl)‐ or 2‐(1,3‐dioxan‐2‐yl)benzoates 2 , which can subsequently undergo facile lactonization on treatment with CF₃COOH (TFA) in CH₂Cl₂ at 0° to give the desired products in reasonable yields.     

Fluorosilicone elastomer based on the poly[(3,3,3‐trifluoropropyl)methyl‐siloxane‐co‐(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)methylsiloxane]

Fluorosilicone elastomer based on the poly[(3,3,3‐trifluoropropyl)methylsiloxane‐co‐(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)methylsiloxane] was studied. First, the synthesis of fluorosilicone polymer based on the poly[(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)methylsiloxane] (PNFHMS) was examined by the polymerization of 1,3,5‐tris(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)‐1,3,5‐trimethylcyclotrisiloxane (C₄F₉D3) by sodium hydroxide. On the contrast of the polymerization of the commercially available 1,3,5‐tris(3,3,3‐trifluoropropyl)‐1,3,5‐trimethylcyclotrisiloxane (CF₃D3), the polymerization of C₄F₉D3 with sodium hydroxide resulted in the formation of 1,3,5,7‐tetrakis(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)‐1,3,­5,7‐tetramethylcyclotetrasiloxane : [C₄F₉CH₂CH₂(CH₃)SiO]₄ (C₄F₉D4) as the major product. It was due to the easy occurrence of the depolymerization by the back‐biting mechanism, because C₄F₉D4 is more stable ­than 1,3,5,7‐tetrakis(3,3,3‐trifluoropropyl)‐1,3,5,7‐tetramethylcyclotetrasiloxane : [CF₃CH₂CH₂(CH₃)SiO]₄ (CF₃D4). The above result made us to conclude that it was difficult to apply the polymer based on PNFHMS to heat vulcanizable elastomers and to investigate the elastomer based on the poly[(3,3,3‐trifluoropropyl)methylsiloxane‐co‐(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)methylsiloxane]. C₄F₉D3 and CF₃D3 were co‐polymerized successfully by sodium hydroxide and formulated with the silica treated by CF₃D3. The use of silica treated with methylsilyl unit failed, because creep‐hardening phenomenon occurred. This elastomer was evaluated about some mechanical properties, and the resistance to organic solvents, and a fuel. The advantage that can be detected from the introduction of [C₄F₉C₂H₄‐(CH₃)SiO] unit was that the resistance to the polar solvents such as acetone and dimethylformamide was improved. Copyright © 2001 John Wiley & Sons, Ltd.     

Kinetics of the gas‐phase reactions of cyclo‐CF2CFXCHXCHX – (X = H,F, Cl) with OH radicals at 253–328 K

Rate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo‐CF₂CF₂CHFCH₂? (k₁), trans‐cyclo‐CF₂CF₂CHClCHF? (k₂), cyclo‐CF₂CFClCH₂CH₂? (k₃), trans‐cyclo‐CF₂CFClCHClCH₂? (k₄), and cis‐cyclo‐CF₂CFClCHClCH₂? (k₅) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H₂O? O₃? O₂? He gas mixture in an 11.5‐dm³ temperature‐controlled reaction chamber. Rate constants of k₁ = (5.52 ± 1.32) × 10^?13 exp[–(1050 ± 70)/T], k₂ = (3.37 ± 0.88) × 10^?13 exp[–(850 ± 80)/T], k₃ = (9.54 ± 4.34) × 10^?13 exp[–(1000 ± 140)/T], k₄ = (5.47 ± 0.90) × 10^?13 exp[–(720 ± 50)/T], and k₅ = (5.21 ± 0.88) × 10^?13 exp[–(630 ± 50)/T] cm³ molecule^?1 s^?1 were obtained at 253–328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%–15% uncertainty to the uncertainty of k₁–k₅. The reactivity trends of these OH radical reactions were analyzed by using a collision theory–based kinetic equation. The rate constants k₁–k₅ as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their C? H bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo‐CF₂CF₂CHFCH₂? , trans‐cyclo‐CF₂CF₂CHClCHF? , cyclo‐CF₂CFClCH₂CH₂? , trans‐cyclo‐CF₂CFClCHClCH₂? , and cis‐cyclo‐CF₂CFClCHClCH₂? , respectively, by scaling from the lifetime of CH₃CCl₃. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532–542, 2009     

Correlation of Solvolytic Reactivities. A New YBnBr Scale for Benzylic Bromides

Solvolysis of 2-bromo-2-(4′-fluoromethyl)phenyladamantane (4), and 2-bromo-2-(4′-trifluoromethyl)phenylpropane (5) were carried out in a number of solvents, and their rate constants measured. Significant deviation from linear logk-Y_Br plots was observed, and the order of reactivities, e.g., k(100M) > k(90E) > k(80A), was in the reverse order of Swain's solvent parameter B. Different extent of solvation to the localized and the delocalized cationic transition state was then likely to play an important role. Similar result was also found in the solvolysis of 1-bromo-2,2,2-trifluoro-1-(4′-methylphenyl)-1-phenylethane (6). A new Y scale, Y_BnBr, for the correlation of solvolytic reactivities of benzylic bromides based on k(4) was established. Intervention of solvent assistance in the solvolysis of 5 is discussed.     

