烷基对蒽衍生物在水-乙腈中用硝酸铈铵氧化机理的影响

在水-乙腈混合溶剂中用(NH~4)~2Ce(NO~3)~6氧化烷基蒽. 甲基, 乙基和环丙基蒽经历氧化-水解-氧化-水解-消除-氧化-去质子历程, 得到蒽环氧化产物, 消除烷基(或氢原子)的可能顺序是:H＞CH~3＞C~2H~5. 当蒽环的1,9-位连着1,2-亚乙基桥时, 却经由氧化-去质子-氧化水解-氧化(或消除)历程, 得到侧链氧化产物. 烷基的本质对多核芳烃的氧化机理有显著的影响.     

1，9－乙撑基蒽和1，9－乙撑基－10－甲基蒽的单电子氧化

报道了１，９－乙撑基蒽和１，９－乙撑基－１０－甲基蒽在ＣＨＣｌ_３／吡啶中与碘反应的机理。它们的单电子氧化生成游离基正离子，该过程存在侧链去质子和吡啶进攻蒽环两种竞争反应。蒽环上引入乙撑基使侧链氧化远比环氧化占优势。乙撑基比甲基容易去质子。     

1,9—乙撑基蒽和1,9—乙撑基—10—甲基蒽的单电子氧化

报道了１，９－乙撑基蒽和１，９－乙撑基－１０－甲基蒽在ＣＨＣｌ３／定点 与碘反应的机理，它们的单电子氧化生成游离基正离子，该过程存在侧链去质子和吡啶进攻蒽环两种竞争反应，蒽环上引入乙撑基使侧链氧化远比环氧化占优势，乙撑基比甲基容易去质子。     

原油空气氧化前后多环芳烃组分的气相色谱-质谱分析

采用柱层析法对空气氧化前后的原油进行族组分分离,利用气相色谱-质谱(GC-MS)分离测定其芳香烃组分,分析多环芳烃组分的变化.结果表明,随着氧化过程的进行,烷基化多环芳烃占多环芳烃的含量从氧化前的71.5%增加到92.0%(175℃)和90.2%(225℃).轻质组分萘和菲的优势逐渐被重质组分艹屈取代.侧链少的多环芳烃比侧链多的更易氧化.氧化后,其他稠环化合物蒽、萤蒽、芘、苯并蒽含量降低,苯并萤蒽含量增加;苯并芘在175℃氧化后含量降低,而在225℃氧化后含量增加.与此同时,175℃氧化后生成了原油所不含有的三芳甾烃、联苯和苯并呋喃.     

几种β-烷基萘的催化脱氢环化的研究

在铬铝催化剂上,温度400—500℃和空速0.1—0.87时~(-1)的反应条件下,研究了β-正庚萘、β-(2-甲基丁基)萘、β-(1-丙基丁基)萘和β-(1-丁基丁基)萘的脱氢环化。β-烷基萘的烷基侧链结构对脱氢环化反应有明显的影响。β-(2-甲基丁基)萘的脱氢环化同β-(3-甲基丁基)萘比较类似,生成30％的2-甲基蒽;但同β-(1-甲基丁基)萘较少类似,仅生成约5％的菲。当β-烷基萘的烷基侧链碳原子多于6个时,不仅在烷基侧链与萘环碳原子之间可以脱氢环化,生戍菲、蒽及其同系物,而且在烷基侧链碳原子之间也可以脱氢环化生成苯井芴和(?)等稠环芳烃,在β-烷基萘脱氢环化的同时,还伴随有裂解反应;烷基侧链愈长,裂解现象就越严重。     

碳苷研究 XXVII. 黑豆素非环类似物的合成

本文报道天然黄酮碳苷黑豆素非环类似物的合成, 以2,4-二羟基苯乙酮为原料, 经酚羟基的单苄基化、Claisen重排、醇醛缩合、I2/DMSO/浓度H2SO4关环五步反应得到黄酮; 用Claisen重排, 分别在黄酮环生成之前和生成之后引入8-位取代基侧链, 收率国产高。修饰8-位烯丙基侧链, 得到了六个黑豆素类似物, 共中8的7-位为游离羟基。     

