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An oxazolidine is a five-membered ring compound consisting of three
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
atoms, a nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
atom and an oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
atom. The O atom and NH group are the 1 and 3 positions, respectively. In oxazolidine derivatives, there is always a carbon atom between the O and N atoms (or it would be an ''isoxazolidine''). All of the carbon atoms in oxazolidines are reduced (compare to oxazole
Oxazole is the parent compound for a vast class of heterocyclic aromatic organic compounds. These are azoles with an oxygen and a nitrogen separated by one carbon. Oxazoles are aromatic compounds but less so than the thiazoles. Oxazole is a weak ...
and oxazoline
Oxazoline is a five-membered heterocyclic organic compound with the formula . It is the parent of a family of compounds called oxazolines (emphasis on plural), which contain non-hydrogenic substituents on carbon and/or nitrogen. Oxazolines are the ...
). Some of their derivatives, the oxazolidinediones, are used as anticonvulsants.
Oxazolidines were first synthesized over 100 years ago.
Monooxazolidines
Oxazolidines that are the precursor to bisoxazolidines are in effect mono-oxazolidines. They are also used as moisture scavengers in polyurethane and other systems.Dioxooxazolidines
Oxazolidines where the carbon centers at the 1 and 3 positions arecarbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containi ...
s are called dioxooxazolidines. Some of these are commercial fungicides including chlozolinate, vinclozolin, and famoxadone.
Bisoxazolidines
Bisoxazolidines are chemical compounds that contain two oxazolidine rings. They are used as performance modifiers inpolyurethane
Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from ...
coatings and paints. The rings hydrolyze
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis ...
in the presence of moisture to give amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen
Hydrogen is the chemical element wi ...
and hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...
groups, which can then react with diisocyanate
In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...
s, polyisocyanates and polyurethane prepolymers to form a coating. The amine groups will form urea linkages and the hydroxyl group will form urethane links. The use of a bisoxazolidine in a polyurethane system can prevent the unwanted reaction between isocyanate and moisture resulting in coating defects, as a result of carbon dioxide release. This moisture-triggered curing route is preferential to moisture cure. As the ring opening reaction is catalyzed
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
by acids, usually organic acids or anhydrides of carboxylic acids are added in a small amount.
The choice of linker between the two oxazolidine rings has a large impact on the performance when used to cure isocyanates. A rigid linker group increases a polyurethanes toughness. A flexible linker group imparts flexibility and increases elongation of a coating. These differences are the reason why bisoxazolidines are used to enhance the performance of polyurethane systems. Usually the rings are linked by esters, urethanes, carbonate or have the two rings fused together. A key intermediate in manufacturing bisoxazolidines is 2- -(propan-2-yl)-1,3-oxazolidin-3-ylthanol. The hydroxy group on the molecule allows for further reaction with hexamethylene diisocyanate
Hexamethylene diisocyanate (HDI) is the organic compound with the formula (CH2)6(NCO)2. It is classified as an diisocyanate. It is a colorless liquid. It has sometimes been called HMDI but this not usually done to avoid confusion with Hydrogenate ...
for example.
Isoxazolidines
In an isoxazolidine nitrogen and oxygen occupy adjacent positions (1 and 2) in the ring: this is the saturated analogue ofIsoxazole
Isoxazole is an electron-rich azole with an oxygen atom next to the nitrogen. It is also the class of compounds containing this ring. Isoxazolyl is the univalent radical derived from isoxazole.
Occurrence
Isoxazole rings are found in some natura ...
.
Isoxazolidines can be produced by the nitrone-olefin (3+2) cycloaddition reaction.
See also
*Imidazole
Imidazole (ImH) is an organic compound with the formula C3N2H4. It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. In chemistry, it is an aromatic heterocycle, classified as a diazole, and has non-a ...
, an analog with the oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
atom replaced by a nitrogen aton.
* Thiazole
Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen. The term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular fo ...
, an analog with the oxygen atom replaced by a sulfur atom.
* Benzoxazole, where the oxazole is fused to another aromatic ring.
* Pyrrole, an analog without the oxygen atom.
* Furan, an analog without the nitrogen atom.
* Oxazoline
Oxazoline is a five-membered heterocyclic organic compound with the formula . It is the parent of a family of compounds called oxazolines (emphasis on plural), which contain non-hydrogenic substituents on carbon and/or nitrogen. Oxazolines are the ...
, which has only one double bond reduced.
* Oxazolidinedione, which has two in-cycle keto groups (a carbamate and a lactam).
* Oxazolidinone
2-Oxazolidone is a heterocyclic organic compound containing both nitrogen and oxygen in a 5-membered ring.
Oxazolidinones
Evans auxiliaries
Oxazolidinones are a class of compounds containing 2-oxazolidone in the structure. In chemistry, they are ...
, which has an in-cycle carbamate.
References
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