- Contrasting reactivity of mono- versus Bis-2,2,6,6-tetramethylpiperidide lithium aluminates towards polydentate lewis bases: Co-complexation versus deprotonation
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Two closely related lithium alkylaluminium amides LiAl(TMP)2iBu2 and LiAl(TMP)iBu3 (TMP: 2,2,6,6-tetramethylpiperidide) have been compared in their reactivity towards six polydentate Lewis bases containing either N or O donor atoms or a mixed N,O donor set. Seven of the twelve potential organometallic products of these reactions, which were carried out in hexane solution, have been crystallographically characterised. Three of these structures, [Li(-Me2NCH2CHCH2CH2CHO)(-TMP)Al(iBu)2], [Li(-Me2NCH2CH2OCH2)(-TMP)Al(iBu)2], and [Li(-Me2NCH2CH2OCHCH2NMe2)(-TMP)Al(iBu)2] reveal that the bis-amide LiAl(TMP)2iBu2 deprotonates (aluminates) the multifunctional Lewis base selectively at the carbon atom adjacent to oxygen with the anion generated captured by the residue of the base. In contrast, the mono-amide LiAl(TMP)iBu3 in general fails to deprotonate the Lewis bases but instead forms co-complexes with them as evidenced by the molecular structures of [Me2NCH2CHCH2CH2CH2O·Li(-iBu)(-TMP)Al(iBu)2], [Me2NCH2CH2OMe·Li(- iBu)(-TMP)Al(iBu)2], and [MeOCH2CH2OMe·Li(-iBu)(-TMP)Al(iBu)2]. Providing an exception to this pattern, the mono-amide reagent deprotonates chiral R,R,-N,N,N′,N′-tetramethylcyclohexanediamine to afford [Li(-CH2NMeC6H10NMe2)2Al(iBu)2], the final complex to be crystallographically characterised. All new products have been spectroscopically characterised through 1H, 7 Li, and 13C NMR studies. Reaction mixtures have also been quenched with D2O and analysed by 2D NMR spectroscopy to ascertain the full metallation versus co-complexation picture taking place in solution.
- Campbell, Ross,Crosbie, Elaine,Kennedy, Alan R.,Mulvey, Robert E.,Naismith, Rachael A.,Robertson, Stuart D.
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Read Online
- Visible-Light-Driven α-Allenylic C-O Bond Cleavage and Alkenyl C-S Formation: Metal-Free and Oxidant-Free Thiolation of Allenyl Phosphine Oxides
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A visible-light photoredox cleavage of α-allenylic C-O bond and alkenyl C-S formation is disclosed for the first time. The thiolation of allenyl phosphine oxides with diaryl disulfides occurs smoothly in metal-free and mild conditions, affording novel S,P-bifunctionalized butadienes with moderate to excellent yields. Mechanistic studies explain the cleavage of a C(sp3)-O(Ar) bond in initiating a key alkenyl radical intermediate.
- Zhang, Ling,Zhu, Jie,Ma, Jing,Wu, Lei,Zhang, Wei-Hua
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Read Online
- Reactions of a stable phosphinyl radical with stable aminoxyl radicals
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Reaction of stable phosphinyl radical 1a with AZADO gave aminoxyphosphine 3 as the primary product by selective radical coupling at 140 °C. Compound 3 decomposed to phosphorane 4, silyl phosphinate 5, and aminophosphine 6 at room temperature. The molecular structures of 4-6 were determined by X-ray structural analysis. The homolytic N-O bond cleavage of 3 and the subsequent silyl migration of the resulting phosphinoyl radical 7 would be key steps in the reaction.
- Ishida, Shintaro,Hirakawa, Fumiya,Iwamoto, Takeaki
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Read Online
- 2,2,6,6-tetramethylpiperidinium chloride
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Crystals of 2,2,6,6-tetramethylpiperidinium chloride, C9H20N+.Cl-, crystallized from dichloromethane solution. Hydrogen bonding between the piperidinium and chloride ions [d(N-H...Cl) = 3.16 and 3.30A] links the units into alternating chains running parallel to the crystallographic b axis.
- Kaplan, Ruth W.,Turnbull, Mark M.
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Read Online
- A large-scale low-cost access to the lithium 2,2,6,6-tetramethylpiperidide precursor
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Wolff-Kishner-Huang reduction of the cheap 2,2,6,6-tetramethyl-4- piperidinone (2) provides the expensive 2,2,6,6-tetramethylpiperidine (1), the precursor to lithium 2,2,6,6-tetramethylpiperidide, in high yield. As specified in the detailed protocol, the reaction can be conveniently carried out on a >10 mol laboratory scale. Georg Thieme Verlag Stuttgart.
- Kampmann, Detlef,Stuhlmueller, Georg,Simon, Roger,Cottet, Fabrice,Leroux, Frederic,Schlosser, Manfred
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Read Online
- Photochemical Synthesis of 1,4-Dicarbonyl Bifluorene Compounds via Oxidative Radical Coupling Using TEMPO as the Oxygen Atom Donor
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A visible-light-induced metal-free synthesis of 1,4-dicarbonyl compounds from alkyne-containing aryl iodides via photochemical C-I bond cleavage, intramolecular cyclization, oxidation, and intermolecular radical coupling sequence is reported. TEMPO was employed as the oxygen atom donor in this transformation. This protocol provided a new strategy for the synthesis of 1,4-dicarbonyl bifluorene compounds.
- Xu, Jincheng,Ding, Aishun,Zhang, Yanbin,Guo, Hao
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Read Online
- Copper-Catalyzed Cascade N-Dealkylation/N-Methyl Oxidation of Aromatic Amines by Using TEMPO and Oxygen as Oxidants
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A novel tandem N-dealkylation and N-methyl aerobic oxidation of tertiary aromatic amines to N-arylformamides using copper and TEMPO has been developed. This methodology suggested an alternative synthetic route from N-methylarylamines to N-arylformamides.
