Glycol: any of a class of organic chemicals characterized by having
separate two hydroxyl (-OH) groups, contribute to high water
solubility, hygroscopicity and reactivity with many organic
compounds, on usually linear and aliphatic carbon chain. The
general formula is CnH2n(OH)2 or (CH2)n(OH)2. The wider meaning
names include diols, dihydric alcohols, and dihydroxy alcohols.
Polyethylene glycols and polypropylene glycols are sometimes called
polyglycols which are derived by polymerization of ethylene oxide
and propylene oxide respectively. Polyethylene glycols are
water-soluble at all molecular weights, but polypropylene glycols
become increasingly less water-soluble at high molecular weights.
Ethylene glycol, HOCH2CH2OH, is the simplest member of the glycol
family. Mono-, di- and triethylene glycols are the first three
members of a homologous series of dihydroxy alcohols. They are
colourless, essentially odourless stable liquids with low
viscosities and high boiling points.
Ethylene glycol is a colourless, odourless, involatile and
hygroscopic liquid with a sweet taste. It is somewhat viscous
liquid; miscible with water; boiling point **8 C, melting point *3
C; soluble in ethanol, acetone, acetic acid, glycerine, pyridine,
aldehydes; slightly soluble in ether; insoluble in oil, fat,
hydrocarbones. It is prepared commercially by oxidation of ethylene
at high temperature in the presence of silver oxide catalyst,
followed by hydration of ethylene oxide to yield mono-, with di-,
tri-, and tetraethylene glycols as co-products. The yields of
ethylene glycol are depend on pH conditions. The acid-catalyzed
condition in the presence of excess water provides the highest
yield of monoethylene glycol. Because of its low freezing point,
involatility and low corrosive activity, it is widely used in
mixtures of automobile antifreeze and engine-cooling liquids.
Ethylene glycol has become increasingly important in the plastics
industry for the manufacture of polyester fibers and resins,
including polyethylene terephthalate, which is used to make plastic
bottles for soft drinks (PET bottles). MEG is the raw material in
the production of polyester fiber, PET resins, alkyd, and
unsaturated polyester. Diethylene glycol, CH2OHCH2OCH2CH2OH, is
similar in properties to MEG, but with a higher boiling point,
viscosity, and specific gravity.
