Search results for "amalgam"
showing 8 items of 38 documents
Studien zum Vorgang der Wasserstoffübertragung, 68. Die reduktive Überführung aromatischer Säurechloride in Diarylacetylene mit Lithiumamalgam in ein…
1983
Endioldiester A, die durch “Acylierende reduktive Dimerisierung” mit Lithiumamalgam (Li/Hg) nach (1) zuganglich sind, werden mit zwei weiteren Reduktionsaquivalenten nach (2) durch “Reduktive Eliminierung” in Acetylenderivate ubergefuhrt. Hierbei hat sich praparativ das Eintopfverfahren in der Zweistufenarbeitsweise bewahrt. Auch mit Natriumamalgam (Na/Hg) und Kaliumamalgam (K/Hg) gelingt die reduktive Eliminierung nach (2) sowohl von cis- als auch von trans-Endiol-diestern zu Acetylenverbindungen mit guten Ausbeuten. Voraussetzung fur den erfolgreichen Ablauf der Reaktion (2) ist die direkte Verknupfung von zwei Aromaten mit der C C-Doppelbindung in den Endiol-diestern. Endiol-diester mit …
Electrochemical Syntheses of Carboxylic Acids from Carbon Dioxide
1987
The first report on the reduction of carbon dioxide is due to the venerable name of Hermann Kolbe, who, in 1861, published with R. Schmitt the reduction of carbon dioxide to formate with metallic potassium (1). Seven years later he introduced to the Chemical Society in London his assistant E. Drechsel, who “after many unsuccessful experiments, made during several years” (2) at the end succeeded in reducing carbon dioxide to oxalate with metallic sodium or with potassium amalgam in anhydrous conditions. Soon afterwards Beketov (3) and Royer (4) opened the series of papers dealing with the direct involvement of carbon dioxide in electrolytic processes. Since then the reduction of carbon dioxi…
ChemInform Abstract: Two-Carbon Bridge Substituted Cocaines: Enantioselective Synthesis, Attribution of the Absolute Configuration, and Biological Ac…
2010
In an effort to learn more about the general structure-activity relationships of cocaine with the aim to elucidate those structural features that might confer antagonistic properties to such analogues, we describe herein our synthetic efforts to prepare two-carbon bridge functionalized (methoxylated and hydroxylated) analogues. Our approach makes use of a modification of the classical Willstatter synthesis of cocaine: Mannich type cyclization of acetonedicarboxylic acid monomethyl ester with methylamine hydrochloride and 2-methoxysuccindialdehyde in a citrate buffer solution afforded the 6- and 7-substituted 2-carbomethoxy-3-tropinones 3a,b and 4a,b in approximate yields of 64%. Reduction o…
Clinical and histopathological study of the oral multifocal melanoacanthoma : a case report
2019
Melanoacanthoma is a blackened mucocutaneous lesion, mainly affecting individuals with dark skin and exhibiting rapid development. Differential diagnosis includes nevus, amalgam tattoo and melanoma. This article reports a case of a 53-year-old white woman, who exhibited multiple blackened lesions on the gingiva and upper lip. After incisional biopsy, the presence of numerous melanin-containing dendritic cells distributed throughout the epithelial thickness, which were S-100 (+), were observed microscopically. Final diagnosis was multifocal oral melanoacanthoma. Follow-up for 28 months has shown appearing of more lesions in gingiva and upper lip. Therefore, the importance of differential dia…
Teaching the placement of posterior resin-based composite restorations in Spanish dental schools
2012
Objectives: In an area of esthetic dentistry such as posterior composites, in which new materials and techniques are being devolved continuously, it is important to confirm that dental students have a clear understanding of the basic principles of clinical application of this knowledge. Considering that the preparation of dental graduates in Spain may be of interest to competent dental authorities and employers with whom they can work worldwide, this study investigated the teaching of posterior composite restorations in Spanish dental schools. Study design: In late 2009/ early 2010, a questionnaire seeking information on the teaching of posterior composites was emailed to the professor resp…
Oral pigmented lesions:a retrospective analysis from Brazil
2020
Background Pigmented lesions are uncommon in the oral mucosa, and studies investigating the incidence and types of these lesions are desired to improve the diagnostic knowledge of clinicians. The aim of this study was to analyze the distribution of oral pigmented lesions in a Brazilian population. Material and Methods A retrospective descriptive cross-sectional study was performed. Oral pigmented lesions were retrieved from the files of two oral and maxillofacial pathology services from Brazil over a 45-year period (1974-2019). The clinical data and the diagnoses of each case were retrieved and included in a Microsoft Excel® database. Results From 77.074 lesions diagnosed in this period, 76…
Toxicity of Dental Amalgams vs Composite Resins
2016
Ideal qualities of dental materials should include, in terms of biocompatibility, passivity towards oral tissues, so the material should not contain any leachable toxic and diffusible substances, neither release any harmful substance that can cause in time side effects, locally or generally. Even if amalgams are a group of dental materials with a long recorded history, many practitioners blame them, in contradiction with composite resins, especially for releasing free mercury into the body. On the other side, composite resins have reached great biocompatibility specifications, but also have many qualities that need more research, especially long term type.