Carboxylic acid

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

Cellulose hydrothermal conversion promoted by heterogeneous Bronsted and Lewis acids: Remarkable efficiency of solid Lewis acids to produce lactic acid

Abstract: Crystalline cellulose treated in hydrothermal conditions (190 °C, 24 h) is partially solubilised, 30%, into water soluble oligosaccharides/polymers with the formation of small amounts of glucose and 5-HMF. In the presence of solid Bronsted catalysts such as Cs2HPW12O40 and HY zeolite, the extent of the cellulose depolymerisation was not changed when no leaching occurred. However, a quite different products distribution was obtained, in favour of further transformations of glucose and HMF in levulinic and formic acids. On the opposite, solid Lewis acids such as tungstated zirconia (ZrW) and tungstated alumina (AlW) exhibited a remarkable promoting effect on the cellulose depolymerisation which was raised up to 45% while an unexpected decrease of the proportion of water soluble oligosaccharides/polymers was observed. Yields of 27 mol% and 18.5 mol% in lactic acid were achieved on AlW and ZrW, respectively. Moreover, these tungsten based Lewis acids exhibited a good stability and recyclability. The efficiency of the solid Lewis acids ZrW and AlW to produce lactic acid directly from crystalline cellulose was explained by a positive synergy between water autoprotolysis responsible of the cellulose depolymerisation into soluble intermediates which are further converted on the solid Lewis catalyst surface.

Cocrystals of 1,3,5-Cyclohexanetricarboxylic Acid with 4,4‘-Bipyridine Homologues: Acid···Pyridine Hydrogen Bonding in Neutral and Ionic Complexes

Abstract: cis,cis-1,3,5-Cyclohexanetricarboxylic acid (H3CTA) is crystallized with bipyridine bases 1,2-bis(4-pyridyl)ethane (bipy-eta), 1,4-bis(4-pyridyl-2-ethyl)benzene (bipy-etabz), 1,2-bis(4-pyridyl)ethylene (bipy-ete), and 1,4-bis(2-(4-pyridyl)ethenyl)benzene (bipy-etebz) to afford molecular complexes (H3CTA)·(bipy-eta)1.5 1, (H3CTA)·(bipy-etabz) 2, (H2CTA-)·(bipy-ete2H+)0.5 3, and (H2CTA-)·(bipy-etebz2H+)0.5 4. Cocrystal 1 has a super honeycomb hydrogen bond network stabilized by carboxylic acid-bipyridine O−H···N synthon Va. The hexagonal cavity of 34.1 × 36.7 A is filled by parallel triple interpenetration of independent networks. 2 has zigzag chains of synthon Va connected via O−H···O hydrogen bonds. Carboxylic acid to pyridine proton transfer occurs in 3 and 4. These structures have undulated and flat 2D layers of O−H···O- and O−H···O hydrogen bonds that are connected to bipyridinium via N+−H···O- hydrogen bond Vb. H2CTA- anions in 4 form a porous parquet grid of 14.5 × 7.5 A with the channels accommodati...

Photochemically produced carboxylic acids as substrates for freshwater bacterioplankton

Abstract: . High-molecular-weight dissolved organic matter is abundant in humic lakes and is a large potential source of energy for heterotrophic organisms. These substances are hard to degrade enzymatically because of their high aromaticity and complex structure. However, there is increasing evidence that photochemical processes render the material more bioavailable. We demonstrate a substantial photochemical production of four carboxylic acids (oxalic, malonic, formic, and acetic acid) in a humic lake. The combined production rate in the surface water of these four acids was 19 pg C liter-l h-l with natural sunlight. Furthermore, based on radiotracer studies, we found that the amount of carbon assimilated and oxidized to CO, from malonic, formic, and acetic acid exceeded bacterial carbon production, sometimes by more than one order of magnitude. This implies that carboxylic acids were major bacterioplankton substrates. Nevertheless, under natural sunlight at the lake surface, microbial utilization of carboxylic acids was substantially lower than the photochemical production of the acids. Hence, photochemically produced carboxylic acids may accumulate in sunlight exposed environments and may also serve as bacterial substrates after mixing into deeper layers, or during night.

Preparation, Modification, and Crystallinity of Aliphatic and Aromatic Carboxylic Acid Terminated Self-Assembled Monolayers

Abstract: COOH-terminated organic surfaces were prepared by self-assembly of different organothiols, mercaptohexadecanoic acid (MHDA) and mercaptomethylterphenylcarboxylic acid (MMTA), on Au substrates. The SAMs were explored by infrared reflection−absorption spectroscopy and X-ray photoelectron spectroscopy. A rather strong dependence on preparation conditions is observed which explains inconsistencies between previous studies reported for these systems. Using optimized preparation conditions, films with a high degree of molecular orientation could be prepared. A significant amount of disorder, however, is induced by hydrogen bonds between the terminating −COOH groups. An organothiol with a more rigid backbone, MMTA, is demonstrated to yield carboxy-terminated SAMs which are more straightforward to prepare and which show a significantly higher degree of order.