Anilinolysis of nitro‐substituted diphenyl ethers in acetonitrile: The effect of some ortho‐substituents on the mechanism of SNAr reactions

Rate data are reported for the reactions of a series of X‐phenyl 2,4,6‐trinitrophenyl ethers 1a–e [X = H, 4‐NO₂, 2‐NO₂, 2,4‐(NO₂)₂, or 2,6‐(NO₂)₂] with substituted anilines 2a–e [Y = H, 2‐CH₃, 2,4‐(CH₃)₂, 2,6‐(CH₃)₂, or N‐CH₃] in acetonitrile as solvent. For individual amine, kinetic data show that there is little steric hindrance to attack at the 1‐position of the parent molecules, even in the presence of di‐ortho substitution. With each substrate, however, there is evidence for significant steric interactions; such effects leading to rate retardation were very severe for 2,6‐dimethylaniline 2d (2,6‐(CH₃)₂) and N‐methylaniline 2e (Y = N‐CH₃), the deactivating effect of N‐CH₃ in most cases is slightly higher than that of 2,6‐(CH₃)₂. However, the reactions with 2e are base catalyzed whereas those of 2d are not. The corresponding reactions with aniline 2a (Y = H) and mono‐ortho methyl‐substituted aniline 2b (Y = CH₃) are wholly base catalyzed. Only with the dinitro substrates, an uncatalyzed reaction is observed and when X = 2,6‐(NO₂)₂ this pathway takes all the reaction flux. A rationale is provided for the dichotomy of amine effects observed in this investigation. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 37–49, 2010     

The influence of some steric and electron effects on the mechanism of aromatic nucleophilic substitution (SNAr) reactions in nonpolar solvent

Kinetic studies are reported for the reactions with aniline in benzene of a series of X‐phenyl 2,4,6‐trinitrophenyl ethers [X = H; 2‐, 3‐, 4‐CH₃; 2,4‐, or 2,6‐(CH₃)₂] a–f , and the results compared with those of the corresponding nitro derivatives. In the methyl series, kinetic data show that increasing substitution reduces drastically the rates of reactions indicative of the operation of some kind of steric effect. The unfavorable steric congestion at the reaction center appears to be unimportant in determining the kinetic order of the reactions. In general, the second‐order rate constants k_A depend linearly on the square of nucleophile concentration. The change in the kinetic form observed in the nitro derivatives may be largely due to the electron‐withdrawing effect of the group. With the 2,6‐dinitro derivative, however, the uncatalyzed pathway k₂ takes all the reaction flux. Steric hindrance to intermolecular proton transfer from base to the ethereal oxygen of the intermediate is sufficient to make the base‐catalyzed pathway insignificant relative to the k₂ pathway. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 744–750, 2005     

Formation of Stable Rhodium η6‐Arene Complexes with Aniline Derivatives

Three new, hitherto unknown, rhodium complexes with aniline and two of its derivatives (2, 6‐dimethylaniline and N‐methylaniline) are presented. All complexes have been characterized by X‐ray analysis.     

Sensitive determination of chloroanilines in water samples by hollow fiber‐based liquid‐phase microextraction prior to capillary electrophoresis with amperometric detection

A hollow fiber‐based liquid‐phase microextraction method has been developed for enrichment of trace chloroanilines in water samples. Target analytes including aniline, three mono‐chlorinated aniline isomers (o‐chloroaniline, m‐chloroaniline, and p‐chloroaniline) and four mono‐chlorinated methylaniline isomers (2‐chloro‐4‐methylaniline, 3‐chloro‐4‐methylaniline, 4‐chloro‐2‐methylaniline, and 5‐chloro‐2‐methylaniline) were determined by CE with amperometric detection after microextraction. Several factors that affect separation, detection, and extraction efficiency were investigated. Under the optimum conditions, eight aniline compounds could be well separated from other components coexisting in water samples within 25 min, exhibiting a linear calibration over three orders of magnitude (r > 0.998); the obtained enrichment factors were between 51 and 239, and the LODs were in the range of 0.01–0.1 ng/mL. The proposed method has been applied for the analyses of real environmental water and sewage samples with relative recoveries in the range of 83–108%.     

