Enthalpies of dilution of aqueous systems containing hexamethylenetetramine and other nonelectrolytes

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine, alone and in ternary system with each of mannitol, myoinositol, cyclohexanol, formamide, dimethylformamide, and trioxane have been determined. The data have been treated in terms of the Savage-Wood additivity principle and first estimates for the pairwise groups interaction enthalpies of N/N, CH₂/N, CHOH/N, COHN/N and –O–/N have been made. The results are discussed in light of all other known group interaction enthalpies. The limitations and utilities of the Savage-Wood principle are reviewed.     

Synthesis and chromatographic enantioresolution of anti-HIV quinolone derivatives

The successful enantioseparation of five 6-desfluoroquinolones with three polysaccharide-based stationary phases (namely, the cellulose-based Chiralpak IB and the two amylose-based Chiralpak AD-H and Lux Amylose-2) is herein described. The investigated species differ for the nature of substituents and/or the position of the stereogenic centre on the quinolone scaffold.The effect on the enantioseparation performance exerted by the different morphology of the cellulose-based and amylose-based polymers, was systematically evaluated for all compounds. In this frame, the impact of alternative alcoholic (ethanol, 2-ethoxyethanol, methanol, 2-propanol) and acidic (acetic, methanesulfonic and trifluoroacetic acid) modifiers as well as of a “non-standard” solvent (chloroform), was investigated in normal phase conditions along with the stereo-electronic peculiarities of the selected polymers. While 7-[4-(1,3-benzothiazol-2-yl)-2-methyl-1-piperazinyl]-1-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylic acid (1) was enantioresolved with conventional normal-phase conditions by means of the largely employed amylose-based Chiralpak AD-H column, the recruitment of a bulky alcohol (2-ethoxyethanol) succeeded in the enantioresolution of 6-amino-1-methyl-7-[2-methyl-4-(2-pyridinyl)-1-piperazinyl]-4-oxo-1,4-dihydro-3-quinolinecarboxylic acid (2) and 6-amino-1-[1-(hydroxymethyl)propyl]-4-oxo-7-(4-pyridin-2-ylpiperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic acid (3) with the same column. The use of the amylose-based Lux Amylose-2 column, carrying both an electro-withdrawing (chlorine) and an electro-donating (methyl) group on the carbamate residue, allowed to get 6-amino-1-methyl-4-oxo-7-[3-(2-pyridinyl)-1-pyrrolidinyl]-1,4-dihydro-3-quinolinecarboxylic acid hydrochloride (4) enanantioresolved, and 6-amino-1-methyl-4-oxo-7-(3-pyridin-2-ylpiperidin-1-yl)-1,4-dihydroquinoline-3-carboxylic acid (5) enantioseparated.     

3-[Amino(methylthio)methylene]pentane-2,4-dione in the synthesis of functionalized pyridines

New syntheses of functionalized pyridines from 3-[amino(methylthio)methylene]-2,4-pentanedionevia its boron chelates were proposed. The products of condensation of dimethylformamide dimethylacetal with the latter chelates were converted into 3-acetyl-2-methylthio-4-hydroxypyridine by refluxing in BuOH and into 1-alkyl-3-cyano-2-methyl-4-pyridones by treatment with primary amines.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1118–1121, June, 1995.This study was financially supported by the International Science Foundation (Grant M5Q 000).     

Electrospinning of poly(vinylidene fluoride)/dimethylformamide solutions with carbon nanotubes

For conductive carbon nanotube (CN)/polymer composite fibers to be obtained, CNs were incorporated into poly(vinylidene fluoride) (PVDF) in dimethylformamide (DMF) solutions and electrospun to form CN/PVDF fiber mats. The thinnest fiber was 70 nm thick. The percolation threshold for the insulator‐to‐conductor transition was 0.003 wt % CN for CN/PVDF/DMF solutions, 0.015 wt % CN for CN/PVDF spin‐coated films, and 0.04 wt % CN for CN/PVDF electrospun fiber mats. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1572–1577, 2003     

New, optimized preparation of 1,2-dichlorocyclobuten-3,4-dione (C4O2Cl2) from squaric acid and oxalyl chloride

1,2-Dichlorocyclobuten-3,4-dione, a key intermediate in the chemistry of cyclobutenes and their derivatives is obtained by the dimethylformamide catalyzed reaction of squaric acid and oxalyl chloride. The process was optimized by using guidelines from thermodynamics, transport properties, and experimental observations, and gives nearly quantitatively a product which can be easily brought to very high purity.     

Formylation of Secondary Amines with Dimethylformamide Dimethylacetal

Abstract

Secondary amines are formylated by dimethylformamide dimethylacetal, contradicting recent reports on the ethylation of secondary amines by this reagent. This explains why a single derivative is obtained regardless of the alkyl acetal that is used. These formyl derivatives, also formed by reaction with formic acid, are eluted later than the starting material or the corresponding ethyl derivative. Deuterated imipramine and related antidepressants can be prepared by reducing the formyl derivative of the appropriate desalkyl compound with lithium aluminum deuteride.     

TiO2/Mo-TiO2 的制备、表征和光催化活性

 采用溶胶-凝胶法制备了掺 Mo 的 TiO2 粉末, 再由其制得 TiO2/Mo-TiO2 复合物光催化剂. 使用 X 射线光电子能谱、X 射线衍射、透射电镜、N2 吸附-脱附、紫外-可见漫反射光谱和荧光光谱等手段对催化剂进行了表征. 在紫外光照射下, 以甲基橙溶液降解为探针反应, 研究了 Mo 掺杂量对样品光催化活性的影响. 结果表明, Mo-TiO2 催化剂的活性不如纯 TiO2, 这是因为 Mo 离子促进了光生载流子的复合; 而带有 n-n 异质结半导体结构的 TiO2/Mo-TiO2 复合催化剂具有比纯 TiO2 和 Mo-TiO2 催化剂更高的光催化活性. 当 Mo 掺杂摩尔分数为 2%, TiO2:Mo-TiO2 质量比为 10:1 时, 活性是纯 TiO2 的 1.57 倍.