Free-radical Chlorination Research Articles

Identification Complexity of the Products of Free-Radical Chlorination of Indane by Gas Chromatography–Mass Spectrometry

Identification Complexity of the Products of Free-Radical Chlorination of Indane by Gas Chromatography–Mass Spectrometry

Logistic regression in approximation of the results of gas chromatographic analysis of thermally unstable compounds

Regularities and peculiarities of gas chromatographic analysis of thermally unstable compounds were considered on the example of mixture of the reaction products of isopropylbenzene (cumene) free-radical chlorination. The principal constituent in this mixture is (1-chloro-1-methylethyl)benzene, which has the lowest thermal stability, and is partially converted to a-methylstyrene, the only product of its thermal destruction at the chromatograph injector temperatures up to 300 °С. Nevertheless, the results of the study confirms that the gas chromatographic analysis of chloroalkylarenes is possible without their decomposition with the injector temperatures up to 200 °С, even if the analytes contain chlorine atoms at the tertiary carbon atoms and in the “benzylic” positions relative to the aromatic fragment. Similar control of thermal stability of analytes can be recommended for other samples contained potentially unstable constituents. It is shown that thermal decomposition of thermally unstable constituents of samples cannot be revealed from the results of gas chromatographic analysis with capillary columns using variations of their absolute peak areas. Such task can be solved only by using relative peak areas calculated in respect to thermally stable compounds. The dependencies of relative peak areas of unstable constituents vs. temperature (descending), as well as those of their decomposition products (ascending) are characterized by presence of two limits. Low temperature limits correspond to the real content of unstable constituents or their decomposition products is the samples, while the upper limits – to the composition of such samples at their hypothetically complete destruction. Such dependencies can be approximated by logistic regression equation if sampling into capillary columns is carried out at relatively high split ratios (approx. not less than 10 : 1). At lower split ratios the temperature dependencies of peak areas of unstable constituents and products of their transformation are strongly distorted by so-called sample’s composition discrimination effects that make impossible data approximation using logistic regression.

Using 1H NMR Spectroscopy to Study the Free Radical Chlorination of Alkanes

The free radical chlorination of an alkane experiment is often used in the undergraduate laboratory curriculum to introduce students to the free radical mechanism, substituent effects, intermediate...

Modeling the Effect of Potential Nitric Acid Removal During Convective Injection of Water Vapor Over the Central United States on the Chemical Composition of the Lower Stratosphere.

Tropopause‐penetrating convection is a frequent seasonal feature of the Central United States climate. This convection presents the potential for consistent transport of water vapor into the upper troposphere and lower stratosphere (UTLS) through the lofting of ice, which then sublimates. Water vapor enhancements associated with convective ice lofting have been observed in both in situ and satellite measurements. These water vapor enhancements can increase the probability of sulfate aerosol‐catalyzed heterogeneous reactions that convert reservoir chlorine (HCl and ClONO2) to free radical chlorine (Cl and ClO) that leads to catalytic ozone loss. In addition to water vapor transport, lofted ice may also scavenge nitric acid and further impact the chlorine activation chemistry of the UTLS. We present a photochemical model that resolves the vertical chemical structure of the UTLS to explore the effect of water vapor enhancements and potential additional nitric acid removal. The model is used to define the response of stratospheric column ozone to the range of convective water vapor transported and the temperature variability of the lower stratosphere currently observed over the Central United States in conjunction with potential nitric acid removal and to scenarios of elevated sulfate aerosol surface area density representative of possible future volcanic eruptions or solar radiation management. We find that the effect of HNO3 removal is dependent on the magnitude of nitric acid removal and has the greatest potential to increase chlorine activation and ozone loss under UTLS conditions that weakly favor the chlorine activation heterogeneous reactions by reducing NOx sources.