Synthesis,characterization and antibacterial activity of 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoic acid and di‐isopropylammonium [3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoato] triphenylstannate(IV). The crystal structure of [HQ][SnPh3(o‐mpspa)]

Reaction of 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoic acid [H₂(o‐mpspa)] with SnPh₃OH in the presence of di‐isopropylamine resulted in the formation of the complex [HQ][SnPh₃(o‐mpspa)] (where HQ = di‐isopropylammonium cation and o‐mpspa = 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoato), which was characterized by mass spectrometry and vibrational spectroscopy, as well as by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The single‐crystal X‐ray structural analysis of the new complex shows a trigonal‐bipyramidal coordination geometry around the Sn atom where o‐mpspa behaves as a bidentate chelating ligand. Dimeric units arise from the existence of N? H…O hydrogen bonds between the NH₂ group of the di‐isopropylammonium cation and the oxygen atoms of the two neighbouring carboxylato groups. The bacteriostatic activity of the complex is also reported. Copyright © 2007 John Wiley & Sons, Ltd.     

Copper(II) Complexes with N‐(9‐anthracenyl)‐N′‐(3‐pyridyl)urea (L) and a Derivative of L: Synthesis,Structure, and Fluorescent Properties

Three copper(II) complexes, [Cu₂(OAc)₄L₂] · 2CH₃OH ( 1 ), [CuBr₂L′₂(CH₃OH)] · CH₃OH ( 2a ), and [CuBr₂L′₂(DMSO)] · 0.5CH₃OH ( 2b ) {L = N‐(9‐anthracenyl)‐N′‐(3‐pyridyl)urea and L′ = N‐[10‐(10‐methoxy‐anthronyl)]‐N′‐(3‐pyridyl)urea} have been synthesized by the reaction of L with the corresponding copper(II) salts. Complex 1 shows a dinuclear structure with a conventional “paddlewheel” motif, in which four acetate units bridge the two Cu^II ions. In complexes 2a and 2b , the anthracenyl ligand L has been converted to an anthronyl derivative L′, and the central metal ion exhibits a distorted square pyramidal arrangement, with two pyridyl nitrogen atoms and two bromide ions defining the basal plane and the apical position is occupied by a solvent molecule (CH₃OH in 2a and DMSO in 2b ).     

Ultrafast Relaxation Dynamics of the Excited States of 1‐Amino‐ and 1‐(N,N‐Dimethylamino)‐fluoren‐9‐ones

The dynamics of the excited states of 1‐aminofluoren‐9‐one (1AF) and 1‐(N,N‐dimethylamino)‐fluoren‐9‐one (1DMAF) are investigated by using steady‐state absorption and fluorescence as well as subpicosecond time‐resolved absorption spectroscopic techniques. Following photoexcitation of 1AF, which exists in the intramolecular hydrogen‐bonded form in aprotic solvents, the excited‐state intramolecular proton‐transfer reaction is the only relaxation process observed in the excited singlet (S₁) state. However, in protic solvents, the intramolecular hydrogen bond is disrupted in the excited state and an intermolecular hydrogen bond is formed with the solvent leading to reorganization of the hydrogen‐bond network structure of the solvent. The latter takes place in the timescale of the process of solvation dynamics. In the case of 1DMAF, the main relaxation pathway for the locally excited singlet, S₁(LE), or S₁(ICT) state is the configurational relaxation, via nearly barrierless twisting of the dimethylamino group to form the twisted intramolecular charge‐transfer, S₁(TICT), state. A crossing between the excited‐state and ground‐state potential energy curves is responsible for the fast, radiationless deactivation and nonemissive character of the S₁(TICT) state in polar solvents, both aprotic and protic. However, in viscous but strong hydrogen‐bond‐donating solvents, such as ethylene glycol and glycerol, crossing between the potential energy surfaces for the ground electronic state and the hydrogen‐bonded complex formed between the S₁(TICT) state and the solvent is possibly avoided and the hydrogen‐bonded complex is weakly emissive.     