- Li, Dianjun,Wang, Shihaozhi,Yang, Jiale,Yang, Jinhui
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supporting information
p. 6768 - 6772
(2021/12/31)
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- Photo-induced thiolate catalytic activation of inert Caryl-hetero bonds for radical borylation
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Substantial effort is currently being devoted to obtaining photoredox catalysts with high redox power. Yet, it remains challenging to apply the currently established methods to the activation of bonds with high bond dissociation energy and to substrates with high reduction potentials. Herein, we introduce a novel photocatalytic strategy for the activation of inert substituted arenes for aryl borylation by using thiolate as a catalyst. This catalytic system exhibits strong reducing ability and engages non-activated Caryl–F, Caryl–X, Caryl–O, Caryl–N, and Caryl–S bonds in productive radical borylation reactions, thus expanding the available aryl radical precursor scope. Despite its high reducing power, the method has a broad substrate scope and good functional-group tolerance. Spectroscopic investigations and control experiments suggest the formation of a charge-transfer complex as the key step to activate the substrates.
- K?nig, Burkhard,Wang, Hua,Wang, Shun
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supporting information
p. 1653 - 1665
(2021/06/17)
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- Catalytic CO2 hydrosilylation with [Mn(CO)5Br] under mild reaction conditions
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Carbon dioxide hydrosilylation with earth-abundant transition-metal catalysts is an attractive alternative for the design of greener and cost-effective synthetic strategies. Herein, simple [Mn(CO)5Br] is an efficient precatalyst in the hydrosilylation of carbon dioxide with Et3SiH under mild reaction conditions. Using THF as a solvent, triethylsilylformate Et3SiCH(O)O was obtained in 67% yield after 1 h at 50 °C and 4 bar of CO2 pressure. The selectivity of the reaction was tuned by changing the solvent to a mixture of THF and toluene producing bis(triethylsilyl)acetal (Et3SiO)2CH2 in 86% yield. The CO2 hydrosilylation was also effective at room temperature and atmospheric pressure using either THF or the mixture THF/toluene as the solvent resulting in high Et3SiH conversion (92%–99%) but with a decrease in the selectivity. Radical trapping experiments indicated the participation of radical species in the catalytic mechanism. To the best of our knowledge, this is the first report on CO2 hydrosilylation catalyzed by transition-metal radical intermediates.
- García, Juventino J.,González, Tania
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- Iron-Catalyzed ?±,?-Dehydrogenation of Carbonyl Compounds
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An iron-catalyzed α,β-dehydrogenation of carbonyl compounds was developed. A broad spectrum of carbonyls or analogues, such as aldehyde, ketone, lactone, lactam, amine, and alcohol, could be converted to their α,β-unsaturated counterparts in a simple one-step reaction with high yields.
- Zhang, Xiao-Wei,Jiang, Guo-Qing,Lei, Shu-Hui,Shan, Xiang-Huan,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 1611 - 1615
(2021/03/03)
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- Chemoselective Catalytic α-Oxidation of Carboxylic Acids: Iron/Alkali Metal Cooperative Redox Active Catalysis
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We developed a chemoselective catalytic activation of carboxylic acid for a 1e- radical process. α-Oxidation of a variety of carboxylic acids, which preferentially undergo undesired decarboxylation under radical conditions, proceeded efficiently under the optimized conditions. Chemoselective enolization of carboxylic acid was also achieved even in the presence of more acidic carbonyls. Extensive mechanistic studies revealed that the cooperative actions of iron species and alkali metal ions derived from 4 ? molecular sieves substantially facilitated the enolization. For the first time, catalytic enolization of unprotected carboxylic acid was achieved without external addition of stoichiometric amounts of Br?nsted base. The formed redox-active heterobimetallic enediolate efficiently coupled with free radical TEMPO, providing synthetically useful α-hydroxy and keto acid derivatives.
- Tanaka, Tsukushi,Yazaki, Ryo,Ohshima, Takashi
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supporting information
p. 4517 - 4524
(2020/03/05)
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- Metal-Free Direct Deoxygenative Borylation of Aldehydes and Ketones
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Direct conversion of aldehydes and ketones into alkylboronic esters via deoxygenative borylation represents an unknown yet highly desirable transformation. Herein, we present a one-step and metal-free method for carbonyl deoxy-borylation under mild conditions. A wide range of aromatic aldehydes and ketones are tolerated and successfully converted into the corresponding benzylboronates. By the same deoxygenation manifold with aliphatic aldehydes and ketones, we also enable a concise synthesis of 1,1,2-tris(boronates), a family of compounds that currently lack efficient synthetic methods. Given its simplicity and versatility, we expect that this novel borylation approach could show great promise in organoboron synthesis and inspire more carbonyl deoxygenative transformations in both academic and industrial settings.
- Huang, Chia-Yu,Li, Chao-Jun,Li, Jianbin,Qiu, Zihang,Wang, Haining
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supporting information
p. 13011 - 13020
(2020/09/01)
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- Copper/TEMPO Redox Redux: Analysis of PCET Oxidation of TEMPOH by Copper(II) and the Reaction of TEMPO with Copper(I)
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Copper salts and organic aminoxyls, such as TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl), are versatile catalysts for aerobic alcohol oxidation. Previous reports in the literature contain conflicting proposals concerning the redox interactions that take place between copper(I) and copper(II) salts with the aminoxyl and hydroxylamine species, TEMPO and TEMPOH, respectively. Here, we reinvestigate these reactions in an effort to resolve the conflicting claims in the literature. Under anaerobic conditions, CuIIX2 salts [X = acetate (OAc), trifluoroacetate (TFA), and triflate (OTf)] are shown to promote the rapid proton-coupled oxidation of TEMPOH to TEMPO: CuIIX2 + TEMPOH → CuIX + TEMPO + HX. In the reaction with acetate, however, slow reoxidation of CuIOAc occurs. This process requires both TEMPO and HOAc and coincides with the reduction of TEMPO to 2,2,6,6-tetramethylpiperidine. Analogous reactivity is not observed with trifluoroacetate and triflate species. Overall, the facility of the proton-coupled oxidation of TEMPOH by CuII salts suggests that this process could contribute to catalyst regeneration under aerobic oxidation conditions.