Introducing Students to a Synthetic and Spectroscopic Study of the Free Radical Chlorine Dioxide

This advanced undergraduate chemistry laboratory exercise takes advantage of the unique spectroscopic properties of the free radical chlorine dioxide to allow for a direct comparison of its symmetric stretch in both the ground and excited states. It incorporates several subject areas covered in an undergraduate chemistry degree (synthesis, spectroscopy, and computational chemistry) and is suitable for an advanced level inorganic, physical, or integrated chemistry laboratory course. Students synthesize aqueous chlorine dioxide, analyze a vibronic progression of the symmetric stretch in the excited state using UV–vis spectroscopy, and also record the energy of the symmetric stretch in the ground state using Raman spectroscopy. In addition to offering advanced undergraduate students the opportunity to study the chemistry of a radical first-hand, this exercise also reinforces the use of synthetic techniques for the purpose of studying how a molecule’s physical properties vary with the electronic state. An opt...

Identification of organic reaction products in the absence of additivity of chromatographic retention indices. Chloro derivatives of methyl-tert-butyl ketone

As a result of a joint interpretation of mass spectra and gas chromatographic retention indices more than ten products of free radical chlorination of methyl-tert-butyl ketone are identified. They contain from one to six chlorine atoms in the molecule and were not previously characterized either by mass spectrometric or chromatographic reference data. It is found that retention index increments corresponding to a gradual increase in the number of chlorine atoms in the molecule per unit are non-additive and vary in wide ranges (from 53 i.u. to 219 i.u.), which does not hinder the use of separate elements of additive schemes for the estimation of the indices of products of such non-regioselective reactions.

Identification of the products of nonregioselective organic reactions by chromatography-mass spectrometry: Chloro derivatives of dialkyl ethers

The possibilities of GC-MS identification of the products of free-radical chlorination of dialkyl ethers are considered. The principal feature of this problem was the absence of appropriate reference information (both mass spectra and GC retention indices) for chloro derivatives of ethers. It was shown that all monochloro and selected dichloro derivatives can be identified on the basis of joint interpretation of their mass spectra combined with evaluating the retention indices using different additive schemes.

Plasma‐Assisted Synthesis of Chlorinated Polyvinyl Chloride (CPVC) Using a Gas–Solid Contacting Process

AbstractPlasma‐assisted synthesis of CPVC, using a gas–solid contactor, is presented as a novel process of PVC chlorination. The basic principle is to use cold plasma to generate free radical chlorine and activate the surfaces of PVC particles at the same time. Accordingly, the chlorination process can be decoupled into two steps: plasma‐enhanced chlorination on the particle surface and chlorine transfer from the surface to the core of the particle. Experiments were carried out in a DBD plasma fixed‐bed reactor. The results demonstrated the high efficiency of this process, i.e., a total of 3 h operation with plasma can achieve up to 67% of the chlorine content in PVC particles. The characterization results by SEM/EDS, TGA, and Raman spectra showed that CPVC made by this process had the desired microstructure and the thermal stability similar to that of the commercial CPVC products. magnified image

The Paramagnetic Stable Free Radical Chlorine Dioxide Reduces Post-surgical Adhesion Formation

The Paramagnetic Stable Free Radical Chlorine Dioxide Reduces Post-surgical Adhesion Formation

Chromatographic Identification of Cyclohexane Chlorination Products by an Additive Scheme for the Prediction of Retention Indices

Identification of the products of free-radical chlorination of cyclohexane seems to be a complex analytical problem due to the following principal reasons: (1) the available reference information (both standard mass spectra and gas chromatographic retention indices, RI) is strongly restricted to the data for only few simplest congeners, (2) mass spectra of isomeric chlorinated derivatives are practically indistinguishable, and (3) the number of isomers increases with the growing number of chlorine atoms in the molecule until six. To solve this problem, the modified additive scheme for precalculation of the RIs of chlorinated cyclohexanes on standard non-polar polydimethyl siloxane stationary phases was proposed and used. This approach is based on the data for congeners with fewer number of chlorine atoms in the molecule; the principal feature is its applicability to a diastereomers. The final set of both experimental and precalculated RI values permits us to identify unambiguously more than 20 products of cyclohexane chlorination in reaction mixtures. Different modes of the quality control of evaluated retention indices are discussed.