俄罗斯直馏柴油中硫化物的分离富集与结构鉴定

采用选择性氧化剂和还原剂对俄罗斯直馏柴油中的硫醚类硫化物和噻吩类硫化物分别进行分离和富集,得到两者的浓缩液。运用质谱技术对分离出的硫化物结构进行鉴定。结果表明:氧化还原法是分离俄罗斯直馏柴油中硫化物的有效方法;硫醚类硫化物浓缩液中鉴定有烷基四氢噻吩和烷基四氢噻喃类化合物,四氢噻喃类硫化合物的烷基取代碳数在C4~C13范围;噻吩类硫化物浓缩液中有烷基侧链长度为C0~C9之间的苯并噻吩,烷基侧链长度为C0~C3之间的二苯并噻吩。     

丙酮醇作用下3-亚烷基酮的区域选择性加氢还原反应

本文报道了一种室温、空气氛围下，以丙酮醇为还原剂的3-亚烷基氧化吲哚环外C=C双键选择性加氢还原反应合成3-取代氧化吲哚的方法。在碳酸钾存在下，丙酮醇与3-亚烷基氧化吲哚在甲醇中反应得到13个3-烷基取代氧化吲哚，其中6个为新化合物；机理分析表明:该反应符合加成-消除机理。     

离子液体对淀粉酶催化反应的影响

用分光光度法研究了二烷基咪唑氯类和二烷基咪唑磷酸酯类离子液体对淀粉酶催化反应的影响,通过吸光度的变化来测定淀粉水解的程度。 结果表明,这两类离子液体对淀粉酶催化反应均有明显的抑制作用,其中1-己基-3-甲基咪唑氯[HMIM]Cl的抑制作用最大。 而且,对于相同的阴离子,随着阳离子咪唑环烷基取代基链长的增加,抑制作用也增加。     

蒽环与苯环间的光化学Ⅳ.烷氧基取代基与光化学反应

蒽的光化学反应在很多领域有广泛的应用,如超分子体系的标记剂,敏化剂,分子荧光传感器等,使蒽的光化学-直成为最重要的光化学反应之一[1-3].我们在近年发现3,5-二烷氧基苯基蒽衍生物可以发生蒽环与苯环间的光致可逆环加成反应,反应是定量进行的,这种光致可逆反应性能可以用作分子光开关器件,在材料科学中有着重要的应用前景[4];进一步的研究结果表明,苯环上的取代基对蒽环与苯环间的光致环加成反应有重要的影响.2,5-烷氧基双取代蒽环衍生物、3,5-二烷氧基双取代、3,4,5-三烷氧基取代时,都可以发生蒽环与苯环间的光致环加成反应;但是,苯环上4-单取代、2,3-双取代时,不能发生蒽环与苯环间的光致环加成反应,只能发生蒽环与蒽环间的光致环加成反应;苯环上3-烷氧基单取代时,可发生两种光致环加成反应.蒽环与苯环间的光致环加成反应产物(烯醇醚)在微量酸催化下发生裂解,产生单降解产物(单环酮)和双降解产物(双环酮),蒽环与蒽环间的光致环加成反应产物不能被酸催化下发生裂解,因而得不到单酮和双酮产物.     

Spectral analysis of naringenin deprotonation in aqueous ethanol solutions

The deprotonation of 5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one (naringenin) was studied in aqueous solutions of ethanol and 0.1 mol L^?1 sodium perchlorate at 25°C. The chemical species that contributed to deprotonation were evaluated together with their pure spectral characteristics and concentration profiles by some chemometric methods. The deprotonation constants assigned by pK ₁, pK ₂, and pK ₃ were determined by multivariate curve analysis of spectral data at different pcH values. The pure spectral analysis concordant with the theoretical prediction of deprotonation constants indicates that the acidity of hydroxyl groups in naringenin decreases in the order: 7-OH, 4′-OH, 5-OH. The effects of the solvent on deprotonation were analysed in terms of the linear solvation energy relationships using the model of Kamlet, Abboud, and Taft (KAT). Multiple linear regressions were aimed towards correlating the deprotonation constants with the microscopic parameters containing hydrogen-bond acidity (α), dipolarity/polarisability (π*), and hydrogen-bond basicity (β). The most significant parameter was found to be the hydrogen-bond acidity of binary mixtures.     