- Ryan, Michael C.,Whitmire, Lauren D.,McCann, Scott D.,Stahl, Shannon S.
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supporting information
p. 10194 - 10200
(2019/08/26)
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- A Drastic Effect of TEMPO in Zinc-Catalyzed Stannylation of Terminal Alkynes with Hydrostannanes via Dehydrogenation and Oxidative Dehydrogenation
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With a system consisting of a catalytic zinc Lewis acid, pyridine, and TEMPO in a nitrile medium, terminal alkynes coupled with HSnBu3, providing alkynylstannanes with structural diversity. The resulting alkynylstannane, without being isolated, could be directly used for Pd- and Cu-catalyzed transformations to deliver internal alkynes and more intricate tin-atom-containing molecules. Mechanistic studies indicated that TEMPOSnBu3 formed in situ from TEMPO and HSnBu3 works to stannylate the terminal alkyne in collaboration with the zinc catalyst, and that both of dehydrogenation and oxidative dehydrogenation processes are uniquely involved in a single reaction. (Figure presented.).
- Kai, Yuichi,Oku, Shinya,Sakurai, Kyoko,Tani, Tomohiro,Tsuchimoto, Teruhisa
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supporting information
(2019/08/21)
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- Visible-Light Photocatalytic Synthesis of Amines from Imines via Transfer Hydrogenation Using Quantum Dots as Catalysts
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CdSe/CdS core/shell quantum dots (QDs) can be used as stable and highly active photoredox catalysts for efficient transfer hydrogenation of imines to amines with thiophenol as a hydrogen atom donor. This reaction proceeds via a proton-coupled electron transfer (PCET) from the QDs conduction band to the protonated imine followed by hydrogen atom transfer from the thiophenol to the α-aminoalkyl radical. This precious metal free transformation is easy to scale up and can be carried out by a one-pot protocol directly from aldehyde, amine, and thiophenol. Additional advantageous features of this protocol include a wide substrate scope, high yield of the amine products, extremely low catalyst loading (0.001 mol %), high turnover number (105), and the mild reaction conditions of using visible light or sun light at room temperature in neutral media.
- Xi, Zi-Wei,Yang, Lei,Wang, Dan-Yan,Pu, Chao-Dan,Shen, Yong-Miao,Wu, Chuan-De,Peng, Xiao-Gang
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supporting information
p. 11886 - 11895
(2018/09/25)
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- Method for efficiently preparing 2,2,6,6-tetramethyl piperidine oxide
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The invention discloses a method for efficiently preparing a 2,2,6,6-tetramethyl piperidine oxide, and belongs to the technical field of the chemical material synthesis. The method comprises the following steps: using a compound of magnesium hydrate and kieselguhr as a catalyst, performing an oxidation reaction in the presence of hydrogen peroxide, and filtering, extracting by using ethyl acetateor propyl acetate, after distilling and removing a solvent, to obtain a product. A purity of the product is up to about 99.5%, and a yield of the reaction is improved from 80% in the prior art to 97%.Problems existing in the prior art that the pollution is serious and the yield is low and the like are solved.
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Paragraph 0032-0037; 0044-0061
(2018/11/03)
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- Use for Boron Formates for Reducing Unsaturated Organic Functions
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The present invention relates to a method for reducing unsaturated organic compounds chosen from the group formed by the aldehydes, the ketones, the imines, the carboxylic acids, the amides, and the esters with a boron formate having the formula (I) in the presence of a solvent and optionally a base. The invention also relates to the use of the method for reducing unsaturated organic compounds chosen from the group formed by the aldehydes, the ketones, the imines, the carboxylic acids, the amides, and the esters according to the invention in the preparation of methanol, methylated amines, formaldehyde and alcohols; for the preparation of reactants for Suzuki coupling reactions; and in the manufacturing of vitamins, pharmaceutical products, glues, acrylic fibres, synthetic leather, pesticides.
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Paragraph 0254-0258; 0261
(2018/12/04)
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- 2,2,6,6-Tetramethylpiperidin-1-yloxycarbonyl: A Protecting Group for Primary, Secondary, and Heterocyclic Amines
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The 2,2,6,6-tetramethylpiperidin-1-yloxycarbonyl (Tempoc) protecting group is readily introduced by the reaction of amines with a new acyl transfer reagent, 4-nitrophenyl (2,2,6,6-tetramethylpiperidin-1-yl) carbonate (NPTC). Tempoc has a reactivity profile that complements the commonly used t-butyloxycarbonyl (Boc) and benzyloxycarbonyl (Cbz) protecting groups. Deprotection can be achieved under mild reductive conditions with in situ generated Cu(I) species or by thermolytic cleavage at 135 °C. Mechanistic studies on the deprotection of Tempoc-indole suggest a combination of ionic and radical fragmentation pathways under thermal conditions.