Characterization of polychlorinated alkane mixtures—a Monte Carlo modeling approach

A Monte Carlo model was developed to characterize the molecular composition of polychlorinated alkane mixtures. The model is based upon a simulation of the free-radical chlorination process by which polychlorinated alkane mixtures are produced industrially from n-alkanes. In the model, the free-radical chlorination reaction was simulated by randomly selecting a position on a partially converted alkane molecule for target by chlorine free-radical attack. The relative reactivities of the hydrogen atoms on the alkane chain towards chlorine free-radical substitution were either determined experimentally or extrapolated from experimental results and incorporated into the model. The result of the simulation is the prediction of the detailed molecular composition of any PCA mixture. Good agreement was found when comparing the distribution of molecules predicted by the model to analytically determined distributions of real PCA mixtures. Results from the model were then coupled with rules describing the action of biological enzymes to estimate the upper limit possible for the aerobic biodegradation of PCA mixtures.

An enantiomerically pure potential toxaphene congener: (1R,2S,3S,4R,7S)-2-endo,3-exo,5,5-tetrachloro-7-(chloromethyl)-1,7-bis(dichloromethyl)bicyclo[2.2.1]heptane

A new enantiomerically pure potential toxaphene congener (C10H9Cl9) has been isolated from a reaction mixture obtained by the free radical chlorination of (1S)-2-endo-chloro­bornane and its absolute configuration determined. It crystallizes in the monoclinic space group C2 with two mol­ecules in the asymmetric unit. This is the first report of the preparation of a single enantiomer of a synthetic poly­chloro­terpene on a multi-milligram scale.

Synthesis of 3-Alkenyl-1-azaanthraquinones via Diels-Alder and Electron Transfer Reactions

A convenient route to 3-alkenyl-1-azaanthraquinones via a hetero Diels-Alder reaction between an azadiene and naphthoquinone, a free radical chlorination and an electron transfer reaction is reported.

Effect of Solvents on the Selectivity of Free-Radical Chlorination of Functionalized Ethanes, Propanes, and Tetrachloroethene

Free radical reactions of hydrogen abstraction from methane, ethane, propane, and isobutane by radicals X (X = Cl·, Br·, I·, and CH· 3) are used as an example to study the applicability of the molecular mechanics (MM) method and the modified intermediate neglect of differential overlap method (PM3) to describing the trends in activation energies. The activation energies of only some, but not all, reaction series are adequately described by the MM (if special parameterization is used) and PM3 methods. All of the four reaction series follow the same correlation within the framework of the parabolic model of a transition state. The correlation of activation energies with the energies of highest occupied molecular orbitals (HOMO) of substrates and solvents is explained. For the correct description of trends in the HOMO energies in the series of studied molecules, the PM3 method was parameterized. The MM and PM3 methods are used to reveal the effect of a solvent on the activation energies of the regioselective and substrate-selective free-radical chlorination of substituted ethanes and propanes. The calculations of the structure and strength of complexes formed by solvent molecules, chloroethane, its radical, and the chlorine radical made it possible to propose a mechanism for the solvent effect on regioselectivity. This mechanism consists in the stabilization of the transition state formed by the α-abstraction of a carbon atom from the C–Cl bond in the aromatic solvent. Different trends exist for aromatic and nonaromatic solvents for changes in the activation energies of the competitive chlorination of tetrachloroethene and 1,2-dichloroethane depending on the solvent concentration. These trends can be reduced to one trend if one considers the HOMO energies of solvents and the substrate and takes into account reactant concentrations.

Iodosobenzene Dichloride, a Convenient Reagent for Chloro- and Iodomethoxylation of Double and Triple Bonds

The reaction with a-methylstyrene (VIII) was less selective and afforded in 70% overall yield an inseparable mixture of two isomers IX and X in 75 : 25 ratio according to GC-MS and H NMR data. The formation of reaction product X is an evidence of a contribution from free-radical chlorination of the methyl group in compound IX [or in initial a-methylstyrene (VIII)] effected by PhICl2. It turned out that reaction of styrene (II) with PhICl2 in methanol in the presence of iodine took another route easily providing a product of iodomethoxylation of the double bond XI in 80% yield. Obviously here the iodosobenzene dichloride acted as oxidant for iodine providing its electrophilic intermediates (I + , ICl, or CH3OI). This reaction is perhaps the first example of a simple iodoalkoxylation of alkenes with the use of compounds of polyvalent iodine, and it opens new opportunities for the synthesis of commonly less available iodoalkoxyalkanes [4, 5].