Regioselective Synthesis of 6‐[Chloro(difluoro)methyl]salicylates by [3+3] Cyclocondensations of 1,3‐Bis(trimethylsilyloxy)buta‐1,3‐dienes with 1‐Chloro‐1,1‐difluoro‐4‐(trimethylsilyloxy)pent‐3‐en‐2‐one

The TiCl₄‐mediated [3+3] cyclocondensation of various 1,3‐bis(trimethylsilyloxy)buta‐1,3‐dienes with 1‐chloro‐1,1‐difluoro‐4‐(trimethylsilyloxy)pent‐3‐en‐2‐one provides a regioselective access to novel 6‐(chlorodifluoromethyl)salicylates (=6‐(chlorodifluoromethyl)‐2‐hydroxybenzoates) with very good regioselectivity. For selected products, it was demonstrated that the CF₂Cl group can be transformed to CF₂H and CF₂(Allyl) by free‐radical reactions.     

Synthesis,Structure, and Fluorescent Properties of Lanthanide Complexes Based on 8‐Hydroxyquinoline‐7‐carboxylic Acid

The lanthanide complex [Eu₃(8‐HQCA)₃(COOH)(OH)₂(H₂O)₃]_n · nH₂O (8‐HQCA = 8‐hydroxyquinoline‐7‐carboxylic acid) was synthesized and characterized. Single‐crystal X‐ray diffraction shows that the trinuclear structures are linked by ligands to form 2D layers. The results of DFT calculation shows that energy can be transferred effectively from the ligand to Eu^III ions. A series of heteronuclear complexes {[(Eu_1–xY_x)₃(8‐HQCA)₃(COOH) (OH)₂(H₂O)₃]_n · nH₂O (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8)} were synthesized and their luminescent properties were studied. The results showed that the doping of Y^III ions could change the fluorescent intensity of the Eu^III complex, but could not change their positions.     

Molecular structures of 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]‐ and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinates

The salts 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium saccharinate, C₉H₁₀F₄NO⁺·C₇H₄NO₃S⁻, (1), and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinate, C₉H₉F₅NO⁺·C₇H₄NO₃S⁻, (2), i.e. saccharinate (or 1,1‐dioxo‐1λ⁶,2‐benzothiazol‐3‐olate) salts of pyridinium with –CH₂OCH₂CF₂CF₂H and –CH₂OCH₂CF₂CF₃meta substituents, respectively, were investigated crystallographically in order to compare their fluorine‐related weak interactions in the solid state. Both salts demonstrate a stable synthon formed by the pyridinium cation and the saccharinate anion, in which a seven‐membered ring reveals a double hydrogen‐bonding pattern. The twist between the pyridinium plane and the saccharinate plane in (2) is 21.26 (8)° and that in (1) is 8.03 (6)°. Both salts also show stacks of alternating cation–anion π‐interactions. The layer distances, calculated from the centroid of the saccharinate plane to the neighbouring pyridinium planes, above and below, are 3.406 (2) and 3.517 (2) Å in (1), and 3.409 (3) and 3.458 (3) Å in (2).     

Synthesis of Three‐, Five‐, and Six‐Membered Heterocycles Derived from New β‐Amino‐α‐(trifluoromethyl) Alcohols

Nucleophilic trifluoromethylation of α‐imino ketones 2 , derived from arylglyoxal, with Ruppert–Prakash reagent (CF₃SiMe₃) offers a convenient access to the corresponding O‐silylated β‐imino‐α‐(trifluoromethyl) alcohols. In a ‘one‐pot’ procedure, by treatment with NaBH₄, these products smoothly undergo reduction and desilylation yielding the expected β‐amino‐α‐(trifluoromethyl) alcohols 4 . The latter were used as starting materials for the synthesis of diverse trifluoromethylated heterocycles, including aziridines 5 , 1,3‐oxazolidines 8 , 1,3‐oxazolidin‐2‐ones 9 , 1,3,2‐oxazaphospholidine 2‐oxides 10 , 1,2,3‐oxathiazolidine 2‐oxides 11 , and morpholine‐2,3‐diones 12 . An optically active 5‐(trifluoromethyl)‐substituted 1,3‐oxazolidin‐2‐one 9g was also obtained.     