2,4,6‐Trimethyl‐N‐nitro­aniline

In 2,4,6‐trimethyl‐N‐nitro­aniline (alternatively called mesitylnitramine), C₉H₁₂N₂O₂, the primary nitramino group is planar with a short N—N bond and is nearly perpendicular to the aromatic ring. The methyl group located in the para position is disordered, each H atom having half‐occupancy. The mol­ecules are linked together along the [100] axis by inter­molecular N—H⋯O hydrogen bonds.     

Ruthenium‐Catalyzed Alkylation of Indoles with Tertiary Amines by Oxidation of a sp3 C?H Bond and Lewis Acid Catalysis

Ruthenium porphyrins (particularly [Ru(2,6‐Cl₂tpp)CO]; tpp=tetraphenylporphinato) and RuCl₃ can act as oxidation and/or Lewis acid catalysts for direct C‐3 alkylation of indoles, giving the desired products in high yields (up to 82 % based on 60–95 % substrate conversions). These ruthenium compounds catalyze oxidative coupling reactions of a wide variety of anilines and indoles bearing electron‐withdrawing or electron‐donating substituents with high regioselectivity when using tBuOOH as an oxidant, resulting in the alkylation of N‐arylindoles to 3‐{[(N‐aryl‐N‐alkyl)amino]methyl}indoles (yield: up to 82 %, conversion: up to 95 %) and the alkylation of N‐alkyl or N‐H indoles to 3‐[p‐(dialkylamino)benzyl]indoles (yield: up to 73 %, conversion: up to 92 %). A tentative reaction mechanism involving two pathways is proposed: an iminium ion intermediate may be generated by oxidation of an sp³ C? H bond of the alkylated aniline by an oxoruthenium species; this iminium ion could then either be trapped by an N‐arylindole (pathway A) or converted to formaldehyde, allowing a subsequent three‐component coupling reaction of the in situ generated formaldehyde with an N‐alkylindole and an aniline in the presence of a Lewis acid catalyst (pathway B). The results of deuterium‐labeling experiments are consistent with the alkylation of N‐alkylindoles via pathway B. The relative reaction rates of [Ru(2,6‐Cl₂tpp)CO]‐catalyzed oxidative coupling reactions of 4‐X‐substituted N,N‐dimethylanilines with N‐phenylindole (using tBuOOH as oxidant), determined through competition experiments, correlate linearly with the substituent constants σ (R²=0.989), giving a ρ value of ?1.09. This ρ value and the magnitudes of the intra‐ and intermolecular deuterium isotope effects (k_H/k_D) suggest that electron transfer most likely occurs during the initial stage of the oxidation of 4‐X‐substituted N,N‐dimethylanilines. Ruthenium‐catalyzed three‐component reaction of N‐alkyl/N‐H indoles, paraformaldehyde, and anilines gave 3‐[p‐(dialkylamino)benzyl]indoles in up to 82 % yield (conversion: up to 95 %).     

Room‐temperature Suzuki–Miyaura cross‐coupling reaction with α‐diimine Pd(II) catalysts

An α‐diimine Pd(II) complex containing chiral sec‐phenethyl groups, {bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dichloropalladium (rac‐ C1 ), was synthesized and characterized. rac‐ C1 was applied as an efficient catalyst for the Suzuki–Miyaura cross‐coupling reaction between various aniline halides and arylboronic acid in PEG‐400–H₂O at room temperature. Among a series of aniline halides, rac‐ C1 did not catalyze the cross‐coupling of aniline chlorides and fluorides but efficiently catalyzed the cross‐coupling of aniline bromides and iodides with phenylboronic acid. The catalytic activity reduced slightly with increasing steric hindrance of the aniline bromides. The complexes {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]‐2,3‐butadiene}dichloropalladium and {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]acenaphthene}dichloropalladium were also found to be efficient catalysts for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