- Lizza, Joseph R.,Bremerich, Maximilian,McCabe, Stephanie R.,Wipf, Peter
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p. 6760 - 6764
(2018/10/25)
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- Dynamic Ureas with Fast and pH-Independent Hydrolytic Kinetics
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Low cost, high performance hydrolysable polymers are of great importance in biomedical applications and materials industries. While many applications require materials to have a degradation profile insensitive to external pH to achieve consistent release profiles under varying conditions, hydrolysable chemistry techniques developed so far have pH-dependent hydrolytic kinetics. This work reports the design and synthesis of a new type of hydrolysable polymer that has identical hydrolysis kinetics from pH 3 to 11. The unprecedented pH independent hydrolytic kinetics of the aryl ureas were shown to be related to the dynamic bond dissociation controlled hydrolysis mechanism; the resulting hindered poly(aryl urea) can be degraded with a hydrolysis half-life of 10 min in solution. More importantly, these fast degradable hindered aromatic polyureas can be easily prepared by addition polymerization from commercially available monomers and are resistant to hydrolysis in solid form for months under ambient storage conditions. The combined features of good stability in solid state and fast hydrolysis at various pH values is unprecedented in polyurea material, and will have implications for materials design and applications, such as sacrificial coatings and biomaterials.
- Cai, Kaimin,Ying, Hanze,Cheng, Jianjun
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p. 7345 - 7348
(2018/06/11)
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- A metal-free direct C (sp3)-H cyanation reaction with cyanobenziodoxolones
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A metal-free protocol of direct C(sp3)-H cyanation with cyanobenziodoxolones functioning as both cyanating reagents and oxidants was developed. Unactivated substrates, such as alkanes, ethers and tertiary amines, were thereby transformed to the corresponding nitriles in moderate to high yields. Mechanistic studies indicated that the cyanation proceeded with two potential pathways, which is highly dependent on the substrates: (1) a free radical case for alkanes and ethers and (2) an oxidative case for tertiary amines.
- Sun, Ming-Xue,Wang, Yao-Feng,Xu, Bao-Hua,Ma, Xin-Qi,Zhang, Suo-Jiang
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supporting information
p. 1971 - 1975
(2018/03/23)
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- Iron Catalysis for Modular Pyrimidine Synthesis through β-Ammoniation/Cyclization of Saturated Carbonyl Compounds with Amidines
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An efficient method for the modular synthesis of various pyrimidine derivatives by means of the reactions of ketones, aldehydes, or esters with amidines in the presence of an in situ prepared recyclable iron(II)-complex was developed. This operationally simple reaction proceeded with broad functional group tolerance in a regioselective manner via a remarkable unactivated β-C-H bond functionalization. Control experiments were performed to gain deep understanding of the mechanism, and the reactions are likely to proceed through a designed TEMPO complexation/enamine addition/transient α-occupation/β-TEMPO elimination/cyclization sequence.
- Chu, Xue-Qiang,Cao, Wen-Bin,Xu, Xiao-Ping,Ji, Shun-Jun
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supporting information
p. 1145 - 1154
(2018/06/18)
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- Visible-light-induced tandem cyclization of 2-alkynylanilines with disulfides: A convenient method for accessing benzothiophenes under transition-metal-free and photocatalyst-free conditions
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A simple and efficient strategy for the preparation of benzothiophenes via visible-light-induced cyclization of 2-alkynylanilines with disulfides was developed. The reaction afforded the desired products in good yields at room temperature under transition-metal-free and photocatalyst-free conditions.
- Xie, Xiaoyu,Li, Pinhua,Shi, Qing,Wang, Lei
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supporting information
p. 7678 - 7684
(2017/09/27)
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- Synthetic method of 2,2,6,6-tetramethylpiperidine
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The invention discloses a synthetic method of 2,2,6,6-tetramethylpiperidine. The synthetic method comprises the following steps: filling a catalyst into a fixed-bed reactor; maintaining temperature of a reaction zone at 150-270 DEG C, and supplying hydrogen at the pressure of 1.0-5.0 MPa to the fixed-bed reactor; mixing 2,2,6,6-tetramethylpiperidone and aniline and a solvent, and reacting at 80-170 DEG C for 4h; introducing premixed raw materials into the fixed-bed reactor, evaporating at high temperature to form a gas mixture and fully contacting the gas mixture with a catalyst for cyclization, and carrying out a hydrocracking reaction to obtain a crude product; and carrying out gas-liquid separation, concentrating and rectifying to obtain 2,2,6,6-tetramethylpiperidine. The aniline used in the invention can be recycled, the catalyst has good selectivity and long life and is easy to separate and recovery, and product yield is high. The technology of the invention is simple, and the preparation process has little pollution. The method of the invention is suitable for continuous industrial production. Product quality accords with standards of industrial first-grade products.
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Paragraph 0029; 0030; 0031; 0032; 0033; 0034; 0035; 0036
(2016/11/24)
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- Cu-Catalyzed Cyanation of Arylboronic Acids with Acetonitrile: A Dual Role of TEMPO
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The cyanation of arylboronic acids by using acetonitrile as the "CN" source has been achieved under a Cu(cat.)/TEMPO system (TEMPO=2,2,6,6-tetramethylpiperidine N-oxide). The broad substrate scope includes a variety of electron-rich and electron-poor arylboronic acids, which react well to give the cyanated products in high to excellent yields. Mechanistic studies reveal that TEMPO-CH2CN, generated in situ, is an active cyanating reagent, and shows high reactivity for the formation of the CN- moiety. Moreover, TEMPO acts as a cheap oxidant to enable the reaction to be catalytic in copper. The cyanation of arylboronic acids by using acetonitrile as the "CN" source has been achieved under a Cu(cat.)/TEMPO system. Electron-rich and electron-poor arylboronic acids react well to give the cyanated products in high to excellent yields. Mechanistic studies reveal that TEMPO-CH2CN, generated in situ, is an active cyanating reagent. Moreover, TEMPO, a cheap oxidant, enables the reaction to be catalytic in copper (see scheme; TEMPO=2,2,6,6-tetramethylpiperidine N-oxide).
