Dichloroacetic acid is a liquid at ambient temperature. The melting point of the higher melting of its two forms is +9.7 ºC. The bp is 193-194 ºC, Its density is 1.563. Neat acid is 12.12 molar. In the presence of an immiscible liquid phase ( such as heptane, cyclohexane etc.) it will be the lower phase in the reactor. It is miscible with water and organic solvents (ethanol, diethyl ether, methylene chloride) but only slightly miscible with carbon tetrachloride. Although I can find no data, I would be surprised if it is miscible with trichloroethylene or tetrachloroethylene. Dichloroacetic acid has a pKa of 1.48, meaning that one-half of the molecules are ionized at a pH of 1.48. The strongest acid that can be present in this solvent is protonated dichloroacetic acid. The strongest base that can be present is dichloroacetate.
Anhydrous Acidification without Excess Local Low pH
Because it is a fluid it could be added into refluxing organic solvent, using a continuous dilution head, so that a local excess of strong acid will never be experienced and the mixture will remain completely anhydrous.
High Dissolving Power
The potential dissolution power of the acid is impressive. An 80:20 v/v dichloroacetic acid/methylene chloride mixture can dissolve many otherwise poorly soluble materials including polymers.
Dichloroacetic acid may be an alternative for reactions that are presently considered for neat sulphuric acid, hydroiodic acid, hydroxymethanesulfonic acid, methanesulfonic acid, polyphosphoric acid, trifluoromethanesulfonic acid, or trifluoroacetic acid. Dichloroacetic acid is much cheaper than trifluoroacetic acid although for some applications the greater volatility of the latter will still make it more advantageous.
Dichloroacetates are pharmaceutically acceptable salts. Dichloroacetic acid, therefore, is acceptable at low levels as an impurity in pharmaceutical products and so is attractive as a reagent in drug synthesis.
The Safety & Toxicology data are:
Acid: LD50 rat oral, 2.82 g/kg; rabbit skin, 510 μl/kg; TDL0; rat oral, 3.195 g/kg/90 days; mouse oral, 7.1g/kg/10 weeks.
Sodium salt: LD50: rat oral 5.281 g/kg; mouse, 4.845 g/kg.; i.p.,; TDLo rat oral, 2.45 g/kg./7 weeks, 30.425 g/kg/12 weeks; dog oral, 4.55 g/kg/13 weeks.
Because dichloroacetic acid is a liquid, during the crystallization of dichloroacetate salts, it can be present in excess to contribute to their insolubility by the common ion effect.
The many distinctive properties of this acid should lead to a wider application.
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