4‐(3‐Azaniumylpropyl)morpholin‐4‐ium chloride hydrogen oxalate: an unusual example of a dication with different counter‐anions

The mixed organic–inorganic title salt, C₇H₁₈N₂O²⁺·C₂HO₄⁻·Cl⁻, forms an assembly of ionic components which are stabilized through a series of hydrogen bonds and charge‐assisted intermolecular interactions. The title assembly crystallizes in the monoclinic C2/c space group with Z = 8. The asymmetric unit consists of a 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dication, a hydrogen oxalate counter‐anion and an inorganic chloride counter‐anion. The organic cations and anions are connected through a network of N—H...O, O—H...O and C—H...O hydrogen bonds, forming several intermolecular rings that can be described by the graph‐set notations R₃³(13), R₂¹(5), R₁²(5), R₂¹(6), R₂³(6), R₂²(8) and R₃³(9). The 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dications are interconnected through N—H...O hydrogen bonds, forming C(9) chains that run diagonally along the ab face. Furthermore, the hydrogen oxalate anions are interconnected via O—H...O hydrogen bonds, forming head‐to‐tail C(5) chains along the crystallographic b axis. The two types of chains are linked through additional N—H...O and O—H...O hydrogen bonds, and the hydrogen oxalate chains are sandwiched by the 4‐(3‐azaniumylpropyl)morpholin‐4‐ium chains, forming organic layers that are separated by the chloride anions. Finally, the layered three‐dimensional structure is stabilized via intermolecular N—H...Cl and C—H...Cl interactions.     

Incorporating two different chromophores onto a silicon atom: the crystal structure and photophysical properties of 9‐{4‐[(9,9‐dimethyl‐9H‐fluoren‐2‐yl)dimethylsilyl]phenyl}‐9H‐carbazole

The crystal structure of the title bifunctional silicon‐bridged compound, C₃₅H₃₁NSi, (I), has been determined. The compound crystallizes in the centrosymmetric space group P2₁/c. In the crystal structure, the pairs of aryl rings in the two different chromophores, i.e. 9‐phenyl‐9H‐carbazole and 9,9‐dimethyl‐9H‐fluorene, are positioned orthogonally. In the crystal packing, no classical hydrogen bonding is observed. UV–Vis absorption and fluorescence emission spectra show that the central Si atom successfully breaks the electronic conjugation between the two different chromophores, and this was further analysed by density functional theory (DFT) calculations.     

Rate constants for reaction of 1,2‐dimethylimidazole with benzyl bromide in ionic liquids and organic solvents

The rate constant for the Menschutkin reaction of 1,2‐dimethylimidazole with benzyl bromide to produce 3‐benzyl‐1,2‐dimethylimidazolium bromide was determined in a number of ionic liquids and molecular organic solvents. The rate constants in 12 ionic liquids are in the range of (1.0–3.2) × 10^?3 L mol^?1 s^?1 and vary with the solvent anion in the order (CF₃SO₂)₂ N^? < PF₆^? < BF₄^?. Variations with the solvent cation (butylmethylimidazolium, octylmethylimidazolium, butyldimethylimidazolium, octyldimethylimidazolium, butylmethylpyrrolidinium, and hexyltributylammonium) are minimal. The rate constants in the ionic liquids are comparable to those in polar aprotic molecular solvents (acetonitrile, propylene carbonate) but much higher than those in weakly polar organic solvents and in alcohols. Correlation of the rate constants with the solvatochromic parameter E _T(30) is reasonable within each group of similar solvents but very poor when all the solvents are correlated together. Better correlation is obtained for the organic solvents by using a combination of two parameters, π* (dipolarity/polarizibility) and α (hydrogen bond acidity), while additional parameters such as δ (cohesive energy density) do not provide any further improvement. © 2004 Wiley Periodicals, Inc. *

1 This article is a US Government work and, as such, is in the public domain of the United States of America.

Int J Chem Kinet 36: 253–258, 2004     

Kinetics of the polycondensation and copolycondensation of bis(3‐hydroxypropyl) terephthalate and bis(4‐hydroxybutyl) terephthalate

The kinetics of the polycondensation and copolycondensation reactions of bis(3‐hydroxypropyl) terephthalate (BHPT) and bis(4‐hydroxybutyl) terephthalate (BHBT) as monomers were investigated at 270 °C in the presence of titanium tetrabutoxide as a catalyst. BHPT was prepared by the ester interchange reaction of dimethyl terephthalate and 1,3‐propanediol (1,3‐PD). Through the same method adopted for BHPT synthesis, BHBT was prepared with 1,4‐butanediol instead of 1,3‐PD. With second‐order kinetics applied for polycondensation, the rate constants of the polycondensation of BHPT and BHBT, k₁₁ and k₂₂, were calculated to be 4.08 and 4.18 min^?1, respectively. The rate constants of the cross reactions in the copolycondensation of BHPT and BHBT, k₁₂ and k₂₁, were calculated with results obtained from proton nuclear magnetic resonance spectroscopy analysis. The rate constants during the copolycondensation of BHPT and BHBT at 270 °C decreased in the order k₁₂ > k₂₂ > k₁₁ > k₂₁, indicating that the reactivity of BHBT was larger than that of BHPT at 270 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2435–2441, 2002