- Zhu, Yamin,Li, Linyi,Shen, Zengming
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p. 13246 - 13252
(2015/09/15)
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- Photo Lewis acid generators: Photorelease of B(C6F5)3 and applications to catalysis
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A series of molecules capable of releasing of the strong organometallic Lewis acid B(C6F5)3 upon exposure to 254 nm light have been developed. These photo Lewis acid generators (PhLAGs) can now serve as photoinitiators for several important B(C6F5)3-catalyzed reactions. Herein is described the synthesis of the triphenylsulfonium and diphenyliodonium salts of carbamato- and hydridoborates, their establishment as PhLAGs, and studies aimed at defining the mechanism of borane release. Factors affecting these photolytic reactions and the application of this concept to photoinduced hydrosilylation reactions and construction of siloxane scaffolds are also discussed.
- Khalimon, Andrey Y.,Shaw, Bryan K.,Marwitz, Adam J. V.,Piers, Warren E.,Blackwell, James M.,Parvez, Masood
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p. 18196 - 18206
(2015/10/28)
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- Isolation of a uranium(iii) benzophenone ketyl radical that displays redox-active ligand behaviour
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The first uranium(iii) charge separated ketyl radical complex, Tp2U(OC·Ph2), has been isolated and characterized by infrared, 1H NMR, and electronic absorption spectroscopies, along with X-ray crystallography. Tp2U(OC·Ph2) is a potent two-electron reductant towards N3Mes (Mes = 2,4,6-trimethylphenyl) and (2,2,6,6-tetramethyl-piperidin-1-yl)oxyl (TEMPO), with reducing equivalents derived from the metal centre and the redox-active benzophenone. This journal is
- Matson, Ellen M.,Kiernicki, John J.,Anderson, Nickolas H.,Fanwick, Phillip E.,Bart, Suzanne C.
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supporting information
p. 17885 - 17888
(2015/02/02)
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- Germanium(iii) corrole complex: Reactivity and mechanistic studies of visible-light promoted N-H bond activations
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The [(TPFC)Ge(TEMPO)] (1, TPFC = tris(pentafluorophenyl)corrole, TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) complex was characterized by X-ray diffraction and spectroscopic studies. EPR studies indicate that the weak Ge-O bond in 1 is photo-cleaved to form a tetra-coordinated germanium(iii) radical, [(TPFC)Ge(iii)]. DFT calculations show that the spin density on the germanium center in [(TPFC)Ge(iii)] has a significant s character. Under visible-light irradiation, 1 reacts rapidly with ammonia, primary/secondary aliphatic amines and aniline to produce (TPFC)Ge-NR1R2 (R1R 2 = HH, HnPr, HiPr, HtBu, HPh, Et2, iPr2) complexes in high yields (65-95%). The Royal Society of Chemistry 2014.
- Fang, Huayi,Ling, Zhen,Lang, Ke,Brothers, Penelope J.,De Bruin, Bas,Fu, Xuefeng
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p. 916 - 921
(2014/03/21)
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- Lewis acid-catalyzed oxidation of benzylamines to benzamides
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A novel Lewis acid-catalyzed oxidation of benzylamines to the corresponding amides has been developed. Using 10 mol% of ZnBr2 or FeCl 3 as the catalyst and TBHP as the oxidant, amides were produced under mild conditions. The Royal Society of Chemistry 2012..
- Wu, Xiao-Feng,Bheeter, Charles Beromeo,Neumann, Helfried,Dixneuf, Pierre H.,Beller, Matthias
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supporting information
p. 12237 - 12239
(2013/01/16)
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- Reactions of nitroxides. Part X: Antifungal activity of selected sulfur and selenium derivatives of 2,2,6,6-tetramethylpiperidine
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The antifungal activity of nitroxyl radicals - derivatives of 2,2,6,6-tetramethylpiperidine-1-oxyl with reactive substituents 4-isothiocyanato-, 4-isocyano-, and 4-isoselenocyanato- and of N-formyl-, N-thioformyl-, N-selenoformyl-derivatives of 2,2,6,6-tetramethylpiperidine was investigated. Those of the above compounds, which contain a sulfur or selenium atom are the most active against four fungus plant patogens: Botrytis cinerea, Fusarium culmorum, Phytophthora cactorum, Rhizoctonia solani. 4-Isoselenocyanato-2,2,6,6-tetramethylpiperidine-1-oxyl proved to be the most active compound.
- Zakrzewski, Jerzy,Krawczyk, Maria
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scheme or table
p. 514 - 516
(2011/02/28)
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- Electrochemical oxidation of 1-chloro(bromo)-2,2,6,6-tetramethylpiperidines
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Electrochemical oxidation of 1-haloamines of the 2,2,6,6- tetramethylpiperidine series results in the formation of relatively stable radical-cations, detected by the methods of cyclic voltammetry and ESR spectroscopy. The final products of electrochemical oxidation of these haloamines are stable nitroxyl radicals. Pleiades Publishing, Ltd., 2011.
- Kagan,Yanilkin,Nastapova,Morozov,Zhukova,Kashparov,Kashparova
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scheme or table
p. 2151 - 2156
(2012/03/12)
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- PROCESS FOR PRODUCING METHANOL
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The present invention relates to a novel process for the production of methanol. The process comprises the heterolytic cleavage of hydrogen by a frustrated Lewis pair comprising a Lewis acid and a Lewis base; and the hydrogenation of CO2 with the heterolytically cleaved hydrogen to form methanol.
