Benzyl Iodide Research Articles

Formation of Self-Assembled Monolayers of π-Conjugated Molecules on TiO2 Surfaces by Thermal Grafting of Aryl and Benzyl Halides

We demonstrate the formation of molecular monolayers of π-conjugated organic molecules on nanocrystalline TiO(2) surfaces through the thermal grafting of benzyl and aryl halides. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were used to characterize the reactivity of aryl and benzyl chlorides, bromides, and iodides with TiO(2) surfaces, along with controls consisting of nonhalogenated compounds. Our results show that benzyl and aryl halides follow a similar reactivity trend (I > Br > Cl >> H). While the ability to graft benzyl halides is consistent with the well-known Williamson ether synthesis, the grafting of aryl halides has no similar precedent. The unique reactivity of the TiO(2) surface is demonstrated using nuclear magnetic resonance spectroscopy to compare the surface reactions with the liquid-phase interactions of benzyl and aryl iodides with tert-butanol and -butoxide anion. While the aryl iodides show no detectable reactivity with a tert-butanol/tert-butoxide mixture, they react with TiO(2) within 2 h at 50 °C. Atomic force microscopy studies show that grafting of 4-iodo-1-(trifluoromethyl)benzene onto the rutile TiO(2)(110) surface leads to a very uniform, homogeneous molecular layer with a thickness of ∼0.45 nm, demonstrating formation of a self-terminating molecular monolayer. Thermal grafting of aryl iodides provides a facile route to link π-conjugated molecules to TiO(2) surfaces with the shortest possible linkage between the conjugated electron system and the TiO(2).

Synthesis of new aza crown macrocycles and lariat ethers

Abstract Aza crown macrocycles 3a,b were synthesized in good yield by condensation reaction of 1,3- and 1,4-bis(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)alkanes 1a,b with bis-aldehydes 2a,b. Reactions of 3a,b with methyl or benzyl iodide furnished the target lariat ethers 4a–d.

ChemInform Abstract: 2‐(p‐Tolylsulfinyl)benzyl Halides as Efficient Precursors of Optically Pure trans‐2,3‐Disubstituted Aziridines.

AbstractBase‐mediated treatment of the benzyl iodide (I) with N‐sulfinylaldimines allows a highly efficient access to optically pure trans‐2,3‐disubstituted aziridines.

2‐(p‐Tolylsulfinyl)benzyl Halides as Efficient Precursors of Optically Pure trans‐2,3‐Disubstituted Aziridines

Aziridination of (R)-N-sulfinylaldimines (aryl, heteroaryl and alkenyl derivatives) with 2-(p-tolyl sulfinyl)benzyl iodide in the presence of sodium hexamethyl disilazide takes place with almost complete control of the stereoselectivity (facial and anti/syn) and with very high yields affording optically pure N-sulfinyl trans-2,3-disubstituted aziridines 7. Simultaneous removal of both C- and N-p-tolylsulfinyl groups with tBuLi provides the corresponding trans-NH aziridines 8 without affecting their optical purity. Some experimental results suggest these processes evolve through benzyl halocarbenoids as intermediates, whereas theoretical calculations support the formation of benzyl carbanions. These results have served for revising the mechanistic aspects of the reactions of substituted 2-p-tolylsulfinyl benzylcarbanions with electrophiles.

Thione Esters as Substrates for the Stereoselective Alkylation of Model Compounds of Nonactic Acids

AbstractThe naturally occurring macrotetrolide antibiotic nonactin is used in ammonium ion selective electrodes. To increase the lifetime of nonactin in the semipermeable membrane of these sensors we have developed methods for the introduction of hydrophobic side‐chains. Simple model compounds for nonactic acid such as 5 and 7 were synthesised. Maintaining the cis arrangement of the substituents in the 2,5‐disubstituted tetrahydrofurans proved to be difficult. Three different routes were studied. The enolates obtained by treatment with NaHMDS or KHMDS could be alkylated with benzyl or allyl iodide as electrophiles. Under these conditions a cis/trans isomerisation of the substituents on the tetrahydrofuran ring occurred. A multistep methodology was developed as a synthetic alternative. The sequence consisted of a selective retro‐Michael reaction, a 5‐exo‐tet iodocyclisation and a radical substitution. The products obtained by the two methodologies could be correlated, and thereby a tentative assignment of the relative configurations could be achieved. In the third route the thione ester 18 was deprotonated with tBuOK. At temperatures below –78 °C, the enolate maintained the cis configuration of the substituents at the tetrahydrofuran ring. The alkylated product 12 could be isolated with a satisfactory cis/trans ratio of 85:15. The model compound 12 could be successfully transformed into more hydrophobic derivatives by using either the Heck coupling or the cross‐coupling metathesis transformation.

