An Efficient,Simple and Inexpensive Method for the Preparation of 1,4-Benzoquinone Monoketals via Anodic Oxidation of 1,4-Dimethoxybenzenes

Anodic oxidation of a series of 1-substituted-2,5-dimethoxybenzenes gives 2-substituted-1,1,4,4-tetramethoxycyclohexa-2,5-dienes in almost quantitative crude yield. Selective monohydrolysis of these bis-ketals is possible in many cases, and gives 3-substituted-4,4-dimethoxycyclohexa-2,5-dienones in good to excellent overall yield.     

Preparation of 3,5-diethoxycarbonyl-2,6-dimethyl-1,4-dihydro-isonicotinic acid and 3,5-diacetyl-2,6-dimethyl-1,4-dihydroisoni-cotinic acid and their salts

The reaction of glyoxylic acid with ethyl -aminocrotonate or acetyl-acetone imine has given the corresponding derivatives of 1, 4-dihydro-isonicotinic acid and their water-soluble salts.     

Preparation of 3,5-diethoxycarbonyl-2,6-dimethyl-1,4-dihydro-isonicotinic acid and 3,5-diacetyl-2,6-dimethyl-1,4-dihydroisoni-cotinic acid and their salts

The reaction of glyoxylic acid with ethyl β-aminocrotonate or acetyl-acetone imine has given the corresponding derivatives of 1, 4-dihydro-isonicotinic acid and their water-soluble salts.     

1,4-苯醌衍生物的合成、氧化还原电位和生物活性的研究

合成了一系列具有不同的醌环结构(醌环上的取代基不同,如甲基、甲氧基、氢、氯和溴,或取代基的排列位置不同)的6-正癸基-1,4-苯醌衍生物。系统地研究了它们的结构、氧化还原电位和在线粒体琥珀酸-细胞色素 c 氧化还原晦中生物功能的关系。     

2,6-bisorganylsulfonyl-1,4-dithiafulvenes

Conclusions The reactions of organyl ,-dichlorovinyl sulfones with sulfur-containing nucleophiles, viz., sodium sulfide and salts of alkylxanthic acids, have been studied. A preparative method for synthesizing heretofore unknown 2,6-bisorganylsulfonyl-1,4-dithiafulvenes from organyl ,-dichlorovinyl sulfones and Na₂S·9H₂O in ethanol has been proposed. The isomeric composition of the compounds synthesized was studied, and their easy isomerization in an acidic medium has been established.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 368–372, February, 1980.     

An Efficient Preparation of Coumarins

o-methoxyaryl-aldehydes (or -ketones) react in solid-phase with Meldrum's acid under mild conditions, to give benzylidene derivatives which are cyclized in high yield, with cold sulfuric acid to substituted 3-carboxycoumarins. Thermal decarboxylation, speed up by copper powder, provided an easy access to numerous coumarins.     

An Efficient Preparation of Hexamethyldisilane

The striking reactivity conferred by silicon on organic molecules of widely diverse structural type has prompted considerable interest during the last decade in methods for the generation of silicon-carbon bonds and the subsequent transformations of the resultant organosilicon compounds. The highly nucleophilic silyl anions seem particularly suited to serve as precursors to these organosilicon compounds, although, in some cases, they have been postulated to react as one-electron transfer reagents.¹ Although silyl anions have been known for some time², only recently have efficient in situ methods been devised for the preparation of trimethylsilyllithium³, -sodium⁴ and -potassium⁵ from hexamethyldisilane (1) and methyllithium, sodium methoxide and potassium methoxide, respectively. These trimethylsilyl anions undergo reaction     

Spectrophotometric and Spectrofluorimetric Determination of Famotidine and Ranitidine Using 1,4-Benzoquinone Reagent

ABSTRACT

Spectrophotometric and spectrofluorimetric methods were adopted for the analysis of Famotidine and Ranitidine depending on their reaction with 1,4 Benzoquinone reagent at pH 5.2 and 5.6, respectively. The absorbances of the resulting condensation products were measured at 502 and 508 nm for Famotidine and Ranitidine, respectively. Concentrations adhering to Beer's law were from 40-160 μg.ml^? for Famotidine and from 20-100 μg.ml^? for Ranitidine.

Furthermore the resulting condensation products exhibited fluorescence at 665 nm when excited at 290 nm and the calibration graphs were rectilinear from 0.4-1.4 μg.ml^? for Famotidine and from 0.21 μg.ml^? for Ranitidine.

Different parameters affecting these reactions were thoroughly studied. Also these methods were applied to the pharmaceutical preparations and the results were satisfactory. The validities of the methods were ascertained by the standard addition technique revealing fine results in consideration to the mean recovery percent and standard deviation.

The spectrofluorimetric method was a hundred times more sensitive then the spectrophotometric method. The proposed methods were sensitive, accurate, and precise as statistically compared with the official methods of analysis of Famotidine and Ranitidine.     