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Page/Page column 19-20
(2011/05/05)
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- Determination of basic strength of aliphatic amines through ion pair formation in some ionic liquid solutions
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(Chemical Equation Presented) To have an evaluation of the basic strength of aliphatic amines in ionic liquid solution, the stability constants relevant to the formation of amine/p-nitrophenol ion pairs were determined in different ionic liquids at 298 K.
- D'Anna, Francesca,Vitale, Paola,Noto, Renato
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experimental part
p. 6224 - 6230
(2009/12/08)
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- Quenching of singlet oxygen by tertiary aliphatic amines. Structural effects on rates and products
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A kinetic and product study of the reaction of a series of α-methyl-substituted N-methylpiperidines with thermally generated 1O2 in MeCN was carried out. It was found that as the number of α-methyl groups (Me in α-position relative to the N-atom) increases, the rate of 1O2 quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N-demethylation products and N-formyl derivatives. The same trend was observed for the ratio between N-demethylation and formation of the N-formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme 1 where an exciplex is first formed that by a H-atom transfer process produces an α-amino-substituted C-radical. The latter forms the product of N-demethylation by one electron oxidation, or affords the N-formyl derivative by radical coupling (Scheme 1). Similar results were obtained with N,N-dimethylcyclohexanamine. However, this 'acyclic' amine exhibited behaviors quite distinct from those of the N-methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio.
- Baciocchi, Enrico,Del Giacco, Tiziana,Lapi, Andrea
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p. 2273 - 2280
(2007/10/03)
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- Cyclization of 5-hexenyl radicals from nitroxyl radical additions to 4-pentenylketenes and from the acyloin reaction
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Photochemical Wolff rearrangements were used to form 5-substituted-4-pentenylketenes 1a-1d (RCH=CHCH2X-CH 2CH=C=O: 1a R = H, X = CH2; 1b R = Ph, X = CH 2; 1c R = c-Pr, X = CH2; 1d R = H, X = O), which were observed by IR at 2121, 2120, 2119, and 2126 cm-1, respectively, as relatively long-lived species at room temperature in hydrocarbon solvents. These reacted with the nitroxyl radical tetramethylpiperidinyloxyl (TEMPO, TO·) forming carboxy-substituted 5-hexenyl radicals 3, which were trapped by a second nitroxyl radical forming 1,2 diaddition products 4a-4d. On thermolysis, 4a-4d underwent reversible reformation of the radicals 3, which underwent cyclization forming cyclopentanecarboxylic acid derivatives 6 or 11 as the major products. However, in the case of 1b, the cyclopentane derivative was formed reversibly and on prolonged reaction times the only product isolated was PhCH=CH-(CH2)4CO2H (8b) from hydrogen transfer to Cβ and cleavage of the TEMPO group. Cyclopropylcarbinyl radical ring opening in the cyclized radical 5c from 1c led to the 2-(4-N-tetramethylpiperidinyloxybut-1-enyl)cyclopentane derivative 11 as the major product. In a test for 5-hexenyl radical ring closure in the radical anion intermediate of the acyloin condensation, the ester CH 2=CH(CH2)3CO2Et (12a) gave the acyloin 13a (76%) as the only observed product, while PhCH=CH(CH 2)3CO2CH3 (12b) with Na in toluene gave 21% of the acyloin product 13b and 42% of 2-benzylcyclopentanol (15) from cyclization of the intermediate radical anion.
- Henry-Riyad, Huda,Tidwell, Thomas T.
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p. 697 - 704
(2007/10/03)
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- Thermolysis of N-tetramethylpiperidinyl triphenylacetate: Homolytic fragmentation of a TEMPO ester
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Thermolysis of N-tetramethylpiperidinyl triphenylacetate (7, Ph 3CCO2T, T = 2,2,6,6-tetramethylpiperidinyl) in benzene at 146 °C leads to the formation of triphenylmethane (Ph3CH, 80%), tetramethylpiperidine (TH, 91%), and tetraphenylmethane (Ph4C, 9%). First-order rate constants for the decomposition at 132.8 and 150.0 °C were 2.20 × 10-6 and 2.88 × 10-5 s-1, respectively. In benzene-d6 solvent the triphenylmethane was formed as Ph3CD to the extent of 20%, as determined by 1H NMR and mass spectrometry. The results are interpreted as showing that Ph 3CCC2T undergoes thermolysis by concerted two-bond scission with formation of Ph3C., tetramethylpiperidinyl radicals and CO2. The formation of Ph4C occurs by addition of Ph3C. to benzene, followed by hydrogen atom abstraction from the resulting adduct. Calculations using DFT methods at the B3LYP/6-311++G** level were used to elucidate the bond fission of HCO2T (2), and indicate that cleavage to HCO2. and T. is favored by 7.8 kcal mol-1 relative to cleavage to HC(·)=O and TO., in agreement with the experimental results. Copyright
- Henry-Riyad, Huda,Tidwell, Thomas T.
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p. 559 - 563
(2007/10/03)
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- Reaction of Nitroxides with Sulfur Containing Compounds II [1]. Preparation of Nitroxides Bearing an Isothiocyanate Substituent in View of the Nitroxyl Group Reduction with Thiophosgene
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The reaction of thiophosgene with 2,2,6,6-tetramethylpiperidine-1-oxyl (used as a model nitroxyl radical) was examined. 2,2,6,6-Tetramethylpiperidine and 2,2,6,6-tetramethyl-1-hydroxypiperidine were identified as products. The reaction is not competitive with the reaction of thiophosgene with an amino group. Thus, three nitroxides with an isothiocyanate group were synthesized from thiophosgene and the nitroxides containing the amino substituent.
