Negative ions generated by reactions with oxygen in the chemical ionization source. II. The use of wall-catalyzed oxidation reactions for differentiation of polycyclic aromatic hydrocarbons and their methyl derivatives

Polycyclic aromatic hydrocarbons (PAH) undergo wall-catalyzed oxidation reactions, in conjunction with electron-and ion-molecule reactions, when oxygen is present in the chemical ionization source. Under conditions that promote these wall-catalyzed oxidation reactions (addition of oxygen, elevated ion source temperature) oxidized products are easily detected by measurement of the negative ion chemical ionization (NICI) mass spectra. The NICI mass spectra are dominated by ions that result from electron-capture ionization of oxidation products such as ketones, quinones and anhydrides. In this study the NICI mass spectra of 30 PAH and 46 methyl-substituted PAH were measured. These spectra can be used to differentiate certain isomeric PAH based upon differences in molecular structure. Of particular interest are ions that appear in the spectra of methyl-substituted PAH, which can provide information regarding the position of methyl substituents.     

Detailed mechanism generation. 2. Aldehydes, ketones, and olefins

Generalized reaction classes for the consumption and decomposition of aldehydes, ketones, and olefins are described. These classes are important for generating not only reactions for the consumption of the branching agents of low-temperature hydrocarbon combustion but also reactions of the oxidation of alkenes and the decomposition of cyclic ethers. These reaction classes have been extrapolated from specific reactions of existing validated mechanisms. The reaction patterns making up the class were derived by identifying the reactive center of the specific reactions and the important surrounding functional groups. The rates used currently are definitely "first guesses" based on these specific reactions. The reaction classes in this paper supplement the reaction classes derived from accepted reaction types in the previous paper in this series. The purpose of this paper is to outline a complete (with very few exceptions) set of reaction classes which describe the C(5) and C(6) products of the low-temperature and cyclic ether path in the heptane and isooctane mechanisms.     

Ionic liquid as catalyst and solvent: the remarkable effect of a basic ionic liquid, [bmIm]OH on Michael addition and alkylation of active methylene compounds

A basic ionic liquid, 1-methyl-3-butylimidazolium hydroxide, [bmIm]OH, catalyzes the Michael addition of active methylene compounds to conjugated ketones, carboxylic esters and nitriles. It further catalyzes the addition of thiols to α,β-acetylenic ketones and alkylation of 1,3-dicarbonyl and -dicyano compounds. The Michael addition to α,β-unsaturated ketones proceeds in the usual way, giving the monoaddition products, whereas addition to α,β-unsaturated esters and nitriles leads exclusively to the bis-addition products. The α,β-acetylenic ketones undergo double conjugate addition with thiols producing β-keto 1,3-dithio-derivatives. In the alkylation reaction the acyclic 1,3-diketones are monoalkylated, whereas cyclic ketones undergo dialkylation under identical conditions. All these reactions were carried out without any organic solvent. The ionic liquid can also be recycled.     

Efficient and convenient oxidation of alcohols to aldehydes and ketones with molecular oxygen mediated by In(NO3)3 in ionic liquid [C12mim][FeBr4]

A simple, efficient, and ecofriendly procedure for the aerobic oxidation of alcohols to aldehydes and ketones in the presence of In(NO₃)₃/[C₁₂mim][FeBr₄] in aqueous media has been developed. The oxidation reactions afford the target products in good to high yields and no over-oxidation was observed. The products can be separated by a simple extraction with dichloromethane, and the system can be recycled and reused without loss of activity.     

Selective oxidation of cyclohexanol and 2-cyclohexen-1-ol on O/Au(111): the effect of molecular structure

We combine reactivity studies with infrared reflection absorption spectroscopy to provide molecular-scale insights into the oxidation of two cyclic alcohols, cyclohexanol and 2-cyclohexen-1-ol, by atomic oxygen adsorbed on Au(111). The two alcohols share common features in their reaction pathways: they are both activated by Br?nsted acid-base reactions with adsorbed oxygen. Cyclic ketones, cyclohexanone and 2-cyclohexen-1-one, are the major products, formed from cyclohexanol and 2-cyclohexen-1-ol, respectively. These ketones also undergo secondary ring C-H bond activation. The product distributions reflect a substantial difference in the secondary reactions for these two ketones, which correlate with their gas-phase acidity. The allylic alcohol (2-cylohexen-1-ol) has a greater degree of ring C-H activation, yielding the diketone (2-cyclohexene-1,4-dione) and phenol. Our results provide clear evidence for the importance of C═C functionalities in determining the reactivity of molecules in heterogeneous oxidative transformations promoted on Au-based materials.     

