Phthalic anhydride
- 2- benzofuran- 1 ,3-dione
- Phthalic anhydride
Colorless needles
Fixed
1.53 g · cm -3
131 ° C.
285 ° C.
- Poorly in water ( 6.4 g · l-1 at 20 ° C)
- Soluble in ethanol, diethyl ether, benzene
Risk
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Phthalic anhydride (short PSA) is the anhydride of phthalic acid. The organic compound is an important starting material for the production of synthetic resins, In addition, dyes or pigments.
Production
Phthalic anhydride is obtained by air oxidation of a suitable precursor ( Gibbs - well method). Until the 1960s this was naphthalene from coal tar; Today, crude oil is the basis of the chemical industry, and the vast majority of world production (2000: 4.0 million tonnes) - the beginning of the 1980s it was 85 % - is produced from o -xylene.
Laboratory phthalic anhydride can be prepared by elimination of water by heating phthalic acid ( C8H6O4 )
Under suitable conditions - preferably reduced pressure - distilled or sublimed phthalic anhydride and condenses without the water in a template.
Properties
Phthalic anhydride is a solid, colorless, aromatic odor, needle-like crystals formed. This sublimate easily. The compound melts at 131 ° C and is at 285 ° C in the gaseous state.
Phthalic anhydride dissolves slightly in cold water, ethanol and diethyl ether, however, is well in esters, ketones, halogenated hydrocarbons and benzene.
Technical or not mounted in perfectly tight fitting vessels phthalic anhydride may contain a considerable amount of phthalic acid, since the anhydride is slowly reacted with atmospheric moisture to the acid. Then it must be distilled or sublimed, preferably under reduced pressure.
Use
Phthalic anhydride is mainly used as raw material for the manufacture of plasticizers ( phthalates ) for plastics (especially PVC). Lesser amounts are used as a raw material for synthetic resins or as a component of surface coatings for wood. In addition, there is a raw material in the production of dyes or pigments on the basis of the phthalocyanines. Another technically important reaction of phthalic anhydride is the anthraquinone; first case there is a Friedel- Crafts acylation of benzene.
Analysis reagent
Under suitable conditions, the reaction with alcohols, an acid ester (mono ester), phthalic acid. These esters often crystallize well, so that they can be used for the detection of alcohols in the qualitative analysis. Since they have a carboxylic acid group, they can be titrated with strong bases. With a known initial weight of alcohol and phthalic anhydride, the molecular weight of the alcohol can then be determined.
Safety
Phthalic anhydride is considered allergenic. It is irritating to the eyes, the skin and mucous membranes.