Mechanistic Investigation of H2O2-dependent Chemiluminescence from Tetrabromo-1,4-Benzoquinone

As a H₂O₂-dependent bioluminescent substrate, tetrabromo-1,4-benzoquinone (TBBQ) was first isolated from acorn worm. The mechanism of chemiluminescence (CL) corresponding to the bioluminescence (BL) of acorn worm is largely unknown, let alone the mechanism of BL. In this article, we firstly studied the chemical and physical processes, and mechanism of H₂O₂-dependent CL from TBBQ by theoretical and experimental methods. The research results indicate: the CL process is initiated by a nucleophilic substitution reaction, which leads to the formation of an anionic dioxetane through five consecutive reactions; the anionic dioxetane decomposes to the first singlet excited state (S₁) via a conical interaction of the potential energy surfaces (PESs) between the ground (S₀) and S₁ state; the anionic S₁-state changes to its neutral form by a proton transfer from the solvent and this neutral product is assigned as the actual luminophore. Moreover, the experimental detection of CL, ^.OH and the identifications of 2,3-dibromo maleic acid and 2-bromo malonic acid as the major final products provide direct evidence of the theoretically suggested mechanism. Finally, this study proves that the activity of the H₂O₂-dependent CL from TBBQ is significantly lower than the one from tetrachloro-1,4-benzoquinone (TCBQ), which is caused by the weaker electron withdrawing effect and the stronger heavy atomic effect of bromine.     

An Efficient,Three-component One-pot Preparation of 1,4-Dihydropyridines Containing Novel Substituted Pyrazole under Sulfamic Acid Catalysis

An efficient approach to 1,4‐dihydropyridines containing novel substituted pyrazole is achieved via three‐component reaction of pyrazolyl aldehyde, β‐ketoester, and ammonium acetate in one‐pot under sulfamic acid catalysis.     

An Efficient Preparation of 7-Methoxychromanone

The reaction of m-methoxyphenol 7 with 3-chloropropionaldehyde diethyl acetal 8 and the subsquent treatments gave the corresponding 7-methoxychromanone 6 in overall 54% yield. This method represents an efficient preparation of chromanone.     

2,6-二甲基苯硼酸制备方法的改进

选用硼酸三丁酯为硼化剂,利用格氏试剂法制备了2,6-二甲基苯硼酸,考察了温度、硼化试剂和反应物配比对产率的影响,得出了较佳的合成条件:先由0.1mol2,6-二甲基溴苯与0.12mol镁在43℃反应1.5h制得格氏试剂(产率98.2%),然后与0.2mol硼酸三丁酯在-10℃下发生亲核取代,2h快速升温至20℃,经酸性水解得产品,分离后总产率由有机锂法的51%提高到72.2%,且反应条件更加温和并对产品进行了核磁共振、质谱和IR表征。     

一种高效、快速合成双偶氮化合物的新方法

报道了在丙酮溶液中用Ｆｅ２（ＳＯ４）３．ＸＨ２Ｏ做氧化剂,由取代二芳氨基脲高效合成双偶氮类化合物的新方法,此法反应简单有效,易于操作,后处理简便。     

Transformation of Acetaminophen by Dichromate Oxidation Produces the Toxicants 1,4-Benzoquinone and Ammonium Ions

The reaction of the common pain reliever acetaminophen (paracetamol, 4-acetamidophenol) with dichromate was investigated over time under conditions that simulate wastewater disinfection. The occurrence of the acetaminophen in the water bodies, especially in drinking water resources, has received considerable attentions. In situ chemical oxidation is a promising cost-effective treatment method to remove acetaminophen from water body as it degrades the drug to large extent. Experimental results indicate that the reaction is second order overall and first order with respect to both dichromate and acetaminophen, and has activation energy of 14.1 kJ/mol. The second-order rate constant ranges from 1.56 × 10^?3 to 13.4 × 10^?3 min^?1 at temperature from 35 to 65°C. The acetaminophen degradation rates can be accelerated through increasing reaction temperature and oxidant concentration. The reaction under acid conditions was slightly faster than under alkaline or neutral conditions. Two of the products were unequivocally identified as the toxic compounds 1,4-benzoquinone and ammonium ions. These results demonstrate that acetaminophen is likely to be transformed significantly into toxic product if dichromate is used as an oxidizing agent during wastewater treatment.     

Radical Copolymerization of Allyl and Vinyl Monomers Derived from 1,4-Benzoquinone with Acrylic Acid

Radical copolymerization of allyl and vinyl redox monomers derived from 1,4-benzoquinone with acrylic acid in dimethylformamide was studied.     

Pyrones VII. An Efficient Preparation and the Selective Reduction of Methyl 2,6-Dimethyl-4H-Pyran-4-one-3-Carboxylate

The syntheses of 4H-pyran-4-one-3-carboxylic acids and derivatives which have been previously reported (for example, starting with ketene¹, diketene², or dehydroacetic acid³) normally proceed only in low yield, often requiring rigorous control of the reaction conditions. We have shown that the reaction of dehydroacetic acid (1) with “magic methyl” (methyl fluorosulfonate) produces methyl 2,6-dimethyl-4H-pyran-4-one-3-carboxylate (4) in high yield (85%) under mild conditions.