Propylene glycol
- 57-55-6 [( RS ) -1,2 -dihydroxy ]
- 4254-14-2 [(R ) -1,2 -dihydroxy ]
- 4254-15-3 [(S ) -1,2 -dihydroxy ]
Oily, colorless, almost odorless, hygroscopic, viscous liquid
Liquid
1.04 g · cm -3 ( 25 ° C)
-68 ° C
188.2 ° C
0.11 hPa ( 20 ° C)
Miscible with water, ethanol, acetone, chloroform, insoluble in diethyl ether
1.4324
-501.0 KJ / mol
Template: Infobox chemical / molecular formula search available
1,2- propanediol (1,2- propylene glycol ) is a clear, colorless, nearly odorless and highly hygroscopic liquid. 1,2-propanediol is one of the polyhydric alkanols and is chiral, so there is a ( R)-enantiomer and (S)- enantiomer. Unless explicitly stated otherwise, all figures in this article on the 1:1 mixture (racemate ) of (R ) - enantiomer and the ( S)- enantiomer.
Properties
It is mixable with water and ethanol, acetone and chloroform, with fatty oils are not. At high temperatures above 150 ° C, it is susceptible to oxidation. 1,2-propane diol is a chiral compound ( stereocenter at C2), which is usually used as a racemic mixture.
Safety characteristics
1,2-propanediol has a flash point at 101 ° C. The connection thus forms only at temperatures above this temperature flammable vapor -air mixtures. The explosion range is between 2.6 vol % (80 g/m3) as the lower explosive limit ( LEL) and 12.6 % by volume (400 g/m3 ) and upper explosive limit (UEL ). The ignition temperature is 420 ° C. The fabric falls within the temperature class T2.
Production
1,2-propanediol is produced industrially by hydrolysis of propylene oxide. Depending on the manufacturer, either a high-temperature process, without catalysis at 200-220 ° C or to a catalytic process at 150-180 ° C in the presence of an ion exchange resin or of small quantities of sulfuric acid or alkali is used for this. The final products of these procedures contained 20% 1,2-propanediol ( which is purified by rectification), 1.5% of dipropylene glycol, and small amounts of other polypropylene glycols. 1,2-propanediol can be prepared from the biodiesel and from glycerol, a by-product.
Use and health risks
1,2-propanediol is contained in solvents, and in sanitary products such as skin creams, deodorants and toothpaste as humectant and emollient. 1,2- propanediol is used as cosurfactant in multicomponent systems for the application and is able to promote water-in- oil emulsions. It can markedly improve the solubility of various substances and to ensure a stable dispersion of drugs in ointments. Furthermore, it can often contribute to a significant Absorption enhancement of various substances. The antimicrobial activity makes a use of other preservatives often unnecessary. The potential for irritation to the skin is concentration dependent to a large extent, a small addition of 10 to 15% but is generally considered to be tolerable. Therefore, the use should be appropriate concentration and only when necessary.
1,2-propanediol may be used as a carrier and the carrier solvent for dyes, anti-oxidants, emulsifiers and enzymes. Because of its lower compared to ethylene glycol toxicity is - mixed with water - used as a heat transfer medium in solar thermal or cooling equipment in food processing.
It is approved in the EU as a food additive and is called E 1520.
Technical significance of 1,2- propanediol as a good solvent for rosin. It is also an integral part of so-called fog fluids.
Tobacco and electric cigarettes
By publication of BMELV in May 2005 it became known that 1,2- propylene glycol is included in almost all tobacco products as an additive. Propanediol is added together with glycerin both the cigarette tobacco and the shisha tobacco. Because of the tobacco ordinance of the humectant content is limited to 5% smoke tobacco. As a recent study by the Federal Institute for Risk Assessment (BfR ) significant amounts of glycerol and propanediol was measured in the smoke of wet water pipe tobacco and pointed to potential health hazards, a raising this limit for water pipe tobacco is not expected. In addition, propane is used in aqueous solution in the dampening of humidors, where it is intended to prevent mold growth on the plant (relative humidity about 70%).
1,2- propanediol is also used in so-called electric cigarettes. 1,2-propanediol, glycerol, in addition to the main component in most of these liquids cigarettes. The inhalation of propane irritation of eyes and throat may occur.
Propanediol use in dairy cow feeding
Recently, 1,2- propanediol is used as a feed additive for dairy cows. Due to the ever increasing milk yield of cows that day is now in high- yielding dairy cows by about 50 liters /, it is becoming more common to a decline in milk yield after calving. In particular, in the so- called transit phase, the two weeks before calving, and first lactation appropriate feeding strategies and feed rations has proven the additional administration of 1,2- propanediol to prevent ketosis and to power stabilization in the frame.