Regioselective N-alkylation of imidazo[4,5- b]pyridine-4-oxide derivatives: an experimental and DFT study

Regioselectivities were determined for N-alkylations of imidazo[4,5- b]pyridine-4-oxide and 2-methyl-imidazo[4,5- b]pyridine-4-oxide with benzyl bromide or benzyl iodide at RT using K 2CO 3 in DMF as a base. Experimental attempts have shown that N-1/ N-3 ratios slightly varied according to the substitution on C-2 position. This was confirmed by DFT calculations in solvent phase. This computational study has shown first that this N -benzylation reaction passed through a S N2 mechanism. Moreover, regioselectivity of N-benzylation has appeared essentially governed by ‘steric approach control’. It explained that opposite N-1/ N-3 ratios were obtained with imidazo[4,5- b]pyridine-4-oxide and its 2-methyl-substituted analog. Finally, regioselectivities slightly varied with the nature of benzyl halide.

Octahedral perfluoroalkyl complexes of Ir(III) formed by oxidative addition of perfluoroalkyl iodides to Ir(acac)(CO)2

Oxidative addition of primary, secondary, or benzylic perfluoroalkyl iodides (RF–I) to the phosphine free Ir(I) precursor Ir(acac)(CO)2 1 (acac = 2,4-pentanedionato) proceeds smoothly to afford octahedral Ir(III) products Ir(acac)(I)(RF)(CO)2, A combination of X-ray crystallographic studies and solution spectroscopy shows that these products are the result of overall trans-addition of the C–I bond to iridium, probably a result of thermodynamic control; evidence for a kinetic product resulting from net cis-addition is obtained in one case. Treatment of the Ir(III) compounds with AgOTf (Tf = CF3SO3) illustrates that the iodo ligand is replaced by triflate with retention of stereochemistry at Ir. The resulting triflate complexes are inert to displacement by H2O or H2. The Ir(III) products exhibit very high CO stretching frequencies in the IR, indicating that the CO ligands may be non-classical. A quantitative estimation of the degree of backbonding to the CO ligands in these compounds, and a comparison of the π-acceptor properties of CO and fluoroalkyl ligands, is made using an approach based on Density Functional Theory (DFT) and Natural Bond Orbital analyses.Key words: iridium, fluoroalkyl, oxidation, carbonyl, DFT.

Facile reductive dehalogenation of organic halides with nickel boride at ambient temperature

The hydrodehalogenation of a series of aryl, alkyl, allyl, and benzyl chlorides, bromides, and iodides has been carried out efficiently using nickel boride in methanol at ambient temperature, leading to the corresponding products resulting from hydrogen/halogen exchange.Key words: hydrodehalogenation, reduction, organic halides, sodium borohydride, nickel boride.

Stereoselective Alkylidenation of Ketones with 2-(p-Toluenesulfinyl)benzyl Iodide: Synthesis of Enantiomerically Pure Trisubstituted Epoxides

Alkylidenation of arylmethyl, dialkyl, and cyclic ketones with 2-( p-toluenesulfinyl)benzyl iodide in the presence of NaN(SiMe3)2 takes place with a high or complete control of the facial selectivity at the carbonyl group (up to 98% de) and the carbanion (>98% de), respectively, yielding mixtures of only two optically pure trisubstituted epoxides ( E/Z ratio ranges between 2:1 and >50:1). Removal of the p-tolylsulfinyl group with t-BuLi provides the corresponding (E)-3-phenyl-2,2-disubstituted epoxides without affecting their optical purity.

Selective procedure for the conversion of alcohols into alkyl iodides with SO42-/ZrO2 and NaI at room temperature

Abstract SO 4 2 - / Zr O 2 was employed as a catalyst for the conversion of alcohols into the corresponding iodides using NaI in CH3CN at room temperature. Present procedure is found to be selective for the conversion of benzylic alcohols in the presence of saturated alcohols into benzylic iodides. The catalyst was characterized by XRD, FTIR, elemental analysis, BET surface area and TG–DTA techniques. This protocol provides a mild and efficient way for the one pot conversion of structurally diverse alcohols to their corresponding alkyl iodides with high selectivity. Download : Download full-size image

Allyl and Benzyl Iodides by the Anomalous Action of Iodotrimethylsilane.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Allyl and benzyl iodides by the anomalous action of iodotrimethylsilane

Iodotrimethylsilane (TMSI), routinely used for the dealkylation of ethers and esters, has been found to efficiently convert allyl and benzyl phosphotriesters into the corresponding iodides under mild, Brønsted-neutral conditions. In contrast, alkyl and aryl phosphotriesters were dealkylated to the corresponding phosphates under identical conditions.

