Dipropylene glycol is a clear, colorless, viscous, hygroscopic, odorless liquid with a sweetish taste. It is fully miscible with water and solvation process is exothermic. It dissolves with many lyophilic and lyophobic compounds. Thus, it is miscible in glycols and glycol ethers, polyethylene glycol in Mr range 200-2000, methanol, ethanol, acetone, amines, ethanolamines, diethyl ether, phenol, o-cresol, pyridine and so on. Also dipropylene glycol dissolves substances insoluble in other glycols, e.g. benzene, toluene, styrene, chlorobenzene, chloroform, carbon tetrachloride, vegetable oils (castor, pine, tall).
Dipropylene glycol possesses chemical properties both alcohols and ethers and can by hydrolysed by action of mineral acids releasing propylene glycol. Also it can form mono- and di- ethers and esters being combined with alcohols or carboxylic acids respectively.
In contrast to ethylene glycol derivatives dipropylene glycol is almost non-toxic and can be used in food, cosmetic, pharmaceutical industries and in perfumery.
Industrially dipropylene glycol is manufactured jointly with tripropylene glycol as a by-product of propylene glycol production in propylene oxide hydrolysis process. The commercial product is a mixture of three isomers (see figure): I - di-secondary 1,1'-oxybis(2-propanol) [CAS No 108-61-2], II - secondary-primary 2-(2-hydroxypropoxy)-1-propanol [CAS No 106-62-7] and III - di-primary III - 2,2'-oxybis(1-propanol) [CAS No 110-98-5]. The isomers ratio depends on the catalyst used upon hydrolysis process. In alkalescent media mixture consists of 2% di-primary III, 30-35% of secondary-primary II and 65-70% of di-secondary I. Acidic catalysis (sulfuric acid) results in ratio 10-15% of III, 50-60% of II and 30-35% of I respectively.
as a raw material in polyester resins manufacturing;
as an effective extracting agent for aromatic hydrocarbons from products of reforming process (besides aromatic mixture contain aliphatic hydrocarbons and naphthenes);
as a solvent for printing inks, resins, cellulose nitrates and acetates;
as a component of hydraulic fluids in the mixture with castor oil or water;
as an antifreezing heat carrier;
as an antifreezing and lubricating additive for fuels;
as a reaction media for the processes at high temperatures, e.g. for decarboxylation of quinolinic acid into nicotinic acid;
as a raw material in production of intermediates used in perfumery, cosmetics and fine organic synthesis;
as a feedstock in plasticizers (dipropylene glycol esters, e.g. benzoates) preparation;