48168-03-2Relevant articles and documents
Micellar Effects upon Substitutions by Nucleophilic Anions
Bunton, Clifford A.,Moffat, John R.
, p. 2896 - 2902 (1988)
Micellar effects upon of OH- with p-nitrophenyl diphenyl phosphate or 2,4-dinitro-1-chloronaphthalene have been examined with cetyltrimethylammonium surfactants, (CTAX, X=Cl, Br, (SO4)1/2).Demethylations of methyl benzene- or naphthalene-2-sulfonate by halide ion have been examined. in micelles of CTACl, CTABr, CTA(SO4)1/2, or cetyltrimethylammonium mesylate (CTAOMs) and for demethylation by OH- or SO32- in CTA(SO4)1/2 or CTAOMs.The rate enhancements have been treated in terms of concentrations of the substrates and the nucleophilic anion at the micellar surface.The anion concentrations depended upon nonspecific Coulombic and specific interactions that were calculated by solving the Poisson-Boltzmann equation.The same structural parameters were used in fitting data for reactions with Cl- or Br- as nucleophiles and for systems with Cl- or Br- as inert anions that were competing with OH- or SO32-.The treatment is applicable to mixtures of database to mixtures of dilute mono- and dianions.
Effect of heteroatom insertion at the side chain of 5-alkyl-1H-tetrazoles on their properties as catalysts for ester hydrolysis at neutral pH
Bhattacharya, Santanu,Vemula, Praveen Kumar
, p. 9677 - 9685 (2007/10/03)
Herein we introduce tetrazole and its suitably designed derivatives as powerful ester-cleaving reagents. By first performing a detailed ab initio computational study, we found that, in the side chain of 5-alkyl-1H-tetrazoles, introduction of a heteroatom (e.g., N, O, or S at the α-position of the tetrazole ring) raises the charge on the tetrazole nucleus significantly. All calculations have been performed using restricted Hartree-Fock (RHF) and hybrid ab initio/DFT (B3LYP) methods employing 6-31G* and 6-31+G* basis sets. To estimate the nucleophilicity of these reagents, the charges on conjugate bases of various tetrazole derivatives have been calculated using natural population (NBO) analysis in gas phase and in water. Free energy of protonation (fep) of the 1H-tetrazole derivatives (1-7), free energy of solvation, ΔGaq, and the corresponding pKa values have been calculated by self-consistent reaction field (SCRF) methods applying the polarized continuum model (PCM). Since the calculation indicates that incorporation of heteroatom leads to enhanced nucleophilicity in their deprotonated anionic tetrazole forms, a series of 5-substituted 1H-tetrazole derivatives have been synthesized. These compounds indeed catalyze the hydrolysis of p-nitrophenyl diphenyl phosphate (PNPDPP) and p-nitrophenyl hexanoate (PNPH) efficiently in cationic cetyl trimethylammonium bromide (CTABr) micelles at pH 7.0 and 25 °C. The pseudo-first-order rate constants (k obs) were determined for each catalyst against both substrates. The experimental and theoretical results show that, to achieve better k obs values for the cleavage of PNPDPP and PNPH under micellar conditions, charge on the N- atom (nucleophile) of conjugate base is important. Replacing the α-CH2 in alkyl substituent with S (3), NH (4), or O (5) enhances the accumulation of charge on N- in conjugate bases of tetrazoles and subsequently increases their intrinsic nucleophilic reactivity toward hydrolytic reactions. Significantly large rate enhancements were observed for the cleavage of PNPDPP and PNPH at pH 7.0 in the presence of catalytic system 5/CTABr over background (only CTABr). Tetrazole 4 (α-isomer) showed 4-5-fold superior reactivity over 6 (β-isomer) under identical conditions. Natural charges obtained from NBO analysis (B3LYP/ 6-31+G*) are -0.94 and -0.852 on N- in the conjugate bases of 4 and 6, respectively. This also predicts that 4 is a better nucleophile than 6. All the newly synthesized tetrazole derivatives in micellar media display true catalytic properties by cleaving several fold excess of substrates.
Laser flash photolysis kinetic studies of enol ether radical cations. Rate constants for heterolysis of α-methoxy-β-phosphatoxyalkyl radicals and for cyclizations of enol ether radical cations
Horner, John H.,Taxil, Elsa,Newcomb, Martin
, p. 5402 - 5410 (2007/10/03)
Two series of enol ether radical cations were studied by laser flash photolysis methods. The radical cations were produced by heterolyses of the phosphate groups from the corresponding α-methoxy-β-diethylphosphatoxy or β-diphenylphosphatoxy radicals that