Palladaphosphacyclobutenes as catalysts in Heck and Suzuki reactions

Heck reactions of aryl halides with various olefins and Suzuki reactions of aryl halides with phenylboronic acid catalyzed by palladaphosphacyclobutene have been investigated. The scope of the Heck reaction has been investigated in N,N‐dimethylacetamide at 140 °C using NaOAc as base. Using 0.1% molar ratio of palladaphosphacyclobuyenes, aryl bromides were converted into 1,2‐substitutedethene products in good to high yields through coupling with both vinylarenes and acrylates. Actived aryl chloride reacted with styrene to afford 1,2‐substitutedethene products in moderate yields. The scope of the Suzuki reaction has been conducted in toluene at 110 °C using Cs₂CO₃ as base. Using 0.1% molar ratio of palladaphosphacyclobutene, aryl bromides reacted with phenylboronic acid to afford diaryl derivatives in excellent yield. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of Branched Alkylboronates by Copper‐Catalyzed Allylic Substitution Reactions of Allylic Chlorides with 1,1‐Diborylalkanes

Reported herein is a copper‐catalyzed S_N2′‐selective allylic substitution reaction using readily accessible allylic chlorides and 1,1‐diborylalkanes, a reaction which proceeds with chemoselective C?B bond activation of the 1,1‐diborylalkanes. In the presence of a catalytic amount of [Cu(IMes)Cl] [IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazole‐2‐ylidene] and LiOtBu as a base, a range of primary and secondary allylic chlorides undergo the S_N2′‐selective allylic substitution reaction to produce branched alkylboronates. The synthetic utilities of the obtained alkylboronates are also presented.     

Regio‐ and Enantioselective Synthesis of N‐Allylindoles by Iridium‐Catalyzed Allylic Amination/Transition‐Metal‐Catalyzed Cyclization Reactions

Regio‐ and enantioselective synthesis of N‐allylindoles was realized through an iridium‐catalyzed asymmetric allylic amination reaction with 2‐alkynylanilines and subsequent transition‐metal‐catalyzed cyclization reactions. The highly enantioenriched allylic amines prepared from Ir‐catalysis were treated with catalytic amount of NaAuCl₄ ? 2 H₂O or PdCl₂ providing various substituted N‐allylindoles in excellent yields and enantioselectivities.     

Mechanistic Insight into Hydroboration of Imines from Combined Computational and Experimental Studies

Boron Lewis acid-catalyzed and catalyst-free hydroboration reactions of imines are attractive due to the mild reaction conditions. In this work, the mechanistic details of the hydroboration reactions of two different kinds of imines with pinacolborane (HBpin) are investigated by combining density functional theory calculations and some experimental studies. For the hydroboration reaction of N-(α-methylbenzylidene)aniline catalyzed by tris[3,5-bis(trifluoromethyl)phenyl]borane (BAr^F₃), our calculations show that the reaction proceeds through a boron Lewis acid-promoted hydride transfer mechanism rather than the classical Lewis acid activation mechanism. For the catalyst- and solvent-free hydroboration reaction of imine, N-benzylideneaniline, our calculations and experimental studies indicate that this reaction is difficult to occur under the reaction conditions reported previously. With a combination of computational and experimental studies, we have established that the commercially available BH₃ ⋅ SMe₂ can serve as an efficient catalyst for the hydroboration reactions of N-benzylideneaniline and similar imines. The hydroboration reactions catalyzed by BH₃ ⋅ SMe₂ are most likely to proceed through a hydroboration/B−H/B−N σ-bond metathesis pathway, which is very different from that of the reaction catalyzed by BAr^F₃.     

Direct CH Amidation of Benzoic Acids to Introduce meta‐ and para‐Amino Groups by Tandem Decarboxylation

The Ir‐catalyzed mild C?H amidation of benzoic acids with sulfonyl azides was developed to give reactions with high efficiency and functional‐group compatibility. Subsequent protodecarboxylation of ortho‐amidated benzoic acid products afforded meta‐ or para‐substituted (N‐sulfonyl)aniline derivatives, the latter being inaccessible by other C?H functionalization approaches. The decarboxylation step was compatible with the amidation conditions, enabling a convenient one‐pot, two‐step process.     

