Morpholine, also called 1,4-oxyazocyclohexane, is a colorless, oily liquid with ammonia flavor at room temperature, which can be used as analytical reagent and resin, wax and shellac solvents. Morpholine has characteristics of ether and amine compounds because the heterocyclic ring contains nitrogen and oxygen. Compared to morpholine, the oxygen in the N-heterocyclic ring is replaced by sulfur in the structure of thiomorphline. Thiomorphline is often used as an important structural fragment in the design of new drugs due to its good biological activity.
The secondary amine groups of morpholine and thiomorphline can react with ketone, ester and nitrile to form 1, 4-additive compound by Michael reaction. The most important reaction of morpholine and thiomorphline is the substitution reaction of secondary amine atoms with alcohols, compounds and complexes of acids. Under the atmosphere of H2, morpholine can react with primary or secondary alcohols to form a series of compound molasses derivatives with high conversion rate. Morpholine and dihydric alcohol are able to produce morpholine alcohols and dimorpholine derivatives, which are also able to react with acids to obtain a series of ester drugs.
Fig. 1 the schematic diagram of (a) structures of morpholine and thiomorphline (b) some reactions of morpholine and thiomorphline.
Antioxidants and Stabilizers: The complex formed by morpholine and ascorbic acid is served as a synergistic antioxidant for lipid. N,N-Thiodimorpholine and N-tert-butyl morpholine can be used as antioxidants in lubricating oils. The morpholine salt of gallnut acid is a stabilizer of carotene and vitamin A and an antioxidant of glycerin.
Rubber additives: The major application of thiomorpholine derivatives is the production of rubber additives, in which 4, 4-dithiodimorpholine (DTDM) can be used as a vulcanization agent, and OTOS is also a typical kind of vulcanization promoter.
Medicine: In terms of medicine, morpholine derivatives can be used as analgesics, local anesthetics, antispasmodic and other drugs. Fominoben is a new antitussive agent. Clinically, Morphocycline is used for the treatment of various serious infections caused by tetracycline-sensitive bacteria, and also for the diagnosis of lung cancer. In addition, bimolane is involved with the treatment of psoriasis.
Fig. 2 Structures of compounds containing a thiomorpholine ring and target compound
(Chinese Journal of Medicinal Chemistry 2015, 25, 373-377)
Anti-scaling Agent: Morpholine is widely used as corrosion inhibitor and scale inhibitor for steam boiler, and N-tert-butyl morpholine and morpholine sulfonate has a good corrosion resistance to oil storage tank and pipeline equipment.
Anti-scorching Agent: The product produced by the condensation of morpholine subsulfonyl chloride and phthalimide is a kind of effective anticoke agent, which is a new product developed abroad in recent years.
Metal Corrosion Inhibitor: Some morpholine derivatives are regard as anti-rust agents for metal products to prevent metal from being corroded by the atmosphere and have been widely used in the fields of mechanical vehicles, instruments and medical instruments, etc. Morpholine has the advantage of low toxicity as a metal corrosion inhibitor and has a good development prospect.