席夫碱修饰的MCM-41介孔分子筛与碳酸钾共同催化查尔酮的环氧化反应

将介孔分子筛MCM-41依次与3-氯丙基三乙氧基硅烷、二氨基硫脲和水杨醛反应,得到席夫碱修饰的介孔分子筛MCM-41催化剂,以过氧化氢为氧源,研究了其与K2CO3共同催化α,β-不饱和酮的环氧化反应。 化合物的结构经1H NMR和IR分析确认。 考察了金属盐、溶剂、催化剂用量、反应时间等因素对环氧化反应的影响。 结果表明,室温下α,β-不饱和酮的环氧化反应在短时间内均以较高的产率(最高达93%)得到了相应的产物。 同时,对催化剂的重复利用进行了研究,发现重复使用4次,仍能以较高产率得到环氧化产物。     

Intramolecular reactions of benzylic azides with ketones: competition between Schmidt and Mannich pathways.

The Lewis acid-promoted reactions of benzylic azides with ketones can proceed by two major pathways. The azido-Schmidt reaction involves simple addition of azide to the ketone followed by rearrangement and ring expansion. In addition, benzylic azides can undergo prior rearrangement to afford iminium ions that can subsequently participate in a Mannich reaction. A series of ketones containing an alpha CH2(CH2)nCH(N3)Ph substituent (n = 1-3) was prepared to investigate the dependence of products on ketone ring size and tether length. For all ketones examined, good yields of bicyclic lactams arising from intramolecular Schmidt reaction were obtained when a four-carbon linker was used (n = 1 in the above formulation), but Mannich products predominated for the longer tethers examined (n = 2, 3).     

1,2-联烯基酮的合成与反应

1,2-联烯基酮可以通过2-丙炔基酮异构化反应,相应有机金属试剂中间体与酯、酰氯或酰胺的反应,[2,3]或[3,3]迁移反应,Wittig反应,消除反应,2,3-联烯醇氧化等方法合成。由于联烯酮上含有吸电子基团羰基,它可发生亲核加成、环加成、环化反应。     

Reactive organoallyl species generated from aryl halides and allene: allylation of α,β-unsaturated aldehydes and cyclic ketones employing Pd/In transmetallation processes

Allylation of α,β-unsaturated aldehydes and cyclic ketones promoted by Pd/In transmetallation processes has been studied. The unsaturated aldehydes underwent regioselective 1,2-addition to afford secondary homoally alcohols. The reactions have been performed using Pd(OAc)₂/PPh₃ as catalytic system and metallic indium affording the products in good yields. The same transformation with unsaturated ketones proved to be less efficient, while saturated cyclic ketones delivered generally excellent yields in the presence of CuI. In these latter processes the presence of a distal heteroatom influences the reaction rate.     

Reductive Amination of Aldehydes and Ketones with Sodium Triacetoxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures(1)

Sodium triacetoxyborohydride is presented as a general reducing agent for the reductive amination of aldehydes and ketones. Procedures for using this mild and selective reagent have been developed for a wide variety of substrates. The scope of the reaction includes aliphatic acyclic and cyclic ketones, aliphatic and aromatic aldehydes, and primary and secondary amines including a variety of weakly basic and nonbasic amines. Limitations include reactions with aromatic and unsaturated ketones and some sterically hindered ketones and amines. 1,2-Dichloroethane (DCE) is the preferred reaction solvent, but reactions can also be carried out in tetrahydrofuran (THF) and occasionally in acetonitrile. Acetic acid may be used as catalyst with ketone reactions, but it is generally not needed with aldehydes. The procedure is carried out effectively in the presence of acid sensitive functional groups such as acetals and ketals; it can also be carried out in the presence of reducible functional groups such as C-C multiple bonds and cyano and nitro groups. Reactions are generally faster in DCE than in THF, and in both solvents, reactions are faster in the presence of AcOH. In comparison with other reductive amination procedures such as NaBH(3)CN/MeOH, borane-pyridine, and catalytic hydrogenation, NaBH(OAc)(3) gave consistently higher yields and fewer side products. In the reductive amination of some aldehydes with primary amines where dialkylation is a problem we adopted a stepwise procedure involving imine formation in MeOH followed by reduction with NaBH(4).     

