Phosphoric acid

Abstract: PHOSPHORIC esters play a central part in the biological world bY linking processes of respiration and fermentation with other essential cellular reactions. More tnan twenty substances of this group, mainly sugars and related substances esterified with phosphoric acid, are known to form intermediate in the network of enzymic reactions associated with the breakdown and interconversion of carbohydrates in plants and animals. Both in the intact cell and in the isolated enzyme systems in which these reactions are studied, phosphoric esters usually occur in mixtures, and progress in this important field has depended upon the development of methods for identifying and determining the individual esters present in such mixtures. Existing methods of analysis depend mainly upon the fractionation of salts of the esters and the selective hydrolysis of some of them, under standard conditions, these procedures being supplemented when possible by methods based on more specific reactions given by particular esters. Except when applied to certain relatively simple mixtures, these methods frequently fail to yield diagnostic results.

Abstract: The structural features of the porous type of anodic oxide coating applied to aluminum have been investigated with the electron microscope. These coatings consist of close‐packed cells of oxide, predominately hexagonal in shape, each of which contains a single pore. Pore size is a function of the electrolyte used and is independent of forming voltage. Wall thickness and barrier thickness are primarily a function of forming voltage and are affected to a minor degree by the electrolyte type. Pertinent dimensions of anodic coatings formed in sulfuric acid, oxalic acid, chromic acid, and phosphoric acid electrolytes are presented, and formulas are given for calculating the cell size and pore volume of these coatings.

Abstract: Polybenzimidazole films doped with phosphoric acid are being investigated as potential polymer electrolytes for use in hydrogen/air and direct methanol fuel cells. In this paper, we present experimental findings on the proton conductivity, water content, and methanol vapor permeability of this material, as well as preliminary fuel cell results. The low methanol vapor permeability of these electrolytes significantly reduces the adverse effects of methanol crossover typically observed in direct methanol polymer electrolyte membrane fuel cells.

Abstract: It has been claimed that different ion solutions containing sulfate induce crystal growth and might be a better alternative than conventional acid etching for enamel pretreatment in bracket bonding. It should thus combine optimal bond strength with easy and quick debonding. Two clinical experiments were performed to test this hypothesis. The first experiment dealt with the debonding procedure. Following conditioning with dilute sulfuric acid which contained sodium sulfate (to be termed solution A) on one side of the mouth and etching with 37% phosphoric acid on the other, brackets were bonded on the maxillary and mandibular incisors of twenty dental nurse students. Debracketing and a subsequent cleanup procedure were performed after 2 days. The mode of loosening was mainly between the enamel surface and adhesive on the crystal-growth-conditioned teeth and between the bracket mesh and adhesive on the teeth etched with phosphoric acid. This difference in mode of loosening was statistically significant (P less than 0.001). In the second experiment, which dealt with the clinical bond strength, 250 brackets were bonded in forty patients. One side served as a control and was conventionally acid etched. On the experimental side conditioning was done with solution A in thirty patients. In ten patients, 10% phosphoric acid was added to the dilute sulfuric acid used (to be termed solution B). Failure rates and modes of failure were recorded for a 6-month period.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract: Chiral phosphoric acids derived from axially chiral biar- yls and related chiral Bronsted acids have emerged as an attractive and widely applicable class of enantioselective organocatalysts for a variety of organic transformations. This review focuses on recent achievements in the development of enantioselective transforma- tions using these axially chiral phosphoric acids and their analogues as chiral Bronsted acid catalysts. The contents are arranged accord- ing to the specific types of carbon-carbon bond-forming reactions, followed by carbon-heteroatom bond-forming reactions and func- tional group transformations, including reduction and oxidation. Further applications to combined phosphoric acid and metal com- plex catalytic systems and new aspects in the development of chiral Bronsted acid catalysts are also highlighted.