Carboxylic acid

About: Carboxylic acid is a research topic. Over the lifetime, 48544 publications have been published within this topic receiving 605696 citations.

Esterification of alcohols with acetic acid over zeolites Hβ, HY and HZSM5

Abstract: Kinetic studies on the liquid phase esterification of C3 and C4 alcohols on acetic acid were carried out over zeolites Hβ, HY and HZSM5. The aims of this study were to arrive at the reaction mechanism from the kinetic data and to investigate the effects of the type of alcohol and zeolite type on the reaction mechanism. Zeolite Hβ was found to be the most active for this reaction. The acidity of zeolite determines the extent of the esterification reaction. The esterification reaction was found to follow the Eley–Rideal pathway. Acetic acid is activated by adsorption on the zeolite acid site, which then reacts with the alcohol in the bulk to form the corresponding acetate.

Functionalization and dissolution of nitric acid treated single-walled carbon nanotubes.

Abstract: We report an investigation of the nature and chemical functionalization of nitric acid treated single-walled carbon nanotubes (SWNTs). SWNTs washed with diluted sodium hydroxide solutions were characterized by near-IR, mid-IR, and Raman spectroscopy as well as TEM, and the remaining carboxylic acid content was determined to assess the effect of base washing on the removal of carboxylated carbon fractions, which are generated by the nitric acid treatment. It was found that even after exhaustive washing with aqueous base the purified SWNTs contain carboxylic acid groups in sufficient quantity to prepare high quality soluble SWNT materials by covalent functionalization with octadecylamine.

Identical ring cleavage products during anaerobic degradation of naphthalene, 2-methylnaphthalene, and tetralin indicate a new metabolic pathway.

Abstract: Anaerobic degradation of naphthalene, 2-methylnaphthalene, and tetralin (1,2,3,4-tetrahydronaphthalene) was investigated with a sulfate-reducing enrichment culture obtained from a contaminated aquifer. Degradation studies with tetralin revealed 5,6,7,8-tetrahydro-2-naphthoic acid as a major metabolite indicating activation by addition of a C1 unit to tetralin, comparable to the formation of 2-naphthoic acid in anaerobic naphthalene degradation. The activation reaction was specific for the aromatic ring of tetralin; 1,2,3,4-tetrahydro-2-naphthoic acid was not detected. The reduced 2-naphthoic acid derivatives tetrahydro-, octahydro-, and decahydro-2-naphthoic acid were identified consistently in supernatants of cultures grown with either naphthalene, 2-methylnaphthalene, or tetralin. In addition, two common ring cleavage products were identified. Gas chromatography-mass spectrometry (GC-MS) and high-resolution GC-MS analyses revealed a compound with a cyclohexane ring and two carboxylic acid side chains as one of the first ring cleavage products. The elemental composition was C11H16O4 (C11H16O4-diacid), indicating that all carbon atoms of the precursor 2-naphthoic acid structure were preserved in this ring cleavage product. According to the mass spectrum, the side chains could be either an acetic acid and a propenic acid, or a carboxy group and a butenic acid side chain. A further ring cleavage product was identified as 2-carboxycyclohexylacetic acid and was assumed to be formed by β-oxidation of one of the side chains of the C11H16O4-diacid. Stable isotope-labeling growth experiments with either 13C-labeled naphthalene, per-deuterated naphthalene-d8, or a 13C-bicarbonate-buffered medium showed that the ring cleavage products derived from the introduced carbon source naphthalene. The series of identified metabolites suggests that anaerobic degradation of naphthalenes proceeds via reduction of the aromatic ring system of 2-naphthoic acid to initiate ring cleavage in analogy to the benzoyl-coenzyme A pathway for monoaromatic hydrocarbons. Our findings provide strong indications that further degradation goes through saturated compounds with a cyclohexane ring structure and not through monoaromatic compounds. A metabolic pathway for anaerobic degradation of bicyclic aromatic hydrocarbons with 2-naphthoic acid as the central intermediate is proposed.