Synthesis of β-silyl ketones via reaction of trimethylsilyllthium with unsaturated hydrazones. Application to the synthesis of brevicomin

Trimethylsilyllithium undergoes conjugate addition to dimethylhydrazones of α,β-unsaturated ketones. The resulting metalloenamine intermediates can be alkylated, and the resulting hydrazone products cleaved to give α-substituted-β-silyl ketones. These reactions, together with a silicon-directed Baeyer-Villiger reaction, have been applied to the synthesis of brevicomin.     

Nafion-H?: A recyclable and diastereoselective solid acid catalyst for three-component mannich reaction

One-pot, three-component Mannich reactions of ketones, aldehydes and amines are efficiently catalyzed by heterogeneous Nafion-H? ambient temperature to give the corresponding ??-amino ketones compounds in good to excellent yields. The catalyst can be easily recovered and reused without any decrease of activity for at least four times. Diastereoselective products can be obtained in Mannich reaction of aliphatic ketone.     

Catalytic [4+1] cycloaddition of alpha,beta-unsaturated carbonyl compounds with isocyanides

The GaCl(3)-catalyzed [4+1] cycloaddition reactions of alpha,beta-unsaturated ketones with isocyanides leading to lactone derivatives are described. While some other Lewis acids also show catalytic activity, GaCl(3) was the most efficient catalyst. The reaction is significantly affected by the structure of both the isocyanides and the alpha,beta-unsaturated ketones. Aromatic isocyanides, especially sterically demanding ones and those bearing an electron-withdrawing group, can be used, but aliphatic isocyanides cannot. The bulkiness of substituents at the beta-position of acyclic alpha,beta-unsaturated ketones is an important factor for the reaction to proceed efficiently. Generally, the more the bulky substituent, the higher is the yield. The reaction of alpha,beta-unsaturated ketones bearing geminal substituents at the beta-position gave the corresponding products in high yields. In monosubstituted derivatives, the yields are relatively low. However, substrates having a bulky substituent, such as a tert-Bu group, at the beta-position give high yields. Bulkiness is also required in cyclic alpha,beta-unsaturated ketones, but the effect is small. In alkyl vinyl ketones, the reactivity decreased with the steric bulk of the alkyl group. In aryl vinyl ketones, the presence of an electron-donating group on the aromatic ring decreases the reactivity. The success of the catalysis can be attributed to the low affinity of GaCl(3) toward heteroatoms, compared with usual Lewis acids.     

Pinacol cleavage using iron(III)trisphenanthroline complexes

Oxidative bond cleavage of benzpinacol and 2,3-diphenyl-2,3- butanediol have been effected with two Fe(III)(1,10-phenanthroline)₃ complexes which are thought to undergo electron transfer reactions by an outer sphere mechanism. The products of these reactions are exclusively the corresponding ketones when 2,6-di-t-butylpyridine is added to the solution. In contrast to the facile oxidations of these aromatic substrates, pinacol is not cleaved under these reaction conditions.     

超临界(压缩)二氧化碳介质中的选择氧化

由于超临界二氧化碳（SCCO₂）具有稳定、安全、不燃、清洁无毒、粘度小、扩散快、可压缩的特殊性质,所以使得超临界二氧化碳非常适合作为催化反应的绿色溶剂.除此之外,多种气体在超临界二氧化碳中的溶解度很高,这对于那些受传质阻碍和易引起安全隐患的气相反应来讲,使用SCCO₂作为替代的反应溶剂具有重要的价值。值得指出的是：如果选择超临界二氧化碳作为氧化反应的溶剂,其自身不会发生反应而产生副产物,从而容易得到清洁的产物。本文主要讨论了超临界二氧化碳作为反应介质对醇、烯烃和烷烃等选择氧化反应的影响,通过与传统溶剂比较可以看出超临界二氧化碳作为氧化反应溶剂的优势,对近几年来以分子氧为氧化剂,以超临界二氧化碳为介质的催化选择氧化的反应体系作了综述,并对未来的发展提出了展望。     

Amino acid catalyzed direct asymmetric aldol reactions: a bioorganic approach to catalytic asymmetric carbon-carbon bond-forming reactions.

