Background and overview[1][2]
Polyethylene glycol is a polymer of ethylene oxide hydrolyzate. It is non-toxic and non-irritating and is widely used in various pharmaceutical preparations. Low molecular weight polyethylene glycols are relatively toxic. Overall, the toxicity of glycols is quite low. Topical application of polyethylene glycol, especially mucosal administration, can cause irritating pain. In topical lotions, it increases skin flexibility and has a moisturizing effect similar to that of glycerin. At room temperature, polyethylene glycol grades 200 to 600 are liquid; polyethylene glycol grades 1000 and above are solid.
Liquid grade polyethylene glycol is a transparent, colorless or light yellow viscous liquid with a slight odor. Polyethylene glycol is slightly hygroscopic, less volatile than glycerin, has stable chemical properties, is not easily damaged by hydrolysis, and is highly hydrophilic. It can be dissolved in acetone, ethanol, benzene, glycerin and glycol compounds, and can dissolve many water-soluble inorganic salts and water-insoluble organic matter; the solid level of polyethylene glycol is white or nearly white, and its viscosity is pasty to waxy. The shape is different, slightly sweet. Soluble in acetone, dichloromethane, ethanol and methanol; slightly soluble in aliphatic hydrocarbons and ether, insoluble in fats, fatty oils and mineral oils. All grades of polyethylene glycol are soluble in water. Polyethylene glycols can be mixed with each other and with water in any proportion. High molecular weight polyethylene glycol aqueous solutions can form gels.
Preparation[2]
In industry, polyethylene glycol is produced from ethylene oxide and water, or from ethylene glycol through a step-by-step reaction. When preparing polymers with larger molecular weights, polyethylene glycols with lower molecular weights are often used as initiators. .
1. Progress in ethylene glycol synthesis technology
The current industrial production method of ethylene glycol is mainly through gas-phase oxidation of petroleum ethylene to obtain ethylene oxide, and then through liquid-phase catalytic hydration (called the ethylene route). The non-ethylene route production technology of ethylene glycol is to first synthesize oxalate ester from CO and alcohol, and then hydrogenate to generate ethylene glycol. There are two main synthesis methods. When the electrolyte is formed, the current efficiency reaches 90%, and the ethylene glycol content increases from 15% to 20% to 23%.
1) Formaldehyde coupling method
Mix 30% formaldehyde aqueous solution and an equal volume of sodium hydroxide solution, and drop this mixture into a fixed bed reactor equipped with a zeolite catalyst. The upper and lower parts of the reactor are porcelain rings, which are heated by electric induction. The controlled reaction conditions are temperature 94 ℃, pressure 0.1kPa, space velocity (LHS V) 1.21~2.36. Under these conditions, the formaldehyde conversion rate will be 100%, and the selectivity to generate glycolaldehyde is 75%. .
The method industrialized by the American Du Pont Company in 1968 was to react HCHO and CO in a sulfuric acid solution at 150~225 ℃, 50~100MPa to generate glycolic acid, and then Ethylene glycol is produced by catalytic hydrogenation at 210~215 ℃and 3kPa. The current improved production method is to use paraformaldehyde. In the presence of triethylamine catalyst, paraformaldehyde, water and dioxane are placed in an autoclave at a hydrogen pressure of 10MPa and 150 ℃After reacting for 3 hours, a one-step reaction produced ethylene glycol, of which ethylene glycol accounted for 17.9%, glycerol accounted for 16.1%, and 1,2,3,4-butanetetraol accounted for 5.5%. The improved process combines two steps into one step, using triethylamine instead of sulfuric acid, which greatly reduces the corrosiveness of the equipment, the reaction pressure is also greatly reduced, and the by-product glycerol is also a useful product.
2. Synthesis of polyethylene glycol
Polymerization reaction can adopt gas phase or liquid phase polymerization. In industry, liquid phase polymerization is mostly used, using sodium hydroxide or potassium hydroxide as catalyst, and the reaction takes place in a steel reactor or belt equipped with a circulation pump and an external heat exchanger. carried out in a mechanically stirred batch reactor.
Pharmacological effects[3]
Macromolecular polyethylene glycol (0) is a linear long-chain polymer that fixes water molecules through hydrogen bonds, retaining water in the colon, increasing the water content of feces, thereby softening the feces, and restoring the volume and weight of the feces to normal. Promote the final completion of defecation, thereby improving constipation symptoms.
Indications[4]
Clinically it is mainly used for the symptomatic treatment of adult constipation; preoperative intestinal cleaning preparation; intestinal cleaning preparation before colonoscopy, barium enema and other examinations.
Other uses and markets[2][5]
Polyethylene glycol is used in a variety of pharmaceutical preparations, such as injectables, topical preparations, ophthalmic preparations, oral and rectalIn addition to preparations, polyethylene glycol has been widely used as a phase transfer catalyst. It has a spiral structure and can be folded into holes of different sizes. It can complex with ions of different radii to perform phase transfer catalytic reactions. It can also be used as Williamson’s phase transfer catalyst and is extremely convenient to operate.
Polyethylene glycol is water-soluble and has excellent solubility for a variety of drugs. It is widely used as an ointment base and a carrier for active ingredients. Solid polyethylene glycol can be used as a water-soluble suppository base. Polyethylene glycol has a wide range of compatibility and can be used as a vehicle and adhesive for many pharmaceutical preparations. Polyethylene glycol has a compatibilizing effect and is suitable for various high-quality Production of cosmetics.
Polyethylene glycol can also be used as non-greasy lubricants, softeners and antistatic agents in hair sprays, emulsifying aids and plasticizers in soap making, etc. Polyethylene glycol absorbs 10 to 100 times its own weight in water after cross-linking, and can release it when necessary. Taking advantage of this characteristic, it can be used as a super absorbent resin. Polyethylene glycol can form association complexes with many substances, such as phenolic resins, lignin derivatives, polycarboxylic acids, polyesters, etc. The complexes formed expand its application in new fields.
Main reference materials
[1] New Practical Manual of Veterinary Drugs
[2] Wang Duoren. Application and synthesis progress of polyethylene glycol[J]. Chemical Industry and Engineering Technology, 2000, 21(5): 21-23.
[3] Physician’s Desk Medication Reference
[4] Clinical Prescription Drug Manual
[5] Kong Fanzhi, Wang Haina, Zhong Chongli. Production of polyethylene glycol and its application in toothpaste[J]. Oral Care Products Industry, 2015 (4): 25-27.
