Phosphorous acid
- Phosphorous acid (deprecated)
- Phosphorus (III) - acid
Colorless and odorless, crystalline, hygroscopic solid
Fixed
1.65 g · cm -3
73 ° C.
Decomposition: 100 ° C
- PKS1 = 2.0
- PKa2 = 6.59
Very slightly soluble in water
Risk
Template: Infobox chemical / molecular formula search is not possible
Phosphonic acid, outdated and phosphorous acid, is a water-soluble, crystalline solid with the chemical formula H3PO3.
The preferred tautomeric form of the phosphonic acid is the structure with double-bonded oxygen (P = O), therefore, is a dibasic acid before. Salts and esters of phosphonic acid are phosphonates (obsolete: phosphites ) called. The phosphorus has an oxidation state III in these compounds.
Production
Phosphonic acid is obtained in the laboratory by the hydrolysis of phosphorus ( III) chloride. Concentration of the commercial product up to 99.3 percent, by heating to 80 ° C is possible.
Organic compounds
Organophosphorus compounds of the phosphonic acid with the formula R -PO (OH) 2 (R = alkyl radical or aryl radical ) and esters thereof R -PO (OR) 2 (R = alkyl group) is known as phosphonates. Salts for the obsolete term used phosphites of organic compounds having the structure P (OR ) 3 ( phosphites ). Compounds of this type have important functions in some synthetic methods.
Use
Phosphonic acid is used to manufacture Bleiphosphonat ( a PVC stabilizer), as reducing agents in chemical processes, as a starting material for the preparation of phosphonates such as 1 -hydroxyethane (1,1 -diphosphonic acid ) ( HEDP, with use in a Kalkbinder water softening, in toothpaste, etc.), and used as Langzeitverzögerer in concrete admixtures.
By chance it was discovered in the 1970s that plants treated with phosphorous acid, were very well protected against fungi from the group of oomycetes. In addition to the preventive was also a curative ( healing ) effect until a few days after infection by the fungus are found. Phosphonic acid is very easily absorbed by the plant and will systemically ( acropetally ) distributed in the plant. The transport takes place in the upper organs ( shoot apex, young leaves, flowers, fruit stands) particularly well in the growth phase of a plant. The embedding takes place in the inflorescences and fruits.
Operation
The mechanism of action is not yet fully understood, but is highly complex. A direct effect on the fungus is very low. Mainly based on the effect that the fungus from enriched phosphonate tissue held phosphate relates phosphonate ion. The plant activates its own defense force ( = an induced resistance response of the plant ) so well that an infection is prevented and case of an existing infection, the fungal mycelium is killed after a few days and can heal. The effect is so good that the substance that is found in certain plant strengtheners and foliar fertilizers, even in organic viticulture is employed. It is used for control of downy mildew, a disease caused by Eipilze from the order of Peronosporales disease. A great disadvantage is however that when the later application (approx. from July ) residues can be found in the grapes or wine. The risk of residues depends on the time of application and the delivered dose. The residues are perfectly harmless. Control measures before and just after the Rebblüte ( early to mid- June), cover the most important time of Peronosporabekämpfung. So be avoided residues in wine ( below the detection limit ).
Because of the residue problems and because the substance is absorbed into the plant, the use in organic viticulture against downy mildew is still controversial. Phosphonic acid is a very effective substance against downy mildew and provides a very good alternative to copper in Vorblütebereich dar. under extreme conditions, copper is too weak in its effect and lends itself to enrichment in humus or soil.