Application of Hammond's Postulate. An Activity for Guided Discovery Learning in Organic Chemistry

This paper describes an activity that promotes the more active involvement of organic chemistry students in their learning. In this activity, students are given product distributions and other relevant experimental data concerning the free radical chlorination and bromination of propane. Students are guided in the use of Hammond's postulate to predict transition-state structures and to provide a rationale for the relationship between selectivity and reactivity in these and other reactions. In carrying out the skill exercises, students must also review and apply some of the concepts learned in their general chemistry courses. Because of the wide variety of applications of the Hammond postulate, we believe that this activity, along with the associated discussions, represents an effective teaching/learning model that is particularly useful at the early stages of an organic chemistry series.

Anodic behaviour of carbon materials in NaCl saturated NaAlCl4 fused electrolyte at low temperatures : A cyclic voltammetric study

The anodic behaviour of compacted graphite, graphite powder, glassy carbon and reticulated vitreous carbon electrodes in basic sodium chloroaluminate melt in the temperature range 428–573 K was studied using cyclic voltammetry. Chlorine evolution (> + 2.1 V vs Al) alone was the predominant reaction on the compact glassy carbon and fresh RVC electrodes. On compacted graphite, chlorine-assisted chloroaluminate intercalation was found to be a competitive process to the chlorine evolution. At high sweep rates, intercalation/deintercalation near the graphite lattice edges occur faster than chlorine evolution. Subsequent intercalation, however, is a slow process. Chlorine evolution predominates at higher temperatures and at higher anodic potentials. On graphite powders, a more reversible free radical chlorine adsorption/desorption process also occurs in the potential region below chlorine evolution. The process occurs at the grain boundaries, edges and defects of the graphite powder material. Intercalation/deintercalation processes are mainly responsible for the disintegration of graphitic materials in low-temperature chloroaluminate melts. Repeated intercalation/deintercalation cycles result in the irreversible transformation of the electrode surface and electrode characteristics. The surface area of the electrode is increased substantially on cycling. Electrode materials and operating conditions suitable for chlorine generation, intercalation/deintercalation and chlorine adsorption/desorption and power sources based on these processes are identified in this work.

Relationship of the selectivity effect of aromatic solvents with their electron-donor ability and organic reactant structure in free radical chlorination

The effect of several solvents on the selectivity of the free radical chlorination of 1,1-dichloroethane and 1-chloropropane is studied. The selective action of aromatic solvents on free radical chlorination is explained. This explanation implies that the process involves solvated chlorine atoms and their donor-acceptor complexes with aromatic molecules (ArH→Cl•) as intermediates. Using the findings of this work and previous studies, the ratios of the rate constants for hydrogen-atom abstraction from different positions in chloroethane, 1,1-dichloroethane, 1-chloropropane, and 2-chloropropane by solvated chlorine atoms and ArH→-Cl• complexes are determined. The differences in the activation energies of the competitive hydrogenatom abstractions from different positions in substrates by the ArH→Cl• complexes and solvated chlorine radicals correlate with two HOMO energies of solvent and substrate molecules. The isokinetic relationship is found for all the systems under study (the isokinetic temperature, 523 K).

Herbacic acid, a simple prototype of 5,5,5-trichloroleucine metabolites from the sponge Dysidea herbacea.

Dysidea herbacea, collected at Harrier Reef on the Great Barrier Reef, contains the novel metabolite herbacic acid as the major trichloroleucine metabolite. Herbacic acid appears to be an early product of direct free-radical chlorination of leucine and is a prototype for further transformation of the free carboxylic acid group and generation of complex trichloromethyl metabolites, including natural products of the dysidenin family.

Free Radical Chlorinations in Halogenated Solvents: Are There Any Solvents Which Are Truly Noncomplexing?

The free radical chlorination of alkanes was examined in several solvents. The results of these experiments suggest that Cl• forms complexes with halogenated solvents and that these complexes exhibit higher selectivity in hydrogen abstractions than “free” chlorine atom. The observed selectivity decreases with increasing Cl-content of the solvent (paralleling the increase in the ionization potential of the solvent), and selectivity is greater in bromoalkane solvents compared to chloroalkanes, suggesting that these are donor/acceptor-type complexes.