- Zakrzewski, Jerzy,Hupko, Jarosllaw,Kryczka, Krzysztof
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p. 843 - 850
(2007/10/03)
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- Reactions of the 'stable' nitroxyl radical TEMPO with ketenes: Formation of a unique peroxidic source of aminyl radicals
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Calculations at the B3LYP level predict addition of the radical H2NO to the carbonyl carbon of CH2=C=O to be exothermic by 18.7 kcal/mol. Consistent with this prediction, the ketene Ph2C=C=O reacts at 25 ΔC with tetramethylpiperidinyloxy radical (TEMPO, TO) to yield an unstable species that reacts with oxygen to form the peroxide (OCPh2CO2T)2 (6, T = 2,2,6,6- tetramethylpiperidinyl), whose structure was confirmed by X-ray crystallography. Heating of 6 at 100 ΔC in toluene with TEMPO leads to Ph2C=O, tetramethylpiperidine, and PhCH2OT, indicating that 6 decomposes to form two 2,2,6,6-tetramethylpiperidinyl radicals 15. Kinetic studies of the thermal decomposition of 6 show a 100-fold rate acceleration relative to (PhMe2CO)2. Thermal reactions of TEMPO with the bisketene (Me3SiC=C=O)2 (23) at 90 °C and with the allenylketene 26 also lead to deoxygenation of TEMPO, forming radicals 15, together with 2,3-bis(trimethylsilyl)maleic anhydride (24) and the alkylidenelactone 27, respectively.
- Huang, Wen-Wei,Henry-Riyad, Huda,Tidwell, Thomas T.
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p. 3939 - 3943
(2007/10/03)
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- Interaction between trialkyl phosphites and aminoxyl radicals: A model study for polymer stabilization
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2,2,6,6-Tetramethylpipendine-1-oxyl (TEMPO) and its bis-1-oxyl analogue react with methyl and triisopropyl phosphite forming tetramethylpiperidine phosphite which is the main product of the reaction together with dialkyl phosphates. Minor products are tetramethylpiperidinyldialkyl phosphate and tetramethylpiperidine. The reaction mechanism was elucidated by observing the intermediate formation of the phosphoranyl radical which evolves forming the isolated products. The rate of this reaction is considerably lower compared to the stabilization reaction observed between phosphites and hydroperoxides during polymer oxidation. Thus the former reaction could be considered negligible in terms of polymer stabilization under the conditions studied.
- Mar'in, Alexander,Damiani, Elisabetta,Canestrari, Stefania,Dubs, Paul,Greci, Lucedio
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p. 1363 - 1367
(2007/10/03)
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- Synthesis, electrosynthesis and electrochemical properties of substituted 2,2,6,6-tetramethylpiperidine and the respective stable nitroxyl radicals. XIV
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The various derivatives of 2,2,6,6-tetramethylpiperidine and their stable nitroxyl radicals were investigated by means of chemical, electrochemical and empirical calculation methods. The titration results were calculated by means of TURBO BASIC with PKAS and MINIGLASS algorithm, and the prototropic experimental data were obtained. The reaction ways were calculated on the basis of the formation enthalpie values which were calculated by means of AM 1 (MOPACK) method. On the basis of a voltammetry and an electrolysis under controlled potential the reaction products were analyzed and the yields of the investigated processes were received. The various quasireversible redox reactions of the type stable nitroxyl radical oxoannonium cation were investigated by means of a cyclic voltammetry and electrochemical impedance spectroscopy. The mechanisms of the investigated reactions have been discussed and the reaction schemes are presented. - Key words: derivatives of 2,2,6,6-tetramethylpiperidine; electrolysis; electrochemical impedance spectroscopy; formation enthalpy values; prototropic constants
- Avrutskaya, Inna A.,Novikov, Vasilii T.,Dziegiec, Jozef,Grzejdziak, Andrzej,Krzyczmonik, Pawel,Scholl, Henryk
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- Homolytic Reactivity of Group 14 Organometallic Hydrides toward Nitroxides
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The spontaneous reactions of Et3SiH, Ph3GeH, Bu3SnH, and (Me3Si)3SiH with 2,2,6,6-tetramethyl1-piperidinoxyl (TEMPO) and related nitroxides have been investigated. Metal hydrides characterized by relatively weak metal-hydrogen bonds, like Ph3GeH and Bu3SnH, reduce TEMPO to the corresponding hydroxylamine while no reaction is observed with Et3SiH and Ph3SiH. Tris(trimethylsilyDsilane, on the other hand, is able to reduce the nitroxide to the corresponding hydroxylamine and amine in a ca. 1:1 ratio. By repeating the above reactions in the presence of thermal or photochemical radical initiators, deoxygenation of TEMPO was obtained in high yield with (Me3SD)3SiH and (Me3Si)2Si(H)Me, but not with other silanes, germanes, and stannanes. A mechanism for the reduction of TEMPO by the two trimethylsilyl-substituted silanes is proposed, and kinetic data for the various steps of the overall reaction are reported. In particular rate constants and activation parameters have been measured for the hydrogen transfer reaction from several silanes to the hindered aminyl radical 2,2,6,6-tetramethylpiperidinyl.
- Lucarini, Marco,Marchesi, Emanuela,Pedulli, Gian Franco,Chatgilialoglu, Chryssostomos
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p. 1687 - 1693
(2007/10/03)
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- The functionalization of saturated hydrocarbons. Part 34. A study on the mechanism of tempo trapping in GIF-type systems
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The photolysis of Barton PTOC esters (radical reaction) in presence of Tempo produces alkyl-Tempo in very good yield. Good results are also obtained with Fe(II)-H2O2 system (pyridine, Picolinic Acid, hydrocarbon). In this case the Fe(II)-Fe(IV) manifold is responsible for the formation of the adduct. Using Fe(III)-H2O2, Tempo adduct is formed at the same rate as the oxidation products. Mechanistic studies suggest the oxidation of Tempo by the Fe(V) to give an oxoammonium salt and an Fe(IV) species.