Iminophosphine palladium(II) complexes: synthesis,characterization, and application in Heck cross‐coupling reaction of aryl bromides

Palladium(II) complexes containing phosphorus and nitrogen donor atoms (iminophosphine), dichlorido{N‐[2‐(diphenylphosphino)benzylidene]‐2‐trifluoromethylaniline}palladium(II) 1 , dichlorido{N‐[2‐(diphenylphosphino)benzylidene]‐3‐trifluoromethylaniline}palladium(II) 2 , dichlorido{N‐[2‐(diphenylphosphino)benzylidene]‐2‐methylaniline}palladium(II) 3 , dichlorido{N‐[2‐(diphenylphosphino)benzylidene]‐3‐methylaniline}palladium(II) 4 have been successfully synthesized and fully characterized by FT‐IR and NMR (¹H, ³¹P, ¹⁹F, and ¹³C) spectroscopy techniques. These complexes were first step tested in the reaction of bromobenzene and styrene to determine the optimal coupling reaction conditions and then successfully applied as catalysts for Heck cross‐coupling reactions of activated and deactivated aryl bromides with styrene derivatives and several acrylates. Copyright © 2014 John Wiley & Sons, Ltd.     

The Self Oxidation Reduction of N-Arylhydroxylamines

The reactions of N-phenylhydroxylamine in the presence of dry hydrogen chloride to form azoxybenzene, aniline, 2-chloroaniline and 4-chloroaniline were studied. The molar ratio of the azoxybenzene and aniline obtained was very close to one. A similar reaction was also observed for 2-methyl- and 4-methyl-N-phenylhydroxylamine. A reasonable explanation is that N-phenylhydroxylamine undergoes a self oxidation reduction reaction to give aniline and nitrosobenzene, and the latter subsequently reacts with N-phenylhydroxylamine to give azoxybenzene. The reaction of N-phenylhydroxylamine, catalyzed by trifluoroacetic acid to yield azoxybenzene, was previously studied by Okamoto et al. and was suspected to undergo a similar reaction. We repeated the reaction and evidence for the same self oxidation reduction reaction was found. A mechanism involving the anilenium ion is proposed to account for this reaction.     

The influence of sulfur substituents on the molecular geometry and packing of thio derivatives of N‐methylphenobarbital

The room‐temperature crystal structures of four new thio derivatives of N‐methylphenobarbital [systematic name: 5‐ethyl‐1‐methyl‐5‐phenylpyrimidine‐2,4,6(1H,3H,5H)‐trione], C₁₃H₁₄N₂O₃, are compared with the structure of the parent compound. The sulfur substituents in N‐methyl‐2‐thiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐2‐thioxo‐1,2‐dihydropyrimidine‐4,6(3H,5H)‐dione], C₁₃H₁₄N₂O₂S, N‐methyl‐4‐thiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐4‐thioxo‐3,4‐dihydropyrimidine‐2,6(1H,5H)‐dione], C₁₃H₁₄N₂O₂S, and N‐methyl‐2,4,6‐trithiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenylpyrimidine‐2,4,6(1H,3H,5H)‐trithione], C₁₃H₁₄N₂S₃, preserve the heterocyclic ring puckering observed for N‐methylphenobarbital (a half‐chair conformation), whereas in N‐methyl‐2,4‐dithiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐2,4‐dithioxo‐1,2,3,4‐tetrahydropyrimidine‐6(5H)‐one], C₁₃H₁₄N₂OS₂, significant flattening of the ring was detected. The number and positions of the sulfur substituents influence the packing and hydrogen‐bonding patterns of the derivatives. In the cases of the 2‐thio, 4‐thio and 2,4,6‐trithio derivatives, there is a preference for the formation of a ring motif of the R₂²(8) type, which is also a characteristic of N‐methylphenobarbital, whereas a C(6) chain forms in the 2,4‐dithio derivative. The preferences for hydrogen‐bond formation, which follow the sequence of acceptor position 4 > 2 > 6, confirm the differences in the nucleophilic properties of the C atoms of the heterocyclic ring and are consistent with the course of N‐methylphenobarbital thionation reactions.     