Radiation Chemistry of Organic Molecules in Solid Rare Gas Matrices: 2. Selective Deprotonation of the Primary Radical Cations upon Irradiation of Oxygen-Containing Molecules in Xenon Matrices

The composition of radical products trapped after irradiation of various ethers (dimethyl ether, tetrahydrofuran, methylal, 1,3-dioxolane) or acetaldehyde in xenon matrices at 15–17 K in the presence of electron scavengers was studied by an ESR technique. It was shown that the primary radical cations give corresponding deprotonation products (carbon-centered radicals), rather than stabilize in xenon, under the given experimental conditions. The deprotonation process is characterized by extremely high selectivity; i.e., the only type of radicals resulting from deprotonation at maximum spin density position was observed in each of the cases. The possible mechanism of the reactions and the nature of their selectivity are discussed.     

STM-based molecular detection of "catch-and-release" of protons for bipyridine bound to phenylene-ethynylene thiol

The protonation/deprotonation response of a novel bipyridine containing (phenylene-ethynylene) thiol adsorbed to a Au surface was investigated with scanning tunneling microscopy (STM), showing reversible changes in the average heights (approximately 50 spots) and the height distribution arising from protonation/deprotonation.     

水化介孔氧化硅表面酸碱平衡常数的测定

采用自动电位酸碱滴定技术研究了水化介孔氧化硅的表面脱质子反应.基于悬浮液的酸碱滴定数据,用Gran图法计算得到了介孔氧化硅表面氢离子键位点浓度.利用FITEQL4.0软件,采用双电层恒电容模型计算得到了相应的表面酸碱平衡常数.结果表明,与无定形氧化硅不同,介孔氧化硅表面存在对应于双齿表面硅羟基≡Si2OH和单齿表面硅羟基≡SiOH的两个脱质子常数,分别为pKa1=6.78±0.15,pKa2=10.25±0.22.根据测定得出的介孔氧化硅表面脱质子常数,构建了不同pH条件下,介孔氧化硅表面优势组分分布图,并讨论了表面电容预赋值对氧化硅表面组分分布的影响.     

Halide ions complex and deprotonate dipicolinamides and isophthalamides: assessment by mass spectrometry and UV-visible spectroscopy

The F(-), Cl(-), and Br(-) binding selectivity of bis(p-nitroanilide)s of dipicolinic and isophthalic acids was studied by using competitive electrospray mass spectrometry and UV-Visible spectroscopy. Both hosts prefer binding Cl(-) over either F(-) or Br(-). Host deprotonation was observed to some extent in all experiments in which the host was exposed to halide ions. When F(-) was present, host deprotonation was often the major process, whereas little deprotonation was observed by Cl(-) or Br(-), which preferred complexation. A solution of either host changed color when mixed with a F(-), H(2)PO(4)(-), di- or triphenylacetate solution.     

Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine

First-order rate constants for deprotonation of the alpha-imino carbon of the adduct between 5'-deoxypyridoxal (1) and glycine were determined as the rate constants for Claisen-type addition of glycine to 1 where deprotonation is rate determining for product formation. There is no significant deprotonation at pH 7.1 of the form of the 1-glycine iminium ion with the pyridine nitrogen in the basic form. The value of kHO for hydroxide ion-catalyzed deprotonation of the alpha-imino carbon increases from 7.5 x 10(2) to 3.8 x 10(5) to 3.0 x 10(7) M(-1) s(-1), respectively, with protonation of the pyridine nitrogen, the phenoxide oxyanion, and the carboxylate anion of the 1-glycine iminium ion. There is a corresponding decrease in the pKas for deprotonation of the alpha-imino carbon from 17 to 11 to 6. It is proposed that enzymes selectively bind and catalyze the reaction of the iminium ion with pKa = 17. A comparison of kB = 1.7 x 10(-3) s(-1) for deprotonation of the alpha-imino carbon of this cofactor-glycine adduct (pKa = 17 by HPO4(2-) with k(cat)/K(m) = 4 x 10(5) M(-1) s(-1) for catalysis of amino-acid racemization by alanine racemase shows that the enzyme causes a ca 2 x 10(8)-fold acceleration of the rate of deprotonation the alpha-imino carbon. This corresponds to about one-half of the burden borne by alanine racemase in catalysis of deprotonation of alanine.     