Kinetics and mechanism of the reaction of benzyl halides with zinc in dimethylformamide

AbstractThe reaction of metal zinc with various benzyl halides in dimethylformamide has been studied. The low‐temperature ESR‐spectroscopy is used to show that reaction of zinc with benzyl bromide and benzyl iodide occurs to form benzyl radicals. Benzyl chloride reacts with zinc at 77 K to form benzyl radicals and ion‐radical pairs ${\rm RX}^{\mathop \cdot \limits^ - } - {\rm Zn}^{\mathop \cdot \limits^ + }$. Nevertheless these pairs disappear at temperatures higher than 110 K. The investigation of the reaction stereochemistry and the use of a radical trap provide evidence in favor of a radical mechanism. The optical activity has been proved in the course of the formation of organozinc halide from (+)‐R‐1‐halogen‐1‐phenylethane at low temperature. The kinetic features of the reaction have been studied. Benzyl iodide reacts with zinc at transport‐controlled rate. The reaction of zinc with benzyl chloride and benzyl bromide in DMF occurs according to Langmuir–Hinshelwood scheme, the adsorption of reagents taking place on similar active centers of metal. The kinetic and thermodynamic parameters of the reaction have been clarified. The comparison of kinetic parameters with those reported in literature evidences that the limiting step of reaction is halogen atom transfer (inner sphere electron transfer). Copyright © 2006 John Wiley & Sons, Ltd.

Spectroscopic and structural characterization of products arising from the base-promoted benzylation of 3-sulfolene

Reaction of the title sulfone (1) with benzyl iodide at -78 degrees C in the presence of LiHMDS and using THF/DMPU as solvent affords a chromatographically separable mixture of the compounds 2-5 in a combined yield of 42%. These products have been subjected to comprehensive spectroscopic characterization and the structures of products 2 and 5 established through single-crystal X-ray analyses.

High-Temperature Thermal Decomposition of Benzyl Radicals

The thermal decomposition of the benzyl radical was studied in shock tube experiments using ultraviolet laser absorption at 266 nm for detection of benzyl. Test gas mixtures of 50 and 100 ppm of benzyl iodide dilute in argon were heated in reflected shock waves to temperatures ranging from 1430 to 1730 K at total pressures around 1.5 bar. The temporal behavior of the 266 nm absorption allowed for determination of the benzyl absorption cross-section at 266 nm and the rate coefficient for benzyl decomposition, C6H5CH2 --> C7H6 + H. The rate coefficient for benzyl decomposition at 1.5 bar can be described using a two-parameter Arrhenius expression by k1(T) = 8.20 x 10(14) exp(-40 600 K/T) [s(-1)], and the benzyl absorption cross-section at 266 nm was determined to be sigma(benzyl) = 1.9 x 10(-17) cm2 molecule(-1) with no discernible temperature dependence over the temperature range of the experiments.

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My Contributions to Science and Society

Direct and indirect electrochemical reduction of organic halides in aprotic media

Cyclic voltammetric reduction of 17 different organic halides including alkyl, allyl, and benzyl chlorides, bromides, and iodides in aprotic media (DMF, DMSO, and acetonitrile, AN), containing 0.1 M Bu4NClO4, have been reported at glassy carbon (gc) and graphite as working electrodes. A single two-electron irreversible and diffusion-limited reduction of the carbon-halogen bond is observed, the reduction potentials ranging from −1.20 to −2.70 V (versus silver wire quasireference electrode) depending on the halide, the solvent, and the electrode. Indirect reduction of these 17 halides, however, is effected at much lower potentials (−0.79 to −0.92 V versus SCE) depending on the experimental conditions by in situ electrogenerated superoxide ion (O 2 ⋅− ) by CPE. The products have been characterized by TLC, GC, CV, or chemical estimation. The diorganic peroxide and the organic hydroperoxide were the major products. In case of tertiary alkyl halides, however, alkenes predominated, due to basic nature of O 2 ⋅− in these reactions. These studies indicate sufficient strength of O 2 ⋅− as a nucleophile or base depending on the experimental conditions.

Facile Preparation of Benzylic Iodides Under Solvent‐Free Conditions Using Microwave Irradiation

Benzylic alcohols are rapidly converted to the corresponding benzylic iodides using combination of p‐toluenesulfonic acid (PTSA) and potassium iodide under solvent‐free microwave irradiation conditions.

Facile Preparation of Benzylic Iodides under Solvent‐Free Conditions Using Microwave Irradiation.

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Addition of Electrophilic and Heterocyclic Carbon‐Centered Radicals to Glyoxylic Oxime Ethers.

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