Nucleophilic addition to the double bond of 2,4,6-trinitrostyrene and transformations of adducts

Conditions were found under which 2,4,6-trinitrostyrene derived from 2,4,6-trinitrotoluene adds nucleophiles (thiophenol, aniline, and aliphatic amines) at the vinyl fragment to form the corresponding β-X-ethyl-2,4,6- trinitrobenzenes (X = PhS, PhNH, or R₂N). In the reactions with primary aromatic amines, the initially formed adducts undergo intramolecular replacement of the nitro group followed by aromatization of the indolines that formed to the corresponding N-substituted 4,6-dinitroindoles. Dedicated to Corresponding Member of the Russian Academy of Sciences E. P. Serebryakov on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 1022–1025, April, 2005.     

Amine‐blocked polyisocyanates. I. Synthesis of novel N‐methylaniline‐blocked polyisocyanates and deblocking studies using hot‐stage fourier transform infrared spectroscopy

A series of substituted N‐methylaniline‐blocked polyisocyanates based on 4,4′‐methylenebis(phenyl isocyanate) and poly(tetrahydrofuran) were prepared and characterized thoroughly with FTIR, ¹H NMR, and ¹³C NMR spectroscopy methods. Compared with unsubstituted N‐methylaniline, a blocking agent with an electron‐releasing substituent at the para position took a shorter time, whereas those with an electron‐releasing substituent at the ortho position or an electron‐withdrawing substituent at the ortho and para positions took longer times for the blocking reaction. The thermal dissociation reactions of blocked polyisocyanates were carried out with an FTIR spectrophotometer attached to hot‐stage accessories under dynamic and isothermal conditions. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate the deblocking kinetics and activation parameters. The cure times of blocked polyisocyanates with hydroxyl‐terminated polybutadiene were also determined. The deblocking temperatures, the results of cure‐time studies, and the kinetic parameters revealed that the thermal dissociation of the N‐methylaniline‐blocked polyisocyanates was retarded by electron‐donating substituents and facilitated by electron‐withdrawing substituents. The action of N‐methylanilines as blocking agents for isocyanate was explained by the formation of a four‐center, intramolecularly hydrogen‐bonded ring structure during the thermal dissociation of the blocked polyisocyanates. The formation of such a hydrogen‐bonded ring structure was confirmed and supported by variable‐temperature ¹H NMR studies and entropy parameters, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1557–1570, 2007     

X‐ray crystal structures and MMA polymerization of cadmium(II) complexes with bidentate pyrazole ligands: the formation of monomers or dimers as a function of a methyl substituent on the pyrazole and aniline rings

The reaction of CdBr₂·4H₂O with ancillary ligands, N,N‐bis(1H‐pyrazolyl‐1‐methyl)aniline ( L₁ ), N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐p‐methylaniline ( L₂ ), N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐3,5‐dimethylaniline ( L₃ ), N,N‐bis(3,5‐dimethyl‐1H‐pyrazolyl‐1‐methyl)aniline ( L₄ ) and N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐2,6‐dimethylaniline ( L₅ ) in ethanol yields novel Cd(II) bromide complexes, [L₁CdBr₂]₂ , [L₂CdBr₂]₂ , [L₃CdBr₂]₂ , [L₄CdBr₂] and [L₅CdBr₂] . The X‐ray crystal structures of [L₁CdBr₂]₂ , [L₂CdBr₂]₂ and [L₃CdBr₂]₂ reveal a bromo‐bridged dimeric species with crystallographic inversion symmetry. Conversely, [L₄CdBr₂] and [L₅CdBr₂] exist as monomeric complexes, presumably due to the steric hindrance between the methyl substituents of the two pyrazole groups in the ligand and cadmium centre for [L₄CdBr₂] , and crowding around the cadmium metal by methyl substituents on the aniline residue in the ligand for [L₅CdBr₂] . The geometry at each Cd(II) centre for [L₁CdBr₂]₂ , [L₂CdBr₂]₂ and [L₃CdBr₂]₂ is best described as a distorted trigonal bipyramid. A distorted trigonal bipyramid is achieved in [L₄CdBr₂] by coordinative interaction of the nitrogen atom of the aniline unit and the cadmium atom with a σ plane of symmetry, based on the bond length of Cd―N_aniline (2.759(7) Å). [L₅CdBr₂] exists with a distorted tetrahedral geometry involving non‐coordination of the nitrogen atom of aniline and the Cd centre, resulting in the formation of an eight‐membered chelate ring. The catalytic activity of monomeric, five‐coordinated [L₄CdBr₂] in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60°C resulted in a higher molecular weight and a narrower polydispersity index (PDI) than those obtained with dimeric [L_nCdBr₂]₂ (L_n = L₁ , L₂ , L₃ ) or monomeric tetrahedral [L₅CdBr₂] . Copyright © 2014 John Wiley & Sons, Ltd.     