Time-resolved resonance Raman and density functional theory study of the deprotonation reaction of the triplet state of p-hydroxyacetophenone in water solution

[reaction; see text] Picosecond and nanosecond time-resolved resonance Raman (TR(3)) spectroscopy was employed to investigate the deprotonation/ionization reaction of p-hydroxyacetophenone (HA) after ultraviolet photolysis in water solution. The TR(3) spectra in conjunction with density functional theory (DFT) calculations were used to characterize the structure and dynamics of the excited-state HA deprotonation to form HA anions in near neutral water solvent. DFT calculations based on a solute-solvent intermolecular H-bonded complex model containing up to three water molecules were used to evaluate the H-bond interactions and their influence on the deprotonation reaction and the structures of the intermediates. The deprotonation reaction was found to occur on the triplet manifold with a planar H-bonded HA triplet complex as the precursor species. The HA triplet species is generated within several picoseconds and then decays with a approximately 10 ns time constant to produce the HA triplet anion species after 267 nm photolysis of HA in water solution. The triplet anion species was observed to decay with a time constant of about 90 ns into the ground-state anion species that was found to have a lifetime of about 200 ns. The DFT calculations on the H-bonded complexes of the anion triplet and ground-states species suggest that these anion species are H-bonded complexes with planar quinonoidal structures containing two water molecules H-bonded, respectively, with oxygen lone pairs of the carbonyl and deprotonated hydroxyl moieties. A deactivation scheme of the photoexcited HA in regard to the deprotonation reaction in neutral water solutions was proposed. With the above dynamic and structural information available, we briefly discuss the possible implications of the model HA photochemistry in water solutions for the photodeprotection reactions of related p-HP phototrigger compounds in aqueous solutions.     

Ionization mechanism of oligonucleotides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The ionization of nucleosides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was systematically investigated using adenine (A), thymine (T), guanine (G) and cytosine (C) with several common matrices. Experimental results of the protonation and deprotonation of the bases of A, T, G and C in the matrices 2,5-dihydroxybenzoic acid (2,5-DHB), alpha-cyano-4-hydroxycinnamic acid (alpha-CHCA) and 3-hydroxypicolinic acid (3-HPA) provide an insight into the ionization mechanism of oligonucleotides in MALDI. It was found that the low ion signal from DNA in poly-G in MALDI as reported in earlier work could be attributed to the fact that the base of G is difficult to ionize. Our results suggest that the ionization of DNA in MALDI is dominated by the protonation and deprotonation of bases and it is basically independent of the backbone of DNA. Both the protonation and deprotonation are strongly structure dependent. The protonation is dominated by pre-protonation before laser ablation, while the deprotonation is controlled by the thermal reaction.     

A comparison of the electrophilic reactivities of Zn2+ and acetic acid as catalysts of enolization: imperatives for enzymatic catalysis of proton transfer at carbon

The deprotonation of the alpha-CH3 and alpha-CH2OD groups of hydroxyacetone and the alpha-CH3 groups of acetone in the presence of acetate buffer and zinc chloride in D2O at 25 degrees C was followed by monitoring the incorporation of deuterium by 1H NMR spectroscopy, and the rate laws for catalysis of these reactions by acetate anion and zinc dication were evaluated. Relative to solvent water at a common standard state of 1 M, Zn2+ provides 6.3 and 4.4 kcal/mol stabilizations, respectively, of the transition states for deprotonation of the alpha-CH2OD and alpha-CH3 groups of hydroxyacetone by acetate anion, and a smaller 3.3 kcal/mol stabilization of the transition state for deprotonation of the alpha-CH3 group of acetone. There is only a 1.4 kcal/mol smaller stabilization of the transition state for the acetate-ion-promoted deprotonation of acetone by the Br?nsted acid acetic acid than by Zn2+, which shows that, in the absence of a chelate effect, there is no large advantage to the use of a metal dication rather than a Br?nsted acid to stabilize the transition state for deprotonation of alpha-carbonyl carbon.     

Selective ortho and benzylic functionalization of secondary and tertiary p-tolylsulfonamides. Ipso-bromo desilylation and Suzuki cross-coupling reactions

Kinetic vs thermodynamic deprotonation studies on secondary and tertiary sulfonamides 1 and 2 using n-BuLi have been carried out. While both 1 and 2 show kinetic ortho-metalation, thermodynamic conditions lead to ortho and benzylic deprotonation, respectively (Figures 1 and 2). Metalation of 1 using the n-BuLi/KOtBu superbase led to regioselective benzylic metalation (Figure 4); LDA deprotonation was also briefly explored. Application of the developed conditions allows the synthesis of diverse sulfonamide products 5a-e, 6a-e, 7a,b, and 8a-e. Ipso-bromo desilylation reactions afford sulfonamides 9a,b while Suzuki cross-coupling reactions furnish biaryl sulfonamides 11a-c.