Pyromellitic Dianhydride on:
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Pyromellitic dianhydride (PMDA) is an
PMDA is an electron-acceptor, forming a variety of
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
with the formula C6H2(C2O3)2. It is the double carboxylic acid anhydride
An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the p ...
that is used in the preparation of polyimide polymers such as Kapton
Structure of poly-oxydiphenylene-pyromellitimide
Kapton insulating pads for mounting electronic parts on a heat sink
Kapton is a polyimide film used in flexible printed circuits (flexible electronics) and space blankets, which are used on spac ...
. It is a white, hygroscopic solid. It forms a hydrate.
Preparation
It is prepared by gas-phaseoxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
of 1,2,4,5-tetramethylbenzene (or related tetrasubstituted benzene derivatives). An idealized equation is:
:C6H2(CH3)4 + 6 O2 → C6H2(C2O3)2 + 6 H2O
In the laboratory, it can be prepared by dehydration of pyromellitic acid using acetic anhydride
Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a col ...
.
Reactions
PMDA is an electron-acceptor, forming a variety of charge-transfer complex
In chemistry, a charge-transfer (CT) complex or electron-donor-acceptor complex describes a type of supramolecular assembly of two or more molecules or ions. The assembly consists of two molecules that self-attract through electrostatic forces ...
es. It reacts with amines to diimides, C6H2 CO)2NRsub>2 which also have acceptor properties.
Safety
Evidence suggests that PMDA causesoccupational asthma
Occupational asthma is new onset asthma or the recurrence of previously quiescent asthma directly caused by exposure to an agent at workplace. It is an occupational lung disease and a type of work-related asthma. Agents that can induce occupational ...
.
References
{{Reflist Phthalic anhydrides