C−H Bond Activation/Arylation Catalyzed by Arene–Ruthenium–Aniline Complexes in Water

Water‐soluble arene–ruthenium complexes coordinated with readily available aniline‐based ligands were successfully employed as highly active catalysts in the C?H bond activation and arylation of 2‐phenylpyridine with aryl halides in water. A variety of (hetero)aryl halides were also used for the ortho‐C?H bond arylation of 2‐phenylpyridine to afford the corresponding ortho‐ monoarylated products as major products in moderate to good yields. Our investigations, including time‐scaled NMR spectroscopy and mass spectrometry studies, evidenced that the coordinating aniline‐based ligands, having varying electronic and steric properties, had a significant influence on the catalytic activity of the resulting arene–ruthenium–aniline‐based complexes. Moreover, mass spectrometry identification of the cycloruthenated species, {(η⁶‐arene)Ru(κ²‐C,N‐phenylpyridine)}⁺, and several ligand‐coordinated cycloruthenated species, such as [(η⁶‐arene)Ru(4‐methylaniline)(κ²‐C,N‐phenylpyridine)]⁺, found during the reaction of 2‐phenylpyridine with the arene–ruthenium–aniline complexes further authenticated the crucial roles of these species in the observed highly active and tuned catalyst. At last, the structures of a few of the active catalysts were also confirmed by single‐crystal X‐ray diffraction studies.     

Kinetics and mechanism of the aminolysis of O-ethyl S-phenyl dithiocarbonate in aqueous ethanol

The reactions of secondary alicyclic amines with the title substrate (PDTC) are subjected to a kinetic study in 44 wt.% aqueous ethanol, 25.0°C, ionic strength 0.2 M (KCl). Pseudo-first-order rate coefficients (k_obs) are found under amine excess. Linear plots of [N]/k_obs against 1/[N], where N is the free amine, are obtained for the reactions with piperidine, piperazine, 1-(2-hydroxyethyl)piperazine, and morpholine. The reaction with 1-formylpiperazine exhibits a linear plot of k_obs against [N]². These results are interpreted through a mechanism consisting of two tetrahedral intermediates: a zwitterionic ( T ^±) and an anionic ( T ^?), where the amine catalyzed proton transfer from T ^± to T ^? is partially rate determining for the four former reactions and is fully rate determining for the reaction of 1-formylpiperazine. The rate microcoefficients involved in the reaction scheme are either determined experimentally or estimated. Comparison with the corresponding microcoefficients reported for the same reactions in water reveals that the rate coefficient for formation of T ^± from reactants (k₁) is smaller and that for the reversal of this (k_?1) is larger in aqueous ethanol compared to water, in agreement with the expected structure of the corresponding transition state. Bronsted-type plots are obtained for k₁, k_?1, and K₁ (=k₁/k_?1) with slopes ca. 0.4, ?0.6, and 1.0, respectively. Comparison of the present stepwise reactions with the concerted ones found in the same aminolysis of O-ethyl 2,4,6,-(trinitrophenyl) dithiocarbonate indicates that T ^± is so destabilized by the change of PhS by the 2,4,6-trinitrobenzenethio group that T ^± no longer exists and becomes a transition state. © 1995 John Wiley & Sons, Inc.