- Barton, Derek H. R.,Chabot, Beatrice M.,Hu, Bin
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p. 10301 - 10312
(2007/10/03)
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- Unexpected deoxygenation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) by thiyl radicals through the formation of arylsulphinyl radicals
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2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), upon reaction with thiophenols, undergoes deoxygenation leading mainly to the formation of tetramethylpiperidinium arylsulphinates and arylsulphonates. Other identified products of the reaction are aryldisulphides, 2,2,6,6-tetramethylpiperidine, S-aryl-arylthiosulphonates, N-arylsulphinyl- and N-arylsulphonyl-2,2,6,6-tetramethylpiperidine. The formation of the reaction products is discussed on the basis of the interaction of arylsulphinyl and arylsulphonyl radicals with TEMPO as well as on the basis of the evolution of the arylsulphinyl radical itself.
- Carloni,Carloni, Patricia,Damiani,Damiani, Elisabetta,Iacussi,Iacussi, Marco,Greci,Greci, Lucedio,Stipa,Stipa, Pierluigi,Cauzi,Cauzi, Daniele,Rizzoli,Rizzoli, Corrado,Sgarabotto,Sgarabotto, Paolo
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p. 12445 - 12452
(2007/10/02)
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- Prevention of oxidation in petrochemical extraction solvents
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A wide variety of hindered amine compounds are effective as antioxidant stabilizers to prevent the oxidation of liquid hydrocarbons and of oxygenated compounds, such as sulfolane or tetraethylene glycol, used as extraction solvents in the petroleum industry.
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- Kinetics and mechanism of chlorine exchange between chloramine-T and secondary amines
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The kinetics and mechanisms of chlorine transfer from chloramine-T (CAT) to several amines are second order and independent of p-toluenesulfonamide concentration; thus, the reaction does not involve disproportionation of CAT to dichloramine-T. From the profile of pH versus rate, the following mechanisms were proposed: (1) reaction of the ionized species of CAT with the ionized amine (ionic mechanism) and (2) reaction of the un-ionized species of CAT with the un-ionized amine (nonionic mechanism). The second-order, pH- independent rate constants calculated for the ionic and nonionic mechanisms were 1.6 and 5 x 106 M-1 s-1, respectively. Although these two mechanisms are kinetically indistinguishable, the rate constant for the nonionic mechanism is of the same order of magnitude as those calculated for similar chlorination reactions involving nonionizable chloramines, such as N- chlorosuccinimide, N-chloroquinuclidine, and N-chloro-N- methylbenzenesulfonamide. The proposed mechanism for the chlorine exchange involves a molecule of water in a cyclic, six-membered transition state.
- Dannan,Crooks,Dittert,Hussain
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p. 652 - 656
(2007/10/02)
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- Transient Alkylaminium Radicals in n-Hexane. Condensed-Phase Ion-Molecule Reactions
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Time-resolved fluorescence detected magnetic resonance (FDMR) is used to observe alkylaminium radicals formed in n-hexane solutions by electron pulse radiolysis.The ease of observation of aminium radical FDMR signals increases with increasing alkyl substitution of the amine solutes.The results are discussed in terms of the ion-molecule reactions, such as proton transfer, which compete with electron-transfer processes, i. e., the electron transfer from solute molecules to n-hexane radical cations and geminate recombination.
- Werst, D. W.,Trifunac, A. D.
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p. 1268 - 1274
(2007/10/02)
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- Interaction of tert-Butylcalixarenes with Cyclic Amines
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p-tert Butylcalixarenes 1 and 2 react with the cyclic amines 3 - 8, 10 by proton transfer forming so -called "exo-complexes" between the ammonium and phenolate groups.As well endocyclic as exocyclic amino groups are reactive.The nitroxyl radical 9 does not react with 1 or 2 by the proton transfer reaction.These results demonstrate that an interaction between the nitrogen atom of HALS-compounds, esp. compound 10, with calixarene hydroxylgroups is possible, but an interaction between the corresponding nitroxyl radicals with calixarene hydroxylgroups does not occur.
- Goermar, Gerhard,Seiffarth, Klaus,Schulz, Manfred,Chachimbombo, Chitula Leopoldina
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p. 475 - 479
(2007/10/02)
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- A Reaction of Nitroxides with Ethyl Mercaptane: A Mild Method for the Conversion of Nitroxides into Their Corresponding Amines
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The mild reduction of the nitroxides 1a-j to the corresponding sterically hindered amines 2a-j by means of ethyl mercaptane is reported.The reaction mixtures of 1a,b,g were analyzed by glc/ms.
- Zakrzewski, Jerzy
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p. 803 - 808
(2007/10/02)
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- STERIC FACTORS IN THE SHORT-RANGE SOLVATION OF SECONDARY AMINES
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Steric aspects of the short-range solvation of proton transfer complexes between 2,4-dinitrophenol and various secondary amines was studied in benzene-DMSO and benzene-dioxane mixed solvent systems.Diisopropylamine was hindered when compared with diethylamine, and 2,2,6,6-tetramethylpiperidine was hindered when compared with 2,6-dimethylpiperidine in forming the proton transfer complex.The smaller electron-donating solvent dimethylsulfoxide was capable of solvating the more hindered amines, but the the bulkier dioxane could only solvate diethylamine and dimethylpiperidine readily.Tetrahydropyran could solvate tetramethylpiperidine weakly, inferring that it did not solvate in precisely the same fashion as does dioxane.It is concluded that the solvation structure is sufficiently crowded as to be sensitive to small changes in the structures of the participants.
- Tayh, Jamal A.,Scott, Ronald M.
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p. 297 - 305
(2007/10/02)
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