Direct asymmetric catalytic aldol reactions have been successfully performed using aldehydes and unmodified ketones together with commercially available chiral cyclic secondary amines as catalysts. Structure-based catalyst screening identified L-proline and 5,5-dimethyl thiazolidinium-4-carboxylate (DMTC) as the most powerful amino acid catalysts for the reaction of both acyclic and cyclic ketones as aldol donors with aromatic and aliphatic aldehydes to afford the corresponding aldol products with high regio-, diastereo-, and enantioselectivities. Reactions employing hydroxyacetone as an aldol donor provide anti-1,2-diols as the major product with ee values up to >99%. The reactions are assumed to proceed via a metal-free Zimmerman-Traxler-type transition state and involve an enamine intermediate. The observed stereochemistry of the products is in accordance with the proposed transition state. Further supporting evidence is provided by the lack of nonlinear effects. The reactions tolerate a small amount of water (<4 vol %), do not require inert reaction conditions and preformed enolate equivalents, and can be conveniently performed at room temperature in various solvents. In addition, reaction conditions that facilitate catalyst recovery as well as immobilization are described. Finally, mechanistically related addition reactions such as ketone additions to imines (Mannich-type reactions) and to nitro-olefins and alpha,beta-unsaturated diesters (Michael-type reactions) have also been developed.     

Mechanisms of chain scission and the role of oxidation products in the oxidative radiolysis of ethylenepropylene copolymer

Many works have been devoted to the photo-oxidation of polyolefins but numerous questions remain. The aim of this paper is to constitute a complementary source of informations leading to the radiation oxidation mechanism of these polymers which could explain the chain scission process the basis of the alteration of mechanical and physical properties of polyolefins. It can be seen from our results that the hydroperoxides and the ketones are primary products of the reaction. A new secondary reaction efficiently leading to the alteration of mechanical properties has been proposed.     

Investigation on the regioselectivities of intramolecular oxidation of unactivated C-H bonds by dioxiranes generated in situ

We found that dioxiranes generated in situ from ketones 1-6 and Oxone underwent intramolecular oxidation of unactivated C-H bonds at delta sites of ketones to yield tetrahydropyrans. From the trans/cis ratio of oxidation products 1a and 2a as well as the retention of the configuration at the delta site of ketone 5, we proposed that the oxidation reaction proceeds through a concerted pathway under a spiro transition state. The intramolecular oxidation of ketone 6 showed the preference for a tertiary delta C-H bond over a secondary one. This intramolecular oxidation method can be extended to the oxidation of the tertiary gamma' C-H bond of ketones 9 and 10. For ketone 11 with two delta C-H bonds and one gamma' C-H bond linked respectively by a sp(3) hydrocarbon tether and a sp(2) ester tether, the oxidation took place exclusively at the delta C-H bonds. Finally, by introducing proper tethers, regioselective hydroxylation of steroid ketones 12-14 have been achieved at the C-17, C-16, C-3, and C-5 positions.     

Oxidation of alcohols to aldehydes and ketones using selenium ionic liquid

A new type of ionic liquid supported selenium reagents were synthesized and found to be an excellent catalyst in the oxidation of alcohols to aldehydes and ketones in the presence of 30%H₂O₂.The predictable solubility of ionic liquids allows an easy separation of the oxidation products from the reaction mixture.Furthermore,the oxidation reaction can be carried out using an ionic liquid as the solvent,and the ionic liquid-supported selenium reagents can be recycled and used for four times with a little decrease in catalytic performance.     

The Baeyer–Villiger oxidation of ketones: A paradigm for the role of soft Lewis acidity in homogeneous catalysis

The Baeyer–Villiger oxidation of ketones to the corresponding esters or lactones is a valuable transformation that has been upgraded several times over the last century, from the original use of monopersulfuric acid as oxidant to more atom efficient and environmentally friendly oxidants such as hydrogen peroxide. The latter requires activation with organometallic complexes to explicate its oxidizing power. The catalytic version of the reaction can be achieved with several transition metal catalysts, but major differences are present among the various catalysts proposed in terms of scope of the reaction. In particular, most of the catalytic systems are active towards four-membered ring ketones leading to the corresponding substituted γ-butyro-lactones. Pt^II complexes characterized by the employment of chelating diphosphines turned out to be the most efficient in catalyzing the BV oxidation of a wider range of substrates, in particular cyclohexanones are suitable substrates and acyclic ketones can be converted into the corresponding esters, albeit with low turnover. As long as organometallic catalyzed BV reaction is concerned, Pt^II catalysts show the most versatile activity and selectivity. Such peculiar features are the result of the unique electronic properties of such metal combined with an easily tailored soft Lewis acid character modulated by the proper choice of the ancillary ligands. The enantioselective version of the reaction benefits from these properties and the compatibility of Pt^II species with water enabled the development of asymmetric catalytic BV reactions in water aided by the presence of micelles as dynamic self-assembled environments.